最新刊期
卷 29 ， 期 2 ， 2008
- 摘要：The properties of the weak-coupling magnetopolaron in semiconductor quantum well were studied by using the linear combination operator and a modified LLP variational method considering the electron spin. The mean number of phonons, the ground state energy of the weak-coupling magnetopolaron and the ratio(absolute value) of the electron spin energy to the ground state energy in an infinite quantum well were derived. Numerical results show that the mean number of phonons increases with enhancing the electron-LO-phonon coupling constant and the well width, and at last approaches to the limiting value of the bulk case; the ground state energy of the magnetopolaron becomes two branches from one branch due to the influence of the electron spin, which decreases with increasing the well width and electron-LO-phonon coupling constant, and it also increases with increasing the cyclotron resonance frequency.It depends on the cyclotron resonance frequency and the properties of the well material whether the effect of the electron spin energy in the quantum well can be neglected.关键词：infinite quantum well;magnetopolaron;linear combination operator;mean number of phonons;electron spin103|147|6更新时间：2020-08-12
- 摘要：Recent developments of fabrication techniques have made available structure whose dimensions are much smaller than the characteristic length, such as mean free path and phase-coherence length of an electron. These structures are referred to as mesoscopic system. The physical properties of the mesoscopic system are strongly affected by quantum-interference effects, and one of the interesting phenomena is the persistent current in a ring threaded by magnetic flux. The purpose of this paper is to reveal the behavior of the persistent currents of mesoscopic structure with an impurity by the quantum waveguide theory. It is found that both the transmission coefficient of electron and persistent currents oscillate periodically with changing of magnetic flux with a period of ƒ=1. In the region of 0≤ƒ<1, the antiresonance occurs at ƒ=0.5. When the flowing direction of the current reverses, the amplitude of persistent current in each ring of the double Aharonov-Bohm rings changes.关键词：quantum waveguide theory;mesoscopic structure;δ-function impurity;persistent current125|89|0更新时间：2020-08-12
- 摘要：Photonic crystals are artificially created materials with periodic dielectric constant variations. The simplest one-dimensional photonic crystals are multilayer structures obtained by alternately growing thin-films with different dielectric constants by molecular beam epitaxy. When the dielectric constant of one-dimensional photonic crystal is a sine-squared function in coordinate space, the photonic motion equation is reduced to Mathieu equation.The band construction for this system is discussed based on Bloch theorem,and the system presented automatically band properties.It shows that there are a series of stable zones and unstable zones (forbidden-bands) in the plane of parameter δ and ε. When |ε|→>0, these unstable zones will be reduced to some points in the centre of the forbidden-bands. The unstable zone and the forbidden-band width are found by the perturbation techniques.The result shows that the widths of the first order and second order unstable zones depend on the parameters of dielectric and photonic frequency. By adjusting these parameters, one can obtain the photonic crystals with different band structures and properties.关键词：one-dimensional photonic crystal;refractive index;sine-squared distribution;perturbation techniques;band gap111|92|1更新时间：2020-08-12
- 摘要：By using the optical tranfer matrix method, the band function and the optical transmission properties of mirror symmetrical photonic crystals of two dielectric constant defect layer with imaginary part are stu-died, especially discussing on the case of negation imaginary part and the optical thickness of the defect layer is λ0/4. The investigation results show that several large transmittance gains appear at the transmittance bands if the dielectric constant defects with negative imaginary part are added in the photonic crystals. With the increasing of the ratio of imaginary and real part of defect's dielectric constant, the transmittance gains will change with different rule, but the transmissivity of the defect film at middle wavelength is invariable.The conclusion might be used to multiple channel narrow band filter and multiple channel optical amplification device with different amplificatory multiple synchronously. However, all of the transmittance peaks are minished if the imaginary part of the defect layer's dielectric constant was positive, because the transmittance peaks are absorbed in this case. With the increasing of the imaginary, the transmittance is reducing. The conclusion leads to use photonic crystals for optical amplification device theoretically.关键词：photonic crystal;defect layer with imaginary part of dielectric constant;transmittance gain;transmittance absorption100|108|0更新时间：2020-08-12
- 摘要：Recently, many theoretical and experimental studies of the electromagnetic and optical properties of low-dimensional semiconducting quantum structures have been carried out because of the intrinsic physical interest of these structures as their wide ranging, possible applications in the future. Quantum wires, in particular, play an important role in microelectronic and optoelectronic devices. Since a quantum wire is a one-dimensional structure with the electron motion confined in two-directions, quantum effects are more apparent than that in a two-dimensional quantum structure. In addition, the physical properties of quantum wires may be controlled by applied external electric and magnetic fields. External fields are therefore of great importance in studies on the properties of quantum wires.Following the recent proposal by Sakaki of a quantum wire that can be produced using modern growth techniques, a great deal of theoretical and experimental effort has been directed toward these structures. Li et al. studied the effects of the parabolic potential and confined phonons on a free polaron in a parabolic quantum wire. Yeung et al. investigated the cyclotron resonance of a strong parabolic potential and weak electron-LO-phonon coupling. Chuu et al. have investigated the energies of the ground state and the excited state in cylindrical quantum wires using Pekar alternative approach and perturbation-variational approach. Krishna et al. studied the effects of electron-phonon interaction on the ground and excited state energies of an electron in a polar quantum strip by using a variational method. The properties of polaron and megnetopolaron in cylindrical quantum wires, rectangular quantum wires and parabolic quantum wires have been studied by the method of linear-combination operator and unitary transformation by one of the present authors and co-worker.In this paper, we studied some properties of strong-coupling polarons in a parabolic quantum wires under a finite temperature. The system ground state energy and the mean number of optical phonon are derived by using improved linear combination operators and the variational method. Numerical calculations, for the RbCl crystal as an example, are performed. The results indicate that the mean number and the ground state energy of polaron, the mean number of phonons of the strong-coupling polaron in a quantum wire increase with the increase of the temperature.关键词：quantum wire;polaron;temperature effect;mean number of optical phonon;ground state energy98|101|1更新时间：2020-08-12
- 摘要：Lots of investigator's interests, in the problem of a polaron and magnetopolaron bound to a hydrogenic impurity and interacting with the longitudinal optical phonon field in an ionic crystal or a polar semiconductor, have been maintained over years. Due to the small structures of quantum dot some physical properties such as optical and electron transport characteristics are quite different from those of the bulk mate-rials, especially. There has been great interest in investigation quantum dots both theoretically and experimentally. Many investigators studied the properties of the polaron and magnetopolaron in an asymmetry quantum dots in many aspects by a variety of methods. Recently, the properties of weak-coupling magnetopolaron in an asymmetry quantum dots have been studied using the linear combination operator and the unitary transformation methods by the present authors. However, using linear combination operator method, the influence of the Coulomb field on the properties of bound polaron and bound magnetopolaron in an asymmetry quantum dots has not been fully investigated so far.The influence of the magnetic field on the properties of weak-coupling bound magnetopolaron in an asymmetry quantum dots are studied. The vibrational frequency and the ground state energy of the weak-coupling bound magnetopolaron in an asymmetry quantum dots are derived by using the linear combination operator and the unitary transformation methods. We obtain the expressions of ground state energy and vibrational frequency for the weak-coupling bound magnetopolaron in an asymmetry quantum dots as a function of the transverse and longitudinal effective confinement length of quantum dot, cyclotron resonance frequency of magnetic felid, Coulomb bound potential and the electron-phonon coupling strength. Numerical calculations are performed and the results show that the vibration frequency and the ground state energy of the weak-coupling bound magnetopolaron in an asymmetries quantum dot will increase strongly with decreasing the transverse and longitudinal effective confinement length of quantum dot. The vibrational frequency of the weak-coupling bound magnetopolaron will increase with increasing the cyclotron resonance frequency of magnetic felid and Coulomb bound potential, whereas the ground state energy of bound magnetopolaron will decrease with increasing the Coulomb bound potential and electron-phonon coupling strength关键词：asymmetric quantum dot;bound magnetopolaron;magnetic field;Coulomb bound potential;linear combination operator97|101|0更新时间：2020-08-12
- 摘要：Quantum computing combines computer science with quantum mechanics and is a fast growing research field. In recent years, the outlines of all kinds of achieving quantum computation were devised. In 1999,the suggestion of superconductive electronic charge was designed by Nakamura in Japan,a nanometer-scale superconducting electrode connected to a reservoir via a Josephson junction constitutes an artificial two-level electronic system:a single-Cooper-pair box. In 2001,the plan of geometrical quantum computation was framed by Duan L M et al., the elementary unit of quantum computer is the quantum bit(quanbit). In 2002, based on an idea that spatial separation of charge states will enhance quantum coherence, Li X Q et al. propose a scheme for a quantum computation with the quantum bit constructed from two coupled quantum dots. In 2003, based on the analytical solution to the time-dependent Schdinger equation, Cen L X et al. evaluate the holonomic quantum computation beyond the adiabatic limit. Low dimensional nanostructures has attracted much attention due to their unique electronic and optical properties as well as potential applications in making electronic and optoelectronic devices. Quantum rings (QRs) stand as an alternative to quantum dots(QDs) as zero-dimensional structures. QRs were extensively applied in optoelectronics,microelectronics and quantum communication because its characteristic electronic shell structure, magnetic field response and transport properties. The potential power of quantum ring is based on the ability of quantum systems to be in a superposition of its basic states. Probability density distribution of electron in quantum bit of quantum ring was studied by solving precisely the time-independent Schr-dinger equation. The numerical calculation for InAs quantum rings was carried, the material parameters are μ=0.024m0,m0 is mass of free electron,the inner/outer radius of quantum rings is 20/40 nm. The numerical results indicate that probability density distribution of electron has something to do with coordinate and time. When time t, angle φ and height z are given, it does non-periodicity oscillates with increasing radius ρ. When time, angle and radius are given, it increasing firstly and falling secondly with increasing height and achieves maximum if z=h/2. When time, height and radius are given, it raises firstly and declines with increasing angle and achieves maximum if φ=π. And probability density distribution of electron in quantum bit of quantum ring does periodicity oscillating with time.关键词：quantum ring;quantum bit;Schr-dinger equation95|100|0更新时间：2020-08-12
- 摘要：Organic light-emitting diodes (OLEDs) have been intensively studied in the past several years due to their unique image quality and potential commercial application in flat-panel displays. Since Tang and Van Slyke reported the first double-layer green thin-film OLED with high brightness and low driving voltage, the OLEDs have demonstrated their good prospect around the world for this new display technology. The distingui-shed characteristics of OLEDs for displays include high efficiency, wide viewing angle, fast response time, low power on consumption and potentially low cost. In addition, their low processing temperatures, and thus versatility in substrates, render them suitable for some novel display applications, such as flexible displays. Over the past decade, the OLED display technology has made rapid progress; the major technical issues associated with these advanced OLED structures in general are how to design their optical structures and how to choose suitable materials with required electrical and optical properties. To achieve further advances in the brightness,power efficiency and the color purity of the electroluminescent spectrum of OLEDs, it will be necessary to develop new materials and design suitable device structures with long-term stability and lifetime. The mechanism for electroluminescent (EL) phenomenon involves in the injection of holes from anode and electrons from cathode under forward bias voltage, then the hole-electrons from excitons, and light emission appears through the radiative recombination of excitons. In order to obtain optimal luminance and power efficiency, organic electroluminescence requires the effective injection and recombination of the electrons and holes, and the injection balance of the electron and hole. Therefore, the reasonable device structures and the choice of the function materials of the OLEDs play the important role to improve the brightness,power efficiency and the device's stability.Based on conventional two-layer devices, the double heterostructure three-layer OLEDs with a structure of indium-tin oxide (ITO)/N,N'-diphenyl-N,N'-bis(1-naphthyl)(1,1'-biphenyl)-4,4'-diamine (NPB)/2,9-dimethyl-4,7-diphenyl-1,10-phenan throline (BCP)/8-hydroxyquinoline aluminum (Alq3)/Mg:Ag have been fabricated using vacuum deposition method. Through characterizing the electroluminescence (EL) spectrum and the performance of the devices, the influence of different thickness from the BCP ultrathin film on the performance of OLEDs have been investigated. The results showed that when the thickness of BCP ultrathin film gradually ranges from 0.1 nm to 4.0 nm, the EL spectrum of the OLEDs shift from green to greenish-blue, and at last the device is absolutely blue-emitting from the hole transport layer of NPB. The ultrathin film of the BCP plays the role as not only effectively regulating the recombination region of charge carriers as well as EL spectrum, but also enhancing the brightness and luminance efficiency of OLEDs.关键词：organic light emitting diode(OLED);ultrathin film;BCP;device performance120|264|1更新时间：2020-08-12
- 摘要：Organic light-emitting diodes (OLEDs) based on conjugated polymers have been attracting much attention because of their cheap and easy fabrication with solution-based processing techniques. Full color displays based on organic materials have very attractive prospects and one of the most exciting ones is the use of ink-jet printing to allow direct patterning of conjugated polymer LED pixels. However, achieving "pure-red" emission has proved relatively challenging. In this work the optical properties of varying 5,10,15,20-tetra-p-tolyl-21H, 23H-porphine (TTP) doped poly [2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) were studied. The UV-Vis absorption of Q-band of TTP overlapped the photoluminescent spectra of MEH-PPV. This is a priority for occurrence of Förster-type energy transfer. The photoluminescent spectra of varying TTP doped MEH-PPV showed that the emission of TTP increased as the increasing of the doping level at the excitation wavelength of 500 nm, at which TTP didn't absorb energy, indicating the existence of Frster energy transfer from MEH-PPV to TTP. However, the continuous addition of TTP resulted in the enhanced emission of MEH-PPV at the doping level above 4 percent, due to the self-quenching caused by crystallization of TTP. The devices with varying TTP doped MEH-PPV as light-emitting layers were also fabricated and the structure of the devices was ITO/PEDOT:PSS/TTP doped MEH-PPV/Al[PEDOT:PSS=poly(2,3-dihydrothieno[3,4-b]-1,4-dioxin)/poly(styrenesulfonate)]. The layers of PEDOT/PSS (20 nm) and TTP doped polymers (80 nm) were spun onto ITO substrates and aluminum cathode (100 nm) was deposited under vacuum pressure of about 1×10-3 Pa. The electroluminescent properties of the devices were investigated and TTP dominated red emission was observed. The electroluminescent emission from TTP increased as the increasing of doping level in light-emitting layer. On the other hand, the emission of MEH-PPV reduced gra-dually until the doping level of 8 percent. Then it began to grow. The results of photoluminescence and electroluminescence expressed that the two emission processes followed different mechanisms. TTP could be a center for capturing exitons in electroluminescence and the emission of TTP involved the capture of electrons and holes by itself apart from Frster-type energy transfer from MEH-PPV. The researches on TTP doped conjugated polymers will be helpful to enlarge the application of dye, porphyrin, in OLEDs. Moreover, the researches on the mechanisms of photoluminescence and electroluminescence for the blended systems will provide scientific basis for color tuning of composite materials.关键词：organic electroluminescence;porphyrin;energy transfer102|78|2更新时间：2020-08-12
- 摘要：In this work, BAM phosphors were coated with MgF2 by sol-gel process. The surface morphology and the crystal structure were characterized by SEM, IR and XRD, respectively. The results indicated that the surface of BAM phosphors were evenly coated by MgF2 and the crystal structure of the coated BAM phosphors remained the same as the uncoated samples, i.e. after surface treatment, the luminescence centre of Eu2+ didn't shift, which still remain the emission with wavelength about 450 nm. The surface component of BAM phosphors coated with MgF2 was analyzed qualitatively by EDS. The emitting spectra of BAM phosphor particles coated without and with MgF2 were investigated under 254.7 nm excitation. The results demonstrated that the initial luminance of coated BAM phosphors was lower than the uncoated samples. But after roasting at 550,650℃ for 30 min respectively, the luminescence degradation of the coated BAM phosphors was improved greatly.关键词：BAM phosphor;Sol-Gel;coating;MgF296|78|6更新时间：2020-08-12
- 摘要：The Y3Al5O12:Cex3+(x=0.01,0.03,0.05,0.07,0.09)samples were synthesized by the conventional solid state reaction method as well as co-precipitation method. XRD analysis shows that the synthesized samples are all in single lattice phase with cubic structure,which is consistent with the JCPDS standard card (88-2047). From the SEM analyses, the use of co-precipitation method decreases the synthesis temperature of the samples, and results in fine grains and particles in these materials. In the VUV excitation spectrum of YAG:Ce, three separative peaks are found at 126 nm, 177 nm and 230 nm, respectively. There is a wide asymmetry emission band peaked at about 530～540 nm, and resulted from two transitions of 5d→2F5/2 and 5d→2F7/2 of Ce3+ in the PL emission spectra. The intensity of emission spectra of Y3Al5O12:Ce3+x(x=0.01,0.03,0.05,0.07,0.09)increases as x increases from 0. 01 to 0.05, and then decreases when x increases from 0. 05 to 0.09 further. The phenomenon accords with characteristic concentration quenching.关键词：YAG;VUV;luminescence117|65|2更新时间：2020-08-12
- 摘要：In recent years, Er3+-doped glasses with a broad 1.5 μm emission band originating from 4I13/2-4I15/2 transition of Er3+ have been extensively investigated for use in erbium-doped fiber amplifiers (EDFA). Among the reported materials, Er3+-doped telluride glasses exhibited a wide 1.5 μm emission band and a large stimulated emission section and high 1.5 μm emission efficiency. However, as a host for EDFA, telluride glass has some major drawbacks. One of them is the phonon energy of the glass is about 770 cm-1, which leads to the 4I11/2-4I13/2 nonradiative relaxation rate too slow to allow efficient pumping at 980 nm. To overcome this drawback, S. Shen et al. added WO3, with vibronic energy of W-O bond of 920 cm-1, into the glass to form tungsten-tellurite glasses. This composition modification increased the nonradiative relaxation rate of the 4I11/2-4I13/2 transition and made improvement of population feeding efficiency of 4I13/2 from the 4I11/2 level pumped at 980 nm. In this paper, P2O5 was introduced into Er3+-doped tungsten-tellurite glasses. Emission, absorption and upconversion spectra of the glasses are studied. It is observed that the nonradiative relaxation rate of 4I11/2-4I13/2 transitions and the 1.5 μm emission efficiency increases with the increase of P2O5 content, while, the upconversion luminescence was suppressed. The nonradiative relaxation rate of 4I11/2-4I13/2 transition in a glass with 6% P2O5 is about 3.5 times greater than that without P2O5. The present results indicate that telluride glasses with P2O5 addition may be a promising candidate medium for broadband erbium-doped fiber amplifiers with good performance under the pumping of 980 nm.关键词：optical material;tungsten-telluride glasses;P2O5;nonradiative decay107|85|1更新时间：2020-08-12
- 摘要：CaWO4 nano-crystal phosphor was prepared by a Pechini sol-gel process. X-ray diffraction, scanning electron microscope and photoluminescence spectra were used to characterize the resulting phosphor powders. The results indicate that the phosphor prepared at 750℃ is with pure lattice phase,its emitting peak is at 420 nm and mainly consists of globose particles with an average grain size of about 100 nm. Compared with commercial X-ray intensifying screen the images of X-ray film matched with this novel intensifying screen have higher contrast and resolution.关键词：Penichi sol-gel process;nano-sized phosphor for X-ray intensifying screens;CaWO4114|156|1更新时间：2020-08-12
- 摘要：The ZnO thin films are fabricated by electrodeposition on n-type InP wafers at constant potential. Polarization potential of the deposition of ZnO is firstly confirmed using linear sweep voltammetry in 0.1 mol/L Zn(NO3)2 electrolyte/InP system, which is -1.187 7 V vs. SCE at 20℃. Scanning electron microscopy shows that the thin films become smooth and compact with decreasing applied potential, and the narrow X-ray diffraction peaks also show the good crystal quality of the thin films. The optical properties of ZnO thin films are studied by photoluminescence spectrum measurements. The ZnO thin films obtained at low potential exhibits good photoluminescence.关键词：ZnO thin films;electrodeposition;XRD;PL109|300|1更新时间：2020-08-12
- 摘要：Over the past few years, wide and direct band gap semiconductors have been intensively studied for their application as blue and ultraviolet light emitters. As a wide gap semiconductor, ZnO has a wide band gap of 3.37 eV and a large binding energy of 60 meV. Therefore, ZnO is considered as one of the most pro-mising candidates for short wavelength optoelectronics devices, and it is very important to conduct further studies of the properties of ZnO thin films.(Co,Cu)-codoped ZnO thin films, Zn0.85-xCo0.15CuxO(x=0,0.04,0.06)thin films were deposited on silicon(111) substrates by e-beam evaporation.The structure of Zn0.85-xCo0.15CuxO thin films were investigated using X-ray diffractometer (XRD). Photoluminescent (PL) spectra were measured with Xe lamp excitation light source at room temperature, the excited wavelength was 325 nm.The photoluminescence spectrum reveals that with the increase of doping content of Cu, the emission intensity of Zn0.85-xCo0.15CuxO thin films was enhanced. Moreover, with x=0.06, strong blue double emission peaks were got at 449 nm and at 477 nm for the Zn0.85-xCo0.15CuxO thin films. The luminescence mechanism was also discussed in this paper, The experiments prove that the blue emission is due to transition of electrons from the bottom of the conductor band to zinc vacancy VZn or interstitial zinc Zni to the top of valence band.关键词：Zn0.85-xCo0.15CuxO film;Co;Cu-codoped;photoluminescence91|139|12更新时间：2020-08-12
- 摘要：ZnO films with unusual surface morphology and growth orientation [101] were prepared using oxygen gas and zinc powder adding LiCl or NaCl by CVD method. In the CVD growth process, the ZnO films grew at 550~650℃ for 2 h with adding LiCl and NaCl respectively. The surface morphologies of ZnO films were investigated using FESEM and exhibited rhombus/triangles when the mol ratio of chloride to zinc was 1:1, and hexagonal pyramids when the ratio was 1:10. In as-grown wurtize ZnO film, the rhombus and triangle correspond to the {101} faces, while the hexagon corresponds to the {001} face. Authors concluded the added chloride decreased the surface energy of {101} surface. Meantime, the growth direction was transformed from [002] to [101] with the increasing of chloride concentration as shown in XRD pattern. These results implied that chloride could tune the growth direction of ZnO. This phenomenon could be observed in producing one-dimensional nanostructures but not in films.关键词：CVD;ZnO films;growth direction;growth mechanics118|259|3更新时间：2020-08-12
- 摘要：In past, many papers reported that it was difficult to obtain p-ZnO through N2 splitting. We studies the properties of ZnO films through N2 splitting and N-Al co-doping by our MOCVD system which was improved with RF assisted equipment. The data of SIMS showed that the N concentration reached to 1020~21 cm-3 in ZnO films. On this basic, we have studied the growth and photoelectric-properties of N-Al co-doped ZnO films, the effect of RF power on the crystal quality, surface morphologies and optical properties, through XRD,AFM and PL methods, to compare the properties of N-Al co-doped ZnO films. The result of our experiments indicates that the growth rate of ZnO films increases with increasing N splitting, N-Al co-doped ZnO films display p-type property, but the resistance of N doped ZnO films was rather high which was caused by non-activated N in ZnO films, this revealed that the N-Al co-doping facilitates the activation of N in ZnO films.关键词：MOCVD;RF-assisted;N splitting;N-Al co-doping113|131|0更新时间：2020-08-12
- 摘要：Ag doped ZnO films have been fabricated on single-crystal Si (100) substrates by magnetron sputtering. XRD measurements show that the ZnO:Ag films have high crystallization quality without new phase related to Ag appearing. Doping with Ag can clearly decreases the neutral donor bound exciton emission showed by the low temperature (10 K) photoluminescence spectra; a donor-acceptor pair emission has been observed at 3.315 eV which is attributed to the formation of acceptor defect (Ag substitutes Zn). The level of AgZn acceptor is estimated to be about 110 meV above valence-band maximum. Hall measurements show that Ag doped ZnO films are p-type conductivity with the resistivity about 0.1 Ω·cm, hole concentration about 1.7×1018cm-3,and mobility about 36 cm2/V·s.The two-layer structured ZnO p-n homojunctions have been prepared on Si(100) substrates by depositing Ag doped p-type ZnO film on intrinsic n-type ZnO film using magnetron sputtering. The current-voltage (I-V) characteristics derived from the intrinsic ZnO/Ag doped ZnO two-layer structure clearly show the rectifying characteristics of typical p-n junctions.关键词：Ag doped ZnO;low temperature PL spectra;DAP;homojunction133|188|4更新时间：2020-08-12
- 摘要：ZnO is a wide band-gap semiconductor with good electrical and optical properties. ZnO has higher exciton binding energy of 59 meV at room temperature, leading to a lower threshold, and is favorable for efficient operation of optical devices. Short wavelength devices based on ZnO have become even more interesting. On the other hand, band gap devices based on ZnO/ZnMgO superlattices or quantum wells can confine both excitons and photons in the low dimensions, making the stimulated exciton-related emission process more efficient. Therefore, keeping focus on the MgxZn1-xO films for purpose of exploring its potential applications in ultraviolet optoelectronics is more and more important.High quality MgxZn1-xO alloy films have been grown by plasma-assisted molecular beam epitaxy on c-sapphire (c-Al2O3) substrate. The growth temperature was 800℃, the temperature of the zinc source is fixed at 245℃, and the flow rate of oxygen is 0.8 sccm. The MgxZn1-xO films were obtained with different Mg contents by changing the temperature of the Mg source. The quality of the MgxZn1-xO films was improved by growing ZnO buffer layers at low temperature. Their crystal structures are characterized by X-ray diffraction spectroscopy (XRD). The XRD patterns indicate all the MgxZn1-xO films with the (002) preference orientation of hexagonal wurtzite structure. When x value is varied from 0 to 0.15, the (002) diffraction peak of MgxZn1-xO shifts to the large angle side with increasing Mg contents, and the full wide at half maximum (FWHM) of the diffraction peak is widen with increasing Mg contents. The lattice constant of c-axis decreases from 0.5205 nm to 0.5189 nm as the Mg content increased from 0 to 0.15. The FWHM is only 0.145° for the Mg0.15Zn0.85O film, which exhibited the high quality of the MgxZn1-xO films. The intense ultraviolet emission was shown in photoluminescence spectra at room temperature, which shifts from 3.29 eV(x=0) to 3.54 eV(x=0.15) with increasing x values. The bandgaps of the films were evaluated by using the squared absorption coefficient (α2) of MgxZn1-xO films as a function of photon energy. The origin of the ultraviolet emission is studied by the PL spectra measured at the temperature from 80 K to 280 K. The emission peaks show a redshift, the FWHM of the emission peak widen and the intensities of the emission peak decreased with increasing the temperature. The temperature-dependent PL-integrated intensity of MgxZn1-xO were fitting by the equation:I=I0/[1+Aexp(-E/kBT)] (where E is the activation energy of the thermal quenching process, kB is Boltzmann constant, I0 is the emission intensity at 0 K, T is the thermodynamic temperature, and A is a constant). A fit of the experimental data to the equation yields E=54 meV, which agrees well with the exci-ton binding energy of 59 meV for bulk ZnO. Therefore, the ultraviolet emission peak in PL spectra of the MgxZn1-xO alloy films is attributed to the free exciton emission, indicating the high quality of MgxZn1-xO film.关键词：MgxZn1-xO;P-MBE;photoluminescence122|149|0更新时间：2020-08-12
- 摘要：Recently, much attention has been paid to wurtzite MgxZn1-xO alloys as a promising candidate for applications in optoelectronic devices in the ultraviolet region. ZnO is a wide-band-gap semiconductor with a direct gap of ~3.37 eV. The band gap becomes even larger if Zn atoms are substituted by Mg atoms, which have a similar ionic radius, allowing the construction of ZnO/MgxZn1-xO quantum-well and superlattice devices. One of the important problems that limits the fabrication of MgxZn1-xO alloy is the fact that the thermodynamic solubility limit of MgO in ZnO is about 4%. The problem of Mg concentration in ZnO is excess of 4% without phase segregation is important and necessary to be studied in details.In this paper, MgxZn1-xO films with wurtzite-type structure were fabricated on quartz substrates at 150℃ by electron beam evaporation (EBE) using Mg0.15Zn0.85O target combined with heat treatment. The depen-dence of the microstructure and optical properties of MgxZn1-xO films on the annealing conditions and cooling modes has been investigated using X-ray diffraction (XRD), scanning electron microscope (SEM), absorption and photoluminescence (PL) spectra. In the XRD spectra, no diffraction peaks belonging to MgO were observed. The results showed that MgxZn1-xO films were single wurtzite-type structure. The increasing band gap is not due to quantum confinement effect according to SEM images, but attributed to the formation of MgxZn1-xO alloy films. In the absorption spectra, the blueshift of absorption edges and absorption peaks indicated that the band gap of MgxZn1-xO films was tuned from 3.37 eV to 3.61 eV by changing annealing conditions and cooling modes. As it can be seen, the full-width at half-maximum of the XRD peak for MgxZn1-xO films annealed at 700℃ followed with rapid cooling increases, which indicated the Zn2+ ions in ZnO lattice were successfully substituted by Mg2+ ions. Accordingly, an evident blueshift is observed in photoluminescence spectra for the MgxZn1-xO films annealed at 700℃ followed with rapid cooling, and the PL intensity of near-band-edge (NBE) emission is much higher than that of its visible emission, showing that high quality MgxZn1-xO films were obtained.We controlled on the Mg2+ concentration by changing annealing conditions and cooling modes. By using rapid cooling at high annealing temperature, the high-quality MgxZn1-xO films were achieved. The fabrication of high-quality MgxZn1-xO films makes it possible to obtain light detecting and emitting devices in the UV region.关键词：MgxZn1-xO films;electron beam evaporation;optical property112|92|1更新时间：2020-08-12
- 摘要：The photoluminescence (PL) and photoluminescence excitation spectra (PLE) of selected InxGa1-xN samples grown by metal organic chemical vapor deposition (MOCVD) have been investigated, and the analysis of structural and optical behaviors has been taken to study the existence of the microstructure InGaN alloys on the basis of X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements.XRD reveals that the sample is a single crystalline InxGa1-xN film formed predominantly in (0002) direction, the In mole composition x in InxGa1-xN film is calculated to be about 0.2 according to the Bragg's angle of InxGa1-xN (0002). The AFM plane-view and 3D images of the selected In0.2Ga0.8N sample show almost uniform island-like microstructure appearing to be composed of granular-crystalline in nanometer scale. The islands composed of the grapes-like have an average height of 10 nm at most and a mean size of 300 nm. The self-organized microstructure appeared to form cone and/or pyramid shape and tended to agglomerate island-like surface with RMS roughness about 10 nm, which attributed to Stranski-Krastanov growth mechanism. The comparison between PLE and PL under different exciting or monitoring energy allows determining the existence of wetting layer (WL)in the sample. The PLE and PL measurements show that the resonant absorption is related to the band gap and wetting layer of the alloy at different exciting and monitoring energy. It has been found that PLE peaks of the In0.2Ga0.8N alloy are dominated by 365 nm and 474 nm with monitoring wavelength 545 nm and 493 nm; the broad 545 nm and narrow 493 nm emission peaks are originated from In(Ga)N wetting layer and InGaN region respectively. The structural and optical analyses suggest that the origin of the exciton localization center is the self-formed islands. Hence, the irrelevancy of the PL spectra to the gap energy was explained in terms of fluctuation resulting from variations in grain size or shape. This type of localized center provides another physical model for the proposed localized states in InxGa1-xN epilayers. Further characterization of the InGaN systems is underway to help fully understand the correlation between the structural and the optical pro-perties of self-organized micro-structure of InGaN system.关键词：InGaN;MOCVD;AFM;photoluminescence spectra;photoluminescence excitation spectra124|157|0更新时间：2020-08-12
- 摘要：In the last few years the InGaAs/GaAs heterostructure system has received increasing interest for electronic devices and microwave industries. The strained quantum well (QW) laser has more beneficial effect than other QW lasers. For example, lower threshold current density, wider modulation bandwidth and the emission wavelength of strained QW laser can be adjusted by appropriately changing the strain. With regard to InGaAs/GaAs material system, indium distribution influence on the performances of device directly. Surface segregation of In ions during the growth process is the major factor for the indium distribution in InGaAs/GaAs heterostructure. The heteroepitaxy of InGaAs layer on GaAs substrates is characterized by a strong segregation of In atoms that accumulate at the growth front and substantially modifies the In-composition profile, resulting in different electronic and optical properties of the devices based on that material. Segregation determines the composition profiles of QW in the growth direction in many semiconductor systems, and consequently, the quantized levels are strongly influenced. The samples of InGaAs/GaAs strained QW are grown in Riber 32 compact 21 solid source molecular beam epitaxy (MBE) system equipped with a valved cracker cell for arsenic and reflection high energy electron diffraction (RHEED) for in situ monitoring of the growth process. Growth temperature is calibrated by infrared pyrometer. The photoluminescence (PL) was studied on InGaAs/GaAs strained QW with various different growth temperature and structure parameters. In ions segregation processes was illustrated based on the Muraki model and the differential calculation were compared with experiment results in detail. The results show that some important information was obtained about the effect of indium segregation, desorption and In-Ga intermixing on optical quality of strained quantum well. The effect is serious, and the peak position of PL is blue shifted with increasing the growth temperature. It is demonstrated that indium segregation and In-Ga intermixing have no effect on the optical properties of InGaAs/GaAs strained quantum well with In content below x=0.2 and the growth temperature below 560℃ by PL analysis.关键词：strained quantum well;segregation;desorption;photoluminescence128|159|4更新时间：2020-08-12
- 摘要：It is reported that the design and fabrication of high-brightness and high-power InGaAlP ring-shaped interdigitated red LED. High-brightness and high-power InGaAlP LED is a new kind of visible light LED developed in recent years, which is driven by large current capacity, high luminous efficiency and excellent heat resistance. It has been used in various fields, such as large area displays, traffic lights, back-lighting,aviation lighting and so on. As compared with the conventional LED chip, the ring-shaped interdigitated LED chip is more flexible to integrate with other devices, and it leads the more uniform current spreading. The InGaAlP LED epitaxial layer has six layers. From top to bottom, they are the window layer (p-GaP), the p clad layer(p-InGaAlP), the active layer between clad layers(i-InGaAlP), the n clad layer(n-InGaAlP), distributed Bragg reflectors (DBR) and the n-Substrate(n-GaAs). The epitaxial wafer is tested by scanning electron microscope (SEM) and X-ray double crystal diffraction. The results show the interface of materials is flat, and the integrality and quality of the epitaxial wafer are optimum.The size of chip is 1 mm2.The fabrication of ring-shaped interdigitated LED chip, essentially, is the same as conventional LED chip, involving photolithography, PECVD SiO2, wet etching, evaporation,lift off and rapid thermal annealing using four masks. To control the widths of mesa and n area precisely, the selecting etch technique has been adopted, using HCL;H2O and H2O2 as an InGaAlP etching solution, and the chip is protected by SiO2 and single layer photoresist during the etching. The fabrication of Ⅲ-Ⅴ compound semiconductor p-type Ohmic contact is more difficult than the fabrication of n-type Ohmic contact. So how to fabricate p-type ohmic contact is a second important technology. AuZn/Au is used to be the p-contact metal in this study, and the chips are sintering for 20 s at 400℃ in N2.The I-V characteristics, light emission spectrum, luminous flux, luminous intensity of this LED have been measured. A good characteristic is obtained with turn-on voltage of 1.5 V and forward current of 500 mA at its forward voltage of 3 V. The peak wavelength is 635 nm, which corresponds to red light, and the full width of half maximum is 16.4 nm at injection current of 350 mA. The luminous intensity is 830 mcd. The color coordinates is x=0.694 3,y=0.305 6 and the color index is 18.4. So we will conclude that the high-brightness and high-power InGaAlP red LED is the first step for a wide scope of general illumination with LED in the future, and it will become new focus in both scientific research and industrial investment for its wide application.关键词：LED;InGaAlP;wet etching;p-type ohmic contact139|259|0更新时间：2020-08-12
- 摘要：The forward current-voltage characteristic and forward capacitance-voltage characteristic measurings are the most important methods to study the forward electricity characteristic of GaN light-emitting diodes. We can use the forward alternating current (ac) small signal method to measure the capacitance-voltage characte-ristic of the GaN light-emitting diodes. Some value of GaN light-emitting diodes parameters can be deduced from capacitance-voltage characteristic. The negative capacitance phenomenon of GaN light-emitting diode can be observed by using this method. Measuring the apparent capacitance and resistance by the serial equivalent circuit of LED for measurement, there is an extremum point in apparent resistor-voltage curve. Propose that the basic reason of negative capacitance is that the differential capacitance less than zero by analyzing relation literature. Infering that the differential capacitance of pn junction will grow by leaps and bounds follow the voltage of forward bias grows; the differential capacitance of pn junction will lower till less than zero when the forward bias voltage is higher than the threshold voltage of light-emitting diodes begin emitting light. The current change rate of junction conductor will be max base on current-voltage curve when the forward bias voltage is higher than the threshold voltage of light-emitting diodes begin emitting light, and then the differential capacitance of pn junction fall down quickly for radiative-recombination, so apparent resistor is maximum. We obtain the expression of max apparent resistor. We analyze the extreme point of apparent resistor-voltage curve. The result of theory analysis agree with the experiment. That proved the accuracy of this theory model. The research on apparent resistance phenomenon will be valuable for study the electrical characteristics of GaN light-emitting diodes, and will be valuable for the knowledge improvement of the characteristic and parameter relevant the pn junction internal structure of GaN light-emitting diodes. The study of apparent resistance may open research for novel devices and applications.关键词：GaN light-emitting diode;apparent resistance;forward alternating current (ac) small signal method;current-voltage curve124|154|0更新时间：2020-08-12
- 摘要：In active remote sensing, electrooptical countermeasures, wireless optical remote transmitting and so on, the space-borne laser source carried by a space vehicle is indispensable, the function is unique, powerful and irreplaceable. For accomplishing the intended result in astronautical engineering or in aeronautical engineering, it is necessary to make the intended aim, whose size is finite, be irradiated by laser beam emitting from a right space-borne laser source, and the energy density of the laser beam that irradiates the aim must be enough high. Phase-locked laser diode array is small in size and light in weight, it is quite fit for performing the function of high power space-borne laser whose size must be exigent proper. Meanwhile, in space, the space thermal environment will be influenced by star, planet and space heat sink, a space vehicle is heated and cooled by turns, the change in temperature is violent, to avoid being damaged in space, in this paper, a phase-locked laser diode array who acts as the space-borne laser source in a space vehicle is placed inside the space capsule, only is reflected by the extravehicular reflecting mirrors, the laser beam that emits from the phase-locked laser diode array can pass through the outgoing mirror of the space-borne laser source, and then can transmit into space, the structure of the whole space-borne laser source is periscopic, even so, induced by the varied surrounding space thermal environment, and aggravated by the laser beam that the extravehicular reflecting mirror's reflect, the extravehicular reflecting mirrors will deform stochastically, so the output energy of the space-borne laser source is diverged, at the same time, the normal line of each reflecting mirror surface turns due to the reflecting mirror thermal distortion, so corresponding transferred laser beam has a large deflect, therefore the energy density of the laser beam that can be transmitted to the intended aim and then can treat the aim to be detracted greatly, the performance of the space-borne phase-locked laser diode array will suffer seriously. By way of theoretical derivation, finite element analysis and pertinent experiment, this paper presents clear ideas on the configuration of the space-borne laser source whose emitter is just a phase-locked laser diode array, on characteristics of the space thermal environment that can impact the extravehicular reflecting mirrors, on the optoelectrical field distribution of the phase-locked laser diode array who irradiates the extravehicular reflecting mirrors. Then it makes the laws that govern the action of the deformation of the extravehicular reflecting mirror clear. After that, the novel predistortion technology is presented. To perform the proposed technology in the proposed periscopic space-borne laser source, firstly, the wavefront error induced by the deformation of the extravehicular reflecting mirrors is sensed by the special sensing probe by means of the special echo wave method, after processed by the special processor, the controlled quantity for compensating the outgrowth of the deformation of the extravehicular reflecting mirrors can be obtained, with suitable D/A, high voltage amplifier, the actuating mechanism makes the additive reflecting mirror inside the capsule shape correctly in time, so with right predistortion, after it to be done by the additive reflecting mirror, the laser beam that will be reflected by the extravehicular reflecting mirrors won't be deteriorated by the deformation of the extravehicular reflecting mirror, the experiment demonstrates that the proposed technology makes a space-borne laser diode array adapts to the space thermal environment, guarantees the quality of its output laser beam, this is significant for that laser diode array should be employed in space.关键词：phase-locked laser diode array;space-borne laser source;space flight environment;predistortion;beam quality126|283|0更新时间：2020-08-12
- 摘要：To study how the attenuation of white LED happens and develops, four types of white LED are studied in this paper. Three of them are PLCC-4 type white LED and the other is power white LED. And the PLCC-4 type white LEDs are encapsulated by YAG phosphors, phosphors wafer or RGB LED respectively. The power white LED is encapsulated by YAG phosphors. Four types white LED are lighted continuously and the same type LED is lighted under the same conditions, such as electrical current, environment temperature, and so on. The emission spectra of them are studied in a interval. Usually, the interval is one week time. In this paper, the attenuation of red, green and blue emission is analysed by studying the emission spectrum change, through which to deduce the attenuation of white LED. Four types of white LED were studied and the results indicate that the attenuation mostly results from attenuation of blue LEDs and quenching of phosphors. The attenuating course of PLCC-4 type of white LED encapsulated by phosphors wafer and RGB LED is the same with that encapsulated by YAG phosphors, which is results from the blue LED only. The attenuating course of power white LED is different from PLCC-4 type white LED. Not only attenuation of blue LEDs is the cause of attenuation of power white LED, no less than 80 percent, but quenching of phosphors is also the other factor. More conclusion could be deduced from the study that if radiator is enough perfectly, the attenuation of white LED results from the attenuation of blue LED, but as the system temperature raises, the quenching of phosphors would happen and which will enhance the attenuation of white LED. In this paper, the attenuation of red, green and blue emission are studied by tracking and analysing their spectrum change to deduce the attenuation mechanism of white LED, and the results will provide a reference to the application of white LED and for the further study.关键词：white LED;phosphors;RGB LED;power LED;attenuation148|201|9更新时间：2020-08-12
- 摘要：Recently, people are seeking the lighting source which consumes less energy and has no pollution. Light Emitting Diode (LED) has the advantages over the traditional lamps in the future. The luminous efficiency of blue-light chip and the conversion efficiency of phosphors determine the luminous efficiency of white light LEDs.The thesis experimentally demonstrates luminous efficiency of large-area, high-power blue-light LEDs. We study the high power blue LED and discover the influence of temperature and current on luminous efficiency. When operation temperature increases from 327 K to 380 K,the light efficiency of LED decreases 20%.The temperature rising,the radiation at the potential well decreases, so as to decrease the luminous efficiency. When operation current increases from 50 mA to 350 mA, the luminous efficiency of LED decreases 35%.The current increasing,the more nonequilibrium electron diffuse out of the potential well,so as to decrease luminous efficiency. Enhancing the heat dissipation efficiency and increasing the width of potential well can improve the luminous efficiency. LED should be working under the limit temperature and the saturated current.LED can work at high current relatively when the thermal dissipation is good. The heating generation will decay the lighting performance. Therefore, the thermal dissipation controls the development of the LED and the goal of our investigation is to increase the efficiency of the thermal dissipation. A good packaging technology is the way to solve the heat dissipation problem. But it is a challenge to develop this technology in the limited space of LED.The purpose of heat dissipating technology for LED is to decrease the working temperature of LED's chip.It is necessary to reduce the thermal resistance of LED package.The efficiency and reliabi-lity of solid state lighting devices depends strongly on successful thermal management,because the junction temperature of the chip is the prime driver for effective operation.As the power density continues to increase,the integrity of the package electrical and thermal interconnects become extremely important.401|417|26更新时间：2020-08-12
- 摘要：Si/Si/SiNx/SiO2 multilayers are prepared on Si(100) at room temperature by radio-frequency (RF) magnetron sputtering. The optical properties of these films have been investigated using Fourier Transform Infrared (FTIR) absorption and photoluminescence (PL) spectra, the origins of emission bands in PL spectra are discussed in detail. Strong photoluminescence at 392 nm(3.2 eV) and 670 nm (1.9 eV) is observed, which are caused by the electronic transitions of ≡Si-→ Ev (the valence band top) and Ec ( the conduction band bottom) →≡Si-. It is found that the stretching vibration peak of the Si-O bonds around 1 056 cm-1 in FTIR spectra shifts toward to the lower wave numbers at a high annealing temperature. Accordingly, the PL peak at 370 nm depends upon the annealing temperature, it was suggested that the peak appeared at 370 nm can be related to the SiOx(x<2. 0)defect states level. The Si-N bonds will form again in the Si-rich environment. When the thickness of SiO2 increases, the PL intensity of Si/Si/SiNx/SiO2 multilayers increases. After annealing at 800℃, the strongest PL intensity appears. It was suggested that the bigger thickness of SiO2 in Si/Si/SiNx/SiO2 multilayers, the more beneficial of forming Si-N net in film, and the more effectively PL. The strong PL is relevant with the content of silicon dangling bond ≡Si,nitride dangling bond N, and oxygen-related defects. The quantum confinement-luminescence center (QCLC) model was adopted to interpret the PL results. The gap state model was built in order to explain the PL phenomenon.关键词：Si/Si/SiNx/SiO2 multilayers;Fourier transform infrared absorption;photoluminescence127|204|3更新时间：2020-08-12
- 摘要：The incorporation of rare earth complex into inorganic hybrid host materials has been extensively explored in recent studies, especially focused on SiO2-based materials, and the obtained materials were found to show high improvements for their thermal, mechanical properties and chemical stability. Furthermore, the materials are nanometer-sized luminescent, and become a research attractions as luminescence probes in various types of biological detection.In this paper, the fluorescent nanoparticles were prepared with pAB-DTPAA-APTEOS precursor, TEOS and EuCl3 as raw materials by means of water-in-oil (W/O) microemulsion through controlling copolymerization of tetraethyl orthosilicate (TEOS) and 3-aminopropyl-triethyloxysilane (APTEOS). Fluorescent nanoparticles were characterized with TEM, UV-vis, IR and fluorescence techniques. It can be seen from the TEM image of the phosphor that the fluorescent nanoparticles are spherical and better particle dispersity, with average particle size of 40 nm. The IR spectra of Eu-pAB-DTPAA-AP-SiO2 has two regions, which correspond to Si-C stretching (801 cm-1) and Eu-O stretching (471 cm-1), this confirms the existence of complex Eu-pAB-DTPAA-AP-SiO2. In the UV-vis spectra, compared to the absorption spectrum of pAB-DTPAA,a red shift of the first peak (from 232 nm to 260 nm) was found in the spectrum of the precursor (pAB-DTPAA-APTEOS),no change was observed for the major at 336 nm, which indicates the information of pAB-DTPAA-APTEOS. Furthermore, after EuCl3 was added to the solution of pAB-DTPAA-APTEOS, the red shift phenomena of the absorption peaks were observed. These changes indicate that complex Eu-pAB-DTPAA-AP-SiO2 was formed in the pAB-DTPAA-APTEOS-EuCl3 solution. The excitation and emission spectra of the nanoparticles indicate that the excitation peak wavelength is at 260 nm and the emission peak wavelength is at 615 nm. When the nanoparticles were excited by 260 nm, only the emission lines of 5D0→7FJ(J= 1～4) of Eu3+ were observed, with the hypersensitive 5D0→7F2 transition as the most prominently single radiation peak without splitting. As a new analytical reagent, the fluorescent nanoparticles combine the advantages of luminophore-doped silica nanoparticle probe and lanthanide latex fluorescence probe including smaller size (about 40 nm), high hydrophilicity and biocompatibility. Furthermore, the amino groups directly introduced to the nanoparticles surface by using APTEOS in the preparation made the surface modification and bioconjugation of the nanoparticles easier. The particles are potential of good biocompatibility and can be excepted as efficient biological labels.关键词：SiO2;europium complex;microemulsion;fluorescent nanoparticles;coating131|193|2更新时间：2020-08-12
- 摘要：In a effort to prepare efficient and uniform biolabels,we describe a convenient, one-step sol-gel route to composite polymeric organic-inorganic nanosphere. First, the copolymer precursors were obtained via copolymerizations of styrene (St) and 3-methactyloxylpropyltrimethoxylsilane (KH-570), then the organic-inorganic hybrid materials have been prepared by properly controlling the condition of hydrolysis and condensation of sol-gel materials tetraethyl orthosilicate(TEOS). The copolymer precursors and their hybrid copolymers were explored and characterized by several methods including scanning electron microscope (SEM) and FTIR spectra. The scanning electron microscope(SEM)showed that the nanoparticles are very uniform, they are spherical and monodipersed with a diameter of about 200 nm. The FTIR spectra showed that the organic-inorganic nanoparticles contain polystyrene and silica two materials. The particles were also found to be good carriers for entrapped hydrophobic dyes such as phenylporphyrin molecules. The fluorophores are well protected from the environment when they were doped into the polystyrene network. Because of the hydrophobe polystyrene, water molecules can not contact the phenylporphyrin molecules inside.The outside hydrophilic silica network also help the nanoparticles disperse into the water. The method significantly reduces fluorescent dyes leaching and quenching from the nanoparticles. The emission maximum, compared with the phenylporphyrin DMF solution,change a little. It indicates that this is a physical method for doping dyes. The fluorescent nanoparticles prepared by using the novel method have the advantages such as high fluorescent and good fluorescent stability. The particles are potential of good biocompatibility, since they are a pure silica surfure and can thus be modified easily with many biomolecules for added biochemical functionality. The particles can be accepted as an effective biological labels.关键词：KH-570;copolymer precursors;nanocomposite;sol-gel route120|209|0更新时间：2020-08-12
- 摘要：Activate oxygen is not only closely relevant with many disease's occurrent' but develops also going hand in hand with food oxidation. Therefore sifting natural antioxidant appears very important. The radical scavenging and antioxidant activities of extracts are compared and evaluated from the components of nonessential oils, which are distilled respectively by water extraction, ethanol extraction,and ethyl acetate extraction. Using chemiluminescence systems of superoxide anion, free radical, hydroxyl radical,peroxynitrite and DNA oxidative damage are caused by hydroxyl radical and colorimetric systems of DPPH free radical and lipid pexoxidation. The experiments reveal that the three different extractions of the components of nonessential oils in pelargonium graveolens leaves can not only directly scavenge superoxide anion free radical,hydroxyl radical,DPPH free radical and peroxynitrite, but also has a better ability to obviously mitigate and delay DNA oxidative damage caused by hydroxyl radical and inhibit lipid pexoxidation, so the components of nonessential oils in pelargonium graveolens leaves are effective and multifunctional natural antioxidants and radical scavenger,as we all know that the nonessential oil components is extracted from waste material of essential oil components,at the same time the abstract device and the handicraft is very simple, so our research improved pelargonium graveolens's planting efficiency, and provided possibility to it's comprehensive utilization,and provided data for further research on waste materials of natural spice processes, thus it has important reference meaning to economic environment protection and resource recycle. And at present, research to fragrant plant focuses on essential oil components, both home and abroad research indicated that more antioxidation matter is existence in nonessential oil components, as we all know that the nonessential oil components is extracted from waste material of essential oil components, at the same time the abstract device and the handicraft is very simple, so pelargonium graveolens is a kind of natural plant that is worthy of further being exploited and utilized.关键词：nonessential oil extracts of pelargonium graveolens;free radical;DNA oxidative damage;antioxidant116|237|2更新时间：2020-08-12
- 摘要：The fabricating processes of diamond-based field emission cathode mainly include two modes:growing film and fabricating micro tips or micro-patterned emitters. Growing film is time-consuming and ineffective; micro pattern fabricating is cost-consuming and complicated. Both processes are not adapted to commercial application of large screen field emission displays. The third process was supposed in this paper:coating nano-diamond powders on titanium substrate by spin-coating method. Ohmic contact between diamond coating and Ti substrate could be formed after thermal annealing at proper temperature, which supplies electrons for nano-diamond particles located in coating surface and make them effective emitters. Atomic force microscopy(AFM), scanning electron microscopy(SEM), X-ray diffraction(XRD)and Raman spectroscopy were employed to study the influence of the annealing temperature on bonding effect and field emission properties. Thermal treatment at extreme low or high temperature is not benefit to improve the field emission properties of the samples, while the ones annealed at about 700℃ could gain better bonding state.The samples with different coating thickness were annealed at 700℃ to investigate the effect of the coating thickness on the field emission property. Taking the electron transport and diamond emitter number into considerations, neither the excessive thick nor thin coating is good for amelioration of the emission property. Annealed at 700℃, the sample with nine-layer coating presents better property. The threshold electric field of the sample is 4.6 V/μm, and the current density can reach to 59.7 μA/cm2 at 15.3 V/μm.关键词：nano-diamond coating;titanium substrate;field emission;thermal annealing;bonding122|165|4更新时间：2020-08-12
- 摘要：Carbon based materials with a low or negative electron affinity, such as diamond, diamond-like carbon (DLC), amorphous carbon (a-C), were widely used as cold cathode. Diamond films were generally deposited on the substrates by using chemical vapor deposition (CVD), introducing a hydrocarbon gas diluted with an amount of hydrogen gas. There were a limited number of reports dealing with the field emission characteristics of the globe-like diamond microcrystalline aggregates. The globe-like diamond microcrystalline-aggregates were fabricated by microwave plasma chemical vapor deposition (MPCVD) method in the high methane concentration of H2/CH4=100/10 sccm using a microwave plasma CVD system in our laboratory. The cera-mic with a Ti mental layer was used as substrate. The fabricated diamond aggregates were evaluated by Raman scattering spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD). It concluded that the globe-like diamond microcrystalline-aggregates are composed of diamond.The field emission properties were tested by using a diode structure in a vacuum chamber. A phosphor-coated indium tin oxide (ITO) anode was used for observing and characterizing the field emission. It was found that the globe-like diamond microcrystalline-aggregate exhibited good electron emission properties. The turn-on field was only 0.55 V/μm, and emission current density as high as 11 mA/cm2 was obtained under an applied field of 2.18 V/μm. At the successive operation circles, the turn-on field tends to stabilize at 1.6 V/μm and the current density of 1.1 mA/cm2 is obtained at an electric field of 2.9 V/μm. The Fowler-Nordheim (F-N) plots of the field emission are almost straight line, which indicates that the mechanism of the electron emission from the diamond microcrystalline-aggregate is linked to field emission by tunnel effect. The growth mechanism and field emission properties of the globe-like diamond microcrystalline-aggregates are discussed relating to microstructure and electrical conductivity. We think that the good emission properties of the diamond aggregates are considered to be combined results from the lots of the grain boundaries in the diamonds microcrystalline-aggregates and the emission enhance factor is very high as β=1 328.2.关键词：diamond microcrystalline-aggregate;field emission;chemical vapor deposition108|166|1更新时间：2020-08-12
- 摘要：The limitation of the original definition of the contrast brings about the misconstruing of computing method of panel contrast in some cases where the display effect of LED panel to be appraised. Because of the existing of the misconstruing in some cases, two problems have to be solved primarily in this paper.Generally, the display effect of the LED panel is influenced by many factors (indexes), such an stability, luminance, chromo-contrast, visual angle, etc. But the main indexes inducing the misconstruing mentioned above are contrast and visual angle. So, first of all, the relationship between the contrast calculated by the test method of the LED panel and the visual angle need to be analysed, and a new index, so-called the contrast distributed at any visual angle, must be established to present the relation of the both indexes. As the same act of other indexes, the new index will be used to evaluate the display effect of the LED panel. So at first, the maximal panel brightness and the minimal panel brightness at any visual angle can be measured by BM-7 under a certain illumination intensity, and the contrast at any visual angle will be calculated. On the other hand, the contrast can be calculated by the expression of the test method of LED panel. By comparison, the difference between the results calculated by the both methods mentioned above exists, and the difference is very obvious. The experimental results indicate that the values of the contrast at any visual angle between that computed by LED panel measurement method and that calculated by the real panel brightness are also diffe-rent, and it was also proved that the results from LED panel measurement method are out of accord with the real display effect of LED panel.Secondly, the reason why the computing method is out of accord with the real display effect is due to the complex factors in the real surroundings. So the model of the main external factors which effect the values of the contrast in the real conditions must be analysed in detail, such as the measurement angle and the reflection parameters of extraneous light. Using the module of the reflection parameters, the minimal brightness curve of the extraneous light can be obtained.And comparing with the values measured by BM-7, it is concluded that the main characteristic consistence of two kinds of the curves obtained by different methods exists. Based on the conclusion, using the mo-del of the external factors, a new expression of the contrast can be established to evaluate the display effect of LED panel. And by using this new function relation, the curved surface of the contrast at any visual angle can be simulated. In comparing with the curve of contrast computed by the test method of IED panel, it was proved that the computing method of contrast in the test method of LED panel, as without thinking of the influence of specular reflection of extraneous light, is so idealization, sometimes its result could be not agree with the real display effect of LED panel. Thus, the misconstruing problem can be explained and resolved.关键词：contrast;the effect of panel;the measurement angle;reflection parameters106|165|0更新时间：2020-08-12
- 摘要：The results of the reflectivity measurement of a laser-produced plasma (LPP) source of extreme ultraviolet (EUV) for 13.9 nm are presented. The designed structure with 120 layers of molybdenum/silicon (Mo/Si) multilayer and a period thickness of 7.14 nm was produced by ion beam sputter deposition technique. Because of the absorption by the increase overall thickness, diffusion between layers and surface oxidation (contamination), adjacent normal-incidence, the reflectivity of multilayer at 13.9 nm remains below the theoretical value of 73.2%. The surface roughness of multilayer measured by atom force microscope (AFM) is 0.401 nm.关键词：Mo/Si multilayer;reflectance;extra-ultraviolet wave band96|162|2更新时间：2020-08-12
- 摘要：The "chirped" function is induced to the one dimensional photonic crystals containing negative index media. The transmission spectrum of this type photonic crystal is investigated using the transfer matrix method. The transmission spectrum, as a function of the incident angle and the frequency, is simulated using computing. The results indicate that this photonic crystal has a wider reflect band which is insensitive to the incident angle when the thickness is not much modulated by the "chirped" function. The reason is that the real part of the complete effective index is almost zero, but the imaginary part is more lager. This special property could be used to make high quality reflection lens with wide band and full incident angle.关键词：photonic crystal;negative refraction materials;transfer matrix117|54|1更新时间：2020-08-12
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