(Ga,Mn)As on patterned GaAs(0 0 1) substrates: Growth and magnetotransport

A new type of (Ga,Mn)As microstructures with laterally confined electronic and magnetic properties has been realized by growing (Ga,Mn)As films on -oriented ridge structures with (1 1 3)A sidewalls and (0 0 1) top layers prepared on GaAs(0 0 1) substrates. The temperature- and field-dependent magnetotransport data of the overgrown structures are compared with those obtained from planar reference samples revealing the coexistence of electronic and magnetic properties specific for (0 0 1) and (1 1 3)A (Ga,Mn)As on a single sample.     

Magnetic and magnetotransport properties in the n-type (Ga,Mn)N thin films

We present the magnetic and magnetotransport properties of epitaxial (Ga,Mn)N films with nominal Mn concentration (x=0.1–0.73%) grown by plasma-enhanced molecular beam epitaxy (PEMBE). X-ray diffraction (XRD) reveals that (Ga,Mn)N has the single-phase wurtzite structure without secondary phases. The epitaxial (Ga,Mn)N films were found to exhibit n-type conductivity, ferromagnetic ordering with Curie temperature in the range 550–700 K, and in-plane magnetic anisotropy. The negative magnetoresistance (MR) was observed at temperatures below 50 K and was found to gradually increase with decreasing temperature.     

Electron mobility anisotropy in (Al,Ga)Sb/InAs two-dimensional electron gases epitaxied on GaAs (001) substrates

The electron mobility anisotropy in (Al,Ga)Sb/InAs two-dimensional electron gases with different surface morphology has been investigated. Large electron mobility anisotropy is found for the sample with anisotropic morphology, which is mainly induced by the threading dislocations in the InAs layer. For the samples with isotropic morphology, the electron mobility is also anisotropic and could be attributed to the piezoelectric scattering. At low temperature (below transition temperature), the piezoelectric scattering is enhanced with the increase of temperature, leading to the increase of electron mobility anisotropy. At high temperature (above transition temperature), the phonon scattering becomes dominant. Because the phonon scattering is isotropic, the electron mobility anisotropy in all the samples would be reduced. Our results provide useful information for the comprehensive understanding of electron mobility anisotropy in the (Al,Ga)Sb/InAs system.     

Hot-electron magnetophonon resonances in doped and undoped GaAs/(Ga,Al)As quantum wells studied using photoluminescence

Hot-electron magnetophonon resonances in the effective temperature T_eff of photo-excited carriers in GaAs/Al_xGa_1-xAs quantum wells have been observed using photoluminescence for the first time. The technique has been demonstrated to be applicable to both doped and undoped structures, allowing the hot-electron magnetophonon effect in the latter to be studied. The experimental data are in good agreement with values of T_eff=T_eff(B) calculated using a modell or the energy relaxation of hot two-dimensional carriers in a strong magnetic field.     

Giant modulation of magnetism in(Ga,Mn)As ultrathin films via electric field

Taking the advantages of semiconducting properties and carrier-mediated ferromagnetism in(Ga,Mn)As,a giant modulation of magnetism via electric field in(Ga,Mn)As ultrathin film has been demonstrated.Specifically,huge interfacial electric field is obtained by using ionic liquid as the gate dielectric.Both magnetization and transport measurements are employed to characterize the samples,while the transport data are used to analyze the electric filed effect on magnetism.Complete demagnetization of(Ga,Mn)As film is then realized by thinning its thickness down to ~2 nm,during which the degradation of ferromagnetism of(Ga,Mn)As ultrathin film induced by quantum confinement effect is suppressed by inserting a heavily-doped p-type GaAs buffer layer.The variation of the Curie temperature is more than 100 K,which is nearly 5-times larger than previous results.Our results provide a new pathway on the efficient electrical control of magnetism.     

MBE growth and processing of diluted nitride quantum well lasers on GaAs (1 1 1)B

We have grown by Molecular Beam Epitaxy GaInNAs/GaAs (1 1 1)B quantum wells (QWs) embedded in p-i-n diode and laser diode structures. The impact of the different growth parameters (As flux, growth temperature, growth rate, ion density) on the optical and structural properties of this material is studied by Photoluminescence and Atomic Force Microscopy. Additionally, systematic studies of rapid thermal annealing cycles have been performed to optimize the laser structures. Finally, edge-emitting laser diodes have been processed using these structures. These devices showed room-temperature laser emission above 1.2 μm under pulsed current conditions.     

锂离子电池正极材料LiNi_(1/3)Co_(1/3)Mn_(1/3)O_2的合成及性能研究

采用辐照凝胶法制备了锂离子电池正极用LiNi1/3Co1/3Mn1/3O2粉体材料。采用XRD、SEM和电化学充放电测试对制备材料的结构和性能进行了表征。结果表明:900℃制得的样品具有较好的层状结构,结晶性适中,电化学性能优异:其首次放电容量高达184mA·h/g(2.80～4.50V,C/10),30次循环后的容量保持率为87.4%,表现出较好的充放电容量和循环性能,较之850,950℃煅烧样品具有最小的交流阻抗和直流阻抗。     

弛豫型铁电陶瓷(1-x)Pb(Sc1/2Ta1/2)O3-xPbTiO3研究进展

钽钪酸铅陶瓷具有优良的介电、压电和铁电性能,但烧成温度高、居里点较低。为降低钽钪酸铅陶瓷的烧结温度并提高其居里点,人们合成了钽钪酸铅-钛酸铅(简称PSTT)材料体系。该文综述了弛豫型铁电陶瓷PSTT体系在相图与结构、制备和性能等方面的研究进展,探索了一种合成PSTT陶瓷新工艺,介绍了PSTT材料体系的重要应用领域。     

GaAs-Al_xGa_(1-x)As异质结的热电子磁声子共振测量

在4.2K,我们测量了GaAs-Al_xGa_(1-x)As异质结的二维热电子的磁声子共振。高电场下,SdH振荡消失以后,在二维系统中,除清楚地观察到LO声子振荡外,还观察到X点双TA声子振荡。     

钽钪酸铅-钛酸铅制备工艺研究

采用XRD、SEM等分析技术,研究了制备工艺与(1x)Pb(Sc1/2Ta1/2)O3xPbTiO3(简称PSTT)结晶性能的关系。如选择适当的组分,在适当的温度下采用传统的电子陶瓷混合氧化物法可以获得全钙钛矿相结构的PSTT陶瓷;PSTT陶瓷晶粒细小均匀。     

电光、热释电材料KTa_（1－x）Nb_xO_3的制备、性能及应用

介绍了电光、热释电材料ＫＴａ＿（１－ｘ）Ｎｂ＿ｘＯ＿３单晶、陶瓷、薄膜的制备方法，以及所制备材料的性能和应用。分析了其研究现状，简要论述了其发展趋势。     

AFM observation of OMVPE grown ErP on InP (0 0 1), (1 1 1)A and (1 1 1)B substrates

ErP has been grown on InP (0 0 1), (1 1 1)A and (1 1 1)B substrates by low-pressure organometallic vapor-phase epitaxy. The morphological change with growth temperature has been explored by atomic force microscope. On all the substrates, ErP is grown in island structure. Height and area size of the ErP islands on (1 1 1)A substrate exhibit an obvious dependence on growth temperature. ErP islands grown at 540°C, that is the suitable temperature for ErP formation, gather to step edges to make wires.     

Super-flat interfaces in In0.53Ga0.47As/In0.52Al0.48As quantum wells grown on (411)A InP substrates by molecular beam epitaxy

Effectively atomically flat interfaces over a macroscopic area (“(411)A super-flat interfaces”) were successfully achieved in In_0.53Ga_0.47As/In_0.52Al_0.48As quantum wells (QWs) grown on (411)A InP substrates by molecular beam epitaxy (MBE) at a substrate temperature of 570°C and V/III=6. Surface morphology of the In_0.53Ga_0.47As/In_0.52Al_0.48As QWs was smooth and featureless, while a rough surface of those simultaneously grown on a (100) InP substrate was observed. Photoluminescence (PL) linewidths at 4.2 K from the (411)A QWs with well width of 0.6–12 nm were 20–30 % narrower than those grown on a (100) InP substrate and also they are almost as narrow as each of split PL peaks for those of growth-interrupted QWs on a (100) InP substrate. In the case of the (411)A QWs, only one PL peak with very narrow linewidth was observed from each QW over a large distance (7 mm) on a wafer.     

共沉淀法制备Ba(Mg_(1/3)Ta_(2/3))O_3陶瓷的研究

对用化学共沉淀法制备Ｂａ （Ｍｇ１／３Ｔａ２／３） Ｏ３ （ＢＭＴ） 陶瓷及其烧结特性进行了研究。结果表明其烧结温度比用传统方法降低了１８０～２５０℃。在１ ４００℃时获得了致密的陶瓷,其体积密度达理论密度的９６％ ,晶粒排列紧密,介电特性：Ｑ×ｆ＝ ６５ ０００ ＧＨｚ,εｒ＝ ２３～２５,在ｆ＝ １０ＧＨｚ,ｔ＝ － ２０～＋ ６０℃时τｆ ＝ （０～３）×１０－ ６℃－ １。     

Photoluminescence study of type-II GaAs quantum well wires grown on nano-faced (3 1 1)A surface: Quasi-1D exciton observation?

GaAs/AlAs corrugated superlattices (CSLs) grown on nano-faceted (3 1 1)A GaAs surface were studied using Raman spectroscopy and photoluminescence (PL) techniques. Raman data (splitting of localized transversal optical phonons) have proved structural anisotropy of the CSLs. The structural anisotropy leads to optical anisotropy appeared in strong polarization dependence of PL. Temperature dependence of PL has shown that the CSLs are type-II superlattices. Additional peak in PL spectrum at low (77–100 K) temperatures can be result of quasi-1D exciton appearance in the CSLs.     

Texture and morphology variations in (In,Ga)2Se3 and Cu(In,Ga)Se2 thin films grown with various Se source conditions

Texture and morphology variations in co‐evaporated (In,Ga)₂Se₃ and Cu(In,Ga)Se₂ (CIGS) films grown with various Se source conditions during growth were studied. The Se species of simply evaporated, large molecular Se (E‐Se, low‐sticking coefficient), and RF‐plasma cracked atomic Se (R‐Se, high sticking coefficient) were used in the present work. (In,Ga)₂Se₃ precursor films, which were prepared during the first stage of CIGS film growth by the three‐stage process, showed systematic variations in texture and Na distribution profile with varying evaporative Se (E‐Se) flux. The properties of CIGS films and solar cells also showed systematic variations, and the open‐circuit voltage (V_oc) and fill factor were found to be especially sensitive to the E‐Se flux. R‐Se grown (In,Ga)₂Se₃ precursor films featured granular morphology with strong (105) and (301) peaks in the diffraction pattern, and the texture was very similar to an E‐Se grown film fabricated with a Se to group III metal (In + Ga) flux ratio (P_{[Se]/[In + Ga]}) of about 6, although the nominal P_{[Se]/[In + Ga]} used for an R‐Se source was very small and less than 0.5. The R‐Se grown CIGS films displayed, however, highly dense surfaces and larger grain sizes than E‐Se grown CIGS films. The controllability of film morphology and the Na diffusion profile in (In,Ga)₂Se₃ and CIGS films with various Se source conditions are discussed. Copyright © 2011 John Wiley & Sons, Ltd.     

Ca-B-Si掺杂对Ba(Mg_(1/3)Nb_(2/3))O_3陶瓷介电性能的影响

采用传统电子陶瓷工艺合成了Ca-B-Si(CBS)玻璃掺杂的Ba(Mgl/3Nb2/3)O3微波介质陶瓷,研究了CBS掺杂量对陶瓷微波介电性能的影响。结果表明:CBS掺杂可促进陶瓷烧结并提高B位1:2有序度,进而降低微波介质损耗。当w(CBS)=3%时,陶瓷烧结温度由纯相时的1 500℃以上降至1 250℃,表观密度提高到6.32 g/cm3以上,陶瓷的微波介电性能达到最佳值:εr=26,Q.f=67 800 GHz(8 GHz),τf=25×10–6/℃。该陶瓷有望成为用于高频段微波器件的材料。     

高Q Ba(Zn_(1/3)Ta_(2/3))O_3介质谐振器材料及其在毫米波系统中的应用

叙述了Ｂａ（Ｚｎ１／３Ｔａ２／３）Ｏ３介质谐振器材料的制备、结构、微波性能及典型应用。Ｂａ（Ｚｎ１／３Ｔａ２／３）Ｏ３介质材料介电常数εｒ为２９．５，频率温度系数τ≈０（－５５～＋８５℃），１０ＧＨｚ下最大无载Ｑ值１４７００，在２８ＧＨｚ测得Ｑ值约为４８００。这种材料具有高Ｑ值，特别适用于Ｘ以上波段作为振荡器电路中频率稳定元件。用这种介质谐振器已研制出８ｍｍ介质稳频微带耿氏振荡器，频率稳定度小于１０×１０－６／℃，最大输出功率达１８０ｍＷ。     

Composition-Dependent Photoluminescence Properties and Anti-Counterfeiting Applications of A2AgX3 (A = Rb,Cs; X = Cl,Br, I)

Copper(I) halides are emerging as attractive alternatives to lead halide perovskites for optical and electronic applications. However, blue-emitting all-inorganic copper(I) halides suffer from poor stability and lack of tunability of their photoluminescence (PL) properties. Here, the preparation of silver(I) halides A₂AgX₃ (A = Rb, Cs; X = Cl, Br, I) through solid-state synthesis is reported. In contrast to the Cu(I) analogs, A₂AgX₃ are broad-band emitters sensitive to A and X site substitutions. First-principle calculations show that defect-bound excitons are responsible for the observed main PL peaks in Rb₂AgX₃ and that self-trapped excitons (STEs) contribute to a minor PL peak in Rb₂AgBr₃. This is in sharp contrast to Rb₂CuX₃, in which the PL is dominated by the emission by STEs. Moreover, the replacement of Cu(I) with Ag(I) in A₂AgX₃ significantly improves photostability and stability in the air under ambient conditions, which enables their consideration for practical applications. Thus, luminescent inks based on A₂AgX₃ are prepared and successfully used in anti-counterfeiting applications. The excellent light emission properties, significantly improved stability, simple preparation method, and tunable light emission properties demonstrated by A₂AgX₃ suggest that silver(I) halides may be attractive alternatives to toxic lead halide perovskites and unstable copper(I) halides for optical applications.     

Bi0.5(1-y)(Na1-x-yLix)0.5SryTiO3无铅陶瓷的压电性能和微观结构

利用传统陶瓷工艺制备了新型的Bi0.5(1-y)(Na1-x-yLix)0.5SryTiO3无铅压电陶瓷,并研究了该陶瓷的压电性能和微观结构.研究结果表明,该陶瓷体系具有较好的压电性能,压电常数d33=143 pC/N,径向机电耦合系数kp=0.30,并可在1 100℃/2 h烧结条件下获得致密的陶瓷体.