Low-temperature noninjection approach to homogeneously-alloyed PbSe(x)S(1-x) colloidal nanocrystals for photovoltaic applications

Homogeneously alloyed PbSe(x)S(1-x) nanocrystals (NCs) with their excitonic absorption peaks in wavelength shorter than 1200 nm were developed for photovoltaic (PV) applications. Schottky-type solar cells fabricated with our PbSe?.?S?.? NCs as their active materials reached a high power conversion efficiency (PCE) of 3.44%, with an open circuit voltage (V(oc)) of 0.49 V, short circuit photocurrent (J(sc)) of 13.09 mA/cm2, and fill factor (FF) of 0.54 under Air Mass 1.5 global (AM 1.5G) irradiation of 100 mW/cm2. The syntheses of the small-sized colloidal PbSe(x)S(1-x) NCs were carried out at low temperature (60 °C) with long growth periods (such as 45 min) via a one-pot noninjection-based approach in 1-octadecene (ODE), featuring high reaction yield, high product quality, and high synthetic reproducibility. This low-temperature approach employed Pb(oleate)? as a Pb precursor and air-stable low-cost thioacetamide (TAA) as a S source instead of air-sensitive high-cost bis(trimethylsilyl)sulfide ((TMS)?S), with n-tributylphosphine selenide (TBPSe) as a Se precursor instead of n-trioctylphosphine selenide (TOPSe). The reactivity difference of TOPSe made from commercial TOP 90% and TBPSe made from commercial TBP 97% and TBP 99% was addressed with in situ observation of the temporal evolution of NC absorption and with 31P nuclear magnetic resonance (NMR). Furthermore, the addition of a strong reducing/nucleation agent diphenylphosphine (DPP) promoted the reactivity of the Pb precursor through the formation of a Pb-P complex, which is much more reactive than Pb(oleate)?. Thus, the reactivity of TBPSe was increased more than that of TAA. The larger the DPP-to-Pb feed molar ratio, the more the Pb-P complex, the higher the Se amount in the resulting homogeneously alloyed PbSe(x)S(1-x) NCs. Therefore, the use of DPP allowed reactivity match of the Se and S precursors and led to sizable nucleation at low temperature so that long growth periods became feasible. The present study brings insight into the formation mechanism of monomers, nucleation/growth of colloidal composition-tunable NCs, and materials design and synthesis for next-generation low-cost and high-efficiency solar cells.     

Hybrid nanocrystal/polymer solar cells based on tetrapod-shaped CdSe(x)Te(1-x) nanocrystals

A series of ternary tetrapodal nanocrystals of CdSe(x)Te(1-x) with x = 0?(CdTe), 0.23, 0.53, 0.78, 1 (CdSe) were synthesized and used to fabricate hybrid nanocrystal/polymer solar cells. Herein, the nanocrystals acted as electron acceptors, and poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) was used as an electron donor. It was found that the open circuit voltage (V(oc)), short-circuit current (J(sc)) and power conversion efficiency (η) of the devices all increased with increasing Se content in the CdSe(x)Te(1-x) nanocrystals under identical experimental conditions. The solar cell based on the blend of tetrapodal CdSe nanocrystals and MEH-PPV (9:1?w/w) showed the highest power conversion efficiency of 1.13% under AM 1.5, 80?mW?cm(-2), and the maximum incident photon to converted current efficiency (IPCE) of the device reached 47% at 510?nm. The influence of nanocrystal composition on the photovoltaic properties of the hybrid solar cells was explained by the difference of the band level positions between MEH-PPV and the nanocrystals.     

Conduction intersubband transitions at normal incidence in Si(1-x)Ge(x) quantum well devices

We show theoretically that it is possible to design SiGe-based quantum well structures in which conduction intersubband transitions are induced by normal incidence infrared radiation. A sp(3)d(5)s(*) tight binding model has been adopted to evaluate the electronic states and optical transitions between lowest conduction confined states of a superlattice composed of one pure Ge quantum well separated by SiGe alloys, grown along the [001] direction. We find that significant optical coupling between confined states in the Ge wells is achieved at normal incidence radiation by the off-diagonal elements of the mass tensor. The minimum energy Ge conduction valleys are, in fact, tilted with respect to the [001] growth axis. For comparison we show that no such coupling can be realized for the conduction states confined in a similar structure composed by Si quantum wells because the ellipsoids of the lowest conduction valleys are oriented along the growth direction.     

Thermodynamics of coherently-strained GexSi1-x nanocrystals on Si(001): alloy composition and island formation

We determined the enthalpic and entropic contributions to the thermodynamics of coherently strained nanocrystals grown via deposition of pure Ge on Si(001) surfaces at 600 and 700 degrees C by analyzing their composition profile and local strain. We found that the free energy associated with the entropy of mixing, which drives GexSi1-x alloy formation, was significantly larger than the relaxation enthalpy that produces the islands. Thus, entropy plays a significant role in the evolution of the size and shape of the islands during growth through the strong thermodynamic drive to form an alloy.     

Optoelectronic and dielectric properties of GaAs x Sb1-x ternary alloys

Based on the pseudopotential scheme under the virtual crystal approximation in which the effect of compositional disorder is involved, the dependence of optoelectronic properties of GaAs _x Sb_1-x on alloy composition x have been studied. Our results showed generally good agreement with the available experimental data. The material of interest is found to exhibit features of both direct and indirect band-gap semiconductor depending on the alloy composition x. The method used has been combined with the Harrison bond-orbital model and employed to calculate the dielectric constants and their composition dependence.     

Ambipolar field effect in the ternary topological insulator (Bi(x)Sb(1-x))2Te3 by composition tuning

Topological insulators exhibit a bulk energy gap and spin-polarized surface states that lead to unique electronic properties, with potential applications in spintronics and quantum information processing. However, transport measurements have typically been dominated by residual bulk charge carriers originating from crystal defects or environmental doping, and these mask the contribution of surface carriers to charge transport in these materials. Controlling bulk carriers in current topological insulator materials, such as the binary sesquichalcogenides Bi2Te3, Sb2Te3 and Bi2Se3, has been explored extensively by means of material doping and electrical gating, but limited progress has been made to achieve nanostructures with low bulk conductivity for electronic device applications. Here we demonstrate that the ternary sesquichalcogenide (Bi(x)Sb(1-x))2Te3 is a tunable topological insulator system. By tuning the ratio of bismuth to antimony, we are able to reduce the bulk carrier density by over two orders of magnitude, while maintaining the topological insulator properties. As a result, we observe a clear ambipolar gating effect in (Bi(x)Sb(1-x))2Te3 nanoplate field-effect transistor devices, similar to that observed in graphene field-effect transistor devices. The manipulation of carrier type and density in topological insulator nanostructures demonstrated here paves the way for the implementation of topological insulators in nanoelectronics and spintronics.     

静电纺丝法制备Sr1-xLaxFe12-xCoxO19纳米纤维及其磁性研究

采用溶胶?凝胶过程和静电纺丝技术相结合的方法,制得了PVP/Sr1-xLaxFe12-xCoxO19(x=0～0.5)复合纳米纤维,经过煅烧处理过程,获得了Sr1-xLaxFe12-xCoxO19(x=0～0.5)纳米纤维.通过SEM、TEM、XRD和VSM等技术对样品的形貌、物相、结构以及磁性能进行了表征.结果表明,800℃煅烧后的Sr1-xLaxFe12-xCoxO19(x=0.5)纳米纤维的直径主要分布在80～150 nm;这些纤维在室温下都具有硬磁特性,化学组成对铁氧体的磁性能有着显著的影响,当x≥0.3时,样品中同时出现M型的SrFe12O19、LaFeO3和CoFe2O4;在适当范围内(x≤0.1),La3+-Co2+的掺杂有利于改善锶铁氧体纤维的永磁性能,相应的矫顽力、饱和磁化强度和剩余磁化强度分别为Hc=432.02kA/m,Ms=54.7A.m2/kg,Mr=28.9A.m2/kg,与传统溶胶?凝胶法在相同条件下制得的Sr0.9La0.1Fe11.9Co0.1O19粉体样品相比,磁性能也有显著提高.     

Growth and properties of Zn(1-x)CdxO and Zn(1-x)CdxO/ZnO core/shell nanoparticles

Octylamine capped Zn(1-x)CdxO alloys and Zn(1-x)CdxO/ZnO core/shell nanoparticles have been grown by the thermal decomposing of zinc and cadmium cupferronates in organic solvents. Zn(1-x)CdxO alloys incorprated with different concentration of Cd have been grown by quickly injecting of their precursors at 200 degrees C. Zn(1-x)CdxO/ZnO core/shell nanoparticles are performed by slowly injecting of shell precursors at 180 degrees C. The prepared nanoparticles are characterized by X-ray diffraction, absorption spectrometer, Mirco-Raman spectrometer and transmission electron microscopy. The band gap of ZnCdO alloys shrinks linearly and the crystal lattice expands with an increase of Cd concentration. The growth of ZnO shells on ZnCdO cores enhances the core luminescence dramatically and results in a red shift in the absorption and emission of Zn(1-x)CdxO cores.     

Magnetocaloric Effect in MnCo_(1-x)Al_xGe Compounds

The effects of substitution of Al for Co on magnetic and magnetocaloric properties of MnCo1-xAlxGe (x=0.00, 0.03, 0.05, 0.08, 0.10, 0.13, 0.15, and 0.20) compounds have been investigated by X-ray diffraction (XRD) and magnetization measurements. XRD exhibits that MnCo1-xAlxGe compounds crystallize in the orthorhombic TiNiSi-type structure for x≤0.03 and in the hexagonal Ni2In-type crystal structure for x>0.03. Magnetic measurements show that the Curie temperature can be tuned between 286 and 347 K by changi...     

溅射Cu-Zn-Sn金属预制层后硫(硒)化法制备Cu2ZnSn(SxSe1-x)4薄膜及其光伏特性

采用溅射工艺制备Cu-Zn-Sn金属预制层并尝试在多种退火方案(硫化退火、硒化退火、不同温度下硫化后硒化)下对其进行退火处理,探索出一种只需采用金属预制层即可完成CZTSSe制备的退火工艺制度.通过扫描电镜对比研究了不同退火制度下Cu2ZnSn(SxSe1-x)4薄膜的形貌差异,发现低温硫化后硒化工艺可以有效减少因硫化温度过高引起的薄膜中孔洞较多的问题,有利于薄膜的平整与致密化.在此基础上,采用 X射线荧光光谱、扫描电镜、X 射线衍射及拉曼光谱对不同硫化温度(200 ℃、300℃、400 ℃、500 ℃)下硫化后硒化工艺制备的Cu2ZnSn(SxSe1-x)4薄膜的成分、形貌、物相结构及结晶性能进行了表征和分析.结果表明,300 ℃下硫化后硒化获得的Cu2ZnSn(SxSe1-x)4较其他温度下硫化后硒化获得的产物有着更好的形貌及结晶性能,其器件的光电转换效率为2.09%,远高于500 ℃下硫化后硒化工艺所得薄膜器件的效率(0.94%).     

溶胶-凝胶法合成层状锂离子电池正极材料LiNi(1-x)/3Mn(1-x)/3Co(1-x)/3CrxO2及其电化学性能的研究

采用溶胶-凝胶法制备了层状锂离子电池正极材料LiNi(1-x)/3Co(1-x)/3Mn(1-x)/3CrxO2 (x=0,0.02,0.05,0.1).利用XRD、电化学测试等手段对材料的结构、电化学等性能进行表征.结果表明:LiNi(1-x)/3Co(1-x)/3Mn(1-x)/3CrxO2仍然为层状α-NaFeO2结构;当x=0.02,0.2C充放电首次放电比容量达到195mAh/g,首次放电效率高达到91.7％,并且有着良好的循环性能.     

锂快离子导体Li3-2x(Al1-xTix)2(PO4)3的合成与表征

NASICON型正磷酸盐LiM2(PO4)3(M=Ti,Ge,Zr,Hf)是近来研究得比较深入的锂快离子导体.LiTi2(PO4)3难于烧结得到致密的LiT2(PO4)3陶瓷,且离子电导率很低,在298K时为8.260×10-8 S/cm,613K时为8.241×10-5 S/cm,而当以三价的Al3 离子经传统的固相烧结反应部分取代LiTi2(PO4)3中四价的Ti4 离子后,通过DSC、DTG、电化学阻抗与SEM测试表明,不仅能获得致密度高稳定的产物,而且烧结后得到的锂快离子导体Li3-x(Al1-xTix)2(PO4)3(X=1.0～0.55)体系在室温下的电导率有了巨大的提高.当X=0.85时,组分Li1.3Al0.3Ti1.7(PO4)3离子电导率最大,298K时为1.792×10-6S/cm和613K时为9.210×10-4S/cm.     

Optical constants of V(1-x)W(x)O(2) Films

The spectral complex optical constants in the visible and the near-infrared region of VO(2) and V(1-x)W(x)O(2) films deposited on glass substrates were determined from observed reflectance and transmittance spectra for which the least-squares method was used. In the metallic phase, the optical properties were characterized by the Drude model in wavelength regions longer than 750 nm.     

Fabrication of 3-dimensional PbZr(1-x)Ti(x)O3 nanoscale thin film capacitors for high density ferroelectric random access memory devices

PbZr(x)Ti(1-x)O3 (PZT) thin films were deposited on 3-dimensional (3D) nano-scale trench structures for use in giga-bit density ferroelectric random access memories. PZT thin films were deposited by liquid delivery metalorganic chemical vapor deposition using Pb(thd)2, Zr(MMP)4, and Ti(MMP)4 precursors dissolved in ethyl cyclohexane. Iridium thin films were deposited by atomic layer deposition, and they exhibited excellent properties for capacitor electrodes even at a thickness of 20 nm. The trench capacitor was composed of three layers, viz. Ir/PZT/lr (20/60/20 nm), and had a diameter of 250 nm and a height of 400 nm. Almost 100% step coverage was obtained at a deposition temperature of 530 degrees C. The PZT thin film capacitors with a thickness of 60 nm on a planar structure exhibited a remnant polarization (Pr) of 28 microC/cm2, but the Pr value of the 3D PZT capacitors decreased slightly with decreasing 3D trench pattern size. The transmission electron microscope analysis indicated that the PZT thin films had compositional uniformity in the 3D trench region. Both columnar and granular grains were formed on the sidewalls of the trench capacitors, and their relative proportion exhibited strong size dependence. The trench capacitors with more columnar PZT grains showed good switching behavior under an external bias of 2.1 V and had a remnant polarization of 19-24 microC/cm2.     

La_（1－x）SrxCoO_（3－y）导电陶瓷制备工艺的研究

用固相反应法制备了Ｌａ＿（１－ｘ）Ｓｒ＿ｘＣｏＯ＿（３－ｙ）导电陶瓷材料，研究了制备工艺对烧结性能的影响。实验结果表明：烧结体的致密度取决于预烧温度、烧成温度及保温时间，此外还与成型方法等因素有关。在１０００～１３００℃保温２～１５ｈ获得了高密度、导电性良好的立方钙钛矿型Ｌａ＿（１－ｘ）Ｓｒ＿ｘＣｏＯ＿（３－ｙ）（ｘ＝０．５，０．６）陶瓷材料。用Ｘ射线分析了材料的相组成和结构。     

Diameter-dependent composition of vapor-liquid-solid grown Si(1-x)Ge(x) nanowires

Diameter-dependent compositions of Si(1-x)Ge(x) nanowires grown by a vapor-liquid-solid mechanism using SiH(4) and GeH(4) precursors are studied by transmission electron microscopy and X-ray energy dispersive spectroscopy. For the growth conditions studied, the Ge concentration in Si(1-x)Ge(x) nanowires shows a strong dependence on nanowire diameter, with the Ge concentration decreasing with decreasing nanowire diameter below approximately 50 nm. The size-dependent nature of Ge concentration in Si(1-x)Ge(x) NWs is strongly suggestive of Gibbs-Thomson effects and highlights another important phenomenon in nanowire growth.     

Co(1-x)Mg(x)MoO4 compounds for pressure indicators

Two Co(1-x)Mg(x)MoO(4) oxide compositions (x=0 and x=0.4) were investigated as potential pressure indicators. The first order phase half-transition induced by pressure application from the β to the α form, i.e. from the high temperature/low pressure form to the high pressure/low temperature form, was studied thanks to the powder diffuse reflection (color) evolution versus the applied pressure. Three key parameters were analyzed: (i) the magnesium content, (ii) the powder grain sizes, (iii) the pressure application mode (uniaxial or isostatical). It was shown these three parameters allow tuning the transition pressure in a wide range from few bars to few kbars.     

Constructing anisotropic single-Dirac-cones in Bi(1-x)Sb(x) thin films

The electronic band structures of Bi(1-x)Sb(x) thin films can be varied as a function of temperature, pressure, stoichiometry, film thickness, and growth orientation. We here show how different anisotropic single-Dirac-cones can be constructed in a Bi(1-x)Sb(x) thin film for different applications or research purposes. For predicting anisotropic single-Dirac-cones, we have developed an iterative-two-dimensional-two-band model to get a consistent inverse-effective-mass-tensor and band gap, which can be used in a general two-dimensional system that has a nonparabolic dispersion relation as in the Bi(1-x)Sb(x) thin film system.