Structural and electronic properties of CdTe1-xSex films and their application in solar cells

The performance improvement of conventional CdTe solar cells is mainly limited by doping concentration and minority carrier life time. Alloying CdTe with an isovalent element changes its properties, for example its band gap and behaviour of dopants, which has a significant impact on its performance as a solar cell absorber. In this work, the structural, optical, and electronic properties of CdTe_1-xSe_x films are examined for different Se concentrations. The band gap of this compound changes with composition with a minimum of 1.40 eV for x = 0.3. We show that with increasing x, the lattice constant of CdTe_1-xSe_x decreases, which can influence the solubility of dopants. We find that alloying CdTe with Se changes the effect of Cu doping on the p-type conductivity in CdTe_1-xSe_x, reducing the achievable charge carrier concentration with increasing x. Using a front surface CdTe_1-xSe_x layer, compositional, structural and electronic grading is introduced to solar cells. The efficiency is increased, mostly due to an increase in the short-circuit current density caused by a combination of lower band gap and a better interface between the absorber and window layer, despite a loss in the open-circuit voltage caused by the lower band gap and reduced charge carrier concentration.     

Lattice dynamical investigations on Zn diffusion in zinc oxide

Zinc self diffusion in bulk zinc oxide is studied by lattice dynamical approach here to get more insight into the diffusion in nano ZnO. The results reveal that only cationic self diffusion is dominant over anionic self diffusion and that too by single vacancy mechanism. The results are compared with the available experiments and discussed.     

Lattice parameter and expected density of Au nano-structures sputtered on glass

Gold nano-structures (clusters and layers) were sputtered on the glass substrate. Lattice parameter was determined by X-ray diffraction. Density of Au nano-structures was calculated depending on structures size. Density of gold structures increases from the value of 13.6 · 10³ to 19.3 · 10³ kg m^− 3. Free volume fraction of structures decreases from the value of 48 to 26%.     

The microhardness of CdxHg1-xTe

The Vickers hardness of Cd _x Hg_1–x Te alloys has been measured as a function of composition, from x=0 to x=0.6, and at x=1.0, at 300 K in darkness, on single crystal or large grain polycrystalline samples. Microhardness values ranged from 26 kg mm^–2 for HgTe, rising to 70 kg mm^–2 for x0.6, and dropping to about 50 kg mm^–2 for CdTe, and the dependence on composition indicates that a maximum must occur somewhere in the range 0.6<x<1.0. The hardness-composition curve is discussed in terms of possible models of solid solution hardening in this system, and the results are compared with the behaviour in metallic systems.     

Lattice parameter study of silicon uniformly doped with boron and phosphorus

Powder and single-crystal X-ray techniques have been employed to obtain precise lattice parameters of silicon uniformly doped with boron or phosphorus. Good agreement is found between the two methods. Previous accurate determination of the CuKα₁, effective wavelength has yielded λ=1.540621±0.000006 Å. Particular care has been devoted to the chemical and electrical characterization of the alloys, whose maximum dopant concentrations were 8×10¹⁹ atoms cm^?3 for P and 4.4×10²⁰ atoms cm^?3 for B. A linear dependence of lattice parameter on concentration has been found for P in the whole examined range, while for B a deviation from the linear trend starts at about 2.25×10²⁰ atoms cm^?3. Tetrahedral radii are found to be 1.176 Å for pure Si, 1.07 Å and 0.91 Å respectively for dissolved substitutional P and B. Values of the linear lattice contraction coefficient, volume size factor, Vegard's law factor and elastic strain energy in both alloys are reported and discussed. The deviation from linear trend in borondoped alloys is analysed and it is shown that the phenomenon is insensitive to heattreatments and does not depend on the degree of ionization of boron atoms.     

Effect of nuclear radiation on the microhardness of SAV-1 avials

The microhardness of the initial specimens of SAV-1 avials was experimentally investigated. Modification of this mechanical characteristic as a result of alloy irradiation in the channels of a research nuclear reactor WWR-SM was studied. The nonlinear pattern of material hardening after irradiation at low fluence rates (10¹⁵ – 10¹⁸ neutron/cm²) was revealed. The radiation effect of avial microhardness variations is established to be a certain function of irradiation doses and indentation loads. The possible reasons of an increase in hardness of irradiated specimens are discussed. The radiation-induced hardening of aluminum alloys is assumed to be determined by generation of point flaws and dislocations, blocked by defects and interstitial phase decay products.     

Analysis of microhardness data in TlxIn1−xSe

Microhardness measurements have been performed on Tl _x In_1–x Se semiconductors (x=0.0, 0.2, 0.3 ... 1.0). The microhardness, H, as a function of x shows a maximum at x ca. 0.5. A statistical evaluation of the obtained results leads to a log-normal distribution of the microhardness rather than, as expected, a polynomial one.     

金属Cu纳米晶体的显微硬度及微结构研究

为了研究自悬浮-模压法制备的纳米金属晶体材料的有关性能及微观结构特征,采用自悬浮定向流技术制备出纳米Cu粉,经过常温模压得到金属Cu纳米晶体材料,测试了样品的室温显微硬度,并探讨了不同的压制工艺对金属Cu纳米晶体材料显微硬度的影响;利用X射线衍射谱和正电子湮没技术分别分析了纳米Cu晶体的平均晶粒尺寸和其内部的孔隙状态.研究结果表明:金属Cu纳米晶体的平均晶粒尺寸为25 nm,显微硬度随压制工艺而变化,达1.55～1.90GPa,为粗晶Cu的3～4倍;材料内部缺陷大部分为单空位和空位簇,微孔隙的数量很少.     

Synthesis, morphology, and optical properties of colloidal CdTe/CdSe and CdTe/CdS nanoheterostructures based on CdTe tetrapods

We report the synthesis of colloidal CdTe/CdSe and CdTe/CdS nanoheterostructures based on CdTe tetrapods with a CdSe or CdS shell. The shell growth takes place on the lateral faces of the tetrapod legs, whereas the leg length remains essentially unchanged. Both the CdSe and CdS shell growth shifts the luminescence of the nanoheterostructures to the near-IR range, up to 850 nm, with a quantum yield of up to 20%. Analysis of the kinetics of the shift of the excitonic absorption band during nanoheterostructure growth suggests that the growth rate of CdS exceeds that of CdSe. The variation of the luminescence wavelength with shell thickness is compared to numerical modeling results.     

Molecular beam epitaxy of CdTe and CdxHg1−xTe

Epitaxial layers of Cd_xHg_1?xTe were grown by molecular beam epitaxy on the Te(111) face of CdTe substrates at up to 120 °C. These layers show good crystallinity and a low carrier concentration at 77 K. Their low Hall mobility which seems to be due to twins can be increased by a post-growth annealing.     

Etching and microhardness studies on lead molybdate single crystals

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Knoop microhardness measurements on lithium niobate and lithium tantalate

Knoop microhardness measurements were made on the (11.0), (01.0) and (00.1) planes of the trigonal isostructural compounds lithium niobate and lithium tantalate. The data indicate uniform hardness in the 〈11.0〉 and 〈01.0〉 directions and greater hardness in the [00.1] direction. In accordance with previous findings of hardness anisotropy in materials with hexagonal crystal structure, the present data indicate preferred slip on basal planes. The ratio of hardness to the shear modulus C ₆₆ is close to 0.1, which is usually found in covalent-bonded solids.     

Effect of suspension on mouse bone microhardness

Antiorthostatic (hindlimb) suspension of mice results in a considerable reduction of bone formation at the femur mid-diaphysis. Comparisons with appropriate control groups indicate that this reduction is attributable to the unloading aspect of the model, and not to physiological stress or changes in feeding. Microhardness measurements of bone are used to provide information on site-specific mineralization and structural properties. The microhardness of femora formed during suspension is significantly less than that formed in the bone of control mice. These differences are observed both along the endocortical (11%) and periosteal (8%) perimeters. The microhardness of bone formed prior to the experimental period (extant bone) is not different in comparing suspended and control mice, and increased microhardness values for these areas are observed in comparison to baseline controls. Mice used to control for the physiological stress and feeding portions of the suspension model do not demonstrate reduced microhardness. Thus, the limb unloading effects of suspension, not the induced stress or feeding changes, cause a reduction in microhardness. As microhardness is positively related to mineralization in these bones, it appears that the reduced mineralization accompanying suspension unloading may contribute to compromised structural properties of the bone formed.Now deceased, Dr. Luttges lasting contributions to the subject are acknowledged     

Studies on microhardness of quenched mesolite crystals

Observations and results on studies of the microhardness of {1 0 1} and {1 0 ¯1} faces of natural mesolite crystals are illustrated and explained. Variations in Vickers hardness number (VHN) with temperature of quenching and also with the applied load are discussed.     

Lattice parameter,density, and defect system of VO<Subscript>y</Subscript>

Vanadium monoxide, VO _y has been studied within its homogeneity range using X-ray diffraction and pycnometric density measurements. The density and lattice parameter of VO _y have been shown to vary in a complex manner with oxygen content near the stoichiometric composition VO_1.0. The experimental data have been used to evaluate the vanadium and oxygen vacancy contents in VO _y . We assume that two cubic phases close in lattice parameter coexist near the composition VO_1.0 and form a solid solution.     

SEM characterization of CdTe growth on CdTe(111) by close-spaced sublimation

A close-spaced sublimation (CSS) reactor is used to explore the growth of CdTe thin films on CdTe(111) substrates in order to determine the parameters required for high quality smooth film growth. Growth rates below 1 μm/h were targeted based on a preliminary sublimation study of the substrate material. The CSS technique is of interest due to its low cost and the potential for producing high quality films at higher growth rates compared to molecular beam epitaxy (MBE). Films were characterized by optical and scanning electron microscopy (SEM), atomic force microscopy (AFM), and the film thickness was determined using an alpha-step IQ profilometer. The initial quality of the films was determined by the electron back scattering diffraction (EBSD) technique.