خواص اپتیکی و سنتز لایه های نازک نانوکریستال CdTe

Synthesis and optical characterization of nanocrystalline CdTe thin films

خواص اپتیکی و سنتز لایه های نازک نانوکریستال CdTe

ABSTRACT

From several years the study of binary compounds has been intensified in order to find new materials for solar photocells. The development of thin film solar cells is an active area of research at this time. Much attention has been paid to the development of low cost, high efficiency thin film solar cells. CdTe is one of the suitable candidates for the production of thin film solar cells due to its ideal band gap, high absorption coefficient. The present work deals with thickness dependent study of CdTe thin films. Nanocrystalline CdTe bulk powder was synthesized by wet chemical route at pH≈11.2 using cadmium chloride and potassium telluride as starting materials. The product sample was characterized by transmission electron microscope, X-ray diffraction and scanning electron microscope. The structural characteristics studied by X-ray diffraction showed that the films are polycrystalline in nature. CdTe thin films with thickness 40, 60, 80 and 100 nm were prepared on glass substrates by using thermal evaporation onto glass substrate under a vacuum of 10−6 Torr. The optical constants (absorption coefficient, optical band gap, refractive index, extinction coefficient, real and imaginary part of dielectric constant) of CdTe thin films was studied as a function of photon energy in the wavelength region 400–2000 nm. Analysis of the optical absorption data shows that the rule of direct transitions predominates. It has been found that the absorption coefficient, refractive index (n) and extinction coefficient (k) decreases while the values of optical band gap increase with an increase in thickness from 40 to 100 nm, which can be explained qualitatively by a thickness dependence of the grain size through decrease in grain boundary barrier height with grain size.

 

سنتز لایه های CdTe به روش آنیل کردن در جعبه گرافیتی

Synthesis of high quality CdTe films by graphite box annealing

سنتز لایه های CdTe کیفیت بالا به روش آنیل کردن در جعبه گرافیتی

ABSTRACT

CdTe films were prepared by graphite box annealing of an evaporated CdTe precursor in different ambient conditions in the quartz annealing chamber. Large grain growth was observed for films synthesized at 710 K in argon atmosphere. The films thus produced were characterized by measuring the optical, microstructural and electrical properties.

 

سنتز لایه های نازک نانوکریستالی CdTe به روش تبخیر حرارتی در خلأ

Synthesis, electrical properties and transport mechanisms

of thermally vacuum evaporated CdTe nanocrystalline thin films

سنتز، خواص الکتریکی و مکانیزم های انتقال لایه های نازک نانوکریستالی CdTe

به روش تبخیر حرارتی در خلأ

ABSTRACT

A stoichiometry CdTe nano-structured powder was synthesized by chemical process. Thin films of different thicknesses (40, 60, and 100 nm) of CdTe were prepared by thermal evaporation method onto silicon substrates. Current–voltage (I–V) and capacitance–voltage (C–V) characteristics of CdTe nanocrystalline thin films deposited on p-Si as heterojunction have been investigated. At low voltages, current in the forward direction was found to obey the diode equation and the conduction was controlled by thermionic emission mechanism. Also, various electrical parameters were determined from the I–V and C–V analysis. The thickness dependence of the obtained capacitance–voltage (C–V) characteristics was also considered.

 

سنتز کادمیوم تلوریم Fundamentals of the CdTe synthesis

Fundamentals of the CdTe synthesis

مفاهیم بنیادین سنتز CdTe

ABSTRACT

Different ways to achieve liquid, vapour, solution or even solid synthesis of CdTe are examined from a thermodynamic viewpoint. The catalytic character of the reactions of formation is stressed. The advantages of solution synthesis, mainly using the so-called Cold Travelling Heater Method (CTHM), are shown. Several kilograms of material in a run can be produced by this safe, non-expensive process, which can be easily extended to the production of homogeneous CdZnTe. Purity, homogeneity and possibility to obtain a composition corresponding to the congruent sublimation line are among the assets of this technique.

 

رسوب نشانی لایه های نازک زیرکونیای پایدار شده با ایتریا

Yttria-stabilized zirconia thin films deposited by

pulsed-laser deposition and magnetron sputtering

رسوب نشانی لایه های نازک زیرکونیای پایدار شده با ایتریا،

به روش رسوب دهی لیزری پالسی  و کندوپاش ماگنترونی

ABSTRACT

Yttria-stabilized zirconia (YSZ, ZrO2:Y2O3) was deposited on (100) silicon by two physical vapor deposition techniques: pulsed laser deposition (PLD) and reactive magnetron sputtering (RMS). PLD thin films were grown on silicon substrates at 500 °C from the ablation of a 8YSZ ceramic target by a KrF excimer laser. RMS thin films were obtained by direct current magnetron sputtering of a Zr/Y metallic target in an oxygen/argon atmosphere. The deposition rate of the PLD technique using an UV excimer laser delivering pulses at a repetition rate of 40 Hz was found two orders of magnitude lower than the RMS method one. Both techniques led to the growth of crystalline films with a (111) preferential orientation. PLD films were dense and featureless whereas RMS ones exhibited well defined but compact columnar structure. Growth of a YSZ film of about 1 μm covering a rough and porous commercial anode support (NiO–YSZ cermet) was successfully carried out with both methods.

 

ترموالکتریک و کاربردهای آن Thermoelectrics

Thermoelectrics: a review of present and potential applications

ترمو الکتریک: مروری بر پتانسیل کاربردهای کنونی 

ABSTRACT

Thermoelectric devices are solid state devices. They are reliable energy converters and have no noise or vibration as there are no mechanical moving parts. They have small size and are light in weight. As refrigerators, they are friendly to the environment as CFC gas or any other refrigerant gas is not used. Due to these advantages, the thermoelectric devices have found a large range of applications. In this paper, basic knowledge of the thermoelectric devices and an overview of these applications are given. The prospects of the applications of the thermoelectric devices are also discussed.

 

رسانایی گرمایی ZrB2 و HfB2

Thermal Conductivity of ZrB2 and HfB2

رسانایی گرمایی ZrB2 و HfB2 

ABSTRACT

ZrB2 and HfB2 are proposed for use in hypersonic vehicles and reentry spacecraft where they will be used as thermal management materials for extreme thermal environments. These applications typically include sharp control surfaces (leading/trailing edges) as well as scramjet engine components [1–5]. Hypersonic control surfaces need thermal conductivities (k) that are as high as possible to conduct heat generated from atmospheric friction through the material so that it can be dissipated elsewhere [1, 3]. In addition, higher k values increase thermal shock resistance in high heat flux situations. Because engine components cannot radiate to the atmosphere, lower k refractory materials could be beneficial, depending on the cooling capabilities of the vehicle [3]. From a materials engineering perspective, the effects of processing, composition (intentional additions or from impurities), and the resulting microstructure need to be characterized to design materials with appropriate properties. The goal of this chapter is to review the state-of-the-art with respect to thermal conductivity for single-phase and composite ZrB2 and HfB2 ceramics.

 

جوشکاری فلزات دیرگداز (نیوبیوم، تانتالیوم، مولیبدن و تنگستن) و لحیم کاری گرم آن ها

The welding and brazing of the refractory metals

niobium, tantalum, molybdenum and tungsten 

مروری بر جوشکاری و لحیم کاری گرم فلزات دیرگداز 

نیوبیوم، تانتالیوم، مولیبدن و تنگستن

ABSTRACT

This review covers the present and future problems in the development and welding of niobium, tantalum, molybdenum and tungsten and their alloys. Their metallurgical characteristics are discussed together with the influence of impurities and alloying elements on mechanical properties, alloy development and weldability. Other factors briefly discussed are availability, high temperature strength, ductility and oxidation resistance.

 

افزودن آهن بر سینترینگ فاز مایع کامپوزیت تنگستن- برنز

The effects of Fe additions on the liquid phase sintering of

W-bronze composites

اثرات افزودن آهن بر سینترینگ فاز مایع کامپوزیت تنگستن- برنز

ABSTRACT

In this investigation, experiments were conducted to evaluate the effects of Fe additives in the range of 1–5 wt.% on the densification of different compositions of W–pre-alloy bronze compacts sintered isothermally at temperatures ranging from 900 °C to 965 °C for 2.30 h. The results showed that substantial improvement in hardness by a factor of two folds and density by 10% was achieved for the W–pre-alloy bronze sintered compacts by the addition of 2–3 wt.% Fe as an activator.

 

کامپوزیت های زمینه پلیمری (PMC)

polymer matrix composite (PMC)

کامپوزیت های زمینه پلیمری (PMC) 

ABSTRACT

A high-performance polymer matrix composite (PMC) consists of a thermoset or thermoplastic resin matrix reinforced by fibers that are much stronger and stiffer than the matrix.1 Structural fibers that may be used as the reinforcement phase include carbon, aramid, glass, and many others. PMCs are attractive because they are lighter, stronger, and stiffer than conventional materials, with the additional advantage that their properties and form can be tailored to meet the needs of a specific application. Depending on the characteristics of the resin matrix and fiber reinforcements, PMCs may also be tailored to exhibit such properties as high thermal or electrical conductivity, stealth characteristics, and sensor capabilities.