شناسایی کوآنتوم دات های CdTe در نانوذرات ژلاتینی

Synthesis and characterization of CdTe quantum dots

embedded gelatin nanoparticles 

شناسایی و سنتز کوآنتوم دات های CdTe محاط در نانوذرات ژلاتینی

ABSTRACT

Novel CdTe quantum dots (QDs) embedded gelatin nanoparticles (CdTe/gelatin nanoparticles) were synthesized via a two-step desolvation method. The morphology and size distribution of the nanoparticles were characterized by transmission electron microscope (TEM) and laser particle size analyzer. They are presented spherically and relatively uniform with a diameter of 150 nm. The luminescent properties of the nanoparticles were investigated by using fluorescence spectrophotometry and fluorescence microscopy. The fluorescence stability of nanoparticles was tested in vitro. It was found that the nanoparticles were stable in water and phosphate-buffered saline (PBS) solution (pH 7.4) for at least 15 days. A possible formation mechanism of the CdTe/gelatin nanoparticles was also proposed. The inherent stability and biocompatibility indicate that the nanoparticles are expected to be promising candidates for in vivo biological imaging studies.

 

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 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.

 

اثر پارامترهای جوشکاری ترمیمی بر عمر مفید قالب های دایکست

Effect of repair-welding parameters on life time of

die casting moulds

اثر پارامترهای جوشکاری ترمیمی بر عمر مفید قالب های دایکست

ABSTRACT

In die casting, H13 hot working tool steels are exposed to heat shocking and cracking due to the thermal fatigue which is exerted by die casting process. The gradual destruction of mould surfaces during the service, decreases casting piece quality and limits the mould life time. These moulds are expensive and replacing of them is the main problem of the die casting industries therefore repair-welding of die casting moulds can be helpful. H13 steel has low weldability because of the significant hardening resulted from large amounts of alloying elements. Within this study, results were obtained on the performance of repair welded parts that were welded by three types of filler metals on the thermal fatigue test. The filler metals that are used in this study are H13 tool steel, maraging steel and Co-base alloy. Maximum and minimum life time of the repair welded parts of die casting mould in the thermal fatigue test were obtained from Co-base alloy and H13 hot work steel filler metals, respectively. Repair-welding by maraging filler metal shows the intermediate life time. It seems that repair-welding of H13 moulds by maraging filler metals is more economic because of its lower price in comparison with the Co-base filler metal.

 

اثر عملیات حرارتی بر ریزساختار و خواص مکانیکی آلیاژ فراریزدانه شبه تیتانیوم β

Effect of Heat Treatment on Microstructure and Mechanical

Properties of Ultra-fine Grained Ti-55511 Near β Titanium Alloy

اثر عملیات حرارتی بر ریزساختار و خواص مکانیکی آلیاژ فراریزدانه شبه تیتانیوم β 

ABSTRACT

The ultra-fine grained (UFG) Ti-55511 near β titanium alloy with grain size 0.1∼0.5 μm was prepared by hot rolling. The effects of heat treatment on the microstructure and mechanical properties were investigated using SEM and TEM. The results indicate that both strength and hardness increase firstly and then reduce with increasing of heat treatment temperature from 350°C to 650°C. The peak strength (1486 MPa) appears at 450°C. The strength dramatically reaches to 1536 MPa and then is stablized with increasing of the holding time when heat treated at 450°C. While the elongation increases firstly and then decreases. The microstructure analysis shows that the dynamic recovery occurs and the grain sizes remain at smaller than 1 μm during annealing. The recovery stimulates the grain refinement effect by eliminating the hardening process and stimulating the grain boundary/phase boundary to be stable. The phase transformation of α→α2 and β→ω→α enhances the second phase particle dispersion effect during annealing. However, the ductility of the alloy could significant decrease when the second phase particles grow up to a certain size. The mechanical properties evolution during annealing are mainly related to the effect of strengthening mechanisms.

 

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.