رسوب دهی لیزر پالسی لایه های نازک CdTe و اثر دمای زیرلایه

CdTe thin films grown by pulsed laser deposition

using powder as target: Effect of substrate temperature

لایه های نازک CdTe رشد کرده به روش رسوب دهی لیزر پالسی و با استفاده از

پودر به عنوان ماده هدف : اثر دمای زیرلایه

ABSTRACT

CdTe thin films were deposited by pulsed laser deposition on Corning glass slides using CdTe powder as target. Films were grown at substrate temperatures ranging from room temperature (~25 °C) to 300 °C. The structural, compositional and optical properties were analyzed as a function of substrate temperature. X-ray diffraction shows that CdTe films grown at room temperature have hexagonal phase, while for higher temperatures the films have cubic phase. Raman and EDS indicate that films grew with Te excess, which suggests that CdTe films have p-type conductivity.

 

رسوب نشانی الکتروشیمیایی کادمیوم تلوریم نانوکریستال

Synthesis and characterization of electrochemically

deposited nanocrystalline CdTe thin films

شناسایی و سنتز لایه های نازک نانوکریستال CdTe

به روش رسوب نشانی الکتروشیمیایی

ABSTRACT

Electrodeposition is emerging as a method for the synthesis of semiconductor thin films and nanostructures. In this work we prepared the nanocrystalline CdTe thin films on indium tin oxide coated glass substrate from aqueous acidic bath at the deposition temperature 50 ± 1 °C. The films were grown potentiostatically from −0.60 V to −0.82 V with respect to saturated calomel reference electrode. The structural, compositional, morphological and optical properties were investigated using X-ray diffraction (XRD), energy dispersive analysis by X-rays (EDAX), atomic force microscopy (AFM), and UV–vis spectroscopy respectively and cyclic voltammetery. The structural and optical studies revealed that films are nanocrystalline in nature and possess cubic phase, also the films are preferentially oriented along the cubic (1 1 1) plane. The effect of cadmium composition on the deposited morphology was also investigated. The size dependent blue shift in the experimentally determined absorption edge has been compared with the theoretical predictions based on the effective mass approximation and tight binding approximation. It is shown that the experimentally determined absorption edges depart from the theoretically calculated values.

 

خواص لایه های رسوب نشانی شده CdTe به روش تبخیر باریکه الکترونی

Properties of CdTe films deposited by

electron beam evaporation

خواص لایه های رسوب نشانی شده  CdTe به روش تبخیر باریکه الکترونی 

ABSTRACT

Cadmium telluride thin films were prepared by electron beam evaporation on glass substrates kept at different temperatures in the range 30 - 300 °C. The films were characterized by X-ray diffraction, scanning electron microscopy and optical absorption measurements. The conductivity of the films was measured in the temperature range 100 - 300 K. While the low temperature data (100 - 200 K) could be explained by the variable range hopping process, the high temperature data (200 - 300 K) could be explained on the basis of Seto's model for thermionic emission of the carriers over the grain boundaries. Transmission spectra have indicated a direct band gap around 1.55 eV.

 

شناسایی و سنتز نانوکریستال های CdTe شفاف فوتولومینسنت

Synthesis and characterization of

brightly photoluminescent CdTe nanocrystals

شناسایی و سنتز نانوکریستال های CdTe شفاف فوتولومینسنت

ABSTRACT

A new synthesis procedure for the preparation of spherical shaped CdTe nanocrystals (NCs) is presented, exhibiting bright luminescence with exceptionally high quantum efficiency (up to 85%). The growth of these NCs occurs in a non-coordinating solvent, octadecene, with the addition of oleic acid/tri-octylphosphine stabilizers, CdO as a precursor for the Cd monomers and additional Cd metal particles as a supplementary Cd reservoir source. The dependence of the crystalline quality and the optical properties of the CdTe NCs, on the initial Cd:Te precursors’ molar ratio, and the reaction duration were investigated. It was demonstrated that the NCs’ properties improved significantly as the initial Cd:Te molar ratios are increased. The obtained NCs’ properties were correlated with measurements of the Cd0 concentration in Cd metal particles, CdTe NCs and in Cd monomer solutions.

 

بهبود خصوصیات ترموالکتریکی هگزابورید‌های قلیایی خاکی

Improvement of thermoelectric properties of

alkaline-earth hexaborides

بهبود خصوصیات ترموالکتریکی هگزابورید‌های قلیایی خاکی

ABSTRACT

Thermoelectric (TE) and transport properties of alkaline-earth hexaborides were examined to investigate the possibility of improvement in their TE performance. As carrier concentration increased, electrical conductivity increased and the absolute value of the Seebeck coefficient decreased monotonically, while carrier mobility was almost unchanged. These results suggest that the electrical properties of the hexaboride depend largely on carrier concentration. Thermal conductivity of the hexaboride was higher than 10W/mK even at 1073K, which is relatively high among TE materials. Alloys of CaB6 and SrB6 were prepared in order to reduce lattice thermal conductivity. Whereas the Seebeck coefficient and electrical conductivity of the alloys were intermediate between those of CaB6 and SrB6 single phases, the thermal conductivities of the alloys were lower than those of both single phases. The highest TE performance was obtained in the vicinity of Ca0.5Sr0.5B6, indicating that alloying is effective in improving the performance.

 

مواد الکتروکرومیک

Electrochromic Materials

مواد الکتروکرومیک

ABSTRACT

 A set of materials exhibit electrochromic activity when constituted as a thin film structure whose coloration can be changed reversibly by electrical charging and discharging . there are two types of such electrochromic materials . The first type is uncolored when unpowered and changes to a colored state when a voltage is applied and returns to its uncolored state when the voltage is removed . In the second type an opposite voltage is required to be applied for bleaching ( or decoloration ) .The degree of coloration is a direct visual indication of the state of charing present in the material .

مقدمه الزامات مهندسی برای مواد کامپوزیتی صنعت هوافضا

Introduction: engineering
requirements for aerospace
composite materials

مقدمه الزامات مهندسی برای مواد کامپوزیتی صنعت هوافضا 

ABSTRACT

Composite materials have gained popularity (despite their generally high cost) in high performance products that need to be lightweight, yet strong enough to take high loads such as aerospace structures (tails, wings and fuselages), boat construction, bicycle frames and racing car bodies. Other uses include storage tanks and fishing rods. Natural composites (wood and fabrics) have found applications in aircraft from the first flight of the Wright Brothers’ Flyer 1, in North Carolina on December 17, 1903, to the plethora of uses now enjoyed by man-made (engineered) composite materials on both military and civil aircraft, in addition to more exotic applications on unmanned aerial vehicles (UAVs), space launchers and satellites. Their adoption as a major contribution to aircraft structures followed on from the discovery of carbon fibre at the Royal Aircraft Establishment at Farnborough, UK, in 1964.

وضعیت صنعت در کنترل آخال ها در طی ریخته گری شمش فولادی

State of the Art in the Control of Inclusions during Steel
Ingot Casting

وضعیت صنعت در کنترل آخال ها در طی ریخته گری شمش فولادی

ABSTRACT

This article extensively reviews published research on inclusions in ingot steel and defects on ingot products, methods to measure and detect inclusions in steel, the causes of exogenous inclusions, and the transport and entrapment of inclusions during fluid flow, segregation, and solidification of steel cast in ingot molds. Exogenous inclusions in ingots originate mainly from reoxidation of the molten steel, slag entrapment, and lining erosion, which are detailed in this article. The measures to prevent the formation of exogenous inclusions and improve their removal are provided, which are very useful for the clean steel production of ingot industries.

مواد نیمه رسانا

Semiconducting Materials

مواد نیمه رسانا

ABSTRACT

Semiconductors are materials which have resistivities between the extremes of metallic conductors and insulators. A typical scale of conductivity of materials is depicted in Figure 10.1 . Semiconductors lie approximately between conductors ( with σ > 10⁵ siemen/meter ) and insulators (with σ < 10^-10 siemen/meter ) . Semiconductors are materials with filled valence bands and have a small forbidden energy gap between the upper-filled band and the overlapping vacant energy band . The electric conduction in Semiconductors is effected by two types of charge carriers namely . electrons ( negative charge carriers ) and holes ( positive charge carriers ) .

مواد فروالکتریک

Ferroelectric Materials

مواد فروالکتریک

ABSTRACT

Ferroelectric materials are typically nonlinear dielectrics with the following characteristics :

• They exhibit distinct dependency of permittivity on the intensity of an applied electric field
• The dielectric displacement versus applied electric field follows hysteresis loop characteristics
• The dielectric constant of these materials are invariably very high , on the order of thousands to tens of thousands .
• The dielectric parameters are pronouncedly dependent on temperature and the ferroelectric properities are observed only within a definite range of temperature
• There is presence of spontaneous dielectric polarization in the absence of external electric field And this polarization can be switched in direction by applying an electric field