Wyniki wyszukiwania - Biblioteka Nauki

1

Change of the defect structure in FeAl alloy as a result of its aging at ambient temperature

100%

Kansy J. , Hanc-Kuczkowska A. , Giebel D.

|

2013

|

tom Vol. 58, No. 1

221-224

EN

Positron annihilation lifetime spectroscopy (PALS) was used to study the defect structure of stoichiometric FeAl samples after their slow cooling or quenching from the temperatures of 1000 and 540 centigrade. The high value of positron lifetime in the quenched-in defects suggests that they are mainly of di-vacancy type. After long storage at ambient temperature, the concentration of defects in the samples strongly decreases and mono-vacancies predominate. Annealing at 540 centigrade generates an additional amount of defects may be ascribed to the formation of FeAl2 phase in the FeAl matrix.

2

Model struktury defektów w tlenku CuO

75%

Migdalska M. , Grzesik Z.

|

tom nr 11

529-531

PL

W oparciu o wyniki wcześniejszych badań mechanizmu powstawania fazy CuO na powierzchni Cu2O, uzyskane metodami markerów i dwuetapowego utleniania oraz kinetyki utleniania Cu2O w funkcji temperatury i prężności tlenu, wykazano, że dominującymi defektami punktowymi w tlenku CuO są podwójnie zjonizowane wakacje kationowe. Przedstawiony w niniejszej pracy model struktury defektów uwzględnia fakt, że w zgodności z wynikami badań eksperymentalnych, stężenie defektów jonowych w omawianym tlenku, będącym samoistnym półprzewodnikiem elektronowym, rośnie z prężnością tlenu w potędze 1/2.

EN

Basing on experimental results reported previously and obtained using marker and two-stage oxidation methods as well as oxidation kinetic rates measurements, the defect structure model of CuO has been presented. It has been demonstrated that the predominant point defects in the discussed oxide, being an intrinsic electronic semiconductor are doubly ionized cation vacancies, the concentration of which increases with oxygen activity with power 1/2.

3

Defect structures in InGaN/GaN multiple quantum wells on Si(111) substrates

63%

Wu G. M. , Kao Y. L.

|

tom Vol. 18, nr 1-2

195--198

EN

Purpose: Nitrides are compound semiconductor nanomaterials that are suitable for use in light-emitting diodes. It has been desired to grow high quality gallium nitride crystal thin film on silicon substrates because silicon substrates have the advantages of low cost, large wafer size, and good electrical and thermal conductivity. However, the higher defect density can limit the industrial applications due to lower quantum efficiency. The purpose of this study has been to investigate the crystal defect structure within InGaN/GaN multiple quantum wells on Si(111) substrates. In addition, the variation in quantum well thickness was also explained by the selective area growth model. Design/methodology/approach: InGaN/GaN nano-structures were prepared by metal-organic chemical vapor phase epitaxy (MOVPE) using composite buffer layers. The crystal defect structures in the buried multiple quantum wells on both (0001) and {10-11} sidewalls were carefully studied by transmission electron microscopy. Previous studies on sapphire substrates have been compared and discussed. Findings: The V defect structures have been found in InGaN/GaN multiple quantum wells on Si(111) substrates. A simplified structural model with increasing barrier thickness has been reported. The barrier thickness increased on both (0001) and {10-11} facets along thin film growth. A decreased fill factor based on the selective area growth model was proposed. In addition, the average thin film growth rate was found to be four times higher along (0001) than that along {10-11} facet. As the number of multiple quantum wells increased, the barier thickness increasing was also intensified. Research limitations/implications: The understanding in defect structure could help to modify the processing and design parameters. Originality/value: The V-defect structure and model were reported for the first time using silicon substrates. The different growth rates along defect structures were quantified. High quality gallium nitride crystal could be manufactured along with better substrate design.

4

Scanning thermoelectric and acoustic emission diagnostic of structural inhomogeneities of thermocouple materials

63%

Prokhorenko V. J. , Prokhorenko S. V. , Mudry S. I. , Sheregii E. M. , Dominjuk T. I.

|

2010

|

tom Vol. 10, iss. 1 spec.

381--386

EN

New method for diagnostic of constructional and functional materials by means of thermoelectric and acoustic- emission measurements is proposed. The method allows not only to establish the defect location, but its partial temperature relaxation achieve.

5

Electrical properties of Nb-doped titanium dioxide TiO2 at room temperature

51%

Trenczek-Zając A. , Rekas M.

Materials Science Poland

|

2006

|

tom Vol. 24, No. 1

53--60

EN

Nb-doped TiO2 (0-15 at. % Nb) polycrystalline specimens were prepared by the sol-gel method. Below 10 at. % of Nb, materials were homogeneous and exhibited rutile structure, their lattice parameters changing with Nb concentration according to the Vegard's law. Above 10 at. % of Nb, the second phase TiNb2O7 was formed, detected by X-ray diffractometry. Materials were heated at 1273 K for 3 h in air (pO2 = 210 kPa) and in flow of Ar + 3 vol. % H2 gas mixture (pO2 = 10-15 Pa) and then cooled down. Electrochemical impedance spectroscopy within the frequency range 0.01 Hz-2 MHz has been used to determine electrical properties of the materials. An equivalent circuit composed of a resistor Rgb, a capacitor C connected parallel and a resistor Rb connected in series, well represents the electrical properties of reduced samples. On the other hand, non-Debye elements should be taken into account in construction of the equivalent circuit of oxidized materials. The mechanism of the Nb incorporation has been proposed.