Dobijanje i karakterizacija 2D i 3D funkcionalnih materijala iz klase halkogenida dopiranih srebrom

Abstract

Predmet istraživanja ove doktorske disertacije su bila halkogenidna stakla iz sistema Agx(As40S30Se30)100–x (x = 0, 0.5, 1, 2, 3, 4, 5, 10, 12, 13, 15 at. % Ag) – 3D forma i tanki filmovi preparirani iz prethodno sintetisanih stakala (x ≤ 5 at. % Ag) – 2D forma. Utvrđena je oblasti amorfnosti u faznom dijagramu po odabranom preseku. Ispitivan je uticaj procentualnog udela srebra na fizičke karakteristike sintetisanih stakala i prepariranih tankih filmova koje su od značaja za primenu ovakvih materijala. Izvršena je karakterizacija električnih, optičkih, strukturnih i termičkih osobina na osnovu kojih su izvedeni zaključci o uticaju i modifikaciji strukture As40S30Se30 halkogenidne matrice usled inkorporacije atoma srebra. Strukturna analiza ispitivanih sastava je potvrdila homogenost uzoraka sa manjom koncentracijom srebra (x ≤ 5 at. % Ag), dok je kod uzoraka sa većim procentualnim udelom ovog metala (x = 10, 13, 15 at. % Ag) pokazano da postoji fazna separacija. Kod sastava sa x = 13 i 15 at. % Ag potvrđena je prisutnost kristalnih centara AgAsSe2. Na osnovu rezultata dobijenih DSC tehnikom, pokazano je da pri zagrevanju balk uzoraka dolazi do delimične kristalizacije koja se odvija zapreminski sa dvodimenzionalnim i trodimenzionalnim rastomkristalnih centara. Optička i spektralna ispitivanja su pokazala da uvođenje Ag u matricu stakla As40S30Se30 dovodi do smanjenja širine optički zabranjene zone i kod 3D i 2D uzoraka, kao i da svi sastavi ispoljavaju normalan oblik disperzije indeksa prelamanja. Takođe, rezultati Raman spektroskopije su ukazali na činjenicu da inkorporacija srebra u strukturnu mrežu ispitivanih stakala utiče na formiranje Ag–(S,Se)–As veza, odnosno uzrokuje formiranje novih strukturnih jedinica koje bi mogle uticati na provodljivost ovih sastava. Merenja električnih karakteristika 3D uzoraka izvršena su u jednosmernom i naizmeničnom režimu i pokazano je da koncentracija srebra ima značajan uticaj na električne osobine. Utvrđeni su različiti mehanizmi odgovorni za transport nosilaca naelektrisanja zavisno od koncentracije dopanta. Kompleksni impedansni spektri svih sastava su ukazali na prisustvo temperaturske zavisnosti procesa relaksacije, na ne idealan Debye–vski tip relaksacije, kao i negativni temperaturski koeficijent otpornosti koji je karakterističan za poluprovodnike.

The subject of this dissertation are chalcogenide glasses from the system Agx(As40S30Se30)100–x (x = 0, 0.5, 1, 2, 3, 4, 5, 10, 12, 13, 15 at. % Ag) – 3D form and thin films prepared from previously synthesised glasses (x ≤ 5 at. % Ag) – 2D form. The amorphous area in the phase diagram was determined by the selected tie– line. The influence of the silver percentage on the physical characteristics of the synthesized glasses and prepared thin films was investigated due to the importance of such materials for the application. Characterization of electrical, optical, structural and thermal properties has been performed, based on which conclusions on theinfluence and structure modification of the As40S30Se30 chalcogenide matrix due to the incorporation of silver atoms have been derived. Structural analysis of the investigated samples confirmed the homogeneity of samples with a lower silver concentration (x ≤ 5 at.% Ag), while in samples with a higher percentage content of this metal (x = 10, 13, 15 at.% Ag) it was shown that there was a phase separation. The presence of crystal centers AgAsSe2 was confirmed in the samples with x = 13 and 15 at. % Ag. Based on the results obtained with the DSC technique, it has been shown that by heating the samples, partial crystallization takes place voluminously, with two–dimensional and three–dimensional growth of crystalline centers. Opticaland spectral investigations have shown that the introduction of Ag into the glass matrix As40S30Se30 leads to a reduction in the optical band gap in both 3D and 2D samples, and that all compositions exhibit a normal dispersion of index of refraction. Also, the Raman spectroscopy results pointed to the fact that the incorporation of silver into the structural network of the investigated samples influences the formation of Ag–(S,Se)–As structures that is, causes the formation of new structural units that could affect the conductivity of these compositions. Measurements of the electrical characteristics of the 3D samples were performed in DC and AC regime and it was shown that silver concentration has a significant effect on electrical properties. Different mechanisms that are responsible for the transport of charge carriers depending on dopant concentration were determined. The complex impedance spectra of all compositions indicated the presence of the temperature dependence of the relaxation process, the non–Debye relaxation and the negative temperature coefficient of resistance which is characteristic of the semiconductors.