Preparation and characterisation of 2D and 3D functional materials from the group of chalcogenides doped with silver

Abstract

<p>Predmet istraživanja ove doktorske disertacije su bila halkogenidna stakla iz sistema Ag_x(As₄₀S₃₀Se₃₀)_100&ndash;x (x = 0, 0.5, 1, 2, 3, 4, 5, 10, 12, 13, 15 at. % Ag) &ndash; 3D forma i tanki filmovi preparirani iz prethodno sintetisanih stakala (x &le; 5 at. % Ag) &ndash; 2D forma.<br />Utvrđena je oblasti amorfnosti u faznom dijagramu po odabranom preseku.&nbsp; Ispitivan je uticaj procentualnog udela srebra&nbsp; na&nbsp; fizičke&nbsp; karakteristike sintetisanih stakala i prepariranih tankih filmova koje su&nbsp; od&nbsp; značaja&nbsp; za&nbsp; primenu&nbsp; ovakvih&nbsp; materijala.<br />Izvr&scaron;ena je karakterizacija električnih,&nbsp; optičkih, strukturnih&nbsp; i&nbsp; termičkih&nbsp; osobina&nbsp; na&nbsp; osnovu&nbsp; kojih&nbsp; su izvedeni&nbsp; zaključci&nbsp; o&nbsp; uticaju&nbsp; i&nbsp; modifikaciji&nbsp; strukture As₄₀S₃₀Se₃₀halkogenidne matrice usled inkorporacije atoma srebra. Strukturna analiza ispitivanih sastava je potvrdila homogenost uzoraka sa manjom koncentracijom srebra (x &le; 5 at. %&nbsp; Ag), dok je&nbsp; 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&nbsp; je&nbsp; prisutnost kristalnih centara AgAsSe_2. Na osnovu rezultata dobijenih DSC tehnikom, pokazano je da pri zagrevanju balk uzoraka dolazi do delimične kristalizacije koja se odvija zapreminski sa dvodimenzionalnim&nbsp; i&nbsp; trodimenzionalnim rastomkristalnih centara. Optička i spektralna ispitivanja su pokazala&nbsp; da uvođenje&nbsp; Ag&nbsp; u&nbsp; matricu&nbsp; stakla As₄₀S₃₀Se₃₀&nbsp; dovodi&nbsp; do&nbsp; smanjenja&nbsp; &scaron;irine&nbsp; optički zabranjene zone i kod 3D i 2D uzoraka, kao i da svi sastavi ispoljavaju normalan oblik disperzije indeksa prelamanja. Takođe, rezultati Raman&nbsp; spektroskopije su ukazali&nbsp; na&nbsp; činjenicu&nbsp; da&nbsp; inkorporacija&nbsp; srebra&nbsp; u strukturnu&nbsp; mrežu&nbsp; ispitivanih&nbsp; stakala&nbsp; utiče&nbsp; na formiranje Ag&ndash;(S,Se)&ndash;As veza, odnosno uzrokuje formiranje novih strukturnih jedinica koje bi mogle uticati na provodljivost ovih sastava.&nbsp; Merenja električnih karakteristika 3D uzoraka izvr&scaron;ena su u jednosmernom i naizmeničnom režimu i pokazano je da&nbsp; koncentracija&nbsp; srebra&nbsp; ima&nbsp; značajan&nbsp; uticaj&nbsp; na električne&nbsp; osobine.&nbsp; Utvrđeni&nbsp; su&nbsp; različiti&nbsp; mehanizmi odgovorni za transport&nbsp; nosilaca naelektrisanja zavisno od&nbsp; koncentracije dopanta.&nbsp; Kompleksni impedansni spektri svih sastava&nbsp; su&nbsp; ukazali&nbsp; na prisustvo temperaturske zavisnosti procesa relaksacije, na ne idealan Debye&ndash;vski tip relaksacije, kao i negativni temperaturski koeficijent otpornosti koji je karakterističan za poluprovodnike.</p>

<p>The subject of this dissertation are chalcogenide&nbsp; glasses from the system Agx(As₄₀S₃₀Se₃₀)_100&ndash;x (x = 0, 0.5, 1, 2, 3, 4, 5, 10, 12, 13, 15 at. % Ag) &ndash; 3D form and thin films prepared from previously synthesised&nbsp; glasses (x &le; 5 at. % Ag) &ndash; 2D form. The amorphous&nbsp; area in the phase diagram was determined by the&nbsp; selected&nbsp;&nbsp;&nbsp; tie&ndash; line. The influence of the silver&nbsp; percentage on the physical characteristics of the&nbsp; synthesized glasses and prepared thin films was&nbsp; investigated due to the importance of such materials&nbsp; 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&nbsp; chalcogenide&nbsp; matrix due to the&nbsp; incorporation of silver atoms have been derived. Structural analysis of the investigated samples confirmed the homogeneity of samples with a lower silver concentration (x&nbsp; &le;&nbsp; 5&nbsp; at.%&nbsp; Ag),&nbsp; while&nbsp; in samples with a higher percentage content of&nbsp; this metal (x = 10, 13, 15 at.% Ag) it was shown that&nbsp; there was a phase separation. The presence of crystal&nbsp; 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&ndash;dimensional and three&ndash;dimensional growth of crystalline centers.&nbsp; 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&nbsp; 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&nbsp; Ag&ndash;(S,Se)&ndash;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&nbsp; 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&nbsp; impedance spectra of all compositions indicated the presence of the temperature dependence of the relaxation process, the non&ndash;Debye relaxation and the negative temperature coefficient of resistance which is characteristic of the semiconductors.</p>