Svojstva tankih slojeva Ag2Se naparenih u vakuumu

A recent vacuum deposition method using the topotaxial reaction of Ag and Se allowed us preparation of both epitaxial and polycrystalline Ag2Se layers on NaCl and silica substrates. Low temperature and reproducibility of Ag2Se layers facilitate investigation of this ionic semiconductor. The formation and the reversible phase transition (orthorhombic - cubic) of Ag2Se films are revealed by transmission electron microscopy. Galvanomagnetic properties of 87 nm thick layers with different carrier concentrations were investigated in the temperature range of 77 - 430 K. Properties of poly- and monocrystalline samples are compared. Influence of the phase transformation on the electrical properties are shown.Nedavna metoda naparavanja u vakuumu primjenom topotaksijske reakcije Ag i Se omogućuje izradu epitaksijskih i polikristaliničnih Ag2Se slojeva na NaCl i kremenim podlogama. Niska temperatura i ponovljivost Ag2Se slojeva olakšava proučavanje tog ionskog poluvodiča. Stvaranje i reverzibilan fazni prijelaz (ortorombski-kubni) Ag2Se sloja ustanovljen je transmisijskom elektronskom mikroskopijom. Galvanska svojstva sloja debljine 87 nm s različitim koncentracijama pokretnih nositelja naboja ispitivana su u području temperature 77–430 K. Ispitan je utjecaj faznog prijelaza na električna svojstva

Orientált ionvezető és félvezető vékonyrétegek kialakítása nem orientált hordozókon

A projektben vegyületfélvezető és szuperionos vékonyrétegek szerkezetkialakulási mechanizmusát, elektromos jellemzőit, alternatív előállítási lehetőségét, egyes technológiai vonatkozásait vizsgáltuk. A vizsgált anyagok közül az Ag2Te, CdSe, ZnSe fotoelektromos célokra, az Ag2Se pedig, lineáris GMR tulajdonságai miatt mágneses terek mérésére alkalmazható. A rétegeket topotaxiás módszerrel állítottuk elő. A rétegépülés mechanizmusát TEM mikroszkópos módszerekkel tártuk fel (001) orientációjú, ill. polikristályos Ag rétegek Se gőzzel történő kémiai reakciója során. A rétegek elektromos ellenállás-változását négypontos módszerrel, in situ mértük, és matematikai modellel szimuláltuk. A komplex vizsgálat alapvető fizikai folyamatokat tárt fel: Egykristály (hibamentes) rétegekben a Se diffúziója ill. a kémiai reakció homogén módon megy végbe. A reakciós front sík, amely lassan áthalad a mintán a teljes szelénezésig. Polikristályos mintában megmutatkozik a kristályhibák szerepe: A könnyű szemcsehatár menti diffúzió miatt a reakció ott gyorsabb, az Ag szemcsék lekerekednek, és árkádos Ag2Se/Ag front alakul ki. A Se a szemcsehatárok mentén lejut a hordozóig ahol az Ag-val reagál és a reakció két irányból zajlik a teljes szelénezésig. A folyamat önszabályzó, a sztöchiometrikus összetételt állítja be. Lehűlésnél, allotrop fázisváltozás miatt a réteg kedvező, (001) orientációt vesz fel. A mechanizmusok várhatóan más anyagrendszerekre is általánosíthatók, de ezt még igazolni kell. | In the project, the structure evolution, electrical properties and alternative preparation techniques of compound and superionic semiconductor thin films were studied. The materials; Ag2Te, CdSe, ZnSe can be applied for photovoltaic purposes, while Ag2Se, due to its linear GMR properties, is a candidate for magnetic field sensors. For the preparation of the layers a topotactic method was developed. The mechanism of the structure formation was studied by TEM, in situ electrical measurements and numerical simulations in both (001) oriented and polycrystalline Ag films. The complex study revealed fundamental physical phenomena. In single crystal (defect free) layers the Se diffusion and the chemical reaction occurs homogeniously. A planar reaction front is formed, which propagates across the film until complete selenization. In polycrystalline samples, however, the influence of crystal defects shows up. Due to fast grain boundary (GB) diffusion, the reaction occurs preferentially at the GB-s, and an arch shaped interface of Ag2Se/Ag builds up. Simultaneously, the Se diffuses along the GB-s to the substrate and reacts with Ag. From that stage the reaction occurs on both sides of the Ag layer until completing the selenization. The self controlling process results in stoichiometric composition. On cooling, (001) crystal orientation is formed due to polymorphic phase transition. The mechanisms may be general for numerous two-component systems, but this needs further studies

Sol-derived AuNi/MgAl2O4catalysts: Formation, structure and activityin dry reforming of methane

Ni nanoparticles doped with different amount of gold were supported on MgAl2O4by deposition fromaqueous metal sol producing a series of catalysts with different Au content. The sol procedure was allowedto obtain dispersed metal particles with different composition. The particle size and the particle compo-sition of the sol were maintained even after being deposited on the support. The catalysts, characterizedby several techniques such as TPR, XPS, XRD, TEM, HRTEM and EELS at the different stages of their lifeexhibited significant structural modification. In particular, thermal treatments in reducing and oxidizingenvironment produced NiAu alloy phases and NiO surface segregation, respectively. When testing formethane dry reforming with CO2in temperature ramped reaction, the monometallic nickel catalyst wasmore active at lower temperature whereas the bimetallic catalysts were more active at higher temper-ature. The presence of gold slightly affected the CO/H2ratio due to the occurrence of parallel reactionssuch as the reverse water gas shift reaction (RWGS). Both types of catalysts, monometallic and bimetallicones, deactivated a little with time but the degree of activity loss was not in straightforward relation withAu content due to the different effect of gold on the stability and on the amount of carbon formation.© 2013 Elsevier B.V. All rights reserved

Iron Oxyhydroxide Aerogels and Xerogels by Hydrolysis of FeCl3 ? 6 H2O in Organic Media: early stages

L

Nanopattern formation in UV laser treated a-AlOx and nc-Al/AlOx layers

Hexagonal nanopatterns were fabricated in sputter deposited Al-oxide thin films by means of single UV laser pulses via a layer of self-assembled silica nanospheres. The hexagonal pattern was projected to the surface due to the focussing effect of the silica nanolenses enhancing the local impact of the pulse. As a result of the laser pulse large area ordered structure of nano-pits were formed in RF sputtered amorphous Al-oxide films, while nano-craters were created in DC sputter deposited layers that consist of Al nanocrystals embedded in amorphous matrix. The two different mechanisms governing the nanostructure formation in the a-AlOx and nc-Al/AlOx composite layers were revealed by Atomic Force Microscopy (AFM), cross-sectional Transmission Electron Microscopy (XTEM), spectroscopic ellipsometry and computer simulation

Perpendicular coercivity enhancement of CoPt/TiN films by nitrogen incorporation during deposition

The effect of N incorporation on the structure and magnetic properties of CoPt thin films deposited on glass substrates with TiN seed layers has been investigated. During the deposition of CoPt, introducing 20% N2 into Ar atmosphere promotes the (001) texture and enhances the perpendicular coercivity of CoPt film compared with the film deposited in pure Ar and post-annealed under the same conditions. From the in situ x-ray diffraction results, it is confirmed that N incorporation expands the lattice parameter of CoPt, which favors the epitaxial growth of CoPt on TiN. During the post-annealing process, N releases from CoPt film and promotes the L10 ordering transformation of CoPt. © 2015 AIP Publishing LLC