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Application of new materials offers more sensitive, selective and long-term stable sensor materials. The aim of the present work is to compare gas response to acetone of nanostructured sol-gel auto-combustion derived stoichiometric and excess-iron cubic spinel type nickel-zinc ferrite (Ni 0.3 Zn 0.7 Fe 2+z O 4 where z = 0 and 0.1). Detailed synthesis steps and gas sensing measurement methodology were described. The sensor material was characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM) and direct current (DC) resistance measurements. XRD analysis confirms that samples form the single-phased cubic spinel structure, SEM reveals nanosized grains less than 100 nm in diameter. Plots of resistance versus temperature show adsorbed water contribution to the conductance. With excess-iron, Ni-Zn ferrite changes its DC electrical resistivity, type of conductivity, as well as response to reducing gas (more than 2 times). Obtained relationships can be explained with Fe 2+ formation in the material, thus increasing charge carrier (electron) concentration. This leads down to higher oxygen adsorption ability which can act with test gas.Key words: nickel-zinc ferrite, non-stoichiometry, gas sensor, combustion synthesis [2][3][4][5][6][7]. At the same time information about ferrite gas sensors in comparison with single metal oxide gas sensors is still limited and does not contain data about gas sensing properties of complex or non-stoichiometric iron deficient or excess-iron spinel ferrite compounds, which have essentially different electrical properties. INTRODUCTIONThe conductivity in spinel ferrites is due to hopping of charge carriers (electrons or holes) between cations presented by more than one valence state occupying the octahedral sites [8]. Zinc or cadmium ions show strong affinity to the tetrahedral site, but iron, nickel, manganese, and cobalt ions, for example, show tendency to occupy octahedral sites. Electron hopping between Fe 3+ and Fe 2+ provides ntype, but hole hopping between Ni 3+ ↔ Ni 2+ , Mn 3+ ↔ Mn 2+ , Co 3+ ↔ Co 2+ provides p-type conductivity.The gas sensitivity of metal oxide semiconductor sensors is highly affected by their electric and transport properties [9]. In our previous works, influence of zinc ion concentration on resistance and sensitivity of p-type nickel ferrite [10], as well as iron ion non-stoichiometry effect on resistance and sensitivity of n-type zinc ferrite [11] were investigated. It was found that with zinc addition to nickel ferrite, response to different VOCs decreases, attributed to extinguishing p-type charge carriers (holes) and carrying a small amount of dopants in the semiconductor 167 Gas sensitivity of stoichiometric and excess-iron Ni-Zn ferrite prepared by sol-gel auto-combustion structure. This was confirmed with change of conductivity type by increasing temperature. In case of zinc ferrite response increased by going from iron deficiency to excess due to an increase of Fe 2+ concentration, the charge carrier (electron) concentration increased,...

β-Ga2O3 thin films grown on widely available c-plane sapphire substrates typically exhibit structural defects due to significant lattice and thermal expansion mismatch, which hinder the use of such films in electronic devices. In this work, we studied the impact of a nucleation layer on MOCVD-grown β-Ga2O3 thin film structure and morphology on a c-plane sapphire substrate. The structure and morphology of the films were investigated by X-ray diffraction, atomic force microscopy, transmission and scanning electron microscopy, while the composition was confirmed by X-ray photoelectron spectroscopy and micro-Raman spectroscopy. It was observed that the use of a nucleation layer significantly increases the grain size in the films in comparison to the films without, particularly in the samples in which H2O was used alongside O2 as the oxygen source for the nucleation layer growth. Our study demonstrates that a nucleation layer can play a critical role in obtaining high quality β-Ga2O3 thin films on c-plane sapphire.