Anomalous diffusion of Ga and As from semi-insulating GaAs substrate into MOCVD grown ZnO films as a function of annealing temperature and its effect on charge compensation

The diffusion behavior of arsenic (As) and gallium (Ga) atoms from semi-insulating GaAs (SI-GaAs) into ZnO films upon post-growth annealing vis-`a-vis the resulting charge compensation was investigated with the help of x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy. The films, annealed at 600 °C and 700 °C showed p-type conductivity with a hole concentration of 1.1 × 10¹⁸ cm⁻³ and 2.8 × 10¹⁹ cm⁻³ respectively, whereas those annealed at 800 °C showed n-type conductivity with a carrier concentration of 6.5 × 10¹⁶ cm⁻³. It is observed that at lower temperatures, large fraction of As atoms diffused from the SI-GaAs substrates into ZnO and formed acceptor related complex, (AsZₙ–2VZₙ), by substituting Zn atoms (AsZₙ) and thereby creating two zinc vacancies (VZₙ). Thus as-grown ZnO which was supposed to be n-type due to nonstoichiometric nature showed p-type behavior. On further increasing the annealing temperature to 800 °C, Ga atoms diffused more than As atoms and substitute Zn atoms thereby forming shallow donor complex, GaZₙ. Electrons from donor levels then compensate the p-type carriers and the material reverts back to n-type. Thus the conversion of carrier type took place due to charge compensation between the donors and acceptors in ZnO and this compensation is the possible origin of anomalous conduction in wide band gap materials.This is the publisher’s final pdf. The published article can be found at AIP Advances

Effect of Growth Temperature on Bamboo-shaped Carbon–Nitrogen (C–N) Nanotubes Synthesized Using Ferrocene Acetonitrile Precursor

This investigation deals with the effect of growth temperature on the microstructure, nitrogen content, and crystallinity of C–N nanotubes. The X-ray photoelectron spectroscopic (XPS) study reveals that the atomic percentage of nitrogen content in nanotubes decreases with an increase in growth temperature. Transmission electron microscopic investigations indicate that the bamboo compartment distance increases with an increase in growth temperature. The diameter of the nanotubes also increases with increasing growth temperature. Raman modes sharpen while the normalized intensity of the defect mode decreases almost linearly with increasing growth temperature. These changes are attributed to the reduction of defect concentration due to an increase in crystal planar domain sizes in graphite sheets with increasing temperature. Both XPS and Raman spectral observations indicate that the C–N nanotubes grown at lower temperatures possess higher degree of disorder and higher N incorporation

New insights into CoFe/n-Si interfacial structure as probed by X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy (XPS) is a well known tool in studying the physical and chemical properties of surface/interfaces which provides the element specific, non-destructive and quantitative information. In the present study, information about the surface chemical states of interfacial structure of CoFe thin films on n-Si substrates has been studied from XPS technique. The surface of the samples has also been cleaned from ion beam etching for 30 min with Ar+ ions to record the XPS spectra. The observation shows that the Si atoms are present within the probed surface layer due to interfacial intermixing across the interface which is due to strong chemical reactivity of n-Si substrate. A shift in the binding energy peaks of Fe2p and Co2p has also been observed which could be due to the formation of silicide phases as a result of interfacial intermixing. XPS results have indicated the formation of silicide phases across the interfaces which poses interfacial antiferromagnetic coupling across CoFe/n-Si interface to affect the magnetic behaviour. It has been found that the present XPS results are in well support with our earlier study

Synthesis and Characterization of Cds Nanocrystallites Dispersed in Polymer Matrix

Cadmium sulphide (CdS) nanocrystallites were prepared by sulphuration route with capping in polyethylene oxide (PEO) polymer matrix. It is found that PEO could provide a confined environment for particle nucleation and growth of CdS nanocrystallites. The scanning electron microscopy (SEM) with energy dispersive analysis by X-ray (EDAX) studies confirms the presence of CdS nanocrystallites in polymer matrix. X-ray diffraction (XRD) studies and transmission electron microscopy (TEM) selected area diffraction (SAD) patterns show that these crystallites have hexagonal structure. The TEM and UV-Visible absorption studies indicate uniform size distribution having size around 2.3 nm and band gap of 2.7 eV. X-ray photoelectron spectroscopy (XPS) studies reveal that core level energy positions of the Cd is shifted towards the lower binding energy and has similar chemical environment to that of bulk CdS

Modulus Spectroscopy and Dielectric Dispersion Studies in Alkali Metal Perchlorates

Alkali metal perchlorates (KClO4, RbClO4, and CsClO4) undergo a structural phase transition from the orthorhombic to the cubic phase at elevated temperatures. A detailed dielectric study of these crystals across the phase transition is carried out at different frequencies. The crystals are found to exhibit pronounced dielectric dispersion in the kHz frequency range. The results support the view that these transitions are of order–disorder type. The dielectric behaviour at temperatures above Tc is discussed in terms of modulus spectroscopy. An estimate of conductivity relaxation times above the phase transition temperatures made from modulus spectroscopy data gives values of 3.1, 12.2 and 17.7 μs for KClO4, RbClO4, and CsClO4, respectively