SnO2: A comprehensive review on structures and gas sensors

This review article first presents a summary of current understanding of the magnetic properties and intrinsic ferromagnetism of transition-metal (TM)-doped ZnO films, which are typical diluted magnetic oxides used in spintronics. The local structure and magnetic behavior of TM-doped ZnO are strongly sensitive to the preparation parameters. In the second part, we discuss in detail the effects of doping elements and concentrations, oxygen partial pressure, substrate and its orientation and temperature, deposition rate, post-annealing temperature and co-doping on the local structure and subsequent ferromagnetic ordering of TM-doped ZnO. It is unambiguously demonstrated that room-temperature ferromagnetism is strongly correlated with structural defects, and the carriers involved in carrier-mediated exchange are by-products of defects created in ZnO. The third part focuses on recent progress in TM-doped ZnO-based spintronics, such as magnetic tunnel junctions and spin field-effect transistors, which provide a route for spin injection from TM-doped ZnO to ZnO. Thus, TM-doped ZnO materials are useful spin sources for spintronics.

Ferromagnetism and possible application in spintronics of transition-metal-doped ZnO films

Synthesis and applications of one-dimensional semiconductors

Dilute magnetic oxides are transparent, wide-bandgap materials that behave ferromagnetically when doped with a few percent of a magnetic 3d cation. The magnetism, which appears well below the cation percolation threshold, cannot be understood in terms of the conventional theory of magnetism in insulators; nor can a carrier-mediated ferromagnetic exchange mechanism account for the magnitude of the Curie temperatures, which are well in excess of 400 K. The phenomenon is observed in thin films and nanocrystals, but not in well-crystallized bulk material. Experimental artefacts and segregation of secondary ferromagnetic phases can explain some observations, but the existence of a novel type of magnetism related to defects other than the magnetic dopants is a likely inference from the data.

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Dilute magnetic oxides

Ion beam induced surface and interface engineering

We report room temperature ferromagnetism in single crystal Ce1−xCoxO2−δ (x⩽0.05) films deposited on a LaAlO3(001) substrate. Films were grown by a pulsed laser deposition technique and were thoroughly characterized using x-ray diffraction, high-resolution transmission electron microscopy coupled with electron energy loss spectroscopy and scanning transmission electron microscopy-Z contrast, x-ray photoelectron spectroscopy, optical transmission spectroscopy, and magnetic measurements. These films are transparent in the visible regime and exhibit a very high Curie temperature ∼740–875K with a giant magnetic moment. Our results indicate that the ferromagnetic property is intrinsic to the CeO2 system and is not a result of any secondary magnetic phase or cluster formation.

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Ferromagnetism in Co doped CeO2: Observation of a giant magnetic moment with a high Curie temperature

Growth and characterization of single crystalline tin oxide (SnO2) nanowires

The efficiency of the thermoelectric materials and devices is shown by the dimensionless Figure of merit, ZT. ZT is calculated by multiplying the Seebeck coefficient with square of the electrical conductivity and absolute temperature and dividing it all by the thermal conductivity. Thermoelectric devices were prepared using different multilayered thin film structures in the order of SiO2/SiO2 + Ge/Ge/Sb + Ge/Si/Si + Ge/Ge/Ge + Si by DC/RF Magnetron Sputtering. The prepared thermoelectric devices have been tailored with 5 MeV Si ions bombardment at the different fluences (doses) to form quantum structures in the multilayer thin films to improve the efficiency of the thermoelectric devices. Seebeck coefficients, van der Pauw-four probe resistivity, Hall Effect coefficient, density and mobility have been measured. After the samples were prepared, SEM/EDS data were collected. FIB/SEM images were provided to figure out the cross-section of the fabricated devices. Seebeck coefficients and electrical resistivity results were affected positively if the appropriate ion beam dose was selected.

Highly-Efficient Advanced Thermoelectric Devices from Different Multilayer Thin Films

We prepared 50 periodic nano-layers of electro-cooling system consisting of SiO2/AuxSiO2(1−x) super lattice with Au layer deposited on both sides as metal contacts. The deposited multilayer films have a periodic structure consisting of alternating layers where each layer is 10 nm thick. The purpose of this research is to tailor the figure of merit of layered structures used as thermoelectric generators. The super lattices were then bombarded by 5 MeV Si ions at three different fluences to form nano-cluster structure. Rutherford backscattering spectrometry (RBS) was used to monitor the film thickness and stoichiometry before and after MeV bombardment. We measured the thermoelectric efficiency of the fabricated device before and after 5 MeV bombardment measuring the cross plane thermal conductivity by third harmonic method, measuring cross plane Seebeck coefficient, and measuring electric conductivity using Van der Pauw method. As predicted the electronic energy deposited due to ionization by MeV Si beam in its track produces nano-scale structures which disrupt and confine phonon transmission therefore reducing thermal conductivity, increasing electron density of state so as to increase Seebeck coefficient, and electric conductivity, thus increasing figure of merit.

MeV Si ions bombardment effects on thermoelectric properties of sequentially deposited SiO2/AuxSiO2(1−x) nano-layers ☆

Most of total hip joints are composed of ultra-high molecular weight polyethylene (UHMWPE ). However, as ultra-high molecular weight polyethylene is too stable in a body, wear debris may accumulate and cause biological response such as bone absorption and loosening of prosthesis. In this study, ultra-high molecular weight polyethylene samples were Ag and Ag + N hybrid ion implanted by using MEVVA ion implantation technique to improve its surface properties. Samples were implanted with a fluence of 10 17  ion/cm 2 and extraction voltage of 30 kV. Implanted and unimplanted samples were investigated by thermo-gravimetry analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), optical microscopy (OM) and contact Angle measurement. Thermal characterization results showed that the ion bombardment induced an increase in the % crystallinity, onset and termination degradation temperatures of UHMWPE.

Satilmis Budak

Papers

Ferromagnetism in Co doped CeO2: Observation of a giant magnetic moment with a high Curie temperature

Growth and characterization of single crystalline tin oxide (SnO2) nanowires

Highly-Efficient Advanced Thermoelectric Devices from Different Multilayer Thin Films

MeV Si ions bombardment effects on thermoelectric properties of sequentially deposited SiO2/AuxSiO2(1−x) nano-layers ☆

Thermal characterization of Ag and Ag + N ion implanted ultra-high molecular weight polyethylene (UHMWPE)