A simple INDIUM TIN OXIDE/glass DRA

A novel Dielectric Resonator Antenna, simply made of INDIUM TIN OXIDE coated glass slides placed on a microstrip transmission line, for communication applications is presented. Changes in the bandwidth and gain of the antenna are observed by modifying the dimensions of the INDIUM TIN OXIDE coated glass slides. Changes in gain, directivity and reflection coefficient are observed. A parametric study is conducted on the size of the DRA to understand the effect on bandwidth, reflection coefficient and gain.Comment: INDIUM TIN OXIDE, DRA, directivity, gain, bandwidth, WLAN, WiMA

Vanadium substitution: a simple and efficient way to improve UV sensing in ZnO

UV sensing in pure ZnO is due to oxygen adsorption/desorption process from ZnO surface. Vanadium doping improves UV sensitivity of ZnO. Enhancement in UV sensitivity in doped ZnO is attributed to trapping and de-trapping of electrons at V4+ & V5+-related defect states. An extra electron in the V4+ state is excited under UV illumination while in absence of the same a trapping happens at the V5+ state. An insight to the mechanism is obtained by an analytic study of the response phenomenon

Dielectric/semiconductor interfacial doping to develop solution processed high performance 1 V ambipolar oxide-transistor and its application as CMOS inverter

p-type doping from the dielectric/semiconductor interface of a SnO2 thin film transistor (TFT) has been utilized to develop high carrier mobility balanced ambipolar oxide-transistor. To introduce this interfacial-doping, bottom-gate top-contact TFTs have been fabricated by using two different ion-conducting oxide dielectrics which contain trivalent atoms. These ion-conducting dielectrics are LilnO2 and LiGaO2 respectively, containing mobile Li+ ion. During SnO2 thin film fabrication on top of the ionic dielectric, those trivalent atoms allow p- doping to the interfacial SnO2 layer to introduce the hole conduction in channel of TFT. To realize this interfacial doping phenomena, a reference TFT has been fabricated with Li2ZnO2 dielectric under the same condition that contains divalent zinc (Zn) atom. Our comparative electrical data indicates that TFTs with LilnO2 and LiGaO2 dielectric are ambipolar in nature whereas, TFT with Li2ZnO2 dielectric is a unipolar n-channel transistor which reveals the interfacial doping of SnO2. Most interestingly, by using LilnO2 dielectric, we are capable to fabricated 1.0 V balanced ambipolar TFT with a high electron and hole mobility values of 7 cm2 V-1 s-1and 8 cm2 V-1 s-1 respectively with an on/off ratio >102 for both operations which has been utilized for low-voltage CMOS inverter fabrication

Role of oxygen interstitials in Zn1-xGaxO for faster response to UV light

ZnO doped with Gallium (Ga3+) demonstrates better crystalline nature and conductivity increases. Latent defect states are suppressed. However, due to the larger charge of Ga3+ oxygen interstitials are generated which control the sensing speed. The conductance increases as a consequence of reduced defect states, especially the oxygen vacancies. The photocurrent increases with Galium incorporation, but a more intense increase in the current reduces the sensitivity

Optical Property Study of Charge Compensated (Si, Na) Co-doped ZnO

ZnO is co-doped with Na+ and Si4+ in the ratio 2:1. The ratio was intentionally chosen so that net valence state of dopant theoretically matches that of host. This is to avoid dependence in the amount of oxygen vacancies/interstitials arising out of cationic valence state of the dopant. With such a combination, modifications in structural and optical properties do not depend on excess or deficit of the dopant charge state. For lower doping, Na+ ions behave as interstitial sites which enhance strain, lattice disorder and thereby creating defects. Formation of interstitial defects leads to reduction in bandgap energy and produce orange-red luminescence. For higher doping, Na+ starts substituting at Zn2+ site which helps in reducing strain and lattice disorder and thereby increases bandgap. Inspite of presence of Si4+ with higher charge, there is a gradual increase in oxygen vacancies due to lattice disorder

Structural phase transition, grain growth and optical properties of uncompensated Ga-V co-doped TiO2

Effect of uncompensated Ga-V co-doping on structural phase transition, grain growth process and optical properties of TiO2 is reported here. Inhibition of phase transition due to co-doping is confirmed by X-ray diffraction measurement. Activation energy of phase transition increases from 120KJ/mol (x=0) to 140 KJ/mol (x=0.046) due to Ga-V co-doping. In anatase phase, lattice constants increase by the effect of Ga3+ interstitials. This results in inhibition of phase transition. Anatase phase becomes stable up to ~650 C in co-doped sample whereas for pure TiO2 phase transition starts in between 450-500 C. In anatase phase, strain increases due to co-doping which reduces crystallite size. In rutile phase, grain growth process is enhanced due to co-doping and particles show a rod-like structure with majority 110 facets. Bandgap decreases in both phases and reduced to a visible light region. BET analysis shows that surface area increases from 4.55 m2/g (x=0) to 96.53 m2/g (x=0.046) by Ga-V incorporation which provide a large number of active site for photocatalytic activity. Hence, co-doped anatase nanoparticle can be used as a promising candidate for photocatalytic applications using visible light up to a higher temperature ~650 C.Comment: 22 pages, 12 figure

Defect mediated changes in structural, optical and photoluminescence properties of Ni substituted CeO2

Local and long range structure, optical and photoluminescence properties of sol-gel synthesized Ce1-xNixO2 nanostructures have been studied. The crystal structure, lattice strain and crystallite size have been analyzed. A decrease in lattice parameter may be attributed to substitution of Ce with smaller Ni ion. UV-Vis measurement is used for studying the effect of Ni substitution on bandgap and disorder. The bandgap decreases with Ni substitution and disorder increases. The PL spectra show five major peaks attributed to various defect states. The PL emission decreases with Ni substitution owing to increase in defects which acts as emission quenching centers. The lattice disorder and defects have been studied using Raman spectroscopy. Raman measurement shows that oxygen vacancies related defects are increasing with Ni substitution which causes changes in optical and PL properties. Local structure measurements show that Ni substitution leads to oxygen vacancies which does change host lattice structure notably. Ce4+ to Ce3+ conversion increases with Ni substitution

Structural and dielectric properties of Pb(1-x)(Na0.5Sm0.5)xTiO3 ceramics

A correlation between structure and vibrational properties related to a ferroelectric to paraelectric phase transition in perovskite Pb(1-x)(Na0.5Sm0.5)xTiO3 (PNST - x) polycrystalline powders is discussed. Substitution leads to reduction of tetragonality which is associated with a shift of the phase transition to lower temperatures. The nature of the phase transition gets diffused with increasing substitution.Comment: 5 figures, 1 tabl

Structural and ferroelectric properties of perovskite Pb(1-x)(K0.5Sm0.5)xTiO3 ceramics

PbTiO3 has the highest tetragonal distortion (c/a=1.064) and highest spontaneous polarization among perovskite titanates. But, it is hazardous and hence one needs to reduce Pb content by substituting or reducing Pb content for use in applications. Pb(1-x)(K0.5Sm0.5)xTiO3 (0&x&0.5) perovskite powders were synthesized by sol-gel process, where Pb2+ was replaced by a combination of K+10.5Sm+30.5 (equivalent charge and comparable ionic radius) providing an excellent substitution model to study changes in structural and electrical properties. Vibrational properties and dielectric properties are modified with substitution. A polar tetragonal to a nearly nonpolar cubic phase transition decreases to lower temperatures with substitution due to reduces the lattice strain with substitution. Ferroelectricity is retained even for x=0.5, which has a nearly cubic phase and makes the material technologically important.Comment: 13 pages, 6 figure

Investigation of La and Al substitution on the spontaneous polarization and lattice dynamics of the Pb(1-x)LaxTi(1-x)AlxO3 ceramics

The phase purity and crystal structure of PLTA samples (synthesized via sol-gel process) were confirmed using synchrotron x-ray powder diffraction (wavelength, lmbda= 0.44573 A. Rietveld analyses of powder x-ray diffraction data confirmed the tetragonal structure for compositions with more than 0.18 and cubic structure for the sample with 0.25 composition. Temperature-dependent XRD was performed to investigate the structural change from tetragonal to cubic structure phase transition. Raman spectroscopy at room temperature also confirmed this phase transition with composition. Field emission scanning electron provided information about surface morphology while an energy dispersive x-ray spectrometer attached with FESEM confirmed the chemical compositions of samples. Temperature and frequency dependent dielectric studies showed that the tetragonal to cubic phase transition decreased from 680 K to 175 K with the increase in the x from 0.03 to 0.25, respectively. This is correlated with the structural studies. Electric field dependent spontaneous polarization showed proper ferroelectric loop for 0.06 to 0.18 belonging to a tetragonal phase while after 0.25 composition the spontaneous polarization vanishes.Bipolar strain versus electric field revealed a butterfly loop for 0.06 to 0.18 compositions. Energy storage efficiency initially increases nominally with substitution but beyond 0.18 composition enhances considerably.Comment: 21 pages, 11 figure