Properties of rf-sputtered indium-tin-oxynitride thin films

Indium-tin-oxide (ITO) and indium-tin-oxynitride (ITON) thin films have been fabricated by rf-sputtering in plasma containing Ar or a mixture of Ar and N-2, respectively. The structural, electrical and optical properties of ITON films were examined and compared with those of ITO films. The microstructure of ITON films was found to be dependent on the nitrogen concentration in the plasma. Increasing the amount of nitrogen in the plasma increased the resistivity and reduced the carrier concentration and mobility of the films. The electrical properties of the ITON films improved after annealing. The absorption edge of the ITON films deposited in pure N-2 plasma was shifted towards higher energies and showed reduced infrared reflectance compared to the respective properties of ITO films. The potential of indium-tin-oxynitride films for use as a transparent conductive material for optoelectronic devices is addressed

Impedance Characterization of DNA-functionalization Layers on AlGaN/GaN High Electron Mobility Transistors

AbstractCharacterization and optimization for biosensor implementation with open gate AlGaN/GaN transistors is described. Probe-DNA was immobilized on the gate. As target, complementary DNA at 10-12 - 10-7mol/L was added. To investigate the impedimetric properties of the sensing area, electrochemical impedance spectroscopy was used. For very low frequencies, the bio-functionalization layer was modeled as a membrane with a charge transfer resistor in series with a Warburg element. This component presents impedance to diffusion of electrolyte ions. Its behavior is intermediate between a capacitor and a resistor (membrane impedance). After probe-target matching, the charge transfer resistance and Warburg impedance were increased (lower flow of electrolyte ions through the membrane). Using this working principle, a dynamic detection of targets is proposed

Electrical conductivity and gas-sensing properties of Mg-doped and undoped single-crystalline In2O3 thin films: Bulk vs. surface

This study aims to provide a better fundamental understanding of the gas-sensing mechanism of In2O3-based conductometric gas sensors. In contrast to typically used polycrystalline films, we study single crystalline In2O3 thin films grown by molecular beam epitaxy (MBE) as a model system with reduced complexity. Electrical conductance of these films essentially consists of two parallel contributions: the bulk of the film and the surface electron accumulation layer (SEAL). Both these contributions are varied to understand their effect on the sensor response. Conductance changes induced by UV illumination in air, which forces desorption of oxygen adatoms on the surface, give a measure of the sensor response and show that the sensor effect is only due to the SEAL contribution to overall conductance. Therefore, a strong sensitivity increase can be expected by reducing or eliminating the bulk conductivity in single crystalline films or the intra-grain conductivity in polycrystalline films. Gas-response measurements in ozone atmosphere test this approach for the real application

Electrical conductivity and gas-sensing properties of Mg-doped and undoped single-crystalline In2O3 thin films: Bulk vs. surface

This study aims to provide a better fundamental understanding of the gas-sensing mechanism of In2O3-based conductometric gas sensors. In contrast to typically used polycrystalline films, we study single crystalline In2O3 thin films grown by molecular beam epitaxy (MBE) as a model system with reduced complexity. Electrical conductance of these films essentially consists of two parallel contributions: the bulk of the film and the surface electron accumulation layer (SEAL). Both these contributions are varied to understand their effect on the sensor response. Conductance changes induced by UV illumination in air, which forces desorption of oxygen adatoms on the surface, give a measure of the sensor response and show that the sensor effect is only due to the SEAL contribution to overall conductance. Therefore, a strong sensitivity increase can be expected by reducing or eliminating the bulk conductivity in single crystalline films or the intra-grain conductivity in polycrystalline films. Gas-response measurements in ozone atmosphere test this approach for the real application

Absorption and birefringence study for reduced optical losses in diamond with high NV concentration

The use of diamond color centers such as the nitrogen-vacancy (NV) center is increasingly enabling quantum sensing and computing applications. Novel concepts like cavity coupling and readout, laser threshold magnetometry and multi-pass geometries allow significantly improved sensitivity and performance via increased signals and strong light fields. Enabling material properties for these techniques and their further improvements are low optical material losses via optical absorption of signal light and low birefringence. Here we study systematically the behavior of absorption around 700 nm and birefringence with increasing nitrogen- and NV-doping, as well as their behavior during NV creation via diamond growth, electron beam irradiation and annealing treatments. Absorption correlates with increased nitrogen-doping yet substitutional nitrogen does not seem to be the direct absorber. Birefringence reduces with increasing nitrogen doping. We identify multiple crystal defect concentrations via absorption spectroscopy and their changes during the material processing steps and thus identify potential causes of absorption and birefringence as well as strategies to fabricate CVD diamonds with high NV density yet low absorption and low birefringence.Comment: Accepted by Philosophical Transactions A (DOI: 10.1098/rsta.2022.0314

Zinc oxide as an ozone sensor

Journal of Applied Physics, Vol. 96, nº3This work presents a study of intrinsic zinc oxide thin film as ozone sensor based on the ultraviolet sUVd photoreduction and subsequent ozone re oxidation of zinc oxide as a fully reversible process performed at room temperature. The films analyzed were produced by spray pyrolysis, dc and rf magnetron sputtering. The dc resistivity of the films produced by rf magnetron sputtering and constituted by nanocrystallites changes more than eight orders of magnitude when exposed to an UV dose of 4 mW/cm2. On the other hand, porous and textured zinc oxide films produced by spray pyrolysis at low substrate temperature exhibit an excellent ac impedance response where the reactance changes by more than seven orders of magnitude when exposed to the same UV dose, with a response frequency above 15 kHz, thus showing improved ozone ac sensing discrimination

The Importance of Edge Effects on the Intrinsic Loss Mechanisms of Graphene Nanoresonators

We utilize classical molecular dynamics simulations to investigate the intrinsic loss mechanisms of monolayer graphene nanoresonators undergoing flexural oscillations. We find that spurious edge modes of vibration, which arise not due to externally applied stresses but intrinsically due to the different vibrational properties of edge atoms, are the dominant intrinsic loss mechanism that reduces the Q-factors. We additionally find that while hydrogen passivation of the free edges is ineffective in reducing the spurious edge modes, fixing the free edges is critical to removing the spurious edge-induced vibrational states. Our atomistic simulations also show that the Q-factor degrades inversely proportional to temperature; furthermore, we also demonstrate that the intrinsic losses can be reduced significantly across a range of operating temperatures through the application of tensile mechanical strain.Comment: 15 pages, 5 figures. Accepted for publication in Nano Letter