There has been significant recent interest in the use of surface-functionalized thin film and nanowire wide bandgap semiconductors, principally GaN, InN, ZnO and SiC, for sensing of gases, heavy metals, UV photons and biological molecules. For the detection of gases such as hydrogen, the semiconductors are typically coated with a catalyst metal such as Pd or Pt to increase the detection sensitivity at room temperature. Functionalizing the surface with oxides, polymers and nitrides is also useful in enhancing the detection sensitivity for gases and ionic solutions. The wide energy bandgap of these materials make them ideal for solar-blind UV detection, which can be of use for detecting fluorescence from biotoxins. The use of enzymes or adsorbed antibody layers on the semiconductor surface leads to highly specific detection of a broad range of antigens of interest in the medical and homeland security fields. We give examples of recent work showing sensitive detection of glucose, lactic acid, prostate cancer and breast cancer markers and the integration of the sensors with wireless data transmission systems to achieve robust, portable sensors.

Metabolic syndrome (MetS) in mid‐life is a known risk factor for Alzheimer’s disease & related dementias (ADRD). Racial and ethnic minorities represent under‐represented groups (URGs) in ADRD research. Targeted outreach, recruitment and retention initiatives broaden the reach of Alzheimer Disease Research Centers (ADRC) within prioritized communities. Understanding the association between MetS risk factors and cognition during preclinical ADRD in URGs may elucidate avenues for ameliorating ADRD risk in URGs prior to dementia onset. Generalizability of findings vary by the population represented within an analytic sample. We describe MetS‐cognition relationships within URGs and referral source, a key determinant of our sample composition.

Amorphous InGaZnO4 (alpha-IGZO) thin film transistors (TFTs) are one of the most promising candidates for switches in the active-matrix and driver-integrated circuits of transparent liquid crystal displays and flexible displays. The stability and overall performance of amorphous IGZO TFTs depend to a great extent on the band offsets in gate dielectric/alpha-IGZO heterojunction. The energy discontinuity in the valence band (Delta E-V) and conduction band (Delta E-C) in MgO/IGZO heterojunctions were systematically examined by using X-ray photoelectron spectroscopy (XPS). The MgO gate dielectric was found to have a straddled type band offset alignment on the IGZO. The valence band offset value for the MgO/IGZO heterojunction was determined as 0.81 +/- 0.17 eV using the Ga 2p(3/2), Zn 2p(3/2) and In 3d(5/2) energy levels as references. The bandgap energy difference between the MgO and IGZO led to a corresponding conduction band offset (Delta E-C) of similar to 3.79 eV and a nested interface alignment.

The energy discontinuity in the valence band (Delta E-V) of Y2O3-stabilized ZrO2 (YSZ)/InGaZnO4 (IGZO) heterostructures was obtained from X-ray photoelectron spectroscopy (XPS) measurements. The YSZ exhibited a bandgap of 4.4 eV from absorption measurements. A value of Delta E-V = 0.57 +/- 0.12 eV was obtained by using Ga 2p(3/2), Zn 2p(3/2) and In 3d(5/2) energy levels as references. This implies a conduction band offset (Delta E-C) of 0.63 eV in YSZ/InGaZnO4 heterostructures and a nested interface band alignment.

ZnO nanowires were grown on indium tin oxide (ITO) coated glass substrates at a low temperature of 90 degrees C using an aqueous solution method. The ZnO seeds were coated on the ITO thin films by using a spin coater. ZnO nanowires were formed in an aqueous solution containing zinc nitrate hexahydrate (Zn(NO3)2 x 6H2O) and hexamethylenetetramine (C6H12N4). The pH value and concentration of the solution play an important role in the growth and morphologies of ZnO nanowires. The size of ZnO naonowires increased as the concentration of the solution increased. It was formed with a top surface of hexagonal and tapered shape at low and high pH values respectively. Additionally, the single crystalline structure and optical property of the ZnO nanowires were investigated using high-resolution transmission electron microscopy and photoluminescence spectroscopy.

X-ray photoelectron spectroscopy (XPS) was used to measure the energy discontinuity in the valence band (ΔEV) and conduction band (ΔEC) of various dielectric/IGZO heterostructures. ΔEV values of 0.48{plus minus}0.025 eV for HfO2/IGZO, 0.44{plus minus}0.21 eV for Y2O3/IGZO, 0.81{plus minus}0.17 eV for MgO/IGZO, 0.95{plus minus}0.17 eV for the Al2O3/IGZO, and 1.43{plus minus}0.15 eV for the SiO2/IGZO heterojunctions were obtained, respectively. The bandgap differences between these dielectrics and IGZO would lead to corresponding conduction band offset (ΔEC) values of 2.39-4.74 eV. These results are important for designing structures with good carrier confinement in transparent thin film transistors based on IGZO.

The properties of phosphorus doped ZnO thin films grown on sapphire by pulsed laser deposition were examined, specifically focusing on the effects of undoped ZnO buffer layers. In particular, buffer layers were grown under different conditions; the transport properties of as-deposited and rapid thermal annealed ZnO : P films were then examined. As-deposited films showed n-type conductivity. After rapid thermal annealing, the film on buffer layer grown at a low temperature showed the conversion of carrier type to p-type for specific growth conditions while the films deposited on buffer layer grown at a high temperature remained n-type regardless of growth condition. The films deposited on buffer layer grown at a low temperature showed higher resistivity and more significant change of the transport properties upon rapid thermal annealing. These results suggest that more dopants are incorporated in films with higher defect density. This is consistent with high resolution x-ray diffraction results for phosphorus doped ZnO films on different buffer layers. In addition, the microstructure of phosphorus doped ZnO films is substantially affected by the buffer layer.

We demonstrate the formation of a hybridized plasmon-exciton state exhibiting strong exciton-plasmon coupling in ZnO/Zn(0.85)Mg(0.15)O single quantum wells capped with arrays of Al nanodiscs. Tuning the quantum-well width and the diameter and pitch of the Al nanodisc arrays facilitates a transition from the weak-coupling regime into the strong coupling regime. Finite-difference time-domain simulations substantiate the localization of the plasmonic quadrupole moment within the ZnO quantum-well layer, resulting in a hybridized plasmonexciton state demonstrating a Rabi splitting of roughly 15 meV in heterostructures that exhibit a prominent plasmon quadrupole mode. The significant tunability offered by quantum-well heterostructures like those discussed here provides a flexible system for controlling exciton plasmon coupling in a device-compatible thin-film architecture.

We investigated the size-dependent electrical conductivities of indium zinc oxide stripes with different widths from 50 nm to 4 microm and with the same thickness of 50 nm deposited by RF magnetron sputtering. The size of the indium zinc oxide stripes was controlled by e-beam lithography. The distance of the two Ti/Au Ohmic electrodes along the indium zinc oxide stripes was kept constant at 25 microm. The electrical conductivity decreased as the size of the indium zinc oxide stripes decreased below a critical width (80 nm). The activation energy, derived from the electric conductivity versus temperature measurement, was dependent on the dimensions of indium zinc oxide stripes. These results can be understood as stemming from surface charge trapping from the absorption of oxygen and/or water vapor, which leads to an increase in the energy difference between the conduction energy band and the Fermi energy.

The authors report an investigation of the effects of channel dimensions on the properties of amorphous-InGaZnO4 (a-IGZO) thin-film transistors (TFTs) that are associated with surface depletion and surface/volume ratio. As the channel width decreased below a critical value of around 100 nm, the on current abruptly decreased and the threshold voltage abruptly increased. The magnitude of hysteresis behavior also depended on the channel size. Both of these effects result from the change of channel resistance that can be explained by surface changes due to adsorption of oxygen or water vapor. The authors also investigated short channel a-IGZO TFTs and observed short channel effects below a critical value of channel length of 900 nm. The breakdown electric field of a-IGZO was found to be in the range of 0.4–0.8 MV/cm.

Indium zinc oxide films were grown from targets with two different In atomic concentration [In/(In+Zn)] of 40% and 80% by the pulsed laser deposition technique on glass substrates from room temperature up to 100°C. X-ray diffraction and reflectometry investigations showed that films were amorphous and dense. Thin films (thickness<100nm) exhibited higher optical transmittance and resistivities than thick films (thickness>1000nm), probably caused by a significant decrease of oxygen vacancies due to atmosphere exposure. Films deposited from the In rich target under an oxygen pressure of 1Pa exhibited optical transmittance higher than 85%, resistivities around 5–7×10−4Ωcm and mobilities in the 47–54cm2/Vs range.

The authors report on the fabrication of thin-film transistors (TFTs) using indium-tin-zinc oxides (ITZOs) as active channel layers. Transparent amorphous ITZO semiconductors were deposited at room temperature by rf-magnetron sputtering, followed by an annealing treatment at 100 °C. The electrical properties of the ITZO channel layers deposited at room temperature using rf-magnetron sputtering were investigated by controlling the oxygen partial pressure during deposition and introducing postannealing treatments. The devices operated in an n-type enhancement mode exhibited a clear pinch-off behavior and had an on-to-off ratio of ∼108 with a low off current of 3×10−13 A. A field-effect mobility of 17 cm2/V s and a subthreshold slope of 0.5 V/decade were extracted from the device characteristics. These results suggest that ITZO semiconductors show potential as channel materials that are applicable in flexible transparent TFTs.

The deterministic growth of ZnO nanorods using molecular beam epitaxy is reported. The process is catalyst-driven, as single crystal ZnO nanorod growth is realized via nucleation on Ag islands that are distributed on a SiO 2 -terminated Si substrate surface. Growth occurs at substrate temperatures on the order of 300-500°C. The nanorods exhibit diameters of 15-40 nm and lengths in excess of 1 µm. Nanorod placement can be predefined via location of metal catalyst islands or particles. This, coupled with the relatively low growth temperatures needed, suggests that ZnO nanorods could be integrated on device platforms for numerous applications, including chemical sensors and nanoelectronics.

We report an investigation of the structural properties of CuCr0.95Mg0.05O2 films on c-plane sapphire substrates using pulsed laser deposition. The thin films were grown at different temperatures of 500, 600, and 700°C with an oxygen partial pressure of 10mTorr. c-axis oriented epitaxial CuCr0.95Mg0.05O2 thin films on c-plane sapphire substrates with an in-plan 30° rotation were obtained. The sixfold rotational symmetry in the pole figures from the (012) plane indicates that there are two different types of crystal grains in which the a-axes rotate by 60° with respect to each other around the c-axis. The reason for the 30° rotation is assumed to be the presence of the ∼10% mismatch of oxygen distance between the c-plane sapphire substrate and the CuCr0.95Mg0.05O2 on the c-plane. The epitaxial crystallographic relationship between CuCr0.95Mg0.05O2 and Al2O3 was (0006)CuCrO2//(0003)Al2O3 and [10−10]CuCrO2//[11−20]Al2O3. The presence of twins in the films and the surface morphology were investigated using transmission electron microscopy and scanning electron microscopy, respectively.

We describe the growth and properties of epitaxial (001) CeO 2 on a (001) Ge surface using a hydrogen-assisted pulsed-laser deposition method. Hydrogen gas is introduced during film growth to eliminate the presence of the GeO 2 from the semiconductor surface during the initial nucleation of the metal oxide film. The hydrogen partial pressure and substrate temperature are selected to be sufficiently high such that the germanium native oxides are thermodynamically unstable. The Gibbs free energy of CeO 2 is larger in magnitude than that of the Ge native oxides, making it more favorable for the metal oxide to reside at the interface in comparison to the native Ge oxides. By satisfying these criteria, the metal oxide/semiconductor interface is shown to be atomically abrupt with no native oxide present. Preliminary structural and electrical properties are reported.

Low resistance Ohmic contacts using Ti/Au metallization on n-type amorphous indium zinc oxide (IZO) (n∼5×1020 cm−3) deposited on paper substrates are reported. The minimum specific contact resistivity of 8×10−7 Ω cm2 was achieved on IZO films both as-deposited and for annealing temperatures of up to 125 °C. The contact resistance increased to 4×10−6 Ω cm2 at 175 °C. The sheet resistance was found to vary from 24 to 17 Ω/sq, and the transfer resistance was ∼0.045 Ω mm for the as-deposited and low temperature annealed samples. The contact resistance was independent of measurement temperature, indicating that field emission plays a dominant role in the current transport. Such Ohmic contacts achieved with little or no annealing are important for paper based electronics requiring low temperature processing (<200 °C).

We investigated copper oxides for use as an active layer of p-channel field-effect thin-film transistors (TFTs). Cu2O thin films deposited at room temperature using rf magnetron sputtering were transformed to a CuO phase after an annealing treatment in air above 200 °C. The optical bandgaps of the Cu2O and CuO were 2.44 and 1.41 eV, respectively. The bottom gate structured TFTs fabricated using CuO active layers operated in a p-type enhancement mode with an on/off ratio of ∼104 and field-effect mobility of 0.4 cm2/V⋅s.