Polarization Modulation in Ferroelectric Organic Field-Effect Transistors

The polarization modulation effect of the gate dielectric on the performance of metal-oxide-semiconductor field-effect transistors has been investigated for more than a decade. However, there are no comparable studies in the area of organic field-effect transistors (FETs) using polymer ferroelectric dielectrics, where the effect of polarization rotation by 90 is examined on the FET characteristics. We demonstrate the effect of polarization rotation in a relaxor ferroelectric dielectric, poly(vinylidene fluoride trifluorethylene) (PVDF-TrFE), on the performance of small-molecule-based organic FETs. The subthreshold swing and other transistor parameters in organic FETs can be controlled in a reversible fashion by switching the polarization direction in the PVDF-TrFE layer. X-ray diffraction and electron microscopy images from PVDF-TrFE reveal changes in the ferroelectric phase and domain size, respectively, upon rotating the external electric field by 90. The structural changes corroborate density-functional-theoretical studies of an oligomer of the ferroelectric molecule in the presence of an applied electric field. The strategies enumerated here for polarization orientation of the polymer ferroelectric dielectric are applicable for a wide range of polymeric and organic transistors

Morphology of hydrothermally synthesized ZnO nanoparticles tethered to carbon nanotubes affects electrocatalytic activity for H 2 O 2 detection

We describe the synthesis of zinc oxide (ZnO) nanoparticles and demonstrate their attachment to multiwalled carbon tubes, resulting in a composite with a unique synergistic effect. Morphology and size of ZnO nanostructures were controlled using hydrothermal synthesis, varying the hydrothermal treatment temperature, prior to attachment to carboxylic acid functionalized multi-walled carbon nanotubes for sensing applications. A strong dependence of electrocatalytic activity on nanosized ZnO shape was shown. High activity for H2O2 reduction was achieved when nanocomposite precursors with a roughly semi-spherical morphology (no needle-like particles present) formed at 90 °C. A 2.4-fold increase in cyclic voltammetry current accompanied by decrease in overpotential from the composites made from the nanosized, needle-like-free ZnO shapes was observed as compared to those composites produced from needle-like shaped ZnO. Electrocatalytic activity varied with pH, maximizing at pH 7.4. A stable, linear response for H2O2 concentrations was observed in the 1 “20 mM concentration range

Effects of Annealing on Donor and Acceptor Concentrations in Ga-Doped ZnO Thin Films

Temperature-dependent Hall-effect measurements have been performed on three Ga-doped ZnO thin films of various thicknesses (65, 177, and 283 nm), grown by pulsed laser deposition at 400 °C and annealed at 400 °C for 10 min in Ar, N2, or forming-gas (5% H2 in Ar). The donor ND and acceptor NAconcentrations as a function of sample thickness and annealing conditions are determined by a new formalism that involves only ionized-impurity and boundary scattering. Before annealing, the samples are highly compensated, with ND = (2.8 ± 0.3) × 1020 cm-3 and NA = (2.6 ± 0.2) × 1020 cm-3. After annealing in Ar the samples are less compensated, with ND = (3.7 ± 0.1) × 1020 cm-3 and NA = (2.0 ± 0.1) × 1020 cm-3; furthermore, these quantities are nearly independent of thickness. However, after annealing in N2 and forming-gas, ND and NA are thickness dependent, partly due to depth-dependent diffusion of N2 and H, respectively

Effects of Annealing on Donor and Acceptor Concentrations in Ga-Doped ZnO Thin Films

Temperature-dependent Hall-effect measurements have been performed on three Ga-doped ZnO thin films of various thicknesses (65, 177, and 283 nm), grown by pulsed laser deposition at 400 °C and annealed at 400 °C for 10 min in Ar, N2, or forming-gas (5% H2 in Ar). The donor ND and acceptor NAconcentrations as a function of sample thickness and annealing conditions are determined by a new formalism that involves only ionized-impurity and boundary scattering. Before annealing, the samples are highly compensated, with ND = (2.8 ± 0.3) × 1020 cm-3 and NA = (2.6 ± 0.2) × 1020 cm-3. After annealing in Ar the samples are less compensated, with ND = (3.7 ± 0.1) × 1020 cm-3 and NA = (2.0 ± 0.1) × 1020 cm-3; furthermore, these quantities are nearly independent of thickness. However, after annealing in N2 and forming-gas, ND and NA are thickness dependent, partly due to depth-dependent diffusion of N2 and H, respectively

Growth of New Form of Polycrystalline Silicon Thin Films Synthesized by Hot Wire Chemical Vapor Deposition

In this work, we report on next-generation hot wire chemical vapor deposition technique, we call it ceramics hot-wire CVD. Using a new concept of rectangular ceramics filament holder and confinement of thermal radiation from the filament , a new form of polycrystalline silicon thin films has been developed at low temperature (˜ 250°C). The grains are found to be symmetrically distributed in array along the parallel lines, in (111) direction. On the surface of individual grains, five-fold and six-fold symmetries have been observed and we suspect that we developed buckyball type giant silicon molecular solids with different crystalline silicon lattice other than standard single-crystal silicon structure. We observed rarely found icosaderal symmetry in silicon thin films. This hypothesis has been supported by multiple Raman active transverse optical modes and the crystallographic structure analyzed by X-ray diffraction

Enhancement of Superconducting T\u3csub\u3ec\u3c/sub\u3e (33 K) by Entrapment of FeSe in Carbon Coated Au–Pd₁₇Se₁₅ Nanoparticles

FeSe has been an interesting member of the Fe-based superconductor family ever since the discovery of superconductivity in this simple binary chalcogenide. Simplicity of composition and ease of synthesis has made FeSe, in particular, very lucrative as a test system to understand the unconventional nature of superconductivity, especially in low-dimensional models. in this article we report the synthesis of composite nanoparticles containing FeSe nanoislands entrapped within an ent-FeSe-Pd16Se15–Au nanoparticle and sharing an interface with Pd17Se15. This assembly exhibits a significant enhancement in the superconducting Tc (onset at 33 K) accompanied by a noticeable lattice compression of FeSe along the \u3c001\u3e and \u3c101\u3e directions. the Tc in FeSe is very sensitive to application of pressure and it has been shown that with increasing external pressure Tc can be increased almost 4-fold. in these composite nanoparticles reported here, immobilization of FeSe on the Pd17Se15 surface contributes to increasing the effect of interfacial pressure, thereby enhancing the Tc. the effect of interfacial pressure is also manifested in the contraction of the FeSe lattice (up to 3.8% in \u3c001\u3e direction) as observed through extensive high-resolution TEM imaging. the confined FeSe in these nanoparticles occupied a region of approximately 15–25 nm, where lattice compression was uniform over the entire FeSe region, thereby maximizing its effect in enhancing the Tc. the nanoparticles have been synthesized by a simple catalyst-aided vapor transport reaction at 800 °C where iron acetylacetonate and Se were used as precursors. Morphology and composition of these nanoparticles have been studied in details through extensive electron microscopy

Fabrication and electrical characterization of Schottky diode based on 2-amino-4, 5-imidazoledicarbonitrile (AIDCN)

The junction characteristics of the organic compound 2-amino-4, 5-imidazoledicarbonitrile (AIDCN) on p-type silicon substrate are studied in detail. AIDCN is deposited on silicon substrate using thermal evaporator. Current–voltage (I–V) characteristic of the device is measured at room temperature. The Au/AIDCN/p-Si device shows non-linear I–V characteristic with rectification ratio of 7.2×103 at 5 V. The electronic device parameters such as barrier height, ideality factor, and series resistance are calculated using I–V data and observed to be 0.74 eV, 3.00, and 3.73×104 Ω respectively

Fabrication and characterization of NiO/ZnO p-n junctions by pulsed laser deposition

Transparent and conducting ZnO and NiO films were used for fabrication of p-n junction by pulsed laser deposition. These films were characterized by X-ray diffraction (XRD), atomic force microscopy, UV-visible spectroscopy, and electrical techniques. XRD shows that ZnO films are highly orientated along the (0 0 2) direction, while NiO films have preferred orientation along the (1 1 1) direction. These films are very smooth with surface roughness of ∼1.2 nm. The optical transmittances of ZnO and NiO films are 87% and 64%, respectively. I-V characteristics of the ZnO-NiO junction show rectification. The junction parameters such as ideality factor, barrier height, and series resistance are determined using conventional forward bias I-V characteristics, the Cheung method, and Norde\u27s function. There is a good agreement between the diode parameters obtained from these methods. The ideality factor of ∼4.1 and barrier height of ∼0.33 eV are estimated using current-voltage characteristics

Junction characteristics of pulsed laser deposition grown Gd2O3 on p-silicon

Thin film of gadolinium oxide (Gd2O3) is grown on p-silicon using pulsed laser deposition technique. The current–voltage characteristics of the device show non-linear behavior. The values of various junction parameters such as ideality factor, barrier height and series resistance are determined using different techniques. There is a good agreement between the junction parameters obtained from these methods. The ideality factor and barrier height is estimated to be 2.26 and 0.33 eV, respectively