Surface modification of ZnO on the Zn-polar 0001 face by self-assembled triptycene-based polar molecules along with an increase of electric conductance

Application of self-assembled monolayers (SAMs) is a representative method of surface modification for tuning material properties. In this study we examine the influence of the surface modification by coating the Zn-polar 0001 surface of ZnO single crystal with a SAM of triptycene-based polar molecules in our own technique and investigated temperature dependences of the sheet conductance of the surface with and without the SAM. The sheet conductance at 70 K with the SAM is increased by an order of magnitude, compared to the case without the SAM. We infer that the additional electrons are introduced at the surface by the polar triptycene molecules, whose electropositive hydroxyl groups are supposed to face toward the Zn-polar surface of ZnO. The present result implies that the molecular orientation of the triptycene SAM plays a critical role on the surface properties of oxide semiconductors.

Electrical Signature of Ultrasound-Induced Anisotropic Self-Assembly of Poly(3-Hexylthiophene) (P3HT) during Channel Formation

We probed ultrasound irradiation-induced structural ordering of poly(3-hexylthiophene) (P3HT) chains during solidification of a sonicated P3HT solution by monitoring the temporal evolution of the electrical and spectroscopic signals. We observed a peak source-drain current in the test devices during the electrical channel formation, followed by a significant decrease, which has not been observed in the pristine P3HT solution as the solvent evaporates. Through P3HT concentration-dependent gated-sheet conductance and in-situ Raman spectroscopy measurements during channel formation, we found that the competition between aggregation of the disentangled P3HT chains in solution by sonication and the concentration-dependent chain interactions with solvent evaporation led to a distinct electrical signature in the channel formation of the sonicated P3HT film compared to that of the pristine P3HT. The finding provides insights into new opportunities through optimization between the thermodynamic and kinetic considerations in designing pre-deposition treatments for enhanced charge transport.

Above-light-line Nonlinear Surface Polaritons near a Conductive Interface: Threshold Case

We investigate the TM-polarized nonlinear surface polaritons (NLSP) propagating along aguided structure consisting of a magnetic optically linear medium and a non-magnetic opticallynonlinear medium with saturable permittivity separated by a flat conductive layer of zerothickness. We consider those values of hosting media bulk material parameters for which theNLSP existence (for zero sheet conductance) has threshold character with respect to the wavesintensity. Based on the exact solution of Maxwell's equations we show that the energy andpropagation properties of the NLSP near the above-light-line condition (1 > n > 0) dependconsiderably on the surface conductivity of the layer, even the threshold character of the NLSPcan be lost; for certain sheet conductance values these waves can exist in a linear limit. TheNLSP propagation constant is defined by both the surface conductivity and field intensity andcan be varied in a wide diapason, which gives an opportunity to obtain and control the importantfor quantum information processing 0 n  condition. For a chosen value of the NLSPpropagation constant the NLSP field intensity and energy flux decries when the surfaceconductivity grows; saturation of the nonlinear permittivity leads to an increase of the NLSPenergy flux compared with Kerr-like nonlinearity.

Non-vacuum Thin-film CIGS Modules

Non-vacuum techniques have been used to deposit coatings of copper indium gallium selenide (CIGS) and metal oxide transparent conductors useful for fabricating thin-film photovoltaic modules. Coatings are formed from nanoparticulate precursor materials using spraying, printing and spin-coating methods. Sprayed layers exhibit non-planar morphologies and low particle packing, and CIGS films made from sprayed precursor layers exhibit related non-planar morphologies and residual void space. The surface roughness of spray-derived CIGS films reduces the sheet conductance of overlying coatings; thin coatings of transparent conductors deposited on rough CIGS films exhibit sheet resistances up to two orders of magnitude higher than equivalent coatings on planar surfaces. Slurry additives can improve layer morphology and sintered film properties, but organic additives can leave carbon contamination of the sintered CIGS films. The fabrication of multi-cell modules imposes additional constraints on transparent conductor sheet conductance.

Growth and Characterization of Piezoelectrically Enhanced Acceptor-Type AlGaN/GaN Heterostructures

Acceptor (Mg)-doped AlGaN/GaN heterostructures were grown via MOVPE and compared to similarly doped GaN standard films grown in the same reactor. Chemical analysis of the films, via secondary ion mass spectrometry (SIMS), revealed comparable Mg concentrations of ∼2×1019 atoms/cm3 in all films. The Mg-doped GaN standard sample had a sheet conductance of 7-μS compared to a sheet conductance of 20-μS for an AlGaN/GaN heterostructure. The sheet conductance of the AlGaN/GaN heterostructures was higher due to piezoelectric acceptor doping and modulation doping effects in addition to conventional Mg acceptor doping.

Growth and Characterization of Piezoelectrically Enhanced Acceptor-Type AlGaN/GaN Heterostructures

Acceptor (Mg)-doped AlGaN/GaN heterostructures were grown via MOVPE and compared to similarly doped GaN standard films grown in the same reactor. Chemical analysis of the films, via secondary ion mass spectrometry (SIMS), revealed comparable Mg concentrations of ∼2×1019 atoms/cm3 in all films. The Mg-doped GaN standard sample had a sheet conductance of 7-μS compared to a sheet conductance of 20-μS for an AlGaN/GaN heterostructure. The sheet conductance of the AlGaN/GaN heterostructures was higher due to piezoelectric acceptor doping and modulation doping effects in addition to conventional Mg acceptor doping.