High Potential Barrier Height Research Articles

Influence of grain boundary insulation on nonlinear and dielectric discrepancy in Ni2+/Ni3+ doped CaCu3-xNixTi4O12 ceramics

Two series of CaCu3-xNixTi4O12 (x = 0.0, 0.5, 1.0, 2.5) ceramics doped with Ni2+ and Ni3+ were prepared via the solid-state reaction method. Despite the similar micro-morphologies of the samples, the nonlinear electrical characteristics were enhanced in the Ni3+-doped samples but deteriorated in their Ni2+-doped counterparts. With Ni content increasing, the breakdown field and nonlinear coefficient of Ni3+-doped samples enhanced from 0.54 to 6.14 kV cm−1 and 2.68 to 4.92 respectively while dropped from 0.98 to 0.21 kV cm−1 and 3.48 to 1.03 for Ni2+-doped samples. Impedance spectroscopy analysis revealed significant discrepancies in terms of grain boundaries between the two series of samples, which resulted in their different dielectric properties. The oxygen loss owing to the in situ formation of NiTiO3 was considered to be the crucial factor impeding grain boundary insulation, which was key to the potential barrier formation. In contrast with that of the Ni2+-doped samples, the oxygen loss of the Ni3+-doped samples was compensated by the reduction of Ni3+ to Ni2+. This helped maintain a high potential barrier height and resulted in different nonlinear characteristics of the two series.

Hydrogen-abstraction reactions of fully hydrogenated fullerene cages with the amino radical: a density functional study

ABSTRACTWe have applied density functional theory calculations to study the reactions of NH2 + CnHn (n = 20, 40, 50, 60, 70 and 80). Due to the hard curvature in C20 cage, the NH2• + C20H20 → NH3 + C20H19• reaction is nearly thermoneutral with a high potential barrier height. For the CnHn fulleranes with n > 20 the transition states appear earlier on the reaction paths, as can be anticipated for exothermic reactions. Using the spherical excess parameter, we distinguished different curvatures on the surfaces of fullerane cages. The reaction enthalpies ΔH°298 and potential barrier heights ΔETS of the considered reactions indicate good correlation with the values of ϕi parameter, showing an upward trend with the curvature increasing at carbon sites. We have also investigated the H-abstraction of the chemical derivatives of the C20H20 cage (C20H19–CH3, C20H19–CH2CH3 and C20H19–CH2CH2CH3) in comparison to the corresponding isolated alkanes (CH4, C2H6 and C3H8). Overall, it could be inferred that the H-abstraction from the primary and secondary C–H bonds of isolated alkanes could occur more easily than fullarane derivatives.

1.5 - nm -thick silicon oxide gate films grown at 150°C using modified reactive ion beam deposition with pyrolytic-gas passivation

Low-temperature ultrathin silicon oxide gate film growth using modified reactive ion beam deposition (RIBD) with an in situ pyrolytic-gas passivation (PGP) method is described. RIBD uses low-energy-controlled reactive and ionized species and potentializes low-temperature film growth. By combining RIBD with PGP using N2O and NF3, 1.5-nm-thick silicon oxide gate films with high-potential barrier height energy, 3.51eV, and low-leakage current, less than about 10−5A∕cm2 at 2MV∕cm, can be obtained at a growth temperature of 150°C. From an evaluation of number densities of N, F, and O atoms near the 1.5–5.0-nm-thick RIBD-with-PGP silicon oxide films/Si(100) interfaces, it is believed that interfacial N and F atoms contribute to improve the electrical characteristics and F effectively compensates the residual inconsistent-state bonding sites after the N passivation.

Application of double camel-like gate structures for a GaAs field-effect transistor with extremely high potential barrier height and gate turn-on voltage

In this paper, extremely high potential barrier height and gate turn-on voltage in an n+/p+/n+/p+/n GaAs field-effect transistor employing double camel-like gate structures are demonstrated. The gate potential barrier height of the double camel-like gate is substantially enhanced by the addition of another n+/p+ layer in the gate region, as compared with the conventional n+/p+/n single camel-like gate structure. The influence of gate structure layers on the depletion depth, potential barrier height, transconductance and gate voltage swing are addressed. Experimental results show that a relatively high gate turn-on voltage up to +4.9 V is realized because two reverse-biased junctions of the double camel-like gate structures absorb part of the positive gate voltage. In addition, an extremely broad gate voltage swing greater than 4.6 V with the transconductance above 100 mS mm−1 is observed. These results indicate that the studied device is suitable for linear and signal amplifiers and inverter circuit applications.

A novel GaAs FET with double camel-like gate structure

Extremely high potential barrier height and gate turn-on voltage of a novel GaAs field-effect transistor with n/sup +//p/sup +//n/sup +//p/sup +//n double camel-like gate structure are demonstrated. The maximum electric field and potential barrier height of the double camel-like gate are substantially enhanced by the addition of another n/sup +//p/sup +/ layers in gate region, as compared with the conventional n/sup +//p/sup +//n single camel-like gate. For a 1×100 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> device, a potential barrier height up to 2.741 V is obtained. Experimentally, a high gate turn-on voltage up to +4.9 V is achieved because two reverse-biased junctions of the double camel-like gate absorb part of positive gate voltage. In addition, the transistor action shows a maximum saturation current of 730 mA/mm and an extrinsic transconductance of 166 mS/mm.

Ar+ ion impact desorption of Cu and Ag from the Si(111)-quasi-5 × 5-Cu and [formula omitted] surfaces

The concentration changes of Cu and Ag coverages at the CuSi(111)-√3 × √3-Ag and Si(111)-quasi-5 × 5-Cu surfaces by 5 keV Ar+ ion bombardment have been measured by means of AES and Rutherford backscattering (RBS) techniques in order to determine the cross-sections for their desorption and recoil-implantation. We have evaluated the potential barrier heights for desorption and recoil-implantation from the obtained cross-sections. The potential barrier height for desorption of Ag adsorbates is in accordance with the sublimation energy of Ag metal, and the potential barrier height for recoil-implantation of Ag is consistent with that for the Si(111)-√3 × √3-Ag surface. Together with the observed √3 × √3 LEED pattern for the CuSi(111)-√3 × √3-Ag surface, these results suggest that Ag atoms are accommodated at the top-most surface layer as the Si(111)-√3 × √3-Ag surface. On the other hand, the cross-section for desorption of Cu is smaller than that of Ag, which leads to rather high potential barrier height, and the cross-section for recoil-implantation is considerably larger than that of Ag. For these results, we propose a hypothesis that Cu atoms are buried and located at an interstitial site in the surface layer of the CuSi(111)-√3 × √3-Ag surface. It is also found that the Si(111)-quasi-5 × 5-Cu structure is easily destroyed by Ar+ ion bombardment.

Raman scattering study of surface band-bending at the NEA Cs/p-GaAs(110) surface

We have investigated the band-bending behaviour of a caesium-covered p-GaAs (110) surface by electric-field-induced Raman scattering. A high potential barrier height (approximately 1.5±0.2 eV) was found at high caesium coverage (about 2 monolayers), and we conclude that the metallic property of caesium plays a significant role in this system when the overlayer is thick.