The growth rate and electrical character of nanostructures produced by scanned probe oxidation are investigated by integrating an in situ electrical force characterization technique, scanning Maxwell-stress microscopy, into the fabrication process. Simultaneous topographical, capacitance, and surface potential data are obtained for oxide features patterned on n- and p-type silicon and titanium thin-film substrates. The electric field established by an applied voltage pulse between the probe tip and substrate depends upon reactant and product ion concentrations associated with the water meniscus at the tip-substrate junction and within the growing oxide film. Space-charge effects are consistent with the rapid decline of high initial growth rates, account for observed doping and voltage-pulse dependencies, and provide a basis for understanding local density variations within oxide features. An obvious method for avoiding the buildup of space charge is to employ voltage modulation and other dynamic pulse-shaping techniques during the oxidation pulse. Voltage modulation leads to a significant enhancement of the growth rate and to improvements in the aspect ratio compared with static voltage pulses.

Previous descriptions of scanned probe oxidation kinetics involved implicit assumptions that one-dimensional, steady-state models apply for arbitrary values of applied voltage and pulse duration. These assumptions have led to inconsistent interpretations regarding the fundamental processes that contribute to control of oxide growth rate. We propose a model that includes a temporal crossover of the system from transient to steady-state growth and a spatial crossover from predominantly vertical to coupled lateral growth. The model provides an excellent fit of available experimental data.

A model for scanned probe microscope (SPM) silicon oxidation is presented. The model was derived from a consideration of the space-charge dependence of this solid-state reaction as a function of substrate doping type/level and has been verified experimentally by integrating an in situ electrical force characterization technique, scanning Maxwell stress microscopy (SMM), into the SPM fabrication process. This system enables us to obtain SPM topographic, SMM capacitance, and SMM surface potential information of nanometer-scale oxide features as a function of ionic concentrations within the growing oxide film. SPM oxide properties are compared to those of anodic and thermal oxides. The predictive power of the resulting model is demonstrated by showing how the growth rate and electrical character of the SPM-oxide features can be altered dramatically by modulating the applied oxidation voltage.

The superconducting-gap of MgB2 has been studied by high-resolution angle-resolved photoemission spectroscopy. The results show that superconducting gaps with values of 5.5 and 2.2 meV open on the sigma band and the pi band, respectively, but both the gaps close at the bulk transition temperature, providing a definitive experimental evidence for the two-band superconductivity with strong interband pairing interaction in MgB2. The experiments validate the role of k-dependent electron-phonon coupling as the origin of multiple-gap superconductivity as well as the high transition temperature of MgB2.

Fabrication and electrical characterization of high aspect ratio silicon field emitter arrays Fabrication and characterization of silicon field emitter arrays with focusing electrode by the chemical mechanical polishing processWe fabricated hafnium carbide ͑HfC͒ coated Si field emitter arrays ͑HfC FEAs͒ with an extraction-gate electrode to improve the emission characteristics of Si FEAs. Hafnium carbide thin film was deposited by inductively coupled plasma-assisted magnetron sputtering. The HfC film was characterized by x-ray photoelectron spectroscopy and x-ray diffraction measurement, and was found to be ͑111͒-oriented polycrystalline film. The HfC FEAs exhibited superior performance. An emission of more than 10 mA could be obtained from the 16 000 tip array, which is 20 times higher than that for Si FEAs. The operational voltage for emission of 1 A decreased from 61 to 45 V due to the HfC coating. The long-term emission characteristics were also measured. Si FEAs degraded rapidly even in an ultrahigh vacuum chamber. However, the emission degradation in the HfC FEAs was much slower. The number of active tips was counted using an electrostatic-lens projector, and the results revealed that the HfC FEAs had six times as many tips as the Si FEAs had.