High-precision DC Research Articles

Onset of superfluidity inHe4films adsorbed on disordered substrates

We have studied 4He films adsorbed in two porous glasses, aerogel and Vycor, using high precision torsional oscillator and DC calorimetry techniques. Our investigation focused on the onset of superfluidity at low temperatures as the 4He coverage is increased. Torsional oscillator measurements of the 4He-aerogel system were used to determine the superfluid density of films with transition temperatures as low as 20 mK. Heat capacity measurements of the 4He-Vycor system probed the excitation spectrum of both non-superfluid and superfluid films for temperatures down to 10 mK. Both sets of measurements suggest that the critical coverage for the onset of superfluidity corresponds to a mobility edge in the chemical potential, so that the onset transition is the bosonic analog of a superconductor-insulator transition. The superfluid density measurements, however, are not in agreement with the scaling theory of an onset transition from a gapless, Bose glass phase to a superfluid. The heat capacity measurements show that the non-superfluid phase is better characterized as an insulator with a gap.

DC B–H curve tracer with error correction and constant measuring and drawing speed using microcomputer

A high precision DC B–H curve tracer is developed which uses microcomputer control. The error caused by the drift of DC amplifiers is automatically corrected and the difference between the starting and finishing points of the curve is automatically corrected to zero. The measuring and plotting interval along the curve can be constant. These are totally processed by the microcomputer.

Electron-beam lithography system using a quadrupole triplet

A variable spot-shaping system using an electrostatic quadrupole triplet has been developed to provide a more flexible pattern generation without loss of beam current accompanying a change of dimension of the shaped beam. The quadrupole electron-beam lithography system (QEBS) consists of a LaB6 electron gun, magnetic illuminating lenses, square apertures, an electrostatic quadrupole triplet, and an octopole deflector. The high precision electrostatic quadrupole triplet has been newly developed for this system. The length of the shaped beam can be varied from 0.3 to 30 μm for a rectangular beam and from 1 to 200 μm for a linear beam by adjusting the excitation voltages of the second and the third quadrupoles. The excitation voltages of the quadrupole triplet are controlled by floating digital/analog (D/A) converters with high voltage amplifiers and high-precision dc voltage sources. Preliminary parttern exposures demonstrate that the QEBS is suitable for forming fine line patterns.

Comparator bridge for testing high-precision resistance boxes and dc bridges

Comparator bridge for testing high-precision resistance boxes and dc bridges