M.H. Gordon

Investigating the role of hydrogen in silicon deposition using an energy-resolved mass spectrometer and a Langmuir probe in an Ar/H2 radio frequency magnetron discharge

The plasma parameters and ion energy distributions (IED) of the dominant species in an Ar-H2 discharge are investigated with an energy resolved mass spectrometer and a Langmuir probe. The plasmas are generated in a conventional magnetron chamber powered at 150 W, 13.56 MHz at hydrogen flow rates ranging from 0 to 25 sccm with a fixed argon gas flow rate of 15 sccm. Various Hn+, SiHn+, SiHn fragments (with n = 1, 2, 3) together with Ar+ and ArH+ species are detected in the discharge. The most important species for the film deposition is SiHn (with n = 0, 1, 2). H fragments affect the hydrogen content in the material. The flux of Ar+ decreases and the flux of ArH+ increases when the hydrogen flow rate is increased; however, both fluxes saturate at hydrogen flow rates above 15 sccm. Electron density, ne, electron energy, Te, and ion density, ni, are estimated from the Langmuir probe data. Te is below 1.2 eV at hydrogen flow rates below 8 sccm, and about 2 eV at flow rates above 8 sccm. ne and ni decrease wit...

CrNx and Cr1−xAlxN as template films for the growth of α-alumina using ac reactive magnetron sputtering

Crystalline alumina thin films were deposited on WC–Co substrates using a reactive inverted cylindrical ac magnetron sputtering technique with a chromium oxide prelayer. The interfacial prelayer of chromium oxide was prepared by controlled oxidation of CrNx and Cr1−xAlxN films deposited previously using the same ac reactive magnetron configured with one Cr and Al target. The oxidation was carried out by annealing CrNx and Cr1−xAlxN films in air at 973 and 1373K, respectively. Scanning electron microscopy and energy dispersive x-ray microanalysis were carried out to investigate the thin film surface morphology and composition. The alumina coatings obtained on oxidized CrNx films (templates) were smooth and consisted primarily of κ and α phases. The diffraction peaks from the γ phase were not observed in any of the alumina coatings. The morphology and phase composition of the alumina coatings on the oxidized Cr1−xAlxN films (templates) were strongly dependent on the aluminum content in the films.

Pressure Sensitivity of a Thermal Shear Stress Sensor

This paper reports on the pressure sensitivity testing of MEMS thermal shear stress sensors. The MEMS sensor is a micromachined, vacuum-cavity insulated, thermal shear stress sensor for underwater applications. This paper is focused on the combined experimental and numerical study carried out to examine the effects of changing environmental pressure on the MEMS-based shear stress sensors. Four different sensors were tested experimentally and numerically. The silicon nitride diaphragms for each sensor are 4-μm thick. The length of each diaphragm is 210-μm while the widths are 210-μm, 150-μm, 100-μm, and 75-μm respectively. It is found that reducing the surface area size and increasing the thickness of the sensor diaphragms are effective in minimizing the pressure sensitivity.Copyright

Characterization of laterally aligned carbon nanotubes formed by AC dielectrophoresis

We investigate the relationship between the parameters of the AC electric field and the properties of dielectrophoretically aligned carbon nanotubes (CNTs) between two triangular-shaped micro-electrodes. Specifically, the effects of electrode dimensions, magnitude and frequency of the applied potential, and fluid velocity due to electrothermal force on the resultant aligned CNT trace width are examined. Parameters of the electric field are computed numerically using Ansoftreg. Both transient and steady state results are studied. The transient results shows the CNT trace grows linearly initially. This is followed by an asymptotic widening of the trace before a constant steady-state trace width is reached. The steady-state trace width (1) increases with electrode tip angle, (2) increases with increasing potential, and (3) is not affected by the frequency of the applied potential. The results of the present study provide an important guideline for designing CNT based devices fabricated by dielectrophoresis.

Hardness and Frictional Properties of Alumina Coatings by AC Inverted Magnetron Sputtering Technique

Alumina thin film coatings of 500 nm thickness were deposited on silicon substrates by AC inverted magnetron sputtering technique at 350°C. The effect of deposition power and oxygen partial pressure on the hardness and frictional performances of the alumina coatings were investigated using a nanoindenter. The film hardness varied with both the power and the oxygen partial pressure with the power had more pronounced effect. The maximum hardness of 22 GPa was obtained at an optimum power of 5 kW and oxygen partial pressure of 40%. The coefficient of friction decreased with the increase in hardness.Copyright