RF Pulse Width Research Articles

Effect of Showerhead Configuration on Coherent Raman Spectroscopically Monitored Pulsed Radio Frequency Plasma Enhanced Chemical Vapor Deposited Silicon Nitride Thin Films

The effect of showerhead design, number of holes and geometry, in a parallel plate reactor was studied by measuring the concentration of silane reactant by coherent anti-Stokes Raman scattering (CARS) spectroscopy as a function of radio frequency (rf) pulse width and peak power during pulsed power plasma enhanced chemical vapor deposition (PECVD) of silicon nitride thin films. Film deposition rate, stress, SiH/NH ratio, and thickness and index of refraction homogeneity were correlated with the change in silane concentration for each of the three head geometries: radial, square, and asymmetrical. The asymmetrical head caused plasma quality problems which affected the films' qualities. The square pattern showed good mixing qualities, but produced a film with high compressive stress. The radial head provided the most homogenous film, with respect to index of refraction and film thickness. With a 10 ms pulse width, however, the radial head plasma acted as a continuous plasma for depletion and stress data. The showerhead geometry affects plasma qualities, like stability and intensity, and reactant gas velocities, which in turn affect the nitride film thickness, nitride composition, and stress.

Low-Temperature Deposition of Aluminum Oxide on Polyethersulfone Substrate Using Plasma-Enhanced Atomic Layer Deposition

Very uniform Al 2 O 3 films could be deposited on polyethersulfone (PES) by plasma-enhanced atomic layer deposition (PEALD) using O 2 as O-precursor at temperatures ranging from 90 to 150°C. Although the use of rf plasma was prone to induce bending of the plastic substrate, lowering rf power and deposition temperature could eliminate the bending of the PES substrate in PEALD of an Al 2 O 3 layer. At 100°C, Al 2 O 3 films were deposited successfully by PEALD with 0.3 s rf pulse width and 300 W, with no measurable bending of substrate and decrease of deposition rate. The etch rate of PEALD Al 2 O 3 films deposited at 100°C, was slow as a factor of 2.6 compared to that of ALD Al 2 O 3 films deposited at 100°C.

611 プラズマイオン注入・成膜法による厚膜 DLC の作製

The relaxation of compressive residual stress in a diamond-like carbon (DLC) film was achieved by a hybrid process of plasma-based ion implantation and deposition (PBIID), and made it possible to prepare tick DLC film. The compressive residual stress in the DLC film prepared using acetylene gas was decreased with an increase in the negative pulse voltage for ion implantation from 0.46 GPa at no pulsed voltage to 0.16 GPa at the pulsed voltage of -20 kV. The DLC film had about 0.22 GPa that was little dependent on the RF pulse width.

Dynamic Nuclear Polarization in Pulsed ENDOR Experiments

Properly prepared pulse sequences of microwave and radio frequency have been employed to investigate the effect of polarization transfer from the polarized photo excited triplet state of pentacene inp-terphenyl crystals to the surrounding protons in pulsed ENDOR experiments. The ENDOR signal, measured as the change of electron spin echo (ESE) amplitude, is affected by the mode of RF pulses. WhenB0∥x(the long molecular axis), the ESE amplitude of the high-field transition of the triplet state changes from the maximum positive to zero with a π RF pulse, and to the maximum negative with a 2π pulse, while that of the low-field transition changes from nearly zero to the maximum negative as the RF pulse width increases. The effect is attributed to the strong electron spin polarization produced in the creation of the photoexcited triplet state and the subsequent efficient electron– nuclear polarization transfer process.

Design and evaluation of a compact 50 MW rf source of the PF linac for the KEKB project

A compact 50 MW rf source, an upgraded version of an existing rf source of the PF linac, has been developed for the KEKB project. The rf pulse-width requirement for the 50 MW klystron is 4 μs in order to be used with SLED-type rf compressors. On the basis of a computer simulation, the existing 30 MW klystron has succeeded to produce more than 51 MW at a 310 kV beam voltage with a 4 μs rf pulse width by optimizing the focusing magnetic field. Based on this result, we have designed and tested a new compact 50 MW klystron, the interaction region of which is the same as that of the 30 MW tube. In order to realize a practically reliable tube, we enlarged the cathode diameter, the gun housing and the insulation ceramic-seal. As a result, we have succeeded in obtaining a 50 MW output power with an rf pulse width of 4 μs and a more than 60 MW output power with an rf pulse width of 2 μs from this klystron. Compatibility between the 30 MW klystron and the 50 MW klystron has been aimed at for a socket assembly, such as a focusing electromagnet and a pulse-transformer assembly, with only a small change. These could lead to a compact rf source, which would save on upgrading costs. We can expect an easy construction method, which could be required to be conducted during an interval of machine operation for the Photon Factory.

Optimization of spin-lattice relaxation-time measurements: Statistical analysis by stochastic simulation of inversion-recovery experiments

A study by stochastic simulation of inversion-recovery experiments for measurements of spin-lattice relaxation times that aims at the optimization of the accuracy/time ratio is presented. Parameters such as the estimated uncertainty in the unknown T 1 the rf pulse width, the number and the values of the variable delay times, the value of the fixed delay time, and the signal-to-noise ratio, are considered in the statistical analysis. Two regression methods, the linear (logarithmic) with two adjustable parameters and the nonlinear (exponential) with three adjustable parameters, are employed in the analysis of the simulated data and are compared with one another. The nonlinear method is found to be superior under virtually all practical conditions (including fast repetition rate and nonideal pulse widths). A set of experimental parameters, optimal for T 1 measurements by the inversion-recovery technique and data analysis with the nonlinear three-parameter method, is obtained. Of special interest is the finding that in fast inversion-recovery experiments the fully recovered spectrum should also be measured to markedly improve the accuracy, in a given experimental time, of the measured spin-lattice relaxation time.

Observation on pulse methods in NQR

In nuclear magnetic resonance pulse methods the RF pulse width for greatest amplitude of the free induction decay is the same as the width required for sample saturation; this fact is usually extended to nuclear quadrupole resonance. However, in NQR it is only true for single crystals, but is wrong for a polycrystalline sample. The saturation in a polycrystalline sample is calculated here and this effect is explained.

A FET analogue switch for pulsed NMR receivers

A low-noise FET analogue switch is described which has been used to deal with some of the problems encountered in optimizing the design of a probe for a pulsed NMR spectrometer intended for work on solids. The switch circuit has been used in association with two spectrometers, one for microsecond RF pulses and the other for RF pulsewidths of up to 1 s. In each case the resolution time achieved was limited by the transmitter coil ring down. The switch has negligible insertion loss when on and 84 dB attenuation at 15 MHz when off, thus affording good protection of the receiver system.

Symmetrized pulse sequences in high resolution NMR in solids

A systematic approach is developed for the improvement of the line narrowing efficiency of multipulse cycle sequences. This is based on the symmetrization of pulse cycles and exploits the useful properties of reflection symmetry subcycles. An example of a new pulse sequence is given which removes the dipolar interaction to third order in the time expansion of the logarithmic operator. Ways are discussed for compensating multipulse cycles for the effects of finite rf pulse width and rf inhomogeneity and a fully compensated version of the new pulse sequence is given.

Measurement of RF Peak-Pulse Power by a Sampling-Comparison Method

A method is described whereby RF peak-pulse power may be measured by comparison with CW power at the same frequency. Comparison is made by first sampling the power in a small portion of the RF pulse width and subsequently sampling the same portion of the CW signal whose power level is accurately known. Sampling is accomplished with a fast SPDT coaxial solid-state switch synchronized with the RF pulse. A time delay network allows the sample to be taken anywhere along the RF pulse width. Estimated maximum error for peak power levels to 10 kw is 3 per cent. High CW levels are not necessary since the switch is used in conjunction with directional couplers to cover the power ranges of interest.