Radio frequency power

The optoelectronic properties of the i -Si H films depend on many deposition parameters such as the pressure of the gas, flow rate, substrate temperature, power dissipation in the plasma, excitation frequency, anode—cathode distance, gas composition, and electrode configuration. Deposition conditions that are generally employed to produce device-quahty hydrogenated amorphous Si (i -SiH) are as follows gas composition = 100% SiH flow rate is high, --- dO cm pressure is low, 26—80 Pa (200—600 mtorr) deposition temperature = 250° C radio-frequency power is low, <25 mW/cm and the anode—cathode distance is 1-4 cm. 

The inductively coupled plasma source (Fig. 20.11) comprises three concentric silica quartz tubes, each of which is open at the top. The argon stream that carries the sample, in the form of an aerosol, passes through the central tube. The excitation is provided by two or three turns of a metal induction tube through which flows a radio-frequency current (frequency 27 MHz). The second gas flow of argon of rate between 10 and 15 L min-1 maintains the plasma. It is this gas stream that is excited by the radio-frequency power. The plasma gas flows in a helical pattern which provides stability and helps to isolate thermally the outside quartz tube. 

Ideally, it would be desirable to determine many parameters in order to characterize and mechanistically define these unusual reactions. This has been an important objective that has often been considered in the course of these studies. It would be helpful to know, as a function of such parameters of the plasma as the radio-frequency power, pressure, and rate of admission of reactants, (2) the identity and concentrations of all species, including trifluoromethyl radicals, (2) the electronic states of each species, (3) the vibrational states of each species, and (4) both the rotational states of each species and the average, translational energies of, at least, the trifluoromethyl radicals. 

Figure 6,9. Effective modulation of loser output as a function of radio frequency power applied to a Sharp LTQ24 laser diode at 30 MHz. Data are shown for DC bias of 50 mA ( , 7 mW laser output), 60 mA (O, 14 mW), and 70 mA (a, 19 mW). Reproduced from Ref. 25 with permission,...

Bradley, C.D. Curtis, J.M. Derrick, P.J. Wright, B. Tandem MS of Peptides Using a Magnetic Sector/Quadrapole Hybrid-the Case for Higher Collision Energy and Higher Radio-Frequency Power. Anal. Chem. 1992, 64, 2628-2635. 

If the radio-frequency power is too high, relaxation cannot compete with the disruption of the equilibrium of spins. The population difference between the nuclear magnetic... 

In the conventional NMR experiment, a radio-frequency field is applied continuously to a sample in a magnetic field. The radio-frequency power must be kept low to avoid saturation. An NMR spectrum is obtained by sweeping the rf field through the range of Larmor frequencies of the observed nucleus. The nuclear induction current (Section 1.8.1) is amplified and recorded as a function of frequency. This method, which yields the frequency domain spectrum f(ai), is known as the steady-state absorption or continuous wave (CW) NMR spectroscopy [1-3]. 

Factors that affect the rate of low-temperature ashing other than radiofrequency power and oxygen flow rate are the coal particle size and depth of sample bed. Typical conditions for ashing are a particle size of less than 80 mesh, a sample layer density of 30 mg/cm2, oxygen flow rate of 100 cm3/min, chamber pressure of about 2 torr, and a 50-W net radio-frequency power. The total time required is 36 to 72 hours, and specified conditions must be met during the procedure to obtain reproducible results. 

Analytical glow discharges have conventionally operated with a constant negative dc potential applied to the cathode. There is no reason, however, that they can t be operated through the application of a pulsed potential, an applied rf potential, or a positive potential applied to the cathode. Many variations have been tried alone and in combination with one another. Perhaps the most interesting among these (because of the unique capabilities that it provides) is the radio-frequency-powered discharge. The analysis of nonconductors is covered extensively in a later chapter, but a brief overview is in order here. 

A 1- to 2-kW radio frequency power supply, either free-running or crystal-controlled, drives current through a water- or air-cooled copper tube that acts as the induction coil (often called a load coil). The oscillating current through the load coil produces an oscillating electromagnetic field. 

This chapter deals exclusively with the methods that have been developed for the direct solids analysis of nonconductive samples by glow discharge mass spectrometry. The basic approaches to operation and sample preparation for the three primary methodologies of compaction, secondary cathode, and radio frequency powering are described. Examples of source performance and practical applications of each are taken from the analytical literature. Whereas this chapter de-... 

ANALYSIS BASED ON THE USE OF RADIO FREQUENCY POWERED SOURCES... 

The radio frequency pulse is a very short (tens of microseconds), and a very high power (tens or hundreds of watts) pulse of radio frequency power applied to the probe coil at or very near the Larmor frequency. It has a rectangular envelope the power turns on and instantly reaches full power, then at the end of its duration it goes instantly to zero. The pulse creates an oscillating magnetic field, which can be represented by a vector (the Z i vector ) that rotates in the x-y plane at the frequency of the pulse. The length of the B vector is equal to the amplitude of the radio frequency pulse. 

Formation of platinum fractal-like structures is possible by PA-CVD (19% Ar, 80% O2, 1% SnMe4) on tin oxide thin films using Pt(acac)2 as starting material . The platinum aggregates show a dendritic structure of fractional dimension D ca 1.1-1.6 (Figure 10). The occurrence of such aggregates has been correlated to the concentration of the platinum precursor and to the radio-frequency power applied to the substrate electrode. Fabrication of microsensors integrated on silicon wafers with the help of photoresistors is possible . 

The tubular-type plasma reactor system used in the study consists of a reactor chamber, power supply, monomer feed, and pumping-out units, as depicted in Figure 19.1. One side of the glass tube is connected to a monomer inlet and the other side to a vacuum pump with O-ring joints. A radio frequency power generator of 13.56 MHz is coupled to two capacitive copper electrodes, which are 1 cm wide and 6 cm apart. The radio frequency power was controlled by an L-C matching network and monitored by power meter. 

In order to examine the elfect of flow pattern in a reactor, which is a crucially important design factor of an LCVD reactor, it is necessary to examine the profile of deposition in a simple reactor first. A tubular reactor with an external radio frequency power coupling is ideally suited to the study of the distribution of polymer deposition. In such a reactor, 100% of the monomer passes through the luminous gas phase in the reactor, and the situation is very close to the case in which no bypass of monomer occurs. The experimental setup used for... 

Oxygen reactive-ion etching (O2 RIE) was carried out with a Cooke Vacuum Products (model C71-3) parallel-plate RIE reactor operating at 13.56 MHz. Oxygen pressure and flow rate were 2 Pa and 10 seem (standard cubic centimeters per minute), respectively, and the RF (radio frequency) power density and self-bias were 0.15 W/cm and -350 V, respectively. 

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