Function Of Radio Frequency Power Research Articles

Hollow-cathode chemical vapor deposition of thick, low-stress diamond-like carbon films

A radio-frequency (RF), hollow-cathode plasma source with confining magnetic field is described for the chemical vapor deposition of thick ( > 10 µm), amorphous diamond-like carbon ablator films for inertial confinement fusion applications. Plasma is characterized by optical emission spectroscopy, while properties of the resultant films are measured by a combination of profilometry, Rutherford backscattering spectrometry, elastic recoil detection analysis, X-ray diffraction, Raman spectroscopy, and atomic force microscopy. The dependence of the deposition rate, film density, elemental composition, self-bias and residual stress is reported as a function of RF power. Higher density films were found when using Ar plasma, than N2 or H2 plasma. The coatings produced are x-ray amorphous, exhibit low compressive stress ( ~ 100 MPa), high density ( < 1.7 g/cm3), hydrogen content of ~ 30 at.%, and a low average roughness of 0.75 nm. Applications of these films as tunable-density ablators for inertial confinement fusion experiments are discussed.

Effects of RF power on the growth behaviors of CuAlO2 thin films

Cu–Al–O thin films were deposited on glass substrates by radio frequency (RF) sputtering using an Al–Cu mosaic target under various RF powers at room temperature. The RF power was set at 100, 200, 250, and 300W and the oxygen partial pressure (O2/Ar+O2) was set at 10%. This study examined the crystal structure, electronic structure, valence state, and electrical resistivity properties of the CuAlO2 thin films as a function of RF power and growth rate. The Cu/Al atomic ratios when the RF power was set at 100, 200, 250, and 300W were 0.9, 1, 1.1, and 0.9, respectively. As RF power increased, the crystal structure of the Cu–Al–O film changed from amorphous to crystallized CuAlO2. In addition, the results also show that the growth rate could influence the phase formation behavior. The lowest resistivity of the Cu–Al–O thin films obtained in this study was 1.9kΩ-cm with 250W at room temperature.

Magnetization transfer in lamellar liquid crystals.

This study examines the relationship between quantitative magnetization transfer (qMT) parameters and the molecular composition of a model lamellar liquid crystal (LLC) system composed of 1-decyl alcohol (decanol), sodium dodecyl sulfate (SDS), and water. Samples were made within a stable lamellar mesophase to provide different ratios of total semisolid protons (SDS + decanol) to water protons. Data were collected as a function of radiofrequency power, frequency offset, and temperature. qMT parameters were estimated by fitting a standard model to the data. Fitting results of four different semisolid line shapes were compared. A super-Lorentzian line shape for the semisolid component provided the best fit. The estimated amount of semisolids was proportional to the ratio of decanol-to-water protons. Other qMT parameters exhibited nonlinear dependence on sample composition. Magnetization transfer ratio (MTR) was a linear function of the semisolid fraction over a limited range of decanol concentration. In LLC samples, MT between semisolid and water originates from intramolecular nOe among decanol aliphatic chain protons followed by proton exchange between decanol hydroxyl and water. Exchange kinetics is influenced by SDS, although SDS protons do not participate in MT. These studies provide clinically relevant range of semisolid fraction proportional to detected MTR.

Effects of radio frequency power on the optical and electrical properties of germanium carbon films

The relative integrated intensity of the three components in C 1s with different RF power. • Amorphous germanium carbon films are fabricated by reactive sputtering in a CH 4 + H 2 + Ar mixture. • Optical, electrical and chemical bonding properties are investigated. • The effects of composition and chemical bonding on optical properties are investigated. • We found that high RF power and Ge content can promote the forming of Ge–C bond. We have prepared amorphous hydrogenated germanium carbon (a-Ge 1− x C x :H) films by radio frequency (RF) reactive magnetron sputtering and their composition, optical, electrical and chemical bonding properties are investigated as a function of RF power. The results show that the deposition rate increases and the optical gap of the a-Ge 1− x C x :H films decreases as RF power increases from 30 to 90 W. The decrease of the optical gap is mainly due to the decrease in the carbon content. As increasing RF power, the refractive index of the films increases and the absorption edge shifts to long wavelength region. Besides, the room temperature dark conductivity increase with RF power is due to the decrease of the activation energy connected with the increase of Ge content. Through the analysis of X-ray photoelectron spectroscopy (XPS), we found that the formation of Ge–C bonds in the films is promoted by high RF power connected with relatively high self-bias and Ge content.

Synthesis and tailoring of GaN nanocrystals at room temperature by RF magnetron sputtering

We report here the synthesis of hexagonal GaN nanocrystals on p-silicon substrates by Radio-Frequency (RF) magnetron sputtering without substrate heating or by post-deposition annealing treatment. GaN nanocrystals are synthesized and tailored as a function of RF power at constant Ar and N2 flow rates (working pressure). The observed reduction in grain sizes as a function of RF power has been correlated with an increase in compressive strain. The effect of RF power on crystallite orientation has been determined by diffraction intensities using the degree of c-axis orientation. Atomic force microscopy shows uniform lateral nanocrystal sizes with spherical in shape by insignificant difference in Root-Mean-Square (RMS) roughness values for all the deposited thin films. Transmission electron microscope and field emission-scanning electron microscope studies have been performed to understand the surface morphologies and grain sizes. Thus, tailoring the size of the nanocrystals has been discussed by correlating RF powers, working pressures and cathode voltages on lattice vibrations.

Studies of physical and chemical properties of styrene-based plasma polymer films deposited by radiofrequency Ar/styrene glow discharge

Styrene-based plasma polymer (SPP) films having thickness in the range of 900–1800 nm are deposited from radiofrequency (RF) Ar/styrene glow discharge. Depositions of the SPP films are carried out at working pressure of 1.2 × 10 −1 mbar and in the RF power range of 40–130 W. The physical and chemical properties of the SPP films are investigated as a function of RF power. Optical emission spectroscopy (OES) studies on Ar/styrene glow discharge reveal that the relative concentrations of active plasma species are strongly dependent on the variation of RF power. Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) are used to analyze the internal chemical structures of the films. It is revealed that the SPP film with highest carbon content exhibits enhanced scratch and corrosion resistance behavior along with stable thermal properties. The thermogravimetric (TGA) and gel permeation chromatography (GPC) results suggest the presence of both aliphatic and aromatic units in the SPP films. Attempts are made to correlate the results obtained from OES, FT-IR and XPS analyses with the deposited films properties. The possibility of using SPP films as protective coatings is also explored.

Effect of radio frequency power on the inductively coupled plasma etched Al 0.65Ga 0.35N surface

The etching effects on the surface and electrical characteristics of high Al mole fraction Al x Ga 1− x N ( x = 0.65) have been characterized by X-ray photoelectron spectroscopy (XPS) and transfer length method (TLM) as a function of radio frequency power. XPS results show that the Ga–N and Al–N peaks move to the lower energy after ICP etchings. An increase in the amount of oxygen and a decrease in the amount of nitrogen are observed for the etched samples along with the RF power. The annealing at 450 °C is partly effective on removing the oxygen amount which would come from the C–O component and recovering the N deficiencies on the surface of etched sample. The extracted sheet resistance of the AlGaN layer from TLM increases gradually after ICP etching with an increase of RF power. The correlation between the XPS peaks and the electrical properties of the etched samples has been discussed and the annealing effect on the inverse leakage current of the p-i-n AlGaN solar blind UV detector is examined.

High density mode in xenon produced by a Helicon Double Layer Thruster

A high density ‘blue’ mode has been observed when operating the Helicon Double Layer Thruster (HDLT) with xenon. Using a Langmuir probe and a retarding field energy analyser (RFEA), the plasma source and exhaust have been characterized at various radio frequency (RF) powers and operating pressures. When operating at low RF powers, the HDLT prototype is shown to be in a capacitively coupled mode. As the RF power is increased, a discrete mode transition occurs over a small RF power range (at about 625 W at 0.45 mTorr) and the plasma inside the source increases in density significantly and changes to a bright white/blue colour. This high density mode exhibits hysteresis, and radial measurements inside the source reveal a centrally peaked profile that is indicative of a helicon wave-sustained discharge. The quality, or Q, factor of the matching box is determined as a function of RF power and is shown to decrease in the high density mode, consistent with the increase in plasma density observed. The xenon exhaust of the HDLT prototype is investigated axially with the Langmuir probe and the RFEA and is shown to follow a Boltzmann expansion with an electron temperature of about 6 eV.

Low temperature deposition and effect of plasma power on tin oxide thin films prepared by modified plasma enhanced chemical vapor deposition

This work presents low temperature (200 and 300°C) thin film deposition of tin oxide (SnO2) using modified plasma enhanced chemical vapor deposition as a function of radio frequency power (100–500W). Stannic chloride (SnCl4) was used as precursor and oxygen (O2, 300SCCM) as reactant gas. Fine granular morphology was observed with tetragonal rutile structure grown along the [110] direction, at all the deposition conditions. Higher plasma power resulted in smoother morphology, improved crystallinity, and enhanced conductivity. Electrical resistivity value of as low as ∼0.01Ωcm was obtained at the deposition temperature of 300°C and 250W of plasma power.

Effects of radio frequency power on the chemical bonding, optical and mechanical properties for radio frequency reactive sputtered germanium carbide films

Germanium carbide (Ge1−xCx) films have been prepared by radio frequency (RF) reactive sputtering of a pure Ge(111) target in a CH4/Ar mixture discharge, and their composition, chemical bonding, optical and mechanical properties have been investigated as a function of RF power. The relationship between the chemical bonding and the optical and mechanical properties of the Ge1−xCx films has been explored. The results show that the refractive index of Ge1−xCx films increases from 1.9 to 3.2 and the optical gap decreases from 1.9 to 1.0 eV as RF power increases from 80 to 250 W, which is due to an increase in the germanium content with increasing RF power. Also, it is found that the hardness of Ge1−xCx films increases with increasing RF power, which can be attributed to an increase in the fraction of sp3 Ge–C bonds at the expense of the sp2 C–C bonds in the Ge1−xCx films.

Characterization of the Ba(Sn xTi 1− x)O 3 thin films prepared by radio frequency magnetron sputtering

Ba(Sn x Ti 1− x )O 3 (BS x T 1− x ) thin films prepared by radio frequency (RF) magnetron sputtering in a mixture of O 2/Ar atmosphere have been characterized as a function of RF power. The BS x T 1− x thin films are amorphous when sputtered at RF power = 100 and 125 W. The XRD shows only single perovskite structure phase of BaTiO 3. The intensity of reflection increases with RF power increases from 125 to 175 W. The BS x T 1− x thin films sputtered with RF power at 150 W produced maximum deposition. The effect of the RF power on the Sn/(Sn + Ti) ratio is not significant. The refractive index of the BS x T 1− x thin films increases with increasing RF power. The dielectric constant of the BS x T 1− x thin films increases with increasing Sn content for films sputtered at the same RF power. On the other hand, the dielectric constant of the BS x T 1− x thin films increases when the RF power is increased from 100 to 150 W, but the dielectric constant decreases for RF power greater than 150 W.

Dielectric substrate self-bias and plasma confinement in two-dimensional scanning radio frequency plasma-enhanced chemical vapour deposition

A two-dimensional scanning radio frequency (RF) plasma method was developed for large area deposition in order to avoid difficulties encountered in conventional large RF plasma systems, offering precision control of plasma, improved uniformity of thickness and microstructure, and simplicity of system design. Guarded electrode houses were introduced to form localized plasma thus parasitic plasma or parasitic deposition outside the localized plasma region was eliminated. Different electrode configurations were studied and optimized. Self-bias on dielectric substrate was studied for different electrode configurations as a function of RF power, pressure, and gases. Eliminating parasitic plasma by fully shielding the basing electrode resulted in monitoring signal losses of self-bias. Introducing an isolated plasma house for the biasing electrode enabled the recovery of the self-bias on the biasing electrode without parasitic deposition on substrate outside the localized plasma region. Uniformity optimization within the localized plasma region is no longer a concern in this system. Thickness profile control was achieved by scanning the plasma source over the large substrate. TEM analysis showed that homogenous films were deposited in the scanning deposition system.

Active nitrogen species dependence on radiofrequency plasma source operating parameters and their role in GaN growth

Radiofrequency (RF) nitrogen plasma sources are commonly used for the growth of III-nitrides by plasma-assisted molecular beam epitaxy. Their output mainly consists of a mixture of atomic nitrogen and metastable excited molecules. The relative concentration of these species as a function of RF power and nitrogen gas flow rate has been investigated by plasma optical emission spectroscopy. It is shown that the concentration of excited molecular nitrogen species is monotonically increasing with both parameters while the concentration of nitrogen atoms is almost independent of the nitrogen gas flow rate and increases monotonically with the coupled RF power. As a result of this functional dependence, the plasma source can be tuned to produce mainly excited nitrogen molecules or a mixture of excited molecules and atomic nitrogen. Comparison of the growth rates of gallium nitride films grown under different operating conditions of the RF source with the optical spectroscopy data shows that the metastable excited nitrogen molecules component of the source is the predominant factor contributing in the III-nitrides growth.

Production of Inductively Coupled RF Plasma Using a Ladder-Shaped Antenna

A radio-frequency (RF) excited H2 plasma is produced using a ladder-shaped antenna which is positioned within a plasma chamber and the fundamental characteristics of the plasma are examined. The potential and current fed to the antenna are almost in phase. The plasma parameters are measured as a function of RF power, gas pressure and gas flow rate with a Langmuir probe. It is found that the plasma density is uniform within ±10% over 300 mm. Furthermore, increases in the frequency of the RF power source lead to increases in the plasma density. When a mesh grid is installed between the antenna and the substrate, the plasma density and the plasma potential decrease.

Design and construction of high-frequency transition units for polarized deuterium internal targets

Radio-frequency transition units have been developed in order to produce vector and tensor polarized atomic deuterium beams. Transitions between various hyperfine states were generated using both a medium field transition unit and a resonant cavity structure as a strong field transition unit. Tests were carried out to determine the transition efficiencies of these units as function of radio frequency power, strength of the magnetic holding field, magnetic field gradient, and for the strong field unit, also as function of the position of the atomic beam in the cavity structure. A Stern—Gerlach source equipped with a medium and a strong field unit will provide a tensor polarized deuterium beam with the highest figure of merit at the minimum number of transition units. This polarization scheme allows for rapid reversal of tensor polarization while keeping the vector polarization fixed, and vice versa. The performance of the high-frequency transition units is described well by the results of a quantum-mechanical calculation. We will demonstrate that in a realistic internal target environment the efficiencies for the transitions between the 1–4, 2–6, and 3–5 hyperfine states exceeded in all cases 90% of the theoretical maximum polarization.

Planar RF induction plasma coupling efficiency

The radiofrequency power coupling efficiency of a planar induction source is determined by measurement of the power dissipated in the matching network and inductive coupler. Typically one finds the radiofrequency current to vary between 20 and 60 A (root mean square). The equivalent resistance of the coupling network is determined to be 0.09 Omega , and power coupling efficiency to the plasma is therefore found to be 70-90% with the remaining power lost to ohmic heating of the circuit elements. The efficiency is highest when the plasma-to-inductor distance is least since the increased mutual inductance reduces the radiofrequency inductor current and, hence, ohmic losses. Efficiency of power coupling is nearly constant as a function of radiofrequency power between 200 and 2000 W. Somewhat larger currents are required to sustain a discharge at lower pressures (about 1 mTorr) or when the plasma is not magnetically confined, giving rise to lower coupling efficiencies.