Dual Radio Frequency Research Articles

Correlation of optical absorption and density of paramagnetic centers in a-C:H films

We investigated a-C:H films deposited by dual electron cyclotron resonance radio frequency PECVD by optical absorption and electron spin resonance (ESR) spectroscopy. We show that the variation of the density of paramagnetic centers obtained from electron spin resonance (ESR) spectroscopy can be directly correlated to the low energy part of the optical absorption spectrum revealed by photothermal deflection spectroscopy (PDS). A simple analysis of the low energy part of the optical absorption spectrum is proposed which allows an assessment of the density of states at the Fermi level. We interpret this result in terms of intraband transitions of localized defects situated far from the π−π* band tails which dominate the higher energy part of the optical absorption spectrum.

The effect of applied dc bias voltage on the properties of a-C:H films prepared in a dual dc–rf plasma system

A dual direct current and radio frequency (dc–rf) plasma system was used to deposit hydrogenated amorphous carbon (a-C:H) films from methane plasma. It has the advantages of separately controlling ion density and ion energy by rf power and dc bias, respectively, over conventional simply capacitive-coupled rf-PECVD system. Thus the a-C:H films were obtained at different applied dc biases using CH4 plus H2 as the feedstock. The structural, mechanical and tribological properties of the resulting a-C:H films were investigated as a function of the applied dc bias voltage in the range 0–500V. The results showed that the structure and properties of a-C:H films strongly depended on the applied dc bias voltage. With an increase in the applied dc bias voltage, the deposition rate and the bonded hydrogen content decreased, and the hardness and sp3 content (according to Raman spectra) were shown to reach their maximum values simultaneously at an applied dc bias voltage of 100V. At the same time, the smallest friction coefficient and the best wear-resistance were obtained.

A dual RF resonator system for high-field functional magnetic resonance imaging of small animals

A new apparatus has been developed that integrates an animal restrainer arrangement for small animals with an actively tunable/detunable dual radio-frequency (RF) coil system for in vivo anatomical and functional magnetic resonance imaging of small animals at 4.7 T. The radio-frequency coil features an eight-element microstrip line configuration that, in conjunction with a segmented outer copper shield, forms a transversal electromagnetic (TEM) resonator structure. Matching and active tuning/detuning is achieved through fixed/variable capacitors and a PIN diode for each resonator element. These components along with radio-frequency chokes (RFCs) and blocking capacitors are placed on two printed circuit boards (PCBs) whose copper coated ground planes form the front and back of the volume coil and are therefore an integral part of the resonator structure. The magnetic resonance signal response is received with a dome-shaped single-loop surface coil that can be height-adjustable with respect to the animal’s head. The conscious animal is immobilized through a mechanical arrangement that consists of a Plexiglas body tube and a head restrainer. This restrainer has a cylindrical holder with a mouthpiece and position screws to receive and restrain the head of the animal. The apparatus is intended to perform anatomical and functional magnetic resonance imaging in conscious animals such as mice, rats, hamsters, and marmosets. Cranial images acquired from fully conscious rats in a 4.7 T Bruker 40 cm bore animal scanner underscore the feasibility of this approach and bode well to extend this system to the imaging of other animals.

Analytic model for a dual frequency capacitive discharge

A homogeneous plasma model for dual radio-frequency (rf) discharges driven by two sinusoidal current sources has been analyzed. Under the assumptions of time-independent and collisionless ion motion and inertialess electrons, the analytic expressions for discharge parameters are obtained as a function of the effective parameters such as effective frequency, effective current, and effective voltage. Effective parameters are determined by the ratio of two currents or voltages. Two rf sources are generally coupled to each other through the plasma medium. It is also shown that the reduction of the bulk plasma length due to the sheath size has to be considered for calculating the discharge parameters since the sheath length is not always negligible compared to the bulk plasma length. Furthermore, the dependence of discharge parameters on the low frequency is presented.

The dual frequency radio-frequency sheath revisited

A recent paper (Riboche et al 2003) gave a treatment of this problem as a generalization of earlier work by Lieberman (1988). The expressions produced are intrinsically complicated and there is a natural tendency to resort to numerical methods at an early stage. This note adopts an alternative approach and seeks to evaluate the integrals concerned in a systematic manner so as to obtain analytical expressions, albeit approximations, but ones with known accuracy.

High-resolution state-selected ion-molecule reaction studies using pulsed field ionization photoelectron-secondary ion coincidence method

We have developed an octopole-quadrupole photoionization apparatus at the Advanced Light Source for absolute integral cross-section measurements of rovibrational-state-selected ion-molecule reactions. This apparatus consists of a high-resolution photoionization ion source, a wired ion gate lens, a dual radio-frequency (rf) octopole ion guide reaction gas cell, and a quadrupole mass spectrometer for reactant and product ion detection. The unique feature of this apparatus is the implementation of the high-resolution pulsed field ionization-photoelectron (PFI-PE)-photoion coincidence (PFI-PEPICO) technique, which has allowed the rotational-state selection of diatomic ions for ion-molecule reaction studies. The novel application of the wired ion gate lens for the rejection of false coincidence background ions is described. This application, along with the differential-ion-gate scheme, has made possible the measurements of rovibrational-state-selected absolute integral reaction cross sections for ion-molecule collisions using the PFI-PE-secondary ion coincidence (PFI-PESICO) method. The successful measurement of absolute state-selected cross sections for H2+(X,v+,N+)+Ar(Ne) with v+ up to 17 [the third to the last vibrational state of H2+(X)] demonstrates the high sensitivity of this differential-ion-gate PFI-PESICO method. In order to gain a detailed understanding and to obtain optimal performance of the wired ion gate lens for PFI-PESICO measurements, we have carried out ion trajectory calculations of reactant ions between the photoionization region and the rf-octopole ion guide. On the basis of these calculations, possible future improvements for the application of this differential-ion-gate PFI-PESICO scheme are discussed.

Dual radio frequency sources in a magnetized capacitively coupled plasma discharge

Nonlinear interaction of two radio frequency (RF) sources in a magnetized Ar/C/sub 2/F/sub 6/ capacitively coupled plasma discharge is investigated using a computational model. Results show that application of a radial magnetic field enhances charged and neutral species densities in the plasma reactor due to reduction in electron loss to surfaces and trapping of secondary electron emission generated electrons. Amplitude of RF currents at electrodes also increases with magnetic field strength and source frequency for a given RF voltage. Due to nonlinear nature of plasma sheath, higher harmonics of applied frequencies and source interaction generated harmonics can be observed in electrode currents. Application of magnetic field decreases electron mobility and makes the system less nonlinear, which reduces higher harmonics relative to primary components. Magnetic field also tends to make the RF sources more isolated. Increase in source frequency moves the plasma from electrode edge to the center of the chamber, which redistributes current through the electrodes. If frequencies of the two RF sources are commensurate, nonlinear interaction of RF sources generates subharmonics of primary frequencies.

Spinal Cord Stimulation for Complex Pain: Initial Experience with a Dual Electrode, Programmable, Internal Pulse Generator

Abstract: The objective of this study was to engage in an 18-month follow-up of 20 chronic complex pain patients using a dual electrode, programmable, fully implantable internal pulse generator (IPG) for spinal cord stimulation (SCS). Implant status, stimulation mode, anode-cathode configuration (array), cathode position, paresthesia overlap, complications, Visual Analog Scores (VAS), and overall satisfaction were prospectively examined in 20 patients implanted with dual 4 contact, staggered, percutaneous electrodes (Pisces 3487A, Medtronic, Minneapolis, Minnesota) internalized to a fully implantable, programmable IPG (Synergy 7466, Medtronic, Minneapolis, Minnesota). All patients had undergone initial implantation for chronic complex axial and extremity pain (eg, Failed Back Surgery Syndrome (FBSS), Complex Regional Pain Syndrome (CRPS)) with dual octapolar, radiofrequency (RF) SCS systems (Advanced Neuromodulation Systems 2098, Plano, Texas).1–3 All patients required conversion to the current dual IPG systems due to RF system receiver sensitivity, preventing further antenna coupling).1 Dual quadrupolar IPG SCS outcomes were compared to previous long-term, dual octapolar RF SCS complex pain reports.1–3 Data was collected and analyzed by a disinterested third party. At 18 months, all 20 patients remained implanted. All patients reported using 1 or 2 “best” guarded tripolar or bipolar arrays to maintain favorable paresthesia overlap (77.5%), VAS reduction (9.78 → 4.40), and overall patient satisfaction (80%). Eighty-five percent of “best” anode-cathode configurations were activated on both electrode columns about the physiologic midline of the C 3/4 vertebral segments for upper extremity pain, and the T 9/10 vertebral segments for low back and lower extremity pain. Sixty-seven and one half percent of all electrodes were thoracic and 32.5% were cervical. “Best” arrays were activated as narrow (adjacent contact) guarded cathode tripoles (75%), extended (nonadjacent contact) bipoles/tripoles (15%), or as narrow bipoles (10%). The mean number of active contacts per “best” array was 5.6, with 3.75 anodes and 1.85 cathodes. All patients preferred the current IPG to the prior RF SCS implant, citing RF receiver site sensitivity, difficulty maintaining coupling of the RF antennae, and time intensive RF programming. Conversely, 13 patients (65%) reported IPG site sensitivity that did not affect overall satisfaction. That is, none would convert their current IPG to a smaller IPG to resolve this issue, unless it was of equal longevity. Sixteen patients (80%) were satisfied with the overall level of pain relief, and all (100%) would repeat the IPG SCS implant. This study demonstrates improved overall outcome and patient satisfaction after long-term, dual octapolar RF SCS conversion to dual quadrupolar IPG SCS systems in the same patient population. It also validates prior dual SCS electrode reports of common array configuration, electrode positioning about the physiologic midline, and patient preference of single or dual programmability in the treatment of chronic complex pain.1,4,5 Follow-up of this initial experience with a multicenter study is warranted.

Structural study of amorphous vanadium oxide films for thin film microbattery

Solid-state thin film batteries (TFBs) consisting of amorphous V2O5/Pt/Ti/Si have been fabricated by specially designed dual target magnetron radio frequency (rf) and direct current (dc) sputtering systems at room temperature. It is shown that the discharge capacity of the TFBs is degraded with increasing cycle number; after 450 cycles, the capacity is dropped by ∼54% of the initial value. To investigate the degradation mechanism, the structural properties of as-deposited and cycled LiPON and a-V2O5 films are characterized by transmission electron microscopy (TEM) and x-ray diffraction (XRD) measurements. TEM and XRD results show that the as-deposited LiPON and V2O5 are amorphous. It is, however, shown that cycling causes the occurrence of crystallites (2–6 nm across) not only in the V2O5 film, but also in the LiPON film. Based on the structural and electrochemical results, the cycle-induced degradation of capacity is correlated to the structural change of the LiPON and V2O5.

Nanostructure and mechanical properties of WC–SiC thin films

The mechanical properties of WC–SiC thin films deposited by dual radio frequency magnetron sputtering were investigated. The films were characterized by x-ray photoelectron spectroscopy, x-ray diffraction (XRD), and transmission electron microscopy (TEM) to evaluate the details of the microstructure and degree of amorphization. The results indicate that small additions of SiC (<25%) can significantly increase hardness compared to a pure WC film, but higher SiC contents do not strongly affect hardness. XRD studies show the SiC had a disordering effect. TEM results showed that WC films had coarse porous structure, but films with a low silicon carbide content (approximately 10 to 25 at%) had a denser nanocrystalline structure. Samples with greater than 25% SiC were amorphous. The initial hardness increase at lower SiC contents correlated well with the observed densification, but the transition to an amorphous structure did not strongly affect hardness.

Report of a new technique for enhanced non‐invasive skin rejuvenation using a dual mode pulsed light and radio‐frequency energy source: selective radio‐thermolysis

Report of a new technique for enhanced non‐invasive skin rejuvenation using a dual mode pulsed light and radio‐frequency energy source: selective radio‐thermolysis

Evolving Patterns of Spinal Cord Stimulation in Patients Implanted for Intractable Low Back and Leg Pain

The objective of this study was to examine the programming strategies used in patients with intractable low-back pain treated with epidural spinal cord stimulation (SCS) utilizing paddle electrodes and a radio frequency (RF) stimulator. Programming strategies were examined in a group of patients implanted with a 16-contact paddle electrode and a dual channel RF receiver to treat chronic low-back pain. Baseline data included previous surgical history information, leg and low back pain severity and characteristics, and routine demographic information. Outcome measurements included the visual analog scale (VAS) (1), patient pain relief rating scale, and programming parameters. Patients rated their pain relief on a 5-point scale where 4 = excellent, 3 = good, 2 = fair, 1 = poor and 0 = none. Success was determined to be a pain relief score of "fair" or above. Data were collected during patient visits or by mail, at approximately 6, 12, and 24 months, postoperatively. Immediate postop data were available in 16 patients, 6-month data in 21 patients, 1-year data in 20 patients, and 2-year data in 10 patients, and analyzed for the purposes of examining programming strategies. The most common location for the tip of the electrode (lead) was found to be in the middle of the 8th thoracic vertebrae (N = 26). At the immediate postop assessment, the majority of cathodes were activated in the upper half of T9. By the 6-month follow-up, the majority of cathodes had shifted to the bottom of T9 and top of T10. Overall 88% of cathode locations were changed at one or more study visits. At 2 years, 86% of the programs used four or more active contacts. At 6 months, 83% of the patients reported that the therapy was a success, at 1 year, success was 94%, and by 2 years, success was 75%. Both SCS and chronic pain are dynamic processes. Complex pain patterns, such as the ones of patients who have pain in the low back and in one or both lower extremities, require a high degree of flexibility in the implanted SCS system. The system must provide the capability to redirect the current electronically over at least two segments of the spinal canal, to electronically steer the current in a medio-lateral direction, and to activate multiple electrical contacts simultaneously. The willingness and ability to provide extensive reprogramming in the long term follow-up is also of the utmost importance. Pain and its treatment with SCS is a dynamic process.

Noninvasive Measurement of Oxygenation of Hemoglobin by Direct Transmission of Near-Infrared Energy (700–1000 nm) from an Electronically Tuned Ti: Sapphire Laser Driven by a Dual Radio-Frequency Driving Method

We have applied an electronically tuned Ti: sapphire (ETT) laser controlled with a dual radio-frequency driving (DRD) method to noninvasive measurements of the transmission spectra of a whole human hand in which the bands due to hemoglobin and lipid were identified. Spectra of a human hand that is more than 3 cm thick were obtained in the spectral range from 700 to 1000 nm, allowing one to probe the oxygenation of hemoglobin (Hb). Our study demonstrates that an ETT laser may be used as a potential light source for near-infrared (NIR) spectroscopy in biomedical applications. For the acquisition of NIR transmission spectra of Hb with a good signal-to-noise ratio, the laser emission was programmed electronically to fill up strong absorption bands due to water, and baseline undulation due to detection sensitivity and light scattering. The present study required more stable control of the ETT laser, so we developed the DRD method, achieving high reliability in wavelength (< 0.1 nm) and in intensity (< ± 2% per average in 10 pulses).

On the microstructural, optical and mechanical properties of hydrogenated amorphous carbon films deposited in electron cyclotron resonance plasma

Hydrogenated amorphous carbon (a-C:H) films have been prepared from methane–argon (5%) gas mixture in a dual electron cyclotron resonance radio frequency (ECR-r.f.) glow discharge assisted plasma system. The way in which the optical properties and the residual stresses are related to the film microstructure was systematically analysed in the as-deposited samples, as a function of the self-bias applied to the substrate, ranging from −30 to −600 V. Combined infrared absorption and elastic recoil detection analysis experiments, were used to characterize the vibrational properties and the H content, while optical transmission measurements were employed to determine the optical parameters such as the refractive index ( n ) and the optical gap E 04 . These results are correlated with the residual stress measurements. A good correlation is observed between the variation of E 04 and n and the changes in the total H bonded and content, as a function of the self-bias applied to the substrate. Moreover, the residual stress is found to be compressive and increases with the bias until it reaches a maximum at −120 V, and then decreases monotonically for higher bias. This behaviour, which is affected not only by the [H]/[C] ratio but also by the C H and C C volumetric distortions, can be explained partially by the subimplantation model.

Hydrogen stability in diamond-like carbon films during wear tests

Hydrogen stability has been investigated during wear tests in particular diamond-like carbon films deposited in a dual electron cyclotron resonance radio frequency glow discharge plasma system, at two different substrate bias voltages equal to −30 and −600 V, for series I and series II, respectively. Combined infrared absorption and elastic recoil detection analysis experiments are used to fully characterize the films in their as-deposited state and after wear tests. The results indicate clearly that the total bonded hydrogen content as well as the total hydrogen concentration decrease during wear tests for the two series. Two mechanisms are discussed to explain these results, e.g., the surface contact graphitization due to heating effect and the hydrogen diffusion to the free surface as a result of plastic deformation process.

Graded TiAlN layers deposited by electron cyclotron resonance-assisted reactive sputtering

Graded TiAlN layers were deposited by plasma reactive sputtering assisted by electron cyclotron resonance (ECR). For reactive sputtering, dual cathode radio-frequency magnetron targets, Ti and Al, were used. The layers were deposited using various combinations of variables such as power input, bias substrate voltage, and gas feed composition. The deposition process was monitored by optical emission spectroscopy (OES). The OES results indicate that microwave excitation added to radio-frequency plasma has contrasting effects on the Ti and Al concentration in the gas phase, enhancing titanium and quenching aluminum species reaching the deposited substrate. Thus, by the regulation of the ECR power and the ratio of nitrogen to argon flow, formation of graded layers is possible. The layers formed in this way were characterized with regard to structure, composition, and mechanical properties using an x-ray diffractometer, an Auger electron spectroscopy microscope, and a Vickers microhardness and scratch tester (for adhesion). It was observed that layers deposited at a low ECR power (⩽100 W) yielded an oriented (111) crystalline structure with good adhesion (failure load >70 N). These layers displayed a higher microhardness (∼25 GPa) at substrate bias voltage (∼50 VDC) than that of a grounded substrate (10–15 GPa). However, layers deposited at an ECR power higher than 100 W showed a random or amorphous structure with an intermediate adhesion range (failure load of 30–50 N). The relationship between the processing parameters, the structure, and the properties of the layers formed are presented and discussed.

Optical emission spectroscopy as a tool for designing and controlling the deposition of graded TiAlN layers by ECR-assisted reactive RF sputtering

Abstract Graded TiAlN layers were deposited by plasma reactive sputtering assisted by electron cyclotron resonance (ECR). For reactive sputtering, dual cathode radio-frequency (RF) magnetron targets, Ti and Al, were used. The deposition process was monitored by optical emission spectroscopy (OES). The OES results indicate that microwave excitation added to RF plasma has contrasting effects on Ti and Al concentration in the gas phase, enhancing titanium and quenching aluminium species reaching the deposited substrate. Thus, by the regulation of the ECR power and the ratio of the nitrogen flow to the nitrogen plus argon flow, the formation of graded layers is allowed. This approach was found to be appropriate for controlling and tailoring the interface between a metallic substrate and a hard coating. The layers were deposited on (100) oriented silicon and M2 steel tools using various combinations of variables, such as power input, bias substrate voltage and gas feed composition. The layers were characterized with regard to structure and composition using X-ray diffractometers and Auger electron spectroscopy. Layers deposited on grounded silicon at a low ECR power (≤100 W) were found to have a (111) oriented crystalline structure; the crystallographic orientation is affected by the bias voltage and substrate composition. Layers deposited at an ECR power >100 W had a random or amorphous structure. The relationship between the OES analyses of the plasma layer and the processing parameters, the structure and the composition of the layers formed are presented and discussed.

Characteristics of silicon nitride deposited by plasma-enhanced chemical vapor deposition using a dual frequency radio-frequency source

We have studied the effect of plasma excitation frequency on the properties of plasma-enhanced chemical vapor deposition silicon nitride films. The use of two radio-frequency sources, one at 270 kHz and the other at 13.56 MHz, enabled us to vary film properties such as stress by altering the amount of power supplied by each source. The low-frequency excitation was seen to favor the formation of N—H bonds in the deposited film. The relative amounts of N—H and Si—H bonds in the film were found to determine many of the film properties such as stress, conduction and wet etch rate.

Control of ion energy and flux in a dual radio frequency excitation magnetron sputtering discharge

Mean ion energy and ion flux have been investigated in a low-pressure, radio frequency (rf) magnetron discharge (dual rf excitation plasma) as function of substrate rf power and frequency, plasma excitation rf power and process pressure. Electrical and Langmuir probe measurements were used to determine the self-bias of the electrodes and time-averaged plasma parameter, respectively. The energy and flux of ions bombarding the substrate surface can be accurately controlled in the low-energy range (<50 eV) without affecting the state of the discharge by applying an appropriate rf bias power and frequency to the substrate electrode. A simplified sheath model is used to verify the experimentally obtained linear relationship between substrate rf power and self-bias of the electrode. The ion flux to both electrodes as well as the mean ion energy to the plasma excitation electrode are controlled by the plasma excitation rf power. The increase in process pressure from 5 to 40 mTorr reduces the ion flux to the substrate without changing the mean ion energy. The plasma parameters and their spatial distribution are strongly affected by the magnetic field, which also determines the ion energy flux distribution on the substrate surface.

Atmosphere of Venus as Studied with the Mariner 5 Dual Radio‐Frequency Occultation Experiment

The amplitudes and differential Doppler of two radio signals transmitted to Mariner 5 as it was occulted by Venus are utilized to derive the dayside and nightside ionization distributions in the upper atmosphere, and the temperature and pressure profiles of the lower atmosphere. Both sides of Venus have ionization peaks near the 140‐km altitude level; the daytime peak is 30 times greater in electron number density. The nightside ionosphere extended up to an altitude of at least 1000 km, and the dayside ionization terminated in a plasmapause near an altitude of 500 km. There may be a wake of planetary ionization extending a great distance in the antisolar direction. The neutral atmosphere was probed down to within 35 km of the planetary surface. Differences in the temperature and pressure profiles for the nightside and dayside, and apparent kilometer‐size structure in the atmosphere, are discussed.