Voltage Modulation Technique Research Articles

Emission Characteristics of Cu in Dc Voltage Modulation Applied Glow Discharge Optical Emission Spectrometry

In order to obtain the depth profile of a thin film, we investigated the emission characteristics of a voltage modulation glow discharge to optimize the modulation parameters (modulation voltage, offset voltage, and modulation frequency). In this study, a phase-sensitive detection method with a lock-in amplifier to the modulation technique led to a higher sensitivity and a larger signal-to-noise ratio in the emission analysis compared to the normal dc amplification method. Upon increasing the maximum voltage, the emission intensity of the Cu atomic line (CuI 239.34 nm) increased linearly at a modulation voltage of 400 V and an offset voltage of 300 V. On the other hand, the emission intensity was gradually reduced when a modulation frequency increased. It is advantageous for surface analysis that the voltage modulation technique gives a lower sputtering rate rather than the conventional dc discharge.

Precise determination of manganese in steel by dc glow discharge optical emission spectrometry associated with voltage modulation technique

A voltage modulation technique was applied for the precise and accurate determination of manganese in steels in dc glow discharge optical emission spectrometry. Emission signals from the glow discharge plasma are modulated by a cyclic variation of the discharge voltage so that only the desired signals can be detected at very low noise levels by using a lock-in amplifier. Mn determination in low-alloyed steels was performed to estimate the repeatability of the analytical result. For each measurement, the relative standard deviation (R.S.D.) of the intensities of the Mn I 403.08-nm line was ca 0.1% when a steel sample containing 0.329 mass% Mn was employed. Averaging all analytical values, which are obtained in various discharge conditions, yields statistical information on the precision and accuracy of the analytical values obtained. The relative error from the recommended value is calculated to be 0.5%. The R.S.D. over the analytical values is 1.5%, representing the overall analytical performance of this technique.

Improvement in Aspect Ratio of P-GaAs Oxide Fabricated by Atomic Force Microscope (AFM)-Based Nanolithography Using Pulsed Voltage

An atomic force microscope (AFM)-based surface nanooxidation method was used to fabricate nanoscale p-GaAs oxide. We were able to realize an increase in the aspect ratio by a factor of 2 for oxide dots using a voltage modulation technique. The aspect ratios of oxide dots reached the maximum at a frequency of about 1000 Hz. Moreover, from a duty ratio dependence of aspect ratios of oxide dots, it was considered that optimization of an anodizing time per cycle of a pulsed voltage was necessary. The oxide could be etched by water. By adjusting both oxidation and etching process conditions, a groove with a 40 nm width and 6 nm depth was successfully fabricated. From these results, it was clear that the aspect ratio of p-GaAs oxide could be improved using a pulsed voltage, and optimization of process conditions, particularly the frequency and duty ratio of a pulsed voltage, was necessary to obtain p-GaAs oxide with a high aspect ratio.

Resonance modes of voltage-modulated scanning force microscopy

Mechanical resonance modes of the scanning force microscope (SFM) cantilever in contact conditions provide contrast enhancement in the imaging of surface charges when using voltage modulation techniques tuned to such resonances. Extensions of the method were made as regards the lateral (twisting) and frontal (buckling) modes of the cantilever, as well as the enhanced second harmonic detection of voltage-modulated response at resonance and near-resonance detection in the SFM tapping mode. As an example of application, vibration spectra and images taken on a triglycine sulfate (TGS) single crystal are discussed.

Application of Dc Voltage Modulation Technique to the Determination of Phosphorous and Sulfur in Steel Samples in Glow Discharge Optical Emission Spectrometry.

An applied voltage modulation technique was applied to the high-sensitivity determination of phosphorous and sulfur in steel samples in glow discharge optical emission spectrometry. Emission signals from the glow discharge plasma were modulated by a cyclic variation of the discharge voltage so that only the desired signals could be detected without any noises with a DSP lock-in amplifier. The relative lock-in signals from sputtered species were enhanced compared to those of gas species. The P I 177.49-nm, and the S I 180.73-nm and S I 182.72-nm lines, were selected as the analytical lines. The limit of determination for the P I 177.49-nm line was estimated to be 1.0×10-3mass% P.

Analytical performance of a radiofrequency-powered glow discharge excitation source associated with bias voltage modulation

A 13.56-MHz Grimm-type glow discharge plasma on which external d.c. voltages are superimposed is investigated for the application to optical emission spectrometry. With a voltage modulation technique associated with phase-sensitive detection, the emission intensities can be measured at very low noise levels, enabling the detection power to be improved. The experimental parameters: d.c. voltage, modulation frequency, and Ar pressure, are investigated for obtaining the optimum conditions. It is possible to obtain a detection limit (Cu I 327.40 nm) of 8 × 10–4 wt.% for Cu in Fe-based alloys, while 6.6 × 10–3 wt.% in the case of conventional detection.

Role of space charge in scanned probe oxidation

The growth rate and electrical character of nanostructures produced by scanned probe oxidation are investigated by integrating an in situ electrical force characterization technique, scanning Maxwell-stress microscopy, into the fabrication process. Simultaneous topographical, capacitance, and surface potential data are obtained for oxide features patterned on n- and p-type silicon and titanium thin-film substrates. The electric field established by an applied voltage pulse between the probe tip and substrate depends upon reactant and product ion concentrations associated with the water meniscus at the tip-substrate junction and within the growing oxide film. Space-charge effects are consistent with the rapid decline of high initial growth rates, account for observed doping and voltage-pulse dependencies, and provide a basis for understanding local density variations within oxide features. An obvious method for avoiding the buildup of space charge is to employ voltage modulation and other dynamic pulse-shaping techniques during the oxidation pulse. Voltage modulation leads to a significant enhancement of the growth rate and to improvements in the aspect ratio compared with static voltage pulses.

Unified voltage modulation technique for real-time three-phase power conversion

In this paper, a new voltage modulation technique named "unified pulsewidth modulation (PWM)" is described for high-performance voltage generation in a three-phase voltage-fed inverter. By considering the operation of the inverter, a simple but useful concept named "effective time" can be established and, by fully employing this concept, a new voltage modulation technique is presented with a detailed explanation and actual test results. The results show that various carrier-based PWM schemes can be implemented with reduced computational burden and a seamless change from one modulation scheme to another is possible.

The application of a double voltage modulation technique to a glow discharge source with a supplementary electrode

The Ar spectral lines are suppressed in glow discharge source atomic emission spectroscopy by a double voltage modulation technique with a supplementary electrode. The voltage is modulated between two levels, typically 350 and 700 V. At the lower voltage level mainly the Ar emission occurs where at the higher voltage level both the Ar and the metal atoms sputtered from the sample contribute to the emission. The power supply of the supplementary electrode is switched on when the glow discharge passes from operation at 700 V to 350 V. The intensity of argon gase lines is regulated by the current applied to the supplementary electrode at that period. Therefore, there is no need for electronical amplification and lower voltage adjustment of two operation modes. This modified DVM technique has been applied to the determination of Si and Cu in Al- samples. The suppression of Ar lines is possible, and the elements can be determined without Ar interferences.

Determination of Sign of Surface Charges of Ferroelectric TGS Using Electrostatic Force Microscope Combined with the Voltage Modulation Technique

The sign of surface charges and the surface topography around a domain wall on a cleaved (010) surface of ferroelectric TGS [ (NH2CH2COOH)3·H2SO4] were studied in air at room temperature. Using an electrostatic force microscope (EFM) combined with the voltage modulation technique, we determined the location of the domain wall and the sign of the surface charges around it. At the domain wall, we found a ridge structure with a large peak in the spatial distribution of a feedback signal used to keep the amplitude of the 2ω component of electric force constant. This means that the dielectric constant has a large peak value at the domain wall. Furthermore, in an atomic force microscope (AFM) image in a contact mode, we observed a small step 2–3 Å high at the center of the domain wall.

Background suppression of Ar lines in glow discharge atomic emission spectrometry by a lock-in amplifier and Kalman filter deconvolution

The Ar spectral lines are suppressed in Grimm-type glow discharge lamp atomic emission spectrometry (GDL-AES) by a double voltage modulation technique. The GDL is modulated between two voltage levels, typically 400 and 700 V. At the lower voltage level mainly Ar emission contributes whereas at the higher voltage level both Ar and atoms sputtered from the cathode contribute to the emission. The Ar emission spectrum at the lower voltage level is multiplied by a constant factor to scale it up to the same level of Ar emission found at the higher voltage level. This signal is then subtracted from the signal obtained at the higher voltage level by a lock-in amplifier to obtain the net analyte signal. The digital Kalman filter technique is also applied to background suppression; it is known to be the optimum filter for deconvolution of mixtures in noisy environments. The detection limits are found to be improved by nearly a factor of 10 with both double voltage modulation and Kalman filter techniques.

A.c. corrosion of nickel in sulphate solutions

The corrosion of nickel under the influence of alternating current (a.c.) in pH 1–7 Na2SO4 solutions has been investigated with an alternating voltage (a.v.) modulation technique. The anodic polarization curves and pitting behaviour of nickel were examined with the superimposition of sinusoidal, square, and triangular a.v. over a range of a.v. magnitudes of 0–5000m V r.m.s., and a.v. frequencies of 20–5000 Hz. It was found that a.v. reduced the passive d.c. potential regime by increasing the critical current density prior to passivation and by shifting the active-passive transitional potential toward the positive direction. In acidic sulphate solutions, a.v. increased the current density in the passive regime in a way similar to the addition of chloride ions. A.v. destroyed the passivity and enhanced the pitting corrosion of nickel at both the passive and transpassive d.c. potentials. The passivity of nickel was destroyed regardless of the a.v. waveforms. Triangular a.v. caused the severest destruction of passivity; this was followed by sinusoidal and square wave a.v.

Polarization of Aluminum during AC Corrosion in Sulfate Solutions

An experimental study has been made of the effect of alternating voltage on the corrosion of aluminum in aqueous solutions of (i) , (ii) , (iii) , and (iv) containing 0–5010 ppm Cl− ions. The polarization curves were measured with an alternating voltage (AV) modulation technique using sinusoidal waves, and the pitting behavior of aluminum was examined with constant potentiostatic coulometry and SEM photomicrography. The measurements were made over a range of AV magnitudes from 0 to 1500 mV rms, and AV frequencies from 20 to 600 Hz. The severity of AV effect was found to depend on the presence of an surface film. In alkaline solutions and in the sulfate solution containing a large amount of chloride ions, where no oxide was present on aluminum surface, AV exerted little or no effect on the anodic dissolution reaction of aluminum. In acidic and neutral sulfate solutions, AV enhanced the formation of oxide film at high anodic dc potentials as well as the dissolution of aluminum through the pores of the oxide film. Application of AV did not increase the pitting corrosion of aluminum in sulfate solutions.

The a.c. corrosion of stainless steel—II. The breakdown of passivity of ss304 in neutral aqueous solutions

The effect of alternating current on the corrosion of Type 304 Stainless Steel in aqueous solutions of Na 2SO 4, NaNO 3 and NaCl has been investigated with an alternating voltage (AV) modulation technique, using 60 Hz square wave AV. The anodic and cathodic polarization curves were measured for a range of AV from 0 to 1000 mV and the surfaces of specimens after a potentiostatic coulometry experiment were examined under a scanning electron microscope. It was found that AV shifted the corrosion potential toward the positive direction and the passive-transpassive transitional potential toward the negative direction. AV destroyed the passivity and enhanced the pitting corrosion of the steel in aqueous environments. The behavior was explained with a simple mathematical model. The computer simulated polarization curves for the AV modulation of Type 304 Stainless Steel showed characteristics similar to the experimental curves: good agreement was obtained for the onset of transpassive potentials in the presence of AV.

The a.c. corrosion of stainless steel—II. The polarization of ss304 and ss316 in acid sulfate solutions

An experimental study has been made to examine the effect of alternating current on the corrosion of Types 304 and 316 Stainless Steels in acidic aqueous sulfate solutions. The polarization curves were measured with an alternating voltage (AV) modulation technique and the pitting behavior of the stainless steels was examined with a constant potentiostatic coulometry and SEM photomicrography. The experiments were made with sinusoidal, square and triangular AV over a range of AV frequencies from 60 to 1000 Hz and AV magnitudes from 0 to 1000 mV rms. The results indicate that AV increased the critical current density for passivity and decreased the passive potential regime by shifting the transpassive potential toward the active direction and increasing the current density in the passive regime. The effect was similar to the addition of chloride ions to the corrosion environment. AV enhanced the pitting of the stainless steels at both the passive and transpassive potentials. Passivity was destroyed regardless of the AV waveforms; triangular wave caused the severest destruction, followed by sinusoidal and square waves.

High sensitivity measurement of atomic emission spectra with an applied voltage modulation technique

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTHigh sensitivity measurement of atomic emission spectra with an applied voltage modulation techniqueKazuaki. Wagatsuma and Kichinosuke. HirokawaCite this: Anal. Chem. 1984, 56, 14, 2732–2735Publication Date (Print):December 1, 1984Publication History Published online1 May 2002Published inissue 1 December 1984https://doi.org/10.1021/ac00278a024RIGHTS & PERMISSIONSArticle Views105Altmetric-Citations16LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (477 KB) Get e-Alerts Get e-Alerts

Negative ion forration by attachment of electrons to radicals studied by ion cyclotron resonance spectrometry

It is suggested that some negative ions are formed by attachment of secondary electrons to radicals resulted from positive ion-molecule reactions. The process has been studied using an ion cyclotron resonance cell equipped with venetian-blind type trapping electrodes. A trapping voltage modulation technique was developed to obtain the positive ion signal in the double resonance spectra of negative ion. Formation and solvation of OH − in water vapor have been studied.

The electro-optic coefficients of urea

The two independent electro-optic coefficients of crystalline urea, r63 and r41, are determined experimentally using a voltage modulation technique. The results are compared with theoretical values obtained by direct summation over CNDO/S generated electronic states in a perturbation theory based expression for nonlinear optical coefficients. A further comparison is made with the predicted results of an anharmonic oscillator model for nonlinear optical processes. The results obtained by all three methods, after proper internal field corrections, agree within the limitations of the theoretical calculations and the margins of experimental error.