Energy-resolved Mass Spectrometer Research Articles

Iron Oxide and Iron Sulfide Films Prepared for Dye-Sensitized Solar Cells.

In this paper, the prospects of iron oxide films and their sulfidation for dye-sensitized solar cells (DSSC) are reviewed. Iron oxide thin films were prepared by hollow cathode plasma jet (HCPJ) sputtering, with an admixture of oxygen in the argon working gas and with an iron nozzle as the sputtering target. The discharge was powered by a constant current source in continuous mode and by a constant voltage source in pulsed mode. Plasma composition was measured by an energy-resolved mass spectrometer. Moreover, secondary electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), absorption and Raman spectra of the films are presented. Strong correlation between the color of the iron oxide film and its phase composition was revealed. Iron oxide films were sulfided at 350 °C. A relatively clean pyrite phase was obtained from the magnetite, while the marcasite with admixture of the pyrite phase was obtained from the hematite. Low influence of sulfidation on the films’ microstructure was demonstrated.

Beryllium thin films deposited by thermionic vacuum arc for nuclear applications

The aim of this paper is to investigate the influence of the thermionic vacuum arc (TVA) operation parameters (arc current, arc voltage and thermo-emission filament current) on the Be ion energy and plasma ionization degree, as well as on the topological, structural and mechanical properties of Be thin films.For this purpose, nanocrystalline Be thin films, with thickness of approximately 1 μm, were deposited by TVA on not intentionally heated silicon and stainless steel substrates by varying the arc voltage from 0.8 to 2.0 kV. Topological, structural and mechanical (hardness, Young's modulus, adhesion critical loads, and friction coefficient) properties of Be thin films were investigated using atomic force microscopy (AFM), X-ray diffraction (XRD), scanning electron microscopy (SEM), Rutherford backscattering spectrometry (RBS), nanoindentation and scratch tests.The mechanical behaviour and structural changes are discussed based on TVA plasma diagnostics results. Be ion energy and plasma ionization degree were measured using cold and emissive probes, energy-resolved mass spectrometer and a quartz crystal microbalance.The preferential crystallographic orientation, morphology and packing density are sensitive to the selected processing parameters which, in turn, control, over a wide range, the plasma ionization degree and Be ion energy. The film deposited using an arc voltage value of 1.5 kV exhibits dense structure with low lattice defect density, high hardness, low coefficient of friction, good wear-resistance, fracture toughness and adhesion to the substrate.

Study of low temperature chlorine atom initiated oxidation of methyl and ethyl butyrate using synchrotron photoionization TOF-mass spectrometry.

The initial oxidation products of methyl butyrate (MB) and ethyl butyrate (EB) are studied using a time- and energy-resolved photoionization mass spectrometer. Reactions are initiated with Cl˙ radicals in an excess of oxygen at a temperature of 550 K and a pressure of 6 Torr. Ethyl crotonate is the sole isomeric product that is observed from concerted HO2-elimination from initial alkylperoxy radicals formed in the oxidation of EB. Analysis of the potential energy surface of each possible alkylperoxy radical shows that the CH3CH(OO)CH2C([double bond, length as m-dash]O)OCH2CH3 (RγO2) and CH3CH2CH(OO)C([double bond, length as m-dash]O)OCH2CH3 (RβO2) radicals are the isomers that could undergo this concerted HO2-elimination. Two lower-mass products (formaldehyde and acetaldehyde) are observed in both methyl and ethyl butyrate reactions. Secondary reactions of alkylperoxy radicals with HO2 radicals can decompose into the aforementioned products and smaller radicals. These pathways are the likely explanation for the formation of formaldehyde and acetaldehyde.

The Radial Distribution of Ions and Electrons in RF Inductively Coupled H2/T2B Plasmas

A glow discharge polymer (GDP) was fabricated using trans-2-butene (T2B) and hydrogen (H2) via a plasma-enhanced chemical vapor deposition (PECVD) system. The uniformity of the GDP films was significantly affected by the radial distribution of the H2/T2B plasma parameters. The plasma properties while discharging by a multi-carbon gas source of mixed H2/T2B were investigated during the GDP deposition process. The main positive ions and ion energy distributions in inductively coupled H2/T2B plasmas were analyzed by energy-resolved mass spectrometer (MS), and the electron density and the effective electron temperature were mainly analyzed using a Langmuir probe. The MS results show that the main positive ions in the plasmas are \({\text{C}}_{ 2} {\text{H}}_{ 4}^{ + }\), \({\text{C}}_{ 2} {\text{H}}_{ 6}^{ + }\), \({\text{C}}_{ 3} {\text{H}}_{ 3}^{ + }\), \({\text{C}}_{ 3} {\text{H}}_{ 6}^{ + }\), \({\text{C}}_{ 3} {\text{H}}_{ 8}^{ + }\), \({\text{C}}_{ 4} {\text{H}}_{ 5}^{ + }\), \({\text{C}}_{ 4} {\text{H}}_{ 1 0}^{ + }\), \({\text{C}}_{ 5} {\text{H}}_{ 5}^{ + }\), and \({\text{C}}_{ 5} {\text{H}}_{ 7}^{ + }\) with mass-to-charge ratios (m/e) of 28, 30, 39, 42, 44, 53, 58, 65, and 67, respectively. For a normalized ion intensity, the relative intensities of saturated CH ions increase with increasing radial distance, while the unsaturated CH ions decrease with increasing radial distance. The ion energy distribution of \({\text{C}}_{ 2} {\text{H}}_{ 6}^{ + }\) (m/e = 30) presents a bimodal structure. Additionally, both the electron density and the effective electron temperature decrease with increasing radial distance.

Investigation of working pressure on the surface roughness controlling technology of glow discharge polymer films based on the diagnosed plasma

The effects of working pressure on the component, surface morphology, surface roughness, and deposition rate of glow discharge polymer (GDP) films by a trans-2-butene/hydrogen gas mixture were investigated based on plasma characteristics diagnosis. The composition and ion energy distributions of a multi-carbon (C4H8/H2) plasma mixture at different working pressures were diagnosed by an energy-resolved mass spectrometer (MS) during the GDP film deposition process. The Fourier transform infrared spectroscopy (FT–IR), field emission scanning electron microscope (SEM) and white-light interferometer (WLI) results were obtained to investigate the structure, morphology and roughness characterization of the deposited films, respectively. It was found that the degree of ionization of the C4H8/H2 plasma reduces with an increase in the working pressure. At a low working pressure, the C–H fragments exhibited small-mass and high ion energy in plasma. In this case, the film had a low CH3/CH2 ratio, and displayed a smooth surface without any holes, cracks or asperities. While the working pressure increased to 15 Pa, the largest number of large-mass fragments led to the deposition rate reaching a maximum of 2.11 μm h−1, and to hole defects on the film surface. However, continuing to increase the working pressure, the film surface became smooth again, and the interface between clusters became inconspicuous without etching pits.

Influence of HPPMS pulse parameters on the reactive gas N2 and on the properties of (Cr, Al)N coatings

Abstract In plastics industry molding tools are subjected to adhesive and abrasive wear as well as to corrosion. In this regard, (Cr, Al)N hard coatings deposited by physical vapor deposition (PVD) have a high potential to be used as protective coatings. The high power pulse magnetron sputtering (HPPMS) technology offers several advantages with regard to the deposition of hard coatings. Variation of the pulse length has a significant influence on the current–voltage-characteristic (I–U) of the cathodes, the chemical composition and the mechanical properties of the (Cr, Al)N coatings as well as on the reaction layer on the coating surface, which affect the interactions between the coated tool and the plastic melt in terms of adhesion. The present work deals with investigations of the influence of HPPMS pulse length at constant pulse frequency on the reactive gas N 2 in the deposition process and on the adhesion behavior of (Cr, Al)N coatings towards plastic melt. For this reason, the HPPMS plasma was analyzed at the substrate side via a retarding field energy analyzer (RFEA) and energy resolved mass spectrometer (MS). The RFEA was used to determine ion current densities at different HPPMS pulse length of t on = 40 μs, 80 μs and 200 μs. The MS was used to analyze the intensities of Cr + , Al + , N + and N 2 + in the HPPMS plasma. The results revealed that a decrease of the pulse length leads to an increased ion current density as well as an increased dissociation of molecular nitrogen, which has a significant influence on the chemical composition of the coating. Furthermore the adhesion behavior between coating and plastic melt is influenced by the pulse parameters via the changed chemical composition of the reaction layer on the coating surface. Based on these results, coatings with desirable mechanical properties with regard to wear resistance in plastics processing and a passive layer designed to ensure low adhesion of the plastic melt shall be developed.

Analysis of ion energy distribution at the substrate during a HPPMS (Cr,Al)N process using retarding field energy analyzer and energy resolved mass spectrometer

The ion energy is known to have a strong influence on the properties of coatings deposited by physical vapor deposition (PVD). Therefore, the ion energy distribution (IEDF) especially measured at the substrate side is of great interest for understanding the coating growth. In PVD coating processes the ion energy at the substrate can be adjusted by applying a negative voltage (bias) to the substrate table. In the present work, mass integrated measurements of the IEDF were carried out during a high power pulsed magnetron sputtering (HPPMS) (Cr,Al)N process using a Cr target with 20 plugs of Al within an industrial scale PVD coating unit. The HPPMS cathode was operated with different average powers (1kW, 3kW and 5kW) and pulse lengths (ton) of 40μs, 80μs and 200μs at constant frequency of 500Hz. In a first step, measurements of the IEDF using retarding field energy analyzer (RFEA) were carried out on grounded substrate table and later on using −100V substrate bias. Additionally, measurements of the IEDF were carried out using mass spectrometer (MS) exemplary to compare with the results from RFEA. By comparing the measured IEDFs some limitations of these two different measurement methods were found. The MS underestimates that the amount of high energetic ions and the RFEA measurement are influenced by the incidence angle of the ions. Besides those limitations the influence of cathode power and HPPMS pulse length on the IEDF was studied. At high peak power density, i. e. short pulse length and high average cathode power, a much greater high energetic fraction in the IEDF between 10 and 50eV was found in the results of the RFEA compared to MS results presented here. Also the effective mean ion temperature in the high energetic region of the IEDF was found to increase with increasing peak power density. Furthermore, the effective mean ion temperature was not strongly influenced using substrate bias.

Measurement and modeling of neutral, radical, and ion densities in H2-N2-Ar plasmas

A comprehensive experimental investigation of absolute ion and neutral species densities in an inductively coupled H2-N2-Ar plasma was carried out. Additionally, the radical and ion densities were calculated using a zero-dimensional rate equation model. The H2-N2-Ar plasma was studied at a pressure of 1.5 Pa and an rf power of 200 W. The N2 partial pressure fraction was varied between fN2=0% and 56% by a simultaneous reduction of the H2 partial pressure fraction. The Ar partial pressure fraction was held constant at about 1%. NH3 was found to be produced almost exclusively on the surfaces of the chamber wall. NH3 contributes up to 12% to the background gas. To calculate the radical densities with the rate equation model, it is necessary to know the corresponding wall loss times twrad of the radicals. twrad was determined by the temporal decay of radical densities in the afterglow with ionization threshold mass spectrometry during pulsed operation and based on these experimental data the absolute densities of the radical species were calculated and compared to measurement results. Ion densities were determined using a plasma monitor (mass and energy resolved mass spectrometer). H3+ is the dominant ion in the range of 0.0≤fN2<3.4%. For 3.4<fN2<40%, NH3+ and NH4+ are the most abundant ions and agree with each other within the experimental uncertainty. For fN2=56%, N2H+ is the dominant ion, while NH3+ and NH4+ have only a slightly lower density. Ion species with densities in the range between 0.5% and 10% of ni,tot are H2+, ArH+, and NH2+. Ion species with densities less than 0.5% of ni,tot are H+, Ar+, N+, and NH+. Our model describes the measured ion densities of the H2-N2-Ar plasma reasonably well. The ion chemistry, i.e., the production and loss processes of the ions and radicals, is discussed in detail. The main features, i.e., the qualitative abundance of the ion species and the ion density dependence on the N2 partial pressure fraction, are well reproduced by the model.

Investigating the plasma parameters of an Ar/O2 discharge during the sputtering of Al targets in an inverted cylindrical magnetron

The plasma parameters and reaction kinetics in an inverted cylindrical magnetron chamber have been studied with an energy resolved mass spectrometer during the sputtering of aluminum targets in an Ar/O2 discharge. Mixtures of argon and oxygen were studied as a function of oxygen percentage (0%–90%) in the discharge. The plasma was powered at 4 kW and 40 kHz at a process pressure of 5 mTorr. Al+, Al, AlO, AlO+, O2+, O+, Al2O+, and Ar+ were among the species detected in the discharge. The deposition rate of the deposited thin film decreased with increasing oxygen percentage in the discharge and results indicated that the pure gamma-alumina was obtained when the percentage of oxygen was approximately 70%. The linear plot of energy distributions of the positively charged film forming species changed from a single peak to a bimodal distribution as the percentage of oxygen exceeds 65%. In a log plot, however, the distributions showed multiple peaks ranging from 2 eV to 78 eV. Fluctuations of about 1 eV in peak energies were observed.

Controlling the electron energy distribution function of electron beam generated plasmas with molecular gas concentration: I. Experimental results

This paper, the first in a series of two, presents experimental results demonstrating the control of electron and ion energy distribution functions in electron beam generated processing plasmas by adding trace concentrations of N2 to an Ar background. Measurements of the electron energy distribution function, f0(E), are performed using a Langmuir probe while measurements of the Ar ion energy distribution function are performed using an energy-resolved mass spectrometer. The experimental results agree with modeling results, described in part II of this work, which indicate that inelastic electron collisions with nitrogen molecules provide an energy sink that can be exploited to control the electron energy distribution function.

Negative-ion surface production in hydrogen plasmas: modeling of negative-ion energy distribution functions and comparison with experiments

A negatively biased graphite sample (highly oriented pyrolitic graphite) was placed in a H2 low-pressure plasma. The negative ions were produced on the graphite surface upon positive-ion bombardment. Surface-produced H− negative-ion distribution functions (NIDFs) were measured by means of an energy-resolved mass spectrometer. The shapes of the recorded NIDFs depend not only on the surface production mechanisms but also on the negative-ion trajectories in the plasma and their collection probability by the mass spectrometer. In order to gain an insight into the surface production mechanisms, NIDFs were computed using Stopping and Range of Ions in Matter simulations and calculations of the ion transmission function between the sample and the mass spectrometer detector. The calculations were based on 3D modeling of the sheath potential in the extraction region and 3D modeling of ion transport inside the mass spectrometer. The excellent agreement between experiments and computations led to a better understanding of the experimental NIDFs. The method developed in this work to study H-surface production on graphite can be generalized to any other negative ions and/or surface material.

Mass spectrometric study of discharges produced by a large-area dual-frequency–dual-antenna inductively coupled plasma source

An energy-resolved quadrupole mass spectrometer is used to investigate the time-averaged ion energy distribution (IED) of positive ionic species in an Ar/CF4 (90%/10%) discharge produced by dual-frequency–dual-antenna, next-generation large-area inductively coupled plasma source. The operating pressure is 10 mTorr. Two radio frequencies of 2 MHz (low frequency) and 13.56 MHz (high frequency) are used to initiate and sustain the discharge. The orifice of the mass spectrometer was 100 µm in diameter and placed at 30 mm below the ICP source and 20 mm outside the discharge volume.It is observed that both of the frequencies have significant effect on IEDs of all prominent discharge species. The evolution of IEDs with power shows that the discharge undergoes a mode transition (E to H) as the applied power is increased. At a fixed value of P13.56 MHz (250 and 500 W), the energy spread and the energy separation between two peaks of IEDs increase illustrating enhanced E-mode. Above P13.56 MHz = 500 W, the IEDs show opposite trends, i.e. decreasing energy spread and energy separation between two peaks, showing the strengthening of H-mode. Increasing P13.56 MHz at a fixed value of P2 MHz has similar effects. A comparison of IEDs sampled at a fixed total power (P13.56 MHz + P2 MHz) demonstrates that an IED can be tailored by changing the power ratio (P13.56 MHz/P2 MHz).

Investigating the role of hydrogen in silicon deposition using an energy-resolved mass spectrometer and a Langmuir probe in an Ar/H2 radio frequency magnetron discharge

The plasma parameters and ion energy distributions (IED) of the dominant species in an Ar-H2 discharge are investigated with an energy resolved mass spectrometer and a Langmuir probe. The plasmas are generated in a conventional magnetron chamber powered at 150 W, 13.56 MHz at hydrogen flow rates ranging from 0 to 25 sccm with a fixed argon gas flow rate of 15 sccm. Various Hn+, SiHn+, SiHn fragments (with n = 1, 2, 3) together with Ar+ and ArH+ species are detected in the discharge. The most important species for the film deposition is SiHn (with n = 0, 1, 2). H fragments affect the hydrogen content in the material. The flux of Ar+ decreases and the flux of ArH+ increases when the hydrogen flow rate is increased; however, both fluxes saturate at hydrogen flow rates above 15 sccm. Electron density, ne, electron energy, Te, and ion density, ni, are estimated from the Langmuir probe data. Te is below 1.2 eV at hydrogen flow rates below 8 sccm, and about 2 eV at flow rates above 8 sccm. ne and ni decrease with increased hydrogen flow but the ratio of ni to ne increases. The formation of H+ ions with energies above 36 eV and electrons with energies greater than 2 eV contributes to the decrease in hydrogen content at hydrogen flow rates above 8 sccm. Analysis of the IEDs indicates an inter-dependence of the species and their contribution to the thin film growth and properties.

High rate PECVD of a-C:H coatings in a hollow cathode arc plasma

Amorphous carbon films deposited by plasma-based processes are of increasing importance for tribologi-cal applications, e. g. as protective coatings on components or in order to reduce their friction. However, most plasma-activated CVD and PVD techniques suffer from their poor deposition rate and low economic efficiency. At Fraunhofer FEP, a hollow cathode-based plasma source has been established as a versatile, reliable, and highly efficient tool for plasma pretreatment, plasma-enhanced PVD processes, and reactive gas activation in large volumes. As a further application field, this plasma source has been evaluated for PECVD of amorphous hydrogenated carbon films (a-C:H). Acetylene has been introduced into the hollow cathode plasma as a precursor gas. The plasma composi-tion has been characterized by an energy-resolved ion mass spectrometer. Intense ionization, dissociation, and polymerization effects have been observed, which strongly increase when the argon gas flow rate through the hollow cathode tube is reduced. Moreover, the ion energy distributions show high energy tails up to 100 eV in dependence of the spatial distribution of ion generation. a-C:H films have been deposited on stainless steel and silicon substrates with growth rates up to 1000 nm/min. Nanoindentation measurement of the a-C:H coatings reveal hardness up to 18.2 GPa. In this paper, film properties and compositions will be discussed and related to the corresponding plasma condi-tions obtained by energy-resolved ion mass spectrometry.

The evolution of the IEDFs in a low-pressure HiPIMS discharge

Using an energy-resolved mass spectrometer the evolution of the ion energy distribution function (IEDF) in a high-power impulse magnetron sputtering (HiPIMS) plasma has been measured at low operating pressures. The plasma was maintained using a low-power DC power supply as a pre-ionizer in conjunction with a conventional HiPIMS power supply, allowing reduced times between the initiation of the HiPIMS pulse and plasma ignition. As a result, a stable HiPIMS discharge can be operated at the working pressure down to 86mPa with a typical pulse width, repetition rate and peak power density of 100μs, 100Hz and 450Wcm−2, respectively. Time-averaged IEDF measurements at 10cm from a carbon target surface showed two distinct energy peaks one at low energy (~0eV) and the other at high energy (~10eV) for the detected species Ar+ and C+. The origin of these two peaks can be revealed using a time-resolved acquisition technique. It was found that the high energy peak (corresponding with an effective stopping voltage of 15V) was created during the on-time phase of HiPIMS pulse while the low energy peak dominated the IEDF during the off-time. Increase of the operating pressure to 750mPa results in the depletion of intensity and energy of the energetic peak. At the low pressure condition, with a mean-free-path comparable with the mass spectrometer orifice-target distance, energetic ions are transported ballistically to the instrument orifice. This suggests that forming well-structured films may be achieved in the condition of the collision-free operation.

Plasma characterization and technological application of a hollow cathode plasma source with an axial magnetic field

An efficient plasma source has been established by arranging a hot hollow cathode electron emitter in a strong axial magnetic field, allowing for a reduction of working gas flow by one order of magnitude without loss of discharge stability. Moreover, with the reduction of gas flow not only an increase of the discharge impedance was observed, but also a multiplication of ion current density together with a highly expanded volume of the plasma plume. By means of spatially resolved Langmuir probe measurements, combined with the usage of an energy-resolved mass-spectrometer, plasma density profiles and energy distribution functions of electrons and ions have been measured. Generally, with an increase of the magnetic field and with the reduction of the working gas flow ion energy distribution functions shift from mean values of a few eV to 10 eV and more, while charge carrier densities increase from 10 9 cm − 3 to more than 10 12 cm − 3 . A strongly increased ability to dissociate and ionize reactive gases was observed. Two promising applications related to the coating of tools and components are discussed: the sputter etching with argon ions and the reactive pulse magnetron sputter deposition of wear-resistant chromium nitride layers. Whereas the first mentioned process provides pre-heating and etching rates higher than all actually used in tool coating industry, the second one offers advantages for film growth kinetics leading to significant improvements in composition, structure, surface morphology, and hardness of the deposited layers.

Experimental study and modeling of the electron-attracting sheath: The influence of secondary electron emission

A copper sample facing an energy-resolved mass spectrometer is biased positively beyond plasma potential in low-pressure argon plasma. Some ions are created in the sheath by electrons extracted from plasma and accelerated toward the mass spectrometer where they are detected according to their energy. Ion energy is related to local electrical sheath potential at which the ion has been created. Therefore, the Ion Distribution Function (IDF) allows us to probe in a nonperturbative way electron-attracting sheath potential. We observe a strong decrease of ion signal a few volts before sample bias. We attribute this effect to the presence of secondary electrons shielding positive sample potential. Potential profile and IDFs are computed using a model including secondary emission. The fit of IDFs provides an estimation of secondary emission yield and secondary electron temperature.

Cold-cathode Penning discharge-based ionizer for detection of hyperthermal neutral beams

Plasmas produced in a cold-cathode Penning discharge have been studied for possible use as an active ionizing medium in commercial quadrupole mass/energy analyzers for detection of low-energy neutral beams. Two distinct Penning discharge modes have been examined: (1) high-pressure (HP) mode and (2) high magnetic field (HMF) mode. It is shown that the ionization efficiency in the HP mode is independent of the length of ionization region; however, somewhat high working pressures (p>10(-4) Torr) and large discharge currents limit the practical use of this mode. This is not the case in the HMF mode, which appears at lower pressures, with an effective ionization region length of the order of electron cyclotron radius. The design and operation of a compact (5x4x4 cm(3)), low-maintenance ionizer based on a Penning cell with permanent magnets is described. The ability to ionize 40 eV neutral-argon beams with subsequent detection in a Hiden EQP energy-resolved mass spectrometer is shown. The ionization efficiency of the ionizer was found to be as high as 10(-3). Unlike conventional electron impact ionizers, the Penning discharge configuration allows to eliminate the thermal background component in the detected signal. The ionizer has potential application for the detection of hyperthermal neutral beams of various species.

Time-resolved mass and energy spectral investigation of a pulsed polymerising plasma struck in acrylic acid

This paper details an electrical diagnostic study of the discharge used in the pulsed plasma polymerisation of acrylic acid. The capacitively coupled RF discharge was operated at a frequency of 1 kHz and a pressure of 1.3 Pa. Using a retractable deposition-protected Langmuir probe the time-resolved electron temperature, density and plasma potential in the bulk were obtained. The time-resolved ion energy distribution functions (IEDFs) relative to ground potential for a selection of masses ( m/ z = 19, 55, 73) and the mass spectra (2–100 amu) have been measured by the energy-resolved mass spectrometer using an improved double gating technique. In both the “on” and “off” times of the pulse, the IEDFs for the heavier mass ions are characterised by a single peak ( E p – hereafter – the energy which corresponds with the peak intensity), the position and width of which are determined by the time-dependent plasma potential V p and its distribution across the plasma to the spectrometer, while a weakly bimodal ion energy distribution is present in the IEDF for m/ z = 19 in the “on” time. In the steady “on” time, the relative ion flux (detector count rate) of each species and the energy corresponding to the peak intensity in the IEDFs are constant, the latter ( E p ∼ 47 eV) correlating very well to the probe measured plasma potential. At pulse initiation, V p rises to values > 90 V, however, these energies are not detected in IEDF with our time resolution of 10 μs. In the “off” time, this energy falls with a two-fold decay time, initially sharply to ∼ 23 eV (at the first measured point which was made 1 μs after beginning of the “off” period) and then slowly in the next 150 μs to ∼ 17–18 eV closer to the end of the cycle. The elevation of the E p well above ground is in contrast to that usually observed in pulsed Ar discharges (∼ 10 V higher), due to in this case, charging of the acrylic acid deposited materials on the walls. The time-history of the integrated area under the IEDFs reveals that after the initiation of the “on” time the concentration N of lighter species rises more quickly than the heavier ones. In the “off” time, however, although N 19 becomes negligible after 50 μs, N 73 decreases more quickly than N 55 which is still non-zero at 150 μs. The time resolved mass-spectral reveal the general mass dependency in the concentration rise and fall times of the detected species.

Characterization of an Ar/O 2 magnetron sputtering plasma using a Langmuir probe and an energy resolved mass spectrometer

An argon plasma with a small amount of oxygen in a radio-frequency magnetron sputtering system has been studied experimentally. A Langmuir probe has been used to measure the ion density, electron temperature and plasma potential in the plasma, whereas an energy-resolved mass spectrometer has been used to investigate the ions flowing towards the growing film. It has been found that the argon ion density decreases when the oxygen gas is added to the plasma above a certain flow. A discussion on which process is responsible for this effect is presented.