Some users of our products

Our products are used by many companies, research institutes and academic laboratories. Here are some of our customers.


Citations of our products in customers' publications in peer-reviewed journals

Our products have been used to perform electrical measurements in many experimental research studies dealing with low pressure CCP and ICP, or atmospheric pressure plasma jets. Here is a list of 15 articles citing our products and published  by our customers in peer-reviewed journals.




Excitation of Ar, O2, and SF6/O2 plasma discharges using tailored voltage waveforms: Control of surface ion bombardment energy and determination of dominant electron excitation mode

Guillaume Fischer1, Karim Ouaras2, Etienne Drahi3, Bastien Bruneau2 and Erik V Johnson2

1Institut Photovoltaïque d'Ile-de-France (IPVF), 30 RD128, 91120 Palaiseau, France
2LPICM, CNRS, Ecole polytechnique, Université Paris-Saclay, 91128 Palaiseau, France
3Total SA Renewables, 92069 Paris La Défense Cedex, France



Using Tailored Voltage Waveforms (TVWs) to excite a low pressure, low-temperature plasma discharge, we compare the behavior of three gas mixtures, namely Ar, O2, and SF6O2 mixtures, the last of which is currently used for the plasma-texturing of silicon wafers for photovoltaics. The primary goal of using TVWs is to control the ion bombardment energy at the surface of the wafer, and this control is demonstrated through retarding field energy analyzer (RFEA) measurements. However, the complicated electrical response of the plasma to such waveforms makes the ab-initio prediction of the ion energy difficult, although by using said RFEA measurements, we show that it can be done approximately by using measured electrical data. In addition, we utilize the response of the plasma to mirror-image "sawtooth" waveforms as a predictor of the dominant electron heating mode (α or drift-ambipolar, DA). At equivalent pressures and coupled powers, the Ar and O2 mixtures always display behavior associated with electropositive plasmas (a solely α heating mode). However, with the addition of SF6 to an O2 gas flow, a transition can be observed towards a behavior associated with a more electronegative plasma (i.e. a dominant DA heating mode). This crossover in the dominant heating mode is observed through the relative self-bias voltage for each type of sawtooth waveform, and is therefore a useful predictor of the dominant electron heating mode in low pressure, cold plasma discharges.


Source: Accepted manuscript in PSST, to be published soon (2018)



Influence of the RF electrode cleanliness on plasma characteristics and dust-particle generation in methane dusty plasmas

I. Géraud-Grenier1, W. Desdions1, F. Faubert2, M. Mikikian3, and V. Massereau-Guilbaud1

1 Groupe de Recherches sur l’Energétique des Milieux Ionisés (GREMI), UMR 7344 CNRS/Université d’Orléans, Site de Bourges, 63 avenue de Lattre de Tassigny, 18020 Bourges Cedex, France
2 Institut Universitaire de Technologie (IUT), 63 avenue de Lattre de Tassigny, 18020 Bourges Cedex, France
3 Groupe de Recherches sur l’Energétique des Milieux Ionisés (GREMI), UMR 7344 CNRS/Université d’Orléans, 14 route d’Issoudun, BP 6744, 45067 Orléans Cedex 2, France



The methane decomposition in a planar RF discharge (13.56 MHz) leads both to a dust-particle generation in the plasma bulk and to a coating growth on the electrodes. Growing dust-particles fall onto the grounded electrode when they are too heavy. Thus, at the end of the experiment, the grounded electrode is covered by a coating and by fallen dust-particles. During the dust-particle growth, the negative DC self-bias voltage (VDC) increases because fewer electrons reach the RF electrode, leading to a more resistive plasma and to changes in the plasma chemical composition. In this paper, the cleanliness influence of the RF electrode on the dust-particle growth, on the plasma characteristics and composition is investigated. A cleanliness electrode is an electrode without coating and dust-particles on its surface at the beginning of the experiment.


Source: Géraud-Grenier et al. AIP Conference Proceedings 1925, 020024 (2018)




Powder free PECVD epitaxial silicon by plasma pulsing or increasing the growth temperature

LPICM, CNRS, Ecole Polytechnique, 91128 Palaiseau, France



Crystalline silicon thin films are promising candidates for low cost and flexible photovoltaics. Among various synthesis techniques, epitaxial growth via low temperature plasma-enhanced chemical vapor deposition is an interesting choice because of two low temperature related benefits: low thermal budget and better doping profile control. However, increasing the growth rate is a tricky issue because the agglomeration of clusters required for epitaxy leads to powder formation in the plasma. In this work, we have measured precisely the time evolution of the self-bias voltage in silane/hydrogen plasmas at millisecond time scale, for different values of the direct-current bias voltage applied to the RF electrode and growth temperatures. We demonstrate that the decisive factor to increase the epitaxial growth rate, i.e. the inhibition of the agglomeration of plasma-born clusters, can be obtained by decreasing the plasma OFF time and increasing the growth temperature. The influence of these two parameters on the growth rate and epitaxial film quality is also presented.


Source: Chen et al. 2018 Journal of Physics D: Applied Physics



Experimental benchmark of kinetic simulations of capacitively coupled plasmas in molecular gases

Z Donkó1, A Derzsi1,2, I Korolov1, P Hartmann1, S Brandt2, J Schulze2,3, B Berger2,3,4, M Koepke2, B Bruneau5, E Johnson6, T Lafleur6, J-P Booth6, A R Gibson6,7, D O'Connell7 and T Gans7
1 Wigner Research Centre for Physics, Hungarian Academy of Sciences, 1121 Budapest, Konkoly-Thege Miklós str. 29-33, Hungary
2 Department of Physics, West Virginia University, Morgantown, WV, United States of America
3 Institute for Electrical Engineering, Ruhr-University, Bochum, Germany
4 Electrodynamics and Physical Electronics Group, BTU Cottbus, Germany
5 LPICM-CNRS, Ecole Polytechnique, Palaiseau, France
6 Laboratoire de Physique des Plasmas, CNRS, École Polytechnique, UPMC Univ. Paris 06, Univ. Paris-Sud, Observatoire de Paris, Université Paris-Saclay, Sorbonne Universités, PSL Research University, F-91128 Palaiseau, France
7 York Plasma Institute, Department of Physics, University of York, Heslington, York, United Kingdom



We discuss the origin of uncertainties in the results of numerical simulations of low-temperature plasma sources, focusing on capacitively coupled plasmas. These sources can be operated in various gases/gas mixtures, over a wide domain of excitation frequency, voltage, and gas pressure. At low pressures, the non-equilibrium character of the charged particle transport prevails and particle-based simulations become the primary tools for their numerical description. The particle-in-cell method, complemented with Monte Carlo type description of collision processes, is a well-established approach for this purpose. Codes based on this technique have been developed by several authors/groups, and have been benchmarked with each other in some cases. Such benchmarking demonstrates the correctness of the codes, but the underlying physical model remains unvalidated. This is a key point, as this model should ideally account for all important plasma chemical reactions as well as for the plasma-surface interaction via including specific surface reaction coefficients (electron yields, sticking coefficients, etc). In order to test the models rigorously, comparison with experimental 'benchmark data' is necessary. Examples will be given regarding the studies of electron power absorption modes in O2, and CF4–Ar discharges, as well as on the effect of modifications of the parameters of certain elementary processes on the computed discharge characteristics in O2 capacitively coupled plasmas.


Source: Z Donkó et al 2018 Plasma Phys. Control. Fusion 60 014010




Absolute ozone densities in a radio-frequency driven atmospheric pressure plasma using two-beam UV-LED absorption spectroscopy and numerical simulations

1 York Plasma Institute, Department of Physics, University of York, York YO10 5DD, United Kingdom
2 Experimental Physics II: Application-Oriented Plasma Physics, Ruhr-Universität Bochum, D-44801 Bochum, Germany
3 LPP, CNRS, Ecole Polytechnique, UPMC Univ. Paris 06, Univ. Paris-Sud, Observatoire de Paris, Université Paris-Saclay, Sorbonne Universités, PSL Research University, F-91128 Palaiseau, France
4 Centre for Plasma Physics, Queen's University Belfast, University Road, Belfast BT7 1NN, United Kingdom
5 Current address: KROHNE Innovation GmbH, Ludwig-Krone-Str.5, D-47058 Duisburg, Germany.



The efficient generation of reactive oxygen species (ROS) in cold atmospheric pressure plasma jets (APPJs) is an increasingly important topic, e.g. for the treatment of temperature sensitive biological samples in the field of plasma medicine. A 13.56 MHz radio-frequency (rf) driven APPJ device operated with helium feed gas and small admixtures of oxygen (up to 1%), generating a homogeneous glow-mode plasma at low gas temperatures, was investigated. Absolute densities of ozone, one of the most prominent ROS, were measured across the 11 mm wide discharge channel by means of broadband absorption spectroscopy using the Hartley band centred at λ = 255 nm. A two-beam setup with a reference beam in Mach–Zehnder configuration is employed for improved signal-to-noise ratio allowing high-sensitivity measurements in the investigated single-pass weak-absorbance regime. The results are correlated to gas temperature measurements, deduced from the rotational temperature of the N2 optical emission from introduced air impurities. The observed opposing trends of both quantities as a function of rf power input and oxygen admixture are analysed and explained in terms of a zero-dimensional plasma-chemical kinetics simulation. It is found that the gas temperature as well as the densities of O and O2 influence the absolute O3 densities when the rf power is varied.


Source: A Wijaikhum et al 2017 Plasma Sources Sci. Technol. 26 115004



Spatial Dependence of DNA Damage in Bacteria due to Low-Temperature Plasma Application as Assessed at the Single Cell Level

Angela Privat-Maldonado1,2, Deborah O’Connell2, Emma Welch1, Roddy Vann2, Marjan W. van der Woude1

1 Centre for Immunology and Infection, Department of Biology and Hull York Medical School, University of York, York, U.K

2 York Plasma Institute, Department of Physics, University of York, York, U.K



Low temperature plasmas (LTPs) generate a cocktail of reactive nitrogen and oxygen species (RNOS) with bactericidal activity. The RNOS however are spatially unevenly distributed in the plasma. Here we test the hypothesis that this distribution will affect the mechanisms underpinning plasma bactericidal activity focussing on the level of DNA damage in situ. For the first time, a quantitative, single cell approach was applied to assess the level of DNA damage in bacteria as a function of the radial distance from the centre of the plasma jet. Salmonella enterica on a solid, dry surface was treated with two types of LTP: an atmospheric-pressure dielectric barrier discharge plasma jet (charged and neutral species) and a radio-frequency atmospheric-pressure plasma jet (neutral species). In both cases, there was an inverse correlation between the degree of DNA damage and the radial distance from the centre of the plasma, with the highest DNA damage occurring directly under the plasma. This trend was also observed with Staphylococcus aureus. LTP-generated UV radiation was eliminated as a contributing factor. Thus valuable mechanistic information can be obtained from assays on biological material, which can inform the development of LTP as a complementary or alternative therapy for (topical) bacterial infections.


Source: Privat-Maldonado et al.  Scientific Reports Vol. 6, Article number: 35646 (2016)




Experimental and simulation study of a capacitively coupled oxygen discharge driven by tailored voltage waveforms

, , , and

1 Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, 1121 Budapest, Konkoly Thege Miklós str. 29-33, Hungary

2 Laboratoire de Physique des Plasmas, Ecole Polytechnique-CNRS-Univ Paris-Sud-UPMC, 91128 Palaiseau, France



We report experimental and particle-based kinetic simulation studies of low-pressure capacitively coupled oxygen plasmas driven by tailored voltage waveforms that consist of up to four harmonics of base frequency 13.56 MHz. Experimentally determined values of DC self-bias and electrical power deposition, as well as flux density and flux-energy distribution of the positive ions at the grounded electrode are compared with simulation data for a wide range of operating conditions. Very good agreement is found for self-bias and flux-energy distribution of the positive ions at the electrodes, while a fair agreement is reached for discharge power and ion flux data. The simulated spatial and temporal behaviour of the electric field, electron density, electron power absorption, ionization rate and mean electron energy shows a transition between sheath expansion heating and drift-ambipolar discharge modes, induced by changing either the number of harmonics comprising the excitation waveform or the gas pressure. The simulations indicate that under our experimental conditions the plasma operates at high electronegativity, and also reveal the crucial role of O2(a1Δg) singlet metastable molecules in establishing discharge behavior via the fast destruction of negative ions within the bulk plasma.


Source: Derzsi et al. 2016 Plasma Sources Sci. Technol. 25 015004



Absolute and relative emission spectroscopy study of 3 cm wide planar radio frequency atmospheric pressure bio-plasma source

Xiaolong Deng1, Anton Yu Nikiforov1, Eusebiu-Rosini Ionita2, Gheorghe Dinescu2 and Christophe Leys1

1 Department of Applied Physics, Ghent University, Sint-Pietersnieuwstraat 41 B4, 9000 Gent, Belgium
2 National Institute of Laser, Plasma and Radiation, Magurele-Bucharest, MG-36, Ilfov RO 077125, Romania



The dynamics of low power atmospheric pressure radio frequency discharge generated in Ar gas in long gap of 3 cm is investigated. This plasma source is characterized and analyzed for possible large scale biomedical applications where low gas temperature and potential-less effluent are required. The discharge forms a homogenous glow-like afterglow in ambient air at input power of 30 W with low gas temperature of 330 K, which is desirable in biomedical applications. With absolute calibrated spectroscopy of the discharge, electron density of 0.4 × 1018 m−3 and electron temperature of 1.5 eV are obtained from continuum Bremsstrahlung radiation of the source. Time and spatial resolved emission spectroscopy is used to analyze discharge generation mechanism and active species formation. It is found that discharge dynamics strongly correlates with the discharge current waveform. Strong Ar(2p) excited states emission is observed nearby the electrodes surface on a distance up to 200 m in the plasma sheath region at 10 ns after the current peak, whereas OH(A) emission is uniform along of the interelectrode gap.


Source: Deng et al. 2015 Appl. Phys. Lett. 107, 053702




Characteristics of a long and stable filamentary argon plasma jet generated in ambient atmosphere

M Teodorescu1, M Bazavan2, E R Ionita1 and G Dinescu1,2

1 National Institute for Laser, Plasma and Radiation Physics, Magurele, PO Box Mg36, Bucharest, 077125, Romania
2 Physics Department, University of Bucharest, Magurele, 077125 Bucharest, Romania



We present a study of a long (up to 60 mm) and thin (600 μm) plasma jet generated at 13.56 MHz in argon expanding in an open atmosphere from inside of a thin glass tube. The discharge is operated with one annular external electrode on the tube, in the absence of any grounded electrode in the discharge proximity. The study comprises image, spectral and electrical measurements, aiming to define and understand the operating domains of this plasma jet source. Two plasma zones were identified, which coexist: a long filament accompanied by a diffuse discharge. The coexistence of these plasma zones was studied in the power-mass flow rate parameter space. An electric model is proposed, considering the jet as a radiating antenna, which allows the determination of the main electrical parameters like capacitance, resistance and active RF power dissipated in the discharge. The specific zones on the IV characteristics were assigned to the operating domains observed visually. The spectral emission of plasma has been used to characterize the jet in respect to the gas temperature, excitation temperature and plasma density.


Source: M Teodorescu et al. 2015 Plasma Sources Sci. Technol. 24 025033 doi:10.1088/0963-0252/24/2/025033



Radio-frequency capacitively coupled plasmas in hydrogen excited by tailored voltage waveforms: comparison of simulations with experiments

P Diomede1, D J Economou1, T Lafleur2,3, J-P Booth2 and S Longo4

1 Plasma Processing Laboratory, Department of Chemical & Biomolecular Engineering, University of Houston, Houston, TX 77204-4004, USA
2 Laboratoire de Physique des Plasmas, CNRS, Sorbonne Universités, UPMC Univ Paris 06, Univ Paris-Sud, Ecole Polytechnique, 91128 Palaiseau, France
3 ONERA-The French Aerospace Lab, 91120 Palaiseau, France
4 Dipartimento di Chimica, Universita' degli Studi di Bari, via Orabona 4, 70126 Bari, Italy



A combined computational–experimental study was performed of a geometrically symmetric capacitively coupled plasma in hydrogen sustained by tailored voltage waveforms consisting of the sum of up to three harmonics. Predictions of a particle-in-cell with Monte Carlo collisions/fluid hybrid model were in reasonably good agreement compared to data from an array of experimental plasma diagnostics. The plasma was electrically asymmetric, with a dc self-bias developed, for all but a sinusoidal voltage waveform. Hydrogen ions bombarding the electrodes exhibited different ion flux-distribution functions due to their different masses and collisionality in the sheath. Plasma density, ion flux and absolute value of the dc self-bias all increased with increasing the number of harmonics. The energy of ions bombarding the substrate electrode may be controlled by switching the applied voltage waveform from (positive) 'peaks' to (negative) 'valleys'.


Source: P Diomede et al. 2014 Plasma Sources Sci. Technol. 23 065049 doi:10.1088/0963-0252/23/6/065049



Radio frequency current-voltage probe for impedance and power measurements in multi-frequency unmatched loads

T. Lafleur1, P. A. Delattre1, J. P. Booth1, E. V. Johnson2 and S. Dine3

1 LPP-CNRS, Ecole Polytechnique, 91128 Palaiseau, France

2 LPICM-CNRS, Ecole Polytechnique, 91128 Palaiseau, France

3 SOLAYL SAS, 91400 Orsay, France



A broad-band, inline current-voltage probe, with a characteristic impedance of 50 Ω, is presented for the measurement of voltage and current waveforms, impedance, and power in rf systems. The probe, which uses capacitive and inductive sensors to determine the voltage and current, respectively, can be used for the measurement of single or multi-frequency signals into both matched and unmatched loads, over a frequency range of about 1–100 MHz. The probe calibration and impedance/power measurement technique are described in detail, and the calibrated probe results are compared with those obtained from a vector network analyzer and other commercial power meters. Use of the probe is demonstrated with the measurement of power into an unmatched capacitively coupled plasma excited by multi-frequency tailored voltage waveforms.


Source: T. Lafleur et al. Rev. Sci. Instrum. 84, 015001 (2013);




Radio-frequency capacitively coupled plasmas excited by tailored voltage waveforms: comparison of experiment and particle-in-cell simulations

Pierre-Alexandre Delattre1,2, Trevor Lafleur1, Erik Johnson2 and Jean-Paul Booth1

1 Laboratory of Plasma Physics (LPP), Ecole Polytechnique, CNRS, Palaiseau 91 128, France
2 Laboratory of Physics of Interfaces and Thin Films (LPICM), Ecole Polytechnique, CNRS, Palaiseau 91 128, France



Using a range of different diagnostics we have performed a detailed experimental characterization of a capacitively coupled rf plasma discharge excited by tailored voltage waveforms in argon (3–13 Pa). The applied pulse-type tailored waveforms consist of between 1 and 5 harmonics (with a fundamental of 15 MHz), and are used to generate an electrically asymmetric plasma response, manifested by the formation of a strong dc bias in the geometrically symmetric reactor used. Experimental measurements of the dc bias, electron density, ion current density, ion-flux energy distributions at the electrodes and discharge current waveforms, are compared with a one-dimensional particle-in-cell simulation for the same operating conditions. The experimental and simulation results are found to be in good agreement over the range of parameters investigated, and demonstrate a number of unique features present with pulse-type tailored waveforms, including: increased plasma density and ion flux with the number of harmonics, and a broader control range of the ion bombarding energy.


Source: Pierre-Alexandre Delattre et al 2013 J. Phys. D: Appl. Phys. 46 235201 doi:10.1088/0022-3727/46/23/235201




Capacitively coupled radio-frequency plasmas excited by tailored voltage waveforms

T Lafleur1, P A Delattre1, E V Johnson2 and J P Booth1

1 LPP-CNRS, Ecole Polytechnique, 91128 Palaiseau, France
2 LPICM-CNRS, Ecole Polytechnique, 91128 Palaiseau, France



By applying certain types of 'tailored' voltage waveforms (TVWs) to capacitively coupled plasmas, a dc self-bias and an asymmetric plasma response can be produced, even in geometrically symmetric reactors. Furthermore, these arbitrary applied waveforms can produce a number of interesting phenomena that are not present in typical single-frequency sinusoidal discharges. This electrical asymmetry effect presents emerging possibilities for the improved control of the ion energy and ion flux in these systems; parameters of vital importance to both etching and deposition applications for materials processing. With a combined research approach utilizing both experimental measurements, and particle-in-cell simulations, we review and extend recent investigations that study a particular class of TVW. The waveforms used have a pulse-type shape and are composed of a varying number of harmonic frequencies. This allows a strong self-bias to be produced, and causes most of the applied voltage to be dropped across a single sheath. Additionally, decreasing the pulse width (by increasing the number of harmonics), allows the plasma density and ion flux to be increased. Simulation and experimental results both demonstrate that this type of waveform can be used to separately control the ion flux and ion energy, while still producing a uniform plasma over large area (50 cm diameter) rf electrodes.


Source: T Lafleur et al 2013 Plasma Phys. Control. Fusion 55 124002 doi:10.1088/0741-3335/55/12/124002



Hydrogenated microcrystalline silicon thin films deposited by RF-PECVD under low ion bombardment energy using voltage waveform tailoring

E.V. Johnsona, S. Pouliquenb, P.A. Delattrea, b, J.P. Boothb

a LPICM-CNRS, Ecole Polytechnique, 91128 Palaiseau, France

b LPP-CNRS, Ecole Polytechnique, 91128 Palaiseau, France



We present experimental results for hydrogenated amorphous and microcrystalline silicon (a-Si:H and μc-Si:H) thin films deposited by PECVD while using a voltage waveform tailoring (VWT) technique to create an electrical asymmetry in the reactor. VWT dramatically modifies the mean ion bombardment energy (IBE) during growth, and we show that for a constant peak-to-peak excitation voltage (VPP), waveforms resembling “peaks” or “valleys” result in very different material properties. Using Raman scattering spectroscopy, we show that the crystallinity of the material depends strongly on the IBE, as controlled by VWT. A detailed examination of the Raman scattering spectra reveals that the narrow peak at 520 cm− 1 is disproportionately enhanced by lowering the IBE through the VWT technique. We examine this effect for a range of process parameters, varying the pressure, hydrogen–silane dilution ratio, and total flow of H2. In addition, the Sisingle bondHX bonding in silicon thin films deposited using VWT is characterised for the first time, showing that the hydrogen bonding character is changed by the IBE. These results demonstrate the potential for VWT in controlling the IBE during thin film growth, thus ensuring that application-appropriate film densities and crystallinities are achieved, independent of the injected RF power.


Source: E.V. Johnson et al, Journal of Non-Crystalline Solids, Volume 358, Issue 17, 1 Sept. 2012, Pages 1974–1977 doi:10.1016/j.jnoncrysol.2012.01.014




Separate control of the ion flux and ion energy in capacitively coupled radio-frequency discharges using voltage waveform tailoring

T. Lafleur1,a), P. A. Delattre1, E. V. Johnson1 and J. P. Booth1

1 LPP-CNRS, Ecole Polytechnique, 91128 Palaiseau, France


We experimentally characterize an argon plasma in a geometrically symmetric, capacitively coupled rf discharge, excited by pulse-type tailored waveforms (generated using multiple voltage harmonics). The results confirm a number of predictions made by recent particle-in-cell simulations of a similar system and demonstrate a unique form of control over the ion flux and ion energy in capacitively coupled plasmas; by increasing the number of applied harmonics (equivalent to decreasing the pulse width), it is possible to increase the plasma density and ion flux (together with the power deposition) while keeping the average ion energy on one of the electrodes low and constant.
Source: T. Lafleur et al., Appl. Phys. Lett. 101, 124104 (2012);



Tailored Voltage Waveform Deposition of Microcrystalline Silicon Thin Films from Hydrogen-Diluted Silane and Silicon Tetrafluoride: Optoelectronic Properties of Films

Erik V. Johnson1, Sylvain Pouliquen2, Pierre-Alexandre Delattre1,2 and Jean-Paul Booth2

1 LPICM-CNRS, Ecole Polytechnique, 91128 Palaiseau, France
2 LPP-CNRS, Ecole Polytechnique, 91128 Palaiseau, France


The use of tailored voltage waveforms (TVW's) to excite a plasma for the deposition of thin films of hydrogenated microcrystalline silicon (µc-Si:H) has been shown to be an effective technique to decouple mean ion bombardment energy (IBE) from injected power. In this work, we examine the changes in material properties controlled by this technique through Raman scattering and spectroscopic ellipsometry for films deposited from H2-diluted SiH4, and we examine the electrical properties of such films using temperature dependent conductivity. As the laboratory-scale deposition system used had neither a load lock nor an oxygen filter in the H2 line, accidental O-doping was observed for the µc-Si:H films. We investigated suppression of this doping by adding varying amounts of SiF4, and using an SiF4/Ar pre-etch step to clean the reactor. This technique is shown to be effective in decreasing the accidental doping of the films, and intrinsic µc-Si:H films are produced with an activation energy of up to 0.55 eV. As well, an important difference in the amorphous-to-microcrystalline transition is observed once SiF4 is included in the gas mixture.
Source: Erik V. Johnson et al 2012 Jpn. J. Appl. Phys. 51 08HF01 doi:10.1143/JJAP.51.08HF01