Langmuir Probe Publications

Deposition of rutile (TiO2) with preferred orientation by assisted high power impulse magnetron sputtering

Vitezslav Stranak, Corresponding author contact information, E-mail the corresponding author, Ann-Pierra Herrendorf, Harm Wulff, Steffen Drache, Martin Cadab, Zdenek Hubick, Milan Tichy, Rainer Hippler

Published 15 May 2013


The effect of energetic ion bombardment on TiO2 crystallographic phase formation was studied. Films were deposited using high-power impulse magnetron sputtering (HiPIMS) assisted by an electron cyclotron wave resonance (ECWR) plasma. The ECWR assistance allows a significant reduction of pressure down to 0.075 Pa during reactive HiPIMS deposition and subsequently enables control of the energy of the deposited species over a wide range. Films deposited at high ion energies and deposition rates form rutile with (101) a preferred orientation. With decreasing ion energy and deposition rates, rutile is formed with random crystallite orientation, and finally at low ion energies the anatase phase occurs. It is supposed that particles gain high energy during the HiPIMS pulse while the ECWR discharge is mostly responsible for substrate heating due to dissipated power. However, the energetic contribution of the ECWR discharge is not sufficient for annealing and phase transformation.

Online at Surface and Coatings Technology Volume 222, 15 May 2013, Pages 112–117

Time-resolved Langmuir probe investigation of hybrid high power impulse magnetron sputtering discharges

Steffen Drache, Vitezslav Stranak, Ann-Pierra Herrendorf, Martin Cadab, Zdenek Hubick, Milan Tichy, Rainer Hippler

Published April 2013


The paper focuses on time-resolved diagnostics of unipolar hybrid-dual-High Power Impulse Magnetron Sputtering (hybrid-dual-HiPIMS) discharges. The newly developed sputtering system is based on a combination of dual-HiPIMS with a mid-frequency (MF) discharge. The most important feature of hybrid-dual-HiPIMS systems is the MF pre-ionization which causes/allows: (i) a significant reduction of working pressure by more than one order of magnitude, and (ii) faster ignition and development of HiPIMS pulses. Parameters such as mean electron energy, electron density and electron energy probability function (EEPF) were obtained from time-resolved Langmuir probe diagnostics to demonstrate the aforementioned effects. Calorimetric probe diagnostics were used for determination of the total power density flux. Power flux contributions of particular species, e.g. ions, electrons and neutrals, were estimated as well.

Online at Vacuum Volume 90, April 2013, Pages 176–181

Design and characterization of the Magnetized Plasma Interaction Experiment (MAGPIE): a new source for plasma–material interaction studies

Boyd D Blackwell, Juan Francisco Caneses, Cameron M Samuell, John Wach, John Howard and Cormac Corr

Published 4 October 2012


The Magnetized Plasma Interaction Experiment (MAGPIE) is a versatile helicon source plasma device operating in a magnetic hill configuration designed to support a broad range of research activity and is the first stage of the Materials Diagnostic Facility at the Australian National University. Various material targets can be introduced to study a range of plasma–material interaction phenomena.

Initially, with up to 2.1 kW of RF at 13.56 MHz, argon (10¹⁸–10¹⁹ m⁻³) and hydrogen (up to 10¹⁹ m⁻³ at 20 kW) plasma with electron temperature ~3–5 eV was produced in magnetic fields up to ~0.19 T. For high mirror ratio we observe the formation of a bright blue core in argon above a threshold RF power of 0.8 kW. Magnetic probe measurements show a clear m = +1 wave field, with wavelength smaller than or comparable to the antenna length above and below this threshold, respectively. Spectroscopic studies indicate ion temperatures

Online at Boyd D Blackwell et al 2012 Plasma Sources Sci. Technol. 21 055033

Time-resolved measurement of plasma parameters in the far-field plume of a low-power Hall effect thruster

K Dannenmayer, P Kudrna, M Tichý and S Mazouffre

Published 13 September 2012


Time-resolved measurements using electrostatic probes are performed in the far-field plume of a low-power permanent magnet Hall effect thruster. These measurements are necessary in order to account for the non-stationary behavior of the discharge. The plasma potential is measured by means of a cylindrical Langmuir and a sufficiently heated emissive probe, the electron temperature and density are measured with a cylindrical Langmuir probe. The thruster is maintained in a periodic quasi-harmonic oscillation regime by applying a sinusoidal modulation to a floating electrode in the vicinity of the cathode in order to guarantee repeatable conditions for all measurements. The modulation depth of the discharge current does not exceed approximately 10%. In order to achieve synchronism, the frequency of the modulation has to be close to the natural frequency of the observed phenomena. It is different depending on whether the discharge current or the plasma potential is selected as a reference. The measurements show that the fluctuations of the electron density follow the discharge current fluctuations. The time evolution of the plasma potential and the electron temperature is similar. The time-averaged properties of the discharge remain almost uninfluenced by the modulation. Measurements of the plasma potential with the two different probes are in good agreement. The observed phenomena are similar for Xe and Kr used as propellant gases.

Online at K Dannenmayer et al 2012 Plasma Sources Sci. Technol. 21 055020

Langmuir probe measurements in the intense RF field of a helicon discharge

Francis F Chen

Published 6 September 2012


Helicon discharges have extensively been studied for over 25 years both because of their intriguing physics and because of their utility in producing high plasma densities for industrial applications. Almost all measurements so far have been made away from the antenna region in the plasma ejected into a chamber where there may be a strong magnetic field (B-field) but where the radiofrequency (RF) field is much weaker than under the antenna. Inside the source region, the RF field distorts the current–voltage (I–V) characteristic of the probe unless it is specially designed with strong RF compensation. For this purpose, a thin probe was designed and used to show the effect of inadequate compensation on electron temperature (Te) measurements. The subtraction of ion current from the I–V curve is essential; and, surprisingly, Langmuir's orbital motion limited theory for ion current can be used well beyond its intended regime.

Online at Plasma Sources Sci. Technol. 21 055013

Wave modeling in a cylindrical non-uniform helicon discharge

L. Chang, M. J. Hole, J. F. Caneses, G. Chen, B. D. Blackwell and C. S. Corr

Published 31 August 2012


A radio frequency field solver based on Maxwell's equations and a cold plasma dielectric tensor is employed to describe wave phenomena observed in a cylindrical non-uniform helicon discharge. The experiment is carried out on a recently built linear plasma-material interaction machine: The magnetized plasma interaction experiment [Blackwell et al., Plasma Sources Sci. Technol. (submitted)], in which both plasma density and static magnetic field are functions of axial position. The field strength increases by a factor of 15 from source to target plate, and the plasma density and electron temperature are radially non-uniform. With an enhancement factor of 9.5 to the electron-ion Coulomb collision frequency, a 12% reduction in the antenna radius, and the same other conditions as employed in the experiment, the solver produces axial and radial profiles of wave amplitude and phase that are consistent with measurements. A numerical study on the effects of axial gradient in plasma density and static magnetic field on wave propagations is performed, revealing that the helicon wave has weaker attenuation away from the antenna in a focused field compared to a uniform field. This may be consistent with observations of increased ionization efficiency and plasma production in a non-uniform field. We find that the relationship between plasma density,static magnetic field strength, and axial wavelength agrees well with a simple theory developed previously. A numerical scan of the enhancement factor to the electron-ion Coulomb collision frequency from 1 to 15 shows that the wave amplitude is lowered and the power deposited into the core plasma decreases as the enhancement factor increases, possibly due to the stronger edge heating for higher collision frequencies.

Online at Phys. Plasmas 19, 083511 (2012)

Measurement of plasma parameters in the far-field plume of a Hall effect thruster

K Dannenmayer, P Kudrna, M Tichý and S Mazouffre

Published 29 November 2011


The far-field plume of a 1.5 kW Hall effect thruster is mapped with a Langmuir probe and an emissive probe. Time-averaged measurements of the plasma potential, the electron temperature and the electron number density are performed for different operating conditions of the thruster. The influence of the discharge voltage, the cathode mass flow rate as well as the magnetic field strength is investigated. The plasma potential decreases from 30 V at 300 mm on the thruster axis to 5 V at 660 mm and at 60°, the electron temperature decreases from 5 to 1.5 eV. The electron number density drops from 3.5 × 10¹⁶ to 1 × 10¹⁵ m⁻³ in the far-field plume. The values of the plasma potential and electron temperature measured with the Langmuir probe and the emissive probe are in good agreement.

Online at K Dannenmayer et al 2011 Plasma Sources Sci. Technol. 20 065012

Response of an ion–ion plasma to dc biased electrodes

Lara Popelier, Ane Aanesland and Pascal Chabert

Published 15 July 2011


Electronegative plasmas are plasmas containing a significant fraction of negative ions, when magnetized they are very often segregated: the core is electropositive or weakly electronegative whereas a highly electronegative plasma forms at the periphery. At strong magnetic fields this segregation can lead to the formation of ion–ion plasmas almost free of electrons close to the walls or extraction surfaces and allows access to both positive and negative ions. The PEGASES thruster aims at alternately extracting and accelerating positive and negative ions from the ion–ion plasma region to provide thrust by both types of ions. The acceleration schemes depend on the possible control of the potential in an ion–ion plasma relative to the acceleration grids. In this paper continuous extraction and acceleration of positive ions from the PEGASES thruster is investigated by a retarding field energy analyser. It is shown from the measured ion energy distribution functions that the continuous acceleration potential can be controlled by biasing bare electrodes in contact with the region of the plasma with high electron density (i.e. the weakly electronegative plasma core). A grounded grid placed in the ion–ion region allows consequently the acceleration of positive ions, where the ion velocity is controlled by the bias applied to the electrodes in the plasma core. In contrast, when the grid in the ion–ion region is biased, positive ion beams are not detected downstream of the grid. The results indicate that biasing a grid positively in the ion–ion region may result in an electronegative space-charge sheath in front of the grid, which traps the positive ions inside the thruster.

Online at Lara Popelier et al 2011 J. Phys. D: Appl. Phys. 44 315203

Ion and Photon Surface Interaction during Remote Plasma ALD of Metal Oxides

H. B. Profijt, P. Kudlacek, M. C. M. van de Sanden and W. M. M. Kessels

Published February 25, 2011


The influence of ions and photons during remote plasma atomic layer deposition (ALD) of metal oxide thin films was investigated for different O2 gas pressures and plasma powers. The ions have kinetic energies of ≤35 eV and fluxes of ∼1012–1014 cm−2 s−1 toward the substrate surface: low enough to prevent substantial ion-induced film damage, but sufficiently large to potentially stimulate the ALD surface reactions. It is further demonstrated that 9.5 eV vacuum ultraviolet photons, present in the plasma, can degrade the electrical performance of electronic structures with ALD synthesized metal oxide films.

Online at doi: 10.1149/1.3552663 J. Electrochem. Soc. 2011 volume 158, issue 4, G88-G91

The Influence of Ions and Photons during Plasma-Assisted ALD of Metal Oxides

Harald B. Profijt, Pavel Kudlacek, M. C. M. Van de Sanden and W. M. M. Kessels

Published 2010


The influence of oxygen ions and photons during remote plasma atomic layer deposition (ALD) of metal oxide thin films was investigated for pressures of 0.5-3 Pa and plasma powers of 100-500 W. Ions have kinetic energies of ~15-35 eV and fluxes of ~10^13-10^14 cm^-2 s^-1 towards the substrate surface. The ion energy is low enough to prevent substantial ion-induced film damage, however the total energy flux provided to the substrate is sufficiently large to potentially stimulate the ALD surface reactions, e.g., through ligand desorption and adatom migration. Furthermore, it is demonstrated that the presence of VUV photons with energies of ~9.5 eV can deteriorate the electrical performance of electronic structures with ALD synthesized metal oxide films.

Online at doi: 10.1149/1.3485242 ECS Trans. 2010 volume 33, issue 2, 61-67

Comparison of plasma parameters determined with a Langmuir probe and with a retarding field energy analyzer

D Gahan, B Dolinaj and M B Hopkins

Published 31 July 2008


A comparison is made between plasma parameters measured with a retarding field energy analyzer (RFEA), mounted at a grounded electrode in an inductive discharge, and a Langmuir probe located in bulk plasma close to the analyzer. Good agreement between measured plasma parameters is obtained for argon gas pressure in the range 2–10 mTorr. Parameters compared include time averaged plasma potential, the tail of the electron energy distribution function (EEDF), the electron temperature and the ion flux. This highlights the versatility of the RFEA for determining plasma parameters adjacent to the surface where probe measurements are not easily made. Combination of the probe and energy analyzer has enabled the measurement of the EEDF to a higher energy than otherwise possible.

Online at D Gahan et al 2008 Plasma Sources Sci. Technol. 17 035026 doi:10.1088/0963-0252/17/3/035026