Nicholas Braithwaite - Academia.edu (original) (raw)

Papers by Nicholas Braithwaite

Bulletin of the American Physical Society, Oct 22, 2009

Submitted for the GEC09 Meeting of The American Physical Society How valid is the concept of a bi... more Submitted for the GEC09 Meeting of The American Physical Society How valid is the concept of a bi-Maxwellian distribution? N.S. BRAITHWAITE, R.N. FRANKLIN, The Open University-The sheath of a plasma with two distinct negative species was examined by Braithwaite and Allen (1988). There is no doubt of its validity to describe the situation in electronegative plasmas at low pressures when the species are electrons and negative ions, and much of the understanding of such plasmas has resulted. Though it may be convenient to describe the electron energy distribution in electropositive plasmas as if there are two distinct species, one needs to be careful in deriving such things as a modified Bohm criterion. In most situations there is but one distribution and one cannot distinguish "red" and "blue" electrons. The electrons move between different parts of the distribution by a process of "diffusion" well described by Tsendin (2009). Thus unless different parts of the total electron distribution clearly do not interact, results obtained by assuming two independent populations with different densities and temperatures lack validity.

Bulletin of the American Physical Society, Oct 22, 2009

Submitted for the GEC09 Meeting of The American Physical Society High accuracy identification of ... more Submitted for the GEC09 Meeting of The American Physical Society High accuracy identification of microwave hairpin resonances MARK BOWDEN, VLADIMIR SAMARA, NICHOLAS BRAITHWAITE, The Open University-The quarter-wave hairpin resonator is a useful density diagnostic in low pressure plasmas. Among its advantages are the immediacy and potential accuracy of the determination of electron density by a microwave frequency measurement. One difficulty in making high precision measurements has been the identification of the precise resonant frequency because of the shape of the resonance and the background signal on which it is superimposed. In a development of the hairpin method the mean potential of the hairpin is directly modulated at a few kHz while a separate, inductively coupled microwave signal is swept through the range of resonance. When immersed in a plasma the low frequency modulation perturbs the electron density in the immediate vicinity of the hairpin, impressing a modulation on the resonant frequency. At resonance there is a sharp phase change in the modulated microwave reflection (referenced to the modulation input). This aids identification of the resonance since all other structure in the microwave signal reflected from the hairpin is unaffected. This provides a simple determination of the resonance that can be readily implemented in software for automated measurements, with time resolution restricted only by the modulation period. The method has been demonstrated in a GEC reference cell with pulsed and steady CCP excitation at 13.56 MHz.

Sensors and Actuators A-physical, Oct 1, 2009

A new method of exposing silicon/semiconductor wafers to a mixture of radicals is described, in w... more A new method of exposing silicon/semiconductor wafers to a mixture of radicals is described, in which these species are generated in an oxygen-rich gas discharge confined between a concentric pair of annular mesh electrodes surrounding the wafers. This approach allows the wafer surfaces to be treated without damage from the energetic ions, strong electric fields, and high UV fluxes associated with direct treatment by exposure to gas discharge plasmas. The process is compared with direct oxygen plasma activation for its latitude with respect to treatment duration, effect on wafer surface roughness and bond strength. Wider process latitude and reduced surface roughening are obtained for treatment by radicals compared with direct plasma exposure. Comparative analysis of treated and untreated silicon surfaces by X-ray photoelectron spectroscopy indicate that traces of fluorine present on the wafer surface before treatment are removed with great efficiency by the process.

Bulletin of the American Physical Society, Oct 10, 2006

Submitted for the GEC06 Meeting of The American Physical Society Looking for information in the Q... more Submitted for the GEC06 Meeting of The American Physical Society Looking for information in the Q of the hairpin probe NICHOLAS BRAITHWAITE, EVA VASEKOVA, JAFAR AL-KUZEE, The Open University, THE OPEN UNIVERSITY TEAM-A microwave resonator hairpin probe is used to measure the electron density of low pressure low temperature plasma. The probe acts as a quarter wave transmission line that is resonant at a frequency determined by the dielectric properties of the surrounding medium. The quality factor Q of the hairpin resonance has been studied as a function of the pressure of the discharge gas and the power coupled to the discharge, for a number of gasses. The Q values were inferred from the Gaussian fitting of the recorded resonant curves of the probe. The theoretical values of the Q were calculated as a ratio of the energy stored in the cavity and the energy dissipated per one period. Since the dissipated energy depends on the collisions between electrons and the background gas, the quality factor tends to decrease with the gas number density, hence the pressure, as well as the electron number density. The measured values of Q were compared with the theoretical values and found to be in good agreement.

Bulletin of the American Physical Society, Nov 7, 2014

and negative ions from different phases of a pulsed discharge. A cylindrical, inductively coupled... more and negative ions from different phases of a pulsed discharge. A cylindrical, inductively coupled plasma (ICP) was excited between two planar diskelectrodes in mixtures of SF 6 and O 2 at about 20 mTorr. The discharge was pulsed at 2 kHz and 50% duty cycle. The extraction electrode was a 10 mm thick carbon plate (or a 0.8 mm steel plate) with an array of 1 mm holes, held at ground potential. Ions grazing the sides of the extraction holes incidence have a high probability (70-95%) of neutralization. The other electrode was pulse-biased to extract negative or positive ions during the afterglow phase, after an ion-ion plasma had formed. The total flux and velocity distribution of extracted ions was measured using a retarding field analyser. Extraction of mono-energetic positive and negative ion beams with energies in the range 10-300 eV was demonstrated. It was shown that the beam energy can be precisely controlled by the bias waveform tailoring and by positioning of the extraction electrodes.

Applied physics reviews, Jun 1, 2016

Recently, there have been enormous efforts to tailor the properties of graphene. These improved p... more Recently, there have been enormous efforts to tailor the properties of graphene. These improved properties extend the prospect of graphene for a broad range of applications. Plasmas find applications in various fields including materials science and have been emerging in the field of nanotechnology. This review focuses on different plasma functionalization processes of graphene and its oxide counterpart. The review aims at the advantages of plasma functionalization over the conventional doping techniques. Selectivity and controllability of the plasma techniques opens up future pathways for large scale, rapid functionalization of graphene for advanced applications. We also emphasize on atmospheric pressure plasma jet as the future prospect of plasma based functionalization processes.

For guidance on citations see FAQs.

Cambridge University Press eBooks, May 5, 2011

APS, Oct 1, 2000

SF6 plasmas are routinely used for the etching of silicon in a wide range of applications includi... more SF6 plasmas are routinely used for the etching of silicon in a wide range of applications including Micro Electro-Mechanical Systems (MEMS) where etch geometry is of prime importance. Etch geometries are influenced by not only the gas phase chemistry of the plasma but also its electrical potential structure. A range of diagnostics has been deployed to examine the composition of

The process of sound reproduction in a plasma gas was researched initially in the early 1900s wit... more The process of sound reproduction in a plasma gas was researched initially in the early 1900s with development into commercially available plasma loudspeakers in the mid 1950s i and has continued to the present day. In the electro-acoustic transduction mechanism, the charged particles gain energy in the electric field and, through collisions, transfer this energy to the surrounding air molecules causing a rapid increase in the gas temperature and the dimensions of the gas volume. An ac modulation (here in the audio frequency range) of the electric field gives rise to a temperature modulation (sufficient to produce sound). As in natural lightning, the rapid expansion in the ionised column though the air produces external pressure variations at the modulation frequency. Spatial and temporal measurement of the gas temperature and the dimensional changes of the plasma relative to the audio modulation frequency can identify the nature of the thermal expansion. This provides a direct approach to understanding its relationship to the sound pressure wave that is generated. For the atmospheric pressure RF ‘warm’ plasma used in this project, the gas temperature was measured through spectroscopy by measuring the rotational line emission from nitrogen molecules. The short relaxation time between rotational to translational stage in the molecule means that a comparison between a modelled spectrum for this system and the intensity of rotational lines yields the gas temperature. For analysis of dimensional changes, the optical emissions have been measured using a CCD camera and, through Abel inversion, the radial variation can be determined from the line of sight intensity cross sections. In the final stage of this work, the various parametric investigations are being brought together to produce an overall model of a plasma loudspeaker system.

A heuristic algorithm for detecting the state of a turbo molecular pump from its sound. Find what... more A heuristic algorithm for detecting the state of a turbo molecular pump from its sound. Find what you want from DORA: All of DORA This Collection. Advanced Search. DORA. DORADe Montfort University Open Research Archive. ...

Review of Scientific Instruments, Sep 1, 2006

No related articles were found.

Pure and Applied Chemistry, 1990

The electron energy distribution function (EEDF) in a low pressure processing discharge is a good... more The electron energy distribution function (EEDF) in a low pressure processing discharge is a good indicator of the state of the plasma. Chemical kinetics are especially sensitive to the EEDF and the electron population plays a central role in coupling power into the desired surface reactions. M e s s development and transfer will be aided by a knowledge of the EEDF and its sensitivity to various process parameters. The EEDF can be measured using an electrostatic probe to sample the electron population by drawing a small current from the plasma. Electron and ion density and a characteristic electron (Maxwellian) temperature can be deduced from probe data. Furthermore, the current-voltage characteristic of the probe represents integrated EEDF information which can be recovered by differentiation. The practical use of this probe technique is considered for a variety of plasmas (both DC and RF generated). The problems associated with processing plasmas such as deposition and RF excitation are discussed with particular emphasis on 13.56MHz capacitively coupled systems. Typical data are viewed in terms of energy resolution and accuracy and conditions necessary for reliable data acquisition are considered.

Frontiers in Education, Nov 29, 2023

Teaching roles and communication strategies in interactive web broadcasts for practical lab and f... more Teaching roles and communication strategies in interactive web broadcasts for practical lab and field work at a distance.

Journal of Physics E: Scientific Instruments, Aug 1, 1987

... An electrostatic probe technique for mplasma ... authors' attention was drawn to an ... more ... An electrostatic probe technique for mplasma ... authors' attention was drawn to an article by Mosburg et a1 (1983) in which the idea of a driven probe scheme is ... p 564 Boschi A and Magistrelli F 1963 Effect of an RF signal on the characteristic of a Langmuir probe Nuouo Cimento ...

Journal of Physics D, Mar 11, 2010

We describe measurements of plasma properties of pulsed, low pressure, capacitively coupled disch... more We describe measurements of plasma properties of pulsed, low pressure, capacitively coupled discharges operated in argon. The research aims to determine the effect of modulating the radiofrequency power during the discharge part of the pulse cycle. Measurements of local electron density and optical emission were made in capacitively-coupled rf discharges generated in a Gaseous Electronics Conference (GEC) reference reactor. Gas pressure was in the range 7-70 Pa, rf power in the range 1-100 W and pulse durations in the range of 10 µs-100 ms. The results indicate that the ignition and afterglow decay processes in pulsed discharges can be controlled by modulating the shape of applied radiofrequency pulse.

Applied Physics Letters, Nov 14, 2005

A microwave measurement of electron density in low-pressure plasmas can be based on a hairpin pro... more A microwave measurement of electron density in low-pressure plasmas can be based on a hairpin probe. The hairpin forms a transmission line that supports a quarter-wavelength standing wave. The resonance is related to the relative permittivity of the surroundings, and hence, in a plasma, electron density can be evaluated. For improved fidelity, a general model is developed to include the effects of positive and negative space-charge sheaths formed around the hairpin wires. The former tends to lower the resonance, whereas the latter tends to raise it initially. This is qualitatively in agreement with experiments in dc argon plasmas.

Review of Scientific Instruments, Jul 1, 2000

This article describes how to extract accurate information about a plasma from a capacitively cou... more This article describes how to extract accurate information about a plasma from a capacitively coupled planar probe that is biased using pulsed radio-frequency excitation. The conditions necessary to observe correct saturation of the probe current are investigated, particularly the use of correct geometry and biasing for the guard ring. With these precautions the probe is an effective diagnostic for electron tail temperature at energies beyond those probed by conventional cylindrical probes. The dynamic response of the probe is investigated using conventional sweep voltages and shows the onset of displacement current and inertial effects associated with ions and electrons. In addition the effect of insulating films on the probe surface is examined, showing how the probe continues to operate even when it is coated. Characteristic changes caused by the presence of an insulating film give information about its electrical properties and its thickness.

Measurement Science and Technology, Aug 1, 1991

Two electrostatic probes have been tested simultaneously in the same plasma. The passive design u... more Two electrostatic probes have been tested simultaneously in the same plasma. The passive design uses a distributed inductive chain to block RF signals from the probe tip. The tip itself is capacitively coupled to a secondary ring electrode of large area, which effectively drives the probe tip potential in phase with the plasma space potential. The active design substitutes an externally generated sinusoidal signal (synchronous with the plasma excitation) of controllable phase and amplitude for the signal from the ring. Both probes were located on the mid-plane of a capacitively coupled RF plasma. In most cases the passive probe is found to float more positive than the active one. Both probes give results in close agreement when the plasma excitation is predominantly sinusoidal. The passive probe has a broad-band response which enables its tip to follow more closely non-sinusoidal RF potentials in the plasma. The active probe is more expensive in terms of components external to the plasma chamber but is considerably simpler to construct.

Bulletin of the American Physical Society, Oct 22, 2009

Submitted for the GEC09 Meeting of The American Physical Society How valid is the concept of a bi... more Submitted for the GEC09 Meeting of The American Physical Society How valid is the concept of a bi-Maxwellian distribution? N.S. BRAITHWAITE, R.N. FRANKLIN, The Open University-The sheath of a plasma with two distinct negative species was examined by Braithwaite and Allen (1988). There is no doubt of its validity to describe the situation in electronegative plasmas at low pressures when the species are electrons and negative ions, and much of the understanding of such plasmas has resulted. Though it may be convenient to describe the electron energy distribution in electropositive plasmas as if there are two distinct species, one needs to be careful in deriving such things as a modified Bohm criterion. In most situations there is but one distribution and one cannot distinguish "red" and "blue" electrons. The electrons move between different parts of the distribution by a process of "diffusion" well described by Tsendin (2009). Thus unless different parts of the total electron distribution clearly do not interact, results obtained by assuming two independent populations with different densities and temperatures lack validity.

Bulletin of the American Physical Society, Oct 22, 2009

Submitted for the GEC09 Meeting of The American Physical Society High accuracy identification of ... more Submitted for the GEC09 Meeting of The American Physical Society High accuracy identification of microwave hairpin resonances MARK BOWDEN, VLADIMIR SAMARA, NICHOLAS BRAITHWAITE, The Open University-The quarter-wave hairpin resonator is a useful density diagnostic in low pressure plasmas. Among its advantages are the immediacy and potential accuracy of the determination of electron density by a microwave frequency measurement. One difficulty in making high precision measurements has been the identification of the precise resonant frequency because of the shape of the resonance and the background signal on which it is superimposed. In a development of the hairpin method the mean potential of the hairpin is directly modulated at a few kHz while a separate, inductively coupled microwave signal is swept through the range of resonance. When immersed in a plasma the low frequency modulation perturbs the electron density in the immediate vicinity of the hairpin, impressing a modulation on the resonant frequency. At resonance there is a sharp phase change in the modulated microwave reflection (referenced to the modulation input). This aids identification of the resonance since all other structure in the microwave signal reflected from the hairpin is unaffected. This provides a simple determination of the resonance that can be readily implemented in software for automated measurements, with time resolution restricted only by the modulation period. The method has been demonstrated in a GEC reference cell with pulsed and steady CCP excitation at 13.56 MHz.

Sensors and Actuators A-physical, Oct 1, 2009

A new method of exposing silicon/semiconductor wafers to a mixture of radicals is described, in w... more A new method of exposing silicon/semiconductor wafers to a mixture of radicals is described, in which these species are generated in an oxygen-rich gas discharge confined between a concentric pair of annular mesh electrodes surrounding the wafers. This approach allows the wafer surfaces to be treated without damage from the energetic ions, strong electric fields, and high UV fluxes associated with direct treatment by exposure to gas discharge plasmas. The process is compared with direct oxygen plasma activation for its latitude with respect to treatment duration, effect on wafer surface roughness and bond strength. Wider process latitude and reduced surface roughening are obtained for treatment by radicals compared with direct plasma exposure. Comparative analysis of treated and untreated silicon surfaces by X-ray photoelectron spectroscopy indicate that traces of fluorine present on the wafer surface before treatment are removed with great efficiency by the process.

Bulletin of the American Physical Society, Oct 10, 2006

Submitted for the GEC06 Meeting of The American Physical Society Looking for information in the Q... more Submitted for the GEC06 Meeting of The American Physical Society Looking for information in the Q of the hairpin probe NICHOLAS BRAITHWAITE, EVA VASEKOVA, JAFAR AL-KUZEE, The Open University, THE OPEN UNIVERSITY TEAM-A microwave resonator hairpin probe is used to measure the electron density of low pressure low temperature plasma. The probe acts as a quarter wave transmission line that is resonant at a frequency determined by the dielectric properties of the surrounding medium. The quality factor Q of the hairpin resonance has been studied as a function of the pressure of the discharge gas and the power coupled to the discharge, for a number of gasses. The Q values were inferred from the Gaussian fitting of the recorded resonant curves of the probe. The theoretical values of the Q were calculated as a ratio of the energy stored in the cavity and the energy dissipated per one period. Since the dissipated energy depends on the collisions between electrons and the background gas, the quality factor tends to decrease with the gas number density, hence the pressure, as well as the electron number density. The measured values of Q were compared with the theoretical values and found to be in good agreement.

Bulletin of the American Physical Society, Nov 7, 2014

and negative ions from different phases of a pulsed discharge. A cylindrical, inductively coupled... more and negative ions from different phases of a pulsed discharge. A cylindrical, inductively coupled plasma (ICP) was excited between two planar diskelectrodes in mixtures of SF 6 and O 2 at about 20 mTorr. The discharge was pulsed at 2 kHz and 50% duty cycle. The extraction electrode was a 10 mm thick carbon plate (or a 0.8 mm steel plate) with an array of 1 mm holes, held at ground potential. Ions grazing the sides of the extraction holes incidence have a high probability (70-95%) of neutralization. The other electrode was pulse-biased to extract negative or positive ions during the afterglow phase, after an ion-ion plasma had formed. The total flux and velocity distribution of extracted ions was measured using a retarding field analyser. Extraction of mono-energetic positive and negative ion beams with energies in the range 10-300 eV was demonstrated. It was shown that the beam energy can be precisely controlled by the bias waveform tailoring and by positioning of the extraction electrodes.

Applied physics reviews, Jun 1, 2016

Recently, there have been enormous efforts to tailor the properties of graphene. These improved p... more Recently, there have been enormous efforts to tailor the properties of graphene. These improved properties extend the prospect of graphene for a broad range of applications. Plasmas find applications in various fields including materials science and have been emerging in the field of nanotechnology. This review focuses on different plasma functionalization processes of graphene and its oxide counterpart. The review aims at the advantages of plasma functionalization over the conventional doping techniques. Selectivity and controllability of the plasma techniques opens up future pathways for large scale, rapid functionalization of graphene for advanced applications. We also emphasize on atmospheric pressure plasma jet as the future prospect of plasma based functionalization processes.

For guidance on citations see FAQs.

Cambridge University Press eBooks, May 5, 2011

APS, Oct 1, 2000

SF6 plasmas are routinely used for the etching of silicon in a wide range of applications includi... more SF6 plasmas are routinely used for the etching of silicon in a wide range of applications including Micro Electro-Mechanical Systems (MEMS) where etch geometry is of prime importance. Etch geometries are influenced by not only the gas phase chemistry of the plasma but also its electrical potential structure. A range of diagnostics has been deployed to examine the composition of

The process of sound reproduction in a plasma gas was researched initially in the early 1900s wit... more The process of sound reproduction in a plasma gas was researched initially in the early 1900s with development into commercially available plasma loudspeakers in the mid 1950s i and has continued to the present day. In the electro-acoustic transduction mechanism, the charged particles gain energy in the electric field and, through collisions, transfer this energy to the surrounding air molecules causing a rapid increase in the gas temperature and the dimensions of the gas volume. An ac modulation (here in the audio frequency range) of the electric field gives rise to a temperature modulation (sufficient to produce sound). As in natural lightning, the rapid expansion in the ionised column though the air produces external pressure variations at the modulation frequency. Spatial and temporal measurement of the gas temperature and the dimensional changes of the plasma relative to the audio modulation frequency can identify the nature of the thermal expansion. This provides a direct approach to understanding its relationship to the sound pressure wave that is generated. For the atmospheric pressure RF ‘warm’ plasma used in this project, the gas temperature was measured through spectroscopy by measuring the rotational line emission from nitrogen molecules. The short relaxation time between rotational to translational stage in the molecule means that a comparison between a modelled spectrum for this system and the intensity of rotational lines yields the gas temperature. For analysis of dimensional changes, the optical emissions have been measured using a CCD camera and, through Abel inversion, the radial variation can be determined from the line of sight intensity cross sections. In the final stage of this work, the various parametric investigations are being brought together to produce an overall model of a plasma loudspeaker system.

A heuristic algorithm for detecting the state of a turbo molecular pump from its sound. Find what... more A heuristic algorithm for detecting the state of a turbo molecular pump from its sound. Find what you want from DORA: All of DORA This Collection. Advanced Search. DORA. DORADe Montfort University Open Research Archive. ...

Review of Scientific Instruments, Sep 1, 2006

No related articles were found.

Pure and Applied Chemistry, 1990

The electron energy distribution function (EEDF) in a low pressure processing discharge is a good... more The electron energy distribution function (EEDF) in a low pressure processing discharge is a good indicator of the state of the plasma. Chemical kinetics are especially sensitive to the EEDF and the electron population plays a central role in coupling power into the desired surface reactions. M e s s development and transfer will be aided by a knowledge of the EEDF and its sensitivity to various process parameters. The EEDF can be measured using an electrostatic probe to sample the electron population by drawing a small current from the plasma. Electron and ion density and a characteristic electron (Maxwellian) temperature can be deduced from probe data. Furthermore, the current-voltage characteristic of the probe represents integrated EEDF information which can be recovered by differentiation. The practical use of this probe technique is considered for a variety of plasmas (both DC and RF generated). The problems associated with processing plasmas such as deposition and RF excitation are discussed with particular emphasis on 13.56MHz capacitively coupled systems. Typical data are viewed in terms of energy resolution and accuracy and conditions necessary for reliable data acquisition are considered.

Frontiers in Education, Nov 29, 2023

Teaching roles and communication strategies in interactive web broadcasts for practical lab and f... more Teaching roles and communication strategies in interactive web broadcasts for practical lab and field work at a distance.

Journal of Physics E: Scientific Instruments, Aug 1, 1987

... An electrostatic probe technique for mplasma ... authors' attention was drawn to an ... more ... An electrostatic probe technique for mplasma ... authors' attention was drawn to an article by Mosburg et a1 (1983) in which the idea of a driven probe scheme is ... p 564 Boschi A and Magistrelli F 1963 Effect of an RF signal on the characteristic of a Langmuir probe Nuouo Cimento ...

Journal of Physics D, Mar 11, 2010

We describe measurements of plasma properties of pulsed, low pressure, capacitively coupled disch... more We describe measurements of plasma properties of pulsed, low pressure, capacitively coupled discharges operated in argon. The research aims to determine the effect of modulating the radiofrequency power during the discharge part of the pulse cycle. Measurements of local electron density and optical emission were made in capacitively-coupled rf discharges generated in a Gaseous Electronics Conference (GEC) reference reactor. Gas pressure was in the range 7-70 Pa, rf power in the range 1-100 W and pulse durations in the range of 10 µs-100 ms. The results indicate that the ignition and afterglow decay processes in pulsed discharges can be controlled by modulating the shape of applied radiofrequency pulse.

Applied Physics Letters, Nov 14, 2005

A microwave measurement of electron density in low-pressure plasmas can be based on a hairpin pro... more A microwave measurement of electron density in low-pressure plasmas can be based on a hairpin probe. The hairpin forms a transmission line that supports a quarter-wavelength standing wave. The resonance is related to the relative permittivity of the surroundings, and hence, in a plasma, electron density can be evaluated. For improved fidelity, a general model is developed to include the effects of positive and negative space-charge sheaths formed around the hairpin wires. The former tends to lower the resonance, whereas the latter tends to raise it initially. This is qualitatively in agreement with experiments in dc argon plasmas.

Review of Scientific Instruments, Jul 1, 2000

This article describes how to extract accurate information about a plasma from a capacitively cou... more This article describes how to extract accurate information about a plasma from a capacitively coupled planar probe that is biased using pulsed radio-frequency excitation. The conditions necessary to observe correct saturation of the probe current are investigated, particularly the use of correct geometry and biasing for the guard ring. With these precautions the probe is an effective diagnostic for electron tail temperature at energies beyond those probed by conventional cylindrical probes. The dynamic response of the probe is investigated using conventional sweep voltages and shows the onset of displacement current and inertial effects associated with ions and electrons. In addition the effect of insulating films on the probe surface is examined, showing how the probe continues to operate even when it is coated. Characteristic changes caused by the presence of an insulating film give information about its electrical properties and its thickness.

Measurement Science and Technology, Aug 1, 1991

Two electrostatic probes have been tested simultaneously in the same plasma. The passive design u... more Two electrostatic probes have been tested simultaneously in the same plasma. The passive design uses a distributed inductive chain to block RF signals from the probe tip. The tip itself is capacitively coupled to a secondary ring electrode of large area, which effectively drives the probe tip potential in phase with the plasma space potential. The active design substitutes an externally generated sinusoidal signal (synchronous with the plasma excitation) of controllable phase and amplitude for the signal from the ring. Both probes were located on the mid-plane of a capacitively coupled RF plasma. In most cases the passive probe is found to float more positive than the active one. Both probes give results in close agreement when the plasma excitation is predominantly sinusoidal. The passive probe has a broad-band response which enables its tip to follow more closely non-sinusoidal RF potentials in the plasma. The active probe is more expensive in terms of components external to the plasma chamber but is considerably simpler to construct.