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`High flux beam source of thermal rare-gas metastable atoms
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`1980 J. Phys. E: Sci. Instrum. 13 381
`
`(http://iopscience.iop.org/0022-3735/13/4/004)
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`TSMC-1105
`TSMC v. Zond, Inc.
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`J. Phys. E: Sci. Instrum., Vol. 13, 1980. Printed in Great Britain
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`Apparatus and techniques
`minimises shock overloads. This simple technique ensures
`rapid application of an accurate load. The rate of penetration
`of the indenter is thus essentially material-dependent and
`therefore enables comparisons to be made with results from
`other hardness tests, e.g. Brinell andVickers toBritishStandards
`specification. The load is maintained for a known time (e.g.
`15 s) prior to removal; recovery is allowed for a second fixed
`period. The transducer readings corresponding to the unde-
`formed sample surface, the depth of penetration under load
`and the recovered depth of indentation are fed into a computer
`which calculates the hardness and elastic modulus of the
`material, as well as parameters such as the diameter and
`volume of the indentation and the radius of the recovered
`surface. The tester can also be used to obtain data on time-
`dependent properties such as creep compliance: the load is
`maintained for the desired period and data are collected
`continuously.
`
`5 Conclusions
`This indentation tester has already been used successfully in
`the investigation of pharmaceutical tablets (Aulton et a1 1974,
`Aulton and Tebby 1976). The versatility of the tester can be
`considerably increased by changes in indentation load, type
`and size of indenter tip, and transducer characteristics.
`However, we consider the realistic applications of this instru-
`ment to be limited to materials with hardness values between
`5 and 1000 MPa.
`We suggest that this indenter could find wide use in the
`characterisation and routine quality control of materials such
`as polymer films and plastics, foodstuffs (e.g. fruit, chocolate,
`ice-cream), pharmaceuticals, and soft metals such as lead.
`
`References
`Aulton M E and Tebby H G 1976 Time-dependent
`deformations of tablets during indentation testing
`J. Pharm. Pharmac. 28 Suppl. 66P
`Aulton M E, Tebby H G and White P J P 1974
`Indentation hardness testing of tablets
`J. Pharm. Pharmac. 26 Suppl. 59P
`
`High flux beam source of thermal
`rare-gas metastable atoms
`
`D W Fahey, W F Parks and L D Schearer
`Physics Department, University of Missouri, Rolla,
`Missouri 65401
`
`Received 9 April 1979, in final form 5 October 1979
`
`Abstract A high-flux beam source has been constructed for
`the production of helium, neon and argon metastable atoms.
`The source is a DC electric discharge maintained in an
`expanding gas. A metastable flux of 3.5 x 1014, and 7.2 x 1013
`atoms s-1 sr-1 has been achieved with most probable
`energies of 66, 72 and 74 meV for the helium, neon and
`argon sources, respectively. Time-of-flight measurements
`showed the widths of the respective velocity distributions to
`be 45 %, 27 % and 27 %.
`
`1 Introduction
`A novel metastable beam source was recently described by
`Leasure et a1 (1975), whose design employed a weak, high-
`voltage corona discharge between a sharp needle and a
`cone-shaped anode. The discharge was maintained across a
`substantial pressure gradient. This source provided up to 1014
`metastable helium and argon atoms s-1 sr-1 with beam
`energies between 5 eV (helium) and 74eV (argon). The
`attractive features of this source were its relative simplicity
`and high flux.
`We report here modifications to the Leasure et a1 design
`which result in a further simplification, enhanced beam flux,
`species-independent energies, and importantly, beam energies
`only slightly in excess of thermal energies. The source is
`capable of providing very stable thermal energy beams of
`helium, neon, and argon metastable atoms with flux values
`near 1014 metastable atoms s-1 sr-1.
`
`2 Source design and operation
`The source is essentially a low-voltage discharge between a
`sharp needle and cone-shaped skimmer electrode. The dis-
`charge is maintained across a pressure gradient created by
`differentially pumping a gas nozzle. The source design is
`shown in figure 1. A vacuum fitting is mounted in a vacuum
`
`Figure 1 Beam source schematic showing Pyrex tube (A),
`boron nitride nozzle (B), skimmer (C), and needle or needle
`array (D).
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`0022-3735/80/040381+02 501.50 0 1980 The Institute of Physics
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`TSMC-1105 / Page 2 of 4
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`Apparatus and techniques
`wall and seals around a 7 mm OD Pyrex glass tube (A) that
`extends into the vacuum chamber. A machined piece of boron
`nitride (B) is attached with epoxy to form a cap for the end of
`the glass tube. A small hole drilled in this cap serves as the
`nozzle opening. The skimmer is a cone-shaped piece of
`stainless steel (C) with a small hole at the apex. Inside the glass
`tube behind the nozzle, several steel hypodermic needles are
`supported to lie near the axis of the tube. The skimmer piece
`is attached with an aluminium gasket to a vacuum wall to
`allow differential pumping of the source. Gas is admitted to
`the glass tube by a micrometer leak valve mounted outside of
`the vacuum chamber. The source region is contained inside a
`a lOcm Corning Pyrex glass cross which is evacuated by a
`300 I s-l oil diffusion pump. The reaction region is a 97 1
`stainless-steel chamber in which the pressure is maintained
`below 1.3 x 10V Pa (10-6 Torr).
`The needles behind the nozzle are the cathode of the
`electric discharge and hence are maintained at a negative
`potential with respect to the skimmer which is kept at ground
`potential. Since the needle electrode is a cold-cathode type,
`the application of the voltage necessary to sustain the dis-
`charge is not generally sufficient to initiate a discharge. It is
`therefore necessary to apply an initiating high-voltage pulse
`simultaneously with a negative DC sustaining voltage in order
`to turn on the source. The DC source discharge after initiation
`by the high voltage pulse is maintained at 3 mA and 400 V.
`The optimum nozzle pressures for the three source gases
`used were measured with a Wallace and Tiernan dial gauge to
`be 6.7 kPa (50 Torr) for He, 11.3 kPa (85 Torr) for Ne, and
`6.0 kPa (45 Torr) for Ar. The background pressure in the
`source region at these operating pressures was measured with
`an ionisation gauge at low emission current to be between
`0.13 and 0.20 Pa (1.0 and 1.5 mTorr). At 0.13 Pa helium
`background pressure the mass flow rate was determined to be
`66 Pa I s-1. The beam flux is a slowly varying function of
`operating nozzle pressure. At 2.7-6.7 KPa (20-50 Torr)
`below optimum pressure the source discharge cannot be
`sustained, and at 6.7-13.3 kPa above optimum pressure the
`beam flux is reduced to zero after slowly decreasing from the
`optimum value.
`The stability of the source output at 3 mA emission was very
`good. Degradation in source yield from use results primarily
`from wearing of the nozzle opening. After a run period of a
`month at several hours a day, the nozzle diameter is virtually
`unchanged as measured with a travelling microscope.
`
`3 Beam diagnostics
`The beam was characterised using two very different detection
`methods. The first method of detecting the beam made use of
`particle detectors. The second method used the detection of
`optical emission resulting from the interaction of the beam
`components with a strontium vapour target. Two types of
`particle detectors were used to observe all beam components
`and to estimate the absolute flux and energy of the com-
`ponents. For all diagnostic measurements, the beam was kept
`free of charged species by maintaining an adequate voltage on
`a set of parallel sweep plates mounted after the skimmer.
`
`3.1 Particle detection
`For direct particle detection, both a copper-beryllium particle
`multiplier and a specially designed metastable detector were
`used. Copper-beryllium dynodes have shown better than 50 %
`efficiency for secondary electron ejection by slow metastables
`and up to 20 % efficiency for photons below 200 nm (Dunning
`et a( 1975, Smith 1972). The surface is also sensitive to fast
`neutral ground state particles and ions of sufficient kinetic
`energy. The particle multiplier was used with a chopper wheel
`
`382
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`to analyse the time of flight (TOF) spectrum for different
`component species and their respective velocities. The
`multiplier was mounted in the chamber such that it could
`undergo displacements of up to 60cm in order to allow
`accurate measurements.
`The TOF spectrum for the helium, neon and argon beams as
`observed with the particle multiplier revealed only two peaks.
`The first is identified as the detection of resonant photons from
`the source discharge and the second as the detection of the
`respective metastable species of the source gas. A sample TOF
`spectrum is shown in figure 2 for the helium source. The
`photon peak is established by the fact that its shape matches
`the aperture function, as it must for photons, and by the fact
`that the position of the peak in time with respect to the chopper
`wheel reference signal and the shape of the peak remain
`unchanged for multiplier displacements. The velocity of the
`slower peak is established equally by its separation in time
`from the photon peak and from its displacement in time
`resulting from a spatial displacement of the multiplier.
`
`t
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`I
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`I
`0
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`I
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`I
`0 2
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`I
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`I
`04
`Time imsl
`Figure 2 TOF spectrum for the helium source for a detector-
`to-chopper wheel separation of 85 cm.
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`0 6
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`t
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`I
`08
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`t
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`I I
`1 0
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`The most probable velocity and velocity distribution of the
`metastable species were obtained by assuming a weighted
`Gaussian for the distribution (Anderson and Fenn 1965). It
`was determined by numerical integration that, for these
`measurements, the detector current was well approximated by
`the ideal case in which the chopper wheel aperture was open
`for a time negligible compared to the time of flight. In this
`ideal case the velocity distribution, f ( v ) , is proportional to the
`time-of-flight spectrum, Z ( t ) , multiplied by t 2 , where ut is the
`detector-to-chopper wheel separation. The most probable
`velocities of the calculated distribution for the three metastable
`species were 1.8 x 103 m s-l. 8.3 x 102 m s-1 and 6.0 x 102 m
`s-1 for helium, neon and argon, respectively, for source
`conditions of 3 mA discharge current and optimum nozzle
`pressures. These velocities correspond to energies of 66 meV,
`72 meV and 74 meV, respectively. The half-widths of the
`velocity distributions were 45 % for helium and 27 % for neon
`and argon.
`The specially designed metastable detector incorporates the
`principal features of a gas cell used by Dunning and Smith
`(1971) to measure secondary emission coefficients. With this
`detector absolute flux measurements of
`the metastable
`component of the beam were obtained. The sensitive surface
`was a disc of chemically cleaned stainless steel or copper from
`which secondary electrons ejected by the beam were measured.
`The secondary electron ejection coefficients for the target
`surface for the three metastable species lie very close to unity
`(Dunning and Smith 1971). The flux at 3 mA emission and
`optimum pressure for the helium, neon and argon metastables
`
`TSMC-1105 / Page 3 of 4
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`Apparatus and techniques
`was 3.5 x 1014, 1.5 x 1014, and 7.2 x 1013 atoms s-1 sr-l,
`respectively. The flux values obtained for the different target
`surfaces agreed within the coefficient uncertainty. The photon
`flux was shown to contribute much less than 1 % of the total
`secondary current.
`
`3.2 Strontium optical emission
`The metastable character of each beam was established
`independently of particle detectors by observing the optical
`excitation produced in strontium vapour titrated into the beam
`path. The metastable beam components react with strontium
`in Penning ionising collisions which can leave the strontium ion
`in an excited state. The resultant excited state emission is
`monitored as evidence of the metastable beam component. A
`spectrum of the strontium emission for each metastable beam
`revealed the SrII 52P3:2-552S1:2 emission line as the most
`intense in the visible region. This result agrees with flowing-
`afterglow emission studies that have been performed in our
`laboratory. Thus, with the added information that the beam
`energies are near thermal energy, the observed strontium
`emission is sufficient evidence of the metastable character of
`the beam.
`
`4 Source performance
`The beam source of metastable helium, neon and argon atoms
`has proved to be highly reliable and very stable, operating
`many hours per day over several months without attention.
`The high beam flux and the high stability have permitted us to
`observe the formation of coherently excited ions in Penning
`ionisation (Fahey et al 1978).
`We have also successfully extended the operation of this
`source to include molecular systems such as nitrogen. In this
`system a significant flux of A3C metastable nitrogen molecules
`is obtained. Nozzle seeding techniques to increase the beam
`velocity have also been successful. In argon, for example, the
`velocity is enhanced by a factor of 2 by the addition of
`hydrogen. In the neon source the addition of helium results in
`a 20% velocity enhancement.
`
`Acknowledgment
`This research is supported by the Office of Naval Research.
`
`References
`Anderson J B and Fenn J B 1965 Velocity distributions in
`molecular beams from nozzle sources
`Phys. Fluids 8 780-7
`Dunning F B and Smith A C 1971 Secondary electron
`ejection from metal surfaces by metastable atoms. I1
`Measurements of secondary emission coefficients using a gas
`cell method
`J. Phys. B: Atom. Molec. Phys. 4 1696-710
`Dunning F B, Rundel R D and Stebbings R F 1975
`Determination of secondary electron ejection coefficients for
`rare gas metastable atoms
`Rev. Sci. Instrum. 46 697-701
`Fahey D W, Parks W F and Schearer L D 1978 Aligned,
`excited ions from Penning ionization
`Bull. Am. Phys. Soc. 23 1088
`Leasure E L, Mueller C R and Ridley T Y 1975 ‘Hot’
`metastable atom, molecular beam source
`Rev. Sci. Instrum. 46 635-7
`Smith A B 1972 Notes on the performance and application
`of EM1 windowless particle detectors
`EMI Electronics Ltd Document RIP034
`
`3*
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`J. Phys. E: Sci. Instrum., Vol. 13, 1980. Printed in Great Britain
`
`An apparatus for the
`measurement of initial magnetic
`permeability as a function
`of temperature
`
`E Cedillo,t J Ocampo,? V Riverag and R Valenzuelag
`t Departamento de Ciencia de Materiales, Escuela Superior
`de Fisica y Matemkticas, Instituto Politecnico Nacional,
`Mexico
`$ Centro de Investigacibn de Materiales, Universidad
`Nacional Autbnoma de Mexico, Mexico Apartado Postal
`70-360, Mexico 20, D F
`
`Received 29 May 1979, in final ,form 31 October 1979
`
`Abstract A simple apparatus for the study of the quasi-static
`initial magnetic permeability as a function of temperature is
`presented. It is based on the Faraday law of electromagnetic
`induction and is especially suited for toroidal samples of
`ferrimagnetic compounds. The measurements can be
`performed at frequencies from 1 to 100 kHz, and
`temperatures from 80 to 900 K. In addition to the initial
`permeability and the Curie temperature, this apparatus
`provides a qualitative determination of the chemical
`homogeneity of the samples.
`
`1 Introduction
`The initial magnetic permeability is a very microstructure-
`sensitive property. The study of the thermal variations of
`initial permeability of polycrystalline ferrites has contributed
`to significant improvements in our knowledge of the magneti-
`sation mechanisms (Globus and Duplex 1966). It can also be
`used as a quality test (Globus and Valenzuela 1975) in the
`preparation of ferrite samples.
`Measurement of initial permeability as a function of tem-
`perature is generally performed by measuring the inductance
`of a toroidal sample on an impedance bridge at different
`temperatures. However, this technique can be tedious if the
`temperature intervals are very narrow and an interesting
`phenomenon can be missed if they are very widely spaced. At
`the Curie point the initial permeability falls from a high value
`(generally its maximum) to near 1. The verticality of this drop
`provides an evaluation of the sample’s chemical homogeneity.
`Clearly, it is difficult to estimate the homogeneity using this
`technique.
`In this paper we describe a simple apparatus for recording
`continuously the initial permeability as a function of the
`temperature, from 80 to 900 K. This apparatus is especially
`suited for toroidal samples of ferrimagnetic oxides.
`
`2 Basis of the apparatus
`The toroidal sample is used as a transformer core, and a
`sinusoidal current ip is established in the primary coil. As a
`consequence of the induction a voltage V, appears at the
`secondary coil:
`
`Vs = d+/dt
`where ns is the number of turns in the secondary coil.
`As
`
`(1)
`
`ip = io e-W,
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`0022-3735/80/040383+04 $01.50 0 1980 The Institute of Physics
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`TSMC-1105 / Page 4 of 4
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