Ion implantation and thermal annealing of α-Al2O3-Nov.19,2010

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    H. Naramoto, C.W. White, J.M. Williams, C.J. McHargue, O.W.

    Holland., M.M. Abraham, and B.R. Appleton

    Solid State Division, OakRidge National Laboratory, Oak Ridge, Tennessee

    Presentation by: Younes Sina

    Ion implantation and thermal annealingof-Al2O3 single crystals

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    Experimental

    Single crystal of Al2O3 of high purity

    (100 ppm total) with low dislocation

    density (103-104 cm-2) from Union

    Carbide Corp., and Crystal System, Inc.

    Sample preparation

    Disc specimens were cut perpendicular(to within 2) to the (c axis)

    and (a axis) from single

    crystalline rods using a diamond saw.

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    Experimental

    Sample preparation

    These specimens were polished to a mirrorlike surface

    finish with a fine diamond paste(< 1 Qm mesh) andannealed at 1200 C in air for 120 h to remove the

    surface damage induced by mechanical polishing.

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    280 or 300 keV

    52 Cr+

    1016-1017 ions/cm2

    7 off

    Current density : < 210-6 amp/cm2

    Estimated temperature during implantation due

    to beam heating : 150C

    Implanted region

    Unimplanted region(virgin)

    musk

    Experimental

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    Thermal annealing in air

    1 hr800C to 1600 C

    RBS

    Ion scattering /channeling

    Using 2 MeV4

    He+

    Experimental

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    Determine the depth profile of the implanted species

    Depth distribution of damage in the lattice

    Lattice location of the impurity

    Using RBS to

    Experimental

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    Experimental

    Some details about RBS

    There are no strong nuclear reaction to complicate the

    backscattering analysis using 2 MeV 4He+.

    Random spectra were obtained while continuously rotating the

    crystal to average over all crystallographic directions.

    The specimens were covered with a stainless- steel plate with a

    small open aperture for analysis to minimize the charge buildup.

    The probing beam current was held to b10 nA ( b1 mm diameter).The scattered ion detector was cooled with Freon to b22C, which

    improved the energy resolution to b14 keV.A scattering angle of 160was used for analysis.

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    Lattice location measurements were carried out using

    both aligned axial channeling spectra as well as detailed

    angular scans across the following major axes andplanes:

    , , , {0001} , {1-210} , and {10-10}

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    Experimental

    Angular scan measurements were taken only after

    annealing to T=1300 and 1500.

    After these temperatures, substantial recovery of

    displacement damage in both the Al and O sublattices

    occurs.

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    Experimental

    The valence state of the implanted impurity after

    thermal annealing was determined using standard

    Electron Paramagnetic Resonance (EPR) absorption

    measurements.

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    Experimental

    EPR absorption measurement were made using a

    K- band microwave spectrometer (35 GHz, 1.2 cm-1)

    with the magnetic field applied perpendicular to the

    axis of the crystal.

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    Experimental

    Changes in the hardness were measured by the useof the Knoop microhardness technique.

    A force of 0.147 N was used inorder to confine the impression

    depth to the near- surface region

    (b0.3Q which is correspondsroughly to the full width of a typical

    Gaussian distribution of theimplanted impurity ).

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    Results and Discussion

    Implantation damage

    2- MeV He+ backscattering spectra from 52Cr(280 keV,

    31016/cm2) implanted -Al2

    O3

    .

    Random

    aligned

    virgin

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    Results and Discussion

    Implantation damage

    2- MeV He+ backscattering spectra from 52Cr(280 keV,

    31016/cm2) implanted -Al2

    O3

    .

    Random

    aligned

    virgin

    Al surface peak

    O surface peak

    (Random)Yield

    (Aligned)Yieldmin !

    %1.2(Al)min }

    %6.0(O)min }

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    Results and Discussion

    The near-surface region was not turned

    amorphous by implantation (the aligned

    yield after implantation dose not reach the

    random value).

    We have not observed a completely disordered surface

    region up to dose of 11017/cm2. This is in contrast to the

    case of semiconductors such as Si, where dose of 1014-

    1015/cm2 would be sufficient to turn the near- surface region

    completely amorphous.

    Random aligned

    virgin The implanted Cr shows a small

    channeling effect (the aligned yield

    is b85% of the random yield)

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    Results and Discussion

    The fact that Al2O3 is not turned amorphous at theseimplantation energies and doses is inconsistent with the

    existence of a reordering process during implantation.

    The implanted Cr shows a small channeling effect (the

    aligned yield is b85% of the random yield), againsuggesting a reordering process during implantation.

    Sample temperatures during implantation are estimatedto less than 150C, and if the ion beam current is

    reduced by an order of magnitude, there is no significant

    change in the damage distribution.

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    Results and Discussion

    Effect of integrated dose

    Effect of integrated dose on the damage distribution produced as

    a result of 300- keV implantation.

    Random

    Align virgin

    Align (11016/cm2)

    Align (11017/cm2)

    The near-surface region is

    relatively damage free.

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    Results and Discussion

    The main effect of increasing dose is to broaden the damage

    profile to greater depth with little or no increase in the magnitudeof the damage level.

    Higher surface peak

    11017/cm2)

    11016

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    Results and Discussion

    Plot of the dose dependence of minmeasured in the Al substrate at a depth

    corresponding to the peak in the implanted

    Cr distribution.

    These result shows that min (Al)is essentially independent of

    implantation dose, indicating a

    saturation of damage along all

    three crystallographic direction.

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    Results and Discussion

    Thermal annealing behavior of 52Cr(300 keV, 11017/cm2) implanted -Al2O3

    Thermal annealing behavior No change in the damage distribution in the O or Cr

    Damage recovery for Cr &O

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    Results and Discussion

    Thermal annealing behavior

    Thermal annealing behavior of52

    Cr(280 keV, 31016

    /cm2

    ) implanted -Al2O3

    Change in the damage distribution in the Al & O & Cr

    Damage recovery for Cr &O

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    Results and Discussion

    Thermal annealing behavior

    From the results presented so far, it is impossible to

    determine whether Cr becomes substituonal in the Al or

    O sublattice, but the angular scan results clearly show

    that Cr is substitutional in the Al sublattice.

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    Results and Discussion

    Thermal annealing behavior

    52Cr(300 keV, 11017/cm2)52Cr(280 keV, 31016/cm2)

    Random

    aligned

    virgin

    Random aligned

    virgin

    Aligned yield for Al and O is very close to the virgin yield.

    Aligned yield for Al is very close to the virgin yield.

    The dechanneling rate in the near-surface region is greater for the high-dose

    crystal compared to the lower dose case.

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    Results and Discussion

    Thermal annealing behavior

    This increased dechanneling in the near-surface region,

    which is a function of the dose (or concentration) of the

    impurity, may be due to either residual defects or to

    lattice strain resulting from the incorporation of large

    concentrations of Cr into the Al sublattice.

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    Results and Discussion

    Thermal annealing behavior

    Comparison of total and substitutional concentration for 52Cr(300 keV,11017/cm2) in

    -Al2O3 after annealing at 1500

    C

    %98( l)][1

    (Cr)][1(%)Fractiononalsubstituti

    min

    min "

    !

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    Results and Discussion

    Thermal annealing behavior

    Thermal annealing behavior for 52Cr (300 keV, 11016/cm2) in -Al2O3

    Random

    aligned

    virgin

    Random

    aligned

    virgin

    Random

    aligned

    virgin

    Substantial redistribution of the dopant occurs in

    the range of 1500-1600 C.

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    Results and Discussion

    Thermal annealing behavior

    Concentration profile for 52Cr(300 keV, 11017/cm2) in -Al2O3 after annealing at

    1500C and 1600C compared to as-implanted profile.

    Substantial redistribution of the dopant occurs in

    the range of 1500-1600

    C.

    After annealing at 1600C, Cr is

    observed to be redistribution bothtoward the surface and into the crystal.

    Cr diffuses by a substitutional

    diffusion mechanism

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    Results and Discussion

    Thermal annealing behavior

    Results:

    Damage recovery begins selectively in the Al sublattice

    at a temperature ofb800C.Damage recovery begins in the O sublattice at

    b1000C.Incorporation of Cr into substitutional lattice sites

    occurs predominantly in the temperature range 1200-

    1500C. After 1500C annealing, Cr is 95%

    substitutional in the lattice.

    The onset of substitutional Cr diffusion occurs in the

    temperature range 1500-1600C.

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    Results and Discussion

    Thermal annealing behavior

    The features of Cr incorporation can be better

    distinguished by separating the Cr profile into three

    different segments:

    (1)0.05 Qm(2)0.05-0.15 Qm

    (3)0.15-0.3 Qm

    Results:

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    Results and Discussion

    Thermal annealing behavior

    Results:

    (1) 0.05 Qm(2) 0.05-0.15 Qm

    (3) 0.15-0.3 Qm

    Where damage is the least in the as-implanted condition

    The min(Cr) value increases slightly with annealing temperature

    up to 1200C even though min(Al) decreases, indicating no

    further incorporation of Cr at this depth into substitutional lattice

    sites in this temperature range.

    In region (1):In region (1):

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    Results and Discussion

    Thermal annealing behavior

    Results: (1) 0.05 Qm

    (2) 0.05-0.15 Qm(3) 0.15-0.3 Qm

    Surface side of the damage distribution, min(Cr) change very

    little with annealing to 1200C

    In region (2):In region (2):

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    Results and Discussion

    Thermal annealing behavior

    Results: (1) 0.05 Qm

    (2) 0.05-0.15 Qm(3) 0.15-0.3 Qm

    Saturation of damage occurred in the as-implanted state,

    min(Cr) decreased with annealing up to b1200C.

    In region (3):In region (3):

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    Results and Discussion

    Thermal annealing behavior

    Results:

    (1) 0.05 Qm

    (2) 0.05-0.15 Qm

    (3) 0.15-0.3 Qm

    These results suggest that up to 1200C, damage

    recovery in Al sublattice competes with Cr

    incorporation.With annealing to 1500C, min(Cr)

    decreases substantially in region (2) and (3), whilethe aligned yield in the oxygen sublattice increases

    slightly. These results suggest that Cr incorporation

    in region (2) and (3) may be accompanied by oxygen

    indiffusion from the surface during annealing at thehigher temperatures.

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    Results and Discussion

    Results:

    Thermal annealing behavior

    Summary of thermal annealing result for52Cr(300 keV, 11017/cm2) in -Al2O3

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    Results and Discussion

    Lattice location of implanted 52Cr in Al2O3 after thermal annealing

    4a

    4c

    4b

    4d 7b

    7c7a

    5a5b

    5c

    Results presented in previous Figs. suggest that implanted Cr is

    substitutional in -Al2

    O3

    after thermal annealing to temperatures

    in the range of 1300-1500 C, because the implanted Cr exhibits

    a pronounced channeling effect. However these measurements

    alone are not sufficient to determine weather Cr is substitutional

    in the Al or O sublattice.

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    Results and Discussion

    Lattice location of implanted 52Cr in Al2O3 after thermal annealing

    To determine whether Cr is substitutional in the Al or Osublattice, angular scans across the major axis and

    planes are necessary.

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    Results and Discussion

    Lattice location of implanted 52Cr in Al2O3 after thermal annealing

    Axial angular scans for 2-MeV He+ incident on virgin -Al2O3(depth range=0.05-0.35)

    Yield of particles scattered from Al and O atoms in depth interval 0.05-0.35 Qmnormalized to the random value plotted as a function of tilt angle away from the major

    axis or plane

    2 1/2: full width at half maximum of the channeling dip

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    Results and Discussion

    Lattice location of implanted 52Cr in Al2O3 after thermal annealing

    Planar angular scans for 2-MeV He+ incident on virgin -Al2O3(depth range=0.05-0.35)

    2 1/2: full width at half maximum of the channeling dip

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    Results and Discussion

    Lattice location of implanted 52Cr in Al2O3 after thermal annealing

    "! 1021cutx"! 0001cutz

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    Results and Discussion

    Lattice location of implanted 52Cr in Al2O3 after thermal annealing

    Calculated and measured planar channeling critical half angles

    (1/2) for 2-MeV He+ scattering from Al, O, and Cr atoms in virgin

    and Cr-implanted -Al2O3.

    Uncertainties in the experimental critical half angles are estimated to be 10% of the measured

    value.

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    Results and Discussion

    Lattice location of implanted 52Cr in Al2O3 after thermal annealing

    Calculated and measured axial channeling critical half angles(1/2) for 2-MeV He

    + scattering from Al, O, and Cr atoms in virgin

    and Cr-implanted -Al2O3.

    Uncertainties in the experimental critical half angles are estimated to be 10% of the measured

    value.

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    Results and Discussion

    Lattice location of implanted 52Cr in Al2O3 after thermal annealing

    Critical angles for both axis and planar were calculatedusing Barrett method:

    2/112/1 )]/)([ EmVk Q] !

    Adjustable parameters

    k=0.76, m=1.6 (for planar critical angles)k=0.83, m=1.2 (for axial critical angles)

    Mean one- dimensional vibrational amplitude( for planes)

    Mean two- dimensional vibrational amplitude( for axis)

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    Results and Discussion

    Lattice location of implanted 52Cr in Al2O3 after thermal annealing

    The potential was calculated using a model given by :

    0VVV il ji !Contribution to the continuum potential due to

    the jth atomic species in the ith plane

    A constant to make the minimum potential energy equal to zero

    Such a model assumes that mixed atomic sheets such

    as the Al2 + O sheet in the {10-10} planar channel can

    be treated as a superposition of atomic sheets each

    with a unique atomic species.

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    Results and Discussion

    Lattice location of implanted 52Cr in Al2O3 after thermal annealing

    Thermal vibrational amplitudes were determined usinga Debye model of the solid with a Debye temperature

    of 1034K.

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    Results and Discussion

    Lattice location of implanted 52Cr in Al2O3 after thermal annealing

    Static continuum potential for the various major planes in Al2O3. The atomic

    constituent is indicated for each plane in a given configuration by the atomic

    symbol, and a superscript which indicates relative atomic abundance.

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    Results and Discussion

    Lattice location of implanted 52Cr in Al2O3 after thermal annealing

    O3

    Al

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    Results and Discussion

    Lattice location of implanted 52Cr in Al2O3 after thermal annealing

    (Al green, O red)

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    Results and Discussion

    Lattice location of implanted 52Cr in Al2O3 after thermal annealing

    There is a good agreement between experiment andtheory data of channeling critical half angles.

    Therefore all assumptions during calculated angles

    can be justified.

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    Results and Discussion

    Lattice location of implanted 52Cr in Al2O3 after thermal annealing

    Angular scans on implanted crystals were obtained using

    crystals implanted to dose of 1 and 31016/cm2 after thermal

    annealing at temperatures of 1300 and 1500 C.

    Angular scan across the axis for 52Cr (300 keV, 11016/cm2) in Al2O3 after

    1300C annealing.

    Critical angles for scattering from Al and Cr have approximately the same width.

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    Results and Discussion

    Lattice location of implanted 52Cr in Al2O3 after thermal annealing

    Critical angles for scattering from Al and Cr haveapproximately the same width but different from O.

    Most of Cr atoms are substitutional in the Al sublattice

    There are some Cr and O atoms in interstitial lattice

    sites after annealing at 1300C. Interstitial Cr can

    trap O atoms and diffuses in from surface during

    annealing.

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    Results and Discussion

    Lattice location of implanted 52Cr in Al2O3 after thermal annealing

    Al & O critical angle after Cr implantation and annealing

    Al O

    1300C

    Al & O critical angle for the virgin sample

    Al critical angle is considerably wider on the

    implanted crystal compared to the virgin,

    indicating that damage recovery is not complete

    after annealing at this temperature.

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    Results and Discussion

    Lattice location of implanted 52Cr in Al2O3 after thermal annealing

    Axial angular scan for 52Cr(280keV, 31016/cm2) in -Al2O3

    1500 C thermal annealing

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    Results and Discussion

    Lattice location of implanted 52Cr in Al2O3 after thermal annealing

    Planar angular scan for 52Cr(280keV, 31016/cm2) in -Al2O3

    1500 C thermal annealing

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    Results and Discussion

    Lattice location of implanted 52Cr in Al2O3 after thermal annealing

    Axial angular scan for52Cr(280keV, 31016/cm2) in

    -Al2O3

    1500 C thermal annealing

    Al & O critical angle for the

    virgin sample

    Axial angular scan for52Cr(300keV,

    31016/cm2) in -Al2O3

    1300 C thermal annealing

    Comparison of axial/planar angular scans for different cases shows that critical angle

    in higher annealing temperature is closer to the virgin case.

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    Results and Discussion

    Lattice location of implanted 52Cr in Al2O3 after thermal annealing

    Conclusion: Near-surface region is not turn completely

    amorphous with Cr implantation on sapphire at

    doses less than 1017/cm2.

    Upon annealing, damage recovery beginsselectively in the Al sublattice at T~800 C.

    Recovery in the oxygen sublattice begins at

    T~1000 C for Cr.

    After Cr implantation followed by thermalannealing at ~1500 C, the implanted impurity is

    observed to be >95% substitutional in the Al

    sublattice.

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    Valence state of implanted 52Cr

    The valence state of the implanted impurity can bedetermined usingElectron Paramagnetic Resonance

    absorption (EPR) techniques.

    The EPR spectrum of substitutional trivalent chromium

    ions (Cr3+) in Al2O3 may be described by the followingspin Hamiltonian:

    ]3/)1([)(2

    ! B SSSDSHSHgSHgH zyyxxBzzB QQ

    1cm0.382D1.987,g1.984,g3/2,S B

    !!!!

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    EPR spectroscopy is the measurement and interpretation of the

    energy differences between the atomic or molecular states.

    These measurements are obtained because the relationship

    between the energy differences and the absorption of electro-

    magnetic radiation.

    To acquire a spectrum, the frequency of the electromagnetic

    radiation is changed and the amount of radiation which passesthrough the sample with a detector is measured to observe the

    spectroscopic absorptions.

    EPR Spectroscopy

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    EP

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    EP

    R

    Like a proton, an electron has a spin, which gives it a magnetic

    property known as a magnetic moment.

    When an external magnetic field is supplied, the paramagneticelectrons can either orient in a direction parallel or antiparallel to

    the direction of the magnetic field .

    This creates two distinct energy levels for the unpaired electrons

    and measurements are taken as they are driven between the two

    levels.

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    -Al2O3 with trace Cr3+ impurity

    Valence state of implanted 52Cr

    52Cr(300keV, 11016/cm2) in -Al2O3

    EPR line shape of high

    field Cr3+ absorption line

    (Ms=-1/2Ms=-3/2)

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    Microhardness change of Al2O3 with52Cr implantation followed by thermal annealing

    HARDNESS CHANGES DUE TO ANNEALINGFor implanted Cr(1017/cm2) and Zr (41019/cm2) in - Al2O3

    Annealing temperature(C)

    Th k

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    Kurdish rug with hexagonal grid

    Thank you

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    EPR spectroscopy is the measurement and interpretation of the

    energy differences between the atomic or molecular states.

    These measurements are obtained because the relationship

    between the energy differences and the absorption of electro-

    magnetic radiation.

    To acquire a spectrum, the frequency of the electromagnetic

    radiation is changed and the amount of radiation which passesthrough the sample with a detector is measured to observe the

    spectroscopic absorptions.

    EPR Spectroscopy

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    EP

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    R

    Like a proton, an electron has a spin, which gives it a magnetic

    property known as a magnetic moment.

    When an external magnetic field is supplied, the paramagneticelectrons can either orient in a direction parallel or antiparallel to

    the direction of the magnetic field .

    This creates two distinct energy levels for the unpaired electrons

    and measurements are taken as they are driven between the two

    levels.