ex situ hillsboro, or 6. bennemannk.h.,(ed ... photoelastic modulators fall 2001 6 introduction...

In 1845 Michael Faraday carried out a series of experiments to determinewhether linearly polarised light, when passed through a transparentinsulator, was influenced by strong electric fields. Despite Faraday’srenowned experimental skills, he failed to observe any effects. Frustrated,he turned his attention to magnetic fields. Eventually, using quality opticalglass that he had made himself some twenty years previously, he was ableto detect a small magneto-optical change that became known as the

. Amazingly, 30 years later in 1875, the Rev. John Kerr, a closecollaborator of William Thompson (later Lord Kelvin), repeated Faraday’squest to demonstrate that electric fields can influence the polarisation stateof optical radiation as it passes though a transparent material. It is a tributeto the keen experimental skills of Kerr that, where Faraday had failed, hewas successful. Using a variety of materials, including glass and later anumber of liquids, he demonstrated the electro-optic effect. In thefollowing year on the 26th August 1876, at the annual meeting of theBritish Association for the Advancement of Science held in Glasgow, theRev. John Kerr announced a further discovery of an effect that has sincebecome known as the . Using linearly polarisedlight from a narrow paraffin flame, Kerr showed that a change inpolarisation state occurred on reflection from a polished, soft iron pole-piece of a strong electromagnet (Figure 1).

Faraday effect

Kerr magneto-optic effect

(continued on page 2)

H INDS INS TR U ME N TS , I N C .

APPLICATIONSNEWS FOR USERSOF PHOTOELASTICMODULATORS

FALL 2001

Introduction

Magnetism in a New Light

Magneto-Optic Kerr Effect2001 R&D 100 AwardExicor R&D Series®

A B O U T T H E A U T H O R

MAGNETO-OPTIC KERR EFFECT

Prof. Ron Atkinson,

Queen’s University

Belfast, UK

by Professor Ron Atkinson, Queen’s University, Belfast, UK

I N S I D E P E M

Professor Ron Atkinson is Head of the Con-densed Matter Physics and Materials ScienceDivision in the Physics Department at theQueen’s University of Belfast. He is also aFellow of the Institute of Physics, a seniormember of IEEE, and Honorary VisitingProfessor in the Department of Physics at theUniversity of Salford. Professor Atkinson tookup a lectureship in the School of Maths andPhysics at Queen’s Belfast in 1973 and isleader of the Thin Film Magneto-Optics andMagnetics group and QUB-Director of theNorthern Ireland Centre for AdvancedMaterials. He has 28 years experimental andtheoretical experience in thin film optics,magneto-optics and magnetics of multilayerednanostructures.

You may also learn more about ProfessorAtkinson and the magneto-optic Kerr effect byvisiting his website at

.http: / /wwwparent.qub.ac.uk/mp/con/magnet ics_group/magnetopt ics .html

Exicor® Wins the 2001 R&D 100 AwardJune 29, 2001, Hinds Instruments was notified that Exicor had beenselected as one of the 100 most technologically significant products of theyear. Through the combined effort and talented contributions of manyHinds employees, Exicor won the prized R&D 100 Award for the develop-ment of the technological innovation used in our birefringence measure-ment systems.

Now in its 39th year, the R&D 100 Award program is international inscope. Entries from the most prestigious companies, national laboratories,research organizations and universities are received then nominated inopen competition. The news media refers to (continued on page 4)

There can be no doubt that the real-time dynamic technique utilising thePEM provides a wealth of information that is lost to more conventionalexperiments where dynamic information, that may only last for a few seconds,is unavailable to the observer.

In addition to the exploitation of linear magneto-optics and, unimagined bythe Rev. John Kerr, there are new developments in magneto-optics that areproviding new opportunities for the application of optics to the study ofmagnetic media. The use of high intensity femtosecond lasers to generatesecond harmonic light, resulting from nonlinear interactions with magneticmedia, is promising to provide additional information about magnetic surfacesand interfaces, particularly in centrosymmetric systems . This new area is beingpursued in several centres around the world, including Belfast, and it isanticipated that the new information will complement that which is alreadybeing produced by the application of linear magneto-optics to the studyof magnetic multilayered systems.

in situex situ

in situ

Hinds Instruments has launched R&D projectsto design and build systems for measurementof low-level birefringence at UV and IRwavelengths. Initial target wavelengths are157 nm, 194 nm, and 1550 nm.

During LASER 2001, in Munich, Germany,Dr. Baoliang (Bob) Wang presented his paper“A Near Infrared Linear BirefringenceMeasurement System Using a PhotoelasticModulator.”

As requested by International SEMATECH,Dr. Wang made a presentation titled, “157 nmBirefringence Measurement System Using PEMTechnology,” at the CaF2 BirefringenceWorkshop during SEMICON West on July 18,2001 in San Francisco, California.

Bibliography1. Faraday M., Proc. R. Soc. 5, 567-569 (1845).

2. Kerr J., Phil. Mag. 3, 321-343 (1877).

3. R. Atkinson, G. Didrichsen, W.R. Hendren, I.W. Salter and R.J. Pollard, Phys.Rev. B,

62, 18, 12 294-12 302 (2000).

5. R. Atkinson, J. Phys.: Condens. Matter. 12, 7735-7745 (2000).

6. Bennemann K.H., (Ed), , Clarendon Press, Oxford, (1998).

R. Atkinson, G. Didrichsen, W.R. Hendren, I.W. Salter and R.J. Pollard, J. Phys.:

Condens. Matter. 13, 691-705 (2001).

Nonlinear Optics in Metals

P H O N E : 5 0 3 / 6 9 0 .2 0 0 0F A X : 5 0 3 / 6 9 0.3 0 0 0TOLL FREE: 1.800/6 8 8.4 4 6 3EMAIL: [email protected] SITES: www.hindspem.com

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HINDS INSTRUMENTS, INC.

U P C O M I N G T R A D E S H O W S

DATE/2002

Jan 22-24

Mar 5 - 6 .

EXHIBIT/CONFERENCE

Photonics West 2002

Microlithography 2002

LOCATION

San Jose, CA

Santa Clara, CA

N E W S A N D E V E N T S(continued from page 4)

FALL 2001 5

Hinds Instruments Introduces the Exicor R&D Seriesfor Research and Commercial Metrology

incorporates an easy to assemble, modify, and align opticsplatform. This modularity allows Exicor R&D to be offered inmany configurations. Numerous hardware and softwareapplication-specific options are available. All models areturnkey systems. Completely automated systems offerbirefringence mapping and statistical analysis of data.Alternatively, Exicor R&D systems with single point andmanual sample translation stages are available formeasurement of small optical materials and for applicationsrequiring only periodic birefringence analysis.

Exicor birefringence measurement systems are currentlyused throughout the world by industry leaders in thedevelopment and manufacture of precision optical materialsfor complex, high resolution optical imaging systems. TheExicor R&D series now offers this unsurpassed technology ina variety of options which allows for adaptation to anyapplication where high sensitivity, low-level birefringencemeasurements are critical.

The same award winning technology developed for theExicor Birefringence Measurement Systems is now availablein a modular, laboratory bench-top instrument forresearchers and laboratory quality control professionals.Like the Exicor AT Series of industrial manufacturing systems,the Exicor R&D Series’ cutting-edge sensitivity is the productof Hinds Instruments’ PEMLabs technology group whichalso pioneered the ultra-low birefringence photoelasticmodulator (PEM). This research quality instrument was de-veloped for any application requiring low-level birefringenceanalysis and characterization of a variety of materials.Birefringence characterization is increasingly important inoptical materials used in many advanced applications. Theseinclude glass, crystal materials, plastic, polymers, siliconwafers, laser materials, thin films, and LCDs.

The new modular design of the R&D Series provides thevalue and versatility necessary for supporting a broad rangeof research and industrial metrology applications. The verti-cal optical bench design of the Exicor R&D systems

the optical components, such as non-zero extinctioncoefficients of polarising prisms. In most situations, evenwhen considering shot-noise limited cases and imperfectcomponents, modulating the optical beam usually increasesprecision. Modulation may, for example, be accomplishedusing a simple chopper, a Faraday magneto-optical modula-tor, or polarisation modulator such as the PEM. The useful-ness of the chopper is restricted and precision is usually notgreat. The Faraday modulator is excellent and allows one toapproach theoretical shot-noise limits of precision. However,such modulators are often heavy, cumbersome and limitedin spectral range. More importantly, it is not possible tomeasure both Kerr rotation and ellipticity simultaneously. Incontrast, the PEM is lightweight, has a wide spectral rangeand operates at high frequency ( = 50 kHz) enabling fastmeasurements to be made. In addition, since the PEM modu-lates the polarisation state of the light passing though it, it ispossible to make measurements of both rotation andellipticity at the same time and with a precision matchingthat of the Faraday modulator.

One of the arrangements for the detection of the polarKerr effect, using the PEM, is also illustrated in Figure 2.

After the sample, the radiation passes through the modu-lator and analyser (set at 45 degrees to the principal planes)and then falls onto a detector. The detected intensity may bewritten

where is related to the source intensity and reflectivity ofthe sample and is the phase introduced by the PEM and isgiven by

Normalising the detector output to the dc componentone has to first– order in and

where is the n Bessel function. The beauty of the

θk kε

I = I0 (1+2(θ δ δ )k kcos – sinε )

δ δ ω ω π )= = .sin t 2 ft0 (

FALL 2001HINDS INSTRUMENTS, INC. 32

(continued from page 1)

Given that the changes produced by this effect are usuallyvery small (< 0.1deg) and are difficult to observe, even withmodern laser sources, the achievement of Kerr was spectac-ular. It is sobering to realise that the effects discovered over125 years ago by Kerr now form the basis of a substantialmagneto-optic recording industry.

Within the Physics Department at the Queen’s Universityof Belfast the work of Kerr continues, where linear first-ordermagneto-optical effects are being used to study the mag-netic properties of single and multiple layer materials. Tomake observations of Kerr magneto-optical effects on bulksamples is difficult enough. To do so at the atomic level,without modern light sources and optical modulation tech-niques, would be virtually impossible. However, it is theparticular technological advantages, robustness and con-venience of the Photoelastic Modulator (PEM) system thatmakes it possible to detect magneto-optical signals pro-duced by sub-atomic magnetic layers relatively easily.

The polar Kerr effect is illustrated phenomenologically inFigure 2, where linearly polarised light is incident normally(or obliquely) on a sample that may be magnetised ( ) in adirection perpendicular to the surface. After reflection, inaddition to the usual Fresnel amplitude component , a smallorthogonal Kerr component appears that, in combinationwith , leads to elliptically polarised light with a complex Kerrrotation and ellipticity given by / <<A full description of the effect, therefore, requires measure-ments of both rotation and ellipticity and it must be remem-bered that each angle may be very small. There are numerousphotometric and ellipsometric techniques available for mak-ing measurements of polarisation states of optical radiation.However, the simplest are often slow in operation and preci-sion is restricted by source instabilities and imperfections in

rk r 1θ θk k k kε ε+ i ≈

Operational Principles

Figure 1: Kerr’soriginal elctromagnetCourtesy of theHunterian Museum,Glasgow.

Magnetismin a NewLight...

Figure. 3.Schematic diagram of the deposition system.HeNe: helium neon laser, A: analyser, P: polariser,RA: rotating analyser, PEM: photoelastic modulator, M: magnetron,PC: computer, S: substrate, D: detector, LA-1: lock-in amp (50kHz),LA-2: lock-in amp (100kHz), F: field switch.

photoelastic modulation technique is that fundamental ( )and second harmonic ( ) signals are generated that aredirectly proportional to the Kerr ellipticity and rotation, re-spectively. Furthermore, the normalisation of these signalswith respect to the measured dc level serves to reduce theeffects of fluctuations in source intensity. Using lock-inamplifiers tuned to each frequency, and following simplecalibration procedures, the Kerr effect can be fully charac-terised dynamically in real-time and with considerablespeed and sensitivity. In the case described below, theprecision was typically of the order of 1 arc sec with aninstrumental time constant of 100 ms. However, this waslimited by the mechanical stability of the experimentalsystem rather than shot-noise or laser instabilities.

With this level of instrumental sensitivity, the team atQueen's has followed the growth dynamics of multiplelayers of materials such as Co-Pt, Co-Pd, and Co-Au, etc.,that have potential for next generation magneto-opticinformation storage. Both ellipsometry and Kerrpolarimetry have been used to monitor the evolution of thephysical properties of various layers in real-time as films aregrown, layer-by-layer, in a sputter deposition vacuumchamber (Figure 3). The results of such experiments givetremendous insight into both the way in which materialproperties develop, as well as fundamentally new phe-nomena. The data that is produced, if obtained comprehen-sively, may be used to optimise the geometrical structure ofthe media in order to bring out the maximum potential forapplications in magneto-optic read-out.

In situ dynamic studies of film growth.

in situ

One of the more spectacular observations that has been maderecently has been the oscillatory nature associated with theKerr signal in Co-Au multilayers . Figure 4 shows an exampleof the actual traces of the Kerr ellipticity signal monitoredduring the deposition of a ten period Co-Au multilayer on a10 nm Au buffer layer. The rapid increase in the Kerr signal isseen on the deposition of the single monolayer of Co that,of course, is the only ferromagnetic component. During thedeposition of the Au there are clear oscillations that are due toelectronic transitions to thickness dependent quantumwelllevels in the Au. Whether these are new magneto-optictransitions or not is a matter of debate. What is clear is thathere, for the first time, they are observed reproducibly,repeatedly and with great clarity in multiple bi-layers and thisis a tribute to the usefulness of the PEM technique. Anotherimportant feature of this trace is the behavior of the signalduring the deposition of the Co layer.

Shown inset, it is clear that the magnetic properties of theCo layer do not switch on immediately. The first few atomsare deposited and, being optically absorbing, they reducethe Kerr signal until eventually they cluster together insufficiently large numbers to collectively switch on theirferromagnetic behavior. When this occurs there is a rapidincrease in the Kerr signal as the Co atoms form orderedperpendicularly orientated moments, as illustrated infigure 5. This occurs at an equivalent layer thickness of about0.16 nm. (continued on page 4)

Figure 2: Arrangement for the detection of the polar Kerr effect.

FALL 2001 4

In the case of Co-Pd multilayers, observations of this typereveal vastly different behaviour . Figure 6 shows real-timetraces of Kerr rotation and ellipticity corresponding to therepeated deposition of Co and Pd onto a 10nm Pd bufferlayer. In this case, the Kerr signal produced on the depositionof the Co is several times larger than one would expect on thebasis of the magneto-optical activity of Co alone. The reasonis simple. As the ferromagnetic properties of the Co switchon there is an immediate polarization of the Pd atoms in theunderlying buffer layer and therefore the observed Kerrsignal results from a combination of both the Co and the Pd.That the Pd is polarized is clearly demonstrated as further Pdis added on top of the Co. This too becomes polarized and

induced magnetic moment of Pd, it is also clear that thismoment varies with distance from the interface. Optical andmagneto-optical modeling using classical electrodynamictheory enables the Belfast team to determine the distribu-tion of the moment of the Pd atoms (Figure 7) and also thefundamental optical and magneto-optical properties of thematerials in their ultrathin film form. From such data it ispossible to calculate the thicknesses required for the Co andPd layers that will maximise the performance of the Co-Pdsystem for magneto-optic readout . Interestingly, the Co-Ptsystem, that is assumed to have very similar properties tothose of Co-Pd, forms in a completely different way. In thecase of Co-Pd the perpendicular anisotropy is very strong andis effective immediately on the formation of the Co mono-layer and remains throughout the deposition of the Pd. Incontrast, the strong anisotropy in Co-Pt does not appearuntil the Pt is added when alloy formation at the interfaceis clearly indicated in the Kerr signal traces.

The information that is being revealed by these techniquesis considerable and has given insight into the formationprocesses in multilayered systems as well as providingphysical data from which optimised material performancecan be determined. (continued on page 6)

there is a further increase in magneto-optic signal. Eventual-ly this reaches a maximum and begins to fall back towardszero. If enough Pd were added, this would reduce themagneto-optical signal to zero owing to the effects ofoptical absorption. In addition to the clear evidence for the

— + -= (1 4J sin 2 t 4J sin t2 k 1 kθ ω ω )ε +… ,II0

Figure 4.Measured variation of the polar Kerr ellipticity during the depositionof the first three bi-layers of a glass/12.5Au/10(0.5Co/3.75nm), multilayer

Figure. 5. Schematic showing perpendicular, ordered Co momentsformed in clusters on a Au surface.

Figure 6. Measured and calculated complex polar Kerr effect duringthe continuous deposition of three Co-Pd bi-layers onto a Pd buffer layer.

Figure 7. Spatial profile of the modulus of the magneto-opticQ-parameter, proportional to magnetic moment, as a function ofdistance through a Co-Pd system.

(continued from page 1)the R&D 100 Awards as “The Oscars of Invention” and the“Nobel prizes of applied research.” Prior winning innova-tions include Polacolor film, the fax machine, the digitalwatch, the Automatic Teller Machine, and the Nicodermanti-smoking patch. Over seventy experts from a wide rangeof disciplines use a series of technical criteria to select 100 ofthe most important, unique, and innovative technologiesfrom among thousands of nominations.

As noted in our communication with the R&D 100Award committee, Exicor technology to date has beenresponsible for contributing to the solution of severalsignificant technical challenges in the semiconductor opticallithography field. These successes signify major strategicadvances for the semiconductor industry as well as thosewho rely on their product improvement stream.

Polariser

Analyser

Sample

PEMLA-1

12 16 20 24Deposition thickness (nm)

Ellipticity

Rotation

10 12 14 1816Total thickness (nm)

-2 0 2 4Distance through layers (nm)

Pd buffer

θk kε

δ δ ω ω π )= = .sin t 2 ft0 (

in situ

FALL 2001 4

Polariser

Analyser

Sample

PEMLA-1

Ellipticity

Rotation

Pd buffer

θk kε

δ δ ω ω π )= = .sin t 2 ft0 (

in situ

FALL 2001 4

Polariser

Analyser

Sample

PEMLA-1

Ellipticity

Rotation

Pd buffer

Faraday effect

H INDS INS TRUMENTS , INC .

FALL 2001

Introduction

Prof. Ron Atkinson,

Belfast, UK

I N S I D E P E M

in situex situ

in situ

2. Kerr J., Phil. Mag. 3, 321-343 (1877).

62, 18, 12 294-12 302 (2000).

Condens. Matter. 13, 691-705 (2001).

DATE/2002

Jan 22-24

Mar 5 - 6 .

EXHIBIT/CONFERENCE

Photonics West 2002

LOCATION

San Jose, CA

Santa Clara, CA

FALL 2001 5

Faraday effect

H INDS INS TR U MEN T S , INC .

FALL 2001

Introduction

Prof. Ron Atkinson,

Belfast, UK

I N S I D E P E M

in situex situ

in situ

2. Kerr J., Phil. Mag. 3, 321-343 (1877).

62, 18, 12 294-12 302 (2000).

Condens. Matter. 13, 691-705 (2001).

DATE/2002

Jan 22-24

Mar 5 - 6 .

EXHIBIT/CONFERENCE

Photonics West 2002

LOCATION

San Jose, CA

Santa Clara, CA

FALL 2001 5

ex situ hillsboro, or 6. bennemannk.h.,(ed ... photoelastic modulators fall 2001 6 introduction...

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