Engineering Commons^™

Infrared Optical Properties Of Mixed-Phase Thin Films Studied By Spectroscopic Ellipsometry Using Boron Nitride As An Example, Mathias Schubert, B. Rheinlander, E. Franke, H. Neumann, T. E. Tiwald, John A. Woollam

Department of Electrical and Computer Engineering: Faculty Publications

We present a microstructure-dependent anisotropic infrared-optical dielectric function model for mixed-phase polycrystalline material from which we derive the transverse and longitudinal-optical modes observable in thin films. Infrared ellipsometry over the wavelength range from 700 to 3000 cm^-1 is then used to determine the phase and microstructure of polycrystalline and multilayered hexagonal and cubic boron nitride thin films deposited by magnetron sputtering onto (100) silicon. The ellipsometric data depend on the thin-film multilayer structure, the layer-phase composition, and the average orientation of the hexagonal grain c axes. In particular, we demonstrate the existence of spectral shifts of longitudinal optical phonons …

Spectroscopic Ellipsometry And Magneto-Optic Kerr Effects In Co/Pt Multilayers, Xiang Gao, Darin W. Glenn, Scott Heckens, Daniel W. Thompson, John A. Woollam

Department of Electrical and Computer Engineering: Faculty Publications

Control of thickness and microstructure is critical in the preparation of ultrathin metallic multilayers for magneto-optic memory, computer read heads, and improved wear surfaces. This paper describes use of in situ spectroscopic ellipsometry to calibrate sputter deposition rates, control layer thicknesses, determine optical constants, and study oxidation rates and processes. In this work, the information gained in situ is used together with ex situ Kerr measurements to determine the complete magneto-optic response including the spectroscopic figure of merit for Co/Pt multilayers.

Frequency-Mixing Detection Of Polarization-Modulated Light Using Different Periodic Analyzers, R.M.A. Azzam

Department of Electrical and Computer Engineering: Faculty Publications

We derive the equations that permit the use of six different periodic analyzers for the frequency- mixing detection (FMD) of polarization -modulated light. The six periodic analyzers are (1) the rotating linear analyzer, (2) rotating half -wave plate and fixed linear analyzer, (3) rotating quarter -wave plate and fixed linear analyzer, (4) rotating linear analyzer and fixed linear analyzer, (5) oscillating -phase retarder and fixed linear analyzer, and (6) oscillating optical rotator and fixed linear analyzer. In all cases, the average polarization and the polarization and intensity modulation parameters of the light beam can be determined easily and explicitly from …

Phase And Microstructure Investigations Of Boron Nitride Thin Films By Spectroscopic Ellipsometry In The Visible And Infrared Spectral Range, Eva Franke, Mathias Schubert, Horst Neumann, Thomas E. Tiwald, Daniel W. Thompson, John A. Woollam, Jens Hahn, Frank Richter

Department of Electrical and Computer Engineering: Faculty Publications

Spectroscopic ellipsometry over the spectral range from 700 to 3000 cm^-1 and from 1.5 to 3.5 eV is used to simultaneously determine phase and microstructure of polycrystalline hexagonal and cubic boron nitride thin films deposited by magnetron sputtering on (100) silicon. The results are obtained from a single microstructure-dependent model for both infrared and visible-light thin-film anisotropic dielectric functions. The optical behavior of high c-BN content thin films is described by an effective medium approximation. We obtain the amount of h-BN within high c-BN content thin films. A thin oriented nucleation layer between the silicon substrate …

Multiple Order Dispersive Optics System And Method Of Use, Blaine D. Johs, Ping He, Steven E. Green, Shakil A. Pittal, John A. Woollam

Department of Electrical and Computer Engineering: Faculty Publications

Disclosed is a dispersive optics system, in the context of ellipsometer or polarimeter and the like systems. which, in use. produces a plurality of "Orders" of essentially single wavelength beams of light from a polychromatic beam of light. In use the availability of more than one "Order" of essentially single wavelength beams of light allows simultaneous measurement of more essentially single wavelength beams of light than would be possible were only one "Order" of essentially single wavelength beams of light present. Filters are present to reduce the effects of stray light on detector elements and to allow separating the wavelengths …

Determination Of The Interfacial Magneto-Optical Effects In Co/Pt Multilayer Structures, Xiang Gao, Daniel W. Thompson, John A. Woollam

Department of Electrical and Computer Engineering: Faculty Publications

In this letter, we present results of a study of the magneto-optical Kerr response in Co/Pt superlattices by solving for optical constants and Voigt parameters of constituent layers in the structure. The absolute values of the Voigt parameters of Co/Pt interfaces were found to be about twice as large as for the Co layer in the superlattice. Furthermore, using the determined optical constants and Voigt parameters, we can generate the Kerr rotations and ellipticities for Co/Pt superlattices or sandwich structures with continuously changed layer thicknesses and different repeat numbers. Comparison of these theoretical results to the experimental magneto-optical responses for …

In-Situ Ellipsometric Control Of Magnetic Multilayer Deposition (Abstract), Xiang Gao, Scott Heckens, John A. Woollam

Department of Electrical and Computer Engineering: Faculty Publications

Correct determination of layer thicknesses on a subnanometer scale is crucial for studies of giant magnetoresistance, magneto-optical (MO) Kerr rotation, magnetic interlayer coupling, and other magnetic properties of metallic multilayers. Some structures such as [Co/Ni] and [Co/Pt] with fewer than 20 repeats are difficult to be analyzed by x-ray diffraction (XRD) due to too little material. In this work, in-situ spectroscopic ellipsometry (in-situ SE) is used to precisely determine the optical constants undisturbed by oxidation, and the growth rates of different metal films deposited in a sputtering chamber. In-situ SE determines both the constant and continuously changing growth rates …

Infrared Ellipsometry On Hexagonal And Cubic Boron Nitride Thin Films, E. Franke, H. Neumann, Mathias Schubert, T. E. Tiwald, John A. Woollam, J. Hahn

Department of Electrical and Computer Engineering: Faculty Publications

Infrared spectroscopic ellipsometry (IRSE) over the wavelength range from 700 to 3000 cm^-1 has been used to study and distinguish the microstructure of polycrystalline hexagonal and cubic boron nitride thin films deposited by magnetron sputtering onto (100) silicon. The IRSE data are sensitive to the thin-film layer structure, phase composition, and average grain c-axes orientations of the hexagonal phase. We determine the amount of cubic material in high cubic boron nitride content thin films from the infrared optical dielectric function using an effective medium approach.

High-Bandwidth Attitude Jitter Determination For Pointing And Tracking Systems, Marcelo C. Algrain

Department of Electrical and Computer Engineering: Faculty Publications

For many reasons smaller spacecraft are becoming more appealing. Because of their lower inertias, these spacecraft are more sensitive to disturbances and likely to have more attitude jitter than the larger units. These jitter levels are unacceptable for some scientific instruments and need to be compensated. In the case of line-of-sight type instruments, the attitude jitter can be mitigated by incorporating a fast steering mirror into the system. To take full advantage of these devices, the spacecraft attitude must be measured at sufficiently high bandwidth, well beyond what is commonly provided by inertial reference units. Various ways to obtain higher …

An Intercomparison Of Two Tunable Diode Laser Spectrometers Used For Eddy Correlation Measurements Of Methane Flux In A Prairie Wetland, David P. Billesbach, Joon Kim, R.J. Clement, S.B Verman, F.G. Ullman

Department of Electrical and Computer Engineering: Faculty Publications

An intercomparison was made between two tunable diode laser spectrometers used to measure methane fluxes by the eddy correlation technique at a prairie wetland site. The spectrometers were built by Unisearch Associates Inc. of Concord, Ontario, Canada, and Campbell Scientific Inc. of Logan, Utah, and were models EMS-50 and TGA-100, respectively. The fluxes were found to agree very well with each other in the range of 0 to 42 mg 􏰑 m-2 h-1.

The TGA-100 was observed to exhibit offset drifts. Most of the time, when the offset was only slowly changing (as compared to the eddy correlation averaging time), …

Estimation Of Surface Snow Properties Using Combined Millimeter-Wave Backscatter And Near-Infrared Reflectance Measurements, Ram M. Narayanan, Sandy R. Jackson

Department of Electrical and Computer Engineering: Faculty Publications

Knowledge of surficial snow properties such as grain size, surface roughness, and free-water content provides clues to the metamorphic state of snow on the ground, which in turn yields information on weathering processes and climatic activity. Remote sensing techniques using combined concurrent measurements of near-infrared passive reflectance and millimeter-wave radar backscatter show promise in estimating the above snow parameters. Near-infrared reflectance is strongly dependent on snow grain size and free-water content, while millimeter-wave backscatter is primarily dependent on free-water content and, to some extent, on the surface roughness. A neural-network based inversion algorithm has been developed that optimally combines near-infrared …