Michael J. DeVries

Dielectric function of amorphous tantalum oxide from the far infrared to the deep ultraviolet spectral region measured by spectroscopic ellipsometry

Amorphous tantalum oxide thin films were deposited by reactive rf magnetron sputtering onto [001] silicon substrates. Growth temperature, oxygen partial pressure, and total gas pressure have been varied to obtain thin films with different densities. The thin films were analyzed by glancing angle-of-incidence x-ray diffraction, atomic force microscopy, and variable angle-of-incidence spectroscopic ellipsometry in the near infrared to vacuum ultraviolet spectral region for photon energies from E=1 to 8.5 eV, and in the infrared region from E=0.03 to 1 eV. We present the dielectric function of amorphous tantalum oxide obtained by line shape analysis of the experimental ellipsometric data over the range from E=0.03 to 8.5 eV (40 μm–145 nm). In the infrared spectral region the ellipsometric data were analyzed using Lorentzian line shapes for each absorption mode observed in the spectra. Amorphous tantalum oxide optical properties in the near infrared to vacuum ultraviolet spectral region were extracted by usin...

Visible and infrared optical constants of electrochromic materials for emissivity modulation applications

Electrochromic materials are being studied for applications involving infrared emissivity modulation. The materials being investigated are amorphous WO3 and poly-crystalline WO3, NiO, and Ta2O5. Hydrogen ions are intercalated into and deintercalated from the films leading to changes in the optical properties of the materials. Visible and infrared ellipsometry are used to measure the optical constants of these materials in various states of ion intercalation and to determine the reversibility of the reactions. The spectral range for the optical constants determination is from 0.3 to 14 μm. Simulations of electrochromic device structures using these optical constants show an emissivity modulation greater than 50% for wavelengths near the peak of the room temperature blackbody curve.

Optical properties of amorphous and polycrystalline tantalum oxide thin films measured by spectroscopic ellipsometry from 0.03 to 8.5 eV

Amorphous tantalum oxide thin films were deposited by reactive r.f. magnetron sputtering onto silicon[001] substrates. Growth temperature, oxygen partial pressure and total gas pressure have been varied for optimizing thin film density. The as-deposited films were annealed in atmosphere at 700°C and transformed into a polycrystalline state. The thin films were analyzed by glancing-angle-of-incidence X-ray diffraction, and variable angle-of-incidence spectroscopic ellipsometry in the near infrared (NIR) to vacuum-ultra-violet (VUV) spectral region for photon energies from 1 to 8.5 eV, and in the infrared (IR) region from 0.03 to 1 eV. We present the IR dielectric functions of amorphous and polycrystalline tantalum oxide, which were obtained by analyzing the experimental ellipsometric data with Lorentzian lineshapes for each phonon resonance absorption. We observe a shift of the characteristic phonon absorption in tantalum oxide to lower frequencies upon sample annealing. The optical properties in the NIR to VUV were analyzed by using a parametric model approach. The dielectric functions obtained thereby were further locally fitted by Lorentzian lineshapes in order to analyze critical point structures due to electronic band-to-band transitions.

Determination of optical anisotropy in calcite from ultraviolet to mid-infrared by generalized ellipsometry

Abstract Generalized (Jones matrix) ellipsometry is gaining considerable interest because of its ability to determine properties of anisotropic samples. Here, the strong uniaxial anisotropy of calcite (calcium carbonate) was investigated using generalized ellipsometry. The wavelength range from 0.73 to 6.5 eV (190 nm to 1.7 μm) was covered using a standard variable angle spectroscopic ellipsometer; from 0.089 to 0.68 eV (1.8–14 μm), using a similar instrument based on a Fourier transform spectrometer. Measurements were made on a single air–calcite interface for which the optic axis lay nominally in the plane of the surface. To determine the optical constants and orientation of cut, both the angle of incidence and rotation of the sample about its surface normal were varied. Properties of the sample were arrived at by optimizing the parameters of a material model such that the calculated normalized Jones matrix elements best matched the measured ones. Localized spectral regions of absorption due to the internal vibrational modes of the carbonate ions were observed in the infrared at energies which differed for the ordinary and extraordinary optical constants. The certainty to which sample properties could be determined was maximized by judicious choice of measurement configurations.

Infrared emittance modulation devices using electrochromic crystalline tungsten oxide, polymer conductor, and nickel oxide

Abstract A prototypical small area electrochromic device was fabricated, and emissivity was measured from 1 to 30 microns. The devices show change in emissivity from about 0.60 to about 0.68, that is a total modulation of 13%. The emittance performance was calculated, based on the reflectivity modulation. One difference between these devices and the more frequently explored visible light transmission devices is the utilization of crystalline tungsten oxide instead of highly disordered amorphous tungsten oxide. The crystalline tungsten oxide and nickel oxide charge storage films are characterized by IR transmission/reflection, and spectroscopic ellipsometry. A theoretical model has been developed which describes the device performance to within 10% of experimental results.

Optical constants of crystalline WO3 deposited by magnetron sputtering

Crystalline WO3−x is an infrared (IR) electrochromic material having possible applications in satellite thermal control and IR switches. Optical constants of electrochromic materials change upon ion intercalation, usually with H+ or Li+. Of primary concern for device design are the optical constants in both the intercalated and deintercalated states. In situ and ex situ ellipsometric data are used to characterize both the deposition process and the optical constants of the films. Ex situ data from a UV-Vis-NIR ellipsometer are combined with data from a mid-infrared Fourier-transform-infrared-based ellipsometer to provide optical constants over a spectral range of 0.031–6.1 eV.

IR ellipsometry studies of polymers and oxygen plasma-treated polymers

Abstract An infrared variable angle spectroscopic ellipsometer (IR-VASE) was used to study organic polymers in the infrared (2.5–14 μm wavelength) spectral region. For the analysis of thin film polymers IR spectroscopic ellipsometry has greater sensitivity over traditional FTIR spectroscopy providing an exciting way to characterize these materials optically. The IR-VASE used in this study is of high accuracy, rotating polarizer, rotating compensator ellipsometer that uses an FTIR spectrometer as a light source. The IR-VASE was used to measure the infrared optical constants of various polymers in both solid and liquid form. These optical constants were then used to model the percentage of water in a thin film of gelatin and the percentage of residual solvent in a thin film of silicone. In addition, the IR-VASE provided a sensitive measurement of silicone chemistry and chemical changes caused by exposure to an oxygen plasma.

Spectroscopic Ellipsometry Characterization of Polymers Modified by Atomic Oxygen and Ultraviolet Radiation

Atomic oxygen (AO) and ultraviolet (UV) radiation-induced surface modifications of several space application polymers are investigated with spectroscopic ellipsometry (SE). The polymers studied include Kapton® polyimide, FEP Teflon®, CV-1144-0 silicone and polyarylene ether benzimidazole (PAEBI). Using in situ and ex situ SE covering a large spectral range from 190 nm to 14 μm, various parameters and trends of the polymers are measured as they are exposed to AO and/or UV light.

Dielectric tensor for interfaces and individual layers in magnetic multilayer structures

The magneto-optical Kerr response of metallic magnetic multilayers has been studied by determining the dielectric tensors (dielectric functions) for individual layers, including the magnetic and nonmagnetic interfacial layers. The diagonal components of these tensors were determined using in situ ellipsometric analysis, where the ellipsometric data were taken in real time during multilayer deposition. The off-diagonal components were determined by regression fitting magneto-optic polar Kerr rotation and ellipticity data to models supported by electromagnetic theory. The Voigt parameters (ratio between off-diagonal and diagonal components of dielectric tensors) were determined from these model fits. Higher magnitudes for the Voigt parameters were found at interfaces, corresponding with stronger Kerr responses observed in those materials. Five different magnetic multilayer systems were studied, including Pt/Co, Pd/Co, Au/Co, Cu/Co, and Pt/Fe multilayer structures. The Voigt parameters for the magnetic layer...

THICKNESS DEPENDENCE OF INTERFACIAL MAGNETO-OPTIC EFFECTS IN PT/CO MULTILAYERS

Spectroscopic ellipsometry and magneto-optic Kerr effects are measured on Pt/Co multilayers with a series of Co layer thicknesses from 0.08 to 1 nm. An electromagnetic theory of multilayered structures allows regression analysis fits between acquired data and parameter dependent model analysis. Recently, we determined the single layer Co magneto-optic Voigt parameter and found that it depends on Co layer thickness. In the present work, we report an in-depth study of interfacial magneto-optic effects for a large number of Pt/Co multilayer samples. Kerr rotation and ellipticity were measured over the spectral range from 200 to 1700 nm. Voigt parameters of the magnetic layers for these Pt/Co multilayer samples with different thicknesses were compared, and the Pt–Co interface thicknesses were determined in terms of the material dielectric tensor.