Materials characterization is the primary application of macro- and micro-Raman spectroscopy in o... more Materials characterization is the primary application of macro- and micro-Raman spectroscopy in our laboratory. Specifically, we wish to correlate chemical bonding and short to long range translational symmetry (including amorphous, highly oriented, polycrystalline, and single crystal materials) to physical, optical and electronic properties of materials and devices. Raman spectroscopy is particularly useful in this capacity because of its origin in the vibrational motions of chemically bonded atoms and its dependence upon crystal symmetry through the polarization selection rules. Furthermore, the high spatial resolution and non-destructive nature of micro-Raman spectroscopy make it ideal for in situcharacterization of electronic and photonic devices. We will present results of materials characterization studies, performed using macro- and micro-Raman spectroscopy, of electronic and photonic devices. In addition, we will discuss how the Raman polarization selection rules can be advantageously applied to device characterization.A primary area of investigation involves the study of ion-implanted and annealed Si by Raman spectroscopy.
Peak-fitting software is frequently written to offer the user a choice of automated peak fitting ... more Peak-fitting software is frequently written to offer the user a choice of automated peak fitting or one that allows the user to enter specific values of peak shape, amplitude, and width. The shapes are most often presented as a choice of percent Gaussian or Lorentzian profile contributions to the peak. To better understand these spectral profiles, we briefly explain the physical basis of the so-called spectral line shapes. Furthermore, we discuss and model the spectral shape, bandwidth, and broadening to help the reader see how the percentage of Gaussian and Lorentzian components contribute to overall peak shape and how two closely spaced and unresolved peaks of different amplitudes or
bandwidths can affect the maximum position and overall appearance of the convolved peak.
Channel waveguides of Rb+ exchanged single-crystal KTiOPO4 were studied by micro-Raman spectrosco... more Channel waveguides of Rb+ exchanged single-crystal KTiOPO4 were studied by micro-Raman spectroscopy. Rb+ exchange causes a disruption of the long-range translational (crystal) symmetry of the lattice and a tilting of the TiO6 octahedra. The ability to nondestructively map the chemical and physical structure related to the optical properties of channel waveguides is demonstrated.
Partial ion exchange of the alkali cation in single-crystal transition metal oxides that have a h... more Partial ion exchange of the alkali cation in single-crystal transition metal oxides that have a high nonlinear susceptibility is a convenient way of fabricating waveguides for second harmonic generation.1-3
We investigated in detail the Raman scattering of barium fluorohalides BaFX (X = Cl, Br, I) in an... more We investigated in detail the Raman scattering of barium fluorohalides BaFX (X = Cl, Br, I) in an effort to characterize changes in structure and chemical bonding. The overall picture that emerges from the BaFX Raman data is that with the compositional change from X = Cl → Br → I, electron density shifts from the axial Ba-X bond to the equatorial Ba-X bonds with compositional change to the heavier halide, and that the charge distribution becomes more delocalized in the halide layers. This change in electron density indicates an increase in covalency of the Ba-X bonds from Cl to I.
The Raman spectra of crystalline and amorphous solids of the same chemical composition can be sig... more The Raman spectra of crystalline and amorphous solids of the same chemical composition can be significantly different primarily because of the presence or absence of spatial order and longrange translational symmetry, respectively. The purpose or goal of this installment of “Molecular Spectroscopy Workbench” is to help readers understand the underlying physics that affect the Raman spectra of crystalline and amorphous solids. Wave vector, reciprocal space, and the Brillouin zone are explained with respect to Raman spectroscopy of solids. Why Are the Raman Spectra of Crystalline and Amorphous Solids Different? Molecular Spectroscopy Workbench
Glass is a unique material that is often encountered in chemical and biological studies as a conv... more Glass is a unique material that is often encountered in chemical and biological studies as a convenient sample holder (vial or microscope slide in particular). If the sample is probed with light in fluorescence and Raman spectroscopic experiments, the contribution from glass is often present and can obscure the spectra from the analyte of interest. It is important to understand the nature of glass photoemission properties to control this potential interference. The Raman spectrum of glass is dominated by peaks around 500 and 1000 cm–1 at the excitation with UV and visible light. A strong broad emission band centered at 880 nm appears when glass is irradiated with near-infrared light, a popular 785 nm laser light in particular. We proved experimentally in this study that this broad band is due to glass photoluminescence and not Raman scattering. In addition, three narrow components were found to contribute to this band, which have different excitation profiles indicating that they or...
David Tuschel Photoluminescence can provide information about the composition and solid-state str... more David Tuschel Photoluminescence can provide information about the composition and solid-state structure of a material. The high spectral resolution of a Raman spectrometer can be useful in performing photoluminescence spectroscopy of solid-state materials, particularly when the emission spectra consist of narrow bands or even lines. Having the capability to perform photoluminescence and Raman spectroscopies simultaneously with the same instrument is advantageous, especially when studying two-dimensional (2D) crystals. When used to perform photoluminescence spectroscopy, the Raman spectrometer becomes two instruments in one. Photoluminescence Spectroscopy Using a Raman Spectrometer Molecular Spectroscopy Workbench
David Tuschel Segmented channel waveguides have been fabricated in single-crystal KTiOPO4 through... more David Tuschel Segmented channel waveguides have been fabricated in single-crystal KTiOPO4 through a topotactic process of partial cation exchange. The ion-exchanged waveguides maintain the high nonlinear susceptibility of KTiOPO4 to function as frequency doubling laser light sources. We applied threedimensional Raman imaging to understand and characterize the changes to the chemical bonding and crystalline structure as well as measure the volumetric structure of the waveguide segments. Three-Dimensional Raman Imaging of Ion-Exchanged Waveguides Molecular Spectroscopy Workbench
David Tuschel The Raman spectra of a particular face of a single crystal can be significantly dif... more David Tuschel The Raman spectra of a particular face of a single crystal can be significantly different if acquired with different microscope objectives. The purpose of this installment of “Molecular Spectroscopy Workbench” is to inform and educate users of micro-Raman instrumentation of the effect of the microscope objective on the Raman spectra of crystals. Furthermore, we explain the underlying physics of changes in relative intensity and even peak position of certain Raman bands depending on the microscope objective used to acquire the spectrum. Changes in peak position are attributed to phonon directional dispersion sampled through wide-angle microscope objectives with different numerical apertures. The Effect of Microscope Objectives on the Raman Spectra of Crystals Molecular Spectroscopy Workbench
Resonance and off-resonance Raman spectroscopy and imaging are used to examine the spatial variat... more Resonance and off-resonance Raman spectroscopy and imaging are used to examine the spatial variation of the solid-state structure and electronic character of few-layer MoS2 flakes. Simultaneous acquisition of photoluminescence spectra with the Raman scattering provides complementary ways of rendering Raman and photoluminescence spectral images of thin-film MoS2. Resonance Raman and Photoluminescence Spectroscopy and Imaging of Few-Layer MoS2 Molecular Spectroscopy Workbench
The fabrication of diamond films by chemical vapor deposition (CVD) has been under development fo... more The fabrication of diamond films by chemical vapor deposition (CVD) has been under development for many years now for applications including hardened surfaces, optical windows, and electrodes. The solid-state structure of these films has a direct impact on the material properties and, therefore, figures of merit of the final product. Crystallinity, single or poly, the number of defects, strain, and even the crystal face can affect performance. Furthermore, the uniformity of such films can affect the overall utility of the final product. Therefore, analytical methods are needed that can characterize the spatially varying structure of CVD diamond films. Application of Raman Polarization Selection Rules: Heterogeneous Solid-State Structure
David Tuschel Were it not for the problem of photoluminescence, only one laser excitation wavelen... more David Tuschel Were it not for the problem of photoluminescence, only one laser excitation wavelength would be necessary to perform Raman spectroscopy. Here, we examine the problem of photoluminescence from the material being analyzed and the substrate on which it is supported. We describe how to select an excitation wavelength that does not generate photoluminescence, reduces the noise level, and yields a Raman spectrum with a superior signal-to-noise ratio. Furthermore, we discuss the phenomenon of resonance Raman spectroscopy and the effect that laser excitation wavelength has on the Raman spectrum. Selecting an Excitation Wavelength for Raman Spectroscopy Molecular Spectroscopy Workbench
Emerging two-dimensional gallium chalcogenides, such as gallium telluride (GaTe), are considered ... more Emerging two-dimensional gallium chalcogenides, such as gallium telluride (GaTe), are considered promising layered semiconductors that can serve as vital building blocks towards the implementation of nanodevices in the fields of nanoelectronics, optoelectronics, and quantum photonics. However, oxidation-induced electronic, structural, and optical changes observed in ambient-exposed gallium chalcogenides need to be further investigated and addressed. Herein, we report on the thickness-dependent effect of air exposure on the Raman and photoluminescence (PL) properties of GaTe flakes, with thicknesses spanning in the range of a few layers to 100 nm. We have developed a novel chemical passivation that results in complete encapsulation of the as-exfoliated GaTe flakes in ultrathin hydrogen–silsesquioxane (HSQ) film. A combination of correlation and comparison of Raman and PL studies reveal that the HSQ-capped GaTe flakes are effectively protected from oxidation in air ambient over the st...
Materials characterization is the primary application of macro- and micro-Raman spectroscopy in o... more Materials characterization is the primary application of macro- and micro-Raman spectroscopy in our laboratory. Specifically, we wish to correlate chemical bonding and short to long range translational symmetry (including amorphous, highly oriented, polycrystalline, and single crystal materials) to physical, optical and electronic properties of materials and devices. Raman spectroscopy is particularly useful in this capacity because of its origin in the vibrational motions of chemically bonded atoms and its dependence upon crystal symmetry through the polarization selection rules. Furthermore, the high spatial resolution and non-destructive nature of micro-Raman spectroscopy make it ideal for in situcharacterization of electronic and photonic devices. We will present results of materials characterization studies, performed using macro- and micro-Raman spectroscopy, of electronic and photonic devices. In addition, we will discuss how the Raman polarization selection rules can be advantageously applied to device characterization.A primary area of investigation involves the study of ion-implanted and annealed Si by Raman spectroscopy.
Peak-fitting software is frequently written to offer the user a choice of automated peak fitting ... more Peak-fitting software is frequently written to offer the user a choice of automated peak fitting or one that allows the user to enter specific values of peak shape, amplitude, and width. The shapes are most often presented as a choice of percent Gaussian or Lorentzian profile contributions to the peak. To better understand these spectral profiles, we briefly explain the physical basis of the so-called spectral line shapes. Furthermore, we discuss and model the spectral shape, bandwidth, and broadening to help the reader see how the percentage of Gaussian and Lorentzian components contribute to overall peak shape and how two closely spaced and unresolved peaks of different amplitudes or
bandwidths can affect the maximum position and overall appearance of the convolved peak.
Channel waveguides of Rb+ exchanged single-crystal KTiOPO4 were studied by micro-Raman spectrosco... more Channel waveguides of Rb+ exchanged single-crystal KTiOPO4 were studied by micro-Raman spectroscopy. Rb+ exchange causes a disruption of the long-range translational (crystal) symmetry of the lattice and a tilting of the TiO6 octahedra. The ability to nondestructively map the chemical and physical structure related to the optical properties of channel waveguides is demonstrated.
Partial ion exchange of the alkali cation in single-crystal transition metal oxides that have a h... more Partial ion exchange of the alkali cation in single-crystal transition metal oxides that have a high nonlinear susceptibility is a convenient way of fabricating waveguides for second harmonic generation.1-3
We investigated in detail the Raman scattering of barium fluorohalides BaFX (X = Cl, Br, I) in an... more We investigated in detail the Raman scattering of barium fluorohalides BaFX (X = Cl, Br, I) in an effort to characterize changes in structure and chemical bonding. The overall picture that emerges from the BaFX Raman data is that with the compositional change from X = Cl → Br → I, electron density shifts from the axial Ba-X bond to the equatorial Ba-X bonds with compositional change to the heavier halide, and that the charge distribution becomes more delocalized in the halide layers. This change in electron density indicates an increase in covalency of the Ba-X bonds from Cl to I.
The Raman spectra of crystalline and amorphous solids of the same chemical composition can be sig... more The Raman spectra of crystalline and amorphous solids of the same chemical composition can be significantly different primarily because of the presence or absence of spatial order and longrange translational symmetry, respectively. The purpose or goal of this installment of “Molecular Spectroscopy Workbench” is to help readers understand the underlying physics that affect the Raman spectra of crystalline and amorphous solids. Wave vector, reciprocal space, and the Brillouin zone are explained with respect to Raman spectroscopy of solids. Why Are the Raman Spectra of Crystalline and Amorphous Solids Different? Molecular Spectroscopy Workbench
Glass is a unique material that is often encountered in chemical and biological studies as a conv... more Glass is a unique material that is often encountered in chemical and biological studies as a convenient sample holder (vial or microscope slide in particular). If the sample is probed with light in fluorescence and Raman spectroscopic experiments, the contribution from glass is often present and can obscure the spectra from the analyte of interest. It is important to understand the nature of glass photoemission properties to control this potential interference. The Raman spectrum of glass is dominated by peaks around 500 and 1000 cm–1 at the excitation with UV and visible light. A strong broad emission band centered at 880 nm appears when glass is irradiated with near-infrared light, a popular 785 nm laser light in particular. We proved experimentally in this study that this broad band is due to glass photoluminescence and not Raman scattering. In addition, three narrow components were found to contribute to this band, which have different excitation profiles indicating that they or...
David Tuschel Photoluminescence can provide information about the composition and solid-state str... more David Tuschel Photoluminescence can provide information about the composition and solid-state structure of a material. The high spectral resolution of a Raman spectrometer can be useful in performing photoluminescence spectroscopy of solid-state materials, particularly when the emission spectra consist of narrow bands or even lines. Having the capability to perform photoluminescence and Raman spectroscopies simultaneously with the same instrument is advantageous, especially when studying two-dimensional (2D) crystals. When used to perform photoluminescence spectroscopy, the Raman spectrometer becomes two instruments in one. Photoluminescence Spectroscopy Using a Raman Spectrometer Molecular Spectroscopy Workbench
David Tuschel Segmented channel waveguides have been fabricated in single-crystal KTiOPO4 through... more David Tuschel Segmented channel waveguides have been fabricated in single-crystal KTiOPO4 through a topotactic process of partial cation exchange. The ion-exchanged waveguides maintain the high nonlinear susceptibility of KTiOPO4 to function as frequency doubling laser light sources. We applied threedimensional Raman imaging to understand and characterize the changes to the chemical bonding and crystalline structure as well as measure the volumetric structure of the waveguide segments. Three-Dimensional Raman Imaging of Ion-Exchanged Waveguides Molecular Spectroscopy Workbench
David Tuschel The Raman spectra of a particular face of a single crystal can be significantly dif... more David Tuschel The Raman spectra of a particular face of a single crystal can be significantly different if acquired with different microscope objectives. The purpose of this installment of “Molecular Spectroscopy Workbench” is to inform and educate users of micro-Raman instrumentation of the effect of the microscope objective on the Raman spectra of crystals. Furthermore, we explain the underlying physics of changes in relative intensity and even peak position of certain Raman bands depending on the microscope objective used to acquire the spectrum. Changes in peak position are attributed to phonon directional dispersion sampled through wide-angle microscope objectives with different numerical apertures. The Effect of Microscope Objectives on the Raman Spectra of Crystals Molecular Spectroscopy Workbench
Resonance and off-resonance Raman spectroscopy and imaging are used to examine the spatial variat... more Resonance and off-resonance Raman spectroscopy and imaging are used to examine the spatial variation of the solid-state structure and electronic character of few-layer MoS2 flakes. Simultaneous acquisition of photoluminescence spectra with the Raman scattering provides complementary ways of rendering Raman and photoluminescence spectral images of thin-film MoS2. Resonance Raman and Photoluminescence Spectroscopy and Imaging of Few-Layer MoS2 Molecular Spectroscopy Workbench
The fabrication of diamond films by chemical vapor deposition (CVD) has been under development fo... more The fabrication of diamond films by chemical vapor deposition (CVD) has been under development for many years now for applications including hardened surfaces, optical windows, and electrodes. The solid-state structure of these films has a direct impact on the material properties and, therefore, figures of merit of the final product. Crystallinity, single or poly, the number of defects, strain, and even the crystal face can affect performance. Furthermore, the uniformity of such films can affect the overall utility of the final product. Therefore, analytical methods are needed that can characterize the spatially varying structure of CVD diamond films. Application of Raman Polarization Selection Rules: Heterogeneous Solid-State Structure
David Tuschel Were it not for the problem of photoluminescence, only one laser excitation wavelen... more David Tuschel Were it not for the problem of photoluminescence, only one laser excitation wavelength would be necessary to perform Raman spectroscopy. Here, we examine the problem of photoluminescence from the material being analyzed and the substrate on which it is supported. We describe how to select an excitation wavelength that does not generate photoluminescence, reduces the noise level, and yields a Raman spectrum with a superior signal-to-noise ratio. Furthermore, we discuss the phenomenon of resonance Raman spectroscopy and the effect that laser excitation wavelength has on the Raman spectrum. Selecting an Excitation Wavelength for Raman Spectroscopy Molecular Spectroscopy Workbench
Emerging two-dimensional gallium chalcogenides, such as gallium telluride (GaTe), are considered ... more Emerging two-dimensional gallium chalcogenides, such as gallium telluride (GaTe), are considered promising layered semiconductors that can serve as vital building blocks towards the implementation of nanodevices in the fields of nanoelectronics, optoelectronics, and quantum photonics. However, oxidation-induced electronic, structural, and optical changes observed in ambient-exposed gallium chalcogenides need to be further investigated and addressed. Herein, we report on the thickness-dependent effect of air exposure on the Raman and photoluminescence (PL) properties of GaTe flakes, with thicknesses spanning in the range of a few layers to 100 nm. We have developed a novel chemical passivation that results in complete encapsulation of the as-exfoliated GaTe flakes in ultrathin hydrogen–silsesquioxane (HSQ) film. A combination of correlation and comparison of Raman and PL studies reveal that the HSQ-capped GaTe flakes are effectively protected from oxidation in air ambient over the st...
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Papers by David Tuschel
bandwidths can affect the maximum position and overall appearance of the convolved peak.
bandwidths can affect the maximum position and overall appearance of the convolved peak.