| 1. |
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| 2. |
- Klionsky, Daniel J., et al.
(författare)
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Guidelines for the use and interpretation of assays for monitoring autophagy
- 2012
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Ingår i: Autophagy. - : Informa UK Limited. - 1554-8635 .- 1554-8627. ; 8:4, s. 445-544
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Forskningsöversikt (refereegranskat)abstract
- In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. A key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process vs. those that measure flux through the autophagy pathway (i.e., the complete process); thus, a block in macroautophagy that results in autophagosome accumulation needs to be differentiated from stimuli that result in increased autophagic activity, defined as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (in most higher eukaryotes and some protists such as Dictyostelium) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the field understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular autophagy assays, we hope to encourage technical innovation in the field.
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| 3. |
- Gogova, Daniela, et al.
(författare)
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Epitaxial growth of β -Ga 2 O 3 by hot-wall MOCVD
- 2022
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 12:5, s. 055022-055022
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Tidskriftsartikel (refereegranskat)abstract
- The hot-wall metalorganic chemical vapor deposition (MOCVD) concept, previously shown to enable superior material quality and highperformance devices based on wide bandgap semiconductors, such as Ga(Al)N and SiC, has been applied to the epitaxial growth ofβ-Ga2O3. Epitaxial β-Ga2O3 layers at high growth rates (above 1 μm/h), at low reagent flows, and at reduced growth temperatures(740 ○C) are demonstrated. A high crystalline quality epitaxial material on a c-plane sapphire substrate is attained as corroborated by a combination of x-ray diffraction, high-resolution scanning transmission electron microscopy, and spectroscopic ellipsometry measurements. Thehot-wall MOCVD process is transferred to homoepitaxy, and single-crystalline homoepitaxial β-Ga2O3 layers are demonstrated with a 201 ¯rocking curve width of 118 arc sec, which is comparable to those of the edge-defined film-fed grown (201) ¯ β-Ga2O3 substrates, indicative ofsimilar dislocation densities for epilayers and substrates. Hence, hot-wall MOCVD is proposed as a prospective growth method to be furtherexplored for the fabrication of β-Ga2O3
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| 4. |
- Gogova, Daniela, 1967-, et al.
(författare)
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Epitaxial growth of β-Ga2O3 by hot-wall MOCVD
- 2022
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Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 12:5
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Tidskriftsartikel (refereegranskat)abstract
- The hot-wall metalorganic chemical vapor deposition (MOCVD) concept, previously shown to enable superior material quality and high performance devices based on wide bandgap semiconductors, such as Ga(Al)N and SiC, has been applied to the epitaxial growth of beta-Ga2O3. Epitaxial beta-Ga2O3 layers at high growth rates (above 1 mu m/h), at low reagent flows, and at reduced growth temperatures (740 degrees C) are demonstrated. A high crystalline quality epitaxial material on a c-plane sapphire substrate is attained as corroborated by a combination of x-ray diffraction, high-resolution scanning transmission electron microscopy, and spectroscopic ellipsometry measurements. The hot-wall MOCVD process is transferred to homoepitaxy, and single-crystalline homoepitaxial beta-Ga2O3 layers are demonstrated with a 201 rocking curve width of 118 arc sec, which is comparable to those of the edge-defined film-fed grown (201) beta-Ga2O3 substrates, indicative of similar dislocation densities for epilayers and substrates. Hence, hot-wall MOCVD is proposed as a prospective growth method to be further explored for the fabrication of beta-Ga2O3.
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| 5. |
- Hilfiker, Matthew, et al.
(författare)
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Anisotropic dielectric function, direction dependent bandgap energy, band order, and indirect to direct gap crossover in α-(AlxGa1−x)2O3 (0≤?≤10≤x≤1)
- 2022
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 121:5
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Tidskriftsartikel (refereegranskat)abstract
- Mueller matrix spectroscopic ellipsometry is applied to determine anisotropic optical properties for a set of single-crystal rhombohedral structure alpha-(AlxGa1-x)(2)O-3 thin films (0 <= x <= 1). Samples are grown by plasma-assisted molecular beam epitaxy on m-plane sapphire. A critical-point model is used to render a spectroscopic model dielectric function tensor and to determine direct electronic band-to-band transition parameters, including the direction dependent two lowest-photon energy band-to-band transitions associated with the anisotropic bandgap. We obtain the composition dependence of the direction dependent two lowest band-to-band transitions with separate bandgap bowing parameters associated with the perpendicular (b(Eg,⊥) = 1.31 eV) and parallel (b(Eg,||) = 1.61 eV) electric field polarization to the lattice c direction. Our density functional theory calculations indicate a transition from indirect to direct characteristics between alpha-Ga2O3 and alpha-Al2O3, respectively, and we identify a switch in band order where the lowest band-to-band transition occurs with polarization perpendicular to c in alpha-Ga2O3 whereas for alpha-Al2O3 the lowest transition occurs with polarization parallel to c. We estimate that the change in band order occurs at approximately 40% Al content. Additionally, the characteristic of the lowest energy critical point transition for polarization parallel to c changes from M-1 type in alpha-Ga2O3 to M-0 type van Hove singularity in alpha-Al2O3.
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| 6. |
- Hilfiker, Matthew, et al.
(författare)
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Anisotropic dielectric functions, band-to-band transitions, and critical points in alpha-Ga2O3
- 2021
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Ingår i: Applied Physics Letters. - : AMER INST PHYSICS. - 0003-6951 .- 1077-3118. ; 118:6
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Tidskriftsartikel (refereegranskat)abstract
- We use a combined generalized spectroscopic ellipsometry and density functional theory approach to determine and analyze the anisotropic dielectric functions of an alpha -Ga2O3 thin film. The sample is grown epitaxially by plasma-assisted molecular beam epitaxy on m-plane sapphire. Generalized spectroscopic ellipsometry data from multiple sample azimuths in the spectral range from 0.73eV to 8.75eV are simultaneously analyzed. Density functional theory is used to calculate the valence and conduction band structure. We identify, for the indirect-bandgap material, two direct band-to-band transitions with M-0-type van Hove singularities for polarization perpendicular to the c axis, E 0 , perpendicular to = 5.46 ( 6 ) eV and E 0 , perpendicular to = 6.04 ( 1 ) eV, and one direct band-to-band transition with M-1-type van Hove singularity for polarization parallel to E 0 , | | = 5.44 ( 2 ) eV. We further identify excitonic contributions with a small binding energy of 7meV associated with the lowest ordinary transition and a hyperbolic exciton at the M-1-type critical point with a large binding energy of 178meV.
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| 7. |
- Hilfiker, Matthew, et al.
(författare)
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Dielectric function tensor (1.5 eV to 9.0 eV), anisotropy, and band to band transitions of monoclinic -(AlxGa1-x)(2)O-3 (x 0.21) films
- 2019
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Ingår i: Applied Physics Letters. - : AMER INST PHYSICS. - 0003-6951 .- 1077-3118. ; 114:23
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Tidskriftsartikel (refereegranskat)abstract
- A set of monoclinic -(AlxGa1-x)(2)O-3 films coherently grown by plasma-assisted molecular beam epitaxy onto (010)-oriented -Ga2O3 substrates for compositions x0.21 is investigated by generalized spectroscopic ellipsometry at room temperature in the spectral range of 1.5eV-9.0eV. We present the composition dependence of the excitonic and band to band transition energy parameters using a previously described eigendielectric summation approach for -Ga2O3 from the study by Mock et al. All energies shift to a shorter wavelength with the increasing Al content in accordance with the much larger fundamental band to band transition energies of Al2O3 regardless of crystal symmetry. The observed increase in the lowest band to band transition energy is in excellent agreement with recent theoretical predictions. The most important observation is that charge confinement in heterostructures will strongly depend on the growth condition due to the strongly anisotropic properties of the band to band transitions.
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| 8. |
- Hilfiker, Matthew, et al.
(författare)
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Elevated temperature spectroscopic ellipsometry analysis of the dielectric function, exciton, band-to-band transition, and high-frequency dielectric constant properties for single-crystal ZnGa2O4
- 2022
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 120:13
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Tidskriftsartikel (refereegranskat)abstract
- We report the elevated temperature (22 degrees C <= T <= 600 degrees C) dielectric function properties of melt grown single crystal ZnGa2O4 using a spectroscopic ellipsometry approach. A temperature dependent Cauchy dispersion analysis was applied across the transparent spectrum to determine the high-frequency index of refraction yielding a temperature dependent slope of 3.885(2) x 10(-5)K(-1). A model dielectric function critical point analysis was applied to examine the dielectric function and critical point transitions for each temperature. The lowest energy M-0-type critical point associated with the direct bandgap transition in ZnGa2O4 is shown to red-shift linearly as the temperature is increased with a subsequent slope of -0.72(4) meV K-1. Furthermore, increasing the temperature results in a reduction of the excitonic amplitude and increase in the exciton broadening akin to exciton evaporation and lifetime shortening. This matches current theoretical understanding of excitonic behavior and critically provides justification for an anharmonic broadened Lorentz oscillator to be applied for model analysis of excitonic contributions.
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| 9. |
- Hilfiker, Matthew, et al.
(författare)
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High-frequency and below bandgap anisotropic dielectric constants in alpha-(AlxGa1-x)(2)O-3 (0 <= x <= 1)
- 2021
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 119:9
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Tidskriftsartikel (refereegranskat)abstract
- A Mueller matrix spectroscopic ellipsometry approach was used to investigate the anisotropic dielectric constants of corundum alpha-(AlxGa1-x)(2)O-3 thin films in their below bandgap spectral regions. The sample set was epitaxially grown using plasma-assisted molecular beam epitaxy on m-plane sapphire. The spectroscopic ellipsometry measurements were performed at multiple azimuthal angles to resolve the uniaxial dielectric properties. A Cauchy dispersion model was applied, and high-frequency dielectric constants are determined for polarization perpendicular (epsilon(infinity,perpendicular to)) and parallel (epsilon(infinity,parallel to)) to the thin film c-axis. The optical birefringence is negative throughout the composition range, and the overall index of refraction substantially decreases upon incorporation of Al. We find small bowing parameters of the highfrequency dielectric constants with b(perpendicular to) = 0:386 and b(parallel to) = 0:307. Published under an exclusive license by AIP Publishing.
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| 10. |
- Hilfiker, Matthew, et al.
(författare)
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Zinc gallate spinel dielectric function, band-to-band transitions, and Gamma-point effective mass parameters
- 2021
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Ingår i: Applied Physics Letters. - : AMER INST PHYSICS. - 0003-6951 .- 1077-3118. ; 118:13
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Tidskriftsartikel (refereegranskat)abstract
- We determine the dielectric function of the emerging ultrawide bandgap semiconductor ZnGa2O4 from the near-infrared (0.75eV) into the vacuum ultraviolet (8.5eV) spectral regions using spectroscopic ellipsometry on high quality single crystal substrates. We perform density functional theory calculations and discuss the band structure and the Brillouin zone Gamma-point band-to-band transition energies, their transition matrix elements, and effective band mass parameters. We find an isotropic effective mass parameter (0.24m(e)) at the bottom of the Gamma-point conduction band, which equals the lowest valence band effective mass parameter at the top of the highly anisotropic and degenerate valence band (0.24m(e)). Our calculated band structure indicates the spinel ZnGa2O4 is indirect, with the lowest direct transition at the Gamma-point. We analyze the measured dielectric function using critical-point line shape functions for a three-dimensional, M-0-type van Hove singularity, and we determine the direct bandgap with an energy of 5.27(3) eV. In our model, we also consider contributions from Wannier-Mott type excitons with an effective Rydberg energy of 14.8meV. We determine the near-infrared index of refraction from extrapolation (1.91) in very good agreement with results from recent infrared ellipsometry measurements (root epsilon(infinity)= 1.94) [M. Stokey, Appl. Phys. Lett. 117, 052104 (2020)]. Published under license by AIP Publishing.
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| 11. |
- Kilic, Ufuk, et al.
(författare)
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Broadband Enhanced Chirality with Tunable Response in Hybrid Plasmonic Helical Metamaterials
- 2021
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Ingår i: Advanced Functional Materials. - : WILEY-V C H VERLAG GMBH. - 1616-301X .- 1616-3028. ; 31:20
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Tidskriftsartikel (refereegranskat)abstract
- Designing broadband enhanced chirality is of strong interest to the emerging fields of chiral chemistry and sensing, or to control the spin orbital momentum of photons in recently introduced nanophotonic chiral quantum and classical optical applications. However, chiral light-matter interactions have an extremely weak nature, are difficult to control and enhance, and cannot be made tunable or broadband. In addition, planar ultrathin nanophotonic structures to achieve strong, broadband, and tunable chirality at the technologically important visible to ultraviolet spectrum still remain elusive. Here, these important problems are tackled by experimentally demonstrating and theoretically verifying spectrally tunable, extremely large, and broadband chiroptical response by nanohelical metamaterials. The reported new designs of all-dielectric and dielectric-metallic (hybrid) plasmonic metamaterials permit the largest and broadest ever measured chiral Kuhns dissymmetry factor achieved by a large-scale nanophotonic structure. In addition, the strong circular dichroism of the presented bottom-up fabricated optical metamaterials can be tuned by varying their dimensions and proportions between their dielectric and plasmonic helical subsections. The currently demonstrated ultrathin optical metamaterials are expected to provide a substantial boost to the developing field of chiroptics leading to significantly enhanced and broadband chiral light-matter interactions at the nanoscale.
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| 12. |
- Kilic, Ufuk, et al.
(författare)
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Tunable plasmonic resonances in Si-Au slanted columnar heterostructure thin films
- 2019
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Ingår i: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- We report on fabrication of spatially-coherent columnar plasmonic nanostructure superlattice-type thin films with high porosity and strong optical anisotropy using glancing angle deposition. Subsequent and repeated depositions of silicon and gold lead to nanometer-dimension subcolumns with controlled lengths. We perform generalized spectroscopic ellipsometry measurements and finite element method computations to elucidate the strongly anisotropic optical properties of the highly-porous Si-Au slanted columnar heterostructures. The occurrence of a strongly localized plasmonic mode with displacement pattern reminiscent of a dark quadrupole mode is observed in the vicinity of the gold subcolumns. We demonstrate tuning of this quadrupole-like mode frequency within the near-infrared spectral range by varying the geometry of Si-Au slanted columnar heterostructures. In addition, coupled-plasmon-like and inter-band transition-like modes occur in the visible and ultra-violet spectral regions, respectively. We elucidate an example for the potential use of Si-Au slanted columnar heterostructures as a highly porous plasmonic sensor with optical read out sensitivity to few parts-per-million solvent levels in water.
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| 13. |
- Korlacki, Rafal, et al.
(författare)
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Strain and Composition Dependencies of the Near-Band-Gap Optical Transitions in Monoclinic (AlxGa1-x)2O3 Alloys with Coherent Biaxial In-Plane Strain on Ga2O3(010)
- 2022
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Ingår i: Physical Review Applied. - : AMER PHYSICAL SOC. - 2331-7019. ; 22:6
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Tidskriftsartikel (refereegranskat)abstract
- The bowing of the energy of the three lowest band-to-band transitions in beta-(AlXGa1-X)2O3 alloys is resolved using a combined density-functional theory (DFT) and generalized spectroscopic ellipsometry approach. The DFT calculations of the electronic band structure of both beta-Ga2O3 and theta-Al2O3 allow the linear portion of the energy shift in the alloys to be extracted, and provide a method for quantifying the role of coherent strain present in the beta-(AlXGa1-X)2O3 thin films on (010) beta-Ga2O3 substrates. The energies of band-to-band transitions are obtained using the spectroscopic ellipsometry eigenpolarization model approach [A. Mock et al., Phys. Rev. B 95, 165202 (2017)]. After subtracting the effects of strain, which also induces additional bowing and after subtraction of the linear portion of the energy shift due to alloying, the bowing parameters associated with the three lowest band-to-band transitions in monoclinic beta-(AlXGa1-X)2O3 are found.
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| 14. |
- Ruder, Alexander, et al.
(författare)
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Mueller matrix ellipsometer using dual continuously rotating anisotropic mirrors
- 2020
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Ingår i: Optics Letters. - : OPTICAL SOC AMER. - 0146-9592 .- 1539-4794. ; 45:13, s. 3541-3544
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate calibration and operation of a single wavelength (660 nm) Mueller matrix ellipsometer in normal transmission configuration using dual continuously rotating anisotropic mirrors. The mirrors contain highly spatially coherent nanostructure slanted columnar titanium thin films deposited onto optically thick gold layers on glass substrates. Upon rotation around the mirror normal axis, sufficient modulation of the Stokes parameters of light reflected at oblique angle of incidence is achieved. Thereby, the mirrors can be used as a polarization state generator and polarization state analyzer in a generalized ellipsometry instrument. A Fourier expansion approach is found sufficient to render and calibrate the effects of the mirror rotations onto the polarized light train within the ellipsometer. The Mueller matrix elements of a set of anisotropic samples consisting of a linear polarizer and a linear retarder are measured and compared with model data, and very good agreement is observed. (C) 2020 Optical Society of America
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| 15. |
- Ruder, Alexander, et al.
(författare)
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Mueller matrix imaging microscope using dual continuously rotating anisotropic mirrors
- 2021
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Ingår i: Optics Express. - : Optical Society of America. - 1094-4087. ; 29:18, s. 28704-28724
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate calibration and operation of a Mueller matrix imaging microscope using dual continuously rotating anisotropic mirrors for polarization state generation and analysis. The mirrors contain highly spatially coherent nanostructure slanted columnar titanium thin films deposited onto optically thick titanium layers on quartz substrates. The first mirror acts as polarization state image generator and the second mirror acts as polarization state image detector. The instrument is calibrated using samples consisting of laterally homogeneous properties such as straight-through-air, a clear aperture linear polarizer, and a clear aperture linear retarder waveplate. Mueller matrix images are determined for spatially varying anisotropic samples consisting of a commercially available (Thorlabs) birefringent resolution target and a spatially patterned titanium slanted columnar thin film deposited onto a glass substrate. Calibration and operation are demonstrated at a single wavelength (530 nm) only, while, in principle, the instrument can operate regardless of wavelength. We refer to this imaging ellipsometry configuration as rotating-anisotropic-mirror-sample-rotating-anisotropic-mirror ellipsometry (RAM-S-RAM-E). (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
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| 16. |
- Stokey, Megan, et al.
(författare)
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Brillouin zone center phonon modes in ZnGa2O4
- 2020
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Ingår i: Applied Physics Letters. - : AMER INST PHYSICS. - 0003-6951 .- 1077-3118. ; 117:5
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Tidskriftsartikel (refereegranskat)abstract
- Infrared-active lattice mode properties of melt-grown high-quality single bulk crystals of ZnGa2O4 are investigated by combined spectroscopic ellipsometry and density functional theory computation analysis. The normal spinel structure crystals are measured by spectroscopic ellipsometry at room temperature in the range of 100cm(-1)-1200cm(-1). The complex-valued dielectric function is determined from a wavenumber-by-wavenumber approach, which is then analyzed by the four-parameter semi-quantum model dielectric function approach augmented by impurity mode contributions. We determine four infrared-active transverse and longitudinal optical mode pairs, five localized impurity mode pairs, and the high frequency dielectric constant. All four infrared-active transverse and longitudinal optical mode pairs are in excellent agreement with results from our density functional theory computations. With the Lyddane-Sachs-Teller relationship, we determine the static dielectric constant, which agrees well with electrical capacitance measurements performed on similarly grown samples. We also provide calculated parameters for all Raman-active and for all silent modes and, thereby, provide a complete set of all symmetry predicted Brillouin zone center modes.
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| 17. |
- Stokey, Megan, et al.
(författare)
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Infrared-active phonon modes and static dielectric constants in α-(AlxGa1−x)2O3 (0.18 ≤ x ≤ 0.54) alloys
- 2022
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 120:11
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Tidskriftsartikel (refereegranskat)abstract
- We determine the composition dependence of the transverse and longitudinal optical infrared-active phonon modes in rhombohedral α-(AlxGa1−x)2O3 alloys by far-infrared and infrared generalized spectroscopic ellipsometry. Single-crystalline high quality undoped thin-films grown on m-plane oriented α-Al2O3 substrates with x = 0.18, 0.37, and 0.54 were investigated. A single mode behavior is observed for all phonon modes, i.e., their frequencies shift gradually between the equivalent phonon modes of the isostructural binary parent compounds. We also provide physical model line shape functions for the anisotropic dielectric functions. We use the anisotropic high-frequency dielectric constants for polarizations parallel and perpendicular to the lattice c axis measured recently by Hilfiker et al. [Appl. Phys. Lett. 119, 092103 (2021)], and we determine the anisotropic static dielectric constants using the Lyddane–Sachs–Teller relation. The static dielectric constants can be approximated by linear relationships between those of α-Ga2O3 and α-Al2O3. The optical phonon modes and static dielectric constants will become useful for device design and free charge carrier characterization using optical techniques.
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| 18. |
- Stokey, Megan, et al.
(författare)
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Infrared dielectric functions and Brillouin zone center phonons of alpha-Ga2O3 compared to alpha-Al2O3
- 2022
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Ingår i: Physical Review Materials. - : AMER PHYSICAL SOC. - 2475-9953. ; 6:1
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Tidskriftsartikel (refereegranskat)abstract
- We determine the anisotropic dielectric functions of rhombohedral alpha-Ga2O3 by far-infrared and infrared generalized spectroscopic ellipsometry and derive all transverse optical and longitudinal optical phonon mode frequencies and broadening parameters. We also determine the high-frequency and static dielectric constants. We perform density functional theory computations and determine the phonon dispersion for all branches in the Brillouin zone, and we derive all phonon mode parameters at the Brillouin zone center including Raman-active, infrared-active, and silent modes. Excellent agreement is obtained between our experimental and computation results as well as among all previously reported partial information from experiment and theory. We also compute the same information for alpha-Al2O3, the binary parent compound for the emerging alloy of alpha-(AlxGa1-x)(2)O-3, and use results from previous investigations [Schubert, Tiwald, and Herzinger, Phys. Rev. B 61, 8187 (2000)] to compare all properties among the two isostructural compounds. From both experimental and theoretical investigations, we compute the frequency shifts of all modes between the two compounds. Additionally, we calculate overlap parameters between phonon mode eigenvectors and discuss the possible evolution of all phonon modes into the ternary alloy system and whether modes may form single-mode or more complex mode behaviors.
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| 19. |
- Stokey, Megan, et al.
(författare)
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Optical phonon modes, static and high-frequency dielectric constants, and effective electron mass parameter in cubic In2O3
- 2021
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Ingår i: Journal of Applied Physics. - : AMER INST PHYSICS. - 0021-8979 .- 1089-7550. ; 129:22
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Tidskriftsartikel (refereegranskat)abstract
- A complete set of all optical phonon modes predicted by symmetry for bixbyite structure indium oxide is reported here from a combination of far-infrared and infrared spectroscopic ellipsometry, as well as first principles calculations. Dielectric function spectra measured on high quality, marginally electrically conductive melt grown single bulk crystals are obtained on a wavelength-by-wavelength (also known as point-by-point) basis and by numerical reduction of a subtle free charge carrier Drude model contribution(. )A four-parameter semi-quantum model is applied to determine all 16 pairs of infrared-active transverse and longitudinal optical phonon modes, including the high-frequency dielectric constant, epsilon(infinity) = 4.05 +/- 0.05. The Lyddane-Sachs-Teller relation then gives access to the static dielectric constant, epsilon(DC) = 10.55 +/- 0.07. All experimental results are in excellent agreement with our density functional theory calculations and with previously reported values, where existent. We also perform optical Hall effect measurements and determine for the unintentionally doped n-type sample a free electron density of n = (2.81 +/- 0.01) x 10(17) cm(-3), a mobility of mu = (112 +/- 3) cm(2)/(Vs), and an effective mass parameter of (0.208 +/- 0.006)m(e). Density and mobility parameters compare very well with the results of electrical Hall effect measurements. Our effective mass parameter, which is measured independently of any other experimental technique, represents the bottom curvature of the Gamma point in In2O3 in agreement with previous extrapolations. We use terahertz spectroscopic ellipsometry to measure the quasi-static response of In2O3, and our model validates the static dielectric constant obtained from the Lyddane-Sachs-Teller relation. Published under an exclusive license by AIP Publishing.
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