Philip Batson - Academia.edu (original) (raw)

Papers by Philip Batson

Physical review, Nov 30, 2020

We report spatially resolved measurements of free carrier collective excitations in a doped semic... more We report spatially resolved measurements of free carrier collective excitations in a doped semiconductor. Using ∼10 meV resolution electron energy loss spectroscopy (EELS) in an electron microscope with Å spatial resolution, we identify both surface and bulk carrier plasmons at infrared energies in a freestanding film of indium tin oxide (ITO). The interference patterns of long wavelength propagating surface carrier plasmons are revealed using spatially resolved EELS, from which we extract a dispersion relation. We further show that the energies of these plasmons vary near the surfaces and grain boundaries of the film due to band bending. Modeling based on dielectric theory agrees very well with experimental results. Finally, carrier plasmons in amorphous and crystalline ITO films are compared. These results should also be helpful for understanding the free carrier plasmons in other doped semiconductors in nanoscale volumes.

Bulletin of the American Physical Society, Mar 16, 2017

interplay between surface and bulk phenomena gives rise to a variety of interesting features, esp... more interplay between surface and bulk phenomena gives rise to a variety of interesting features, especially for lowerdimensionality systems, and provide the opportunity for the realization of applications in, for instance, optoelectronics and photonics. Such features are triggered by excitonic states that are suppressed at the bulk counterparts of the material. Here we use a combination of monochromated, aberration-corrected scanning transmission electron microscopy (STEM) and density functional theory (DFT) calculations to study the effect of excitons on the valence-electron energy-loss (VEEL) spectra of the wide-band-gap hexagonal boron nitride (hBN). The experimental VEEL spectra are acquired using the state-of-art monochromated aberration corrected Nion Ul-traSTEM with 8 meV energy resolution. Theoretically, the excitonic effects on the VEEL spectra are understood by solving the Bethe-Salpeter equation (BSE). Within the combined theoretical scheme, we are able to study hBN systems with increasing number of sheets and demonstrate the transition from the pure 2D monolayer to the bulk hBN.

Trabajo presentado al: "Progress In Electromagnetics Research Symposium" celebrado en M... more Trabajo presentado al: "Progress In Electromagnetics Research Symposium" celebrado en Moscu (Rusia) del 19 al 23 de Agosto de 2012.

MRS Proceedings, 1983

ABSTRACTElemental microanalysis, using x-rays and electron energy loss scattering, has been shown... more ABSTRACTElemental microanalysis, using x-rays and electron energy loss scattering, has been shown to be possible with electron beam probe sizes down to 0.5nm. This paper will discuss some practical problems, such as specimen drift, signal magnitude, and probe-specimen interaction when the probe is made very small. These problems have arisen in two studies: 1) an investigation of as segregation in poly-crystalline Si and 2) imaging of metal spheres with surface and bulk plasmon inelastic scattering.

Small, Mar 13, 2022

BaSnO3 exhibits the highest carrier mobility among perovskite oxides, making it ideal for oxide e... more BaSnO3 exhibits the highest carrier mobility among perovskite oxides, making it ideal for oxide electronics. Collective charge carrier oscillations, plasmons, are expected to arise in this material, thus providing a tool to control the nanoscale optical field for optoelectronics applications. Here, we demonstrate the existence of relatively long-lived plasmons supported by high-mobility charge carriers in La-doped BaSnO3 (BLSO). By exploiting the high spatial and energy resolution of electron energy-loss spectroscopy with a focused beam in a scanning transmission electron microscope, we systematically investigate the dispersion, confinement ratio, and damping of infrared localized surface plasmons (LSP) in BLSO nanoparticles. We find that the LSPs in BLSO are highly spatially confined compared to those sustained by noble metals and have relatively low loss and high quality factor compared to other doped oxides. Further analysis clarifies the relation between plasmon damping and carrier mobility in BLSO. Our results support the use of nanostructured degenerate semiconductors for plasmonic applications in the infrared region and establish a relevant alternative to more traditional plasmonic materials.

Nanoscale, 2019

Using a linearly polarized (LP) incident light source, as seen in Equation 1, with an electric fi... more Using a linearly polarized (LP) incident light source, as seen in Equation 1, with an electric field of amplitude 1 V/m, we simulated the optical properties of nanostars using a model developed in the RF Module of COMSOL Multiphysics 5.0.

Microscopy and Microanalysis, Aug 1, 2022

During my graduate work at Cornell in the 1970's, it became very clear to me that Electron Energy... more During my graduate work at Cornell in the 1970's, it became very clear to me that Electron Energy Loss Spectroscopy provided a fascinating look into the detailed behavior of nanoscale materials. At the time, however, there were very few instruments that were capable of obtaining reproducible and detailed spectroscopic information, because of the lack of adequate spatial and energy resolution, as well as methods for recording data with sufficient statistical accuracy. My thesis research was, therefore, heavily involved with implementation of computer control for the Wien Filter electron spectrometer recently built there by Curtis and Silcox.[1] As I completed that work and began to take data, I became aware of the work of John Spence on the energy loss spectroscopy of aluminum during his graduate years in Melbourne, particularly regarding his discovery of excess multiple scattering at the two plasmon energy loss.[2] I also noticed this in my data, [3, 4] and so I was very interested to meet him at the second Cornell EELS meeting in 1978. I was impressed with his clarity, excitement, and vision of what might be obtained using the new STEM imaging he was exploring with John Cowley. He did not disappoint me throughout his career.

Proceedings ... annual meeting, Electron Microscopy Society of America, Aug 1, 1981

Analytical Electron Microscopy has been made possible through large technological advances in ele... more Analytical Electron Microscopy has been made possible through large technological advances in electron microscopes and in their associated data taking equipment. Among these advances are successful field emission electron sources, allowing reasonable current densities in small probe sizes; and computer based data acquisition systems for characteristic x-ray (EDX) and electron energy loss (EELS) detection, allowing simple viewing and easy processing for elemental analysis. These advances tend to bring new and complex problems of their own, however. For instance, a field emission source routinely produces a 3.5 to 5 Å sized probe in the VG Microscopes, Ltd. HB5 STEM. But a specimen drift of about 20 Å per minute, coupled with a 60 Hertz beam deflection of about 10 Å in an ambient magnetic field of about 4 mG, makes it difficult to confidently analyze areas smaller than about 50 Å in diameter during a ten minute experiment. Problems with presently available data acquisition systems arise from the need to synchronize the data taking device with the microscope.

Proceedings ... annual meeting, Electron Microscopy Society of America, 1988

During the past several years we have begun to understand many features of the core loss excitati... more During the past several years we have begun to understand many features of the core loss excitations including absolute crosssections, extended fine structure, (EXELFS) and near edge fine structure. (ELNES) In electronic materials near interfaces or defects, we expect the valence and conduction bands to be modified by the existence of isolated resonances, broadening of the band edges, or a completely filled gap region. These electronic changes have been observed with high resolution EELS in the low energy loss region (0-3eV) where direct inter-band transitions are likely. The present work is aimed at determining if pre-edge structure near the core loss scattering may reflect local changes in the electronic structure as well. There are two major experimental difficulties: 1) the necessary energy resolution is of order 0.1-0.3eV in order to define the shape of the core edge; and 2) the energy differential scattering cross section is small (of order 10-23cm2eV-1). At IBM I have addressed these problems by constructing a high resolution energy loss spectrometer system with parallel recording to allow signal collection in reasonable times.

Microscopy and Microanalysis, Aug 1, 2018

Microscopy and Microanalysis, Jul 15, 2003

After installation of the Nion spherical aberration corrector in the IBM 120kV VG Microscopes HB5... more After installation of the Nion spherical aberration corrector in the IBM 120kV VG Microscopes HB501 STEM, it has been apparent that the probe size has become about 0.78Å, somewhat smaller than expected. [1, 2] While this is a welcome outcome, it does present difficulties in understanding, particularly given that we have identified some very real issues relating to interpretation of the results. [3]

Science Advances, Mar 22, 2023

Liquid-phase chemical exfoliation can achieve industry-scale production of two-dimensional (2D) m... more Liquid-phase chemical exfoliation can achieve industry-scale production of two-dimensional (2D) materials for a wide range of applications. However, many 2D materials with potential applications in quantum technologies often fail to leave the laboratory setting because of their air sensitivity and depreciation of physical performance after chemical processing. We report a simple chemical exfoliation method to create a stable, aqueous, surfactant-free, superconducting ink containing phase-pure 1T′-WS 2 monolayers that are isostructural to the air-sensitive topological insulator 1T′-WTe 2 . The printed film is metallic at room temperature and superconducting below 7.3 kelvin, shows strong anisotropic unconventional superconducting behavior with an in-plane and out-of-plane upper critical magnetic field of 30.1 and 5.3 tesla, and is stable at ambient conditions for at least 30 days. Our results show that chemical processing can make nontrivial 2D materials that were formerly only studied in laboratories commercially accessible.

Proceedings ... annual meeting, Electron Microscopy Society of America, Aug 1, 1971

Recent experiments have shown that, for suitable alloy systems (Al-Cu, Al-Mg), it is possible to ... more Recent experiments have shown that, for suitable alloy systems (Al-Cu, Al-Mg), it is possible to detect changes in composition ∼ 1 atomic wt. % with a spatial resolution 10nm, by measuring shifts in the energy loss spectrum of electrons transmitted through a specimen in an electron microscope. The sensitivity and accuracy of the technique for microanalysis is limited by several factors: (i) the energy-loss spectrum is recorded photographically and then traced on a photodensitometer; the resulting curve is smoothed by hand and the data points are transferred to a computer; (ii) since both voltage and intensity scales are non-linear at this stage, they are adjusted by reference to calibration plates; (iii) even for a monochromatic incident beam, the half-peak full width of the 15 eV plasmon loss in Al is 1 eV; for Al-Mg alloys a composition change of 1% corresponds to a shift in the plasmon peak of 0.055 eV and so curve-fitting techniques must be applied to the corrected data.

Microscopy and Microanalysis, Aug 1, 2018

With the introduction of the Nion Co. Hermes high resolution monochromator, sub-10 meV resolution... more With the introduction of the Nion Co. Hermes high resolution monochromator, sub-10 meV resolution EELS has become a reality for electron microscopy.[1] This has enabled an IRlike spectroscopy in aloof scattering,[2] and mapping of bulk and surface phonon modes in a single MgO nanocube.[3] Theoretical work has also begun.[4] However, below about 50 meV, where the phonon systems must be treated with a scattering theory at finite temperature our understanding is still developing.[5] There, we expect Boson occupation statistics to affect the observed EELS results, giving both energy gain, and modification of energy loss results. There turn out to be three kinds of scattering events: 1) spontaneous emission of a collective phonon by the probe, an energy loss process, 2) an induced emission by occupied phonon modes, also an energy loss process, and 3) an induced absorption, or electron energy gain. We begin by writing the scattering probability for EELS in the familiar dielectric form, or equivalently, using the Dynamical Form factor, S(q, ω) [5]

Hydrogen production by photoelectrochemical (PEC) water splitting has remained challenging for co... more Hydrogen production by photoelectrochemical (PEC) water splitting has remained challenging for commercialization mainly due to the limited durability of integrated photoelectrodes owing to failure of the interfacial connection between the photoabsorber(s) and catalyst(s). Although multijunction III-V semiconductors have been popular choices as photoabsorbers in PEC devices and have yielded a high solar-to-hydrogen (STH) efficiency > 19% using platinum group metal (PGM) catalysts, they rapidly corrode in aqueous electrolytes. Here, a bifunctional interface comprised of a titanium dioxide (TiO2) corrosion barrier and titanium nitride diffusion barrier (TiN, 1nm thickness) was created to protect the interface between the GaInP2/GaAs III-V tandem photocathode and the PGM-free catalyst. This strategy enables use of elevated temperatures to crystallize and fuse together the Ni5P4 catalyst particles and the TiO2 without damaging the sensitive III-V photoasbsorber. The combination of ult...

Physical Review Materials

High quality, ultrathin, superconducting films are required for advanced devices such as hot-elec... more High quality, ultrathin, superconducting films are required for advanced devices such as hot-electron bolometers, superconducting nanowire single photon detectors, and quantum applications. Using Hybrid Physical-Chemical Vapor Deposition (HPCVD), we show that MgB2 films as thin as 4 nm can be fabricated on the carbon terminated 6H-SiC (0001) surface with a superconducting transition temperature above 33K and a rms roughness of 0.7 nm. Remarkably, the film quality is a function of the SiC surface termination, with the Cterminated surface preferred to the Si-terminated surface. To understand the MgB2 thin film/ SiC substrate interactions giving rise to this difference, we characterized the interfacial structures using Rutherford backscattering spectroscopy/channeling, electron energy loss spectroscopy, and x-ray photoemission spectroscopy. The MgB2/SiC interface structure is complex and different for the two terminations. Both terminations incorporate substantial unintentional oxide layers influencing MgB2 growth and morphology, but with different extent, intermixing and interface chemistry. In this paper, we report measurements of transport, resistivity, and critical superconducting temperature of MgB2/SiC that are different for the two terminations, and link interfacial structure variations to observed differences. The result shows that the C face of SiC is a preferred substrate for the deposition of ultrathin superconducting MgB2 films.

Physical review, Nov 30, 2020

We report spatially resolved measurements of free carrier collective excitations in a doped semic... more We report spatially resolved measurements of free carrier collective excitations in a doped semiconductor. Using ∼10 meV resolution electron energy loss spectroscopy (EELS) in an electron microscope with Å spatial resolution, we identify both surface and bulk carrier plasmons at infrared energies in a freestanding film of indium tin oxide (ITO). The interference patterns of long wavelength propagating surface carrier plasmons are revealed using spatially resolved EELS, from which we extract a dispersion relation. We further show that the energies of these plasmons vary near the surfaces and grain boundaries of the film due to band bending. Modeling based on dielectric theory agrees very well with experimental results. Finally, carrier plasmons in amorphous and crystalline ITO films are compared. These results should also be helpful for understanding the free carrier plasmons in other doped semiconductors in nanoscale volumes.

Bulletin of the American Physical Society, Mar 16, 2017

interplay between surface and bulk phenomena gives rise to a variety of interesting features, esp... more interplay between surface and bulk phenomena gives rise to a variety of interesting features, especially for lowerdimensionality systems, and provide the opportunity for the realization of applications in, for instance, optoelectronics and photonics. Such features are triggered by excitonic states that are suppressed at the bulk counterparts of the material. Here we use a combination of monochromated, aberration-corrected scanning transmission electron microscopy (STEM) and density functional theory (DFT) calculations to study the effect of excitons on the valence-electron energy-loss (VEEL) spectra of the wide-band-gap hexagonal boron nitride (hBN). The experimental VEEL spectra are acquired using the state-of-art monochromated aberration corrected Nion Ul-traSTEM with 8 meV energy resolution. Theoretically, the excitonic effects on the VEEL spectra are understood by solving the Bethe-Salpeter equation (BSE). Within the combined theoretical scheme, we are able to study hBN systems with increasing number of sheets and demonstrate the transition from the pure 2D monolayer to the bulk hBN.

Trabajo presentado al: "Progress In Electromagnetics Research Symposium" celebrado en M... more Trabajo presentado al: "Progress In Electromagnetics Research Symposium" celebrado en Moscu (Rusia) del 19 al 23 de Agosto de 2012.

MRS Proceedings, 1983

ABSTRACTElemental microanalysis, using x-rays and electron energy loss scattering, has been shown... more ABSTRACTElemental microanalysis, using x-rays and electron energy loss scattering, has been shown to be possible with electron beam probe sizes down to 0.5nm. This paper will discuss some practical problems, such as specimen drift, signal magnitude, and probe-specimen interaction when the probe is made very small. These problems have arisen in two studies: 1) an investigation of as segregation in poly-crystalline Si and 2) imaging of metal spheres with surface and bulk plasmon inelastic scattering.

Small, Mar 13, 2022

BaSnO3 exhibits the highest carrier mobility among perovskite oxides, making it ideal for oxide e... more BaSnO3 exhibits the highest carrier mobility among perovskite oxides, making it ideal for oxide electronics. Collective charge carrier oscillations, plasmons, are expected to arise in this material, thus providing a tool to control the nanoscale optical field for optoelectronics applications. Here, we demonstrate the existence of relatively long-lived plasmons supported by high-mobility charge carriers in La-doped BaSnO3 (BLSO). By exploiting the high spatial and energy resolution of electron energy-loss spectroscopy with a focused beam in a scanning transmission electron microscope, we systematically investigate the dispersion, confinement ratio, and damping of infrared localized surface plasmons (LSP) in BLSO nanoparticles. We find that the LSPs in BLSO are highly spatially confined compared to those sustained by noble metals and have relatively low loss and high quality factor compared to other doped oxides. Further analysis clarifies the relation between plasmon damping and carrier mobility in BLSO. Our results support the use of nanostructured degenerate semiconductors for plasmonic applications in the infrared region and establish a relevant alternative to more traditional plasmonic materials.

Nanoscale, 2019

Using a linearly polarized (LP) incident light source, as seen in Equation 1, with an electric fi... more Using a linearly polarized (LP) incident light source, as seen in Equation 1, with an electric field of amplitude 1 V/m, we simulated the optical properties of nanostars using a model developed in the RF Module of COMSOL Multiphysics 5.0.

Microscopy and Microanalysis, Aug 1, 2022

During my graduate work at Cornell in the 1970's, it became very clear to me that Electron Energy... more During my graduate work at Cornell in the 1970's, it became very clear to me that Electron Energy Loss Spectroscopy provided a fascinating look into the detailed behavior of nanoscale materials. At the time, however, there were very few instruments that were capable of obtaining reproducible and detailed spectroscopic information, because of the lack of adequate spatial and energy resolution, as well as methods for recording data with sufficient statistical accuracy. My thesis research was, therefore, heavily involved with implementation of computer control for the Wien Filter electron spectrometer recently built there by Curtis and Silcox.[1] As I completed that work and began to take data, I became aware of the work of John Spence on the energy loss spectroscopy of aluminum during his graduate years in Melbourne, particularly regarding his discovery of excess multiple scattering at the two plasmon energy loss.[2] I also noticed this in my data, [3, 4] and so I was very interested to meet him at the second Cornell EELS meeting in 1978. I was impressed with his clarity, excitement, and vision of what might be obtained using the new STEM imaging he was exploring with John Cowley. He did not disappoint me throughout his career.

Proceedings ... annual meeting, Electron Microscopy Society of America, Aug 1, 1981

Analytical Electron Microscopy has been made possible through large technological advances in ele... more Analytical Electron Microscopy has been made possible through large technological advances in electron microscopes and in their associated data taking equipment. Among these advances are successful field emission electron sources, allowing reasonable current densities in small probe sizes; and computer based data acquisition systems for characteristic x-ray (EDX) and electron energy loss (EELS) detection, allowing simple viewing and easy processing for elemental analysis. These advances tend to bring new and complex problems of their own, however. For instance, a field emission source routinely produces a 3.5 to 5 Å sized probe in the VG Microscopes, Ltd. HB5 STEM. But a specimen drift of about 20 Å per minute, coupled with a 60 Hertz beam deflection of about 10 Å in an ambient magnetic field of about 4 mG, makes it difficult to confidently analyze areas smaller than about 50 Å in diameter during a ten minute experiment. Problems with presently available data acquisition systems arise from the need to synchronize the data taking device with the microscope.

Proceedings ... annual meeting, Electron Microscopy Society of America, 1988

During the past several years we have begun to understand many features of the core loss excitati... more During the past several years we have begun to understand many features of the core loss excitations including absolute crosssections, extended fine structure, (EXELFS) and near edge fine structure. (ELNES) In electronic materials near interfaces or defects, we expect the valence and conduction bands to be modified by the existence of isolated resonances, broadening of the band edges, or a completely filled gap region. These electronic changes have been observed with high resolution EELS in the low energy loss region (0-3eV) where direct inter-band transitions are likely. The present work is aimed at determining if pre-edge structure near the core loss scattering may reflect local changes in the electronic structure as well. There are two major experimental difficulties: 1) the necessary energy resolution is of order 0.1-0.3eV in order to define the shape of the core edge; and 2) the energy differential scattering cross section is small (of order 10-23cm2eV-1). At IBM I have addressed these problems by constructing a high resolution energy loss spectrometer system with parallel recording to allow signal collection in reasonable times.

Microscopy and Microanalysis, Aug 1, 2018

Microscopy and Microanalysis, Jul 15, 2003

After installation of the Nion spherical aberration corrector in the IBM 120kV VG Microscopes HB5... more After installation of the Nion spherical aberration corrector in the IBM 120kV VG Microscopes HB501 STEM, it has been apparent that the probe size has become about 0.78Å, somewhat smaller than expected. [1, 2] While this is a welcome outcome, it does present difficulties in understanding, particularly given that we have identified some very real issues relating to interpretation of the results. [3]

Science Advances, Mar 22, 2023

Liquid-phase chemical exfoliation can achieve industry-scale production of two-dimensional (2D) m... more Liquid-phase chemical exfoliation can achieve industry-scale production of two-dimensional (2D) materials for a wide range of applications. However, many 2D materials with potential applications in quantum technologies often fail to leave the laboratory setting because of their air sensitivity and depreciation of physical performance after chemical processing. We report a simple chemical exfoliation method to create a stable, aqueous, surfactant-free, superconducting ink containing phase-pure 1T′-WS 2 monolayers that are isostructural to the air-sensitive topological insulator 1T′-WTe 2 . The printed film is metallic at room temperature and superconducting below 7.3 kelvin, shows strong anisotropic unconventional superconducting behavior with an in-plane and out-of-plane upper critical magnetic field of 30.1 and 5.3 tesla, and is stable at ambient conditions for at least 30 days. Our results show that chemical processing can make nontrivial 2D materials that were formerly only studied in laboratories commercially accessible.

Proceedings ... annual meeting, Electron Microscopy Society of America, Aug 1, 1971

Recent experiments have shown that, for suitable alloy systems (Al-Cu, Al-Mg), it is possible to ... more Recent experiments have shown that, for suitable alloy systems (Al-Cu, Al-Mg), it is possible to detect changes in composition ∼ 1 atomic wt. % with a spatial resolution 10nm, by measuring shifts in the energy loss spectrum of electrons transmitted through a specimen in an electron microscope. The sensitivity and accuracy of the technique for microanalysis is limited by several factors: (i) the energy-loss spectrum is recorded photographically and then traced on a photodensitometer; the resulting curve is smoothed by hand and the data points are transferred to a computer; (ii) since both voltage and intensity scales are non-linear at this stage, they are adjusted by reference to calibration plates; (iii) even for a monochromatic incident beam, the half-peak full width of the 15 eV plasmon loss in Al is 1 eV; for Al-Mg alloys a composition change of 1% corresponds to a shift in the plasmon peak of 0.055 eV and so curve-fitting techniques must be applied to the corrected data.

Microscopy and Microanalysis, Aug 1, 2018

With the introduction of the Nion Co. Hermes high resolution monochromator, sub-10 meV resolution... more With the introduction of the Nion Co. Hermes high resolution monochromator, sub-10 meV resolution EELS has become a reality for electron microscopy.[1] This has enabled an IRlike spectroscopy in aloof scattering,[2] and mapping of bulk and surface phonon modes in a single MgO nanocube.[3] Theoretical work has also begun.[4] However, below about 50 meV, where the phonon systems must be treated with a scattering theory at finite temperature our understanding is still developing.[5] There, we expect Boson occupation statistics to affect the observed EELS results, giving both energy gain, and modification of energy loss results. There turn out to be three kinds of scattering events: 1) spontaneous emission of a collective phonon by the probe, an energy loss process, 2) an induced emission by occupied phonon modes, also an energy loss process, and 3) an induced absorption, or electron energy gain. We begin by writing the scattering probability for EELS in the familiar dielectric form, or equivalently, using the Dynamical Form factor, S(q, ω) [5]

Hydrogen production by photoelectrochemical (PEC) water splitting has remained challenging for co... more Hydrogen production by photoelectrochemical (PEC) water splitting has remained challenging for commercialization mainly due to the limited durability of integrated photoelectrodes owing to failure of the interfacial connection between the photoabsorber(s) and catalyst(s). Although multijunction III-V semiconductors have been popular choices as photoabsorbers in PEC devices and have yielded a high solar-to-hydrogen (STH) efficiency > 19% using platinum group metal (PGM) catalysts, they rapidly corrode in aqueous electrolytes. Here, a bifunctional interface comprised of a titanium dioxide (TiO2) corrosion barrier and titanium nitride diffusion barrier (TiN, 1nm thickness) was created to protect the interface between the GaInP2/GaAs III-V tandem photocathode and the PGM-free catalyst. This strategy enables use of elevated temperatures to crystallize and fuse together the Ni5P4 catalyst particles and the TiO2 without damaging the sensitive III-V photoasbsorber. The combination of ult...

Physical Review Materials

High quality, ultrathin, superconducting films are required for advanced devices such as hot-elec... more High quality, ultrathin, superconducting films are required for advanced devices such as hot-electron bolometers, superconducting nanowire single photon detectors, and quantum applications. Using Hybrid Physical-Chemical Vapor Deposition (HPCVD), we show that MgB2 films as thin as 4 nm can be fabricated on the carbon terminated 6H-SiC (0001) surface with a superconducting transition temperature above 33K and a rms roughness of 0.7 nm. Remarkably, the film quality is a function of the SiC surface termination, with the Cterminated surface preferred to the Si-terminated surface. To understand the MgB2 thin film/ SiC substrate interactions giving rise to this difference, we characterized the interfacial structures using Rutherford backscattering spectroscopy/channeling, electron energy loss spectroscopy, and x-ray photoemission spectroscopy. The MgB2/SiC interface structure is complex and different for the two terminations. Both terminations incorporate substantial unintentional oxide layers influencing MgB2 growth and morphology, but with different extent, intermixing and interface chemistry. In this paper, we report measurements of transport, resistivity, and critical superconducting temperature of MgB2/SiC that are different for the two terminations, and link interfacial structure variations to observed differences. The result shows that the C face of SiC is a preferred substrate for the deposition of ultrathin superconducting MgB2 films.