Fumio Ohuchi - Academia.edu (original) (raw)

Papers by Fumio Ohuchi

APS Division of Plasma Physics Meeting Abstracts, Nov 1, 2008

To overcome the temperature barrier set by impurity radiation losses in the earlier TCS experimen... more To overcome the temperature barrier set by impurity radiation losses in the earlier TCS experiments, TCS-upgrade (TSCU) has been built with particular focus on obtaining UHV compatible wall surfaces. To further minimize impurity ingestion into plasma, wall-conditioning techniques including glow discharge cleaning (GDC), siliconization and Ti-gettering are being carried out in TCSU. The chemical and morphological characterization of the wall surfaces is done using x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). This study presents an overview of the surface analytical studies on the wall surfaces throughout the first year of TCSU operation. The effect of GDC, siliconization and Ti-gettering on TCSU surfaces, along with subsequent glow discharges and plasma shots, will be discussed. Additional data from experiments carried out in a separate system for detailed study of these techniques will be presented.

Journal of Crystal Growth, 1999

Single crystalline Ga Se thin "lms were grown on GaAs(1 0 0) by molecular beam epitaxial (MBE) un... more Single crystalline Ga Se thin "lms were grown on GaAs(1 0 0) by molecular beam epitaxial (MBE) under Se-rich atmosphere. Re#ection high-energy electron di!raction (RHEED) analysis suggests that the Ga Se thin "lm is epitaxially grown on GaAs(1 0 0) with their 11 0 02 crystallographic directions aligned with each other. The electronic structure determined by the ultraviolet photoelectron spectroscopy (UPS) and electron energy loss spectroscopy (EELS) revealed the forbidden band gap of 2.7 eV. Transmission electron microscopy has shown that vacancies are distributed on one set of +1 1 1, crystal planes of-Ga Se structure by forming a (3;(3 con"guration, resulting in the three times larger modulation periodicity along one of the 11 1 02 crystal directions into vacancy ordered-Ga Se structure. The crystal structure was consistent to a model proposed by LuK bbers and Leute (J. Solid State Chem. 43 (1982) 339). There are two sets of planar defects, microtwin with +1 1 1, type twin planes and stacking faults. High population of planer defects observed in the thin "lm was regarded as a result of Ga vacancy ordering in the crystal structure of Ga Se .

We have undertaken a detailed analysis of the X-ray photoelectron spectra obtained from the three... more We have undertaken a detailed analysis of the X-ray photoelectron spectra obtained from the three polymorphs of Al 2 SiO 5 ; andalusite, sillimanite, and kyanite. Comparison of the spectra was made based on the chemical bonding and structural differences in the Al-and Si-coordination within each polymorph. The spectra for Si(2p) for all three polymorphs are nearly identical, consistent with the fact that all the Si atoms are in 4-fold (tetrahedral) coordination, whereas the binding energies, peak shapes, and peak widths for Al(2p) vary depending on the type of polymorph. The upper-valence band for all three polymorphs is characterized by four main features derived from O(2p), Al(3s), Al(2p), Si(3s), and Si(3p), and the differences in their contributions are observed. The density of state of the Al 2 SiO 5 polymorphs is relatively featureless compared to those observed from α-SiO 2 and α-Al 2 O 3 , suggesting that the orbital overlaps span a greater range in energy. The observed band...

41st Structures, Structural Dynamics, and Materials Conference and Exhibit

Journal of Vacuum Science and Technology

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures

Vertically aligned ZnO nanorod arrays have been synthesized on c-plane sapphires at a low tempera... more Vertically aligned ZnO nanorod arrays have been synthesized on c-plane sapphires at a low temperature of 400 degrees C using catalyst-free inductively coupled plasma (ICP) metal organic chemical vapor deposition (MOCVD) technique by varying the ICP powers. Diameters of the ZnO nanorods changed from 200 nm to 400 nm as the ICP power increased from 200 to 400 Watt. TEM and XRD investigations indicated that the ZnO nanorod arrays grown at ICP powers above 200 Watt had a homogeneous in-plane alignment and single crystalline nature. PL study at room temperature (RT) and 6 K confirmed that the ZnO nanorod arrays in the present study are of high optical quality as well as good crystalline quality, showing only exciton-related emission peaks without any trace of defect-related deep level emissions in visible range. The blueshift of exciton emission peak in RTPL spectra was also found as rod diameter decreased and it is deduced that this shift in emission energy may be due to the surface resonance effect resulted from the increased surface-to-volume ratio, based on the observation and behavior of the surface exciton (SX) emission in the high-resolution 6 K PL spectra.

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures

The influence of substrate temperature on the growth of InGaAs layers on (111)B GaAs, has been st... more The influence of substrate temperature on the growth of InGaAs layers on (111)B GaAs, has been studied. Photoluminescence (PL) spectra obtained from GaAs/InGaAs single quantum well structures show strong dependence on InGaAs growth temperature. As the growth temperature increases, PL peaks shift to a higher energy, which is attributed to reevaporation of indium from the InGaAs layer during the growth

Berichte der Bunsengesellschaft für physikalische Chemie

... Met. 15, 339 (1981). [S] W. Laqua and H. Schmalzried, Kinetic Decomposition ofTer-nary Phases... more ... Met. 15, 339 (1981). [S] W. Laqua and H. Schmalzried, Kinetic Decomposition ofTer-nary Phases A,B,X, in a Chemical Potential Gradient of the Nonmetallic Component X, ed. NA Gokcen, Chemical Metallurgy - A tribute to Carl Wagner, AIME-Proceedings 1981. ...

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 1998

We have studied the epitaxial growth of GaSe, a layered van der Waals material, on GaAs, a zinc-b... more We have studied the epitaxial growth of GaSe, a layered van der Waals material, on GaAs, a zinc-blende-structure semiconductor. This heterostructure exhibits a 6% lattice mismatch, and is a prototypical example of van der Waals epitaxy, where the weak van der Waals interaction allows the misfit to be accommodated without the formation of electronically active defects. GaSe was supplied to the growing surface from a single GaSe Knudsen cell. Reflection high energy electron diffraction and x-ray photoemission spectroscopy studies of the nucleation of GaSe indicate Se reacts with the GaAs surface to remove the surface dangling bonds prior to GaSe formation. This is followed by the oriented growth of stoichiometric GaSe layers, that are rotationally aligned with the underlying GaAs substrate. The termination of the GaAs dangling bonds most likely occurs by Se substitution for As in the surface layer of GaAs͑111͒ B and by direct bonding of Se to surface Ga on GaAs͑111͒ A surfaces. In addition, photoemission measurements indicate that the subsurface Se uptake into the GaAs͑111͒ A lattice is higher than that in the ͑111͒ B lattice.

Journal of Vacuum Science and Technology a Vacuum Surfaces and Films, May 1, 1992

Among a number of modern surface sensitive analytical techniques, Auger electron spectroscopy (AE... more Among a number of modern surface sensitive analytical techniques, Auger electron spectroscopy (AES) is extensively applied for glass surface research because of its superior characteristics. AES is generally considered as a nondestructive technique; however, a number of reports have shown that the incident electron beam can alter the surface composition of the solid being analyzed. Compositional changes in glass is particularly severe in glasses containing alkali ions and it is manifested by the time dependent alkali Auger signal loss during electron bombardment. The fundamental mechanisms of alkali Auger signal loss from glass surfaces during electron bombardment are described. It is shown that this is the result of electric field enhanced diffusion and electron stimulated description.

Journal of Applied Physics, Jun 15, 2007

ABSTRACT Thermopower and electrical conductivity of sodium-doped vanadium pentoxide (V2O5) thin f... more ABSTRACT Thermopower and electrical conductivity of sodium-doped vanadium pentoxide (V2O5) thin films synthesized by a solution technique were investigated. An aqueous solution based V2O5 thin film is a good candidate for thin film devices using ink-jet deposition and screen printing techniques. To improve its thermoelectric properties for practical applications, Na was systematically introduced into V2O5 as a dopant to study how it influences the thermoelectric properties. A melt-quench technique was implemented to dope various concentrations of sodium ions into sol-gel solutions, and thin films were fabricated from these. X-ray diffraction showed that the Na doped V2O5 samples dominantly form the crystalline phase β-NaxV2O5. It was shown that by increasing the Na concentration, the electrical conductivity could be increased by a factor of up to ∼ 104, whereas the Seebeck coefficient decreased only by a half. Direct measurement of the thermoelectric power output verified that the power factor was improved up to 350 times. Temperature dependent characteristics of the electrical conductivity and the temperature independence of Seebeck coefficient, respectively, in a range of temperatures examined, suggested that the transport mechanism was a small polaron hopping type. A significant increase in the electrical conductivity was ascribed to the increase in the polaron population and the reduction of the activation energy due to formation of β-NaxV2O5.

APS Division of Plasma Physics Meeting Abstracts, Nov 1, 2008

To overcome the temperature barrier set by impurity radiation losses in the earlier TCS experimen... more To overcome the temperature barrier set by impurity radiation losses in the earlier TCS experiments, TCS-upgrade (TSCU) has been built with particular focus on obtaining UHV compatible wall surfaces. To further minimize impurity ingestion into plasma, wall-conditioning techniques including glow discharge cleaning (GDC), siliconization and Ti-gettering are being carried out in TCSU. The chemical and morphological characterization of the wall surfaces is done using x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). This study presents an overview of the surface analytical studies on the wall surfaces throughout the first year of TCSU operation. The effect of GDC, siliconization and Ti-gettering on TCSU surfaces, along with subsequent glow discharges and plasma shots, will be discussed. Additional data from experiments carried out in a separate system for detailed study of these techniques will be presented.

Journal of Crystal Growth, 1999

Single crystalline Ga Se thin "lms were grown on GaAs(1 0 0) by molecular beam epitaxial (MBE) un... more Single crystalline Ga Se thin "lms were grown on GaAs(1 0 0) by molecular beam epitaxial (MBE) under Se-rich atmosphere. Re#ection high-energy electron di!raction (RHEED) analysis suggests that the Ga Se thin "lm is epitaxially grown on GaAs(1 0 0) with their 11 0 02 crystallographic directions aligned with each other. The electronic structure determined by the ultraviolet photoelectron spectroscopy (UPS) and electron energy loss spectroscopy (EELS) revealed the forbidden band gap of 2.7 eV. Transmission electron microscopy has shown that vacancies are distributed on one set of +1 1 1, crystal planes of-Ga Se structure by forming a (3;(3 con"guration, resulting in the three times larger modulation periodicity along one of the 11 1 02 crystal directions into vacancy ordered-Ga Se structure. The crystal structure was consistent to a model proposed by LuK bbers and Leute (J. Solid State Chem. 43 (1982) 339). There are two sets of planar defects, microtwin with +1 1 1, type twin planes and stacking faults. High population of planer defects observed in the thin "lm was regarded as a result of Ga vacancy ordering in the crystal structure of Ga Se .

We have undertaken a detailed analysis of the X-ray photoelectron spectra obtained from the three... more We have undertaken a detailed analysis of the X-ray photoelectron spectra obtained from the three polymorphs of Al 2 SiO 5 ; andalusite, sillimanite, and kyanite. Comparison of the spectra was made based on the chemical bonding and structural differences in the Al-and Si-coordination within each polymorph. The spectra for Si(2p) for all three polymorphs are nearly identical, consistent with the fact that all the Si atoms are in 4-fold (tetrahedral) coordination, whereas the binding energies, peak shapes, and peak widths for Al(2p) vary depending on the type of polymorph. The upper-valence band for all three polymorphs is characterized by four main features derived from O(2p), Al(3s), Al(2p), Si(3s), and Si(3p), and the differences in their contributions are observed. The density of state of the Al 2 SiO 5 polymorphs is relatively featureless compared to those observed from α-SiO 2 and α-Al 2 O 3 , suggesting that the orbital overlaps span a greater range in energy. The observed band...

41st Structures, Structural Dynamics, and Materials Conference and Exhibit

Journal of Vacuum Science and Technology

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures

Vertically aligned ZnO nanorod arrays have been synthesized on c-plane sapphires at a low tempera... more Vertically aligned ZnO nanorod arrays have been synthesized on c-plane sapphires at a low temperature of 400 degrees C using catalyst-free inductively coupled plasma (ICP) metal organic chemical vapor deposition (MOCVD) technique by varying the ICP powers. Diameters of the ZnO nanorods changed from 200 nm to 400 nm as the ICP power increased from 200 to 400 Watt. TEM and XRD investigations indicated that the ZnO nanorod arrays grown at ICP powers above 200 Watt had a homogeneous in-plane alignment and single crystalline nature. PL study at room temperature (RT) and 6 K confirmed that the ZnO nanorod arrays in the present study are of high optical quality as well as good crystalline quality, showing only exciton-related emission peaks without any trace of defect-related deep level emissions in visible range. The blueshift of exciton emission peak in RTPL spectra was also found as rod diameter decreased and it is deduced that this shift in emission energy may be due to the surface resonance effect resulted from the increased surface-to-volume ratio, based on the observation and behavior of the surface exciton (SX) emission in the high-resolution 6 K PL spectra.

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures

The influence of substrate temperature on the growth of InGaAs layers on (111)B GaAs, has been st... more The influence of substrate temperature on the growth of InGaAs layers on (111)B GaAs, has been studied. Photoluminescence (PL) spectra obtained from GaAs/InGaAs single quantum well structures show strong dependence on InGaAs growth temperature. As the growth temperature increases, PL peaks shift to a higher energy, which is attributed to reevaporation of indium from the InGaAs layer during the growth

Berichte der Bunsengesellschaft für physikalische Chemie

... Met. 15, 339 (1981). [S] W. Laqua and H. Schmalzried, Kinetic Decomposition ofTer-nary Phases... more ... Met. 15, 339 (1981). [S] W. Laqua and H. Schmalzried, Kinetic Decomposition ofTer-nary Phases A,B,X, in a Chemical Potential Gradient of the Nonmetallic Component X, ed. NA Gokcen, Chemical Metallurgy - A tribute to Carl Wagner, AIME-Proceedings 1981. ...

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 1998

We have studied the epitaxial growth of GaSe, a layered van der Waals material, on GaAs, a zinc-b... more We have studied the epitaxial growth of GaSe, a layered van der Waals material, on GaAs, a zinc-blende-structure semiconductor. This heterostructure exhibits a 6% lattice mismatch, and is a prototypical example of van der Waals epitaxy, where the weak van der Waals interaction allows the misfit to be accommodated without the formation of electronically active defects. GaSe was supplied to the growing surface from a single GaSe Knudsen cell. Reflection high energy electron diffraction and x-ray photoemission spectroscopy studies of the nucleation of GaSe indicate Se reacts with the GaAs surface to remove the surface dangling bonds prior to GaSe formation. This is followed by the oriented growth of stoichiometric GaSe layers, that are rotationally aligned with the underlying GaAs substrate. The termination of the GaAs dangling bonds most likely occurs by Se substitution for As in the surface layer of GaAs͑111͒ B and by direct bonding of Se to surface Ga on GaAs͑111͒ A surfaces. In addition, photoemission measurements indicate that the subsurface Se uptake into the GaAs͑111͒ A lattice is higher than that in the ͑111͒ B lattice.

Journal of Vacuum Science and Technology a Vacuum Surfaces and Films, May 1, 1992

Among a number of modern surface sensitive analytical techniques, Auger electron spectroscopy (AE... more Among a number of modern surface sensitive analytical techniques, Auger electron spectroscopy (AES) is extensively applied for glass surface research because of its superior characteristics. AES is generally considered as a nondestructive technique; however, a number of reports have shown that the incident electron beam can alter the surface composition of the solid being analyzed. Compositional changes in glass is particularly severe in glasses containing alkali ions and it is manifested by the time dependent alkali Auger signal loss during electron bombardment. The fundamental mechanisms of alkali Auger signal loss from glass surfaces during electron bombardment are described. It is shown that this is the result of electric field enhanced diffusion and electron stimulated description.

Journal of Applied Physics, Jun 15, 2007

ABSTRACT Thermopower and electrical conductivity of sodium-doped vanadium pentoxide (V2O5) thin f... more ABSTRACT Thermopower and electrical conductivity of sodium-doped vanadium pentoxide (V2O5) thin films synthesized by a solution technique were investigated. An aqueous solution based V2O5 thin film is a good candidate for thin film devices using ink-jet deposition and screen printing techniques. To improve its thermoelectric properties for practical applications, Na was systematically introduced into V2O5 as a dopant to study how it influences the thermoelectric properties. A melt-quench technique was implemented to dope various concentrations of sodium ions into sol-gel solutions, and thin films were fabricated from these. X-ray diffraction showed that the Na doped V2O5 samples dominantly form the crystalline phase β-NaxV2O5. It was shown that by increasing the Na concentration, the electrical conductivity could be increased by a factor of up to ∼ 104, whereas the Seebeck coefficient decreased only by a half. Direct measurement of the thermoelectric power output verified that the power factor was improved up to 350 times. Temperature dependent characteristics of the electrical conductivity and the temperature independence of Seebeck coefficient, respectively, in a range of temperatures examined, suggested that the transport mechanism was a small polaron hopping type. A significant increase in the electrical conductivity was ascribed to the increase in the polaron population and the reduction of the activation energy due to formation of β-NaxV2O5.