Hiromi Kuramochi - Academia.edu (original) (raw)

Papers by Hiromi Kuramochi

E-journal of Surface Science and Nanotechnology, 2006

The dopant type and carrier concentration in a patterned semiconductor sample with three differen... more The dopant type and carrier concentration in a patterned semiconductor sample with three different doping regions were measured by scanning nonlinear dielectric microscope (SNDM). SNDM is used in the way of a scanning capacitance microscopy (SCM) with a new detection mechanism based on frequency detection. The topographic, pn-distribution and the carrier concentration images of a patterned semiconductor sample were measured at the same time. In concurrence with a demonstration of the SNDM-SCM measurements, the influence of an adsorbed water layer on measurements is evaluated in the vacuum and in the air over a relative humidity (RH) range of 20 to 80%. Adverse affects on capacitance measurements due to the variation in RH are revealed.

Nanotechnology, Feb 28, 2007

Carbon nanotube (CNT) probes enhance the stability of the nano-oxidation process under dynamic-mo... more Carbon nanotube (CNT) probes enhance the stability of the nano-oxidation process under dynamic-mode operation. In this paper we investigate how the hydrophobic nature of the CNT allows oxide nanostructures to be fabricated with constant aspect ratio over a wide range of relative humidity values. In particular, we characterize oxide growth by measuring both the integrated ionic current and volume expansion. Behaviour of different CNT probes was compared to assess individual stability and performance under identical voltage and humidity conditions. While much remains to be established about the relationship between exposure conditions and dynamic-mode parameters on nanoscale oxide fabrication, hydrophobicity is a key factor in the improved reliability of CNT probes over conventional ones.

Japanese Journal of Applied Physics, Mar 27, 2006

Surface Science, Sep 1, 2004

Scanning probe microscope nano-oxidation is carried out on H-passivated Si(0 0 1) surfaces using ... more Scanning probe microscope nano-oxidation is carried out on H-passivated Si(0 0 1) surfaces using a humidity control atomic force microscope (AFM) in contact and dynamic modes. To achieve high precision nano-oxidation at large scale, the original tube-scanner-based AFM unit is modified: horizontal movement of the whole sample block (sample stage and the scanner) is operated by an additional XY piezo stage, whilst its vertical movement is controlled by a piezo tube-scanner. The high linearity of the horizontal movement is demonstrated by high resolution oxide patterns which are fabricated after the instrumental modification using standard AFM cantilevers and a modified AFM cantilever with an added carbon nano-tube on tip.

Japanese Journal of Applied Physics, Apr 1, 2005

The Sullivan model is adopted for the interaction parameters of fluid-fluid and wall-fluid potent... more The Sullivan model is adopted for the interaction parameters of fluid-fluid and wall-fluid potentials in binary mixtures. The capillary condensation in 'two-coexisting-phases' and 'three-coexisting-phases' open system confined between WO parallel walls ss studied analytically by a dynamical approach. The result shows that not only a first-order bul also a continuous hmsition is possible. The two systems sludied in the present paper have no apparent diffetmce in theit wetting behaviours, and their phase diagram conshucted in terms of the two components of the wall-fluid potential is a segment of an ellipse.

Nanotechnology, Dec 22, 2003

Faradaic current during anodic oxidation is measured over a relative humidity range of 40-70% usi... more Faradaic current during anodic oxidation is measured over a relative humidity range of 40-70% using an atomic force microscope with humidity control. The level of detected current during the fabrication of oxide dots on H-passivated Si(001) is in the picoampere (pA) level. Current flow began immediately (within a few milliseconds) after applying an oxidation voltage above a threshold value and

Surface Science, Nov 1, 2007

ABSTRACT The advantage of the CoFe-coated carbon nanotube (CNT) probes in a magnetic force micros... more ABSTRACT The advantage of the CoFe-coated carbon nanotube (CNT) probes in a magnetic force microscope (MFM) is verified on in-plane magnetized soft magnetic materials. CoFe-coated CNT, standard and low-moment MFM probes were used to observe closure domains in square and rectangular Permalloy elements. The perturbative effect of the CNT–MFM probe was far less than that of a standard MFM probe. Domain walls were clearly observed as a pair of dark and bright lines which was in agreement with the micromagnetic simulations. The vortex core was also clearly observed using the CNT–MFM probes.

Nanotechnology, Jul 2, 2004

Carbon nanotube-attached atomic force microscope probes were successfully used without nanotube b... more Carbon nanotube-attached atomic force microscope probes were successfully used without nanotube bending to make simultaneous precision nano-oxidation and faradaic current measurements in the dynamic mode. Probe oxidation on H-passivated Si(001) surfaces was carried out by two methods involving vector-scan and raster-scan with a much higher resolution and precision compared to the nanofabrication by standard cantilevers. Faradaic current of the order of a sub-picoampere was detected during nano-oxidation using a carbon nanotube probe, accurately reflecting the subtle difference in the oxidation reaction. The minute current detection through the AFM tip is sensitive enough for the detection of very thin oxides and small-sized features. The dimension of the meniscus during nano-oxidation, which is indispensable for establishing the mechanism model, was evaluated, based on the in situ faradaic current detection and edge broadening.

Journal of the Korean Physical Society, Jun 1, 2013

On the ferromagnetic-film-coated carbon nanotube for a magnetic force microscope (CNT-MFM) probe,... more On the ferromagnetic-film-coated carbon nanotube for a magnetic force microscope (CNT-MFM) probe, the stability of the magnetic structure in an external magnetic field was investigated using a three-dimensional micromagnetic simulation. When a magnetic field was applied along the longitudinal direction, in the direction opposite that of the magnetization of the probe, the direction of the magnetic moments of the probe remained the same up to-200 mT and then reversed all at once. When a magnetic field was applied along horizontal direction, the direction of the magnetic moments gradually tilts with increasing field. MFM observations seem to be possible for magnetic fields up to 100 ∼ 150 mT, judging from the magnetic structure of the probe. In contrast, the magnetic structures of pyramidal probes show vortex-like magnetic structure and low tolerance to an external magnetic field. The CNT-MFM probe is relatively robust under an external magnetic field due to the strong shape anisotropy attributed to its cylindrical shape.

Materials transactions, 2003

We have investigated magnetic domain structures of MnAs thin films grown on GaAs substrates by a ... more We have investigated magnetic domain structures of MnAs thin films grown on GaAs substrates by a magnetic force microscope. We observed, by an atomic force microscope, rectangular defects along GaAs [110] direction which disperse randomly on the surface of MnAs/ GaAs (001). The Curie temperature of MnAs is 45 C, and it is successfully confirmed directly by the variable temperature magnetic force microscope observation. We also investigated magnetic domain structures of MnAs/GaAs (111)B, and no apparent relation was observed between the topographic structure and the magnetic domain structure.

Applied Physics Letters, Feb 27, 2006

A self-synchronized voltage pulse application method was demonstrated as an effective control of ... more A self-synchronized voltage pulse application method was demonstrated as an effective control of the nano-oxidation using a dynamic force microscope. By creating a cyclic water meniscus using the large oscillation amplitude, self-synchronized voltage pulses can be realized during application of a continuous voltage to the sample. The modification of the probe-sample distance was equal to the change in the applied voltage pulse duration on the order of submicroseconds. This method realized the ultrastable control of the water meniscus formation.

Journal of Applied Physics, Jan 15, 2005

CoCr films were deposited on three types of GaAs substrates, GaAs(001), GaAs(111), and Al oxide∕G... more CoCr films were deposited on three types of GaAs substrates, GaAs(001), GaAs(111), and Al oxide∕GaAs(001). The perpendicular magnetic properties were investigated by magneto-optical Kerr-effect measurements. The direct deposition of the CoCr film on the GaAs substrate did not show any perpendicular magnetic properties. This fact indicates that the lattice distortion influenced by the GaAs lattice suppresses the perpendicular magnetism. The CoCr film on the Al oxide layer showed a tilted squarelike hysteresis loop. The thickness dependence of the hysteresis loop and the magnetic force microscopy showed that the onset thickness of ferromagnetism was 6.5nm. The domain size of the CoCr films monotonously decreases with the increasing thickness (6.5–75nm).

Physica E-low-dimensional Systems & Nanostructures, May 1, 2001

A huge positive magnetoresistance e ect, more than 10 000% at room temperature, has been discover... more A huge positive magnetoresistance e ect, more than 10 000% at room temperature, has been discovered in MnSb granular ÿlms. Granular ÿlms consisting of nanoscale MnSb dots were fabricated on a sulfur-passivated GaAs (0 0 1) substrate by molecular-beam epitaxy, then covered with an Sb thin layer. The MnSb granular ÿlms exhibit a strong in-plane anisotropy of the magnetic-ÿeld-sensitive current-voltage characteristics. When a constant voltage, above the threshold value, is applied in the [1 1 0] direction of the GaAs (0 0 1) surface, a steep change in the current, which we term magnetoresistive switch (MRS), is driven by the huge magnetoresistance e ect under a relatively low magnetic ÿeld (less than about 0:2 T). On the other hand, less than 1% magnetoresistance e ect was observed when the voltage was applied in the [1 1 0] direction of the GaAs surface. The origin of the anisotropy is discussed in terms of the microscopic structural anisotropy at the heterointerface.

Applied Physics Letters, May 5, 2004

A faradaic current on the order of a sub-pico-ampere was detected while fabricating two-dimension... more A faradaic current on the order of a sub-pico-ampere was detected while fabricating two-dimensional oxide nanostructures on H-passivated Si(001) surfaces. The detected faradaic current has been shown to faithfully reflect the degree of probe oxidation with a clear dependence on the variation of voltage and the tip speed. The faradaic current in dynamic mode can serve as a sensitive monitor of the nano-oxidation reaction for implementing precise closed-loop control of the oxide growth.

Journal of Applied Physics, Aug 15, 2004

A comprehensive analysis of the electrical current passing through the tip-substrate junction dur... more A comprehensive analysis of the electrical current passing through the tip-substrate junction during oxidation of silicon by scanning probe microscopy (SPM) is presented. This analysis identifies the electronic and ionic contributions to the total current, especially at the initial stages of the reaction, determines the effective contact area of the tip-substrate junction, and unifies the roles of space charge and meniscus formation. In this work, we concentrate on noncontact SPM oxidation. We analyze simultaneous force-distance and current-distance curves to demonstrate that total current flow during noncontact oxidation is significantly less for noncontact mode than for contact oxidation, although the resulting oxide volume is nearly identical. Ionization of water layers and mobile charge reorganization prior to and following meniscus formation is also shown to alter the tip-substrate capacitance and, therefore, the bending of the SPM cantilever.

Journal of Applied Physics, Aug 15, 2004

A comprehensive analysis of the electrical current passing through the tip-substrate junction dur... more A comprehensive analysis of the electrical current passing through the tip-substrate junction during oxidation of silicon by scanning probe microscopy (SPM) is presented. This analysis of experimental results under dc-bias conditions resolves the role of electronic and ionic contributions, especially for the initial stages of the reaction, determines the effective contact area of the tip-substrate junction, and unifies the roles of space charge and meniscus formation. In Part I of this work, we demonstrate that SPM oxidation is governed by a maximum charge density generated by electronic species within the junction at the onset of the oxidation process. Excess charge is channeled into lateral diffusion, keeping the charge density within the reaction zone constant and reducing the aspect ratio of the resulting oxide features. A uniform charge density implies that SPM oxides contain a fixed defect concentration, in accordance with the space-charge model. The effective (electrical) thickness of SPM oxides determined by these defects is investigated by Fowler-Nordheim analysis. We conclude that most of the electrical current involved in high voltage SPM oxidation of Si does not actually induce surface oxide growth, and that lateral diffusion and small aspect ratios are unavoidable aspects of contact-mode conditions.

Surface Science, Sep 1, 2006

ABSTRACT We systematically investigated thickness and magnetization variations of the domain stru... more ABSTRACT We systematically investigated thickness and magnetization variations of the domain structures of MnAs films on GaAs(0 0 1) using magnetic force microscopy (MFM) at room temperature. The observed thickness range is from 5 to 500 nm. The magnetic domain structures drastically change with increasing thickness because of the existence of the thickness-dependent periodic ridge-groove structure. The domain structures also depend on the magnetization histories. The MnAs films with the thickness of less than 50 nm have no groove structure and the single magnetic domain is realized at the remanent state. In the thickness more than 100 nm, on the other hand, the groove structures of paramagnetic β-MnAs appear. The complex magnetic domain structures of MnAs films result from the paramagnetic groove structures, the uniaxial anisotropy and weak perpendicular anisotropy.

E-journal of Surface Science and Nanotechnology, 2006

The dopant type and carrier concentration in a patterned semiconductor sample with three differen... more The dopant type and carrier concentration in a patterned semiconductor sample with three different doping regions were measured by scanning nonlinear dielectric microscope (SNDM). SNDM is used in the way of a scanning capacitance microscopy (SCM) with a new detection mechanism based on frequency detection. The topographic, pn-distribution and the carrier concentration images of a patterned semiconductor sample were measured at the same time. In concurrence with a demonstration of the SNDM-SCM measurements, the influence of an adsorbed water layer on measurements is evaluated in the vacuum and in the air over a relative humidity (RH) range of 20 to 80%. Adverse affects on capacitance measurements due to the variation in RH are revealed.

Nanotechnology, Feb 28, 2007

Carbon nanotube (CNT) probes enhance the stability of the nano-oxidation process under dynamic-mo... more Carbon nanotube (CNT) probes enhance the stability of the nano-oxidation process under dynamic-mode operation. In this paper we investigate how the hydrophobic nature of the CNT allows oxide nanostructures to be fabricated with constant aspect ratio over a wide range of relative humidity values. In particular, we characterize oxide growth by measuring both the integrated ionic current and volume expansion. Behaviour of different CNT probes was compared to assess individual stability and performance under identical voltage and humidity conditions. While much remains to be established about the relationship between exposure conditions and dynamic-mode parameters on nanoscale oxide fabrication, hydrophobicity is a key factor in the improved reliability of CNT probes over conventional ones.

Japanese Journal of Applied Physics, Mar 27, 2006

Surface Science, Sep 1, 2004

Scanning probe microscope nano-oxidation is carried out on H-passivated Si(0 0 1) surfaces using ... more Scanning probe microscope nano-oxidation is carried out on H-passivated Si(0 0 1) surfaces using a humidity control atomic force microscope (AFM) in contact and dynamic modes. To achieve high precision nano-oxidation at large scale, the original tube-scanner-based AFM unit is modified: horizontal movement of the whole sample block (sample stage and the scanner) is operated by an additional XY piezo stage, whilst its vertical movement is controlled by a piezo tube-scanner. The high linearity of the horizontal movement is demonstrated by high resolution oxide patterns which are fabricated after the instrumental modification using standard AFM cantilevers and a modified AFM cantilever with an added carbon nano-tube on tip.

Japanese Journal of Applied Physics, Apr 1, 2005

The Sullivan model is adopted for the interaction parameters of fluid-fluid and wall-fluid potent... more The Sullivan model is adopted for the interaction parameters of fluid-fluid and wall-fluid potentials in binary mixtures. The capillary condensation in 'two-coexisting-phases' and 'three-coexisting-phases' open system confined between WO parallel walls ss studied analytically by a dynamical approach. The result shows that not only a first-order bul also a continuous hmsition is possible. The two systems sludied in the present paper have no apparent diffetmce in theit wetting behaviours, and their phase diagram conshucted in terms of the two components of the wall-fluid potential is a segment of an ellipse.

Nanotechnology, Dec 22, 2003

Faradaic current during anodic oxidation is measured over a relative humidity range of 40-70% usi... more Faradaic current during anodic oxidation is measured over a relative humidity range of 40-70% using an atomic force microscope with humidity control. The level of detected current during the fabrication of oxide dots on H-passivated Si(001) is in the picoampere (pA) level. Current flow began immediately (within a few milliseconds) after applying an oxidation voltage above a threshold value and

Surface Science, Nov 1, 2007

ABSTRACT The advantage of the CoFe-coated carbon nanotube (CNT) probes in a magnetic force micros... more ABSTRACT The advantage of the CoFe-coated carbon nanotube (CNT) probes in a magnetic force microscope (MFM) is verified on in-plane magnetized soft magnetic materials. CoFe-coated CNT, standard and low-moment MFM probes were used to observe closure domains in square and rectangular Permalloy elements. The perturbative effect of the CNT–MFM probe was far less than that of a standard MFM probe. Domain walls were clearly observed as a pair of dark and bright lines which was in agreement with the micromagnetic simulations. The vortex core was also clearly observed using the CNT–MFM probes.

Nanotechnology, Jul 2, 2004

Carbon nanotube-attached atomic force microscope probes were successfully used without nanotube b... more Carbon nanotube-attached atomic force microscope probes were successfully used without nanotube bending to make simultaneous precision nano-oxidation and faradaic current measurements in the dynamic mode. Probe oxidation on H-passivated Si(001) surfaces was carried out by two methods involving vector-scan and raster-scan with a much higher resolution and precision compared to the nanofabrication by standard cantilevers. Faradaic current of the order of a sub-picoampere was detected during nano-oxidation using a carbon nanotube probe, accurately reflecting the subtle difference in the oxidation reaction. The minute current detection through the AFM tip is sensitive enough for the detection of very thin oxides and small-sized features. The dimension of the meniscus during nano-oxidation, which is indispensable for establishing the mechanism model, was evaluated, based on the in situ faradaic current detection and edge broadening.

Journal of the Korean Physical Society, Jun 1, 2013

On the ferromagnetic-film-coated carbon nanotube for a magnetic force microscope (CNT-MFM) probe,... more On the ferromagnetic-film-coated carbon nanotube for a magnetic force microscope (CNT-MFM) probe, the stability of the magnetic structure in an external magnetic field was investigated using a three-dimensional micromagnetic simulation. When a magnetic field was applied along the longitudinal direction, in the direction opposite that of the magnetization of the probe, the direction of the magnetic moments of the probe remained the same up to-200 mT and then reversed all at once. When a magnetic field was applied along horizontal direction, the direction of the magnetic moments gradually tilts with increasing field. MFM observations seem to be possible for magnetic fields up to 100 ∼ 150 mT, judging from the magnetic structure of the probe. In contrast, the magnetic structures of pyramidal probes show vortex-like magnetic structure and low tolerance to an external magnetic field. The CNT-MFM probe is relatively robust under an external magnetic field due to the strong shape anisotropy attributed to its cylindrical shape.

Materials transactions, 2003

We have investigated magnetic domain structures of MnAs thin films grown on GaAs substrates by a ... more We have investigated magnetic domain structures of MnAs thin films grown on GaAs substrates by a magnetic force microscope. We observed, by an atomic force microscope, rectangular defects along GaAs [110] direction which disperse randomly on the surface of MnAs/ GaAs (001). The Curie temperature of MnAs is 45 C, and it is successfully confirmed directly by the variable temperature magnetic force microscope observation. We also investigated magnetic domain structures of MnAs/GaAs (111)B, and no apparent relation was observed between the topographic structure and the magnetic domain structure.

Applied Physics Letters, Feb 27, 2006

A self-synchronized voltage pulse application method was demonstrated as an effective control of ... more A self-synchronized voltage pulse application method was demonstrated as an effective control of the nano-oxidation using a dynamic force microscope. By creating a cyclic water meniscus using the large oscillation amplitude, self-synchronized voltage pulses can be realized during application of a continuous voltage to the sample. The modification of the probe-sample distance was equal to the change in the applied voltage pulse duration on the order of submicroseconds. This method realized the ultrastable control of the water meniscus formation.

Journal of Applied Physics, Jan 15, 2005

CoCr films were deposited on three types of GaAs substrates, GaAs(001), GaAs(111), and Al oxide∕G... more CoCr films were deposited on three types of GaAs substrates, GaAs(001), GaAs(111), and Al oxide∕GaAs(001). The perpendicular magnetic properties were investigated by magneto-optical Kerr-effect measurements. The direct deposition of the CoCr film on the GaAs substrate did not show any perpendicular magnetic properties. This fact indicates that the lattice distortion influenced by the GaAs lattice suppresses the perpendicular magnetism. The CoCr film on the Al oxide layer showed a tilted squarelike hysteresis loop. The thickness dependence of the hysteresis loop and the magnetic force microscopy showed that the onset thickness of ferromagnetism was 6.5nm. The domain size of the CoCr films monotonously decreases with the increasing thickness (6.5–75nm).

Physica E-low-dimensional Systems & Nanostructures, May 1, 2001

A huge positive magnetoresistance e ect, more than 10 000% at room temperature, has been discover... more A huge positive magnetoresistance e ect, more than 10 000% at room temperature, has been discovered in MnSb granular ÿlms. Granular ÿlms consisting of nanoscale MnSb dots were fabricated on a sulfur-passivated GaAs (0 0 1) substrate by molecular-beam epitaxy, then covered with an Sb thin layer. The MnSb granular ÿlms exhibit a strong in-plane anisotropy of the magnetic-ÿeld-sensitive current-voltage characteristics. When a constant voltage, above the threshold value, is applied in the [1 1 0] direction of the GaAs (0 0 1) surface, a steep change in the current, which we term magnetoresistive switch (MRS), is driven by the huge magnetoresistance e ect under a relatively low magnetic ÿeld (less than about 0:2 T). On the other hand, less than 1% magnetoresistance e ect was observed when the voltage was applied in the [1 1 0] direction of the GaAs surface. The origin of the anisotropy is discussed in terms of the microscopic structural anisotropy at the heterointerface.

Applied Physics Letters, May 5, 2004

A faradaic current on the order of a sub-pico-ampere was detected while fabricating two-dimension... more A faradaic current on the order of a sub-pico-ampere was detected while fabricating two-dimensional oxide nanostructures on H-passivated Si(001) surfaces. The detected faradaic current has been shown to faithfully reflect the degree of probe oxidation with a clear dependence on the variation of voltage and the tip speed. The faradaic current in dynamic mode can serve as a sensitive monitor of the nano-oxidation reaction for implementing precise closed-loop control of the oxide growth.

Journal of Applied Physics, Aug 15, 2004

A comprehensive analysis of the electrical current passing through the tip-substrate junction dur... more A comprehensive analysis of the electrical current passing through the tip-substrate junction during oxidation of silicon by scanning probe microscopy (SPM) is presented. This analysis identifies the electronic and ionic contributions to the total current, especially at the initial stages of the reaction, determines the effective contact area of the tip-substrate junction, and unifies the roles of space charge and meniscus formation. In this work, we concentrate on noncontact SPM oxidation. We analyze simultaneous force-distance and current-distance curves to demonstrate that total current flow during noncontact oxidation is significantly less for noncontact mode than for contact oxidation, although the resulting oxide volume is nearly identical. Ionization of water layers and mobile charge reorganization prior to and following meniscus formation is also shown to alter the tip-substrate capacitance and, therefore, the bending of the SPM cantilever.

Journal of Applied Physics, Aug 15, 2004

A comprehensive analysis of the electrical current passing through the tip-substrate junction dur... more A comprehensive analysis of the electrical current passing through the tip-substrate junction during oxidation of silicon by scanning probe microscopy (SPM) is presented. This analysis of experimental results under dc-bias conditions resolves the role of electronic and ionic contributions, especially for the initial stages of the reaction, determines the effective contact area of the tip-substrate junction, and unifies the roles of space charge and meniscus formation. In Part I of this work, we demonstrate that SPM oxidation is governed by a maximum charge density generated by electronic species within the junction at the onset of the oxidation process. Excess charge is channeled into lateral diffusion, keeping the charge density within the reaction zone constant and reducing the aspect ratio of the resulting oxide features. A uniform charge density implies that SPM oxides contain a fixed defect concentration, in accordance with the space-charge model. The effective (electrical) thickness of SPM oxides determined by these defects is investigated by Fowler-Nordheim analysis. We conclude that most of the electrical current involved in high voltage SPM oxidation of Si does not actually induce surface oxide growth, and that lateral diffusion and small aspect ratios are unavoidable aspects of contact-mode conditions.

Surface Science, Sep 1, 2006

ABSTRACT We systematically investigated thickness and magnetization variations of the domain stru... more ABSTRACT We systematically investigated thickness and magnetization variations of the domain structures of MnAs films on GaAs(0 0 1) using magnetic force microscopy (MFM) at room temperature. The observed thickness range is from 5 to 500 nm. The magnetic domain structures drastically change with increasing thickness because of the existence of the thickness-dependent periodic ridge-groove structure. The domain structures also depend on the magnetization histories. The MnAs films with the thickness of less than 50 nm have no groove structure and the single magnetic domain is realized at the remanent state. In the thickness more than 100 nm, on the other hand, the groove structures of paramagnetic β-MnAs appear. The complex magnetic domain structures of MnAs films result from the paramagnetic groove structures, the uniaxial anisotropy and weak perpendicular anisotropy.