The Experts below are selected from a list of 219 Experts worldwide ranked by ideXlab platform
Yoshihiro Hishiyama - One of the best experts on this subject based on the ideXlab platform.
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A method for origin correction of Raman band frequencies in the first order Raman spectrum for carbon materials and Raman frequency of G band versus d002 plots
Carbon, 2008Co-Authors: Akira Yoshida, Yutaka Kaburagi, Yoshihiro HishiyamaAbstract:A method was developed to correct the Raman frequencies of the D, G and D, bands in the first order Raman spectrum for carbon materials with an incident excitation beam of 514.5 nm. It was demonstrated that the lighting of the Ne lamp set at a proper position in the Raman spectrometer during the measurement of the first order spectrum causes superposition of the 556.28nm line from Ne lamp at 1458.52cm-1 in Raman shift scale on the first order Raman spectrum, being of use as a standard. There could be a practical application on the plots of the Raman frequency of the G band (G-RF) vs. interlayer spacing don for carbon materials in assessing quality. The method is demonstrated for determination of G-RF for a cleaved surface of a Kish Graphite, an HOPG edge plane, PC basal planes, a polished surface of commercially available isotropic Graphite, a buffed surface of glass-like carbon and side surfaces of benzene-derived vapor-grown carbon fibers.
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Kish Graphite as a magnetic field sensor
Carbon, 2004Co-Authors: Yutaka Kaburagi, Yuichiro Asano, Yoshihiro HishiyamaAbstract:Magnetoresistance effect (MRE) and Hall effect have been applied to magnetic field sensors. As materials for the field sensor due to MRE, semiconductor compounds and ferromagnetic metals have been used, but Graphite materials have not, though Graphite exhibits positive magnetoresistance. A purified high quality Kish Graphite (KG) exhibits a large transverse magnetoresistance ∆ρ/ρ even at room temperature. KG is a Graphite flake precipitated from molten iron at high temperatures [1]. When the flakes are made at a very high temperature above boiling point of iron and purified carefully, they have higher crystallinity than that of HOPG and exhibit a nature very similar to single crystal Graphite. In the present study, therefore, a sensitive magnetic field sensor was tried to prepare using such KG flakes. On the MRE sensors, a magnetic field is measured as a voltage change ∆V induced by the magnetic field under a constant electric current: ∆ρ/ρ = ∆V/V. ∆V increases with the increase of the sample voltage V under zero magnetic field, if the defect concentration in the sample does not increase with increasing V. V increases with the increase of current, sample length and sample thickness. However, the power W increases with increasing current I as W = IR, where R is the sample resistance, i.e. Joule heat generates and temperature of the sample should rise under a large current flow. In the case of KG, sample sizes are limited because of flakes. Therefore, reducing the sample thickness is important factor to increase V and ∆V in the present study, but a careful treatment for reducing the thickness is needed to increase ∆ρ/ρ, i.e. not to increase the defect concentration.
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stm study of surfaces of Kish Graphite doped by iron
Carbon, 2001Co-Authors: E Bourelle, Yoshihiro Hishiyama, Yutaka Kaburagi, Michio InagakiAbstract:Iron doping effect on Kish Graphite (KG) flakes at 2800°C was studied by observing structural defects, pores and hillocks, at different depth of the specimens under STM and by measuring residual resistivity ratio (RRR) values. A low RRR value of the KG flakes indicates a high density of defects in the specimen. The defects were formed due to the diffusion of iron clusters, which were assumed to occur across and along basal planes of the Graphite; the former created pores and the latter hillocks. In KG flakes heat-treated at 2800°C, the increase in the number of the hillocks can be explained by the diffusion to the outer parts of iron impurities trapped in the KG flakes along the basal planes of the Graphite. Iron doping with a small change in RRR values led to the formation of pores at near depth of the flake, with mainly diffusion of iron to the inside of the flake. Iron doping with a large change in RRR values led to the diffusion of iron to the inside of the flake following mainly by the reversed diffusion of iron, forming hillocks.
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Electronic properties of Kish Graphite crystals with low values of residual resistivity ratio
Carbon, 1998Co-Authors: Yutaka Kaburagi, Yoshihiro HishiyamaAbstract:Electronic properties, such as in-plane electrical resistivity ρ, transverse magnetoresistance Δρ/ρ0, Hall coefficient RH and absolute thermoelectric power S, were investigated for Kish Graphite (KG) specimens with residual resistivity ratio RRR lower than 10. Measurements of mass magnetization were also carried out. A linear dependence of Δρ/ρ0 on magnetic field in fields above about 2 T and an anomalous positive RH were observed at 77 K. S was entirely positive, although phonon drag effects were clearly observed in the temperature dependence. The shifts of RH and S toward the positive side are attributed to excess holes. On the other hand, no anomalous behaviors were found on ρ and a- and c-axes mass susceptibilities. Annealing effect on Δρ/ρ0 and RH for one of the KG specimens by heat-treatments up to 2950°C was also examined. After annealing at 2950°C, Δρ/ρ0 increased and exhibited an usual field dependence similar to that for KG with RRR>10, while RH remained positive. The origin of the excess holes in KG with RRR
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electronic properties of Kish Graphite crystals with low values of residual resistivity ratio
Carbon, 1998Co-Authors: Yutaka Kaburagi, Yoshihiro HishiyamaAbstract:Electronic properties, such as in-plane electrical resistivity ρ, transverse magnetoresistance Δρ/ρ0, Hall coefficient RH and absolute thermoelectric power S, were investigated for Kish Graphite (KG) specimens with residual resistivity ratio RRR lower than 10. Measurements of mass magnetization were also carried out. A linear dependence of Δρ/ρ0 on magnetic field in fields above about 2 T and an anomalous positive RH were observed at 77 K. S was entirely positive, although phonon drag effects were clearly observed in the temperature dependence. The shifts of RH and S toward the positive side are attributed to excess holes. On the other hand, no anomalous behaviors were found on ρ and a- and c-axes mass susceptibilities. Annealing effect on Δρ/ρ0 and RH for one of the KG specimens by heat-treatments up to 2950°C was also examined. After annealing at 2950°C, Δρ/ρ0 increased and exhibited an usual field dependence similar to that for KG with RRR>10, while RH remained positive. The origin of the excess holes in KG with RRR<10 is assumed to be the presence of a slight amount of iron impurities.
Yutaka Kaburagi - One of the best experts on this subject based on the ideXlab platform.
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A method for origin correction of Raman band frequencies in the first order Raman spectrum for carbon materials and Raman frequency of G band versus d002 plots
Carbon, 2008Co-Authors: Akira Yoshida, Yutaka Kaburagi, Yoshihiro HishiyamaAbstract:A method was developed to correct the Raman frequencies of the D, G and D, bands in the first order Raman spectrum for carbon materials with an incident excitation beam of 514.5 nm. It was demonstrated that the lighting of the Ne lamp set at a proper position in the Raman spectrometer during the measurement of the first order spectrum causes superposition of the 556.28nm line from Ne lamp at 1458.52cm-1 in Raman shift scale on the first order Raman spectrum, being of use as a standard. There could be a practical application on the plots of the Raman frequency of the G band (G-RF) vs. interlayer spacing don for carbon materials in assessing quality. The method is demonstrated for determination of G-RF for a cleaved surface of a Kish Graphite, an HOPG edge plane, PC basal planes, a polished surface of commercially available isotropic Graphite, a buffed surface of glass-like carbon and side surfaces of benzene-derived vapor-grown carbon fibers.
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Kish Graphite as a magnetic field sensor
Carbon, 2004Co-Authors: Yutaka Kaburagi, Yuichiro Asano, Yoshihiro HishiyamaAbstract:Magnetoresistance effect (MRE) and Hall effect have been applied to magnetic field sensors. As materials for the field sensor due to MRE, semiconductor compounds and ferromagnetic metals have been used, but Graphite materials have not, though Graphite exhibits positive magnetoresistance. A purified high quality Kish Graphite (KG) exhibits a large transverse magnetoresistance ∆ρ/ρ even at room temperature. KG is a Graphite flake precipitated from molten iron at high temperatures [1]. When the flakes are made at a very high temperature above boiling point of iron and purified carefully, they have higher crystallinity than that of HOPG and exhibit a nature very similar to single crystal Graphite. In the present study, therefore, a sensitive magnetic field sensor was tried to prepare using such KG flakes. On the MRE sensors, a magnetic field is measured as a voltage change ∆V induced by the magnetic field under a constant electric current: ∆ρ/ρ = ∆V/V. ∆V increases with the increase of the sample voltage V under zero magnetic field, if the defect concentration in the sample does not increase with increasing V. V increases with the increase of current, sample length and sample thickness. However, the power W increases with increasing current I as W = IR, where R is the sample resistance, i.e. Joule heat generates and temperature of the sample should rise under a large current flow. In the case of KG, sample sizes are limited because of flakes. Therefore, reducing the sample thickness is important factor to increase V and ∆V in the present study, but a careful treatment for reducing the thickness is needed to increase ∆ρ/ρ, i.e. not to increase the defect concentration.
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stm study of surfaces of Kish Graphite doped by iron
Carbon, 2001Co-Authors: E Bourelle, Yoshihiro Hishiyama, Yutaka Kaburagi, Michio InagakiAbstract:Iron doping effect on Kish Graphite (KG) flakes at 2800°C was studied by observing structural defects, pores and hillocks, at different depth of the specimens under STM and by measuring residual resistivity ratio (RRR) values. A low RRR value of the KG flakes indicates a high density of defects in the specimen. The defects were formed due to the diffusion of iron clusters, which were assumed to occur across and along basal planes of the Graphite; the former created pores and the latter hillocks. In KG flakes heat-treated at 2800°C, the increase in the number of the hillocks can be explained by the diffusion to the outer parts of iron impurities trapped in the KG flakes along the basal planes of the Graphite. Iron doping with a small change in RRR values led to the formation of pores at near depth of the flake, with mainly diffusion of iron to the inside of the flake. Iron doping with a large change in RRR values led to the diffusion of iron to the inside of the flake following mainly by the reversed diffusion of iron, forming hillocks.
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Electronic properties of Kish Graphite crystals with low values of residual resistivity ratio
Carbon, 1998Co-Authors: Yutaka Kaburagi, Yoshihiro HishiyamaAbstract:Electronic properties, such as in-plane electrical resistivity ρ, transverse magnetoresistance Δρ/ρ0, Hall coefficient RH and absolute thermoelectric power S, were investigated for Kish Graphite (KG) specimens with residual resistivity ratio RRR lower than 10. Measurements of mass magnetization were also carried out. A linear dependence of Δρ/ρ0 on magnetic field in fields above about 2 T and an anomalous positive RH were observed at 77 K. S was entirely positive, although phonon drag effects were clearly observed in the temperature dependence. The shifts of RH and S toward the positive side are attributed to excess holes. On the other hand, no anomalous behaviors were found on ρ and a- and c-axes mass susceptibilities. Annealing effect on Δρ/ρ0 and RH for one of the KG specimens by heat-treatments up to 2950°C was also examined. After annealing at 2950°C, Δρ/ρ0 increased and exhibited an usual field dependence similar to that for KG with RRR>10, while RH remained positive. The origin of the excess holes in KG with RRR
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electronic properties of Kish Graphite crystals with low values of residual resistivity ratio
Carbon, 1998Co-Authors: Yutaka Kaburagi, Yoshihiro HishiyamaAbstract:Electronic properties, such as in-plane electrical resistivity ρ, transverse magnetoresistance Δρ/ρ0, Hall coefficient RH and absolute thermoelectric power S, were investigated for Kish Graphite (KG) specimens with residual resistivity ratio RRR lower than 10. Measurements of mass magnetization were also carried out. A linear dependence of Δρ/ρ0 on magnetic field in fields above about 2 T and an anomalous positive RH were observed at 77 K. S was entirely positive, although phonon drag effects were clearly observed in the temperature dependence. The shifts of RH and S toward the positive side are attributed to excess holes. On the other hand, no anomalous behaviors were found on ρ and a- and c-axes mass susceptibilities. Annealing effect on Δρ/ρ0 and RH for one of the KG specimens by heat-treatments up to 2950°C was also examined. After annealing at 2950°C, Δρ/ρ0 increased and exhibited an usual field dependence similar to that for KG with RRR>10, while RH remained positive. The origin of the excess holes in KG with RRR<10 is assumed to be the presence of a slight amount of iron impurities.
C.r. Loper - One of the best experts on this subject based on the ideXlab platform.
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the formation of Kish Graphite
Carbon, 1991Co-Authors: C.r. LoperAbstract:Abstract The formation mechanism of Kish Graphite has been studied by observing the morphology developed under a number of experimental conditions. Kish Graphite is formed on the free surface of molten iron and grows in a foliated dendritic manner. However, this surface formation mode may be suppressed in favor of Graphite formation within the melt by increasing the cooling rate and avoiding the presence of oxygen at the melt surface. Oxygen not only affects the Graphite morphology by attacking the growth front of Kish Graphite crystal, but promotes nucleation of Graphite on the melt surface. Increased cooling rates and exposure of the melt to oxygen favor the formation of a foliated dendritic structure. On the other hand, slow cooling and avoidance of oxygen result in the formation of a Graphite sheet over the melt surface. In addition, sulfur has been shown to play an important role in the formation of Kish Graphite.
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Kish a source of crystalline Graphite
Carbon, 1991Co-Authors: C.r. LoperAbstract:Abstract The crystallographic characteristics and the form and distribution of impurities of Kish Graphite were investigated, demonstrating the ideal, or near-ideal, crystal structure of Kish Graphite. The impurity studies indicated that special attention is needed for the development of suitable and effective recovery procedures. Some flexible Graphite sheets were also fabricated from Kish Graphite to demonstrate the potential of possible applications.
Michio Inagaki - One of the best experts on this subject based on the ideXlab platform.
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New Carbons - Control of Structure and Functions - CHAPTER 2 – Highly Oriented Graphites
New Carbons - Control of Structure and Functions, 2020Co-Authors: Michio InagakiAbstract:This chapter describes three kinds of highly oriented Graphites, namely, Kish Graphite, highly oriented pyrolytic Graphite (HOPG), and Graphite films derived from polyimides, their preparation, with particular emphasis on the control of a high degree of orientation, crystallographic structures, and different properties.. A part of the carbon precipitates as a separated phase from iron to form Graphites. These Graphites precipitated from molten iron at high temperatures are known as Kish Graphite. These Kish Graphite flakes were the center of attraction when the flakes were found to have single crystal nature when produced at a very high temperature. To obtain highly crystallized Graphite flakes, which can be regarded as single crystals, purification in a flow of halogen gas at high temperatures is essential. Polyimides have been developed as thermoresistant polymers and are used in different fields, especially in the field of electronics. Some polyimide films are found to give a Graphite film with rather high crystallinity through a simple heat treatment under atmospheric pressure. HOPG is inferior in crystallinity to Kish Graphite, but has an advantage in being able to have a large size. This is the reason HOPG has been used as the samples for various fundamental scientific researches, instead of single crystals.
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Host effect for intercalation of CuCl2 in molten salt
Carbon, 2003Co-Authors: Michio Inagaki, Zheng-de WangAbstract:Abstract A remarkable host effect on the intercalation of CuCl2 in a molten salt system of CuCl2-KCl was observed. Even after 12 days in the molten salt at 380°C, no Graphite intercalation compounds (GICs) were obtained from the Graphite films prepared from a polyimide Kapton, while from highly oriented pyrolytic Graphite and Kish Graphite with similar physical sizes, GICs were obtained within one day and from natural Graphite flakes with the size of 400 μm, within two hours. The Graphite film containing more defects (H-film) was transformed to the stage-2 GIC at 500° by applying Cl2 pressure, but the more perfect film (O-film) did not under the same condition.
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stm study of surfaces of Kish Graphite doped by iron
Carbon, 2001Co-Authors: E Bourelle, Yoshihiro Hishiyama, Yutaka Kaburagi, Michio InagakiAbstract:Iron doping effect on Kish Graphite (KG) flakes at 2800°C was studied by observing structural defects, pores and hillocks, at different depth of the specimens under STM and by measuring residual resistivity ratio (RRR) values. A low RRR value of the KG flakes indicates a high density of defects in the specimen. The defects were formed due to the diffusion of iron clusters, which were assumed to occur across and along basal planes of the Graphite; the former created pores and the latter hillocks. In KG flakes heat-treated at 2800°C, the increase in the number of the hillocks can be explained by the diffusion to the outer parts of iron impurities trapped in the KG flakes along the basal planes of the Graphite. Iron doping with a small change in RRR values led to the formation of pores at near depth of the flake, with mainly diffusion of iron to the inside of the flake. Iron doping with a large change in RRR values led to the diffusion of iron to the inside of the flake following mainly by the reversed diffusion of iron, forming hillocks.
Y Hishiyama - One of the best experts on this subject based on the ideXlab platform.
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Low temperature anomalies in thermoelectricity of highly oriented Graphite in relation to sample quality
Carbon, 2003Co-Authors: Y HishiyamaAbstract:Abstract The thermoelectric power S of various specimens of Kish Graphite and highly oriented pyrolytic Graphite was studied in relation to the sample quality at temperatures ( T ) between 1.3 and 280 K. The resistivity ratio between 300 and 4.2 K used as a measure of structural perfection ranges from 1.6 to 35.8. A thermoelectric transport coefficient β xx (0) has been determined for specimens with resistivity ratios of 10.0 and 35.8. s as well as β xx (0) show a common behavior as follows; a negative dent at about 3.0–4.4 K, a sharp peak at about 6.5–14 K, a pronounced negative dip around 20–37 K and a broad peak somewhere between 125 and 160 K. The dent and peak depend strongly on the quality of the specimen: The former is a new finding and may be due to some unknown type of the phonon drag effect, while the latter is due to the two-stage phonon drag effect proposed by Sugihara et al . based on their own observations.
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a scaling approach to the transverse magnetoresistance of Kish Graphite at 77 k
Carbon, 1997Co-Authors: Y Kaburagi, Y HishiyamaAbstract:A scaling of magnetoresistance Δϱϱ0 was examined using Bϱ0 at liquid nitrogen temperature for Kish Graphite (KG) specimens with different values of residual resistivity ratio RRR between 3.92 and 35.6. The plots of Δϱϱ0 against Bϱ0 and the exponent n against Bϱ0 in Δϱϱ0 ∞ Bn varied systematically with RRR. The exponent n against Bϱ0 plots showed a minimum and maximum of n. The values of the minimum and maximum decrease with decreasing RRR, and the values of Bϱ0 at the minimum and the maximum approach each other with the decrease of RRR. The minimum and maximum seem to coincide for the specimen with lower RRR than 3.92. The saturation of n around n = 1 is found in the high Bϱ0 region only for the specimens with RRR < 8.
