Tohru Tsuruoka - Academia.edu (original) (raw)
Papers by Tohru Tsuruoka
ACS applied electronic materials, Sep 2, 2020
Variable capacitance functions are demonstrated utilizing the transport of Li ions in a simple Pt... more Variable capacitance functions are demonstrated utilizing the transport of Li ions in a simple Pt/lithium phosphorous oxynitride (LiPON)/Pt structure. The capacitance originates mainly from the formation of an electrochemical double layer (EDL) at the interfaces between LiPON and Pt at lower frequencies. Voltage applications drive Li ions from the positively-biased electrode to the negatively-biased one. At higher voltages, the number of Li ions at the positive electrode decreases to zero, which makes their contribution to the total EDL capacitance vanish. As a result, the LiPON capacitor exhibits decreased capacitance as voltage bias is increased, similar to what is found in a varactor diode. The upper frequency limit of the capacitance variation increases with increased temperature, which seems to be determined by the ionic conductivity of the LiPON matrix. A voltage-controlled oscillator (VCO) operation is also demonstrated by incorporating the LiPON variable capacitors into a resistor-capacitor oscillator circuit. The VCO clearly shows that the oscillation frequency of the output waveforms is exponentially increased by an increase in input direct-current voltage, which behavior is the same as a varactor diodebased VCO. The results indicate that this ionic variable capacitor can be used as a building block in analog and mixed signal electronic circuits.
Japanese Journal of Applied Physics, 2018
The Japan Society of Applied Physics, Jul 22, 2016
Japanese Journal of Applied Physics, Feb 19, 2018
The rate limiting process in first resistive switching, called the "forming process", is determin... more The rate limiting process in first resistive switching, called the "forming process", is determined by measuring the switching time of an as-fabricated Cu/Ta 2 O 5 /Pt atomic switch as a function of the ambient temperature and the Ta 2 O 5 thickness. The temperature dependence is well fitted by the Arrhenius equation, suggesting that a certain activation process dominates the switching phenomenon. The switching time increases linearly as the Ta 2 O 5 thickness increases. The results herein clearly suggest that the rate limiting process is the drift of Cu cations in the Ta 2 O 5 layer. We determine that the activation energy is 0.4 eV.
Materials horizons, 2018
Self-assembled mesoporous fullerene C70 cube-shaped crystals with crystalline frameworks displaye... more Self-assembled mesoporous fullerene C70 cube-shaped crystals with crystalline frameworks displayed enhanced PL intensity (around 15 times higher intensity compared to bulk C70) due to the high degree of crystallinity in their pore walls.
Langmuir, Jan 4, 2013
Herein we report the surfactant-triggered assembly of fullerene (C60) into 3D flowerlike microcry... more Herein we report the surfactant-triggered assembly of fullerene (C60) into 3D flowerlike microcrystals at the liquid-liquid interface. C60 crystals were grown using a liquid-liquid interfacial precipitation (LLIP) method by layering surfactant solution in butanol with a saturated solution of C60 in benzene. In the LLIP method, it is suggested that the crystal formation mechanism is driven by supersaturation related to the low C60 solubility in alcohol. We found that the dimensions of the synthesized C60 flowers depend on the concentration and surfactant type. In the absence of surfactant (i.e., in the butanol/benzene system), 1D C60 nanowhiskers (nanorods) and C60 nanotubes (diameter 400 nm-2 μm and length 5-20 μm) are obtained. However, when surfactants are incorporated into the system flowerlike microcrystals consisting of C60 nanotubes are observed. For instance, crystals grown at the interface of a 0.01% diglycerol monolaurate (C12G2) nonionic surfactant in butanol with benzene lead to the formation of flower-shaped microcrystals of average sizes in the range of 10-35 μm. To the best of our knowledge, this is the first example of the surfactant-assisted assembly of C60 crystals. X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements have shown that fullerene flowers have a hexagonal structure with cell dimensions of a = 2.539 nm and c = 1.021 nm, which differ from that of pristine C60. Mixtures of flower-shaped C60 crystals and free-standing C60 nanotubes are found in the 0.1% C12G2/butanol system. However, clusters or giant aggregates of nanowhiskers lacking any specific shape are observed in the 1% C12G2/butanol system although these crystals exhibit hexagonal close-packed structures. Flower-shaped C60 microcrystals are also observed with anionic surfactants cetyltrimethylammonium bromide (CTAB) and cetyltrimethylammonium chloride (CTAC). C60 flowers obtained from 0.01% CTAB and 0.01% CTAC also exhibit hexagonal structures with cell dimensions of a = 2.329 nm and c = 1.273 nm, a = 2.459 nm and c = 0.938 nm, respectively. Our C60 flowers exhibit intense photoluminescence (PL) and a blue-shifted PL intensity maximum compared to the same parameters for pristine C60, demonstrating the potential to control the optoelectronic properties of fullerene-based nanostructures.
Science and Technology of Advanced Materials, Feb 27, 2023
Advances in atom and single molecule machines, 2020
Three-terminal atomic switches control formation and annihilation of a conductive path between a ... more Three-terminal atomic switches control formation and annihilation of a conductive path between a source and a drain by the electric field applied through a gate electrode. Advantage of the three-terminal atomic switches to the two-terminal atomic switches is that a signal line of the three-terminal atomic switches is separated from a signal line, which increases their controllability especially when used as logic devices. Three-terminal atomic switches are classified into two types by a species of controlled ions that form a conductive path. One type controls metal cations, so that a conductive path is a metal filament. The other type controls oxygen ions, so that a conductive path is an oxygen deficient conductive region. Both types show nonvolatile switching with a high on/off ratio over five orders of magnitude.
The Japan Society of Applied Physics, Jul 10, 2018
The Japan Society of Applied Physics, Jul 22, 2016
Solid State Ionics, Dec 1, 2018
Three-terminal structures have an advantage over two-terminal structures in logic applications an... more Three-terminal structures have an advantage over two-terminal structures in logic applications and neuromorphic circuits, However, three-terminal operation based on Valence Change RAM still requires a larger gate bias to form/dissolve a conductive path between the source and the drain, especially for turning off. Here, reduction in gate bias and gate leakage current in nonvolatile operation of oxygen vacancy drift-controlled threeterminal ReRAM is demonstrated by W/Ti (gate)/TaO x (resistance switching layer)/Pt (source), Pt (drain) structure. Introduction of a Ti thin layer between W and TaO x layers prevents a conductive channel formation between gate and source/drain electrodes. Consequently, as-fabricated high resistance between gate and source/ drain is kept, resulting in smaller gate leakage current. We also achieved interface engineering on a sidewall structure of Pt (source)/SiO 2 (insulator)/Pt (drain) multi-layer, reducing in an operating bias from 10 V to 4 V or less.
ACS Applied Materials & Interfaces, Apr 6, 2023
Nanotechnology, Apr 11, 2011
The switching time of a Cu(2)S-based gap-type atomic switch is investigated as a function of temp... more The switching time of a Cu(2)S-based gap-type atomic switch is investigated as a function of temperature, bias voltage, and initial off-resistance. The gap-type atomic switch is realized using a scanning tunneling microscope (STM), in which the formation and annihilation of a Cu-atom bridge in the vacuum gap between the Cu(2)S electrode and the Pt tip of the STM are controlled by a solid-electrochemical reaction. Increasing the temperature decreases the switching time exponentially with an activation energy of about 1.38 eV. Increasing the bias voltage also shortens the switching time exponentially, exhibiting a greater exponent for the lower bias than for the higher bias. Furthermore, faster switching has been achieved by decreasing the initial off-resistance between the Cu(2)S electrode and STM tip. On the basis of these results, we suggest that, in addition to the chemical reaction, the electric field in the vacuum gap plays a significant role in the operation of a gap-type atomic switch. This investigation advances our understanding of the operating mechanism of an atomic switch, which is a new concept for future electronic devices.
The Japan Society of Applied Physics, Jul 6, 2021
ACS applied electronic materials, Sep 2, 2020
Variable capacitance functions are demonstrated utilizing the transport of Li ions in a simple Pt... more Variable capacitance functions are demonstrated utilizing the transport of Li ions in a simple Pt/lithium phosphorous oxynitride (LiPON)/Pt structure. The capacitance originates mainly from the formation of an electrochemical double layer (EDL) at the interfaces between LiPON and Pt at lower frequencies. Voltage applications drive Li ions from the positively-biased electrode to the negatively-biased one. At higher voltages, the number of Li ions at the positive electrode decreases to zero, which makes their contribution to the total EDL capacitance vanish. As a result, the LiPON capacitor exhibits decreased capacitance as voltage bias is increased, similar to what is found in a varactor diode. The upper frequency limit of the capacitance variation increases with increased temperature, which seems to be determined by the ionic conductivity of the LiPON matrix. A voltage-controlled oscillator (VCO) operation is also demonstrated by incorporating the LiPON variable capacitors into a resistor-capacitor oscillator circuit. The VCO clearly shows that the oscillation frequency of the output waveforms is exponentially increased by an increase in input direct-current voltage, which behavior is the same as a varactor diodebased VCO. The results indicate that this ionic variable capacitor can be used as a building block in analog and mixed signal electronic circuits.
Japanese Journal of Applied Physics, 2018
ACS applied electronic materials, Sep 2, 2020
Variable capacitance functions are demonstrated utilizing the transport of Li ions in a simple Pt... more Variable capacitance functions are demonstrated utilizing the transport of Li ions in a simple Pt/lithium phosphorous oxynitride (LiPON)/Pt structure. The capacitance originates mainly from the formation of an electrochemical double layer (EDL) at the interfaces between LiPON and Pt at lower frequencies. Voltage applications drive Li ions from the positively-biased electrode to the negatively-biased one. At higher voltages, the number of Li ions at the positive electrode decreases to zero, which makes their contribution to the total EDL capacitance vanish. As a result, the LiPON capacitor exhibits decreased capacitance as voltage bias is increased, similar to what is found in a varactor diode. The upper frequency limit of the capacitance variation increases with increased temperature, which seems to be determined by the ionic conductivity of the LiPON matrix. A voltage-controlled oscillator (VCO) operation is also demonstrated by incorporating the LiPON variable capacitors into a resistor-capacitor oscillator circuit. The VCO clearly shows that the oscillation frequency of the output waveforms is exponentially increased by an increase in input direct-current voltage, which behavior is the same as a varactor diodebased VCO. The results indicate that this ionic variable capacitor can be used as a building block in analog and mixed signal electronic circuits.
Japanese Journal of Applied Physics, 2018
The Japan Society of Applied Physics, Jul 22, 2016
Japanese Journal of Applied Physics, Feb 19, 2018
The rate limiting process in first resistive switching, called the "forming process", is determin... more The rate limiting process in first resistive switching, called the "forming process", is determined by measuring the switching time of an as-fabricated Cu/Ta 2 O 5 /Pt atomic switch as a function of the ambient temperature and the Ta 2 O 5 thickness. The temperature dependence is well fitted by the Arrhenius equation, suggesting that a certain activation process dominates the switching phenomenon. The switching time increases linearly as the Ta 2 O 5 thickness increases. The results herein clearly suggest that the rate limiting process is the drift of Cu cations in the Ta 2 O 5 layer. We determine that the activation energy is 0.4 eV.
Materials horizons, 2018
Self-assembled mesoporous fullerene C70 cube-shaped crystals with crystalline frameworks displaye... more Self-assembled mesoporous fullerene C70 cube-shaped crystals with crystalline frameworks displayed enhanced PL intensity (around 15 times higher intensity compared to bulk C70) due to the high degree of crystallinity in their pore walls.
Langmuir, Jan 4, 2013
Herein we report the surfactant-triggered assembly of fullerene (C60) into 3D flowerlike microcry... more Herein we report the surfactant-triggered assembly of fullerene (C60) into 3D flowerlike microcrystals at the liquid-liquid interface. C60 crystals were grown using a liquid-liquid interfacial precipitation (LLIP) method by layering surfactant solution in butanol with a saturated solution of C60 in benzene. In the LLIP method, it is suggested that the crystal formation mechanism is driven by supersaturation related to the low C60 solubility in alcohol. We found that the dimensions of the synthesized C60 flowers depend on the concentration and surfactant type. In the absence of surfactant (i.e., in the butanol/benzene system), 1D C60 nanowhiskers (nanorods) and C60 nanotubes (diameter 400 nm-2 μm and length 5-20 μm) are obtained. However, when surfactants are incorporated into the system flowerlike microcrystals consisting of C60 nanotubes are observed. For instance, crystals grown at the interface of a 0.01% diglycerol monolaurate (C12G2) nonionic surfactant in butanol with benzene lead to the formation of flower-shaped microcrystals of average sizes in the range of 10-35 μm. To the best of our knowledge, this is the first example of the surfactant-assisted assembly of C60 crystals. X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements have shown that fullerene flowers have a hexagonal structure with cell dimensions of a = 2.539 nm and c = 1.021 nm, which differ from that of pristine C60. Mixtures of flower-shaped C60 crystals and free-standing C60 nanotubes are found in the 0.1% C12G2/butanol system. However, clusters or giant aggregates of nanowhiskers lacking any specific shape are observed in the 1% C12G2/butanol system although these crystals exhibit hexagonal close-packed structures. Flower-shaped C60 microcrystals are also observed with anionic surfactants cetyltrimethylammonium bromide (CTAB) and cetyltrimethylammonium chloride (CTAC). C60 flowers obtained from 0.01% CTAB and 0.01% CTAC also exhibit hexagonal structures with cell dimensions of a = 2.329 nm and c = 1.273 nm, a = 2.459 nm and c = 0.938 nm, respectively. Our C60 flowers exhibit intense photoluminescence (PL) and a blue-shifted PL intensity maximum compared to the same parameters for pristine C60, demonstrating the potential to control the optoelectronic properties of fullerene-based nanostructures.
Science and Technology of Advanced Materials, Feb 27, 2023
Advances in atom and single molecule machines, 2020
Three-terminal atomic switches control formation and annihilation of a conductive path between a ... more Three-terminal atomic switches control formation and annihilation of a conductive path between a source and a drain by the electric field applied through a gate electrode. Advantage of the three-terminal atomic switches to the two-terminal atomic switches is that a signal line of the three-terminal atomic switches is separated from a signal line, which increases their controllability especially when used as logic devices. Three-terminal atomic switches are classified into two types by a species of controlled ions that form a conductive path. One type controls metal cations, so that a conductive path is a metal filament. The other type controls oxygen ions, so that a conductive path is an oxygen deficient conductive region. Both types show nonvolatile switching with a high on/off ratio over five orders of magnitude.
The Japan Society of Applied Physics, Jul 10, 2018
The Japan Society of Applied Physics, Jul 22, 2016
Solid State Ionics, Dec 1, 2018
Three-terminal structures have an advantage over two-terminal structures in logic applications an... more Three-terminal structures have an advantage over two-terminal structures in logic applications and neuromorphic circuits, However, three-terminal operation based on Valence Change RAM still requires a larger gate bias to form/dissolve a conductive path between the source and the drain, especially for turning off. Here, reduction in gate bias and gate leakage current in nonvolatile operation of oxygen vacancy drift-controlled threeterminal ReRAM is demonstrated by W/Ti (gate)/TaO x (resistance switching layer)/Pt (source), Pt (drain) structure. Introduction of a Ti thin layer between W and TaO x layers prevents a conductive channel formation between gate and source/drain electrodes. Consequently, as-fabricated high resistance between gate and source/ drain is kept, resulting in smaller gate leakage current. We also achieved interface engineering on a sidewall structure of Pt (source)/SiO 2 (insulator)/Pt (drain) multi-layer, reducing in an operating bias from 10 V to 4 V or less.
ACS Applied Materials & Interfaces, Apr 6, 2023
Nanotechnology, Apr 11, 2011
The switching time of a Cu(2)S-based gap-type atomic switch is investigated as a function of temp... more The switching time of a Cu(2)S-based gap-type atomic switch is investigated as a function of temperature, bias voltage, and initial off-resistance. The gap-type atomic switch is realized using a scanning tunneling microscope (STM), in which the formation and annihilation of a Cu-atom bridge in the vacuum gap between the Cu(2)S electrode and the Pt tip of the STM are controlled by a solid-electrochemical reaction. Increasing the temperature decreases the switching time exponentially with an activation energy of about 1.38 eV. Increasing the bias voltage also shortens the switching time exponentially, exhibiting a greater exponent for the lower bias than for the higher bias. Furthermore, faster switching has been achieved by decreasing the initial off-resistance between the Cu(2)S electrode and STM tip. On the basis of these results, we suggest that, in addition to the chemical reaction, the electric field in the vacuum gap plays a significant role in the operation of a gap-type atomic switch. This investigation advances our understanding of the operating mechanism of an atomic switch, which is a new concept for future electronic devices.
The Japan Society of Applied Physics, Jul 6, 2021
ACS applied electronic materials, Sep 2, 2020
Variable capacitance functions are demonstrated utilizing the transport of Li ions in a simple Pt... more Variable capacitance functions are demonstrated utilizing the transport of Li ions in a simple Pt/lithium phosphorous oxynitride (LiPON)/Pt structure. The capacitance originates mainly from the formation of an electrochemical double layer (EDL) at the interfaces between LiPON and Pt at lower frequencies. Voltage applications drive Li ions from the positively-biased electrode to the negatively-biased one. At higher voltages, the number of Li ions at the positive electrode decreases to zero, which makes their contribution to the total EDL capacitance vanish. As a result, the LiPON capacitor exhibits decreased capacitance as voltage bias is increased, similar to what is found in a varactor diode. The upper frequency limit of the capacitance variation increases with increased temperature, which seems to be determined by the ionic conductivity of the LiPON matrix. A voltage-controlled oscillator (VCO) operation is also demonstrated by incorporating the LiPON variable capacitors into a resistor-capacitor oscillator circuit. The VCO clearly shows that the oscillation frequency of the output waveforms is exponentially increased by an increase in input direct-current voltage, which behavior is the same as a varactor diodebased VCO. The results indicate that this ionic variable capacitor can be used as a building block in analog and mixed signal electronic circuits.
Japanese Journal of Applied Physics, 2018