Akira Heya

<jats:title>Abstract</jats:title> <jats:p>The effects of soft X-ray irradiation and atomic hydrogen annealing (AHA) on the reduction of graphene oxide (GO) to obtain graphene were investigated. To clarify the interaction between soft X-rays and GO, soft X-rays of 300 eV and 550 eV were used for C 1s and O 1s inner-shell electron excitation, respectively at the NewSUBARU synchrotron radiation facility. Low-temperature reduction of the GO film was achieved by using soft X-ray at temperatures below 150 °C at 300 eV, and 60 °C at 550 eV. O-related peaks in X-ray photoelectron spectroscopy, such as the C–O–C peak, were smaller at 550 eV than those at 300 eV. This result indicates that excitation of the core–shell electrons of O enhances the reduction of GO. Soft X-rays preferentially break C–C and C–O bonds at 300 and 550 eV, respectively.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The reduction of graphene oxide (GO) through atomic hydrogen annealing (AHA) and soft X-ray irradiation is investigated using microwell substrates with μm-sized holes with and without Ni underlayers. The GO film is reduced through AHA at 170 °C and soft X-ray irradiation at 150 °C. In contrast, some GO films are not only reduced but also amorphized through soft X-ray irradiation. The effect of the Ni underlayer on GO reduction differs between AHA and soft X-ray irradiation. In AHA, the difference in GO reduction between SiO<jats:sub>2</jats:sub> and Ni underlayer was originated from the atomic hydrogen density on sample surface. On the other hand, in soft X-ray irradiation, the difference in GO reduction between SiO<jats:sub>2</jats:sub> and the Ni underlayer originates from the excited electrons generated by soft X-ray irradiation. Reduction without damage is more likely to occur in the suspended GO than in the supported GO.</jats:p>

The effect of atomic hydrogen exposure on hydrogenated amorphous carbon (a-C:H) films was investigated by X-ray photoelectron spectroscopy (XPS). From the dependence of the wide-scan XPS spectra of an a-C:H film on atomic hydrogen exposure, it was shown that the film was etched with an etching rate of 0.2 nm min-1. In addition, by analyzing the C 1s XPS spectra, the coordination of C atoms in the a-C:H film was investigated as a function of the atomic hydrogen exposure and photoelectron emission angle. This indicated that the coordination of C atoms at the surface of the a-C:H film was not influenced by atomic hydrogen exposure. Therefore, we propose that the depth profile of a-C:H films can be measured with no damage using atomic hydrogen etching.

An extreme ultraviolet (EUV) light with a wavelength of 13.5 nm has been introduced to 7 nm FinFET technology. Optical elements such as Mo/Si multilayer mirror in lithography equipment are contaminated with hydrocarbon during the EUV light irradiation. The reflectance of the mirrors is decreased by carbon contamination. Therefore, the removal method of the carbon contamination is required for reduction of maintenance cost. The surface treatment using atomic hydrogen generated by a heated tungsten mesh, called as atomic hydrogen annealing (AHA), have been investigated for cleaning of the optical elements used in the synchrotron facility. The Au/Cr/Si substrate, Ni mirror and Ni diffraction grating with carbon contamination were cleaned and the reflectance of the mirrors was recovered by AHA. In addition, the AHA conditions could be optimized for cleaning of Mo/Si multilayer mirrors from the relationship between the treatment conditions and degradation. Furthermore, to clarify the reaction of atomic hydrogen with not only C-C bond but also C-O bond, the graphene oxide (GO) film was also treated by AHA. The C-O-C bonds in the GO films were preferentially reduced by AHA. It is found that the surface contamination consisting of hydrocarbon and/or C-O bond on the optical elements is removed without damage. The ability of atomic hydrogen to clean the optical elements had been confirmed. The findings are useful for the advanced lithography technology using EUV light.

© 2020 SPST. The surface treatment using atomic hydrogen genareted by a heated tungsten mesh was investigated for the cleaning of the optical elements used in the synchrotron facility. We call the surface-tretament by the atomic hydrogen annealing (AHA). The Au and Ni mirors and Ni and Mo diffraction gratings with carbon contamination were cleaned by the chemical reaction and thermal effect due to the recombination of the atomic hydrogens during AHA. The carbon contamination was removed and the reflactance of the Au and Ni mirrors was recovered by AHA. The AHA conditions could be optimaized for cleaning of Mo/Si multilayer mirrors from the relationship between the treatment condition and degradation. In addition, to clarify the removal reaction of the carbon contamination, the two-types of amorphous carbon (a-C) films were used. The etching rate of the a-C film by AHA was strongly related to the hydrogen content, atomic density and sp2/sp3 component of a-C film.

Inexpensive and sensitive graphite electrodes were fabricated by applying flame annealing to pencil-graphite rods (PGRs) as electrodes for water electrolysis cells. The resin (polymer, binder) on the surface of PGR was removed by flame annealing to make it porous, and the graphite electrodes with high activity and low cost were obtained. By flame annealing the PGR, although the PGR electrode became active upon water electrolysis, the PGR electrode became instable for long-time operation. The effects of flame annealing on PGR for water electrolysis were analyzed by SEM, FT-IR spectroscopy, Raman spectroscopy, NEXAFS, and electrochemical impedance spectroscopy (EIS).

In synchrotron radiation (SR) optical devices coated with oxidation-prone metal, such as Niand Cr, the UV-03 ashing method cannot be used for removal of the contaminated carbon film deposited during use in the beamlme. We have demonstrated that surface treatment technology using atomic hydrogen is effective as a new contaminated carbon film removal technology. Hydrogen gas was flowed into contact with a tungsten mesh (catalyst) heated to 1700 C to obtain atomic hydrogen. By flowing this atomic hydrogen on the surface of the SR mirror, deposited contaminants could be almost completely removed. The reflectance of the mirror recovered from about 14% to about 70% at the C-K absorption region. The reflectance also increased by about 20% at a photon energy greater than 300 eV because of the removal of carbon film and the reduction of native oxide at the mirror surface.

Low temperature (&lt;= 400 degrees C) formation of orientation-controlled large (&gt;= 10 gm) Ge-on-insulator (GOI) structures is desired to fabricate 3-dimensional large-scale integrated circuits (LSIs), where Ge-based functional devices are stacked on Si-LSIs. For this purpose, Si-seeded pulse-laser annealing (PLA) combined with low temperature substrate heating (&lt;= 400 degrees C) has been developed. Here, a-Ge stripes on Si substrates partially covered with insulating films are subjected to PLA, where single edges of the a-Ge stripes directly contact Si seeding substrates through opening windows of insulating films. PLA at room temperature generates lateral growth of Ge layers from Si-seeding substrates. However, the growth length is short (similar to 1 pm), which is attributed to very short melting time. To increase the melting time, low-temperature (5400 C) substrate heating during PLA is examined. As a result, very large (similar to 20 gm) orientation-controlled GOI is obtained by combining substrate heating (400 C) with PLA. Detailed electron microscopy analysis reveals very high crystallinity of the grown layers. Consequently, high-quality rapid-melting growth of Ge becomes possible at a low processing temperature of similar to 400 C. This thermally-assisted (similar to 400 C) Si -seeded PLA will facilitate realization of 3 dimensional LSIs.

We examined the dynamics of interstitial atoms and vacancies in amorphous Si (a-Si) and a-Ge films crystallized by flash lamp annealing in consideration of the self-diffusion coefficients of Si and Ge. We found that the interstitial atoms play an important role in the liquid-phase crystallization (LPC) of a-Si films, whereas the vacancies are more important for the solid-phase crystallization (SPC) of a-Si films along with the LPC and SPC of a-Ge films. For Si, the crystal defect density of the film crystallized by LPC was higher than that of the film crystallized by SPC; the opposite result was achieved for Ge. This phenomenon is considered to be attributed to the existence of interstitial atoms introduced in Si. The thermodynamic calculated results related to the relationship between the point defect and SPC or LPC supported the crystallization mechanism. (C) 2017 The Japan Society of Applied Physics

An input/output characteristics of the inverter composed of the DNA/Si-MOSFET and the parasitic capacity was studied. The DNA was bridged between the Si electrodes those serve as the source and drain with the 120nm-gap-length. At VDD=0V and VDD=3V, the output characteristic was almost the same. The reason of this phenomenon is that the space charge layer of the DNA/Si-MOSFET changes due to the charge capture or emission and the parasitic capacitance changes synchronized with the gate voltage.

The low-temperature formation of nanocrystalline Si (nc-Si) in SiOx film is one of the key technologies in the realization of Si-based photonics and memories. We proposed a low-temperature nc-Si formation method with soft X-ray irradiation. The nc-Si formation depended on the Si/O atomic ratio in the pristine SiOx film. The Si-rich regions in SiOx films with Si/O ratios higher than 0.67 were crystallized by atomic migration via electron excitation with soft X-ray irradiation at a photon energy near the core level of Si 2p. nc-Si with a mean size of 20nm was formed by soft X-ray irradiation at a low temperature of 660 degrees C. (C) 2017 The Japan Society of Applied Physics

Atomic hydrogen annealing (AHA) was investigated as a novel method to reduce graphene oxide (GO). In this method, high-density atomic hydrogen is generated on a hot tungsten (W) surface through a catalytic cracking reaction. The X-ray photoelectron spectra show that the GO films were reduced by AHA at low temperature. The GO film resistance, measured using the four-point probe method, decreased by 6 orders of magnitude when treatment was carried out with a W mesh temperature of 1780 degrees C, a sample temperature of 241 degrees C, and for a treatment time of 3600 s. A reduced graphene oxide (r-GO) film having a low resistance of 272 ohm was obtained by AHA. AHA allows fine control over the obtained physical properties. We expect that these r-GO films obtained by using AHA at low temperature will be used for producing electrical devices. (C) 2017 Elsevier B.V. All rights reserved.

A novel activation method for a B dopant implanted in a Si substrate using a soft X-ray undulator was examined. As the photon energy of the irradiated soft X-ray approached the energy of the core level of Si 2p, the activation ratio increased. The effect of soft X-ray irradiation on B activation was remarkable at temperatures lower than 400 degrees C. The activation energy of B activation by soft X-ray irradiation (0.06 eV) was lower than that of B activation by furnace annealing (0.18 eV). The activation of the B dopant by soft X-ray irradiation occurs at low temperature, although the activation ratio shows small values of 6.2x10(-3) at 110 degrees C. The activation by soft X-ray is caused not only by thermal effects, but also electron excitation and atomic movement.

Coulomb blockade/staircase phenomena of deoxyribonucleic acid (DNA) molecule have been observed so far. Here, we show a non-Coulomb blockade/staircase phenomenon of holes in a mesoscopic scale lambda-DNA, which serves as a channel on SiO2/Si structure. It is considered that the phenomena are due to the penetration of the wave function in the DNA into the Si source and drain electrodes via the contacts constructed by DNA/allyl glycidyl ether/Si electrodes.

Effect of atomic hydrogen annealing (AHA) on graphene oxide (GO) was investigated. In AHA, the high-density atomic hydrogen is generated on heated tungsten (W) surface by catalytic cracking reaction. From X-ray photoelectron spectra, GO films were reduced by AHA. The sheet resistance of the GO film was decreased by 5 orders of magnitude at W mesh temperature of 1780 degrees C, sample temperature of 220 degrees C and treatment time of 1800 s. The reduction of GO films relates chemical reaction due to atomic hydrogen because the GO films was not reduced by He treatment. The C-O-C bonds in GO films were preferentially reduced by AHA.

The energy loss of solar cell due to the recombination of holes and electrons which are excited by the incident solar beam is approximately 20% of all the loss-mechanisms. We simulated the solar cell with Metal-Insulator-Semiconductor(MIS) structure and fabricated the MIS solar cell using the Silicon-on-Insulator(SOI) substrate. Back gate bias restrains the recombination of holes and electrons, therefore, the carrier life time is extended and the conversion efficiency is improved by the electric field effect in the power generation layer. It was clarified that the conversion efficiency with a gate bias of 2.5V was increased 50 times larger than that without it.

Hot Mesh Deposition (HMD) method was investigated as a formation method of graphene. The HMD method can control the structure of composition by using decomposed molecule of pentacene. It is expected that graphene or graphene nanoribbon is formed by this apparatus. It is cleared that the molecular structure of the deposited organic film was changes by changing distance of mesh and substrate (DMS). In addition, it is confirmed that an organic film having a structure close to pentacene dimer and trimer were deposited by HMD using two heated catalysts.

The formation of nanocrystal silicon (nc-Si) in SiOx is one of the key technologies for the realization of high-quality solar cells. The SiOx films were deposited on a quartz substrate by a reactive sputtering. The Si/O ratio of the SiOx films were changed from 0.56 to 2.07. The nc-Si in SiOx film was characterized by Raman scattering spectroscopy. The Crystalline fractions of all samples after FLA were almost 100%. The size of nc-Si was estimated to 9 nm by Raman peak position. It is shown that the grain size of nc-Si was not changed by the Si/O ratio. On the other hand, the full width at half maximum (FWHM) of Raman peak due to crystal phase was changed by the Si/ O ratio of SiOx film.

Structural properties and influence of thermal treatment on electrical properties for organic thin-film transistor (OTFT) with 3nm-thickness active layer pentacene were investigated. The pentacene film was preferentially oriented to (00l) of thin-film phase and carriers conducted thought standing molecules slantingly. The carrier mobility of the ultrathin OTFT was decreased, and the threshold voltage was shifted to negative direction by thermal treatment. For the ultrathin OTFT, the carrier conduction was affected by H2O and O-2 because of change in the interface state and the hole localization state by adsorption of O-2 and H2O and oxidation.

Two types of phenylenevinylene terthiophene with and without cyano side substitution were synthesized to investigate the effect of the molecular structure on optoelectronic properties. The oligothiophene with cyano side substitution exhibited large bathochromic effect and behaved as organic electron acceptors with decrease in field effect conductivity due to increase in dipole moment.

We presented the novel structure of the solar cell that has the metal-oxide-semiconductor (MOS) diode at the side wall of the power generation layer (1). The purpose of this research is to simulate influence of the field-effect on the recombination of carriers for the micro-wall solar cell. It was found that the increase ratio of conversion efficiency under the gate voltage application is 4.5 times at the maximum in comparison with non-gate application corresponding to the conventional solar cell.

Ge thin film is expected as an active layer in a thin-film transistor (TFT) because the electron mobility of Ge is larger than that of Si. In this study, the crystallization of Ge thin film by soft X-ray irradiation and the improvement of interface property of poly-Ge/SiO2 in poly-Ge TFT by atomic hydrogen annealing (AHA) are investigated for realization of high-performance poly-Ge TFT. The drain current (I-d) did not depend on the gate voltage (V-g) before AHA treatment. However, as the AHA treatment time increased, the I-d decreased and the Id came to depend on V-g. The on/off ratio of 10 was obtained by AHA for 360 min. It is found that the defect density in poly-Ge film and at poly-Ge/SiO2 interface can be reduced by AHA slightly.

Molecular alignment behavior of pentacene molecules sublimed on photoreactive liquid-crystalline polymer (PLCP) layer that are work as a photoalignment layer were explored. Pentacene molecule aligned perpendicular to the director of PLCP with edge-on to the substrate while pentacene on surface region of the bilayer forms the same structure as pentacene-alone substrate that covered the anisotropic edge-on pentacene structure on PLCP surface.

It is clarified that the SiNX film with a thickness of 1.7 nm, which was formed at the interface between the poly-Si source/drain and Al layer, suppresses the hump phenomenon of TFT with a channel length of 10 mu m. The mechanism of the hump suppression by this structure is discussed. It is thought that the fixed charge in the SiNX film suppresses the formation of the parasitic channel in the poly-Si edge by the Coulomb repulsion.

Amorphous silicon germanium (a-Si1-xGex)films were crystallized by irradiation with soft X-rays of various photon energies. The crystallization upon soft X-ray irradiation is related to Ge concentration, photon energy, and photon flux density. The Ge atom was the trigger for the crystallization of the SiGe film because the atomic migration of Ge atoms was enhanced by electron excitation during soft X-ray irradiation, compared with Si atoms. As the photon energy decreased from 130 to 50 eV, the crystalline fraction increased. In the Si0.5Ge0.5 film, the ratio of peaks attributable to the crystal phases to those attributable to the amorphous phases of Si-Si, Si-Ge, and Ge-Ge bonds changed with irradiated photon energy. This is explained by the relationship between the orbital energies of Si 2p and Ge 3d and the photon energy of irradiated soft X-rays, because the electron excitation probability was determined by this relationship. Therefore, it is considered that soft X-ray irradiation crystallization occurred via the exitation of electrons from the core level. (C) 2014 The Japan Society of Applied Physics

A heated tungsten (W) mesh, set between a pentacene source and a substrate in a vacuum chamber, was used to prepare a bulk-phase pentacene film and a pentacene-based organic semiconductor film. Since the pentacene molecules come into contact with the heated W mesh before reaching the substrate, their thermal energy is increased prior to deposition. As the mesh temperature was increased from 23 to 1200 degrees C, the intensity ratio of bulk to thin-film phases increased from 0 to 9.7. Above 1300 degrees C there is a notable decomposition reaction, the products of which were identified as dihydropentacene, p-distrylbenzene, and 2,2'-dimethyl-1,1'-binaphthalene. These decomposed precursors are expected to provide a potential source of large graphene sheets and graphene nanoribbons. (C) 2014 Elsevier B.V. All rights reserved.

It is clarified that the SiNX film with a thickness of 1.7 nm, which was formed at the interface between the poly-Si source/drain and Al layer, suppresses the hump phenomenon of TFT with a channel length of 10 mu m. The mechanism of the hump suppression by this structure is discussed. It is thought that the fixed charge in the SiNX film suppresses the formation of the parasitic channel in the poly-Si edge by the Coulomb repulsion.

An etching method for organic semiconductor materials called atomic hydrogen treatment was investigated. In this method, the high-density atomic hydrogen is generated on a heated tungsten surface by a catalytic cracking reaction. Also pentacene films are etched at 0.07 nm/s in tungsten temperature of 1700 degrees C and sample holder of 60 degrees C. It is considered that the patterning of organic films using atomic hydrogen at low temperatures without plasma damage is useful for the realization of flexible semiconductor devices. (C) 2014 The Japan Society of Applied Physics

Low-temperature crystallization of Si, Ge and SiXGe1-X films by SR-soft x-ray irradiation using short undulator light is examined. By setting the photon energy to that of the core electron orbital, the crystallization is examined experimentally and discussed theoretically from a view point of Ge diffusion. The temperature during the crystallization of Si, Ge or Si0.5Ge 0.5 by soft x-ray was 80 to 140 degree C lower than that by the conventional rapid thermal annealing. The elementary process of the soft x-ray irradiation is thought to be the atom-diffusion following the localized excitation of the core-electrons and the generation of Coulomb repulsion. For the low-temperature crystallization, the quasi-nuclei are formed via the elementary process.