齋藤 洋司

In this study, we developed a sensing device that can detect deoxyribonuclease (DNase) based on the electrical properties of deoxyribonucleic acid (DNA). We estimated the equivalent circuit between the electrodes with immobilized DNA and investigated whether the characteristics of the electrodes change before and after the DNase reaction. This method detects DNase by simply evaluating the electrical properties of DNA without using a fluorescent reagent. Therefore, inexpensive and highly accurate measurements can be performed with simple operations. However, detection sensitivity must be increased for practical feasibility. Hence, we investigated whether DNA immobilization is restricted by changing the shape of the electrode to a triangle with sharp edges, which may improve the sensitivity of DNase. Additionally, we attempted to detect DNase from an extremely small amount of sample solution using a microchannel. The device was able to quantitatively analyze DNase I activity with a detection limit of 5.5 × 10-5unit/μL. The results demonstrate the effectiveness of the proposed sensing device for various medical applications.

In this study, we developed a sensing device that can detect deoxyribonuclease (DNase) based on the electrical properties of deoxyribonucleic acid (DNA). We estimated the equivalent circuit between the electrodes with immobilized DNA and investigated whether the characteristics of the electrodes change before and after the DNase reaction. This method detects DNase by simply evaluating the electrical properties of DNA without using a fluorescent reagent. Therefore, inexpensive and highly accurate measurements can be performed with simple operations. However, detection sensitivity must be increased for practical feasibility. Hence, we investigated whether DNA immobilization is restricted by changing the shape of the electrode to a triangle with sharp edges, which may improve the sensitivity of DNase. Additionally, we attempted to detect DNase from an extremely small amount of sample solution using a microchannel. The device was able to quantitatively analyze DNase I activity with a detection limit of 5.5 x 10(-5) unit/mu L. The results demonstrate the effectiveness of the proposed sensing device for various medical applications.

Serum deoxyribonuclease I (DNase I) can serve as a functional biomarker for the therapeutic monitoring of acute myocardial infarction and other diseases. Here, we demonstrate that the electrical properties of DNA molecules can be exploited to monitor enzymatic activity. A label-free DNA biosensor for the detection of DNase I activity was devised based on electrochemical impedance spectroscopy (EIS). Multiple lambda phage DNA molecules were immobilized between two electrodes in a polydimethylsiloxane reservoir. An equivalent circuit estimated from the EIS measurement was used to calculate the impedance of DNA molecules between the electrodes. DNase detection was then achieved by measuring the increase in impedance, after DNA cleavage by DNase I. This was assessed by the impedance-increase ratio, defined as R-after/R-before (where R-before and R-after represent the resistance between the electrode-immobilized DNA molecules before and after DNase I treatment, respectively). After treatment with DNase I at a concentration 10(-2) unit/mu L, a reproducible impedance-increase ratio of approximately 3.3 times was obtained, with a standard deviation of less than 20%. When DNase solutions of various concentrations were introduced, we succeeded in obtaining a definite correlation between DNase concentration and impedance-increase rate, within the range of 10(-4) unit/mu L to 10(-1) unit/mu L.

This paper presents a novel microdevice which detects deoxyribonuclease (DNase) electrically. The present device can be applied to diagnoses of diseases such as acute myocardial infarction and monitoring of DNase-free water used in genetic research. Multiple DNA molecules were immobilized between two electrodes in a microchannel, and DNase detection was achieved by measuring the increase in impedance between the electrodes after DNA cleavage by DNase. When DNase solutions of various concentrations were introduced, we succeeded to obtain a definite correlation between impedance increase rate and DNase concentration from 10-5 to 10-1 unit/μl.

Cold atmospheric-pressure plasma (CAP) has been emerging as a promising tool for cancer therapy in recent times. In this study, we used a CAP device with nitrogen gas (N2CAP) and investigated the effect of the N2CAP on the viability of cultured cells. Moreover, we investigated whether N2CAP-produced hydrogen peroxide (H2O2) in the medium is involved in N2CAP-induced cell death. Here, we found that the N2CAP irradiation inhibited cell proliferation in the human embryonic kidney cell line HEK293T and that the N2CAP induced cell death in an irradiation time- and distance-dependent manner. Furthermore, the N2CAP and H2O2 increased intracellular calcium levels and induced caspase-3/7 activation in HEK293T cells. The N2CAP irradiation induced a time-dependent production of H2O2 and nitrite/nitrate in PBS or culture medium. However, the amount of H2O2 in the solution after N2CAP irradiation was too low to induce cell death. Interestingly, carboxy-PTIO, a nitric oxide scavenger, or BAPTA-AM, a cell-permeable calcium chelator, inhibited N2CAP-induced morphological change and cell death. These results suggest that the production of reactive nitrogen species and the increase in intracellular calcium were involved in the N2CAP-induced cell death.

To prepare antireflection coating (ARC) by wet process is important technology for low cost fabrication of solar cells. In this research, we consider the optical reflectance of a three layer stack structure of ARC films on the pyramidally textured single-crystalline silicon substrates. Each layer of the ARC films is deposited by a spin-coating method. The triple layers consist of SiO2, SiO2-TiO2 mixture, and TiO2 films from air to the silicon substrate in that order, and the refractive index is slightly increased from air to the substrate. Light reflection can be reduced further mainly due to graded index effect. The optimized three layer structure ARC shows that the reflectance is below 0.048 at the wavelength of 600 nm.

For the purpose of application to biosensors, we newly characterized the electrical properties of the λDNA molecules. The electrical properties were investigated with complex impedance plot obtained from electrochemical impedance spectroscopy (EIS) measurements. After the λDNA molecules were introduced between two aluminum electrodes, they were electrostatically stretched and immobilized by applying an AC voltage of 1 MHz and 20 Vp-p. From the complex impedance of the λDNA molecules, an equivalent circuit was obtained as a series connection of two parallel circuits consisting of the resistances and the parasitic capacitances. The DNA molecules which were immobilized and evaluated in this study can be applied to electrical detection of deoxyribonuclease (DNase), enzyme for nonspecific DNA cleavage, which is a candidate biomarker for acute myocardial infarction.

We fabricated silicon solar cells with spin-coated sol-gel alumina passivation layers on the rear side. Spin-coated alumina passivation films have moderate passivation quality and are inferior to atomic layer deposited passivation films. However, low-cost and low temperature process of the sol-gel deposition is still beneficial for the cells using commercially available Cz silicon wafers. Thus, we consider an applicability of the spin-coated alumina passivation layer for rear side passivation. Dependence of cell efficiency on contact spacing and contact diameter of a rear electrode was investigated by both experiments and numerical calculation. The experimental results indicated that conversion efficiency of the cell is enhanced from 9.1% to 11.1% by optimizing an aperture ratio and contact spacing of the rear passivation layers. Numerical calculation indicated that small contact diameter with low aperture ratio of a rear passivation layer is preferable to achieve good cell performance in our experimental condition. We confirmed the effectivity of the spin-coated alumina passivation films for rear surface passivation of the low-cost silicon solar cells.

We prepared alumina passivation films for p-type silicon substrates by sol-gel wet process mainly using aluminum isopropoxide (Al(O-i-Pr)(3)) as a precursor material. The precursor solution was spin-coated onto p-type silicon substrates and then calcined for 1 hour in air. Minority carrier lifetime of the passivated wafers was evaluated for different calcination temperature conditions. We also compared the passivation quality of the alumina passivation films using different alumina precursor, aluminum acetylacetonate (Al(acac) 3). Obtained effective minority carrier lifetime indicated that the lifetime is strongly depends on the calcination temperature. The substrate calcined below 400 degrees C shows relatively short lifetime below 100 mu sec. On the other hand, the substrate calcined around 500 degrees C to 600 degrees C indicates lifetime from 250 to 300 mu sec. Calcination temperature dependence of the lifetime for the samples using Al(O-i-Pr)(3) precursors shows almost the same as that using Al(acac)(3).

The authors have investigated a process for randomly texturing single- and multicrystalline Si solar cells by plasmaless dry etching with a chlorine trifluoride gas. Although the reflectance of as-textured surfaces was easily reduced to below 10% at a wavelength of 600 nm in our previous study, the increase of the efficiency of the randomly textured solar cells was insufficient. This insufficient improvement was considered to be due to submicron structures formed by the dry texturing. In this study, the authors aimed to enlarge the textured structures and improve the electrical characteristics of single- and multicrystalline solar cells by modifying the texturing conditions. Surfaces with reflectance below 12% at 600 nm (corresponding to an estimated weighted reflection of 12%-13% at wavelengths between 300 and 1200 nm) were obtained, and electrical characteristics of multicrystalline solar cells were improved by using plasmaless dry texturing at a relatively high etch rate for around 1 min.

The authors have investigated a process for randomly texturing single-and multicrystalline Si solar cells by plasmaless dry etching with a chlorine trifluoride gas. Although the reflectance of as-textured surfaces was easily reduced to below 10% at a wavelength of 600 nm in our previous study, the increase of the efficiency of the randomly textured solar cells was insufficient. This insufficient improvement was considered to be due to submicron structures formed by the dry texturing. In this study, the authors aimed to enlarge the textured structures and improve the electrical characteristics of single-and multicrystalline solar cells by modifying the texturing conditions. Surfaces with reflectance below 12% at 600 nm ( corresponding to an estimated weighted reflection of 12%-13% at wavelengths between 300 and 1200 nm) were obtained, and electrical characteristics of multicrystalline solar cells were improved by using plasmaless dry texturing at a relatively high etch rate for around 1 min. (C) 2016 American Vacuum Society.

We prepared alumina passivation films deposited by a sol-gel wet process for silicon substrates. Aluminum acetylacetonate was used as a precursor, and the solution was spin-coated onto silicon substrates. Calcination temperature dependence of the passivation quality of the films was evaluated mainly by measuring effective lifetime using a photo conductance decay technique and capacitance-voltage measurements. Also, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy were carried out to evaluate film properties. A large amount of negative fixed charge density (Q(f) = -3.1 x 10(12) cm(-2)) exists in the films calcined at 300 degrees C. On the other hand, a long effective lifetime of 400 mu s was obtained for the sample calcined at 600 degrees C, and the passivation films had a large amount of positive fixed charge density (Q(f) = 3.6 x 10(12) cm(-2)) with a low interface state density. (C) 2015 Elsevier B.V. All rights reserved.

Antireflection coating (ARC) prepared by a wet process is beneficial for low cost fabrication of photovoltaic cells. In this study, we investigated optical properties and morphologies of spin-coated TiO2 ARCs on alkaline textured single-crystalline silicon wafers. Reflectance spectra of the spin-coated ARCs on alkaline textured silicon wafers exhibit no interferences and low reflectance values in the entire visible range. We modeled the structures of the spin-coated films for ray tracing numerical calculation and compared numerically calculated reflectance spectra with the experimental results. This is the first report to clarify the novel optical properties experimentally and theoretically. Optical properties of the spin-coated ARCs without interference are due to the fractional nonuniformity of the thickness of the spin-coated ARCs that cancels out the interference of the incident light.

A method is proposed for decomposing volatile organic compounds by atmospheric pressure non-thermal plasma with photocatalytic effects. We tried benzene decomposition by using an atmospheric pressure plasma system with an inner electrode made of stainless, titanium, and oxidized titanium. The electrode temperature was controlled typically between 100°C and 300°C. Dry air including benzene with a content of 1000 ppm was introduced into the plasma reactor. The benzene decomposition rate with the titanium electrode was higher than that with the stainless electrode. The benzene decomposition rate with the oxidized titanium electrode was higher than that with the titanium electrode. We consider that the enhanced benzene decomposition reaction with the oxidized titanium electrode is due to the photocatalytic effect of the oxidized layer. A specific energy density below 1800 J/L is required to achieve a benzene decomposition rate of 95%.

We investigated a texturing process for crystalline Si solar cells by dry etching with chlorine trifluoride (ClF3) gas without plasma excitation. Recently our research group demonstrated improved electrical characteristics of single-crystalline Si solar cells textured by dry etching of the phosphorus-doped layers. In this report, we attempted to improve the electrical properties of multi-crystalline Si solar cells by modifying the experimental procedure and optimizing the process conditions. The reflectance of the treated surfaces was around 10% at 600 nm without an anti-reflection film. We demonstrated the characteristics of multi-crystalline solar cells by random-texturing by plasmaless etching. This is the first report to prove the validity of plasmaless dry texturing for multi-crystalline Si solar cells.

Surface texturing methods using an alkaline solution for monocrystalline Si (c-Si) solar cells have been widely accepted to improve cell performance. However, multicrystalline Si (mc-Si) cells are difficult to be texturized by alkaline etching, because the grains in the substrates are randomly oriented. In this study, we considered a HF/HNO3/H2SO4 acid solution for texturing the mc-Si cells. We evaluated the morphology of the textured surfaces and the reflectance spectra from the surfaces. The deep dimple textured structures are formed on the surfaces for only 30 seconds of the acid texturing process. This behavior results from the effect of H2SO4 in the solution. This process obtains up to 14.7% conversion efficiencies of the acid textured cells. These conversion efficiencies are up to 1.3 times larger than those of the mirror-etched cells.

We have investigated on a random-texturing process for multi-crystalline Si solar cells by plasmaless dry etching, with chlorine trifluoride (ClF 3) gas treatments. The reflectance of textured surfaces was reduced to below 20% at a wavelength of 600 nm. In this study, we tried to improve the electrical characteristics by modifying the fabrication process. The substrate surfaces were dry etched by chlorine trifluoride gas and subsequently etched with an acid solution to form appropriate textured structures. The improved electrical characteristics were demonstrated. Copyright © 2013 The Institute of Electronics, Information and Communication Engineers.

Reflection loss of silicon solar cells can be reduced by texturing the surfaces. We investigated the texturization process for crystalline Si solar cells using chlorine trifluoride (ClF(3)) gas treatments. Reflectance of textured surfaces was reduced to below 10% at the wavelength of 600 nm. However, the efficiency increase for the random-textured solar cells was below 10% and was much less than the increase for the absorbed light in the substrates after texturization. In this study, we tried to improve the electrical characteristics of textured cells by modifying the fabrication process. The diffused layers were treated with chlorine trifluoride gas to form textured structures. The reflectance of the textured surface, obtained by the maskless etching with ClF(3), was approximately 17.8% at the wavelength of 600 nm. Solar cells with textured substrates were fabricated and their improved performance was demonstrated. (C) 2010 Elsevier B.V. All rights reserved.

Reflection loss of silicon solar cells can be reduced by texturization of the surfaces. In this study, single- and multi-crystalline silicon substrates were treated with chlorine trifluoride (ClF3) to create honeycomb-textured structures. We investigated surface structures and optical properties of the textured surfaces. By the treatment with ClF3 gas, the reflectance of the textured surface without anti-reflection coating was obtained to be below 20% at wavelengths between 300 and 800nm. The solar cells using the textured substrates were fabricated and their improved performances were demonstrated. circle dot 2007 Elsevier B.V. All rights reserved.

We prepared lanthanum oxynitride films on p-type Si(100) substrates by electron beam evaporation. The films were deposited by evaporating lanthanum at a substrate temperature of 300 degrees C, and introducing oxygen and nitrogen radicals into a chamber. After the thermal annealing of the films at 600 degrees C for 30 min, the composition and depth profile of the films were investigated by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES), respectively. We found that lanthanum oxynitride films suppress Si diffusion from the substrate as compared with lanthanum oxide films.

The reaction between glass-like carbon (GC) and chlorine trifluoride (CIF3) gas was investigated with weight measurements. surface analysis, and gas desorption measurements, where the CIF3 gas is used for the in situ cleaning of tubes in silicon-related fabrication equipment. From Auger electron spectroscopy and X-ray photoelectron spectroscopy measurements. a carbon monofluoride, -(CF)(n)-, film near the surface of GC is considered to be grown onto the GC surface above 400 degreesC by. the chemical reaction with CIF3, and this thickness of the fluoride film depends on the temperature. The grown fluoride film desorbs by annealing in a vacuum up to 600 degreesC. Although GC is apparently etched by CIF3 over 600 degreesC. the etch rate of GC is much lower than that of SiC and quartz. (C) 2004 Elsevier B.V. All rights reserved.

Bolometer-type infrared (IR) sensors were fabricated using undoped polycrystalline silicon (poly-Si) films, the temperature coefficient of resistance of which was 7 %/K. The device size was 50 x 50 mum(2). A bridge structure with an air gap about 50 mum deep was formed to reduce thermal conduction to the substrate from the sensing region, by plasmaless dry etching with chlorine trifluoride gas. The voltage responsivity of the fabricated sensor was 1.3 x 10(4) V/W at a bias voltage of 1.5 V.

Several percent of nitrogen was incorporated only near the top surfaces of thermally grown oxides, by surface fluorination at room temperature followed by an atomic nitrogen treatment at 550degreesC. The dependences of the nitrogen content and the thickness of the nitrided layer on the process condition were studied by angle-resolved X-ray photoelectron spectroscopy. A model of the nitridation process was also proposed. MOS capacitors with boron-doped polycrystalline silicon gates were fabricated using the nitrided ultrathin oxide. From the capacitance-voltage measurements we confirmed that the nitrided oxide would more effectively prevent boron penetration in comparison with the conventional oxide films. The proposed technique is a unique process for obtaining high-quality ultrathin dielectrics.

Silicon substrates and thermally grown oxide films were exposed to ClF3 gas at various temperatures between room temperature and 600degreesC. Above room temperature, the activation energy of the silicon etch rate is 0.18 eV. The activation energy of SiO2 etch rate below 400degreesC is estimated to be 0.12+/-0.01 eV. The obtained etch selectivity of silicon with respect to the SiO2 is 100-300 between room temperature and 400degreesC. An enhanced etch rate is observed for the n-type silicon with low resistivity near room temperature. The ClF3 gas, which has appropriate vapor pressure, has useful properties not only for in-situ cleaning but also for micromachining of silicon-related materials.

We annealed ultrathin silicon oxynitride films at high temperatures and in high vacuum, and investigated a role of nitrogen in structural stability with angle resolved X-ray photoelectron spectroscopy. The desorption rate of oxygen from the oxynitride films is much less than that from oxide films at 800 degreesC, Incorporated nitrogen does not desorb from the films, although Si-N bonds are gradually broken above 800 degreesC. Incorporated nitrogen enhances the thermal stability of the oxynitride films. (C) 2001 Elsevier Science B.V. All rights reserved.

We propose reactive gases, which can be easily decomposed, as the etching gas to avoid "greenhouse effects." In this article, the etching reaction between silicon and the trifluoro-acetyl-fluoride (CF3COF) gas is demonstrated, using a remote plasma at room temperature. The etching reaction is significantly enhanced by the addition of oxygen and remote-plasma excitation. The etch rate of silicon and oxide by CF3COF/O-2 is larger than that by CF4/O-2 and C2F6/O-2 at the same O-2 content. According to the optical emission study, however, the density of excited fluorine decreases in the plasma by the added oxygen into the CF3COF system. Photoelectron studies indicate that the major role of the additional oxygen is to remove the deposited fluorocarbon films from the surfaces. (C) 2001 American Vacuum Society. [DOI: 10.1116/1.1326942].

Nitrogen incorporation into oxide surfaces is required to prevent the penetration of boron from the polycrystalline silicon gate to the substrate in metal-oxide-semiconductor devices. We incorporate nitrogen only into the oxide surfaces by fluorination at room temperature and a subsequent atomic nitrogen treatment at temperatures below 550 degrees C. incorporated nitrogen atoms are found to be bound to silicon atoms and oxygen atoms by X-ray photoelectron spectroscopy. Moreover, surface roughness is improved by the nitridation process. The proposed technique is a unique process to obtain high-quality ultrathin dielectrics.

In recent years, silicon oxynitride films have drawn attention as high-quality dielectrics, with decreasing the feature size in the integrated circuits. In this study, we try direct oxynitridation of silicon by remote-plasma-excited nitrogen and oxygen gaseous mixtures at the temperatures between 600 degrees C and 800 degrees C. We investigate the initial growth and bonding structures in the oxynitride films by in-situ X-ray photoelectron spectroscopy (XPS) measurements. With the oxynitridation time, the surface concentration of nitrogen gradually increases, but that of oxygen shows nearly-saturation-behavior after rapid increase in the just initial stage. We found the two peaks derived from both N-Si(2) and N-Si(3) bonds in the photoelectron spectra of N 1s core levels in the initial stage. With the oxynitridation time, the N-Si(3) bonds increase gradually and dominate the nitride bonds in the grown films. (C) 1998 Elsevier Science B.V. All rights reserved.

We demonstrate to the acceleration of the moistureless etching reaction between the silicon native oxide and the anhydrous hydrogen fluoride (AHF) gas, using remote-plasma-excited Ar gas at room temperature. The etching reaction is significantly enhanced by the remote-plasma-excitation for both the chemically grown native oxide films and the dehydrated oxide films. Then, we attempt to improve the selectivity of the oxide etching with respect to silicon by introducing hydrogen into this system, and to realize the highly selective etching of native oxide with respect to silicon. With the increase of the hydrogen partial pressure, the etch rate of silicon rapidly decreases due to the suppression of the density of fluorine radicals in the gas phase. We have confirmed the value of the etch rate selectivity to be at least 4.

The adsorption of anhydrous hydrogen fluoride (AHF) on the surfaces of silicon native oxide was investigated by in situ X-ray photoelectron spectroscopy (XPS) in order to understand the reaction between HF and the oxide films at room temperature. A significant amount of the component is located at 670.0 eV binding energy in the observed XPS spectra, and is most likely derived from HF molecules. Moreover, the surface density of F-Si bonds slowly increases with the AHF exposure. We also attempted to accelerate the etching of the native oxide without moisture, supplying the AHF gas with remote-plasma-excited Ar, and obtained the enhanced etch rate.

The influence of the hydrogenation treatment on the conduction mechanism in the undoped polycrystalline silicon films near room temperature was investigated. The two current components are predicted from the temperature dependence of the conductivity in the films. We consider the hopping current in addition to the conventional thermionic (or drift) current. We have also found the hydrogenation induced increase phenomena of resistivity in the undoped polycrystalline silicon films and its activation energy, and qualitatively explain those by the decrease of the hopping current, which would relate to the band tail states, and that of the thermionic current, which would relate to the midgap states. From the analysis of the current components, it takes longer time for the passivation of the band tail states than that of the midgap states. (C) 1997 American Institute of Physics.

Re-crystallization of implanted layers and electrical activation of implanted As atoms by vacuum-ultraviolet (VUV) light irradiation in silicon substrates below 470 degrees C were investigated by means of sheet resistance measurements and reflection high-energy electron diffraction (RHEED). The reduction in the process temperature by irradiation of VUV light onto the implanted layer at 1 Wcm(-2) is estimated to be about 50 degrees.

Adsorption of tungsten hexafluoride on hydrogen-terminated silicon and silicon dioxide surfaces was investigated by in situ x-ray photoelectron spectroscopy in order to understand the selectivity loss occurring for chemical vapor deposition (CVD) of W films. It is found that WF6 molecules adsorb onto hydrogen-terminated silicon and silicon dioxide surfaces at faces at room temperature. When the substrates exposed to WF6 are annealed at 400 degrees C in ultrahigh vacuum, W and WF remain on silicon substrates, but all absorbates desorb from silicon dioxide surfaces. Only the reaction between WF6 and the substrates leads to the growth of tungsten films below 400 degrees C. If the WF6 gas is introduced with remote plasma-excited iir gas. induced WFx (x=0, 1,.., 6) molecules adsorb onto the silicon dioxide surfaces at room temperature. WFy(y=0,.., 3) adsorbates remain after the subsequent annealing at 400 degrees C, and cause the nucleation of W by CVD. Moreover, orine adsorbates are mainly bound to oxygen atoms after the annealing, implying the breaking of the Si-O bonds. The chemical pretreatment by an KF solution also breaks the Si-O bonds of the silicon dioxide surface, and creates a situation similar to that for the plasma-treated sample. The breaking of Si-O bonds additionally may contribute to the adsorption of WFx molecules.