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In doped Si nanowires (SiNWs) boron (B) atoms segregate to the surface oxide layers during thermal oxidation, while phosphorus (P) atoms preferentially pile up in Si crystalline regions close to the Si/SiO2 interface. Here we report on micro-Raman scattering and electron spin resonance (ESR) measurements showing that B atoms can be stabilized at the crystalline Si core region in codped SiNWs with average diameters of 20–30 nm because of the strong interaction between B and P atoms during thermal oxidation below 800 °C. Theoretical calculation clearly demonstrated the effect of B–P pairing, which can stabilize the B atoms in the Si side. In the B–P pairing configuration, dopant passivation—beyond simple compensation—occurs, making the impurities electrically inactive.

We investigated the prevalence of occult hepatitis B virus (HBV) infection in Japanese chronic hemodialysis patients. Hemodialysis patients (n = 1041) were screened for occult HBV. The presence of hepatitis B surface antigen (HBsAg), hepatitis B surface antibody, and hepatitis B core antibody (anti-HBc) was determined by various chemiluminescent immunoassays. HBV-DNA was quantified in patients positive for anti-HBc using quantitative real-time polymerase chain reaction. Among the 1041 patients, six (0.6%) were HBsAg-positive and 218 (20.9%) were anti-HBc-positive. All HBsAg-positive patients also tested positive for the presence of HBV DNA. Of 212 HBsAg-negative and anti-HBc-positive patients, three were positive for HBV DNA. Our study showed that the prevalence of occult HBV infection in chronic hemodialysis patients from eastern Japan was 0.3%.

*1 Institute of Applied Physics, University of Tsukuba, 1-1-1 Ten'nodai, Tsukuba, Ibaraki 305-8573, bk200820379@s.bk.tsukuba.ac.jp *2 Graduate School of Information Sciences and Electrical Engineering, Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395,Japan *3 Department of Health Sciences, School of Medicine, Kyushu University, 3-1-1 Maidashi, Fukuoka 812-8582, Japan *4 Electronics and Photonics Research Institute, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba, Ibaraki305-8565, Japan

Silica glass can be ablated using focused laser plasma soft X-rays. The ablation technique enables us to fabricate trenches with a width as narrow as 50 nm. In the present paper, we have investigated the nano-ablation process. The soft X-ray irradiation causes a silica surface broken into almost atomic species. Ionic species have kinetic energies higher than that gained by heating to the boiling point. We measured the ablation depth as a function of the soft X-ray fluence. The depth analysis revealed that soft X-rays are absorbed in a silica surface with an effective absorption depth of 10 nm. The result indicates that the energy density of the soft X-rays per unit volume at the threshold fluence is comparable to that required for breaking silica glass into atomic species. Further, the results suggest that ablation occurs before diffusion of absorbed energy into the surrounding region. In addition to energy absorption, repulsive forces between ionic species may cause ablation of the silica surface by soft X-ray irradiation. These properties of soft X-ray ablation may make possible the nano-ablation of silica glass. © 2011 Wiley Periodicals, Inc. Electron Comm Jpn, 94(9): 30–35, 2011; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.10354

We are investigating the micromachining of silica glass using extreme ultraviolet (EUV) light from laser-produced plasma (LPP). The present investigation deals with the ablation using EUV light of around 13.5 nm and 11 nm generated in laser-produced Sn plasma and Xe plasma, respectively. CO2 laser and Nd:YAG lasers were used as pump lasers. The EUV radiation was focused on the surface of silica glass through the meshed mask using an ellipsoidal mirror coated with gold film. The results showed that the silica glass was successfully ablated by EUV light from the Nd:YAG-LPP. The maximum ablation rate was 42 nm per shot for 11-nm light, and 25 nm per shot for 13.5-nm light. On the other hand, EUV radiation from the CO2-LPP did not ablate the silica glass. This is presumably caused by the lower EUV irradiation intensity due to the long pulse duration of the CO2 laser.

Silica glass can be ablated using focused laser plasma soft X-rays. The ablation technique enables us to fabricate trenches with a width as narrow as 50 nm. In the present paper, we have investigated the nano-ablation process. The soft X-ray irradiation cause silica surface broken into almost atomic species. Ionic species have kinetic energies higher than that gained by heating up to the boiling point. We measured ablation depth as a function of soft X-ray fluence. The analysis of the depth revealed that soft X-rays are absorbed in silica surface with a effective aborption depth of 10 nm. The result leads to that the energy densty of the soft X-rays per unit volume at the threshold fluence is comparable to that required for breaking silica glass into atomic species. Futher, the results suggests that ablation occurs before diffusion of absorbed energy into the surroudning region. In addition to the energy absorption, repulssive force between ionic species may cause ablation of silica surface by soft X-ray irradiation. These properties of soft X-ray ablation may achieve nano-ablation of silica glass.

We have investigated nanomachining of inorganic materials using laser plasma soft X-rays. The soft X-rays were generated by irradiating Ta targets with pulsed Nd:YAG laser light. The laser plasma soft X-rays were focused using an ellipsoidal mirror, which is designed so as to focus soft X-rays at around 10 nm efficiently. The focused soft X-rays were incident to the surfaces of inorganic materials such as silica glass, LiF, CaF2, and LiNbO3. It is found that these materials are ablated by soft X-ray irradiation. In particular, silica glass can be ablated at rates of 0.2 to 150 nm/shot, which can be controlled by the intensity of soft X-rays. It is remarkable that silica can be ablated smoothly with a roughness of 1 nm after 10 shots of soft X-ray irradiation at a rate of 50 nm/shot. In order to demonstrate nanomachining of silica glass, we used contact masks on top of silica glass plates fabricated by electron beam lithography technique. The silica glass plates were irradiated with laser plasma soft X-rays through the windows of the contact masks. We found that nanofabrication of trenches with a width of 70 nm was performed clearly. © 2008 Wiley Periodicals, Inc. Electron Comm Jpn, 91(4): 45– 51, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10080

Hydrogen passivation of phosphorus (P) donors and defects in P-doped silicon nanowires (SiNWs) were investigated by electron spin resonance (ESR) at 4.2 K. P doping was performed during the synthesis of SiNWs by laser ablation. Phosphorus doping into substitutional sites of crystalline Si in SiNWs was demonstrated by detection of an ESR signal with a g-value of 1.998, which corresponds to conduction electrons in crystalline Si. ESR signals related to defects in surface oxide layer and at interface between surface oxide and crystalline Si core were observed. These P donors and the defects were partially passivated by hydrogen and oxygen atoms as seen in bulk Si.

We have investigated micromachining of a variety of materials by irradiation with laser plasma soft X-rays (LPSXs) at around 10 nm. The pulsed LPSXs were generated by irradiation of a Ta target in a vacuum chamber with Nd:YAG laser light at 532 nm, with a pulse duration of 7 ns, at a fluence of ~104 J/cm2. The LPSXs were focused on the surfaces of samples using an ellipsoidal mirror that is designed so that LPSXs at around 10 nm are focused efficiently. We found that quartz glass plates are ablated by LPSX irradiation at a typical rate of 48 nm/shot. Furthermore, the ablated regions have smooth surfaces with a roughness less than 10 nm after 10 shots of LPSX irradiation. It is demonstrated that quartz glass is machined with a lateral resolution higher than 100 nm. In addition to quartz glass, the LPSX processing can be applied to micromachining of a variety of materials such as Pyrex, CaF2, LiF, LiNbO3, Si and silicone.

We have investigated nanomachining of inorganic materials using laser plasma soft X-rays. The soft X-ray was generated by irradiating Ta targets with pulsed Nd:YAG laser light. The laser plasma soft X-rays were focused using an ellipsoidal mirror, which is designed so as to focus soft X-rays at around 10 nm efficiently. The focused soft X-rays were incident to the surfaces of inorganic materials such as silica glass, LiF, CaF2 and LiNbO3. It is found that these materials are ablated by soft X-ray irradiation. In particular, silica glass can be ablated at rates of 0.2-150 nm/shot, which can be controlled by the intensity of soft X-rays. It is remarkable that silica can be ablated smoothly with a roughness of 1 nm after 10 shots of soft X-ray irradiation at a rate of 50 nm/shot. In order to demonstrate nanomachining of silica glass, we used contact masks on top of silica glass plates fabricated by electron beam lithography technique. The silica glass plates were irradiated with laser plasma soft X-rays through the windows of the contact masks. We found that nanofabrication of trenches with a width of 70 nm are performed clearly.

Effects of amorphous carbon (a-C) thin film coating over carbon nanotubes (CNTs) on the field emission characteristics have been studied. Large-area surface-wave plasma (SWP) device was used both for growth of multi-wall CNTs on Ni-evaporated Si substrate and for deposition of a-C thin layer over CNTs. Field emission characteristics of the a-C film-coated CNTs prepared with different CVD durations were investigated. Experimental results show that the emission performance was significantly improved by coating a-C film typically with a thickness of 0.6–1 μm, that is, the ignition voltage for electron emission was reduced from 240 V for the sample of CNTs only to 110 V for that of CNTs deposited with a-C film during 60 min. The surface morphology has been also studied using the field emission type scanning electron microscopy (FE-SEM). It was deduced that the reduction of ignition voltage was due to the field enhancement originated from grain shape structures of the surface after a-C film deposition.

We measured real-time spectra of light transmitted through SiO2 specimens during irradiation of amplified ultrashort laser. The real-time spectra exhibit a peak at around 400 nm. The observation and identification of defects were performed by measurements of electron spin resonance (ESR). Both dependences of the peak at around 400 nm on irradiation time and laser power are in good agreement with those of the ESR signal intensity of positively charged oxygen vacancies (E′ center: O3≡Si·). This strong correlation shows that self-trapped excitons are created followed by the formation of the E′ center and finally that of ESR inactive centers, namely, oxygen-deficiency centers (ODCs: O3≡Si-Si≡O3 or O3≡Si:).

Laser ablation using nanosecond pulsed laser light includes some important transient processes during and after laser irradiation. In this paper, the optical absorption of semiconductors and the energy relaxation of excited electrons and holes are briefly described, followed by rapid phase transformation such as transient melting and vaporization which lead to laser ablation of materials. Initial processes of vaporization of solids due to laser ablation have been investigated by several time-resolved measurements. Here we describe a method of time-resolved soft X-ray absorption spectroscopy measurement to show an example of the initial plume produced by laser ablation of Si. This technique gives us information of the time dependence of ejection of Si atoms and Si ions (Si+˜Si4+), and their time-dependent spatial profiles. In addition to nanosecond pulsed laser ablation, characteristics of femtosecond pulsed laser ablation is also discussed, which has been very important to applications.

Droplet-free deposition of Si nanoparticle films has been studied applying time-resolved imaging of Si nanoparticles formed by laser ablation of Si targets in Ar gas. We found that Si nanoparticles can be deposited not only on substrates facing to the targets but also on substrates placed beside the target. We further confirmed using a scanning tunneling microscope (STM), Si nanoparticles with sizes of 5–8 nm are deposited on substrates placed beside the target and using a scanning electron microscope (SEM) on the substrates, no droplets are observed.

We fabricated P-doped Si nanocrystallites embedded in SiO 2 films and have investigated by photoluminescence (PL) spectroscopy and electron spin resonance (ESR) spectroscopy. The films were fabricated by annealing of P-doped SiO x films that were deposited by laser ablation of P 2 O 5 -coated Si targets in O 2 gas. Visible PL from nanocrystallites is enhanced at room temperature by 10 times as intense as undoped ones. ESR spectroscopy revealed that deposition at high energy density is effective for defect-free deposition. Furthermore, P atoms are found to be doped in the crystallites and electron–hole pairs bound to the P atoms are suggested to be responsible for the enhanced PL. In addition, we found a P-related center located at interface region between P-doped films of Si nanocrystallites and Si substrates, with a large hyperfine splitting of ∼80 G observed at 20 and 40 K.

The time-and spatially-resolved properties of laser ablated carbon, boron and silicon particles were measured by LAPXAS (Laser Plasma Soft X-ray Absorption Spectroscopy). The maximum speed of positively charged ions is higher than those of neutral atoms and negatively charged ions. The spatial distributions of the laser-ablated particles in the localized rare gas environment were measured. In helium gas environment, by the helium cloud generated on the top of ablation plume depressed the ablation plume. There is no formation of silicon clusters till 15μs after laser ablation in the argon gas environment.

application/pdf, We have performed electron spin resonance (ESR) measurements on Er-doped GaAs grown with oxygen codoping by metal organic chemical vapor deposition. An isotropic line (an effective g value, g = 5.95) which had been already reported was observed in samples without oxygen codoping. On the other hand, for samples with oxygen codoping other strong anisotropic ESR lines originated from four kinds of Er3 + (4f11) centers (A, B, C, and D) were newly observed in addition to the weaker isotropic line. The anisotropic g tensors obtained by analyzing the angular dependence of the ESR lines indicate that B and C centers are of orthorhombic C2v symmetry, A center has lower symmetry than orthorhombic symmetry, and D center is of trigonal C3i symmetry. The ESR intensities of A, B, and C centers were approximately two orders of magnitude higher than that of the isotropic line with g = 5.95. The ESR intensity of D center was one order of magnitude lower than those of A, B, and C. The Er concentration dependence of the relative ESR intensities of these centers was investigated, which indicates (i) the ESR intensities of A and D increase with increasing Er concentration, and (ii) those of B and C are saturated above the Er concentration [Er] >= 1018 cm – 3. The ESR measurement under light illumination, as well as the Er concentration dependence, suggests that the B center with C2v symmetry corresponds to the dominant Er luminescent center under host photoexcitation.

We have investigated direct nanomachining of inorganic materials using laser plasma soft X-rays. Soft X-rays (X) were generated by irradiation of Ta targets (Ta) with 532 nm Nd:YAG laser light(Y) with a pulse duration of 7 ns, at an energy density of about 10/sup 4/ J/cm/sup 2/. Under the condition, Ta plasma emit soft X-rays at around 10 nm. The soft X-rays were focused on samples (Q) with a spot size of 150 /spl mu/m, using an ellipsoidal mirror (M) that we designed so as to focus soft X-rays at around 10 nm efficiently. It was confirmed that SiO/sub 2/ has optical absorption at around 10 nm. We found that synthetic quartz glass, fused silica, Pyrex, HF, CaF/sub 2/, Al/sub 2/O/sub 3/ and LiNbO/sub 3/ can be machined smoothly by irradiation with laser plasma soft X-rays. Typically, quartz glass is ablated at 40 nm/shot, and has a surface roughness less than 10 nm after 10 shots. In order to investigate lateral resolution, we fabricated a WSi contact mask with 200-nm-pitch line-and-space patterns on quartz glass. We found that quarts glass plates can be machined at a resolution less than 100 nm. In conclusion, we have established a technique for nanomachining a wide variety of inorganic materials using laser plasma soft X-rays at a precision less than 100 nm.

application/pdf, We have performed electron spin resonance (ESR) measurements on Yb-doped n-type and p-type InP layers epitaxially grown by metalorganic chemical vapor deposition. ESR spectra of Yb3 + (4f13) were observed in both n-type and p-type samples. However, the ESR intensity of Yb3 + (4f13) for n-type samples was found to be much lower than that for p-type samples. This suggests that most Yb ions in Yb-doped n-type InP are in the Yb2 + (4f14) state rather than in the Yb3 + (4f13) state. Thus an electron captured by the trap level formed by Yb in the band gap of InP is not located outside the Yb 4f shell as reported previously, but accommodated in the Yb 4f shell.

We have investigated responses of polymers to EUV radiation from laser-produced plasmas beyond ablation thresholds and micromachining. We concentrated on fabricate precise 3D micro-structures of PDMS, PMMA, acrylic block copolymers (BCP), and silica. The micromachining technique can be applied to three-dimensional micro-fluidic and bio-medical devices. The EUV processing is a promising to realize a practical micromachining technique. In the present work, we used two EUV radiation sources; (a) Wide band EUV light in a range of 10{300 eV was generated by irradiation of Ta targets with Nd:YAG laser light at 500 mJ/pulse. (b) Narrow band EUV light at 11 and 13 nm was generated by irradiation of solid Xe and Sn targets, respectively, with pulsed TEA CO2 laser light. The generated EUV light was condensed onto the materials at high power density beyond the ablation thresholds, using ellipsoidal mirrors. We found that through-holes with a diameter of one micrometer an be fabricated in PMMA and PDMS sheets with thicknesses of 4-10 micrometers, at 250 and 230 nm/shot, respectively. The effective ablation of PMMA sheets can be applied to a LIGA-like process for fabricating micro-structures of metals for micro- and nano-molds. PDMS sheets are ablated if it is irradiated with EUV light beyond a distinct threshold power density, while PDMS surfaces were modified at lower power densities. Furthermore, BCP sheets were ablated to have 1-micrometer structures. Thus, we have developed a practical technique for micromachining of PMMA, PDMS and BCP sheets in a micrometer scale.

Time- and space-resolved characteristics of laser-ablated carbon particles were studied by x-ray absorption spectroscopy. Absorption peaks from the 1s→2p transition of neutral carbon atom ( C 0), C −, C +, and C 2+ ions were observed, An absorption peak from 1s→π* and a broad absorption maximum from the 1s→σ* transition of small clusters were also observed. Neutral carbon, C −, C +, and small carbon clusters were emitted from the sample long after laser irradiation. Spatial distributions of laser-ablated carbon particles in the localized helium-gas environment were measured. In the helium-gas environment, the ablation plume was depressed by the helium cloud generated on the top of the ablation plume.

We have performed x-ray absorption measurements of laser-ablated Si particles in vacuum and in Hegas environment. It is found that the spatial distributions of laser-ablated particles are very different between the two cases. This suggests that a higher-density region of helium gas is formed at the top of the plume of the ablated particles, and free expansion of particles is restrained by this helium cloud. Moreover, the spectrum obtained at 260 ns indicates that it takes more than 260 ns to form Si clusters. It is also demonstrated that Al particles can be sputtered in vacuum by laser-ablated Si particles if an Al plate is placed in front of the plume.

We have studied dynamical mechanism of laser ablation using combined time- and spatially-resolved measurements of laser plasma soft x-ray absorption spectroscopy and visible light emission imaging/spectroscopy. The obtained results indicate that there are no significant formation of silicon clustres and no growth of silicon nanoclusters till 2.55 ms after laser ablation. We have fabricated nanocluster-based silicon films by laser ablation in ambient gases and investigated photoluminescence at room temperature from the films. It is found that the growth of silicon nanocluster-based films with visible light emission can be well controlled by means of novel laser ablation methods.

Spectra of light transmitted through SiO2 specimens were measured during irradiation of amplified 800 nm ultrashort (400 fs) laser with a repetition rate of 100 kHz. The spectra exhibit a broad dispersion including a peak at around 450 nm, and the peak wavelength and the intensity are found to significantly depend on the irradiation time. Positively charged oxygen vacancies (E′ center) and oxygen-deficiency centers (ODCs) with neutral charge were observed by electron spin resonance (ESR) and photoluminescence (PL), respectively, after irradiation. The formation of the E′ center and the subsequent transformation to ODCs significantly depend on the laser power density. The correlation between the intensity of the peak at around 450 nm and the ESR signal intensity of the E′ center, and also the observation of PL spectrum due to ODCs suggest that self-trapped excitons exhibiting the peak at around 450 nm are created through multi-photon absorption, followed by the formation of the E′ center, and this finally leads to the formation of ODCs.

We have investigated a technique for micromachining inorganic transparent materials. In the technique, patterning and coloration are performed by the direct irradiation of materials with pulsed laser soft x rays and the patterned areas are ablated using ultraviolet laser light. The technique utilizes the high precision of the soft x rays and the high energy density of conventional laser light. For demonstration, we irradiated quartz plates with Ta laser plasma soft x rays. This results in generation of transient surface opaque layers that absorb more than 40% of the 266nm Nd:YAG laser light. Applying the technique, quartz plates are found to be ablated smoothly at 85nm∕shots.

We measured real-time spectra of light transmitted through SiO2 specimens during irradiation of amplified ultrashort laser with a fluence of 540 mJ/cm2. The real-time spectra exhibit a peak at around 400 nm, which significantly depends on the irradiation time. The observation and identification of defects were performed by measurements of electron spin resonance (ESR). Both dependences of the peak at around 400 nm on irradiation time and laser power are in good agreement with those of the ESR signal intensity of positively charged oxygen vacancies (E′ center). This strong correlation shows that self-trapped excitons are created followed by the formation of the E′ center and finally that of ESR inactive centers, namely, oxygen-deficiency centers.

We have performed time-and-space resolved X-ray absorption spectroscopy with a time resolution of 10 ns to study laser-ablated Si particles in a time scale ranging from 0 ns to 120 ns. Neutral and charged particles produced by laser ablation are observed through X-ray absorption spectra. Assignments of transitions from 2s and 2p initial states to higher Rydberg states of Si atom and ions are achieved, and we experimentally determine the LI \kern-1ptI,I \kern-1ptI \kern-1ptI absorption edges of neutral Si atom ( Si0) and Si ions such as Si+, Si2+, Si3+ and Si4+. The main ablated particles are found to be Si atom and Si ions in the initial stage of 0 ns to 120 ns. The relative amounts depend strongly on times and laser energy densities. We find that the spatial distributions of particles produced by laser ablation are changed with supersonic helium gas bombardment, but no cluster formation takes place. This suggests that a higher-density region of helium gas is formed at the top of the plume of ablated particles, and free expansion of particles is restrained by this helium cloud, and that it takes more than 120 ns to form Si clusters.

We have investigated ablation process of silica glass induced by X-ray irradiation. X-rays around 100 eV were generated by irradiation of Ta targets with Nd:YAG laser light. The laser plasma soft X-rays have a pulse duration of 10 ns. The soft X-rays were focused on silica surfaces at up to 10 8 W/cm 2 . We found that silica glass can be ablated by X-ray irradiation. Typically, the ablated surface have a roughness of 1 nm after ablation by 500 nm in depth. Further, trenches with a width of 50 nm can be clearly fabricated on silica surface. Thus, high quality, practical micromachining can be achieved by the X-ray technique. It is remarkable that more precise features can be fabricated on silica surface than the thermal diffusion length. The results implies non-thermal ablation process. We observed ions ejected from silica surfaces during the irradiation and found that ions are almost atomic species such as Si + , O + , Si 2 + , O 2 + , SiO + . The results revealed that silica surfaces are broken into atomic species by X-ray irradiation. Among X-ray ablated species, 0.5-15 % are estimated to be ionized. Even though 0.5 % atoms are ionized in silica surface, the energy density of Coulomb repulsive force is higher than the energy density of binding energy of silica glass. Therefore, we can conclude that Coulomb repulsion between X-ray generated ions are essential for X-ray ablation of silica glass.

We have investigated responses of PDMS, PMMA and acrylic block copolymers (BCP) to EUV light from laserproduced plasma beyond ablation thresholds and micromachining. We generated wide band EUV light around 100 eV by irradiation of Ta targets with Nd:YAG laser light. In addition, narrow band EUV light at 11 and 13 nm were generated by irradiation of solid Xe and Sn targets, respectively, with pulsed CO2 laser light. The generated EUV light was condensed onto samples, using an ellipsoidal mirror. The EUV light was incident through windows of contact masks on the samples. We found that through-holes with a diameter of 1 μm can be fabricated in PDMS sheets with thicknesses of 10 μm. PDMS sheets are ablated if they are irradiated with EUV light beyond a threshold power density, while PDMS surfaces were modified by irradiation with the narrow band EUV light at lower power densities. Effective ablation of PMMA sheets can be applied to a LIGA-like process for fabricating micro-structures of metals using the practical apparatus. Furthermore, BCP sheets were ablated to have micro-structures. Thus, we have developed a practical technique for microma chining of PMMA, PDMS and BCP sheets in a micrometer scale.

Gaining an understanding the dynamic behaviors of dopant atoms in silicon nanowires (SiNWs) is the key to achieving low-power and high-speed transistor devices using SiNWs. The segregation behavior of boron (B) and phosphorus (P) atoms in B- and P-doped SiNWs during thermal oxidation was closely observed using B local vibrational peaks and Fano broadening in optical phonon peaks of B-doped SiNWs by micro-Raman scattering. Electron spin resonance (ESR) signals from conduction electrons were used for P-doped SiNWs. Our results showed that B atoms preferentially segregate in the surface oxide layer, whereas P atoms tend to accumulate in the Si region around the interface of SiNWs. The radial distribution of P atoms in SiNWs was also investigated to prove the difference segregation behaviors between of P and B atoms.

We have found recently that there are optimum values of laser irradiation time and spot size for laser Solid Phase Epitaxial (SPE) growth of GaAs. The amorphous GaAs layers with a thick-ness of 600 @/Ar35@/ used in the study were produced by P+ ion implantation. Both 1.7W Ar ion laser and 4W Kr ion laser irradiations were used. The optimum values for SPE of the time and spot diameter were 67ms and 1 μm for the Ar ion laser and 17ms and 10 μm for the Kr laser. The 1 μm spot diameter is the smallest ever reported. For the Kr ion laser irradiation under these conditions, the speed of the laser SPE growth was as high as 30 μm/sec and the tempera-ture was as low as 560°C. The quality of the laser SPE growth layers was evaluated by the peak heights of the LO phonon Raman lines.

application/pdf, We have investigated the dynamic formation of silicon nanoparticles after pulsed-laser ablation of a silicon target into argon gas, in order to fabricate the nanoparticles that exhibit visible photoluminescence with higher efficiency. The nanoparticles growing in argon gas were detected by measuring plasma emission resulting from decomposition of the nanoparticles by a second pulsed-laser beam. It was directly observed that the nanoparticles grow on the time scale of 1 ms.

Laser plasma soft X-rays were applied to fabricate nano- and microstructures on surfaces of transparent materials. The optimized X-ray optics and nano-ablation process of silica glass will be emphasized as key device and process.

We have investigated nano-ablation of silica glass and ablation process using focused laser plasma soft Xrays. Laser plasma soft X-rays were generated by irradiation of a Ta target with Nd:YAG laser light. The soft X-rays were focused on silica glass plates using an ellipsoidal mirror at fluences up to 1 J/cm 2 .I n order to fabricate nano-trenches, a silica glass plate was irradiated with laser plasma soft X-rays through the windows of a line and space mask. We demonstrated fabrication of nano-trenches with a width of 50 nm. It should be noted that the feature size is more precise than that estimated from the thermal diffusion length for the 10-ns X-rays (i.e. 80 nm). Furthermore, the ablated area has a depth of 470 nm and a roughness of 1 nm after ten shots of irradiation. Thus, the X-ray irradiation technique have a significant feature of direct nanomachining. The ablation occurs at fluences F beyond a ablation threshould Fth and ablation depth per pulse D obeys the law D =1 /α ln(F/Fth), where α is an effective absorption coefficient. These results suggest that absorbed energy is accumulated in the absorbed region without energy diffusion until ablation occurs. In addition, time-resolved mass spectroscopy revealed that silica glass is broken into atomic ions and atomic neutrals during ablation. Because Si + and O + ions have kinetic energies of 10–30 eV, non-thermal process such as Coulomb explosion may be driving force behind the ablation. Such non-thermal process enables us to fabricate nano-structures on silica glass.

We have investigated the formation process of silicon nanoparticles after laser ablation of silicon targets in argon gas. The nanoparticles exhibit bright photoluminescence in the visible wavelength range and can be applied to opto-electronic devices. In order to observe silicon nanoparticles, we have developed a decomposition method. The nanoparticles were probed by detecting light emission resulting from decomposition using a second laser. This method enables us to observe nanoparticles that cannot be observed directly by the methods applied so far. We have observed that the nanoparticles grow in time periods of 1.0–1.8 ms following ablation in Ar gas at 5 Torr when Si targets are ablated at 5 J/cm2 with a pulse width of 7 ns. The nanoparticles begin to grow above ablation spots slightly apart from the targets just after thermalization of the plume. We also found that the growth is delayed at higher fluxes of ablation laser light.

We have investigated ablation of inorganic materials using pulsed and focused soft X-rays. Soft X-rays in a range of 1-500 eV were produced by irradiation of Ta targets with Q-switched Nd:YAG laser light (532 nm, 0.5-0.8 J/pulse) with a pulse duration of 10 ns in a vacuum chamber. The soft X-rays were focused on the surfaces of inorganic materials using an ellipsoidal mirror at approximately 0.1 J/cm2. The ellipsoidal mirror is designed so as to focus soft X-rays at about 100 eV efficiently, while it can not reflect soft X-rays above 200 eV. We found that synthetic quartz glass, Pyrex, LiF, CaF2, Al2O3 and LiNbO3, can be ablated by focused and pulsed soft X-rays. Typically, synthetic quartz glass is ablated at 50 nm/shot. We found that ablation occurs at X-ray fluences beyond the ablation threshold. Using a nano-scaled contact mask, trenches with a width of 50 nm and an aspect ratio of 1 are formed. The result indicates the diffusion length of absorbed energy during irradiation is less than 50 nm and that the accumulation results in ablation. The technique can also be applied to basic research of the interaction of intense soft X-rays with materials and resulting damage to the materials.

We have investigated micromachining of inorganic transparent materials by direct soft X-ray ablation. The pulsed soft X-rays were generated by irradiation of a Ta target in a vacuum chamber with Nd:YAG laser light at 532 nm, with a pulse duration of 7 ns, at a fluence of 10 4 J/cm 2 . The laser plasma soft X-rays (LPSX's) were focused on the surfaces of specimens using an ellipsoidal mirror that is made from silica glass and coated with Au. The ellipsoidal mirror is designed so that LPSX's at arount 10 nm are focused efficiently. The fluence of LPSX's on the specimens is roughly estimated to be 0.1 J/cm 2 . We found that quartz glass plates are machined by pulsed LPSX's irradiation at a rate of 48 nm/shot. Furthermore, the quartz plates have smooth surfaces with a roughness less thatn 10 nm after 10 shots of LPSX irradiation and sharp edges with a steepness less than 100 nm. In addition to quartz glass, the LPSX processing can be applied to micromachining of a variety of materials such as Pyrex, CaF 2 , LiF, LiNbO 3 , Si and silicone. We found a transient state induced by LPSX irradiation of quartz glass. The transient state absorbs 266 nm light. We irradiated quartz glass with 266 nm Nd:YAG laser light and LPSX's simultaneously and found that ablation is enhanced to have a rate of 85 nm/shot. With X-ray imaging optics, nanomachining of inorganic transparent materials should be achieved.

We have investigated microfabrication of inorganic transparent materials using laser plasma soft X-rays with the diffraction limit of 10 nm. As a soft X-ray source, we used Ta laser plasma soft X-rays, whch has a light emission band at around 10 nm. A SiO2 film was confirmed to have absorption band in the soft X-ray region. Micromachining a quartz plate was demonstrated by irradiation with focused soft X-rays and pulsed 266 nm Nd:YAG laser light. The quartz plates are ablated smoothly at 85 nm/shots. It is found that more than 40% of 266 nm laser light is absorbed by the quartz plates just after soft X-ray irradiation at room temperature. Thus, it is shown that a transient state such as an X-ray generated exciton (X-ray exciton), which have absorption band in UV region, are generated by soft X-ray irradiation. The micromachining technique (X-ray exciton method) can utilize the high space resolution of soft X-ray and the high energy density of conventional UV/visible laser light. Further, we found that a variety of materials such as SiO2, LiNO3, Si, CaF2, LiF and Al2O3 are ablated smoothly by irradiation of the focused laser plasma soft X-rays without 266 nm laser light.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Objective Although hormone replacement therapy (HRT) improves menopausal depressive symptoms, women unresponsive to HRT need an antidepressant drug as an effective adjunctive therapy. The aim of this study was to assess whether the herbal medicine Unkei-to has an impact on HRT-resistant menopausal depressive symptoms as an effective adjunctive therapy combined with HRT. Methods Twenty-four HRT-resistant menopausal depressive women were randomly assigned to group 1 (n = 12) or group 2 (n = 12). Subjects in group 1 were accessioned into 6 months of open treatment with Unkei-to as an adjunctive therapy and changed to Toki-shakuyaku-san for 6 months following a 1-month washout period. Group 2 started with Toki-shakuyaku-san for 6 months and then changed to Unkei-to for 6 months following a 1-month washout period. Results Three months' treatment with Unkei-to as an adjunctive therapy significantly improved Zung's Self-Rating Depression Scale (ZSDS) scores, State-Anxiety (STAI-1) scores, and Trait-Anxiety (STAI-2) scores noted before treatment, and this effect continued at 6 months. Treatment with Unkei-to was also significantly effective in reduction of ZSDS scores, STAI-1 scores, and STAI-2 scores at 3 months compared with Toki-shakuyaku-san treatment, and this effect continued at 6 months. Conclusions Unkei-to is another option as an adjunctive herbal therapy in HRT-resistant menopausal depressive women.

We demonstrate an electron excitation effect in silicon nanocrystals (SiNCs) embedded in a SiO2 layer treated with hydrogen atoms for passivation of interface defects. Using electron spin resonance (ESR) measurements of quasi-conduction electrons (QCE) excited at lower temperatures, we observed the enhancement of the number of QCE in SiNCs by light irradiation. The electron excitation effect is retained at temperatures lower than 250 K after stopping the light irradiation. The dependence on the size of SiNCs and on excitation laser wavelength suggest that the main memory process is caused by photo-induced electron charging induced through electron excitation of interface states between SiNCs and SiO2.