Journal of the Society of Materials Science, Japan, 2015
The mist chemical vapor deposition (mist CVD) method, which uses ultrasonically atomized solution... more The mist chemical vapor deposition (mist CVD) method, which uses ultrasonically atomized solutions as sources, is an environmental friendly and cost-effective technology for the growth of compound semiconductors. This growth process is realized under atmospheric pressure and allows us to use many kinds of salts, complexes, and compounds with low toxicity for sources. Using the oxidizability of water including the source, most of the previous reports of the mist-CVD method are on oxide materials. In this study, we fabricated zinc sulfide (ZnS) films by mist-CVD method using thiourea-based water solutions as sources. Investigating the growth of ZnS by mist-CVD under various growth conditions and experimental setups, we proposed zinc-chloride complexes are necessary for the growth of ZnS and vaporized mist sources act as precursors.
Longitudinally excited CO 2 laser with tail-free short pulse
High-Power Lasers and Applications VII, 2014
We developed a longitudinally excited CO2 laser with a tail-free short laser pulse. In a discharg... more We developed a longitudinally excited CO2 laser with a tail-free short laser pulse. In a discharge tube, two structures were researched. One is a shingle scheme that is constituted of a 45 cm-long discharge tube. Another is a tandem that is constituted of two 30 cm-long discharge tubes connected with an intermediate electrode were used. In gas media, CO2- rich mixture (CO2: N2= 20: 1) was used to reduce a laser pulse tail. The laser system did not require expensive and scarce helium. A fast discharge (<1 μs) in a low gas pressure (<1.8 kPa) produced a tail-free laser pulse with the pulse width of about 100 ns. The single scheme produced an output energy of 4.7 mJ by a charging voltage of -36.3 kV, and the tandem scheme produced an output energy of 9.3 mJ by a charging voltage of -25.2 kV. The tandem scheme produced higher spike pulse by lower voltage than the single scheme. Therefore, the tandem scheme will be effective in longitudinally excited CO2 lasers with simple and compact designs.
Red-fluorine-atom (Red-F * ) laser oscillation (λ = 630-780 nm) and strong fluorescence of VUV-F ... more Red-fluorine-atom (Red-F * ) laser oscillation (λ = 630-780 nm) and strong fluorescence of VUV-F 2 emission (λ = 157 nm) are observed in a lamp-like discharge in a longitudinal discharge excitation tube. The laser tube consists of a 30 cm long Pyrex glass pipe with an inner diameter of 2 mm, and a step-up transformer coupled directly to the discharge tube without a high-voltage switch. Excitation is produced by wall-coupled discharge. The laser pulse width is 6.1 ns at 100 Torr (13.3 kPa, with an F 2 concentration of 5 %) when a slow-rising voltage pulse of -40 kV (rise time: 253 ns) is applied. VUV-F 2 emission of a 24.5 ns (FWHM) pulse width was generated simultaneously with the red-F * laser.
Comparison of modified driver circuit and capacitor-transfer circuit in longitudinally excited N2 laser
The Review of scientific instruments, 2013
We developed a modified driver circuit composed of a capacitance and a spark gap, called a direct... more We developed a modified driver circuit composed of a capacitance and a spark gap, called a direct-drive circuit, for a longitudinally excited gas laser. The direct-drive circuit uses a large discharge impedance caused by a long discharge length of the longitudinal excitation scheme and eliminates the buffer capacitance used in the traditional capacitor-transfer circuit. We compared the direct-drive circuit and the capacitor-transfer circuit in a longitudinally excited N2 laser (wavelength: 337 nm). Producing high output energy with the capacitor-transfer circuit requires a large storage capacitance and a discharge tube with optimum dimensions (an inner diameter of 4 mm and a length of 10 cm in this work); in contrast, the direct-drive circuit requires a high breakdown voltage, achieved with a small storage capacitance and a large discharge tube. Additionally, for the same input energy of 792 mJ, the maximum output energy of the capacitor-transfer circuit was 174.2 μJ, and that of th...
We developed a longitudinally excited CO2 laser with a tandem discharge tube. The tandem scheme w... more We developed a longitudinally excited CO2 laser with a tandem discharge tube. The tandem scheme was constituted of two 30-cm long discharge tubes connected with an intermediate electrode. Two parts, each consisting of a charged capacitance and a 30-cm long discharge tube, were electrically connected in parallel and switched by a spark gap. The tandem scheme produced a short laser pulse like that of a TEA-CO2 laser with a charging voltage of −24.8 kV, which was smaller than the −40.0 kV charging voltage of our previous CO2 laser. At a gas pressure of 3.8 kPa, the spike pulse width was 145 ns, the pulse tail length was 58.8 μs, the output energy was 52.0 mJ, and the spike pulse energy was 2.4 mJ. We also investigated the dependence of the laser pulse and the discharge voltage on gas pressure.
Longitudinally excited N2 lasers without high-voltage switches
Review of Scientific Instruments, 2008
We have developed novel excitation circuits without high-voltage switches for two longitudinally ... more We have developed novel excitation circuits without high-voltage switches for two longitudinally excited N2 lasers (wavelength: 337nm). One uses a single tube without a trigger and the other uses a tandem tube with a trigger. In both systems, the discharge tube acts as a switch. In the single-tube system, the laser output energy was 125.8μJ and the efficiency was 0.16% at 18Torr (2.4kPa) when a slow-rising voltage pulse of −28kV was applied (rise time: 21.3μs). In the tandem-tube system, the laser output energy was 259.4μJ and the efficiency was 0.11% at 18Torr when a slow-rising voltage pulse of −48kV was applied (rise time: 27μs).
Nitrogen laser oscillation is observed in a lamplike discharge within a longitudinal excitation t... more Nitrogen laser oscillation is observed in a lamplike discharge within a longitudinal excitation tube. The laser consists of a 30cm-long Pyrex glass tube with an inner diameter of 2.5 mm and a step-up transformer directly coupled to the discharge tube without a high-voltage switch. The excitation is produced by wall-coupled discharge. The laser output energy is 1.7 mJ at 12 Torr (1.6 kPa) and 40 Hz when applying a slow-rising voltage pulse of 37 kV (rise time of 572 ns).
Electronic properties of individual CdSe colloidal nanodots have been investigated by conductive-... more Electronic properties of individual CdSe colloidal nanodots have been investigated by conductive-tip atomic force microscopy (AFM). Submonolayer-thick films of the colloidal nanodots were fabricated on a self-assembled monolayer of alkanethiol molecules formed on Au(1 1 1) surfaces for single dot measurements. First, we simultaneously imaged the topography and conductivity of isolated single dots by AFM operating in contact mode with a conductive tip under appropriate bias voltages. In the current image, it is found that the dot regions have higher electric resistances due to tunneling resistance through the CdSe dots. We found a 10-nm scale electric inhomogeneity around the dots, which may correspond to the previously reported etch-pits of Au(1 1 1) surfaces formed during the deposition of the alkanethiol molecules. Then, current-voltage characteristics were measured with the conductive tip positioned on the single dots; large changes in the conductivity which suggest resonant tunneling through the quantized energy level in the dot were observed even at room temperature.
journal of the Japan Society for Testing Materials, Sep 15, 2018
We fabricated field-effect transistors (FETs) using ammonium sulfide-treated PbS colloidal nano-d... more We fabricated field-effect transistors (FETs) using ammonium sulfide-treated PbS colloidal nano-dot (CND) films. After the ligand molecules were removed from the CNDs by the ammonium sulfide treatment, many cracks were observed in the atomic force microscope image of the PbS ND monolayer that was formed by horizontal lifting method. Those cracks were filled and almost disappeared after we repeated the formation of the PbS CND monolayer and removal of the ligand molecules for three times. The FETs fabricated with the cracked PbS ND films exhibited serious bias stress effect and very low hole mobility of 5.6×10 -5 cm 2 V -1 s -1 , which were attributed to the carrier traps existing on the NDs surface. On the other hand, the carrier mobility of the FETs with the crack-free PbS ND films was improved to be 1.1×10 -3 cm 2 V -1 s -1 because the cracks were filled and the trap density was significantly reduced.
Pentacene memory transistors using ligand-exchanged and energy-level controlled PbS colloidal nano-dots for carrier trapping layers
The Japan Society of Applied Physics, Jan 26, 2021
We fabricated pentacene memory transistors using a monolayer of ligand-exchanged and energy-level... more We fabricated pentacene memory transistors using a monolayer of ligand-exchanged and energy-level-controlled PbS colloidal nanodots (NDs) as charge-trapping layers, and it was demonstrated that the writing and retention times were reduced and increased, respectively. This result is explained with a model that the memory effect is due to the electrons tunneled from the pentacene layer into the PbS NDs when a writing voltage was applied. According to this model, the writing and retention characteristics were improved because of the lowered electron energy levels in the NDs.
The opto/electronic properties of single quantum dots (QDs) have attracted much attention due to ... more The opto/electronic properties of single quantum dots (QDs) have attracted much attention due to their potential for applications to various future devices. We have been employing conductive probe AFM for measuring quantized energy levels of single QDs prepared by colloidal synthesis [1]. In contrast to measurements on QDs prepared by MBE [2], a difficulty we suffered was interaction between the probe and the colloidal QDs. We have shown that the use of conductive CNT tips can prevent such problems [3]. Here, we show that the use of monolayer films of close-packed colloidal QDs allows us to perform stable conduction measurements even with standard probes. Thin films of 1-2nm of Ti followed by 20nm of Pt were sputtered on Si(001) substrates, whereon monolayer CdSe QD films were prepared by horizontal adsorption. The nearly close-packed QDs are stably attached to the substrate, enabling us to perform local conduction measurement using AFM without tip-QD interaction. We report the film...
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Papers by Kazuyuki Uno