the first approximation, but they actually have some interactions with each other and also with the inner surface of the cell walls, which are often made of glass. Specifically, the atom-surface interactions cause undesired effects that cannot be easily understood and controlled, such as broadening and frequency shifts of resonance lines [3,4]. There have been many studies to understand surface-related phenomena in alkali metal vapor cells, such as anti-spinrelaxation coatings [5], surface modification to cause conductivity of cells [6] and stray electric fields [7], testing of several different surface materials for laser traps [8], direct measurements of adsorption/desorption dynamics [9], and measurement of passivation of a surface with alkali metal atoms, called "curing" [10]. However, there have mostly been only indirect studies of surfaces via atoms in the gas phase. Direct characterization of surfaces using standard surface science techniques has been very limited for atomic physics purposes [11].The same is true for studies of light-induced atom desorption [12]. This phenomenon has attracted particular attention in laser cooling and trapping experiments using ultrahigh vacuum cells, into which atoms can be loaded quickly on demand from the surface by LIAD techniques [13,14]. However, most LIAD studies [13,[15][16][17][18][19] focused only on desorbed atoms, and lack of basic knowledge of the surface itself leads to a poor understanding of desorption mechanisms and also some contradictory practical information. For example, one group reported that LIAD from quartz glass is not effective [20], but another loaded a magneto-optical trap in a quartz cell by LIAD [16].Following our previous study [21], we introduce surface analysis for glass surfaces, for which LIAD measurements were then carried out by focusing on differences between vitreous silica (synthetic quartz) and commercial borosilicate glass (Pyrex), which are the most commonly used Abstract We analyzed the surfaces of vitreous silica (quartz) and borosilicate glass (Pyrex) substrates exposed to rubidium (Rb) vapor by X-ray photoelectron spectroscopy (XPS) to understand the surface conditions of alkali metal vapor cells. XPS spectra indicated that Rb atoms adopted different bonding states in quartz and Pyrex. Furthermore, Rb atoms in quartz remained in the near-surface region, while they diffused into the bulk in Pyrex. For these characterized surfaces, we measured light-induced atom desorption (LIAD) of Rb atoms. Clear differences in time evolution, photon energy dependence, and substrate temperature dependence were found; the decay of LIAD by continuous ultraviolet irradiation for quartz was faster than that for Pyrex, a monotonic increase in LIAD with increasing photon energy from 1.8 to 4.3 eV was more prominent for quartz, and LIAD from quartz was more efficient at higher temperatures in the range from 300 to 580 K, while that from Pyrex was almost independent of temperature.
Streamer discharges in water, which are a pre-breakdown phenomenon caused by underwater discharge, have gained attention because of the development of plasma-based technologies for water purification and medical treatment. In this study, a single-shot pulsed negative high voltage of –18 to –21 kV with a rise time of 100 ns was applied to a needle electrode in ultrapure water, and streamers were continuously imaged using an optical system combining a high-speed video camera, a streak camera, and an ultra-high-speed camera with a microscope lens. These observations were synchronized with the applied voltage and the discharge current to investigate the effect of the discharge on streamer propagation. Negative streamers propagated with a velocity of 820 ± 50 m/s in the presence of pulsed currents, and 100 ± 20 m/s when pulsed currents were absent. The streak camera detected light emission when the pulsed currents appeared, and it was also observed that 1480 m/s pressure waves were generated during streamer propagation. Furthermore, we developed a simple new method of imaging weak density changes similar to those detected using the Schlieren method or Mach–Zehnder interferometer. This method simply involves inserting a pair of polarizing plates on the optical axis, so that the pressure waves can also be imaged in two-dimensional photographs. Our results indicated that the pressure waves were generated from the propagating streamer head when the pulsed currents appeared in the waveform. Analysis of temporal resolution with nano-second order clarified that the branching phenomenon occurred at different times resulting in the branching streamer propagation with different directions.
Fine bubbles generated by plasma in water that we named as "Plasma Fine Bubbles," have high potential to generate long-life ultrafine bubbles due to electrical charges. It is shown that the residual bubbles formed by collapse of streamer gas channels which show a similar process of cavitation bubbles in various points such as growth, shrink, collapse, rebound, and fragmentation. There are also introductions about ultrafine bubbles measured by a dynamic laser scattering method, amount of electrical charge of plasma fine bubbles estimated by analyzing their movements under application of an intense electric field strength, evidence of hydrogen gas generation in laser/spark induced bubbles and a distinguishing method for between gas bubbles and solid particles.
Electrical properties and microstructures were investigated between a-IGZO and metal electrodes. We should use Cu-Mn or Ti electrodes as the contact promoter and diffusion barrier. Ohmic behaviors were obtained with Cu-Mn and Ti after annealing at 250 °C. TFT showed high performance with theses. This is due to reduced a-IGZO and oxygen deficient region. IntroductionAmorphous In-Ga-Zn-O (a-IGZO) TFTs have been considered for practical application to large-sized LCDs with high resolution and high frequency and to OLED displays. In combination with the high mobility a-IGZO channel layer, low resistance electrodes are essential for the decrease of RC delay. Although Cu is a choice of material to decrease the RC delay, problems with Cu are poor adhesion, interdiffusion and high contact resistance with the a-IGZO or the oxide insulator. Therefore, it is necessary to choose suitable electrode for a-IGZO TFT structure. In order to solve these problems, Cu can be used with a Mo or Ti as a contact promoter. However, complicated etching process is required with these electrode structures. Alternatively, Cu can be used with a Cu-based alloy instead of Mo or Ti. In comparison with the Mo or Ti contact electrode, the Cu/Cu alloy electrode structure is expected to have advantages such as easy wet etching of the entire electrode and a good wet etching selectivity between the electrode and the a-IGZO channel layer. In the past, we reported Cu-Mn alloy as an interconnect material for LSI circuits, and showed the formation of the reaction layer with a SiO 2 insulating layer that could act as a diffusion barrier layer as well as an adhesion layer [1]. We also reported a good contact property between Cu-Mn and a-IGZO [2]. In this work, we investigated the contact properties and TFT properties of a Cu-Mn alloy electrode as well as Cu, Al, and Ti electrodes. Moreover, a good wet etching selectivity between the Cu-Mn alloy electrodes and a-IGZO can realize the fabrication of back-channel etching TFTs, which means the use of less photo-mask steps than those of etch-stop layer TFTs. The obtained results were compared to show the superior properties of the Cu-Mn electrode. Experimental ProcedureThe a-IGZO films of 50 nm thickness were deposited on TEOS / Si substrates by RF magnetron sputtering of a sintered InGaZnO4 ceramic target. For TLM measurement, the resistivity of a-IGZO was controlled to be ~ 5 × 10 -1 Ω·cm by sputtering a-IGZO at a processing pressure (Ar + 0.5% O 2 ) of 1 × 10 -1 Pa at a RF power of 50 W and at a deposition rate of 18 nm/min. On the a-IGZO layer, four different metals were deposited as metal electrodes; Cu, Cu-4 at.%Mn, Ti and Al. Rectangular pads of 60 × 120 μm 2 area were formed using lithography and lift-off processes. Samples were annealed in the Ar atmosphere at 250ºC for 1 h. Interface reaction between the metal electrodes and a-IGZO was investigated by TEM analysis. For TFT characterization, the resistivity of a-IGZO was controlled to be ~ 1 × 10 3 Ω·cm by depositing the layer at a processing pressure (Ar...
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