Generation Of Atomic Hydrogen Research Articles

In-situ atomic hydrogen generation: A key to elevating membrane cleaning via citric acid-modified Fenton-like system

Oxidation process has been widely used to clean irreversible membrane fouling, and the development of novel oxidative cleaning process has attracted worldwide attention. In this study, a novel cleaning process with the combination of sodium percarbonate (SPC), citric acid (CA), and ferrous ion (Fe(II)) was introduced to remove organic fouling derived from the complexation of humic acid (HA) and calcium ions (Ca2+) for the first time. Remarkably, both flux recovery and resistance removal could reach 99 % within one hour. The efficiency and durability of this novel cleaning system were confirmed through comprehensive characterization and cyclic cleaning test of the ultrafiltration membranes. Furthermore, it effectively removed various natural organic matter-induced fouling and performed well in long-term experiments. This outstanding performance is due to the synergy between oxidative hydroxyl radicals (HO) and reductive atomic hydrogen (H*) in SPC/CA/Fe(II). Analysis of intermediate/final products confirmed that H* is generated through the reaction of CA and HO and absorbed by HA. Confocal laser scanning microscopy (CLSM) revealed that this absorption makes HA more susceptible to HO attack, resulting in enhanced cleaning performance. This mechanism demonstrates the potential of advanced reduction–oxidation systems for membrane cleaning, offering new insights for the development of novel cleaning methods.

Zero-dimensional N-doped carbon quantum dots and palladium co-modified titanium electrodes enhance the electrocatalytic degradation of oxytetracycline hydrochloride

Reducing the amount of precious metals and improving their catalytic activities are difficult problems in the field of electrocatalysis. In this study, Pd/N-CQDs/Ti electrodes were prepared by introducing the N element into zero-dimensional carbon quantum dots and then compounded with Pd metal, and the electron transfer mechanism was explored. The results showed that the composite electrode degraded OTC up to 90.41% (60 min) at natural pH with an energy consumption of only 0.288 kWh/m3. The Pd/N-CQDs/Ti electrode formed a Pd-N-CQDs interface due to the electronic metal-carbon interaction (EMCI). In this, electrons are transferred from Pd to N, and the Pd-N interface plays a major role in hydrogen precipitation and the generation of atomic hydrogen. The generated H* ,·OH, and HClO all contribute to the degradation of OTC. According to the cycling experiments, the Pd/N-CQDs/Ti electrode showed good stability. When applied to OTC degradation in real water bodies, good reactivity was still maintained. Toxicity assessment of the degradation intermediates by ECOSAR and TEST showed that the electrode could effectively reduce the biotoxicity of OTC. In this study, the interface of the catalytic electrode was tuned to enhance its intrinsic activity, which provides an efficient strategy for electrocatalytic remediation of antibiotic contamination.

Hydrogen permeation through steel during cathodic polarization of lubricating oils in a modified Devanathan–Stachurski cell

In lubricated tribo-contacts, hydrogen ingress in steel is possible due to chemical reactions of lubricant components like base oils or additives, and/or contamination upon service particularly water, and/or corrosion processes, and/or electrostatic fields or current flow. Absorbed by the metal, atomic hydrogen may cause serious deleterious effects on the physical–chemical and mechanical properties, reducing the material’s ability to withstand the design loads. The present research work is focused on analyzing the influence of electric field on lubricating oils in contact with steel surface. In order to evaluate the possibility of atomic hydrogen generation and permeation into the steel under cathodic polarization of lubricating oils the electrochemical permeation technique developed by Devanathan and Stachurski is used. The input cell of a Devanathan–Stachurski set up is appropriately modified by realizing a very close distance between the working electrode (steel membrane) and a Pt counter electrode with the oil between. This significantly increases the sensibility of the set up and allows the application of larger voltage and higher temperature to enable hydrogen generation from lubricating oils. The complex effects of cathodic polarization, temperature, additives and presence of water in model lubricating oils on atomic hydrogen permeation into steel is discussed.

Hydroxyl Radical Production via a Reaction of Electrochemically Generated Hydrogen Peroxide and Atomic Hydrogen: An Effective Process for Contaminant Oxidation?

An electrochemical advanced oxidation process (EAOP) is demonstrated with a catalytic cathode capable of simultaneously catalyzing the hydrogen evolution reaction (HER) and the oxygen reduction reaction (ORR) with resultant in situ generation of atomic hydrogen (H*) and hydrogen peroxide (H2O2). A palladium-coated carbon-PTFE gas diffusion electrode (Pd/C GDE) was used as a catalytic cathode with hydroxyl radical (•OH) formed as a result of the reaction of electrogenerated H* with H2O2. As both the HER and ORR can be induced to occur at the same cathode, the H*/GDE process results in more effective degradation of organic contaminants than can be achieved by a conventional H*/H2O2 process involving direct addition of H2O2. At circumneutral pH, 82.7% of added formate was degraded after 2 h treatment at an applied potential of -1.0 V vs Ag/AgCl with relatively low concentrations of generated H2O2 remaining in the solution. We also show that H* and H2O2 (and thus •OH) can be electrogenerated effectively over a wide range of pH (3.2-7.0). These results suggest that by in situ generation of H* and H2O2, the H*/GDE process is able to produce significant amounts of •OH without external chemical addition and thus offers an alternative method for abatement of aqueous organic contaminants.

Generation of atomic hydrogen by Ni-Fe hydroxides: Mechanism and activity for hydrodechlorination of trichloroethylene

Atomic hydrogen (H•) is highly reactive for the hydrodechlorination of trichloroethylene (TCE). In this work, we found that the coprecipitation of Ni2+ and Fe2+ at neutral pH led to an unprecedented catalytic generation of H•. The generated H• effectively dechlorinate TCE to nontoxic ethylene and ethane, and Fe2+ is the only electron donor. The abundant adsorbed H• produced with a Ni/Fe ratio of 0.4 enhances hydrogen evolution reaction causing a low efficiency for hydrodechlorination. In contrast, the active absorbed H• is generated in the crystal lattice of Ni-Fe hydroxides with a Ni/Fe ratio of 3.0 causing highly efficient hydrodechlorination of TCE. This work not only reveals the mechanism of catalytic hydrodechlorination by Ni-Fe hydroxides at neutral pH, but also provides a novel approach to detoxify TCE in contaminated water using facile precipitated Ni-Fe hydroxides.

Ammonia production using iron nitride and water as hydrogen source under mild temperature and pressure

Ammonia generation was studied in the reaction between water and nitrogen-containing iron at 323 K and atmospheric pressure. Similar to metallic Fe, the interstitial compound Fe3N reduced water through Fe oxidation to produce hydrogen gas, while the N combined with atomic hydrogen to produce ammonia as a byproduct. The addition of carbon dioxide to this system accelerated the reaction with concomitant consumption of carbon dioxide. The promoted ammonia production upon addition of carbon dioxide can be attributed to the generation of atomic hydrogen from the redox reaction of carbonic acid and Fe, as well as removal of used Fe from the reaction system through the formation of a soluble carbonato complex. When carbonate was added to the reaction system, the production rates of ammonia and hydrogen increased further. The results here confirmed that ammonia can be synthesized from iron nitride under mild conditions by utilizing carbon dioxide.

Electrochemical Hydrogenation of Toluene to Methylcyclohexane over Rh-Modified Pt Nanoparticles: Effect of Rh Coverage and Electrochemical Surface Area

Introduction Organic hydrides are known to be hydrogen carriers to achieve large-scale storage/transportation system of hydrogen. Especially, a couple of toluene (TL) and its hydrogenation product, methylcyclohexane (MCH), is promising because they are liquids at ambient temperature and pressure to use existing infrastructure and MCH has high hydrogen storage density (6.1 wt.%). In general, MCH is regenerated by the hydrogenation of TL with molecular hydrogen on appropriate catalysts, and another chemical or electrochemical process is required for the production of molecular hydrogen. However, electrochemical hydrogenation of TL to MCH is one-pot process, in which the electrochemical generation of atomic hydrogen by one-electron reduction of H+ and the hydrogenation of TL with atomic hydrogen consecutively proceed on the same catalyst surface. The standard potential of the electrochemical TL hydrogenation process is more positive than that of hydrogen evolution reaction, indicating the former is more energy-saving.1, 2 Pt nanoparticles loaded on carbon (Pt/C) are active for electrochemical hydrogenation of TL to MCH.1, 2 Recently, it has been found in our group that Rh-modified Pt/C (Rh/Pt/C) catalysts exhibited higher current for electrochemical hydrogenation of TL than Pt/C. In order to evaluate the specific activity and investigate the relationship between electrochemical hydrogenation activity and Rh loading or Rh coverage (θ Rh), it is necessary to separately evaluate the electrochemical surface areas (ECSAs) of Pt and Rh, but it is difficult because the potential region of hydrogen adsorption/desorption for Pt and Rh overlaps. In this study, we have succeeded in separately evaluating the ECSAs of Pt and Rh for Rh/Pt/C catalysts with different quantities of deposited Rh by using the difference in CO stripping potential between Pt and Rh, and estimated the Rh coverage (θ Rh) to discuss the relationship with catalytic activity. Experimental The commercial Pt/C (Tanaka Kikinzoku Kogyo, TEC10E50E) powder was dispersed in ultrapure water. Different concentrations (1.2, 2.4, 3.6 and 4.8 mM) of rhodium chloride aqueous solutions were added into the dispersion, followed by hydrogen bubbling for 1 h at 30 °C. The final black powder is named Rh0.19/Pt/C, Rh0.38/Pt/C, Rh0.56/Pt/C and Rh0.76/Pt/C hereafter. For the preparation of a catalyst electrode, each catalyst ink was cast on a GC substrate (diameter: 5 mm) and dried overnight to make a working electrode. The counter electrode, reference electrode and electrolyte were a platinized Pt electrode, reversible hydrogen electrode (RHE) and 0.5 M H2SO4 aqueous solution, respectively. For the ECSA evaluation, CO was saturated into the electrolyte solution at 0.30 V. After removing dissolved CO by Ar-bubbling, the electrode potential was stepped from 0.30 to 0.75 V, and kept at this potential for 15 s to preferentially desorb CO adsorbed on the Rh surface. After that, cyclic voltammogram was measured between 0.05 and 1.2 V. Results and Discussion The θ Rh increased with the Rh/Pt mole ratio for Rh/Pt/C catalysts, and stagnated as the Rh/Pt mole ratio excessed 0.38 (Fig. 1). However, the fraction of ECSA of Rh (ECSARh) to total ECSA of Pt and Rh (ECSARh/Pt/C) continued to increase with the Rh/Pt mole ratio, suggesting that Rh was preferentially accumulated on deposited Rh as θ Rh reached ca. 0.2. The Tafel slope of the electrochemical hydrogenation of TL on the Rh0.19/Pt/C, Rh0.38/Pt/C, Rh0.56/Pt/C and Rh0.76/Pt/C catalysts was ca. 34, 34, 33 and 32 mV dec-1, respectively. Each Tafel slope was close to that for the Pt/C catalyst, suggesting that electrochemical TL hydrogenation on Rh/Pt/C follows the same reaction mechanism and rate-determining step, which is the addition reaction of adsorbed TL with atomic hydrogen. The change in hydrogenation current per ECSAPt (j Pt) at 0 V vs. RHE with the Rh/Pt mole ratio showed the similar tendency to that in θ Rh (Fig. 1), suggesting that the electrochemical hydrogenation of TL preferentially occurs at the interface between Pt and Rh.Galvanostatic electrolysis of 30 vol.% TL with the Pt/C and Rh/Pt/C catalysts at −200 mA cm−2 was carried out with polymer electrolyte membrane electrolysis cell. It was found by GC/MASS analysis that sole reaction product in the electrochemical hydrogenation of TL was MCH. The faradaic efficiency for MCH production and conversion of TL to MCH were also increased with the increase of θ Rh, and the side reaction, hydrogen generation, was suppressed. These results clearly indicate that the Rh/Pt/C catalysts are superior to Pt/C. References 1 Y. Bao, T. W. Nappom, K. Nagasawa, S. Mitsushima, Electrocatalysis, 10, 184 (2019).2 S. Mitsushima, Y. Takakuwa, K. Nagasawa, Y. Sawaguchi, Y. Kohno, K. Matsuzawa, Z. Awaludin, A. Kato, Y. Nishiko, Electrocatalysis, 7, 127 (2016). Figure 1

Window-type rupture of carbon steel pipe in a hydroprocessing plant of a petroleum refinery due to ammonium bisulfide corrosion

The window-type rupture of a carbon steel piping in a refinery hydrocracking plant was investigated to identify the root cause of failure. The comprehensive investigation included visual examination, optical and scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and hardness measurements. The results of the investigation indicated that the failure of the piping was as a result of an aggressive corrosion reaction contributed by ammonium bisulfide (ABS) and turbulence. An increase in the throughput, change in the feed quality and localized turbulence due to geometry synergized the corrosion reaction. The aggressive conditions that existed in the system led to accelerated erosion corrosion. The accelerated erosion-corrosion resulted in the thinning of the pipe at the location and finally in the brittle window rupture of the pipe. The aggressive corrosion reaction also resulted in the generation of atomic hydrogen, which entered into the steel and caused hydrogen-induced cracking (HIC) at the thinned locations. Recommendations made to avoid reoccurrence of the incidence of corrosion and failure included reducing the severity of corrosive conditions and up-gradation of the material of construction to Alloy 825.

Hydrogen Reduction of MoF6 and Molybdenum Carbide Formation in RF Inductively Coupled Low-Pressure Discharge: Experiment and Equilibrium Thermodynamics Consideration

The physical plasma parameters, temperature and electron number density, are studied in the RF-IC (RF inductively coupled) discharge at a reduced pressure of 3 Torr in mixtures of MoF6 with Ar, H2 and CH4. The emission spectra of mixtures are investigated. It is shown that in the presence of argon, the concentration of free electrons in plasma and dissociation rate of MoF6 increase. A main role of molecular hydrogen is the generation of atomic hydrogen that binds atomic fluorine and leads to the formation of gaseous and solid products. Exhaust gas mixtures exiting the reactor are analyzed by mass spectrometry. It is shown that for all cases, the conversion of MoF6 into reaction products is close to 100%. A thermodynamic analysis of the equilibrium composition of MoF6 systems with Ar, H2 and CH4 was carried out and the obtained results are in good agreement with experimentally observed composition of the solid and gas phases. Analysis of solid deposits from mixture MoF6/H2/Ar revealed the presence of molybdenum powder and large amount of amorphous MoFx. The deposit obtained from mixtures with methane, MoF6/H2/Ar/CH4, contained crystalline molybdenum carbide, Mo3C2.

Catalytic Reactivation of Industrial Oxygen Depolarized Cathodes by in situ Generation of Atomic Hydrogen.

Electrocatalytically active materials on the industrial as well as on the laboratory scale may suffer from chemical instability during operation, air exposure, or storage in the electrolyte. A strategy to recover the loss of electrocatalytic activity is presented. Oxygen-depolarized cathodes (ODC), analogous to those that are utilized in industrial brine electrolysis, are analyzed: the catalytic activity of the electrodes upon storage (4 weeks) under industrial process conditions (30 wt % NaOH, without operation) diminishes. This phenomenon occurs as a consequence of surface oxidation and pore blockage, as revealed by scanning electron microscopy, focused ion beam milling, X-ray photoelectron spectroscopy, and Raman spectroscopy. Potentiodynamic cycling of the oxidized electrodes to highly reductive potentials and the formation of "nascent" hydrogen re-reduces the electrode material, ultimately recovering the former catalytic activity.

Effects of plastic deformations on the electrochemical and stress corrosion cracking behaviors of TC2 titanium alloy in simulated seawater

In this work, the electrochemical and stress corrosion cracking (SCC) behaviors of TC2 titanium alloy with varying plastic deformation in simulated seawater were investigated using electrochemical and slow strain rate test methods. Results show that the plastic deformation increases hardness and electrochemical activity and decreases elongation and reduction in area simultaneously. The increase in electrochemical activity enhances the anodic dissolution and the generation of hydrogen atoms, resulting in the increase of SCC susceptibility.

SiH4 enhanced dissociation via argon plasma assistance for hydrogenated microcrystalline silicon thin-film deposition and application in tandem solar cells

We investigate the influence of argon plasma assistance on the depletion of SiH4 in the preparation of μc-Si:H films via plasma-enhanced chemical vapor deposition (PECVD). From optical emission spectrometry (OES) data of the μc-Si:H deposition, we infer that the excited Ar+ and metastable Ar* states enhance the dissociation of SiH4 and H2 molecules to generate ultra-depletion of SiH4. The ultra-depletion of SiH4 increases the μc-Si:H thin-film deposition rate from 4.5 Å/s to 23.4 Å/s at 6-sccm flow of SiH4. This ultra-depletion condition facilitates the gradual substitution of H2 by Ar, which leads to reduced crystallinity at low argon fractions (far), preferential crystallographic orientation along the (111) direction, and fluctuation of the hydrogen content and microstructure factor (R). Thus, the properties of the μc-Si:H thin films can be controlled via control of the atomic hydrogen generation and physical sputtering effects. The highest photosensitivity (2.2 × 103) is observed at far = 56%. Furthermore, we fabricate an a-Si:H/μc-Si:H tandem solar cell with a total thickness of 1450 nm. The cell exhibits an initial efficiency of 11.44%, and the efficiency reduces to 10.24% after 1000 h of light soaking. The cell also exhibits a significantly higher Voc × FF stability over that of Jsc.

On-Board Hydrogen Production: Warm Plasma Chain Catalysis

Here we demonstrate an advanced on-board hydrogen production by warm plasma chain catalysis for fuel-cell electric vehicles (FCEVs) with high specific productivity and transient operation. Methanol, air and steam reactants as two specific feeds are fed into the reactor without soot formation and catalyst sintering. Oxidative pyrolysis reaction (OPR) by plasma, steam reforming (SR), and pyrolysis at high temperature, and SR and water gas shift (WGS) at medium temperature over catalysts occur subsequently for the coupled process. The heat with OPR is efficiently utilized by the subsequent endothermic reactions. Hydrogen selectivity of 99% (59 vol.%, 4.1 SLM) with methanol conversion of 92% is achieved. A fascinating match of energy efficiency of 91% (of methanol to hydrogen) and the atomic hydrogen generation of 88% is stressed. It can be attributed to the chain catalysis of (oxidative) pyrolysis and WGS in sequence (as well as SR), which is initiated by warm plasma.

Formation of bubbles by hydrogen attack and elastic–plastic deformation of the matrix

Steel pipes used in oil industry are subjected to environmental conditions, which may provoke generation of atomic hydrogen at their surface by electro-chemical processes. A part of the atomic hydrogen recombines to molecules and the remaining part enters the bulk of the pipe and causes the well known hydrogen attack with several negative effects. One of them is the formation and growth of bubbles. Hydrogen atoms diffuse in steel to the surface of the bubbles, they recombine there to gas molecules and increase the gas pressure in the bubbles. The pressure may then reach a value sufficient for the growth of the bubbles by elastic or elastic–plastic deformation of the matrix.The problem of kinetics of bubble formation and growth nucleated at an inclusion is treated by a thermodynamic model combining diffusion of hydrogen from the system surface to the bubble surface with the growth of the bubble by elastic or elastic–plastic deformation of the matrix. The processes are driven by the release of the Helmholtz free energy of hydrogen. The according driving force is spent for dissipation by diffusion, for elastic or elastic–plastic deformation of the matrix and for the increase of the bubble surface energy. The model is demonstrated on several simulations of bubble growth kinetics in iron and copper.

Electron spin resonance study of chemical reactions and crossover processes in a fuel cell: Effect of membrane thickness

Spin trapping ESR experiments were performed in a fuel cell inserted in the resonator of the ESR spectrometer, and allow visualization of crossover processes and separate detection of chemical reactions at anode and cathode. The membrane-electrode assembly (MEA) consisted of the perfluorinated 3M membranes and Pt as catalyst; the detection of unstable intermediates was possible with 5,5-Dimethyl-1-pyrroline N-oxide (DMPO) as the spin trap. The major goal was to determine the effect of membrane thickness on the type and intensity of the spin adducts; MEAs with membrane thicknesses of 25 μm, 50 μm and 100 μm were studied. DMPO/H and DMPO/OOH adducts were detected in most experiments and their presence is explained by the generation of hydrogen atoms, H·, at the catalyst, and reaction with crossover O2. A strong effect of membrane thickness was detected: For a 25 μm thickness the relative intensities of DMPO/H and DMPO/OOH are similar at both anode and cathode. For 100 μm thickness the relative intensity of DMPO/H at the cathode decreased significantly, due to decreased H2 crossover. At the anode DMPO/H was the only adduct detected; the absence of DMPO/OOH is assigned to negligible O2 crossover. The results provide evidence for the involvement of hydrogen atoms in the membrane degradation. Enhancement of crossover rates in thinner membranes is expected to reduce membrane durability.

Hot-Wire Generated Atomic Hydrogen and its Impact on Thermal ALD in TiCl4/NH3 System

We present the generation of atomic hydrogen made by the dissociation of molecular hydrogen upon collision with a tungsten (W) filament kept at a high temperature (T ≈ 1600–1900°C). We demonstrate the ability to create atomic hydrogen and to introduce it in short pulses in experiments on etching of tellurium (Te) films. We further utilize the generated atomic hydrogen (H) to explore its impact on surface reactions in the TiCl4/NH3 precursor system. Atomic hydrogen is introduced in pulses additionally to TiCl4 and NH3 with different pulse sequences. For the TiCl4/NH3/H sequence, there is no influence on the process compared to the ALD without H-pulses. The growth rate remains at 0.02 nm/cycle and the oxygen (residual gas) content - at 3–5 at%. For the TiCl4/H/NH3 pulse sequence, the growth rate decreases to 0.01 nm/cycle and the oxygen content increases to 30–35 at%. Only TiCl4/H pulses result in no growth after the formation of approximately one monolayer. Similar effect occurs after introducing NH3 via the hot filament, pointing to the decomposition of NH3 and the formation of atomic hydrogen.

Effects of macroscopic propagation on spectra of broadband supercontinuum harmonics and isolated-attosecond-pulse generation: Coherent control of the electron quantum trajectories in two-color laser fields

Recently it was shown that broadband supercontinuum harmonics can be produced from the long-trajectory electrons in the single-atom response by the coherent control of the electron trajectories through optimized two-color laser fields. Such supercontinuum harmonics can be superposed to generate an isolated sub-30-attosecond (as) pulse [Liu et al., Phys. Rev. A 84, 033414 (2011)]. In this paper, we investigate the effect of macroscopic propagation on the supercontinuum harmonic spectra and the subsequent attosecond-pulse generation of atomic hydrogen. The time-dependent Schr\"odinger equation is solved accurately and efficiently by means of the time-dependent generalized pseudospectral method. The effects of macroscopic propagation are investigated in near and far field by solving Maxwell's equation. The results show that the contribution of short-trajectory electron emission is increased when the macroscopic propagation is considered. However, the characteristics of the dominant long-trajectory electron emission (in the single-atom response case) are not changed, and an isolated 53 as pulse can be generated in the near field. Moreover, in the far field, the contribution of long-trajectory electron emission is still dominant for both on-axis and off-axis cases. As a result, an isolated 42 as pulse can be generated directly. Similar results are obtained when the atomic target position is changed. Therefore, the proposed method for the single ultrashort attosecond-pulse generation can be realized by means of the coherent control of the electron quantum paths in appropriately optimized two-color laser fields.

Effect of an inter-electrode distance in VHF-PECVD and gas flow ratios on a-SiGeC:H films and solar cells by using monomethyl germane as a germanium source

Hydrogenated amorphous silicon–germanium–carbide (a-SiGeC:H) has been fabricated by monomethyl germane (MMG, GeH3CH3) under various deposition conditions, inter-electrode distance (dele) in VHF-PECVD and gas flow ratios. With decreasing dele, it is observed from optical emission spectroscopy (OES) that the generation of atomic hydrogen in plasma gradually increases. It is also found that the enhanced atomic hydrogen tends to take both Ge and C away from growing surfaces, leading to the decrease in Ge and C contents. The total content of hydrogen bonds increases as a result of the increase in both SiH and GeH bonds as the dele decreases. Consequently, the a-SiGeC:H solar cells fabricated at narrower dele exhibit the improved performance. Even though the optical band gap (Eopt) of the a-SiGeC:H increases with decreasing dele, the quantum efficiency (QE) spectra reveal even an increasing trend of long wavelength regions because of the significant improvement in i-layers. It is also confirmed that a lot lower MMG/SiH4 was needed for the films having certain Eopt, when fabricated near amorphous-to-crystalline transition, and the solar cell fabricated near the transition region shows the better performance.

Porous Alumina Template based Versatile and Controllable Direct Synthesis of Silicon nanowires

ABSTRACTHighly densely packed, self-organized silicon nanowires with very narrow diameter distribution were synthesized within porous anodic alumina templates with electrodeposited catalytic metal nanoparticles. For successful catalytic metal nanoparticle deposition, electrochemical-, and chemical barrier layer thinning process was investigated following anodization process. Controlled pulsed electrodeposition process was carried out for a volume calibration of desired catalytic metal nanoparticle deposition inside nanopore arrays using different metal-ion containing electrolyte. Not only single metal nanoparticles, but also multi metal nanoparticles layers were filled inside PAA to enhance metal filling aspect, and to control the volume of nanoparticles more precisely. Using multilayered metal nanoparticles resulted on different SiNW’s growth behavior depending on the types of underlying metal nanoparticles.SiNWs were successfully synthesized using hot-filament assisted chemical vapor deposition system. Although silicon precursor gas can generally be dissociated at relatively low temperatures, the use of a hot filament activation help decreasing process temperature, and also, highly activated atomic hydrogen generation via the tungsten hot filament placed at gas inlet helps preventing parasitic amorphous silicon deposition on either the alumina membrane surface or the pore wall which hinders appropriate growth of SiNWs in PAA by nanopores clogging. Such densely packed, self-organized SiNWs are of high interest in many application fields like nanoelectronics, optoelectronics, and energy storage/conversion devices etc.

The wavelength dependence of high-order harmonic generationand attosecond pulses from atom in infrared laser field

Basing on the strong-field approximation, we study high harmonic generation of hydrogen atom exposed to the long wavelength infrared laser field, and analyze the wavelength dependence of conversion efficiency of high-order harmonic generation near the cut-off position. It is found that high-order harmonic yield is much lower near cut-off than in the beginning of the plateau of the harmonic generation, but the width of the attosecond pulse is narrowed with increasing wavelength.