Anomalously deep penetration of hydrogen and deuterium in assemblies from Nb foils and deuterated polyethylene (CD<Subscript>2</Subscript>)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> under the pulse high temperature hydrogen plasma

Studies of the storage and redistribution of hydrogen atoms under pulse high temperature hydrogen plasma that was obtained using a PF-4 Plasma Focus facility in a multilayered structure (sandwich) which consists of two high-purity niobium foils and a deuterium polyethylene film pressed between them have been carried out using the method for elastic recoil detection (ERD). It was established that, with an increase in pulses of the PF-4 facility, the redistribution of implanted hydrogen atoms for large depths occurs in the two Nb foils and deuterated polyethylene. The depths substantially exceed the projective range of paths of hydrogen ions (at their maximum velocity of ∼10⁸ cm/s). A maximum hydrogen concentration of 45 at % is reached in the nearest surface of the second Nb foil to the PF-4 at 20 pulses of hydrogen plasma. An X-ray diffraction analysis showed the presence of a niobium hydride phase in both Nb foils. The redistribution of deuterium atoms from the bound state of deuterated polyethylene into the near-surface layer and the bulk material of the second Nb foil was detected as well. This phenomenon can be attributed to the transfer of implanted hydrogen atoms through the foil assembly and the transfer of deuterium from deuterated polyethylene into the near-surface layer of the second foil under the effect of powerful shock waves that are created by pulse hydrogen plasma and by acceleration in the diffusion of hydrogen and deuterium in the strain field induced by the shock wave.     

Study of deuterium and hydrogen distributions in Ta|CD<Subscript>2</Subscript>|Ta,Ta|Ta|CD<Subscript>2</Subscript>|Ta|Ta,and Nb|CD<Subscript>2</Subscript>|Nb assemblies after exposure to high-temperature argon plasma

Assemblies made of Ta|CD₂|Ta, Ta|Ta|CD₂|Ta|Ta and Nb|CD₂|Nb foils are irradiated with pulses of high-temperature argon plasma created by means of a “Plasma Focus” setup. The irradiated foil samples are investigated by recording the recoil nuclei of hydrogen and deuterium. It is found that hydrogen and deuterium are redistributed in foil stacks. The ultradeep penetration of light gas impurities (hydrogen and deuterium) can be explained by the influence of shock waves on the foils and accelerated diffusion under an external force.     

Abnormally deep penetration of hydrogen into niobium under the influence of the pulse high-temperature plasma

The process of storing and redistributing hydrogen atoms under the action of pulse high-temperature hydrogen plasma obtained on the PF-4 plasma focus (PF) plant in an assembly of three high-purity niobium foils is studied by the elastic recoil detection (ERD) method. It is determined that, as the number of hydrogen plasma pulses increases, the implanted hydrogen atoms are redistributed at larger depths in an assembly of niobium foils which significantly exceed the projected range of hydrogen ions (when their maximal velocity reaches ??10⁸ cm/s). A maximum hydrogen concentration of up to 60 at % is reached in the nearest (to PF-4) surface of the third Nb foil under the action of 20 hydrogen plasma pulses. The observed phenomenon can be attributed to the ejections of implanted hydrogen atoms under the action of high-power shock waves created in niobium foils by the pulse hydrogen plasma and/or by the accelerating diffusion of hydrogen atoms under the action of compression-straining waves at the front of the shock wave with redistributions of hydrogen atoms at larger depths. Similar behavior is found in assemblies of two or three and more nickel, vanadium, niobium, and tantalum foils of different thicknesses, including foil assemblies made of heterogeneous materials, which were also studied.     

Hydrogen transport in a niobium-foil assembly under the action of high-temperature hydrogen plasma on a plasma focus setup

The process of hydrogen transport under the action of hydrogen-plasma pulses in the Plasma Focus (PF-4) setup in an assembly of niobium foils with thicknesses of 110 μm each is studied. It is established that the implanted hydrogen is transported to large depths in the Nb foils under the action of the hydrogen plasma. These depths considerably exceed the paths of hydrogen ions from the plasma as the maximum ion velocities are on the order of 10⁸ cm/s. The highest concentration of hydrogen (up to 60 at %) is reached on the surface of the third Nb foil of the assembly. The discovered phenomenon can be explained by the action of shock waves of arising stresses upon the transport and redistribution of hydrogen to considerable depths.     

Deuterium accumulation in an assembly of nickel foils irradiated by high-temperature deuterium plasma

The accumulation of deuterium in an assembly of nickel foils by the pulsed irradiation of a deuterium plasma is studied. It is established that implanted deuterium is transferred to a much greater depth than that corresponding to the projective range of deuterium plasma ions with a maximum velocity of 10⁸ cm/s. The maximum concentration (up to 4 at % deuterium) is observed in the second Ni foil. The observed phenomenon can be explained by the action of shock waves and concomitant stresses on the transport and redistribution of deuterium to greater depths.     

Dynamics of hydrogen in Ta in the mK-region

The low-temperature diffusion of hydrogen and deuterium in Ta was investigated using the method of perturbed angular correlation. In an ealier paper we reported the results of measurements above 4 K. These experiments have now been extended down to 10 mK. We found that the configuration of trapped hydrogen and deuterium changes, if the sample is cooled from 4.2 K to 10 mK. We suggest that this change is due to a transition of an extended to a more localized wave function of H (D).     

Mechanical Properties and Electronic Structure of N and Ta Doped TiC: A First-Principles Study

The first principles calculations based on density functional theory (DFT) are employed to investigate the mechanical properties and electronic structure of N and Ta doped TiC. The result shows that the co-doping of nitrogen and tantalum dilates the lattice constant and improves the stability of TiC. Nitrogen and tantalum can significantly enhance the elastic constants and elastic moduli of TiC. The results of B/G and C₁₂-C₄₄ indicate tantalum can markedly increase the ductility of TiC. The electronic structure is calculated to describe the bonding characteristic, which revealed the strong hybridization between C-p and Ta-d and between N-p and Ti-d. The hardnessis is estimated by a semi-empirical model that is based on the Mulliken overlap population and bond length. While the weakest bond takes determinative role of the hardness of materials, the addition of Ta sharply reduces the hardness of TiC.     

Lattice expansion of niobium and tantalum due to dissolved hydrogen and deuterium

The volume change of niobium and tantalum due to interstitially dissolved hydrogen and deuterium has been determined by means of X-ray Bragg scattering. The volume increase in niobium is the same for hydrogen and deuterium $\text{δν=(0.174±0.005)Ω}$(Ω: atomic volume). A small isotope effect has been observed in the case of tantalum, $\text{Δν=(0.155±0.002) Ω}$ for hydrogen and $\text{Δν=(0.143±0.005)Ω}$ for deuterium.     

Structural characterization of mixed Ta–Re oxide films

Thin films of mixed Ta and Re oxides have been produced by reactive dc magnetron co-sputtering of pure Ta and Re metal targets in Ar–O₂ atmosphere. The structural evolution of these films has been studied as a function of the composition, starting from a pure tantalum oxide film up to about 82% rhenium content. The composition and the structure of the films have been investigated by using X-ray diffraction and micro-Raman spectroscopy. For low Re content (20%), islands of a well crystallized phase, based on ReO₄ groups, appear in the films still composed by pure amorphous tantalum oxide, while a mixed disordered solid phase is found for the highest Re concentration (82%).     

Diffusion of deuterium in tantalum from internal friction measurements (Gorsky effect)

The long-range diffusion of deuterium in tantalum has been investigated as a function of temperature by means of the anelastic process due to redistribution of deuterium impurities between compressed and dilated regions of the sample, under an applied stress alternating at about 4 Hz. The diffusion coefficient was found to obey an Arrhenius-type law in the temperature range 200–390 K; a deviation was observed at lower temperatures. The diffusion parameters in the exponential region areD _0D=(3.3±1.5)×10⁻⁴ cm²/s, andW _D=(0.176±0.008) eV.     

The role of atomic hydrogen in pre-epitaxial silicon substrate cleaning

The cleaning of silicon (Si) surfaces is a very important issue for the fabrication of novel semiconductor devices on the nanoscale. Established methods for the removal of organic impurities and the native or chemical oxide are often combined with high temperature desorption steps. However, devices with small feature sizes will be unfunctional if, for example, out-diffusion of dopants is not prevented. In this paper we present two possible processes for low-temperature cleaning: an atomic hydrogen source, based on dissociative adsorption of hydrogen at a heated tantalum (Ta) surface and a hydrogen DC plasma source as a part of an UHV cluster tool. The influence of atomic hydrogen on carbon and oxide removal is surveyed and the existing model for native oxide etching with an argon/hydrogen DC plasma is adapted.     

Raman spectra of potassium, rubidium, and thallium hydrogen phthalates

The polarized Fourier-transform Raman spectra of oriented single crystals of K, Rb, and Tl hydrogen phthalates, as well as of deuterated potassium hydrogen phthalate, are studied in the range 50–3300 cm^?1 in different scattering geometries. The frequencies of internal vibrations in the spectra of these compounds are assigned to vibrations of the orthophenylene and carboxyl groups. The replacement of K with Rb or Tl leads to an insignificant low-frequency shift of vibrations. A multiband structure of OH(D) stretching vibrations is observed in the range 1900–2800 cm^?1 in the spectra of all hydrogen phthalates, which is caused by Fermi-resonance interactions. A number of additional bands are observed in the spectrum of deuterated potassium hydrogen phthalate, which indicates that deuterium atoms partially replace hydrogen atoms in both the orthophenylene and the carboxyl groups.     

Electronic modifications and surface reactivity of an ion bombarded graphite surface

The first steps of structural and electronic modifications of a graphite surface bombarded with argon, hydrogen and deuterium ions were investigated using high resolution electron energy loss spectroscopy (HREELS). The energy and the damping of the low energy plasmon mode of graphite (E//C mode) were studied with respect to the bombardment settings. We show that argon bombardment affects the energy of the plasmon mode, while no similar change is observed after hydrogen (deuterium) bombardments. This can be related to the variation of inter-planar distance between two graphene layers. Moreover, the damping of the plasmon mode can be correlated with the interstitial defect concentration. Concerning the reactivity of the bombarded surfaces, we demonstrate that deuterium bombardment produce a non-deuterated surface. This last is very reactive to a further atomic deuterium exposure, as it is shown by the formation of C-D bondings. The deuterated sites can be removed after thermal annealings between 473 and 783 K. The occurrence of a chemical erosion mechanism accompanying this deuteration is discussed.     

Surface enhancement of molecular ion H_2~+ yield in a 2.45-GHz electron–cyclotron resonance ion source

High current hydrogen molecular ion beam is obtained with a specially designed stainless steel liner permanent magnet2.45-GHz electron–cyclotron resonance(ECR) ion source(PMECR II) at Peking University(PKU). To further understand the physics of the hydrogen generation process inside a plasma chamber, theoretical and experimental investigations on the liner material of the plasma chamber in different running conditions are carried out. Several kinds of materials, stainless steel(SS), tantalum(Ta), quartz, and aluminum(Al) are selected in our study. Experimental results show that stainless steel and tantalum are much better than others in H~+_2 generation. During the experiment, an increasing trend in H~+_2 fraction is observed with stainless steel liner after O_2 discharge inside the ion source. Surface analyses show that the roughness change on the surface after O_2 discharge may be responsible for this phenomenon. After these studies, the pure current of H~+_2 ions can reach 42.3 mA with a fraction of 52.9%. More details are presented in this paper.     

Nearly golden-ratio order in Ta metallic glass

The formation of mono-atomic tantalum(Ta)metallic glass(MG)through ultrafast liquid cooling is investigated by ab-initio molecular dynamics(MD)simulations.It is found that there exists nearly golden ratio order(NGRO)between the nearest and second nearest atoms in Ta MG,which has been indirectly confirmed by Khmich et al.and Liang et al..The NGRO is another universal structural feature in metallic glass besides the local five-fold symmetry(LFFS).Further analyzing of electronic structure shows that the obvious orientation of covalent bond could be attributed to the NGRO in amorphous Ta at 300 K.     

EuS/Ta异质结的极大磁电阻效应

在铁磁/超导异质结中,铁磁体的交换场通过近邻效应将导致超导体准粒子态密度的塞曼劈裂.基于该效应,在外磁场不强的情况下,通过外加磁场可以有效地调节铁磁/超导界面处的交换作用,从而实现超导体在正常态和超导态之间转换,产生极大磁电阻.本文利用脉冲激光沉积方法制备了EuS/Ta异质结并研究了其电磁特性.Ta在3.6 K以下为超...     

Small size plasma tools for material processing at atmospheric pressure

A small size radiofrequency plasma jet source able to produce cold plasma jets at atmospheric pressure is presented. The surface modification of polyethylene terephtalate, polyethylene and polytetrafluorethylene foils is performed by using a scanning procedure. The contact angle measurements reveal that the treatment leads to hydrophilicity increase. The roughening of surface, specific to each material is noticed. A significant improvement of adhesion is obtained as result of atmospheric plasma treatments.     

块状Ta2O5-TiO2复合气凝胶的制备与表征

 以乙醇钽、钛酸丁酯为原料,以乙醇为溶剂,通过溶胶-凝胶法及超临界干燥成功制备了Ta₂O₅-TiO₂复合气凝胶。用场发射扫描电镜（SEM）、透射电镜（TEM）、扫描电镜模式下的电子能谱仪（EDS）以及比表面积吸附仪（BET）对其进行表征。结果表明:该气凝胶是由粒径在nm量级的Ti和Ta的羟基氧化物胶体颗粒堆积而成的低密度、高比表积的多孔网络结构材料,孔径分布主要集中在5~15 nm,比表面积为492.9 m²/g,密度为90 mg/cm³左右。     

稠密氘和氢氘混合等离子体辐射不透明度的研究

用强平面激波对氘和氢氘等摩尔混合气体进行冲击压缩 ,产生密度约为 3.7× 10 - 3 — 7.0×10 - 3 g/cm3 等离子体.由记录的等离子体发光过程的上升前沿 ,确定了氘和氢氘等离子体光谱吸收系数随光学波长变化. Plasma is generated by passage of strong planar shock wave through gas. Initial experiments in deuterium and equal mol mixture of hydrogen and deuterium have been performed to produce plasma with 3.7×10 -3-7.0×10 -3 g/cm 3density. The variation of the opacity of the plasma with wavelength is measured by recording the risetime of the emitted light.     

Observation of opposite 4f-surface core level binding energy shifts for W(111) and Ta(111)

Surface 4f core level binding energy shifts have been measured in photoemission from W(111) and Ta(111). The surface shift was found to change sign across the row of 5d-metals: for the topmost layer of Ta(111) a +0.40 eV shift toward higher binding energy is found, whereas for W(111) the shift is -0.43 eV toward lower binding energy. The shifts are shown to be dependent on surface crystallography. Chemical shifts are determined for saturation coverage of hydrogen.