Grazing-incidence electron microscopy of surface blisters in single- and polycrystalline tungsten formed by H, D and He irradiation

Blisters on single- and polycrystalline tungsten surfaces formed by hydrogen and helium ion irradiation were investigated by grazing-incidence electron microscopy (GIEM) with an ultra-high-voltage transmission electron microscope. It was found that the blister skin thickness formed by D⁺ irradiation of polycrystalline tungsten (PCW) was considerably larger than the calculated ion range of the implants; however, this skin thickness (or blister depth) is not related to the pre-existing grain boundaries in the PCW. Blister formation was also observed with GIEM for single crystal tungsten (SCW) irradiated with H⁺, D⁺, and He⁺. The critical ion fluence for blister formation in SCW is estimated to be ∼10²³ H⁺(D⁺)/m² for H(D) and ∼10²¹ He⁺/m² for He. The size of the blisters and their skin structure depends on the irradiating conditions. Typical skin thickness was about 50-150 nm. Based on the assumption that gas particles (H₂, D₂, and He) accumulate within the blisters during H⁺, D⁺, and He⁺ irradiation, the GIEM measurements provide a means to derive an estimate of the amount of gas so accumulated, by reproducing the observed blister shapes with finite element method (FEM) calculations. From the GIEM images and FEM calculations we have estimated the number of implanted ions being retained in the blisters, and compared these amounts with published retention measurements. A mechanism for the blister formation is proposed based on the present results.     

Reduced partition function ratios of hydrogen species adsorbed on platinum cluster Pt19 studied by density functional theory

Geometry optimization and estimation of H/D reduced partition function ratios (RPFRs) of Pt₁₉–H, Pt₁₉–H⁺, Pt₁₉–H₂, and Pt₁₉–H₂⁺ models of hydrogen species adsorbed on surfaces of metallic platinum particles, were carried out based on the density functional theory. Two types of optimized structures were obtained for Pt₁₉–H and Pt₁₉–H⁺, and three for Pt₁₉–H₂ and Pt₁₉–H₂⁺. Stabilization energy consideration suggested that the most probable structure for Pt₁₉–H and Pt₁₉–H⁺ is the one in which H/H⁺ is bonded to a Pt atom, and that for Pt₁₉–H₂ and Pt₁₉–H₂⁺ is the one in which two H/H⁺s are bonded to two adjacent Pt atoms with no direct bonding between the two H/H⁺s. The value of RPFR obtained for those structures ranged from 3.9303 to 4.4014 at 25 °C. Interaction between two adjacent H–Pt bonds seems to slightly enhance the mutual RPFR values.     

Raman scattering and SEM studies of graphite and silicon carbide surfaces bombarded with energetic protons,deuterons and helium ions

Experimental investigations on the chemical and physical effects of 10–15 keV H₁⁺, D₁⁺ and He⁺ ion bombardments to fluences up to 10¹⁹ ions/cm² on graphite and SiC have been conducted using the techniques of Raman scattering and scanning electron microscopy (SEM). Raman scattering data for ion bombarded graphite reveal the formation of an amorphous surface layer as indicated by the appearance of a broad band in the spectrum centered at 1525 cm which replaces the bands due to microcrystalline carbon at 1585 cm^?1 and 1360 cm^?1. The microcrystalline structure could be partially restored upon vacuum annealing at 1040°C for several hours. A weak, broad band centered at 2150 cm also appears after bombardment which is indicative of the formation of ?C = C? bonds. Surfaces of “KT” SiC were also amorphized on ion bombardment as indicated by changes in the Raman spectra. Chemical trapping of the incident h₁⁺ and D₁⁺ ions to form bulk C-H, C-D and Si-H species was observed. Preferential sputtering of Si leaving a carbon rich surface region also occurred. Blister formation was observed in the SEM studies.     

The evolution of hydrogen from proton irradiated glassy carbon

Glassy carbon was irradiated with 15 keV H⁺ ion beam. It was observed that the implanted hydrogen is unstable in material and evolves as H, H₂ and H₂O. Post-irradiation evolution of H, H₂ and H₂O from proton irradiated glassy carbon was monitored by temperature programmed desorption (TPD) in the period of 30 days. In between irradiation and TPD measurements the irradiated samples were stored in air. The evolution of the molecular hydrogen, although the protons are implanted deeply below the surface of the disordered glassy carbon, proceeds over the same mechanism as in the case of low-energy H-atoms chemisorbed on the very surface of an ideal graphite structure.     

Tungsten Blister Formation Kinetic as a Function of Fluence,Ion Energy and Grain Orientation Dependence Under Hydrogen Plasma Environment

This work deals with the formation kinetic of tungsten (W) blisters under smooth plasma conditions, i.e. low hydrogen flux and energy in order to analyze the first stages of their formation. In addition, we focus on determining the W grain orientation where blisters grow preferentially. For this purpose, mirror-polished polycrystalline tungsten samples were exposed to hydrogen plasma under fixed hydrogen flux of 2.2 × 10²⁰ m^?2 s^?1, with a fluence in the range of?~?10²⁴ m^?2, ion energy of?~?20, 120 and 220 eV, and sample surface temperature of?~?500 K. The formation of blisters at the surface was investigated using SEM, AFM and EBSD to determine the size, the distribution and the orientation of grain where blisters are formed, respectively. The critical fluence for initiating blisters was established around 2.3 × 10²⁴ m^?2. The evolution of blister size distribution and density is discussed as function of fluence and ion energy. At lower ion energy, i.e. 20 eV, only nanoblisters (less than 150 nm) are observed whatever the fluence value (1.5 and 2.3 × 10²⁴ m^?2). At higher ion energy i.e. 120 and 220 eV, micrometric (~ few to tens of µm) blisters are observed and their density highly depends on fluence. We show that blisters can also be formed on (001) oriented grains contrarily to previous results from the literature where the (111) orientation seemed more favorable. Such information is of importance for tungsten based fusion tokamak operation and design.     

Optical and electrical characterizations of Mn doped p-type β-FeSi2

β-FeSi₂ has attracted increasing attention as a promising material for optoelectronic and thermoelectronic devices due to a high optical absorption coefficient (α) of about 10⁵ cm⁻¹ near 1.0 eV and its chemical stability at higher temperatures. For the future practical use of this material in devices, the control of each electrical conductivity type and the improvement of the material quality are highly required. Although unintentionally doped β-FeSi₂ layers formed on n-type Si(1 0 0) by the conventional electron-beam deposition (EBD) have typically shown n-type conductivity, the p-type β-FeSi₂ layers were formed by the introduction of Mn impurity using ion-implantation at room temperature (RT) and subsequent annealing procedures. In this study, we aimed to make p-type β-FeSi₂ by implantation of ⁵⁵Mn⁺ ions into EBD-grown n-type β-FeSi₂ layers/n-Si, where ⁵⁵Mn⁺ ions were implanted at two different temperatures (T_sub) of RT and 250°C using an energy and a dose of 300 keV and 2.68 × 10¹⁵ cm⁻², respectively. Their optical and electrical properties, which ought to be affected by implantation and annealing temperatures (T_a2), were investigated by Raman scattering, optical transmittance, reflectance and van der Pauw measurements. The results showed that the ⁵⁵Mn⁺ doping with T_sub=RT and higher thermal annealing at T_a2=900°C produced p-type layers of good quality with maximum hole mobility of 454.5 cm²/Vs at about 65 K.     

Deuterium permeation behavior for damaged tungsten by ion implantation

The deuterium (D) permeation behaviors for ion-damaged tungsten (W) by 3 keV D₂⁺ and 10 keV C⁺ were studied. The D permeability was obtained for un-damaged W at various temperatures. For both D₂⁺ and C⁺ implanted W, the permeability was clearly reduced. But, for the D₂⁺ implanted W, the permeability was recovered by heating at 1173 K and it was almost consistent with that for un-damaged W. In the case of C⁺ implanted W, the permeability was not recovered even if the sample was heated at 1173 K, indicating that the existence of carbon would prevent the recovery of permeation path in W. In addition, transmission electron microscope (TEM) observation showed the voids were grown by heating at 1173 K and not removed, showing the existence of damages would not largely influence on the hydrogen permeation behavior in W in the present study.     

Deuterium Plasma Focus as a Tool for Testing Materials of Plasma Facing Walls in Thermonuclear Fusion Reactors

This paper presents the first verification of the fast ion beam (FIB) and fast plasma stream (FPS) properties computed using the Lee code. Recent estimates of FIB and FPS properties in PF-400J from interferometric images are compared to our computed results. Reasonable agreement is found in the comparison of several quantities. Our computed power flow density (energy flux) and integral damage factor are 2.45 × 10¹² Wm^?2 (2 times of experimental value) and 1.78 × 10⁸ Wm^?2 s^0.5 (~almost the same as experimental value) respectively, for target placed at 1.5 cm from the anode top of PF-400J. This verification gives us confidence to proceed to systematic numerical calculations on the PF-400J and similar small plasma focus devices (PF50, NX2, NX3, FMPF-3, INTI PF) to obtain FIB properties (ion beam energy, ion beam flux, ion beam fluence, beam ion number, ion beam current, power flow density, and damage factor). These results confirm that the plasma focus, including small ones, could be useful to study the effects of cumulative pulses on target materials being considered for plasma facing walls in future tokamak or laser-implosion fusion reactors.     

Effects of environment on annealing behavior of In+ implanted c-axis sapphire

Single crystal samples of 〈0001〉α-Al₂O₃ were implanted with 360 keV indium ions of doses of 1 × 10¹⁶ and 3 × 10¹⁶ ions/cm², at room temperature (RT). The implanted samples were annealed isothermally in air or in flowing high purity argon ambient at 900°C for 2 or 12 h. The damage and thermal annealing were evaluated using Rutherford Backscattering Spectrometry and Channeling (RBS-C) and X-ray Diffraction (XRD). Amorphization of sapphire was not observed, despite damage energy densities up to 105 dpa (displacements per atom obtained from TRIM code calculation) for the Al sublattice, which indicated that self-annealing was severe during In ion implantation of sapphire at RT. RBS-C measurement revealed differences in the annealing characteristics of the implanted indium ions that depended on the annealing environment. The XRD spectrum indicated the presence of the In₂O₃ phase in the subsurface region of the sample after annealing in air.     

Scattering of 10–30 keV H+, H2+ and H3+ from surfaces: Excited state composition and scattered H+ flux

An experimental study has been made of H and H⁺ scattering from metal surfaces under 10 to 30 keV H⁺, H₂⁺ and h₃⁺ bombardment. Light emission from the point of ion beam impact on the surface includes Doppler broadened lines from excited backscattered neutral projectiles. Slow recoils suffer radiationless de-excitation at the surface so that only fast recoils survive to emit photons; the coefficient for radiationless de-excitation is determined by analysis of the line shape. Using the measured de-excitation coefficient, we have predicted the excited backscattered flux as a function of incident projectile energy, and this agrees well with experiment. In a separate experiment we have measured directly the angular distribution of H⁺ scattered from a surface when an H⁺ beam is incident at an angle of 70° to the surface normal.     

Damage accumulation and annealing in 6H–SiC irradiated with Si+

Damage accumulation and annealing in 6H-silicon carbide (α-SiC) single crystals have been studied in situ using 2.0 MeV He⁺ RBS in a 〈0 0 0 1〉-axial channeling geometry (RBS/C). The damage was induced by 550 keV Si⁺ ion implantation (30° off normal) at a temperature of −110°C, and the damage recovery was investigated by subsequent isochronal annealing (20 min) over the temperature range from −110°C to 900°C. At ion fluences below 7.5 × 10¹³ Si⁺/cm² (0.04 dpa in the damage peak), only point defects appear to be created. Furthermore, the defects on the Si sublattice can be completely recovered by thermal annealing at room temperature (RT), and recovery of defects on the C sublattice is suggested. At higher fluences, amorphization occurs; however, partial damage recovery at RT is still observed, even at a fluence of 6.6 × 10¹⁴ Si⁺/cm² (0.35 dpa in the damage peak) where a buried amorphous layer is produced. At an ion fluence of 6.0 × 10¹⁵ Si⁺/cm² (−90°C), an amorphous layer is created from the surface to a depth of 0.6 μm. Because of recovery processes at the buried crystalline–amorphous interface, the apparent thickness of this amorphous layer decreases slightly (<10%) with increasing temperature over the range from −90°C to 600°C.     

Reactive sputtering of simple condensed gases by kev ions III: Kinetic energy distributions

Condensed gas layers of H₂O, NH₃ and CO at 15–20 K have been bombarded by 6 keV H⁺₂ and 3 keV He⁺ and Ar⁺ ions. Mass spectra of the neutral species sputtered from these layers have been measured. There is a substantial yield of products which originally were not in the target material, and which have thus been formed in chemical reactions induced by the ion bombardment. The relative yields of some of the products have been found to increase with decreasing incident ion mass. This is mainly attributed to the larger amount of energy deposited by electronic stopping in such situations. From CO a nonvolatile residue is left after ion irradiation. From a layer of H₂O frozen on top of the CO-residue H₂CO was detected.     

Reactive sputtering of simple condensed gases by keV ions II: Mass spectra

Condensed gas layers of H₂O, NH₃ and CO at 15–20 K have been bombarded by 6 keV H⁺₂ and 3 keV He⁺ and Ar⁺ ions. Mass spectra of the neutral species sputtered from these layers have been measured. There is a substantial yield of products which originally were not in the target material, and which have thus been formed in chemical reactions induced by the ion bombardment. The relative yields of some of the products have been found to increase with decreasing incident ion mass. This is mainly attributed to the larger amount of energy deposited by electronic stopping in such situations. From CO a nonvolatile residue is left after ion irradiation. From a layer of H₂O frozen on top of the CO-residue H₂CO was detected.     

Magnetic behavior of Ni+ implanted silica

Ni⁺ has been implanted in amorphous silica layers and silica glasses at two dose levels (10¹⁶ and 10¹⁷ Ni⁺ cm⁻²) and two different energies (30 and 160 keV). Superparamagnetic and ferromagnetic behaviors were observed with a SQUID magnetometer at RT and 5 K, respectively. Using Langevin’s theory, the size of the metallic nanoparticles were deduced to ranges between 2 and 6.5 nm in good agreement of HRTEM observations. The E′ type center and the neutral oxygen vacancy (NOV) defects were observed by UV–Vis absorption. Finally, in samples annealed at 600°C under Ar or Ar + H₂ atmospheres two different phenomena were observed: the reduction of Ni²⁺ to Ni⁰ and the elimination of defects introduced by implantation.     

Characterization of Thick Tungsten Coating on Cu Alloy Substrate Prepared by Electrodeposition

The W coating with the thickness over 1 mm was obtained by pulse electrodeposition on large CuCrZr alloy in a Na₂WO₄–WO₃ molten salt. The composition of this system keeps unchanged with the duration of electrodeposition. The coating’s structure, morphology and contents were investigated by XRD, XPS and SEM. The electrodepostion tungsten coating was compact and without void. The residual stress in surface of W coating was calculated to be a compressive stress with the value of 225 MPa. The W coating comprised an inner tooth-like layer and an outer columnar layer. The bonding strength between W coating and CuCrZr susbtrate was near 60 MPa; the thermal conductivity parallel to the crystal growth direction was measured to be 150.86 W m^?1 K^?1.     

Post-annealing temperature dependence of blistering in high-fluence ion-implanted H in Si 〈1 0 0〉

This study examined the influence of post-annealing temperature on blister formation and growth in ion-implanted H in Si 〈1 0 0〉. Ion energy levels of 40 and 100 keV and fluences of 2 × 10¹⁶ and 5 × 10¹⁶ cm⁻² were investigated. Post-annealing treatments were performed using the furnace annealing (FA) method with temperatures ranging from 200 to 600 °C for a duration of 1 h. Raman scattering spectroscopy (RSS), optical microscopy (OM), secondary ion mass spectrometry (SIMS), atomic force microscopy (AFM), and cross-sectional transmission electron microscopy (XTEM) were employed to explore the mechanisms behind the smart cut technique. The results revealed that variations among the transformation of the VH₃ (or V₂H₆) defect complex phase into the Si(1 0 0):H bonding configuration phase (RSS results), the appearance of optically detectable blisters and craters (OM results), the average depth of craters (AFM results), the trapping of hydrogen atoms and gettering of oxygen atoms (SIMS results), and the damaged microstructures (XTEM results) against post-annealing temperature were in close correspondence. It was also found that the optimal post-annealing temperature for blister formation and growth was 550 °C.     

Isothermal Re-Emission of Hydrogen Implanted into Isotropic Graphite

Isothermal re-emission of hydrogen from graphite implanted with 5 keV H₂ ⁺ ion beam up to saturation (3×10¹⁸/cm²) at room temperature has been studied by means of the elastic recoil detection (ERD) technique at temperatures of 450, 500, 550 and 600°C. It is found that the concentration of retained hydrogen decreases rapidly in the beginning and then decreases very gradually as the annealing time increases.

The re-emission profiles have been analyzed taking into account local molecular recombination between activated hydrogen atoms and that between an activated hydrogen atom and a trapped one together with retrapping of the activated hydrogen atom. It is shown that the re-emission of hydrogen by isothermal annealing occurs mainly due to the former type of local molecular recombination and that the activation energy of the thermally activated detrapping rate constant is 0.50±0.04eV. Moreover, it is shown that an analytical expression for the re-emission profile reproduces reasonably well the observed thermal desorption spectra.     

Surface damage of metallic glasses by argon ion bombardment

The surface damage of metallic glasses Fe₄₀Ni₄₀P₁₄B₆, Fe₄₀Ni₃₈Mo₄B₁₈, Fe₄₀Ni₄₀B₂₀, Fe₈₀B₂₀ and Ni₆₄Zr₃₆ under argon ion bombardment at room temperature has been investigated. Blister formation was observed in the dose range of 1 × 10¹⁷ to 1 × 10¹⁸ ions/cm². At higher doses, blisters disappeared with concurrent roughening of the bombarded surface. Erosional features like cones and pyramids are not observed. Argon induced blisters also disappeared on room temperature aging without any further bombardment after blister formation. Post-irradiation annealing at high temperatures (673 and 873 K) resulted in blister formation, severe surface exfoliation and pin-hole formation. The precipitation of the implanted argon into bubbles is also observed.     

Endotaxial growth of InSb nanocrystals at the bonding interface of the In+ and Sb+ ion implanted SOI structure

Growth of InSb nanocrystals at the Si/SiO₂ bonding interface of silicon-on-insulator (SOI) structures has been studied as a function of the annealing temperature. SOI structures with the ion implanted regions above and below the bonding interface were produced as a result of the hydrogen transfer of the Sb⁺ ion implanted silicon layer from first silicon substrate to the In⁺ ion implanted SiO₂ layer thermally-grown on the second silicon substrate. Rutherford backscattering spectrometry and high-resolution transmission electron microscopy (XTEM) were used to study the properties of the prepared structures. Up-hill diffusion of In and Sb atoms from the implantation regions toward the bonding interface as well as subsequent interface-mediated growth of InSb nanocrystals were observed as the annealing temperature achieved 1100 °C. The strain minimizing orientations of the Si and InSb lattice heteropairs were obtained from XTEM analysis of the grown nanocrystals.     

Experimental study of pulse neutron irradiation damage in SiGe HBT

The response to transient irradiation of npn SiGe HBT (BG35 SiGe BiCMOS), i.e. device under test (DUT) was studied with online measurement of 1 MeV equivalent pulse neutron fluence of 0.8 × 10¹³n/cm². The differently biased DUT1 and DUT2 in test circuit were irradiated in the first day with neutron fluence (0.8 × 10¹³n/cm²) termed as Fluence1 and with an additional neutron fluence (0.8 × 10¹³n/cm²) in the second day to make Fluence2 equals to 1.6 × 10¹³n/cm². The experimental results show that pulsed neutron irradiation causes voltage surges in the DUTs exhibited by a negative and positive peak known to be radiation damage (RD). The RD in DUTs induced by pulse neutron Fluence1 initially created unstable displacement defects and the defects later reordered (cluster defects) to form more stable configurations via neutron Fluence2. The irradiated DUTs experienced online instantaneous annealing after 2.03 × 10^?9 s and offline measurement (i.e. without irradiation) of DUTs showed recovery to normal mode of operation after 24 h annealing. The level of pulse peaks in the base voltage terminals of DUT1 and DUT2 were compared as V_b2Fluence1 > V_b1Fluence1 and V_b2Fluence2 > V_b1Fluence2. A comprehensive analysis of RD region in DUTs with reference to Area (A₁, A₂), Peak (P₁, P₂), Height (H), and Full width at half maximum (FWHM) were investigated.