Formation Of Surface Blisters Research Articles

Observation of Large Surface Area Exfoliation in Hydrogen Implanted Ge

Large surface area exfoliation of the hydrogen (H)‐implanted Ge is investigated in this work. H+ ions with a fluence of 1 × 1017 cm−2 are implanted in Ge samples at liquid nitrogen and room temperature (RT). The formation of surface blisters and craters is observed in the samples annealed between 300 and 450 °C after implantation. Interestingly, samples implanted at RT show large surface area exfoliation extending over several hundreds of micrometer region after annealing. Secondary ion mass spectroscopy (SIMS) and depth‐resolved Raman spectroscopy are used to characterize the depth profile of implanted H+ ions and stress in the damage region, respectively. The formation of the damage band filled with extended planar defects in the form of nanocracks is observed using a cross‐sectional transmission electron microscope (TEM). The physical understanding of the H‐induced internal pressure and stress in the surface blisters/craters is carried out using Föppl–von Karman theory of thin plates.

Transient grating spectroscopy of thermal diffusivity degradation in deuterium implanted tungsten

Using transient grating spectroscopy, we measure thermal diffusivity and surface acoustic wave speed in tungsten exposed to different fluences of deuterium plasma. Scanning electron microscopy (SEM) shows the formation of surface blisters that have similar morphology for all fluences considered. A significant reduction in thermal diffusivity and surface acoustic wave speed occurs as a result of plasma exposure. A saturation of the thermal diffusivity reduction with fluence is seen. Deuterium ion flux density appears to play a more important role in thermal diffusivity reduction than exposure time. These observations have important implications for plasma facing components in future fusion reactors.

On the mechanisms of hydrogen-induced blistering in RF-sputtered amorphous Ge

Hydrogenated amorphous germanium, a-Ge:H, is a material of interest for optoelectronic applications such as solar cells and radiation detectors because of the material's potential to extend the wavelength sensitivity of hydrogenated amorphous silicon. For such applications, the best structural quality is required. Here, we investigate the mechanisms of blister formation in a-Ge:H films obtained by RF (radio frequency) sputtering when submitted to annealing. By a Fourier transform IR spectroscopy study of the Ge–H stretching vibrations, it is found that annealing increases the density of GeH2 dihydrides residing on the internal surfaces of nanovoids which increase their size because of that. The thermal energy supplied by annealing also favours the breakage of the Ge–H bonds with consequent release inside the cavities of atomic H which then reacts to produce molecular H2. The expansion of the H2 gas causes the nanovoids to enhance their volume up to the formation of surface blisters. The presence of H2 in the blisters is confirmed by the activation energy for the onset of blistering as measured by Arrhenius plots. The reduced H content observed by elastic recoil detection analysis and secondary neutral mass spectrometry in the annealed samples where blister bursting took place further supports the hypothesis of H2 filling the blisters before they explode.

Blister formation on 13Cr2MoNbVB ferritic-martensitic steel exposed to hydrogen plasma

The influence of pre-irradiation specimen deformation level on surface blister formation and sub-surface cracking of dual-phase 13Cr2MoNbVB ferritic-martensitic steel was studied using glow discharge hydrogen plasma with ion energy of 1 keV to fluences of 2 × 1025 H/m2. Protium was used for most studies, but deuterium was used for measuring the depth dependence of hydrogen diffusion. Formation of blisters was observed in the temperature range 230–340 K. It was found that pre-irradiation deformation caused changes in the threshold fluences of blister formation and also in blister size distribution. Subsurface cracks located on grain boundaries far beyond the implantation zone were formed concurrently with blisters, arising from hydrogen diffusion and trapping at defects. It was observed that cracks as long as 1 mm in length were formed in 95% deformed steel at depths up to 500 μm from surface.

Microstructural modifications in tungsten induced by high flux plasma exposure: TEM examination

We have performed microstructural characterization using transmission electron microscopy (TEM) techniques to reveal nanometric features in the sub-surface region of tungsten samples exposed to high flux, low energy deuterium plasma. TEM examination revealed formation of a dense dislocation network and dislocation tangles, overall resulting in a strong increase in the dislocation density by at least one order of magnitude as compared to the initial one. Plasma-induced dislocation microstructure vanishes beyond a depth of about 10 μm from the top of the exposed surface where the dislocation density and its morphology becomes comparable to the reference microstructure. Interstitial edge dislocation loops with Burgers vector a0/2〈111〉 and a0〈100〉 were regularly observed within 6 μm of the sub-surface region of the exposed samples, but absent in the reference material. The presence of these loops points to a co-existence of nanometric D bubbles, growing by loop punching mechanism, and sub-micron deuterium flakes, resulting in the formation of surface blisters, also observed here by scanning electron microscopy.

The effects of the annealing time on helium implantation in Si

The modifications induced in silicon samples by helium implantation before and after isothermal annealing at 673 K have been investigated. The surface morphology has been detected by atomic force microscopy. A hillock structure is observed on the sample surface before and after annealing for 5–10 min. Surface blister formation is observed with an increasing annealing time. The variation of crystal damage with annealing time has been investigated by Rutherford backscattering/channeling. The intensity of the damage peak first increases with annealing time, reaches maximum at an annealing time of 60 min and then decreases. Helium-induced bubbles and residual defects have been observed by transmission electron microscopy, which shows that dislocations are close to the bubbles.

Effect of alloying elements on heat treatment response of aluminium high pressure die castings

High pressure die cast (HPDC) aluminium components that respond to age hardening cannot normally be solution treated at high temperatures because the presence of internal porosity and entrapped gases leads to the formation of surface blisters. Parts may also become dimensionally unstable due to swelling. These factors that prevent heat treatment present significant limitations to the utilisation of HPDC components. Now it has been found that blistering and dimensional change can be avoided by using much shorter solution treatment times and lower temperatures. Experiments with alloys 360 (Al–9·5Si–0·5Mg) and 380 (Al–8·5Si–3·5Cu) have shown that strong responses to age hardening are still possible following these modified solution treatments. In the current paper, the role of critical alloying elements is considered in both current specification Al–Si–Cu–(X) alloys, and also in newly developed alloy compositions. It is shown that 0·2% proof strengths over 400 MPa may be readily achieved by heat treating conventionally produced die castings.

Effect of temperature on layer separation by plasma hydrogenation

We have studied hydrogen diffusion in plasma hydrogenated Si∕SiGe∕Si heterostructure at different temperatures. At low temperature, intrinsic point defects in the molecular beam epitaxy grown Si capping layer are found to compete with the buried strain SiGe layer for hydrogen trapping. The interaction of hydrogen with point defects affects the hydrogen long-range diffusion, and restricts the amount of hydrogen available for trapping by the SiGe layer. However, hydrogen trapping by the capping layer is attenuated with increasing hydrogenation temperature allowing more hydrogen to be trapped in the strain SiGe layer with subsequent surface blister formation. A potential temperature window for plasma hydrogenation induced layer separation is identified based on the combined considerations of trap-limited diffusion at low temperature and outdiffusion of H2 molecule together with the dissociation of Si–H bonds inside of H platelet at high temperature.

Formation of nanovoids/microcracks in high dose hydrogen implanted AlN

Aluminium nitride (AlN) epitaxial layers grown on sapphire were implanted with 100 keV hydrogen, H2+ ions with doses in the range of 5 × 1016 cm–2 to 2.5 × 1017 cm−2 and subsequently annealed at temperatures up to 800 °C in order to observe the formation of surface blisters. The implantation-induced damage in AlN was analyzed by cross-sectional transmission electron microscopy, which revealed a band of defects extending from 330–550 nm from the surface of AlN. Higher magnification TEM images showed the formation of nanovoids that are distributed in the damage band. Upon annealing these nanovoids agglomerate leading to the formation of microcracks. Due to the overpressure of hydrogen trapped in the microcracks, surface blisters are eventually formed in the hydrogen implanted AlN. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Investigation of blistering kinetics in hydrogen implanted aluminium nitride

Epitaxial layers of aluminium nitride (AlN) grown on sapphire by hydride vapour phase epitaxy (HVPE) were implanted with 100 keV hydrogen, H+2, ions with doses in the range of 5 × 1016–2.5 × 1017 cm−2 and subsequently annealed in ambient air at temperatures between 450 and 750 °C in order to determine the kinetics of surface blister formation in AlN. The Arrhenius plot of the blistering time versus temperature shows two different activation energies for the formation of surface blisters: 0.44 eV in the higher temperature regime of 550–750 °C and 1.16 eV in the lower temperature regime of 450–550 °C. The implantation-induced damage was analyzed by cross-sectional transmission electron microscopy, which revealed a band of defects extending from 330 to 550 nm from the surface of AlN. The XTEM image of the implanted and annealed AlN displayed clearly the formation of microcracks that ultimately lead to the formation of surface blisters.

Investigation of Blistering Phenomena in Hydrogen-Implanted GaN and AlN for Thin Film Layer Transfer Applications

ABSTRACTHigh dose hydrogen implantation-induced blistering phenomena in GaN and AlN have been investigated for potential thin film layer transfer applications. GaN and AlN were implanted with 100 keV H2+ ions with various ion doses in the range of 5´1016 to 2.5´1017 cm−2. After implantation the samples were annealed at higher temperatures up to 800°C in order to observe the formation of surface blisters. In the case of GaN only those samples that were implanted with a dose of 1.3´1017 cm−2 or higher showed surface blistering after post-implantation annealing. For AlN the samples those were implanted with a dose of 1.0´1017 or 1.5´1017 cm−2 displayed surface blistering after post-implantation annealing. Cross-sectional transmission electron microscopy was utilized to observe the microscopic defects that eventually cause surface blistering. Large area microcracks, as revealed in the XTEM images, were clearly observed in the case of both GaN and AlN after post-implantation annealing. A comparison of the hydrogen implantation-induced blistering in GaN and AlN has also been presented.

Narrow fluence window of hydrogen-implantation-induced exfoliation in ZnO

Zinc oxide (ZnO) bulk crystals were implanted by 100 keV H+2 ions with various fluences in the range of 5 × 1016 to 3 × 1017 cm−2 and subsequently annealed at temperatures up to 800 °C in order to observe the formation of surface blisters or exfoliation. The ZnO crystals implanted up to a fluence of 2.2 × 1017 cm−2 did not show any surface blistering/exfoliation even after post-implantation annealing, while those crystals implanted at or above a fluence of 2.8 × 1017 cm−2 already exhibited exfoliated surfaces in the as-implanted state. The ZnO crystals implanted with a fluence of 2.5 × 1017 cm−2 showed surface exfoliation only after post-implantation annealing. Cross-sectional transmission electron microscopic images showed that a large number of nanovoids were formed within the implanted zone of ZnO. These nanovoids served as precursors for the formation of microcracks leading to the exfoliation of ZnO layers.

Heat Treatment of High-Pressure Die Castings

High-pressure die-cast Al alloys cannot normally be heated at high temperatures due to the presence of pores containing entrapped gases, which lead to the formation of surface blisters. It has been found that blistering can be avoided by using considerably shorter solution-treatment times and lower temperatures. Experiments with alloys 360 (Al-9.5Si-0.5Mg) and 380 (Al-8.5Si-3.5Cu) have shown that strong responses to age hardening are still possible following these modified solution treatments.[1, 2, 3] For T6 tempers, increases in 0.2 pct proof stress of 80 pct for 360 and 115 pct for 380 have been obtained compared with as-cast values. Using a T4 temper, ductility is improved without any sacrifice in strength.

Investigation of helium implantation induced blistering in InP

Four-inch InP wafers were implanted with 100 keV helium ions with a dose of 5×10 16 cm −2 and subsequently annealed in air in the temperature range of 225–400°C in order to determine the blistering kinetics of these wafers. An Arrhenius plot of the blistering time as a function of reciprocal temperature revealed two different activation energies for the formation of surface blisters in InP. The activation energy was found to be 0.30 eV in the higher temperature regime of 300–400 °C and 0.74 eV in the lower temperature regime of 225–300 °C. The implantation induced damage was analyzed by cross-sectional transmission electron microscopy, which revealed a band of defects extending from 400–700 nm from the surface of InP. The damage band was found to be decorated with a large number of nanovoids having diameters between 2 and 5 nm. These nanovoids served as precursors for the formation of microcracks inside InP upon annealing, which led to the formation of surface blisters.

Investigation of hydrogen implantation induced blistering in GaN

AbstractA systematic investigation of surface blister formation on GaN epitaxial layers implanted with 100 keV H2+ ions with a dose of 1.3×1017 cm–2 and annealed at various temperatures in the range of 350–700 °C was carried out. Two different activation energies were found for the formation of surface blisters: 1.79 eV in the lower temperature regime of 350–400 °C and 0.48 eV in the higher temperature regime of 400–700 °C. The depth and width of the blisters were determined using a stylus profilometer. The hydrogen implantation‐induced damage was assessed using cross‐sectional transmission microscopy revealing a band of defects extending from 230–500 nm from the surface of GaN. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Vacuum assisted high pressure die casting of aluminium alloys

High pressure die castings usually contain gas porosity due mainly to the entrapment of air or gas in the melt during the very high speed injection of the molten metal into the cavity. In this paper, the advantages of using an evacuated die cavity during mould filling were evaluated. ASTM standard die casting tensile specimens of three Al alloys, Al–5%Si, Al–8%Si and Al–18%Si, were cast on a Buhler shot control die casting machine equipped with a Fondarex vacuum assist system. The effect of vacuum assistance on the porosity distribution and mechanical properties of the produced castings were studied in detail. Selected specimens were also subjected to a T6 tempering treatment to evaluate the formation of surface blisters and effects on the mechanical properties. It was found that the volume of gas porosity and the pore sizes in the castings were significantly reduced by using vacuum assistance during die casting. As a result, the density and the mechanical properties, particularly the tensile strength and ductility, were improved markedly. An optimum injection speed was also identified for producing high performance castings. After heat treatment, vacuum assisted die cast parts showed much less surface blistering when compared to conventional die cast parts, demonstrating that vacuum assisted die castings are promising for heat treatment at elevated temperatures to improve the mechanical properties.

The influence of boron ion implantation on hydrogen blister formation in n-type silicon

We have studied the formation of surface blisters in 〈100〉 n-type silicon following co-implantation with boron and hydrogen. The silicon substrates had four different n-type dopant levels, ranging from 1014 to 1019 cm−3. These substrates were implanted with 240 keV B+ ions to a dose of 1015 cm−2, followed by a rapid thermal anneal at 900 °C for 30–60 s to force the boron atoms into substitutional lattice positions (activation). The samples were then implanted with 40 keV H+ to a dose of 5×1016 cm−2. The implanted H+ distribution peaks at a depth of about 475 nm, whereas the distribution in the implanted B+ is broader and peaks at about 705 nm. To evaluate the role of the B+ implantation, control samples were prepared by implanting with H+ only. Following the H+ implantation, all the samples were vacuum annealed at 390 °C for 10 min. Blisters resulting from subsurface cracking at depths of about 400 nm, were observed in most of the B+ implanted samples, but not in the samples implanted with H+ only. This study indicates that the blistering results from the coalescence of implanted H into bubbles. The doping with B facilitates the short-range migration of the H interstitials and the formation of bubbles. A comparison of the observed crack depth with the depth of the damage peak resulting from the H+ implantation (evaluated by the computer code TRIM) suggests that the nucleation of H bubbles occurs at the regions of maximum radiation damage, and not at the regions of maximum H concentration. For given values of B+ and H+ doping, the blister density was found to decrease with increasing n-type doping, when the boron is activated. Blister formation was also observed in B+ implanted samples which had not been activated. In this case, the blister density was found to increase with increasing value of n-type doping.

The Influence of Damage and Dopant on the Blister Formation in Hydrogen Implanted Silicon

ABSTRACTWe have studied the formation of surface blisters in <100> n-type silicon following coimplantation with boron and hydrogen. In this work we study the effect of having the boron depth larger than the hydrogen depth. The silicon substrates had four different dopant levels, ranging from 1014 cm−3 to 1019 cm−3. The Si substrates were first implanted with B ions at 240 keV (Rp = 705nm) to a dose of 1015cm−2. Some of the B implanted samples were left in their as-implanted state, others were given a rapid thermal anneal (RTA) at 900°C. Boron implanted and virgin n-type Si samples were then implanted at cryogenic temperatures with 40 keV H+ (Rp= 475nm) to a dose of 5 x 1016 cm−2. Following H+ implantation, all the samples were vacuum annealed at 390°C for 10 minutes and examined for hydrogen blister formation. No blistering was observed in samples implanted with H only. In all cases, the blister depth was consistently found to be strongly correlated with H damage profile rather than the H or B concentration profiles. These results will be discussed in terms of defect-dopant interactions and the influence of doping on H kinetics and H-bubble nucleation.

Incipient Electrochemical Oxidation of Highly Oriented Pyrolytic Graphite: Correlation between Surface Blistering and Electrolyte Anion Intercalation

Electrochemical oxidation of highly oriented pyrolytic graphite (HOPG) electrodes in KNO 3 electrolyte solution at a carbon submonolayer level was shown in a previous paper to produce raised, bubblelike features, giving the appearance of shallow blisters. The blisters were established to be hollow, with a top surface of intact HOPG lattice and an inner one of graphitic oxide. This paper explores the relationship of the intercalating properties of the electrolyte anion to the blister formation on HOPG. Cyclic voltammetry, atomic force microscopy, optical microscopy, and in situ atomic force microscopy/electrochemistry results are presented. Surface blister formation is observed to occur in 1 M LiCIO 4 , 1 M (NH4) 2 SO 4 , 1 M HNO 3 , and 1 M H 2 SO 4 aqueous electrolytes as a result of potential scans (+1.50 to +1.90 V vs SSCE, depending on the electrolyte) that pass a few carbon monolayers of charge or less. Blister formation on HOPG in 1 M KOH electrolyte is observable but at significantly higher levels of oxidative charge, whereas blisters were not observed in 1 M K 2 HPO 4 and 1 M H 3 PO 4 electrolytes. These results are consistent with literature Raman intercalation data that indicate phosphate does not readily intercalate into HOPG, supporting a model in which blister formation reflects electrolyte anion intercalation followed by subsurface gas evolution.

Mathematical modelling of exfoliation corrosion in high strength aluminium alloys

A mathematical model was developed for the formation of surface blisters during the exfoliation corrosion of wrought high strength aluminium alloys. The internal pressure of the blisters was calculated together with the dimensions that define the extent and the severity of the degradation. The effects of the elongated grain shape and of the heat treatment condition on exfoliation corrosion were investigated theoretically and found to compare favourably with experimental observations.