Preparation Of Foils Research Articles

Nanocrystalline TiAl-V Intermetallics Hot Pressed from Ball Milled Powders

The TiAl-V alloys compositions were chosen from the γ-phase stability region up to maximum 20 at. % vanadium. The elemental powders were initially blended to desired composition of Ti-52.7Al-5V, Ti-55.4Al-10V, Ti-57.7Al-15V and Ti-60.4Al-20V (numbers indicate at. %). The milling was performed in a high energy planetary mill Fritsch Pulverisette P/4 resulted in formation of the almost fully amorphous structure after 40 hours. The formation of Al(Ti, V) solid solution was observed after 20 hours of milling. Longer milling caused amorphization of most of the material and formation of metastable phase in the alloy with the highest content of vanadium. TEM observation of powders after 40 hours of milling allowed to identify 50 nm wide nano-layers within individual particles. The origin of layered structure was explained as resulting from the mechanical alloying process, not from the thin foil preparation. The electron diffraction and bright field techniques revealed the amorphous and partially nanocrystalline structure within milled powders. Uni-axial hot pressing at 700°C under 200 MPa of milled powders allowed to obtain a bulk samples with density of about of 94 % of theoretical one. The X-ray diffraction revealed the two phases γ+α 2 structure. TEM studies have shown the nanometer range grain size structure with a mean size of about 20-30 nm. The diffraction pattern appeared in a ring like pattern without preferred pattern orientation. Some larger grains has shown a parallel aligned defects causing streaks in the diffraction indicating basal Ti 3 Al plane defects. Their existence indicate disordering within intermetallic grains in spite of 700°C annealing.

Focused Ion Beam (FIB): A novel technology for advanced application of micro- and nanoanalysis in geosciences and applied mineralogy

The Focused Ion Beam (FIB) tool has been successfully used as both a means to prepare site-specific TEM foils for subsequent analysis by TEM, as well as a stand-alone instrument for micromachining of materials. TEM foil preparation with FIB technique has drastically changed traditional TEM specimen preparation because it allows site-specific foil preparation. FIB consists of cutting electron transparent foils through Ga-ion milling on a bulk sample. Optical microscopy together with a micromanipulator is used to transfer the foil from the specimen to a TEM grid coated with a holey carbon support film. No further carbon coating is required. This novel technology offers significant benefits in precision and speed of preparing site-specific TEM foils from inclusions in minerals, grain boundaries, microfossils, thin films on substrates and various coatings. FIB cut TEM foils can be investigated with modern TEM techniques such as various diffraction techniques, analytical electron microscopy (AEM) including line scan and elemental mapping, electron energy-loss spectroscopy (EELS) and high-resolution electron microscopy (HREM). With the FIB instrument (FEI FIB200) operated since fall 2002 at GFZ Potsdam we have prepared and investigated several hundreds of high quality TEM foils from silicates, carbonates, metals alloys, ceramic materials and diamond.

Nature of Surface and Bulk Defects Induced by Epitaxial Growth in Epitaxial Layer Transfer Wafers

Surface defects and bulk defects on SOI wafers are studied. Two new metrologies have been proposed to characterize surface and bulk defects in epitaxial layer transfer (ELTRAN) wafers. They included the following: i) laser scattering particle counter and coordinated atomic force microscopy (AFM) and Cu-decoration for defect isolation and ii) cross-sectional transmission electron microscope (TEM) foil preparation using focused ion beam (FIB) and TEM investigation for defect morphology observation. The size of defect is 7.29 urn by AFM analysis, the density of defect is 0.36 /cm<TEX>$^2$</TEX> at as-direct surface oxide defect (DSOD), 2.52 /cm<TEX>$^2$</TEX> at ox-DSOD. A hole was formed locally without either the silicon or the buried oxide layer (Square Defect) in surface defect. Most of surface defects in ELTRAN wafers originate from particle on the porous silicon.

TEM thin foil preparation for ceramic composites with multilayered matrix

A method for preparing thin foils for transmission electron microscopy (TEM) has been developed in the field of ceramic matrix composites (CMC). These composites belong to the last generation. They are developed for high temperature applications in oxidative environment (1350 °C). They possess a self-healing capability. Their design is based on a multilayered matrix. A refinement of the regular ion-milling technique was necessary to thin the samples and to proceed to a full observation of the inner matrix of the composite by TEM. In a regular CMC, the matrix is homogeneous and thereafter it has not to be fully inspected from the fiber to the surface. This sampling technique unable to thin the complete sequence of the different layers in the vicinity of large pores where the ion-milling technique is known to be very difficult. High resolution TEM as well as electron energy loss spectroscopy can be managed anywhere in the core sequence of the matrix.

High-resolution transmission electron microscopy on aged InP HBTs

We have used high-resolution transmission electron microscopy (HRTEM), with focused-ion-beam preparation of foils, to study InP HBT devices, both as-fabricated and after aging in life tests. The technology is HRL's G1 process. We found that even after aging for the equivalent of 2 × 10 7 h under normal operating conditions, the visible damage is extremely benign: the base and emitter contacts are completely intact, there is no evidence of significant Au or Pt migration into the semiconductor, and minor crystal disorder that develops does not extend more than 100 nm below the metal–semiconductor interfaces. Except for these regions, the intrinsic devices are completely devoid of any anomalous features, to within the 0.3 nm resolution limit of the measurements. These observations provide strong evidence that failure mechanisms involving migration of metal from the ohmic contacts, or extended crystal defects, do not limit the reliability of this technology. The small disorder under the base contacts can probably explain the increases of gain ( β) observed early in our life tests, and small increases in the base-collector leakage occurring later in the life tests. The minor disorder under the emitter contacts can probably explain the moderate increase of emitter resistance observed late in our life tests. But the mechanism for the eventual decline in β, observed after a long period of stress, for the equivalent of 10 7 h of normal operation, is not apparent from the HRTEM images.

Surface-Stress Induced Macroscopic Bending of Nanoporous Gold Cantilevers

We report the preparation of composite foils consisting of two layers, one solid gold and one nanoporous gold. Tip displacements of several millimeters are observed when the foils are immersed in aqueous electrolytes and the electrochemical potential varied. This suggests that nanoporous metals could be used as the active component in actors, and it demonstrates for the first time that changes in the surface stress f of the metal−electrolyte interface can induce a macroscopic strain, orders of magnitude larger than the amplitudes which are reached in conventional cantilever bending experiments used to measure f.

A test preparation of thick carbon stripper foils for RCS of J-PARC

Japan-Proton Accelerator Research Complex requires thick carbon stripper foils (300–500 μg/cm 2) to strip electrons from the H − beam supplied by the linac before injection into the Rapid Cyclic Synchrotron. The 400 MeV H − beam from the linac has a pulse length of 0.5 ms with a repetition rate of 25 Hz and an average beam current of 335 μA. For this high-energy and high-intensity beam, the conventional carbon stripper foils will be ruptured in a very short time. Thus, long-lived thick carbon stripper foils are indispensable to this next-generation accelerator. For this purpose, we prepared carbon stripper foils of 130 μg/cm 2 by means of a controlled AC–DC arc discharge method. The preparation procedure is described and lifetime tests with a 3.2 MeV Ne + beam of 3–4 μA are reported.

A new UHV system for the preparation of carbon stripper foils by laser plasma ablation deposition

Laser plasma ablation of spectroscopically pure graphite under UHV conditions is a well established method for the preparation of thin carbon stripper foils. Such foils with their structure of randomly oriented nanocrystallites can best withstand ion irradiation damage. Accelerator users around the world are interested in this type of carbon stripper foils due to a guaranteed reproducibility, quality, thickness and uniformity given by the procedure. In addition a high reproducible yield with a low effort for floating, mounting and slackening is desired. Users of high-energy accelerators want to profit from this development, but need stripper foils of up to 500 μg/cm 2 for the relevant charge state equilibrium whereas carbon foils of this type could only be prepared with an upper limit of 10 μg/cm 2 in the existing set up. The new design was aimed to overcome all thickness limitations. The crucial component of the laser plasma ablation technique is the laser entrance window which becomes opaque during carbon ablation. A new plant which overcomes this problem is being assembled. Due to a higher source-to-window distance and a better laser light transmission, caused by slightly changed laser plasma conditions, the life of the laser entrance window before exchange could be prolonged by a factor of five. Presumably, there are no thickness limitations anymore due to a vacuum interlock that permits the exchange of the entrance window without breaking the vacuum in the ablation-deposition chamber.

Preparation of thin foils for transmission electron microscopy from hydrogenated intermetallic compounds

A preparation method has been developed for thin foils for transmission electron microscopy (TEM) from powdered intermetallic compounds as a result of hydrogenation, in which powder samples are embedded in a Ni plate formed by electroless plating and then the assembly consisting of the Ni plate and the embedded powder samples are ion-milled. This method is successfully applied to some typical hydrogen-absorbing intermetallic compounds such as LaNi 5, FeTi and TiMn 2. In this method, Ni plating is carried out at ambient temperature, at which possible rearrangement of lattice defects that are introduced during hydrogenation is minimized and areas thin and wide enough for TEM observations are successfully produced because of the small difference in the sputtering yield between the Ni plate and these intermetallics. For thin foils produced by this method, not only lattice defects such as dislocations introduced into the bulk of powder samples can be characterized but also the crystallography of cracking and surface layers of powder samples can be characterized.

Electrolytic preparation of metallic thin foils with large electron-transparent regions

This paper presents a successful technique for the preparation of thin foils for examination in the transmission electron microscope with large regions of electron-transparent material. The technique is also demonstrated to achieve similar large, thin areas from the cross-section of very thin materials down to a sheet thickness of approximately 180 μm.

An original route for the preparation of hard FePt

The preparation of FePt hard magnetic foils by an original procedure is described in this paper. The process associates cyclic co-deformation of Fe and Pt foils down to the nanometer scale (total thickness of multilayer ≈100 μm) followed by heat treatment in the temperature range 450–550°C. The formation of the high-anisotropy L1 0 FePt phase results from controlled diffusion and an ordering phase transformation. Coercivities as high as 0.9 T were measured in a VSM at room temperature following annealing at 450°C for 48 h. The coercivity of this sample was decreased by half when measured at 600 K while its energy product decreased from 100 kJ/m 3 at 300 K to 25 kJ/m 3 at 600 K.

Extractive Metallurgy of Beryllium

A comprehensive review of the extractive metallurgy of beryllium is presented. Due to the strategic importance and element of secrecy surrounding the metal, any open literature on beryllium is rather limited. However, this review has been made to cover all important aspects of beryllium extraction technology namely, resources of the metal; processing of ores; reduction of fluoride and oxide to get metal and alloy; refining of the metal; post preparation processes to shape metal through powder metallurgical route and preparation of foils and ceramics. Special attention has been given to the topic of toxicology and pollution control. Recycling of beryllium will form the concluding section. Information on the removal of impurities during the preparation of intermediate products as well as during reduction to metal and its alloys are described with process principles. Thus this review, with the help of discussion on each unit process and at the same time emphasising on the problems faced in large scale handling of this toxic metal and its compounds, shall provide substantial information presently available on the extractive metallurgy of beryllium.

Microstructure Evolution of Alloy 600 during Dry Oxidation

Correlations between the oxidation processes and the mechanical properties have been examined for the Ni based alloy (Alloy 600). Heat treatments for 24 hours at 500°C were carried out under vacuum and in air, both leading to oxidation of the metal. The effect of oxidation on the local mechanical properties has been studied on cold rolled specimens by means of microhardness tests performed with increasing load, in order to determine these properties in the depth of the sheet. The results show that air oxidation softens significantly the material, just under the oxide. The microstructures of the oxides formed in vacuum and in air were characterised by cross - section TEM and EDS analysis. The dislocation microstructures were observed on tensile strained specimens before and after heat treatment, using, respectively, electropolished and ion - milled thin foils. Slight differences in the dislocation distribution are reported; however, these results must be interpreted with great care due to possible effects of the thin foil preparation process, namely defect generation during ion milling.

Nature of Surface and Bulk Defect Induced by Low Dose Oxygen Implantation in Separation by Implanted Oxygen Wafers

Two new metrologies have been proposed to characterize unknown surface and bulk defects in separation by implanted oxygen (SIMOX) wafers. They included the following: i) laser scattering particle counter plus coordinated atomic force microscope (AFM) and Cu-decoration for defect isolation and ii) cross-sectional transmission electron microscope (TEM) foil preparation using focused ion beam (FIB) and TEM investigation for defect morphology observation. Three types of surface defects were found and described as follows: i) a hole with a locally thinned top silicon layer (Park Defect A), ii) a hole formed locally without either a silicon or a buried oxide layer (Park Defect B), and iii) a hole formed with both a locally thinned top silicon and a buried oxide layer (Park Defect C). In addition, a bulk defect was found to occur as locally distributed square-shaped pits accompanied by the disappearance of the buried oxide layer (isolation defect). All surface and bulk defects in SIMOX wafers originate from oxide particle generation by electrostatic discharge and mechanical abrasion between the wafer and the pin of the wafer holder during oxygen ion implantation.

Preparation of thin plastic conductive foils for use in a position-sensitive micro-channel plate detector system

For the detection of recoiling nuclei at the focal plane of the Argonne Fragment Mass Analyzer (FMA), a device employing position-sensitive micro-channel plates (MCP) was constructed. Heavy ions, when traversing a thin foil within the detector, produce secondary electrons, which are deflected by an electrostatic mirror onto the micro-channel plates where they are multiplied and counted. This thin foil serves the dual roles of producing these electrons as well as providing an electrode for the electric field. A further constraint placed upon the foil is that it should not interact detrimentally with the heavy-ion beam, and be strong enough to withstand the force produced by the potential gradient of the electric field. Preparation techniques for the thin metallized plastic films needed for this detector system are described and their performance is evaluated.

Extractive Metallurgy of Beryllium

A comprehensive review of the extractive metallurgy of beryllium is presented. Due to the strategic importance and element of secrecy surrounding the metal, any open literature on beryllium is rather limited. However, this review has been made to cover all important aspects of beryllium extraction technology namely, resources of the metal; processing of ores; reduction of fluoride and oxide to get metal and alloy; refining of the metal; post preparation processes to shape metal through powder metallurgical route and preparation of foils and ceramics. Special attention has been given to the topic of toxicology and pollution control. Recyclfng of beryllium will form the concluding section. Information on the removal of impurities during the preparation of intermediate products as well as during reduction to metal and its alloys are described with process principles. Thus this review, with the help of discussion on each unit process and at the same time emphasising on the problems faced in large scale handling of this toxic metal and its compounds, shall provide substantial information presently available on the extractive metallurgy of beryllium.

Preparation and comparative testing of advanced diamond-like carbon foils for tandem accelerators and time-of-flight spectrometers

The sputter preparation technique for thin diamond-like carbon (DLC) foils, advantageously used for ion-beam stripping and timing in accelerator experiments, has been optimized to improve the quality and the performance of the foils. Irradiation lifetimes of 5 μg/cm 2 DLC foils prepared by this technique have been compared with those for foils of approximately the same thickness, prepared by laser plasma ablation and for ethylene cracked foils when bombarded by 11 MeV Cu − - and Au −-ion beams of ∼1 μA beam current at the Heidelberg MP-tandem. Standard carbon arc-evaporated foils were used as references. In these experiments, DLC stripper foils appeared to have a mean lifetime approximately two times longer than ethylene-cracked foils regardless of ion species, and compared favorably with foils prepared by laser ablation method. All these foils lasted at least, 10 times longer than standard carbon foils, when irradiated in the MP terminal. Approximately, the same improvement factor was confirmed with 3 μg/cm 2 DLC stripper foils irradiated with 2.3 MeV Ni-beams at the Pelletron accelerator in Lund. Unlike standard carbon foils, most of the advanced lifetime foils exhibited thinning during long irradiation, under clean vacuum. This suggests that sputtering of the foil by the heavy-ion beam might be a dominant process, responsible for the observed failure of these long-lived strippers. Along with specifically corrugated self-supporting DLC beam strippers, we succeeded in the fabrication of very smooth and ultra thin (∼0.5 μg/cm 2) DLC foils, mounted on grids and used as start foils for the ToF spectrometers applied in ion beam analysis.

TEM investigation of wear mechanisms during metal machining

An enhanced technique for the preparation of cross-sectional thin foils of CVD coated cemented carbide inserts after metal cutting for studies by analytical transmission electron microscopy is presented. The technique is described in detail and involved the following main steps: (i) controlled CVD deposition, (ii) cutting test, (iii) deposition of a protective PVD film atop the wear crater and (iv) preparation of the cross-sectional thin foils of the chip-tool interface. The technique ensured electron transparency to be obtained on the crater wear land and the whole chip-tool contact length area could be studied in cross-section by transmission electron spectroscopy (TEM). The use of CVD multilayer technique together with PVD technique contributed to the further facts: the positions of the thin foils within the coating layer could be controlled in detail and the coating-chip interface could be studied. The coating investigated was a κ-Al 2O 3-TiC multilayer which was produced by chemical vapour deposition (CVD). The κ-Al 2O 3→ α-Al 2O 3 phase transformation in the metastable κ-Al 2O 3 coating was confirmed to occur locally during metal cutting on the rake face. The transformed α-Al 2O 3 exhibited a relatively high degree of plasticity during metal cutting. Plastic deformation and ductile fracture of α-Al 2O 3 formed as a result of the phase transformation of κ-Al 2O 3 were identified as being the main mechanisms leading to crater wear. The wear mechanisms of Al 2O 3 coating in general and the microstructural changes occurring in the κ-Al 2O 3 and transformed α-Al 2O 3 regions during metal cutting are described in detail.

Transmission Electron Microscope Specimen Preparation of Metal Matrix Composites Using the Focused Ion Beam Miller

The focused ion beam (FIB) miller has been widely accepted as a powerful tool in the semiconductor industry. However, it is now finding applications in more general materials science applications. The high resolution, energetic gallium ion beam can rapidly and precisely section materials to reveal their internal structure; one particularly valuable application being the preparation of thin foils for TEM examination, especially from heterogenous materials.To date, TEM sample preparation using FIBs has concentrated on semiconductor cross-sections [1], powders [2], and surface treated materials, e.g. galvanized steels [3]. However, thin foils of grossly heterogeneous materials, such as metal-matrix composites, are also difficult to prepare using conventional methods and are therefore well suited to sectioning using the FIB. In this study, thin foils were prepared from two composite materials: a 7075 aluminium alloy containing a 20% volume fraction of SiC particles and a FeAl alloy containing a 60% volume fraction of WC particles.

Application of the electron channeling contrast imaging technique to the study of dislocations associated with cracks in bulk specimens

The application of the electron channeling contrast imaging (ECCI) technique to the study of dislocation behavior in the region of crack tips in high-purity stoichiometric single crystal NiAl is presented. Because the ECCI technique, which is based on the dependence of the intensity of backscattered electrons on the incident beam orientation with respect to the crystal lattice and defects near the specimen surface, allows near-surface defects to be imaged in bulk specimens, it has specific advantages over transmission electron microscopy approaches. The technique eliminates the tedious task of thin foil preparation and avoids many of the constraints imposed by the thin foils. Dislocations associated with crack propagation were observed by examining bulk 4-point bend specimens deformed in situ in a field emission gun scanning electron microscope. Dislocations were directly imaged in the crack tip region as well as along the crack paths. Crack deflection and blunting were observed to occur primarily by plastic zone formation in the immediate region of the crack tip.