Small Volume Of Material Research Articles

Thermomagnetic Behavior of Magnetic Susceptibility—Heating Rate and Sample Size Effects

Thermomagnetic analysis of magnetic susceptibility k(T) was carried out for a number of natural powder materials from soils, baked clay and anthropogenic dust samples using fast (11oC/min) and slow (6.5oC/min) heating rates available in the furnace of Kappabridge KLY2 (Agico). Based on the additional data for mineralogy, grain size and magnetic properties of the studied samples, behaviour of k(T) cycles and the observed differences in the curves for fast and slow heating rate are interpreted in terms of mineralogical transformations and Curie temperatures (Tc). The effect of different sample size is also explored, using large volume and small volume of powder material. It is found that soil samples show enhanced information on mineralogical transformations and appearance of new strongly magnetic phases when using fast heating rate and large sample size. This approach moves the transformation at higher temperature, but enhances the amplitude of the signal of newly created phase. Large sample size gives prevalence of the local micro- environment, created by evolving gases, released during transformations. The example from archeological brick reveals the effect of different sample sizes on the observed Curie temperatures on heating and cooling curves, when the magnetic carrier is substituted magnetite (Mn0.2Fe2.70O4). Large sample size leads to bigger differences in Tcs on heating and cooling, while small sample size results in similar Tcs for both heating rates.

Investigation of hydrogen assisted cracking in acicular ferrite using site-specific micro-fracture tests

Hydrogen assisted cracking (HAC) is a common type of failure mechanism that can affect a wide range of metals and alloys. Experimental studies of HAC are cumbersome due to various intrinsic and extrinsic parameters and factors (associated with stress, hydrogen and the materials microstructure) contributing to the hydrogen crack kinetics. The microstructure of many materials consists of diverse constituents with characteristic features and mechanical properties which only occur in very small material volumes. The only way to differentiate the effect of these individual constituents on the hydrogen crack kinetics is to miniaturise the testing procedures. In this paper we present a new experimental approach to investigate hydrogen assisted crack growth in a microstructural constituent, i.e. acicular ferrite. For this purpose, sharply notched micro-cantilevers were fabricated with a Focus Ion Beam within this selected microscopic region. Acicular ferrite can be found in many ferrous alloys including ferritic weld metal and has specific features that control its intrinsic susceptibility to HAC. These features were characterised via Electron Backscatter Diffraction and the specimens were subsequently loaded under uncharged and hydrogen charged conditions with a nano-indenter. The outcomes of the testing, demonstrated that the threshold stress intensity factor, Kth, to initiate crack propagation in acicular ferrite ranges between 1.56MPam1/2 and 4.36MPam1/2. This range is significantly below the values of Kth reported for various ferrous alloys in standard macro-tests. This finding indicates that the mechanisms and resistance to HAC at micro-scale could be very different than at the macro-scale as not all fracture toughening mechanisms may be activated at this scale level.

The compensational boundary method to calculate the projected contact area of nanoindentation in atomistic simulations

The atomistic simulation of nanoidentation has become a powerful method to probe the mechanical behaviour and properties of small volumes of materials. It is crucial to calculate the projected contact area (PCA) accurately in order to obtain a reliable value of nanoindentation hardness. In this work, atomistic simulations of nanoindentation were performed on the Cu(111) and Ag(111) surfaces, and a new compensational boundary method is proposed to calculate the PCA. Compared with other available methods, this method provides a clear physical implication, and works well independently of the contact depth and the deformation behaviour of the material. It is also concluded that the widely-used experimental Oliver–Pharr (O–P) method significantly underestimates the PCA in atomistic simulations, and does not work for shallow nanoindentation at the nanoscale.

Sensitive ablation of brittle materials with pulsed CO2 laser radiation

The interaction process between pulsed CO2 laser radiation and glass was studied systematically. The concept of the structuring process is related to an absorption-controlled ablation of small elementary material volumes with reduced melt formation, the so-called elementary volume ablation (EVA). For this purpose, suitable pulse parameters were predicted on the basis of the optical and thermal materials properties. These pulses with durations as low as 10 μs and a peak power of up to 600 W were generated using a specific arrangement consisting of a commercially available continuous CO2 laser of high beam quality and a cascade of two interference laser beam modulators. Optical microscopy, scanning electron microscopy, white light interferometry, and tactile profilometry were used to investigate the influence of the CO2 laser pulse parameters on the processing quality. The results obtained from the ablation of borosilicate glass (Borofloat33) and 100 μm thick sheets of cerium doped borosilicate glass demonstrate that the EVA method is a suitable approach to select an appropriate range of processing parameters for a high precision thermal ablation of glass without microcrack formation.

Small Size Specimens Methods for Evaluation of Mechanical Properties

The evaluation of actual mechanical properties of the in-service structures after some time of operation or determination of local properties for detailed FEM simulation yields the necessity to obtain relevant material data with high accuracy from small volume of the experimental material. Therefore, non-destructive or semi-destructive techniques using small size samples are being developed. The use of small-scale samples also enables the evaluation of material properties in various locations of tested component; for example, the mechanical properties of the individual regions of welds, local properties determination for properties anisotropy assessment and properties determination in cases when small volume of the experimental material is available e.g. residual service life assessment of in service components, bulk nanostructured materials… There are shown results of small size tensile tests (M-TT) and small sized fatigue tests (SFT). In the case of small size specimens testing a machining becomes more pronounced that in the case of standard sized specimens. The current study brings information on the machining influence on the expected results obtained by small size specimens in the case of quasi-static tensile tests and fatigue test.

Ultrafast shape change and joining of small-volume materials using nanoscale electrical discharge

Using nanoscale electrical-discharge-induced rapid Joule heating, we developed a method for ultrafast shape change and joining of small-volume materials. Shape change is dominated by surface-tension-driven convection in the transient liquid melt, giving an extremely high strain rate of ~106 s–1. In addition, the heat can be dissipated in small volumes within a few microseconds through thermal conduction, quenching the melt back to the solid state with cooling rates up to 108 K·s-1. We demonstrate that this approach can be utilized for the ultrafast welding of small-volume crystalline Mo (a refractory metal) and amorphous Cu49Zr51 without introducing obvious microstructural changes, distinguishing the process from bulk welding.

Comparison of In Situ Micromechanical Strain-Rate Sensitivity Measurement Techniques

Strain-rate sensitivity (SRS) measurements using transient small-scale techniques are becoming increasingly popular for investigating nanostructured films and microcomponents since they can provide fundamental insights into the plastic deformation mechanisms within small volumes of material. Previously, researchers have typically used either nanoindentation or microcompression strain-rate jump tests on a variety of nanostructured materials and compared the resultant values with bulk compression data as a reference. However, no systematic comparison of the different transient micromechanical techniques has been performed on the same material to establish their relative merits or the consistency of their results. In this study, the SRS of nanocrystalline nickel is investigated using three independent, in situ, transient experimental techniques: miniature tension, nanoindentation, and micropillar compression. The obtained SRS exponents m measured by all techniques were found to be in good agreement, and the resulting apparent activation volume V app of approximately 10 b 3 is consistent with grain boundary diffusion processes and dislocation glide-based plasticity.

Vacuum-Insulated Self-Aligned Nanowire Phase-Change Memory Devices

Phase-change memory (PCM) is an emerging technology for faster nonvolatile memory where a small volume of phase-change material is switched between amorphous and crystalline states to provide distinct logic levels. A major difficulty with these devices is the high-power requirement for set and reset operations. In this brief, we computationally analyze a vacuum-insulated self-aligned Ge2Sb2Te5 nanowire (NW) PCM device and propose a way to control the placement and orientation of the NWs. The analysis is performed using 2-D rotationally symmetric finite-element simulations with temperature-dependent material parameters and accounting for thermoelectric effects. Simulation results predict a $\sim 10\times $ reduction in current required for reset operation and minimal thermal crosstalk when compared with a similarly sized conventional mushroom cell due to effective suppression of lateral heat loss. The operation of the vacuum-insulated NW devices is also almost independent of current polarity (unlike that of the mushroom cell), which can be advantageous for more flexible array programming schemes. These devices can be used to build densely packed PCM with lower power consumption and less thermal crosstalk.

Ultrafast laser and swift heavy ion irradiation: Response of Gd2O3 and ZrO2 to intense electronic excitation

In order to investigate the response of materials to extreme conditions, there are several approaches to depositing extremely high concentrations of energy into very small volumes of material, including ultrafast laser and swift heavy ion (SHI) irradiation. In this study, crystalline-to-crystalline phase transformations in cubic Gd2O3 and monoclinic ZrO2 have been investigated using ultrafast laser irradiation. The phases produced by the extreme conditions of irradiation were characterized by grazing incidence x-ray diffraction (GIXRD) and Raman spectroscopy. Gd2O3 exhibited a cubic-to-monoclinic phase transformation, as evidenced by the appearance of the monoclinic (402¯), (003), (310), and (112¯) peaks in the GIXRD pattern and of four Ag and three Bg Raman modes. ZrO2 underwent a monoclinic-to-tetragonal phase transformation, as evidenced by the emergence of the tetragonal (101) peak in the GIXRD pattern and of Eg and A1g Raman modes. The new phases formed by ultrafast laser irradiation are high temperature polymorphs of the two materials. No evidence of amorphization was seen in the GIXRD data, though Raman spectroscopy indicated point defect accumulation. These results are identical to those produced by irradiation with SHIs, which also deposit energy in materials primarily through electronic excitation. The similarity in damage process and material response between ultrafast laser and SHI irradiation suggests a fundamental relationship between these two techniques.

Geometry of nanoindentation cube-corner cracks observed by FIB tomography: Implication for fracture resistance estimation

When indenting a brittle material with a sharp indenter, cracks can be generated at the corners of the imprint. From the length of these cracks, the fracture resistance can be estimated. This technique is simple and allows characterizing small volumes of materials, especially if nanoindentation cube-corners tips are used. For evaluation of fracture resistance, a number of different models based on crack morphology have been proposed. However, the morphology of the cracks is difficult to determine due to the small scales involved. In this work, indentation fracture with a cube-corner nanoindentation tip on different materials is investigated by FIB tomography to obtain the generated crack morphology. Experimental observations are rationalized in terms of applied load, tip geometry and crystal anisotropy. Once the crack morphology is visualized, the two most commonly used equations for calculating the fracture resistance are discussed. Finally, guidelines for better estimation of fracture resistance are proposed.

Real time power consumption monitoring for energy efficiency analysis in micro EDM milling

Sustainability has become a major concern in many countries and is leading to strict regulations regarding the impact of products and services during their manufacturing, use, and disposal. Power consumption monitoring in manufacturing companies can lead to a reduction of machine tools energy wastes and consequently to lower expenses. To this end, a complete transparency of energy usage among the entire manufacturing facilities is required. Despite the small volume of material processed, micro manufacturing processes are energy intensive and the optimization of energy usage becomes critical for manufacturing sustainability. Electrical discharge machining (EDM) is considered an attractive solution for the manufacturing of microcomponents. In this paper, a low cost and modular data acquisition system, based on open-hardware and open-source software, for online energy consumption monitoring, is presented. The system described is applied for energy efficiency analysis of the micro EDM milling process by using a state of the art commercial machine tool. A number of sensors is connected to the data acquisition system to measure the energy consumption of the main sub-systems of the machine tool, data is recorded through a microcontroller, and sent to the main computer via Wi-Fi for data storage and analysis. Results show that the process efficiency depends on machine parameters but it is always far below 0.01 %. Solutions are suggested to improve the energy efficiency of the machine tool considered in this work.

David John Hugh Cockayne. 19 March 1942 — 22 December 2010

David Cockayne had a wide-ranging and lasting impact on electron microscopy in materials science. He had dual UK and Australian nationality, and his professional career was divided between the two countries. His research was exceptional. His most important scientific contribution was the development (with I. L. F. Ray and M. J. Whelan in Oxford) of the dark-field ‘weak-beam’ technique of transmission electron microscopy, which improved by an order of magnitude (to 1.5 nm) the resolution at which complex crystal lattice defect geometries could be studied. The technique had a significant impact on advancing our understanding of the structure and properties of lattice defects in many materials, and became established as a routine tool in laboratories all over the world; it is still widely used today. With D. R. McKenzie in Sydney he developed a powerful high-precision electron diffraction technique within an electron microscope to study small volumes of amorphous material, orders of magnitude smaller than is possible with X-rays or neutrons, giving nearest-neighbour distances accurate to 0.001 nm. As Director of the University of Sydney Electron Microscope Unit from 1974 to 1999, he led the development of the Unit to provide a first-class centralized service of electron microscopy for the university as a whole. This stimulated other Australian universities to follow his example.

Macroporous silica particles derivatized for enhanced lectin affinity enrichment of glycoproteins.

This chapter details procedures for (1) functionalizing macroporous silica particles with lectins, a class of proteins that have affinity for the glycan moieties on glycoproteins, and (2) utilizing the lectin-silica material for high-performance affinity chromatography (HPAC) to enrich glycoproteins from small volumes of biological sample materials.

Doubling absorption in nanowire solar cells with dielectric shell optical antennas.

Semiconductor nanowires (NWs) often exhibit efficient, broadband light absorption despite their relatively small size. This characteristic originates from the subwavelength dimensions and high refractive indices of the NWs, which cause a light-trapping optical antenna effect. As a result, NWs could enable high-efficiency but low-cost solar cells using small volumes of expensive semiconductor material. Nevertheless, the extent to which the antenna effect can be leveraged in devices will largely determine the economic viability of NW-based solar cells. Here, we demonstrate a simple, low-cost, and scalable route to dramatically enhance the optical antenna effect in NW photovoltaic devices by coating the wires with conformal dielectric shells. Scattering and absorption measurements on Si NWs coated with shells of SiN(x) or SiO(x) exhibit a broadband enhancement of light absorption by ∼ 50-200% and light scattering by ∼ 200-1000%. The increased light-matter interaction leads to a ∼ 80% increase in short-circuit current density in Si photovoltaic devices under 1 sun illumination. Optical simulations reproduce the experimental results and indicate the dielectric-shell effect to be a general phenomenon for groups IV, II-VI, and III-V semiconductor NWs in both lateral and vertical orientations, providing a simple route to approximately double the efficiency of NW-based solar cells.

Analysis of Mechanical Properties of Individual Phases in Steels by Depth Sensing Indentation

The macroscopic mechanical properties of steel are highly dependent upon microstructure, morphology, and distribution of each phase present. Nanomechanical testing (Depth sensing indentation) provides a straightforward solution for quantitatively characterizing each of these phases because it is very powerful technique for characterization of materials in small volumes. Measuring the intrinsic properties of each phase separately in multiphase materials gives information that is valuable for the development of new materials and for modelling [1]. In this work, depth sensing indentation has been used to reveal mechanical properties of different phases in steel sheets.

Ore Minerals Down to Nanoscale: Petrogenetic Implications

Like most minerals, sulphides and oxides are compositionally heterogeneous at the smallest scale. The application of a variety of different techniques is necessary to fully understand their crystal-chemistry, each with its own inherent advantages and dis-advantages, and each with limited ranges of obser-vational scale. Focussed Ion Beam Scanning Electron Microscopy (FIB-SEM) opens up new avenues for in-situ sampling of small volumes of material which have been compositionally characterised by other techniques, including SEM, EPMA and LA-ICPMS. Slices lifted from the surface of a polished section, typically 40 x 20 µm in size and a few µm thick, can be imaged and prepared for Transmission Electron Microscope (TEM) analysis. This procedure allows for bridging micro- to nanoscale observations on a site which is of petrogenetic interest (e.g., Ciobanu et al., 2011). One of the main themes of inquiry is the distribution of trace elements in ores relative to subtle changes in mineral speciation, nanoparticle nucleation or crystal-structural modifications. Here we show examples of the application of FIB-SEM and TEM studies to such topics from across ore geology. 2 Homology in Mixed-Layer Chalcogenides Bismuth minerals are common accessory minerals in gold deposits, and include Pb-Bi-sulphosalts and – tellurides. They form homologous or polysomatic series where small chemical variation from one species to another is linked to modifications of crystal-structural layers (modules or blocks) in a predictive manner. These minerals can thus record subtle variations in the chemistry of an evolving ore system via crystallisation processes at the smallest scale. One example is the tetradymite group, where the crystalchemical formula nBi2·mBi2X3 (X = Te, Se, S; e.g., Cook et al., 2007) indicates that all the phases can be derived from archetypal layers of fixed width, but of variable numbers (n, m) in the stacking sequence. Based on TEM studies that show monotonic decrease of crystal modulation vectors with increase in Bi, the homology in the group has been

Measuring plastic yield stress of magnetron sputtered aluminum thin film by nanoindentation

Experimental determination of plastic properties of thin films with considerable residual stress is always a challenging task. A simple experimental technique is presented for measuring yield stress of aluminum (Al) thin film with residual stress by combining the curvature test with sphere-tip nanoindentation test. Both curvature and nanoindentation tests are carried out on an Al film/Si substrate system. A least square regression fitted equation is proposed and related to residual stress. The residual stress is measured to be 115MPa (tensile) using curvature test, and the yield stress of Al films sputtered on the Si substrates is calculated to be 371MPa using the new fitted equation. This method can also be used to study the plastic properties of other thin films or small volume materials.

Wear Model of Sliding Motion Flat Surfaces Used in Mechanical Engineering

Wear is defined as the process of destruction of the shallow layer of a coupling in a small volume of material, that leads to the wear particle occurence. The mechanism of wear particle formation depends to a great extent on the strain state in the contact area (elastic, plastic, elasto-plastic), on the nature of the material (breaking tenssion, flowing tenssion etc) and on the working conditions (pressure, velocity, temperature etc). The harder material, function on the maximum strain on the friction surface, function on the angle and the geometry of roughness (or abrasive particles) may be elastically or plastically distorted, thus changing the state of the conjugate surface.The paper proposes an answer mode analysis of the materials of a friction coupling with sliding motion, for materials with different hardness.

Towards a protocol for the trace element analysis of glass from rhyolitic shards in tephra deposits by laser ablation ICP‐MS

ABSTRACTLaser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) is used widely to analyse single volcanic glass shards from Quaternary tephra deposits for stratigraphic correlation. As yet, no generally accepted protocol for these analyses exists and published methods report significant differences in crater size and calibration strategies. Using Ca as the ‘internal standard’ (CaI.S.), and not SiI.S., for the analysis of rhyolitic glass can cause significant problems, because of ablation of (i) Ca‐rich phenocrysts, notably ‘ubiquitous’ plagioclase, but also calcic‐amphibole, apatite and allanite or (ii) mounting epoxy resin which can contribute to the Ca internal standard signal. Using CaI.S. can cause underreporting of many elements which concentrate in Ca‐rich phenocrysts, making their ablation difficult to recognize, but when using SiI.S., no such underreporting occurs. Additionally, larger ablation craters (50 µm diameter) potentially incorporate even small volumes of phenocryst material, whereas smaller craters (<20 µm diameter) more frequently miss phenocrysts. Thus, for the LA‐ICP‐MS analysis of rhyolitic glass shards, smaller ablation craters should be employed and calibrated using SiI.S., allowing recognition and removal of analyses incorporating Ca‐rich phenocrysts and avoiding issues related to the ablation of the mounting resin.

Overview of Enhanced Continuum Theories for Thermal and Mechanical Responses of the Microsystems in the Fast-Transient Process

The recently growing demand for production and applications of microscale devices and systems has motivated research on the behavior of small volume materials. The computational models have become one of great interests in order to advance the manufacturing of microdevices and to reduce the time to insert new product in applications. Among the various numerical and computational techniques, still the approaches in the context of continuum theories are more preferable due to their minimum computational cost to simulation on realistic time and material structures. This paper reviews the methods to address the thermal and mechanical responses of microsystems. The focus is on the recent developments on the enhanced continuum theories to address the phenomena such as size and boundary effects as well as microscale heat transfer. The thermodynamic consistency of the theories is discussed and microstructural mechanisms are taken into account as physical justification of the framework. The presented constitutive model is calibrated using an extensive set of microscale experimental measurements of thin metal films over a wide range of size and temperature of the samples. An energy based approach is presented to extract the first estimate of the interface model parameters from results of nanoindentation test.