Micrometer Regime Research Articles

Rapid electrochemical preparation of PVA-protected Pt nanoparticles and their behavior towards methanol oxidation

PVA-protected Pt nanoparticles were electrochemically synthesized using hexachloroplatinic acid as a metal precursor and tested for methanol oxidation. Field emission gun microscopy (FEG) revealed that the absence of PVA allowed the Pt electrodeposit to grow to the micrometer regime, while its presence refined the grain size. The deposition time also played a role in the particle size. Pt nanoparticles with sizes ranging from 70 nm to 300 nm were obtained using long-time potential pulse, while the reduction of the time pulse narrowed the particle-size distribution producing nanoparticles of 20–40 nm in diameter, which exhibited high electrocatalytic activity for methanol oxidation.

MALDI imaging of lipid biochemistry in tissues by mass spectrometry.

As a result of recent advances, remarkable images revealing the distribution of complex lipids in tissues are now generated by matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI IMS). Lipids are amphipathic biomolecules with hydrophobic structural characteristics made by either an initial anion thioester condensation reaction (fatty acid synthase) or by carbocation condensation of branched chain pyrophosphate intermediates (isoprene pathway).1 Lipids play essential roles in cellular function including the self-assembly of phospholipids to form the constitutive outer and inner membrane bilayer of every living cell. Specific components of these membrane phospholipids include species that contain esterified arachidonate that can be enzymatically released to a free acid and transformed to potent signaling molecules (prostaglandins, leukotrienes) with myriad biological effects. The lipid cholesterol is an essential component of bilayer membranes that has a complicated, yet highly regulated biosynthesis. Elevation of cholesterol levels (predominantly as cholesteryl esters) in blood has been implicated in heart disease and is commonly monitored in consideration of human health. Some lipid molecules play the central role in biochemical energy storage in the form of triacylglycerol molecules stored in lipid bodies within most all cells. Mass spectrometry has historically been a tool of choice in biochemical studies of lipids. The sensitivity and specificity of mass spectral data are useful to sort out the complexity of lipid structures to begin to follow biological changes. While techniques such as fluorescence confocal microscopy or ability to engineer proteins that can be expressed in cells with fluorescent tags have become the mainstream of modern biochemical research, such techniques are not amenable to most lipids due to the relatively small size of the lipid molecules and the dynamic nature of their structure in the cell. Recent developments in MALDI IMS have merged specificity of lipid identification with two-dimensional molecular mapping to enable biochemical studies of lipids across regions of a biological tissue. Several significant reasons for the success of MALDI IMS applied to lipid imaging have emerged. The first is the high abundance of various lipids in biological tissues because these hydrophobic molecules constitute the external and internal defining membranes of each cell. These membranes are almost exclusively bilayers composed of phospholipids, sphingolipids, and cholesterol that are closely packed in high local concentrations to render the membrane only semipermeable to water. A second reason is that many lipids, e.g. phospholipids, are already ionized as either phosphate anions or nitrogen centered cations and generate abundant positive or negative ions during the MALDI process. An equally important factor in the success of MALDI IMS of lipids is that the molecular weight of these biomolecules is generally below 1,000 Da, which is an optimal mass range for the most sensitive operation of modern mass spectrometers. Additionally this low molecular weight facilitates diffusion of lipids into a matrix crystal driven by the high concentration of the lipid within the microstructure of the tissue. Because of these fundamental factors coupled with the exciting potential of MALDI IMS, lipid molecules have been frequently used as substrates for the advancement of IMS methodology and instrumentation. Research groups that utilize secondary ion mass spectrometry (SIMS) imaging have embraced lipid biochemistry by moving from inorganic to biological applications, development of larger particle size beams and demonstrations of sub-micron lateral resolution.2,3 Similar development and implementation of instrumentation for MALDI IMS has leveraged lipid diversity, abundance and contrast in rodent brain samples to achieve advancements in technology.4-8 The development of different matrices useful for MALDI IMS,9-16 different methods of matrix application17-23 and different matrix modifiers24,25 have been employed in MALDI IMS experiments to establish the value and parameters of these method modifications for lipid analysis. Advances in biology have been a direct result of our ability to observe biochemical events at the micron and submicron regimes within a tissue. Having a sensitive technique that reveals molecular structure information about specific lipids in a tissue with 10-50 μm resolution and provides information relative to concentration of that lipid, has already provided insight into lipid biochemistry at the tissue level. Since lipids are products of complex, intertwined enzymatic processes, MALDI IMS data reveals the integrated solution to complex reaction pathways that define the living cell in terms of lipid biochemistry. It has become apparent to a host of scientists converging into the use of MALDI IMS from fields as diverse as neuroscience, chemistry, and instrument development that there is a richness and complexity of lipid biochemistry suggested by the exquisite, molecule specific MALDI images created in the course of developing this technology. Many reviews have focused on the technological developments of MALDI IMS of lipids with respect to the issues mentioned above.2,26,27 This review focuses on the lipid biochemistry revealed by MALDI IMS.

X-ray fluorescence (conventional and 3D) and scanning electron microscopy for the investigation of Portuguese polychrome glazed ceramics: Advances in the knowledge of the manufacturing techniques

This work shows the first analytical results obtained by X-Ray Fluorescence (XRF) (conventional and 3D) and Scanning Electron Microscopy with Energy Dispersive System (SEM-EDS) on original Portuguese ceramic pieces produced between the 16th and 18th centuries in Coimbra and Lisbon. Experts distinguished these productions based only on the color, texture and brightness, which originates mislabeling in some cases. Thanks to lateral and spatial resolution in the micrometer regime, the results obtained with μ-XRF were essential in determining the glaze and pigment thicknesses by monitoring the profile of the most abundant element in each “layer”. Furthermore, the dissemination of these elements throughout the glaze is different depending on the glaze composition, firing temperature and on the pigment itself. Hence, the crucial point of this investigation was to analyze and understand the interfaces color/glaze and glaze/ceramic support. Together with the XRF results, images captured by SEM and the corresponding semi-quantitative EDS data revealed different manufacturing processes used by the two production centers. Different capture modes were suitable to distinguish different crystals from the minerals that confer the color of the pigments used and to enhance the fact that some of them are very well spread through the glassy matrix, sustaining the theory of an evolved and careful procedure in the manufacturing process of the glaze.

Monte Carlo simulation code for confocal 3D micro‐beam X‐ray fluorescence analysis of stratified materials

AbstractStratified materials are of great importance for many branches of modern industry, e.g. electronics or optics and for biomedical applications. Examination of chemical composition of individual layers and determination of their thickness helps to get information on their properties and function. A confocal 3D micro X‐ray fluorescence (3D µXRF) spectroscopy is an analytical method giving the possibility to investigate 3D distribution of chemical elements in a sample with spatial resolution in the micrometer regime in a non‐destructive way. Thin foils of Ti, Cu and Au, a bulk sample of Cu and a three‐layered sandwich sample, made of two thin Fe/Ni alloy foils, separated by polypropylene, were used as test samples. A Monte Carlo (MC) simulation code for the determination of elemental concentrations and thickness of individual layers in stratified materials with the use of confocal 3D µXRF spectroscopy was developed. The X‐ray intensity profiles versus the depth below surface, obtained from 3D µXRF experiments, MC simulation and an analytical approach were compared. Correlation coefficients between experimental versus simulated, and experimental versus analytical model X‐ray profiles were calculated. The correlation coefficients were comparable for both methods and exceeded 99%. The experimental X‐ray intensity profiles were deconvoluted with iterative MC simulation and by using analytical expression. The MC method produced slightly more accurate elemental concentrations and thickness of successive layers as compared to the results of the analytical approach. This MC code is a robust tool for simulation of scanning confocal 3D µXRF experiments on stratified materials and for quantitative interpretation of experimental results. Copyright © 2011 John Wiley & Sons, Ltd.

Characterisation of Submicron-Grain Sized Yttria-Stabilised Zirconia Electrolyte for SOFCs

This paper investigates the effect of grain size within the nano to micron regime on ionic conductivity for yttria stabilised zirconia (YSZ) with various yttria levels. The samples were made using either slip casting or die pressing routes and were characterised via the use of 4-point electrical conductivity, AC impedance, high resolution transmission electron microscopy (HRTEM) and a field emission gun scanning electron microscope (FEGSEM). Little variation in ionic conductivity was noted over the range of grain sizes examined; rather the yttria content had the largest effect. The greatest variation was noted between the 3 mol% YSZ and 8 mol% YSZ where the conductivity was seen to vary by ~65% at 850℃. This work forms part of an investigation into the potential use of fine grained zirconias as electrolytes in solid oxide fuel cell (SOFC) applications.

The molding of biological features using a flexible polymer mold

This paper examines two fabrication techniques (soft lithography and UV embossing) employed in the replication of various structures at the micron and single nanometer regimes. Stretched and assembled forms of double stranded (ds) DNA (16–3μm in length) were adsorbed on coated silicon oxide. The collective results show that the resolution of all the thermally cured polymers improves significantly when the processing time between the stamp and the template is increased with s-PDMS demonstrating a lateral resolution of <10nm.

Effect of Pattern Geometry on the Fracture Behavior of Direct Bonded Silicon Wafers

The effect of shallow and deep etched interface patterns on the effective adhesion of silicon-silicon direct bonds is examined. Specifically, fracture loads of double cantilever beam specimens with structured interfaces, with dimensions in micrometer regime, are measured. The results show that the interface fracture load increases as the structures, which are simple pillars, become taller and narrower. These experimental results are in good agreement with finite element modeling results. The fracture surfaces were inspected after testing, and the surfaces generally had very little debris from the bonded pillars. The results of this study may help to aid in the design of temporary bonding processes that use patterned interfaces to tune the failure behavior.

In situ SAXS observation on metal–salt-derived alumina sol–gel system accompanied by phase separation

The structure formation process of hierarchically porous alumina gels has been investigated by in situ small angle X-ray scattering (SAXS). The measurement was performed on the sol-gel solution containing aluminum chloride hexahydrate (AlCl(3)·6H(2)O), poly(ethylene oxide) (PEO), and propylene oxide (PO). The temporal divergence of scattering intensity in the low q regime was observed in the early stage of reaction, indicating that the occurrence of spinodal-decomposition-type phase separation. Detailed analysis of the SAXS profiles revealed that phase separation occurs between weakly branched polymerizing aluminum hydroxide (AH) and PEO. Further progress of the condensation reaction forms phase-separated two phases, that is, AH-rich phase and PEO-rich phase with the micrometer-range heterogeneity. The growth and aggregation of primary particles occurs in the phase-separated AH-rich domain, and therefore, the addition of PEO influences on the structure in nanometer regime as well as micrometer regime. The moderate stability of oligomeric species allows homogeneous condensation reaction parallel to phase separation and successful formation of hierarchically porous alumina gel.

Surface science studies of environmentally relevant iron (oxy)hydroxides ranging from the nano to the macro-regime

In this prospective, new developments in the study of the structure and reactivity of iron oxyhydroxides are reviewed. These materials are of particular interest, since their surfaces control an extraordinary amount of environmental chemistry. Understanding the environmental interfaces at a molecular level often appears to be a daunting scientific endeavor at first glance. Surfaces of interest range from the nano to micron regime and appear in the environment in varying shapes and sizes. Often the powerful suite of vacuum-based surface science tools are not applicable, since the surfaces of environmental particles can vary from amorphous to semi-crystalline and their surface reactivity is often affected by varying levels of surface hydration. However, the introduction of new and powerful surface probes and advancements in computational chemistry are allowing surface scientists to shed light on these hidden interfaces and how they control environmental chemistry.

Time-resolved mapping of neurotransmitter fluctuations by arrays of nanocavity redox-cycling sensors

We introduce a novel device for the spatiotemporal detection of neurotransmitters on-chip. Our device features an array of individually addressable nanocavity sensors that utilize redox-cycling for the localized electrochemical determination of neurotransmitter concentrations. This effect is based on rapid, repeated redox-reactions between two closely spaced electrodes and results in a high amplification of the electrochemical signal of individual molecules. Each sensor is equipped with two independently biased electrodes that are separated by an ∼65 nm wide cavity, thus enabling efficient redox-cycling amplification. The sensors feature entry ports in the micrometer regime and can be closely packed for the chemical mapping at high spatial resolutions.In this paper, we present the devices capabilities in neurotransmitter detection. The sensors are electrochemically characterized and their functionality is demonstrated by measuring localized dopamine fluctuations in a microfluidic channel.

Contact between Submicrometer Silica Spheres

Recently, the scope of the investigation of the deformation mechanism extended to the micrometer and submicrometer regimes. The sphere-substrate contact method was usually used because it is rather difficult to make two micrometer or submicrometer spheres contact each other precisely. Here, we used the sphere-sphere contact method via a novel, simple process to investigate the deformation of spheres. The silica particle size ranges from 400 to 900 nm. Traditionally, the harder the particle, the smaller both the contact radius and the adhesion force. Therefore, it is widely accepted that silica particles should undergo elastic deformation, but we found that silica particles underwent plastic deformation rather than elastic deformation because of van der Waals interaction. The contact radii were observed by scanning electron microscopy (SEM).

Design, Modeling, and Closed-Loop Control of a Complementary Clamp Piezoworm Stage

A novel complementary clamp piezoworm stage was developed to be integrated into a two-axis configuration for tracking profiles in different size regimes. It is based on novel clamp designs that permit complementary action using the same flexure frame in a compact arrangement. A novel direct connection to a commercial slide was used to eliminate backlash and the need for high-precision alignment of a rod and slide. A model was developed and used to design the controller structure and choose thresholds for smooth operation. Complete assessment of the closed-loop performance of a single-axis and dual-axis stage in different regimes was done. The average positioning accuracy of the stage was plusmn20 nm. For tracking applications, the average error of the two-axis stage was 8 nm in the nanometer regime, 1.72 mum in the micrometer regime, and 1.85 mum in the millimeter regime.

Comment on “Influence of growth mode on the structural, optical, and electrical properties of In-doped ZnO nanorods” [Appl. Phys. Lett. 94, 041906 (2009)

First Page

Overview on established and novel FIB based miniaturized mechanical testing using in-situ SEM

Abstract Probing mechanical properties in the micrometer regime is of current interest in materials science. A focused ion beam microscope was employed to fabricate miniaturized specimens, while an indenter installed in a scanning electron microscope was utilized to actuate the samples and record the load and displacement data during the deformation. Examples for miniaturized compression, tension, bending, as well as newly developed bending fatigue and bending fracture experiments are presented, demonstrating the unique flexibility of in-situ mechanical testing in the scanning electron microscope at small length scales.

PH-dependent adsorption of Au nanoparticles on chemically modified Si3N4 MEMS devices

Microelectromechanical systems (MEMS) are devices that represent the integration of mechanical and electrical components in the micrometer regime. Self-assembled monolayers (SAMs) can be used to functionalise the surface of MEMS resonators in order to fabricate chemically specific mass sensing devices. The work carried out in this article uses atomic force microscopy (AFM) and X-ray photoemission spectroscopy (XPS) data to investigate the pH-dependent adsorption of citrate-passivated Au nanoparticles to amino-terminated Si3N4 surfaces. AFM, XPS and mass adsorption experiments, using ‘flap’ type resonators, show that the maximum adsorption of nanoparticles takes place at pH = 5. The mass adsorption data, obtained using amino functionalised ‘flap’ type MEMS resonators, shows maximum adsorption of the Au nanoparticles at pH = 5 which is in agreement with the AFM and XPS data, which demonstrates the potential of such a device as a pH responsive nanoparticle detector.

A New Method of Carbon‐Nanotube Patterning Using Reduction Potentials

Carbon nanotubes (CNTs) have attracted considerable interest as high-stiffness materials and for use in nanodevices, on account of their extraordinary mechanical, chemical, and electrical properties. There have been several examples of CNTs being used to realize devices and composites. However, several hurdles remain to be overcome before CNT-based technology can be deployed on a commercial scale. Among these hurdles are locating and patterning technologies. So far, films of CNT networks have been patterned in the micrometer regime by a variety of techniques, including using a poly(methyl methacrylate) (PMMA) or poly(dimethylsiloxane) (PDMS) stamp, CO2 snow-jet etching, and O2-plasma etching. [4] However, these methods have limitations in commercial applications, such as lack of scalability, low resolution, and low reliability. This paper reports that noble metals, such as Au, Pt, and Ag, can promote the oxidation of CNTs at a relatively low temperature (350 8C), because of the reduction potential of the CNTs (in this study, oxidation means decomposition to CO2). Based on these phenomena, a nanometer-sized, patterned, random network of CNTs is fabricated. This study also examines the difference in the reduction potentials of single-walled and multiwalled CNTs (SWCNTs and MWCNTs, respectively). Scheme 1 summarizes the experimental procedure used to determine the reduction potential of the CNTs and to obtain the novel nanometer-sized patterns of SWCNTs. In order to make a CNT–metal junction, very thin metal films were deposited on a CNT film using electron-beam evaporation. The samples were then annealed in a box furnace at 350 8C in ambient air. In a reactive environment, a material system can be considered a ‘‘galvanic cell’’ if there is electrical contact between two materials with different reduction potentials, and they are in the same electrolyte. Under these conditions, the corrosion rate of the material with the lower reduction potential can be faster than that of the material with the higher reduction potential. The novel method for patterning CNT films was developed by applying this phenomenon. In order to confine the CNTs to a selected area,

Self-Assembled Hollow Spheres of β-Ni(OH)2 and Their Derived Nanomaterials

This paper describes a novel solution-based chemical process to architect hollow spheres of β-Ni(OH)2 with controllable sizes in submicrometer and micrometer regimes. In the synthesis, starting nickel salt (nitrate) is first converted to 6-coordinated nickel ion complex [Ni(EDA)3]2+ (bidentate ligand EDA = C2H4(NH2)2) to avoid rapid solid formation. Hollow and core−shell β-Ni(OH)2 spheres can be obtained with this template-free approach under one-pot conditions. The β-Ni(OH)2 spheres are constructed from petal-like nanobuilding units which in turn are formed from even smaller nanocrystallites. The obtained porous β-Ni(OH)2 spheres have a large specific surface area and show a unimodal pore-size distribution. Several preparative parameters have been examined and optimized. In particular, the concentration of divalent nickel in the starting solutions plays an important role in controlling thickness of the petal-like β-Ni(OH)2 flakes and diameter of spheres. The β-Ni(OH)2 flakes self-assemble into final sphe...

INFLUENCE OF FRICTION AND PROCESS PARAMETERS ON THE SPECIFIC CUTTING FORCE AND SURFACE CHARACTERISTICS IN MICRO CUTTING

For the production of small quantities of micro devices, machining is a low cost alternative to lithographic processing techniques. However, machining shows process specific size-effects upon miniaturization to the micrometer regime. Hence, the orthogonal turning process is chosen to study the influence of process parameters like uncut chip thickness h, cutting velocity vc and cutting edge radius rβ on the cutting force and the surface plastification by two-dimensional, thermo-mechanically coupled finite element simulations. A rate-dependent plasticity law is used for investigation of a normalized medium carbon steel (AISI 1045). Furthermore, the characteristics of the influences of the different parameters are analyzed mathematically by similarity mechanics. In particular, the frictional effects on the cutting process are studied in detail using a friction coefficient μ based on experimental results, and the influences of the process parameters on the cutting force and the plastic deformation of the surface layer are determined numerically. These results are compared with experimental measurements. The specific cutting forces are analyzed and discussed in detail. Size-effects observed experimentally are also found by numerical simulations.

Microstructured templates produced using femtosecond laser pulses as templates for the deposition of mesoporous silicas

A combination of laser-based top-down and chemical bottom-up processes to prepare hierarchical (pore) structures is presented. Polymer templates with dimensions in the micrometer regime are fabricated by two-photon polymerization of an acrylate monomer and are subsequently infiltrated with mesostructured silica using the liquid crystal templating approach. Calcination, which removes both the macro-templating polymer and the nano-templating surfactant molecules, can be carried out so that the morphology of the sample is preserved, delivering SBA-15-type mesoporous constructs which correspond to a replica (or an inverse copy) of the initial polymer structure. This is shown here on simple line structures and on woodpile structures as examples. As the two-photon polymerization allows the controlled construction of various imaginable shapes, mesoporous materials can be constructed with practically any desired morphology on the micrometer scale. The dual pore system of macro- and mesopores classifies these materials as hierarchical pore systems with applications in catalysis and sorption. In addition, the versatility of silica surface chemistry opens new venues for the fabrication of photonic crystals and the general biocompatibility of silica allows the construction of scaffolds for biomedical applications.

Hardness length-scale factor to model nano- and micro-indentation size effects

In this paper, we show that nano- and micro-indentation hardness data can be represented adequately by the strain gradient plasticity (SGP) theory if the uniformity of the dislocation spacing is taken into account. To give relevant information on the plastic deformation process, we suggest to use a hardness length-scale (HLS) factor equal to Ho ⋅ h * , where Ho is the macro-hardness and h* the characteristic scale-length deduced from the hardness–depth relation of the SGP theory. Theoretically, the HLS factor is proportional to both the shear modulus and the Burgers vector, depending on the dislocation spacing. Applied to various crystalline metals, the representation of the experimental HLS factor as a function of the theoretical one shows two distinct linear behaviours related to the micrometer and nanometer depth regimes associated with a uniform dislocation organisation beneath the indenter and with dislocations located at the vicinity of the indenter tip in a largest plastic zone, respectively.