Processing Of Nanostructured Materials Research Articles

Nanoscale 3D Tomography by In-Flight Fluorescence Spectroscopy of Atoms Sputtered by a Focused Ion Beam.

Nanoscale fabrication and characterization techniques critically underpin a vast range of fields, including nanoelectronics and nanobiotechnology. Focused ion beam (FIB) techniques are appealing due to their high spatial resolution and widespread use for processing of nanostructured materials. Here, we introduce FIB-induced fluorescence spectroscopy (FIB-FS) as a nanoscale technique for spectroscopic detection of atoms sputtered by an ion beam. We use semiconductor heterostructures to demonstrate nanoscale lateral and depth resolution and show that it is limited by ion-induced intermixing of nanostructured materials. Sensitivity is demonstrated qualitatively by depth profiling of 3.5, 5, and 8 nm quantum wells and quantitatively by detection of trace-level impurities present at parts-per-million levels. The utility of the FIB-FS technique is demonstrated by characterization of quantum wells and Li-ion batteries. Our work introduces FIB-FS as a high-resolution, high-sensitivity, 3D analysis and tomography technique that combines the versatility of FIB nanofabrication techniques with the power of diffraction-unlimited fluorescence spectroscopy.

Porosity and nanostructure of silicon oxycarbide derived carbon

The unique nanostructure of polymer derived pseudo-amorphous silicon oxycarbide ceramics, which comprises of SiO2 nanodomains, turbostratic graphite, and mixed bond tetrahedral of Si-O/C, enables processing of nanostructured materials with enhanced specific surface area and nanoporosity. Selective etching of the SiO2 nanodomains in a polysilsesquioxane derived SiOC structure left behind highly porous carbonaceous materials with specific surface area in excess of 800 m2g-1, where the obtained porosity and their distribution are remnant of the SiO2 nanodomains. High resolution transmission electron microscopy clearly identified the nanopores and graphene type layers in the oxycarbide derived carbons. The carbon in the SiOC ceramics was found to be better ordered after HF leaching process. Volume fraction of the micropores in the derived carbon was found to increase with the pyrolysis temperature of the parent silicon oxycarbide.

Single Step Laser Transfer and Laser Curing of Ag NanoWires: A Digital Process for the Fabrication of Flexible and Transparent Microelectrodes.

Ag nanowire (NW) networks have exquisite optical and electrical properties which make them ideal candidate materials for flexible transparent conductive electrodes. Despite the compatibility of Ag NW networks with laser processing, few demonstrations of laser fabricated Ag NW based components currently exist. In this work, we report on a novel single step laser transferring and laser curing process of micrometer sized pixels of Ag NW networks on flexible substrates. This process relies on the selective laser heating of the Ag NWs induced by the laser pulse energy and the subsequent localized melting of the polymeric substrate. We demonstrate that a single laser pulse can induce both transfer and curing of the Ag NW network. The feasibility of the process is confirmed experimentally and validated by Finite Element Analysis simulations, which indicate that selective heating is carried out within a submicron-sized heat affected zone. The resulting structures can be utilized as fully functional flexible transparent electrodes with figures of merit even higher than 100. Low sheet resistance (<50 Ohm/sq) and high visible light transparency (>90%) make the reported process highly desirable for a variety of applications, including selective heating or annealing of nanocomposite materials and laser processing of nanostructured materials on a large variety of optically transparent substrates, such as Polydimethylsiloxane (PDMS).

Finite element simulation of the T-shaped ECAP processing of round samples

Grain refinement is the only mechanism that increases the yield strength and toughness of the materials simultaneously. Severe plastic deformation is one of the promising methods to refine the microstructure of materials. Among different severe plastic deformation processes, the T-shaped equal channel angular pressing (T-ECAP) is a relatively new technique. In the present study, finite element analysis was conducted to evaluate the deformation behavior of metals during T-ECAP process. The study was focused mainly on flow characteristics, plastic strain distribution and its homogeneity, damage development, and pressing force which are among the most important factors governing the sound and successful processing of nanostructured materials by severe plastic deformation techniques. The results showed that plastic strain is localized in the bottom side of sample and uniform deformation cannot be possible using T-ECAP processing. Friction coefficient between sample and die channel wall has a little effect on strain distributions in mirror plane and transverse plane of deformed sample. Also, damage analysis showed that superficial cracks may be initiated from bottom side of sample and their propagation will be limited due to the compressive state of stress. It was demonstrated that the V shaped deformation zone are existed in T-ECAP process and the pressing load needed for execution of deformation process is increased with friction.

A numerical model coupling diffusion and grain growth in nanocrystalline materials

The optimization of material properties by tailoring nanoscale microstructure is garnering great attention from both material scientists and manufacturing engineers. One promising research direction is to apply conventional diffusion-based techniques such as nitriding, carburizing, coating and sintering to nanocrystalline materials to achieve unprecedented mechanical and chemical properties. Numerical methods to facilitate the experiment endeavor, however, are rare due to the extreme difficulty in dealing with the nanoscale structure evolution. In this work, a numerical scheme considering both grain growth and diffusion in the nanocrystalline structure is proposed. The diffusion along grain boundary and inner grain is modeled by a Cellular Automata (CA) method. The proposed CA method is stable, insensitive to mesh size, and most importantly numerically efficient, making it suitable for the simulation of long-time, large-scale manufacturing processes. This CA model is then integrated with a Monte Carlo (MC) algorithm to model grain growth, which typically accompanies the diffusion process. As a showcase, the integrated model is then applied to simulate the nitriding process in nanocrystalline iron. The results show that grain growth and impurities have an innegligible effect at the elevated temperature for nanocrystalline iron, consistent with experimental observations. The developed method has the potential to serve as a simulation engine for any diffusion-controlled manufacturing processing of nanostructured materials, enabling a numerical framework to establish the processing-microstructure relation.

High speed direct imaging of thin metal film ablation by movie-mode dynamic transmission electron microscopy.

Obliteration of matter by pulsed laser beams is not only prevalent in science fiction movies, but finds numerous technological applications ranging from additive manufacturing over machining of micro- and nanostructured features to health care. Pulse lengths ranging from femtoseconds to nanoseconds are utilized at varying laser beam energies and pulse lengths, and enable the removal of nanometric volumes of material. While the mechanisms for removal of material by laser irradiation, i.e., laser ablation, are well understood on the micrometer length scale, it was previously impossible to directly observe obliteration processes on smaller scales due to experimental limitations for the combination of nanometer spatial and nanosecond temporal resolution. Here, we report the direct observation of metal thin film ablation from a solid substrate through dynamic transmission electron microscopy. Quantitative analysis reveals liquid-phase dewetting of the thin-film, followed by hydrodynamic sputtering of nano- to submicron sized metal droplets. We discovered unexpected fracturing of the substrate due to evolving thermal stresses. This study confirms that hydrodynamic sputtering remains a valid mechanism for droplet expulsion on the nanoscale, while irradiation induced stress fields represent limit laser processing of nanostructured materials. Our results allow for improved safety during laser ablation in manufacturing and medical applications.

Enhanced structural and phase stability of titania inverse opals

The applications and processing of nanostructured materials at high temperatures require stability of their morphology. However, in such environments (>1000°C), these structures are prone to significant undesired microstructural changes that result in a loss of functional properties. The thermal stability of titania inverse opal films, prepared from self-assembled templates of monodisperse polystyrene spheres by infiltration utilizing atomic layer deposition and subsequent calcination, was assessed. Resistance to grain growth and a shift in the anatase-to-rutile transformation to higher temperatures was observed, with dramatic stability under vacuum. Vacuum annealed samples retained the anatase phase and exhibited minimal grain growth even after 3h at 1300°C. Photonic properties were retained until the transformation onset. The remarkable resistance was attributed to inhibition of surface diffusion and structure-substrate constraints. In addition to being technologically enabling, the results provide further insight into the titania system and its phase transformation mechanism.

Playing Tetris at the nanoscale

The ability to fabricate arrays of functional nanostructures with controlled size, shape and stability, precisely positioned on a substrate of choice, is an ongoing challenge in nanotechnology [1,2]. In this context, the bottom-up approach is emerging as a promising method for the growth and processing of nanostructured materials. This approach is based on the concepts of (organic) self-assembly [3] or (inorganic) selforganization [4] of nanostructures on a suitable substrate [5]. Surface nanotemplates [6], i.e. substrates that are artificially or naturally patterned at the nanoscale, are frequently used to control self-assembly or selforganization processes. Such templates are often able to provide surface cues that may guide the formation of ordered structures, including e.g. tissue regeneration [7]. The 6H-SiC(0001) nanomesh is a particularly interesting template in that it expresses a periodic array of nanopores whose size and spacing can be tailored in the 2–3 nm range [8]. Chen et al. had previously identified this SiC nanomesh as a chemically inert nanoscale template which directs the nucleation and controls the growth of Co clusters during metal vapor deposition, so that a 2D array of Co nanoparticles with relatively uniform spacing and a very narrow size distribution results [8,9]. On page 176 of a recent issue, Chen et al. [10] report the first thorough structural characterization of this 6H-SiC(0001) nanomesh template using complementary surface sensitive techniques. Other recent examples of templates include long-range (e.g. mesoscale) reconstructions [11,12] and step bunching [13], host–guest inclusions formed by metal–organic coordinated networks [14,15] and other types of ‘nanomeshes’ [16]. Despite the widespread use of patterned substrates, the structure and properties of such templates are often poorly understood. Silicon carbide (SiC) is a wide band-gap ( 2.35 eV) semiconductor which has been extensively investigated both for its fundamental interest and for possible applications. This extraordinary IV–IV compound

Nanostructures from severe plastic deformation and mechanisms of large-strain work hardening

Results of experimental investigations of structure evolution processes during processing of nanostructured materials by severe plastic deformation techniques are presented. The obtained results are analyzed on the basis of recent approaches, developed to explain mechanisms of work hardening at large plastic deformations.

Thermal spray processing of nanostructured materials

Thermal spray processing of nanostructured materials

Characterization and sinterability of nanophase titania particles processed in flame reactors

Abstract Flame aerosol reactors are a route for large scale processing of nanostructured materials. However, fundamentals about processing-structure-property relationships have not been extensively researched. This work utilized three different burners to obtain a wide range of flame processing conditions (different time-temperature histories) to study the formation of nanophase titania particles. At low precursor reaction temperatures of about 400 °C, amorphous titania was obtained. At intermediate temperatures of 900 ~ 1430 °C, mixtures of anatase and rutile phase titania were obtained. At high temperatures of 1500 ~ 1570 °C, spherical particles of 100% anatase titania were obtained. A qualitative explanation of the different phase formation has been provided. Transmission Electron Microscopy was used to study particle morphology, size and agglomeration. Sizes of the titania particles produced by the designed burners varied from 10 to 100 nm, depending on processing conditions. In situ light scattering measurements were made to examine the evolution of the particle sizes. Post-sintering experiments were carried out to illustrate superior sinterability of the nanophase titania powders.

Chemical processing and applications for nanostructured materials

This paper presents an overview of recent research performed at Rutgers University and the University of Connecticut on the synthesis and processing of nanostructured materials. Highlights of this collaborative research program include: (1) synthesis of carbide strengthened steel and hard cermet powders from aqueous solution precursors, (2) synthesis of ceramic powders and ceramic matrix composites from metalorganic precursors, (3) densification of powder compacts by liquid phase sintering, (4) formation of high quality coatings by thermal spraying, and (6) demonstration of superior hardness and wear resistance in bulk materials and coatings.