1. Small Scale Synthesis of Nanocrystalline Powders under Ambient Conditions
<ol>
	<li>In a controlled argon atmosphere glove box, place 10 g of the primary element (e.g., Fe in FeNiZr alloy) and 100 g of&#160;stainless steel/tool steel milling balls in the desired milling jar. 
	NOTE: Loading of powder into milling jar inside a glove box is required to ensure minimal uptake in oxygen and/or moisture content 18,19.</li>
	<li>After loading, seal the jar and remove from the glove box. After removal, ensure that jar is fully sealed and load into the appropriate milling machine.</li>
	<li>After performing a 1 h milling cycle, remove the vial and transfer it back into the argon-filled glove box. 
	NOTE: This short run serves to coat all surfaces with the primary element, thereby helping to reduce the transfer of contaminants from milling jar and media to the alloy being produced.</li>
	<li>To synthesize the alloy powders, add a total of 10 g of elemental powders in the desired ratios to the just coated milling jar inside the glove box. Add the required amount of just coated milling balls to the jar such that there is a 10:1 ratio of the mass of the balls to mass of powder. The lid should be placed and tightened on the milling jar before removal from the glove box. After removal, further tightening of the lid should be performed using a wrench and a vice.</li>
	<li>Place the vial in the high energy shaker mill and initiate milling operation (typically on order of 20 h). After the milling is completed, remove the vial and transfer it to the glove box. Carefully remove the lid and transfer the milled powder to the desired sample vial for storage. 
	NOTE: A typical high energy shaker mill used in mechanical alloying is shown in Figure 3A. A schematic showing how high energy milling results in nanocrystalline materials is shown in Figure 3B, with an image showing an average final particle size between 10 and 500 &#181;m shown in Figure 3C.</li>
</ol>
2. Small Scale Synthesis of Nanocrystalline Powders under Cryogenic Conditions
<ol>
	<li>Perform coating run for milling jar and balls as described in Steps 1.1-1.3.</li>
	<li>In controlled atmosphere glove box, fill coated milling jar with desired amount of elemental powders and milling media. After tightening the jar, remove from the glove box.</li>
	<li>Place the milling jar inside a Teflon sleeve and cap, which is then placed in the clamp of the high energy shaker mill.</li>
	<li>Open the dewar containing the cryogen and allow it flow for about 30 min to ensure the milling jar has reached the desired temperature (-196 &#176;C for liquid nitrogen and -186 &#176;C for liquid argon).</li>
	<li>Upon reaching equilibrium, initiate the milling operation until the desired duration has been reached. Upon completion, close the dewar, carefully remove the milling jar from the sleeve and place it in front of a dryer to bring it to room temperature.</li>
	<li>Once the milling jar reaches room temperature, transfer it back inside the controlled atmosphere glove box. Carefully open the milling jar and transfer the powders to desired storage vial. 
	NOTE: A picture of the high energy shaker mill adapted for use at cryogenic temperatures is shown in Figure 4A. Shown in Figure 4B is a milling vial immediately after it has been removed from a cryomilling operation. Figure 4C provides an idea of the number of milling balls typically used in a processing operation.</li>
</ol>
3. Large Scale Synthesis of Nanocrystalline Powders
<ol>
	<li>Load the required elemental alloying powders into a glass jar inside an argon glove box, seal, and remove.</li>
	<li>After attaching the vessel to the high-energy horizontal rotary ball mill, load approximately 1 kg of 440C&#160;stainless steel ball bearings into a stainless steel 8 L vessel contained within a cooling jacket. 
	Note: Images of the various parts of the high energy horizontal rotary ball mill are shown in Figure 5.</li>
	<li>Connect the argon gas line and coolant lines to the vessel. Back-fill and purge the vessel with argon gas to remove air.</li>
	<li>Using a double ball valve, transfer the alloying elemental powders into the milling vessel and then close the valve to seal the chamber.</li>
	<li>Connect the powder extraction system to the milling vessel and then back-fill and purge the extraction system with argon gas to remove air. &#160;</li>
	<li>Start flowing ethylene glycol at -25 &#176;C through the outer jacket of the vessel.</li>
	<li>Begin the milling process for up to 1 kg of elemental powders for the desired amount of time (typically 12-30 h) using rotational energy of 400-800 rpm. Once the milling is completed, transfer the powders to a jar under argon atmosphere. Store the jar in an argon filled glove box.</li>
</ol>

<ol>
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Compared to other synthesis techniques, mechanical alloying is an extremely versatile method for producing metal and alloyed powders with grain sizes &lt;&lt;100 nm. Indeed, mechanical alloying is one of the few ways in which large volumes of nanostructured materials can be produced in a cost effective and easily scalable manner. Furthermore, high-energy ball milling has been shown to vastly increase the limit of solid solubility in many metallic systems in which equilibrium room temperature solubility does not otherwis...

Nanocrystalline metals prepared by high energy mechanical alloying have been shown to exhibit superior mechanical strength as compared to their coarse-grained counterparts. However, as dictated by thermodynamic principles, nanocrystalline microstructures are subject to grain coarsening at elevated temperatures. As such, processing and applications of these materials is currently limited by the ability to create stabilized microstructures in bulk form. Given the potential of these materials, two primary methods are being pursued in an effort to develop such systems. The first, based on a kinetic approach, utilizes several mechanisms to apply a pinning force on the grain boundaries (GBs) in order to prevent grain growth. Typical mechanisms employed to pin the GBs are secondary phases (Zener pinning)1,2,3 and/or solute drag effects4,5. The second method, based on a thermodynamics approach, suppresses grain growth by reducing the GB free energy through solute atoms partitioning to the GBs6,7,8,9,10,11,12,13,14,15,16.
As the first step to developing alloys with a nanograined microstructure, the fundamental understanding into thermodynamic and kinetic principles that govern grain growth and microstructural stability at elevated temperatures was established. Computational materials science was also used to guide alloy development. Using these insights, small scale lots of various alloy powders were produced using high energy milling and evaluated for a broad range of physical and mechanical properties. For the more promising systems, advanced characterization techniques were developed in order to fully link the microstructure of the powder to the observed properties and performance.
Simultaneously, the infrastructure and equipment needed to produce bulk components from the nanocrystalline powders was acquired. Once this equipment was in place, the processing science required to fully consolidate bulk materials from the alloy powders was developed through a series of small scale experiments. Once bulk specimens were available, a series of experiments were performed to understand the mechanical response of these materials under a broad range of conditions (such as fatigue, creep, high strain rate, etc.). The knowledge gained from these experiments has been used to develop possible application spaces that will enable the commercialization of the stabilized bulk nanocrystalline alloys.
Collectively, meeting these tasks has led to the development within the U.S. Army Research Laboratory (ARL) of a nanocrystalline metals research center consisting of 4 main labs. This laboratory complex represents a total investment of 20 million USD and is unique in that it spans aspects of fundamental, applied, and manufacturing science. The primary purpose of these labs is to transition proof-of-concept ideas to the pilot-scale and pre-manufacturing levels. In doing so, it is anticipated that the labs will enable the production of prototype parts, develop the necessary know-how and manufacturing science for scaled-up processing, and allow for linkages internally as well as to external research institutes or industrial partners via the commercialization and transition of this advanced powder technology.
As indicated earlier, the first step is to identify, produce, and rapidly assess new alloy prototypes for both feasibility of synthesis and fabrication into prototype parts. To accomplish this, several unique, custom-designed high energy shaker mills have been constructed with the capability to process powders over a wide range of temperatures from -196 &#176;C to 200 &#176;C. As the name implies, these mills produce approximately 10-20 g of fine powders through the violent shaking action that causes repetitive impacts between powder and grinding media to produce powders in which each particle has a composition in proportion to the starting elemental powder mix. While suitable for the rapid screening of powders, mills of this type are clearly not suitable for powder production on the (near) industrial scale (e.g., kilograms).
Given the need to produce powder in large quantities and in as continuous a process as possible, a search was undertaken to identify potentially viable methods and equipment. Planetary ball mills use a support disk which rotates in the opposite direction from the vertically oriented vials, resulting in particle size reduction due to both grinding and collisions caused by centrifugal forces. Lot sizes for most planetary mills range up to approximately 2 kg. Unlike conventional mills, attritor mills consists of a series of impellers inside a vertical drum. The rotation of the impellers cause the motion of the grinding media, resulting in particle size reduction through collisions between powder, balls, and the impellers. Larger attritor mills are capable of producing over 200 kg per run. Although both of these mills offer significant increases in lot sizes relative to shaker mills, they are not capable of running in a continuous fashion but must rather be loaded and unloaded manually for each run.
Due to these shortcomings, attention shifted to a series of high energy, horizontal rotary ball mills. Capable of processing as much as 200 kg per batch, these mills are also capable of operating under inert atmospheres as well as vacuum. Finally, the milling chamber has been designed with an airlock that allows for the rapid and automated removal of powder once the milling process has been completed. Combined with an automatic powder injection system, this means that the ball mill is capable of running in a fairly continuous manner, thereby making it a highly viable system for industrial settings. Due to these combination of features, ARL has recently purchased and installed two mills and is now engaged in upscaling internal powder processing efforts.
While the powder processing efforts represent a central aspect of on-going efforts, the characterization and consolidation of the most promising alloy powders are also areas of focused research. Indeed, as detailed below, ARL has made notable investments in the requisite analytical and test equipment needed to fully evaluate key features of the new powders. Moreover, successful consolidation of samples now allows for conventional full scale mechanical testing and characterization (e.g., tension, fatigue, creep, shock and ballistic evaluation) of these materials which has typically not been feasible for this class of material. This article reports the protocols utilized at ARL for initial synthesis, scale-up, consolidation and characterization of bulk nanocrystalline metals and alloys.
The two main labs for powder synthesis can be seen in Figure 1. Figure 1A shows the small-scale powder processing lab which enables the rapid development of concepts and alloy design. This lab contains several custom-designed high energy mills with the capability to process powders over a range of temperatures (room temperature to 400 &#176;C and 10 to -196 &#176;C). The lab also contains a custom horizontal tube furnace designed for the rapid assessment of the thermal and microstructural stability (e.g., grain growth studies) of new metal alloys. Finally, the lab also houses several unique small-scale mechanical test setups including tension, shear punch, and impression creep testing devices, as well as a state-of-the-art instrumented nano-indenter. Once thoroughly tested and of shown promise, selected alloys are moved to the large scale processing lab (Figure 1B), where the engineering and manufacturing protocols are developed to allow large scale (e.g., kilogram) production of the specific powder. In total, the labs represent a total investment on the order of 2 million USD and covers the transition of novel metal powders from the lab bench to the pilot-scale manufacturing levels, thereby enabling the production of prototype parts.
High energy ball milling/mechanical alloying is a versatile process for producing nanocrystalline metals and alloys in powder form17. Starting with coarse grained powders (typically mean grain size ~5-10 &#181;m), it is possible to obtain nanocrystalline powders with mean grain size &#60; 100 nm after milling. This milling is routinely performed in a vibratory/shaker mill. The milling vial is filled with the desired amount of powder as well as milling balls, typically stainless steel. This mill shakes the vials in a motion that involves back and forth oscillations with short lateral movements at a rate of approximately 1080 cycles min-1. With each complex motion the balls collide with one another, impact against the inside of the vial and the lid, and simultaneously reduce the powder to finer size. The kinetic energy imparted into the powder is equal to half the mass times the square of the average velocity (19 m s-1) of the bearings. The mill power, e.g. the energy delivered per unit time, increases with the frequency of the mill (15-26 Hz). Taking the typical number of balls and the lowest frequency for a given 20 h period, the total number of impacts exceeds 1.5 billon. During these impacts the powder undergoes repeated fracturing and cold-welding until the point where the constituents are mixed at the atomic level. Microscopically this mixing and refinement of the microstructure is facilitated by localized deformation in the form of shear bands as well as a high density of dislocations and point defects which breaks down the microstructure. Eventually, as the heat of collision raises the local temperature, recombination and annihilation of these defects occurs at a steady state with their generation. The defect structures eventually, though reorganization, result in the formation of smaller and smaller high angle equiaxed grains. Thus, ball milling is a process that induces severe plastic deformation manifested by the presence of a high density of defects. This process allows for increased diffusivity of solute elements and the refinement and dispersion of secondary phases and the overall nanostructuring of the microstructure.
High energy cryomilling is a milling process similar to high energy ball milling except for the fact that the milling vial is maintained at cryogenic temperature during the milling process. In order to achieve a uniform temperature in the vial, the mill has been modified as follows. The milling vial is first placed inside a Teflon sleeve which is then sealed with a Teflon cap. The sleeve is connected to a dewar containing the appropriate cryogen (liquid nitrogen (LN2) or liquid argon (LAr)) through stainless steel and plastic tubing. The cryogen flows through the sleeve throughout the milling process to cool the milling vial and maintain the milling vial at the boiling temperature of the cryogen, such as -196 &#176;C for LN2 and -186 &#176;C for LAr. The low temperatures of cryogenic processing lead to the increased fragmentation of more ductile metals which otherwise cannot be milled at room temperature. Additionally, the cryogenic temperatures reduce thermally activated diffusional processes such as grain growth and phase separation thereby allowing increased refinement of the microstructure and solubility of insoluble elemental species.
The high energy horizontal rotary ball mill is a high energy milling system that consists of a horizontal stainless-steel milling jar with a high-speed rotor with several blades fixed on a drive shaft. The powder to be milled is transferred inside the jar along with the milling balls. Movement of the balls and powder is achieved through the rotation of the shaft inside the jar. The shaft rotates at high speed and the milling steel balls collide, accelerate, and transfer their kinetic energy to the powders. The range of rpm is 100 - 1000 and the average velocity of the balls is 14 m s-1. In particular, mills are equipped to operate over a range of milling temperature (-30 &#176;C to 200 &#176;C high) and can be run under vacuum (mTorr) or in over pressure mode (1500 Torr) (utilizing various types of cover gas). In addition to the base unit, the mill is equipped with a carrier gas discharge unit as well as connection assemblies which allows the loading and unloading of powder under inert gas cover. This apparatus can be seen in Figure 2A along with a typical 8 L steel milling jar (Figure 2B). In addition to the larger mill, ARL has purchased a smaller mill which has been converted to run under liquid nitrogen (Figure 2C). This mill can produce between 100-400 g of processed powder per running cycle.

<table border="0" cellpadding="0" cellspacing="0" width="1063">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">Copper powder</td>
			<td style="width:243px;">Alfa Aesar</td>
			<td style="width:141px;">42623</td>
			<td style="width:331px;">Spherical, -100+325 mesh, 99.9%</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">Tantalum powder</td>
			<td style="width:243px;">Alfa Aesar</td>
			<td style="width:141px;">10345</td>
			<td>99.97%, -325 mesh</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">Iron powder</td>
			<td style="width:243px;">Alfa Aesar&#160;</td>
			<td style="width:141px;">00170</td>
			<td>Spherical, &#60;10 micron, 99.9+%</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">Nickel powder</td>
			<td style="width:243px;">Alfa Aesar</td>
			<td style="width:141px;">43214</td>
			<td>-325 mesh, 99.8%</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">Zirconium powder</td>
			<td style="width:243px;">American Elements</td>
			<td style="width:141px;">ZR-M-03-P</td>
			<td>99.90%</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">SPEX mills (high energy shaker mills)</td>
			<td style="width:243px;">SPEX SamplePrep</td>
			<td style="width:141px;">8000M&#160;</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:349px;">Zoz mills (high energy horizontal rotary ball mill)</td>
			<td style="width:243px;">Zoz GmbH</td>
			<td style="width:141px;">CM01 (small mill) CM08 (large mill)</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:349px;">Focused Ion Beam</td>
			<td style="width:243px;">FEI&#160;</td>
			<td style="width:141px;">Nova600i Nanolab dual beam FIB/SEM</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:349px;">Scanning Electron Microscope</td>
			<td style="width:243px;">FEI&#160;</td>
			<td style="width:141px;">Nova600i Nanolab dual beam FIB/SEM</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">Precision Ion Polishing System</td>
			<td style="width:243px;">Gatan&#160;</td>
			<td style="width:141px;">Model 695</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">Transmission Electron Microscope</td>
			<td style="width:243px;">JEOL&#160;</td>
			<td style="width:141px;">2100F&#160;</td>
			<td>multipurpose field emission TEM</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">Atom Probe Tomography</td>
			<td style="width:243px;">CAMECA</td>
			<td style="width:141px;">&#160;LEAP 5000XR</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">Equal Channel Angular Extrusion</td>
			<td style="width:243px;">ShearForm</td>
			<td style="width:141px;">custom built</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:349px;">Hot Isostatic Press</td>
			<td style="width:243px;">Matsys</td>
			<td style="width:141px;"></td>
			<td></td>
		</tr>
	</tbody>
</table>

processing of bulk nanocrystalline metals at the us army research laboratory

Given their potential for significant property improvements relative to their large grained counterparts, much work has been devoted to the continued development of nanocrystalline metals. Despite these efforts, the transition of these materials from the lab bench to actual applications has been blocked by the inability to produce large scale parts that retain the desired nanocrystalline microstructures. Following the development of a method proven to stabilize the nanosized grain structure to temperatures approaching that of the melting point for the given metal, the US Army Research Laboratory (ARL) has progressed to the next stage in the development of these materials - namely the production of large scale parts suitable for testing and evaluation in a range of relevant test environments. This report provides a broad overview of the ongoing efforts in the processing, characterization, and consolidation of these materials at ARL. In particular, focus is placed on the methodology used for producing the nanocrystalline metal powders, in both small and large-scale amounts, that are at the center of ongoing research efforts.

Approximately 10 g of powder are produced per each run in the high energy shaker mill. After successful synthesis of novel nanocrystalline metals and alloys in high energy shaker mill, scale-up is conducted in a high energy horizontal rotary ball mill.
Typically, nanostructured powders are generated using high energy milling processes, wherein the grain size of a small amount of powder is refined, approximately 10 g per batch. T...

Watch this Scientific Journal Video about Processing of Bulk Nanocrystalline Metals at the US Army Research Laboratory at JoVE.com

Processing of Bulk Nanocrystalline Metals at the US Army Research Laboratory

This paper provides a brief overview of the ongoing efforts at the Army Research Laboratory on the processing of bulk nanocrystalline metals with an emphasis on the methodologies used for the production of the novel metal powders.

Given their potential for significant property improvements relative to their large grained counterparts, much work has been devoted to the continued ...

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9.4K Views.  US Army Research Laboratory. This paper provides a brief overview of the ongoing efforts at the Army Research Laboratory on the processing of bulk nanocrystalline metals with an emphasis on the methodologies used for the production of the novel metal powders.

Video: Processing of Bulk Nanocrystalline Metals at the US Army Research Laboratory

Simulation of the Planetary Interior Differentiation Processes in the Laboratory

A planetary interior is under high-pressure and high-temperature conditions and it has a layered structure. There are two important processes that led to that layered structure, (1) percolation of liquid metal in a solid silicate matrix by planet differentiation, and (2) inner core crystallization by subsequent planet cooling. We conduct high-pressure and high-temperature experiments to simulate both processes in the laboratory. Formation of percolative planetary core depends on the efficiency of melt percolation, which is controlled by the dihedral (wetting) angle. The percolation simulation includes heating the sample at high pressure to a target temperature at which iron-sulfur alloy is molten while the silicate remains solid, and then determining the true dihedral angle to evaluate the style of liquid migration in a crystalline matrix by 3D visualization. The 3D volume rendering is achieved by slicing the recovered sample with a focused ion beam (FIB) and taking SEM image of each slice with a FIB/SEM crossbeam instrument. The second set of experiments is designed to understand the inner core crystallization and element distribution between the liquid outer core and solid inner core by determining the melting temperature and element partitioning at high pressure. The melting experiments are conducted in the multi-anvil apparatus up to 27 GPa and extended to higher pressure in the diamond-anvil cell with laser-heating. We have developed techniques to recover small heated samples by precision FIB milling and obtain high-resolution images of the laser-heated spot that show melting texture at high pressure. By analyzing the chemical compositions of the coexisting liquid and solid phases, we precisely determine the liquidus curve, providing necessary data to understand the inner core crystallization process.

The high-pressure and high-temperature experiments described here mimic planet interior differentiation processes. The processes are visualized and better understood by high-resolution 3D imaging and quantitative chemical analysis.

A planetary interior is under high-pressure and high-temperature conditions and it has a layered structure. There are two important processes that led to ...

Flame Experiments at the Advanced Light Source: New Insights into Soot Formation Processes

The following experimental protocols and the accompanying video are concerned with the flame experiments that are performed at the Chemical Dynamics Beamline of the Advanced Light Source (ALS) of the Lawrence Berkeley National Laboratory1-4. This video demonstrates how the complex chemical structures of laboratory-based model flames are analyzed using flame-sampling mass spectrometry with tunable synchrotron-generated vacuum-ultraviolet (VUV) radiation. This experimental approach combines isomer-resolving capabilities with high sensitivity and a large dynamic range5,6. The first part of the video describes experiments involving burner-stabilized, reduced-pressure (20-80 mbar) laminar premixed flames. A small hydrocarbon fuel was used for the selected flame to demonstrate the general experimental approach. It is shown how species&#8217; profiles are acquired as a function of distance from the burner surface and how the tunability of the VUV photon energy is used advantageously to identify many combustion intermediates based on their ionization energies. For example, this technique has been used to study gas-phase aspects of the soot-formation processes, and the video shows how the resonance-stabilized radicals, such as C3H3, C3H5, and i-C4H5, are identified as important intermediates7. The work has been focused on soot formation processes, and, from the chemical point of view, this process is very intriguing because chemical structures containing millions of carbon atoms are assembled from a fuel molecule possessing only a few carbon atoms in just milliseconds. The second part of the video highlights a new experiment, in which an opposed-flow diffusion flame and synchrotron-based aerosol mass spectrometry are used to study the chemical composition of the combustion-generated soot particles4. The experimental results indicate that the widely accepted H-abstraction-C2H2-addition (HACA) mechanism is not the sole molecular growth process responsible for the formation of the observed large polycyclic aromatic hydrocarbons (PAHs).

Gas sampling from laboratory-scale flames with online analysis of all species by mass spectrometry is a powerful method to investigate the complex mixture of chemical compounds occurring during combustion processes. Coupled with tunable soft ionization via synchrotron-generated vacuum-ultraviolet radiation, this technique provides isomer-resolved information and potentially fragment-free mass spectra.

The following experimental protocols and the accompanying video are concerned with the flame experiments that are performed at the Chemical Dynamics ...

Research and Development of High-performance Explosives

Developmental testing of high explosives for military applications involves small-scale formulation, safety testing, and finally detonation performance tests to verify theoretical calculations. For newly developed formulations, the process begins with small-scale mixes, thermal testing, and impact and friction sensitivity. Only then do subsequent larger scale formulations proceed to detonation testing, which will be covered in this paper. Recent advances in characterization techniques have led to unparalleled precision in the characterization of early-time evolution of detonations. The new technique of Photonic Doppler Velocimetry (PDV) for the measurement of detonation pressure will be shared and compared with traditional fiber-optic detonation velocity and plate-dent calculation of detonation pressure. In particular, the role of aluminum in explosive formulations will be discussed. Recent developments led to the development of explosive formulations that result in reaction of aluminum very early in the detonation product expansion. This enhanced reaction leads to changes in the detonation velocity and pressure due to reaction of the aluminum with oxygen in the expanding gas products.

Developmental testing of high explosives for military applications involves small-scale formulation, safety testing, and finally detonation performance tests to verify theoretical calculations. This paper will share typical development tests associated with the measurement of detonation velocity and detonation pressure.

Developmental testing of high explosives for military applications involves small-scale formulation, safety testing, and finally detonation performance ...

Quantification of Hydrogen Concentrations in Surface and Interface Layers and Bulk Materials through Depth Profiling with Nuclear Reaction Analysis

Nuclear reaction analysis (NRA) via the resonant 1H(15N,&#945;&#947;)12C reaction is a highly effective method of depth profiling that quantitatively and non-destructively reveals the hydrogen density distribution at surfaces, at interfaces, and in the volume of solid materials with high depth resolution. The technique applies a 15N ion beam of 6.385 MeV provided by an electrostatic accelerator and specifically detects the 1H isotope in depths up to about 2 &#956;m from the target surface. Surface H coverages are measured with a sensitivity in the order of ~1013 cm-2 (~1% of a typical atomic monolayer density) and H volume concentrations with a detection limit of ~1018 cm-3 (~100 at. ppm). The near-surface depth resolution is 2-5 nm for surface-normal 15N ion incidence onto the target and can be enhanced to values below 1 nm for very flat targets by adopting a surface-grazing incidence geometry. The method is versatile and readily applied to any high vacuum compatible homogeneous material with a smooth surface (no pores). Electrically conductive targets usually tolerate the ion beam irradiation with negligible degradation. Hydrogen quantitation and correct depth analysis require knowledge of the elementary composition (besides hydrogen) and mass density of the target material. Especially in combination with ultra-high vacuum methods for in-situ target preparation and characterization, 1H(15N,&#945;&#947;)12C NRA is ideally suited for hydrogen analysis at atomically controlled surfaces and nanostructured interfaces. We exemplarily demonstrate here the application of 15N NRA at the MALT Tandem accelerator facility of the University of Tokyo to (1) quantitatively measure the surface coverage and the bulk concentration of hydrogen in the near-surface region of a H2 exposed Pd(110) single crystal, and (2) to determine the depth location and layer density of hydrogen near the interfaces of thin SiO2 films on Si(100).

We illustrate the application of 1H(15N,&#945;&#947;)12C resonant nuclear reaction analysis (NRA) to quantitatively evaluate the density of hydrogen atoms on the surface, in the volume, and at an interfacial layer of solid materials. The near-surface hydrogen depth profiling of a Pd(110) single crystal and of SiO2/Si(100) stacks is described.

Nuclear reaction analysis (NRA) via the resonant 1H(15N,&#945;&#947;)12C reaction is a highly effective method of depth profiling that quantitatively and ...

Light Enhanced Hydrofluoric Acid Passivation: A Sensitive Technique for Detecting Bulk Silicon Defects

A procedure to measure the bulk lifetime (&#62;100 &#181;sec) of silicon wafers by temporarily attaining a very high level of surface passivation when immersing the wafers in hydrofluoric acid (HF) is presented. By this procedure three critical steps are required to attain the bulk lifetime. Firstly, prior to immersing silicon wafers into HF, they are chemically cleaned and subsequently etched in 25% tetramethylammonium hydroxide. Secondly, the chemically treated wafers are then placed into a large plastic container filled with a mixture of HF and hydrochloric acid, and then centered over an inductive coil for photoconductance (PC) measurements. Thirdly, to inhibit surface recombination and measure the bulk lifetime, the wafers are illuminated at 0.2 suns for 1 min&#160;using a halogen lamp, the illumination is switched off, and a PC measurement is immediately taken. By this procedure, the characteristics of bulk silicon defects can be accurately determined. Furthermore, it is anticipated that a sensitive RT surface passivation technique will be imperative for examining bulk silicon defects when their concentration is low (&#60;1012 cm-3).

A RT liquid surface passivation technique to investigate the recombination activity of bulk silicon defects is described. For the technique to be successful, three critical steps are required: (i) chemical cleaning and etching of silicon, (ii) immersion of silicon in 15% hydrofluoric acid and (iii) illumination for 1 min.

A procedure to measure the bulk lifetime (&#62;100 &#181;sec) of silicon wafers by temporarily attaining a very high level of surface passivation when ...

Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization

Polymer-based materials hold promise as low-cost, flexible efficient photovoltaic devices. Most laboratory efforts to achieve high performance devices have used devices prepared by spin coating, a process that is not amenable to large-scale fabrication. This mismatch in device fabrication makes it difficult to translate quantitative results obtained in the laboratory to the commercial level, making optimization difficult. Using a mini-slot die coater, this mismatch can be resolved by translating the commercial process to the laboratory and characterizing the structure formation in the active layer of the device in real time and in situ as films are coated onto a substrate. The evolution of the morphology was characterized under different conditions, allowing us to propose a mechanism by which the structures form and grow. This mini-slot die coater offers a simple, convenient, material efficient route by which the morphology in the active layer can be optimized under industrially relevant conditions. The goal of this protocol is to show experimental details of how a solar cell device is fabricated using a mini-slot die coater and technical details of running in situ structure characterization using the mini-slot die coater.

Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization

Here, we present a protocol to fabricate organic thin film solar cells using a mini-slot die coater and related in-line structure characterizations using synchrotron scattering techniques.

Polymer-based materials hold promise as low-cost, flexible efficient photovoltaic devices. Most laboratory efforts to achieve high performance devices ...

Fabrication and Operation of Acoustofluidic Devices Supporting Bulk Acoustic Standing Waves for Sheathless Focusing of Particles

Acoustophoresis refers to the displacement of suspended objects in response to directional forces from sound energy. Given that the suspended objects must be smaller than the incident wavelength of sound and the width of the fluidic channels are typically tens to hundreds of micrometers across, acoustofluidic devices typically use ultrasonic waves generated from a piezoelectric transducer pulsating at high frequencies (in the megahertz range). At characteristic frequencies that depend on the geometry of the device, it is possible to induce the formation of standing waves that can focus particles along desired fluidic streamlines within a bulk flow. Here, we describe a method for the fabrication of acoustophoretic devices from common materials and clean room equipment. We show representative results for the focusing of particles with positive or negative acoustic contrast factors, which move towards the pressure nodes or antinodes of the standing waves, respectively. These devices offer enormous practical utility for precisely positioning large numbers of microscopic entities (e.g., cells) in stationary or flowing fluids for applications ranging from cytometry to assembly.

Acoustofluidic devices use ultrasonic waves within microfluidic channels to manipulate, concentrate and isolate suspended micro and nanoscopic entities. This protocol describes the fabrication and operation of such a device supporting bulk acoustic standing waves to focus particles in a central streamline without the aid of sheath fluids.

Acoustophoresis refers to the displacement of suspended objects in response to directional forces from sound energy. Given that the suspended objects must ...

Wicking Tests for Unidirectional Fabrics: Measurements of Capillary Parameters to Evaluate Capillary Pressure in Liquid Composite Molding Processes

During impregnation of a fibrous reinforcement in liquid composite molding (LCM) processes, capillary effects have to be understood in order to identify their influence on void formation in composite parts. Wicking in a fibrous medium described by the Washburn equation was considered equivalent to a flow under the effect of capillary pressure according to the Darcy law. Experimental tests for the characterization of wicking were conducted with both carbon and flax fiber reinforcement. Quasi-unidirectional fabrics were then tested by means of a tensiometer to determine the morphological and wetting parameters along the fiber direction. The procedure was shown to be promising when the morphology of the fabric is unchanged during capillary wicking. In the case of carbon fabrics, the capillary pressure can be calculated. Flax fibers are sensitive to moisture sorption and swell in water. This phenomenon has to be taken into account to assess the wetting parameters. In order to make fibers less sensitive to water sorption, a thermal treatment was carried out on flax reinforcements. This treatment enhances fiber morphological stability and prevents swelling in water. It was shown that treated fabrics have a linear wicking trend similar to those found in carbon fabrics, allowing for the determination of capillary pressure.

An experimental method to measure geometrical parameters and the apparent advancing contact angles describing capillary wicking in unidirectional synthetic and natural fabrics is proposed. These parameters are mandatory for the determination of the capillary pressures that must be taken into account for liquid composite molding (LCM) applications.

During impregnation of a fibrous reinforcement in liquid composite molding (LCM) processes, capillary effects have to be understood in order to identify ...

Characterization of Ultra-fine Grained and Nanocrystalline Materials Using Transmission Kikuchi Diffraction

One of the challenges in microstructure analysis nowadays resides in the reliable and accurate characterization of ultra-fine grained (UFG) and nanocrystalline materials. The traditional techniques associated with scanning electron microscopy (SEM), such as electron backscatter diffraction (EBSD), do not possess the required spatial resolution due to the large interaction volume between the electrons from the beam and the atoms of the material. Transmission electron microscopy (TEM) has the required spatial resolution. However, due to a lack of automation in the analysis system, the rate of data acquisition is slow which limits the area of the specimen that can be characterized. This paper presents a new characterization technique, Transmission Kikuchi Diffraction (TKD), which enables the analysis of the microstructure of UFG and nanocrystalline materials using an SEM equipped with a standard EBSD system. The spatial resolution of this technique can reach 2 nm. This technique can be applied to a large range of materials that would be difficult to analyze using traditional EBSD. After presenting the experimental set up and describing the different steps necessary to realize a TKD analysis, examples of its use on metal alloys and minerals are shown to illustrate the resolution of the technique and its flexibility in term of material to be characterized.

This paper provides a detailed method to characterize the microstructure of ultra-fine grained and nanocrystalline materials using a scanning electron microscope equipped with a standard electron backscatter diffraction system. Metal alloys and minerals presenting refined microstructures are analyzed using this technique, showing the diversity of its possible applications.

One of the challenges in microstructure analysis nowadays resides in the reliable and accurate characterization of ultra-fine grained (UFG) and ...

A Novel Method for In Situ Electromechanical Characterization of Nanoscale Specimens

Electrically assisted deformation (EAD) is increasingly being used to improve the formability of metals during processes such as sheet metal rolling and forging. Adoption of this technique is proceeding despite disagreement concerning the underlying mechanism responsible for EAD. The experimental procedure described herein enables a more explicit study compared to previous EAD research by removing thermal effects, which are responsible for disagreement in interpreting previous EAD results. Furthermore, as the procedure described here enables EAD observation in situ and in real time in a transmission electron microscope (TEM), it is superior to existing post-mortem methods that observe EAD effects post-test. Test samples consist of a single crystal copper (SCC) foil having a free-standing tensile test section of nanoscale thickness, fabricated using a combination of laser and ion beam milling. The SCC is mounted to an etched silicon base that provides mechanical support and electrical isolation while serving as a heat sink. Using this geometry, even at high current density (~3,500 A/mm2), the test section experiences a negligible temperature increase (&#60;0.02 &#176;C), thus eliminating Joule heating effects. Monitoring material deformation and identifying the corresponding changes to microstructures, e.g. dislocations, are accomplished by acquiring and analyzing a series of TEM images. Our sample preparation and in situ experiment procedures are robust and versatile as they can be readily utilized to test materials with different microstructures, e.g., single and polycrystalline copper.

A Novel Method for In Situ Electromechanical Characterization of Nanoscale Specimens

Isolating electrical and thermal effects on electrically assisted deformation (EAD) is very difficult using macroscopic samples. Metallic sample micro- and nanostructures together with a custom test procedure have been developed to evaluate the impact of applied current on the formation without joule heating and evolution of dislocations on these samples.

Electrically assisted deformation (EAD) is increasingly being used to improve the formability of metals during processes such as sheet metal rolling and ...