This work was supported by Grant No. CBET-0651283 from the U.S. National Science Foundation and Grant No. 117041PO9621 from Advanced Cooling Technology.

1. Preparation of Silica Nanoparticles for Deposition
<ol>
	<li>Starting with dry silica powder, prepare the sample for coating by first eliminating large aggregates.</li>
	<li>Wash silica particles (diameter of 200 nm, purchased from Gel-Tec Corp.) with ethanol (190 proof pure) and leave the sample under a fume hood till all the moisture evaporates with ethanol.</li>
	<li>Sift particles through a series of metallic meshes (US # 100-400) in order to break any remaining agglomerations.</li>
	<li>Place particles and a small magnetic stirrer bar in the tubular reactor, as shown in Figure 1. Particles should be placed inside the plasma zone.</li>
	<li>Seal the glass reactor by placing an o-ring between two flanges, one at the end of the glass tube and one at the end of the pipe connected to the pump.</li>
	<li>Install the stainless steel clamp ring around the flanges and hand tighten the screw around the clamp.</li>
</ol>
2. Preparation of the Vacuum System
<ol>
	<li>Fill the liquid nitrogen trap, then allow the surface of the trap to become cold. Wait 5 min.</li>
	<li>Add isopropanol in the bubbler and connect to the plasma reactor.</li>
	<li>Seal the bubbler by placing a rubber o-ring around the metal pipe and tighten the nut till the place of pipe to bubbler connection becomes sealed.</li>
</ol>
3. Plasma Deposition Process
<ol>
	<li>Place the bubbler in a water bath with temperature of 34&plusmn;2 &deg;C.</li>
	<li>Turn on the argon gas flow controller and enter 6.00 sccm as the set point.</li>
	<li>Gradually open the gate valve that connects the glass tube to the pump while the pump is working. Perform this step carefully because sudden decrease of pressure may cause the particles to be blown away by the flow. Wait till the pressure reaches 200 mTorr, then leave the gate valve fully open.</li>
	<li>Place the magnetic stirrer under the glass tube and set the speed at 100 rpm.</li>
	<li>Connect the aluminum ring around the tubular glass reactor to the radio frequency, RF, generator and connect the stainless steel clamp to the ground.</li>
	<li>Turn on the matching network (ENI MW-5D) first and then switch the AC line and the RF generator power on. Set the power at 30 W for the entire process.</li>
	<li>After a specific duration of time (10, 20, or 40 min) turn off the matching network, RF generator, and the AC power respectively.</li>
	<li>Close the check valve and then turn off the argon flow controller. Disconnect the bubbler from the valve and gradually increase the reactor pressure to atmospheric.</li>
	<li>Open the clamp and transfer the particles from the tube into a plastic dish using a metallic spatula.</li>
</ol>
4. Preparation of Hollow Particles by Dissolution of Core Material
<ol>
	<li>Place the sample under a fume hood for the entire process of adding hydrofluoric acid.</li>
	<li>Hydrofluoric acid is an extremely corrosive acid and exposure of eye and skin to it may cause permanent damage. Use goggles with a face shield and wear a laboratory coat when handling HF.</li>
	<li>Mix 10 ml of hydrofluoric acid (Aldrich 49%) with 10 ml deionized water and add to the plastic dish that contains the coated particles.</li>
	<li>Place the plastic dish on a magnetic stirrer and allow the core to dissolve for 24 hr.</li>
	<li>After one day dilute the sample with 50 ml deionized water and centrifuge the sample for 1 hr. Discard the liquid layer at the top in a plastic container and transfer the bottom layer that contains the particles in a plastic Petri dish.</li>
	<li>Add 50 ml deionized water and vortex the sample and centrifuge it again. Dispose of the top layer and transfer the particle layer in a clean Petri dish.</li>
	<li>Wash the particles with ethanol, air dry the sample, and transfer hollow particles into a vial with cap and keep the particles in a desiccator.</li>
</ol>
5. Characterization of Permeability (Rate of Core Release)
Materials: Potassium chloride for core materials
<ol>
	<li>Prepare 0.001 molar potassium chloride (KCl) solution by mixing 0.0745 grams KCl with 1 liter deionized water.</li>
	<li>Fill the glass bottle of constant output atomizer model 3076 and install the bottle cap.</li>
	<li>Connect the compressed air hose to a membrane dryer, which is connected to the gas inlet of the atomizer. Then attach a filter to the outlet hose in order to collect KCl nanoparticles.</li>
	<li>Gradually open the compressed air valve and let the air flow through the membrane dryer. Allow the particles accumulate in the filter for 5 hr.</li>
	<li>Close the compressed air valve and carefully remove the filter and collect the particles. Place the particles in a desiccator prior to the coating process.</li>
	<li>Follow protocol 2 and 3 in order to obtain uniformly coated KCl particles.</li>
	<li>Mix coated KCl with 10 ml deionized water in a glass vial. To fully mix the sample, drop a magnetic stirrer into the solution and leave it on a magnetic stirrer. Incubate the sample at 25 &deg;C.</li>
	<li>Insert the conductivity meter probe (Thermo Orion model 105) into the vial and record the conductivity over 30 days.</li>
</ol>
6. Representative Results
We have applied this process to a variety of core materials, including oxides (silica), salts (KCl) and metals (Al), as shown in Figure 2. Transmission electron microscope has been used to confirm the radial uniformity of the films and to measure their thickness. We have successfully coated particles ranging from 37 nm to 200 nm in diameter (Figure 2) but there is no fundamental limitation on the size of particles that can be treated by this method. The rate of shell deposition is approximately 1 nm/min. This rather slow rate makes it possible to control the thickness of the films quite accurately via the deposition time. The plasma-polymerized shell is a permeable barrier, as demonstrated by the fact that the core material can removed by etching or dissolution. Figure 3 shows the hollow shells that remain after the silica core is removed. The removal of the core is complete and the radial uniformity and thickness of the films are quite high. For the purposes of evaluating the permeability through these films, we switched to KCl as the core material since the dissolution of KCl can be monitored very easily through the ionic conductivity of the solution. Figure 4 shows the release of KCl from the core for four samples with different thickness, 20 nm, 40 nm, 75 nm, and 95 nm, respectively. Coated KCl particles were suspended in water and the conductivity of the solution was followed for a period of 30 days. In addition to the four samples, a control that consists of uncoated KCl particles was also monitored. Uncoated KCl particles dissolve within a very short time of approximately 1 min. By contrast, coated KCl shows a significantly slower release rate. The release profile of the coated particles is characterized by initial burst that takes place within the first hr, followed by a much slower release that takes several days to complete, depending on the thickness of the film.
<img alt="Figure 1" src="/files/ftp_upload/4113/4113fig1.jpg" /> 
Figure 1. Schematic representation of the preparation of nanoparticles, plasma deposition, and hollow particle formation.
<img alt="Figure 2" src="/files/ftp_upload/4113/4113fig2.jpg" /> 
Figure 2. TEM images of coated (a), (b) silica particles with d=200 nm, (c) silica particle with d=37 nm, (d) aluminum with d~100 nm, and (e) KCl particle with d=100 nm
<img alt="Figure 3" src="/files/ftp_upload/4113/4113fig3.jpg" /> 
Figure 3. TEM images of hollow particles after etching the (a), (b) silica core with diameter of 200 nm, and (c) KCl core.
<img alt="Figure 4" src="/files/ftp_upload/4113/4113fig4.jpg" /> 
Figure 4. Effect of shell thickness on the release profile. The inset graph shows the release during the first hr.

<ol>
	<li>Xu, X., Asher, S. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+and+Utilization+of+Monodisperse+Hollow+Polymeric+Particles+in+Photonic+Crystals.">Synthesis and Utilization of Monodisperse Hollow Polymeric Particles in Photonic Crystals.</a> Journal of the American Chemical Society. 126, 7940-7945 (2004).</li><li>Lou, X., Archer, L., Yang, Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hollow+Micro-/nanostructures:+Synthesis+and+Applications.">Hollow Micro-/nanostructures: Synthesis and Applications.</a> Advanced Material. 20, (2008).</li><li>Kim, D. J., Kang, J. Y., Kim, K. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Coating+of+TiO2+Thin+Films+on+Particles+by+a+Plasma+Chemical+Vapor+Deposition+Process.">Coating of TiO2 Thin Films on Particles by a Plasma Chemical Vapor Deposition Process.</a> Advanced Powder Technology. 21, 136-140 (2010).</li><li>Marino, E., Huijser, T., Creyghton, Y., van der Heijden, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+and+Coating+of+Copper+Oxide+Nanoparticles+Using+Atmospheric+Pressure+Plasmas.">Synthesis and Coating of Copper Oxide Nanoparticles Using Atmospheric Pressure Plasmas.</a> Surface and Coatings Technology. 201, 9205-9208 (2007).</li><li>Hakim, L., King, D., Zhou, Y., Gump, C., George, S., Weimer, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanoparticle+Coating+for+Advanced+Optical,+Mechanical+and+Rheological+Properties.">Nanoparticle Coating for Advanced Optical, Mechanical and Rheological Properties.</a> Advanced Functional Materials. 17, 3175-3181 (2007).</li><li>Kim, S. H., Kim, J., Kang, B., Uhm, H. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Superhydrophobic+CFx+Coating+via+In-Line+Atmospheric+RF+Plasma+of+He-CF4-H2.">Superhydrophobic CFx Coating via In-Line Atmospheric RF Plasma of He-CF4-H2.</a> Langmuir. 21, 12213-12217 (2005).</li></ol>

No conflicts of interest declared.

One of the biggest challenges in coating nanoparticles is to provide a compatible chemistry between coating and the substrate 1,2. The methodology described here has the advantage that it is not material-specific. Plasma polymers show excellent adhesion on a variety of substrates, including hard metals (Figure 2(c)), silica (Figure 2(c)), silicon, or soft materials (e.g., polymers) without the need for any special surface modification 3,4,5. The technique has the fu...

<table border="1">
<tbody>
 <tr>
 <td>Silica particles</td>
 <td>Geltech Inc.</td>
 <td></td>
 <td></td>
 </tr>
 <tr>
 <td>Potassium chloride (crystals)</td>
 <td>EMD Chemicals Inc.</td>
 <td></td>
 <td></td>
 </tr>
 <tr>
 <td>Isopropyl alcohol (99.9%)</td>
 <td>Sigma-Aldrich</td>
 <td></td>
 <td></td>
 </tr>
 <tr>
 <td>Hydrofluoric acid (48-51%)</td>
 <td>VWR</td>
 <td></td>
 <td></td>
 </tr>
 <tr>
 <td>Pipes and flanges</td>
 <td>Swagelok</td>
 <td></td>
 <td>diameter of &frac14; and 1 inch</td>
 </tr>
 <tr>
 <td>roughing pump</td>
 <td>Edwards</td>
 <td></td>
 <td></td>
 </tr>
 <tr>
 <td>liquid nitrogen trap</td>
 <td>A&amp;N Corporation</td>
 <td></td>
 <td></td>
 </tr>
 </tbody>
</table>

encapsulation and permeability characteristics of plasma polymerized hollow particles

In this protocol, core-shell nanostructures are synthesized by plasma enhanced chemical vapor deposition. We produce an amorphous barrier by plasma polymerization of isopropanol on various solid substrates, including silica and potassium chloride. This versatile technique is used to treat nanoparticles and nanopowders with sizes ranging from 37 nm to 1 micron, by depositing films whose thickness can be anywhere from 1 nm to upwards of 100 nm. Dissolution of the core allows us to study the rate of permeation through the film. In these experiments, we determine the diffusion coefficient of KCl through the barrier film by coating KCL nanocrystals and subsequently monitoring the ionic conductivity of the coated particles suspended in water. The primary interest in this process is the encapsulation and delayed release of solutes. The thickness of the shell is one of the independent variables by which we control the rate of release. It has a strong effect on the rate of release, which increases from a six-hour release (shell thickness is 20 nm) to a long-term release over 30 days (shell thickness is 95 nm). The release profile shows a characteristic behavior: a fast release (35% of the final materials) during the first five minutes after the beginning of the dissolution, and a slower release till all of the core materials come out.

Watch this Scientific Journal Video about Encapsulation and Permeability Characteristics of Plasma Polymerized Hollow Particles at JoVE.com

Encapsulation and Permeability Characteristics of Plasma Polymerized Hollow Particles

We have used plasma enhanced chemical vapor deposition to deposit thin films ranging from a few nm to several 100 nm on nano-sized particles of various materials. We subsequently etch the core material to produce hollow nanoshells whose permeability is controlled by the thickness of the shell. We characterize the permeability of these coatings to small solutes and demonstrate that these barriers can provide sustained release of the core material over several days.

In this protocol, core-shell nanostructures are synthesized by plasma enhanced chemical vapor deposition. We produce an amorphous barrier by plasma ...

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10.7K vues.  The Pennsylvania State University. Nous avons utilisé Plasma Enhanced Chemical Vapor Deposition pour déposer des films minces allant de quelques nm à 100 nm sur plusieurs particules de taille nanométrique de matériaux divers. On suite de gravure du matériau de coeur pour produire nanobilles creux dont la perméabilité est commandé par l'épaisseur de la coque. Nous caractérisons la perméabilité de ces revêtements de petits solutés et de démontrer que ces obstacles peuvent fournir une lib?...

Vidéo: Encapsulation and Permeability Characteristics of Plasma Polymerized Hollow Particles

Investigation of Early Plasma Evolution Induced by Ultrashort Laser Pulses

Early plasma is generated owing to high intensity laser irradiation of target and the subsequent target material ionization. Its dynamics plays a significant role in laser-material interaction, especially in the air environment1-11.
Early plasma evolution has been captured through pump-probe shadowgraphy1-3 and interferometry1,4-7. However, the studied time frames and applied laser parameter ranges are limited. For example, direct examinations of plasma front locations and electron number densities within a delay time of 100 picosecond (ps) with respect to the laser pulse peak are still very few, especially for the ultrashort pulse of a duration around 100 femtosecond (fs) and a low power density around 1014 W/cm2. Early plasma generated under these conditions has only been captured recently with high temporal and spatial resolutions12. The detailed setup strategy and procedures of this high precision measurement will be illustrated in this paper. The rationale of the measurement is optical pump-probe shadowgraphy: one ultrashort laser pulse is split to a pump pulse and a probe pulse, while the delay time between them can be adjusted by changing their beam path lengths. The pump pulse ablates the target and generates the early plasma, and the probe pulse propagates through the plasma region and detects the non-uniformity of electron number density. In addition, animations are generated using the calculated results from the simulation model of Ref. 12 to illustrate the plasma formation and evolution with a very high resolution (0.04 ~ 1 ps).
Both the experimental method and the simulation method can be applied to a broad range of time frames and laser parameters. These methods can be used to examine the early plasma generated not only from metals, but also from semiconductors and insulators.

An experimental method to examine the early plasma evolution induced by ultrashort laser pulses is described. Using this method, high quality images of early plasma are obtained with high temporal and spatial resolutions. A novel integrated atomistic model is used to simulate and explain the mechanisms of early plasma.

Early plasma is generated owing to high intensity laser irradiation of target and the subsequent target material ionization. Its dynamics plays a ...

How to Ignite an Atmospheric Pressure Microwave Plasma Torch without Any Additional Igniters

This movie shows how an atmospheric pressure plasma torch can be ignited by microwave power with no additional igniters. After ignition of the plasma, a stable and continuous operation of the plasma is possible and the plasma torch can be used for many different applications. On one hand, the hot (3,600 K gas temperature) plasma can be used for chemical processes and on the other hand the cold afterglow (temperatures down to almost RT) can be applied for surface processes. For example chemical syntheses are interesting volume processes. Here the microwave plasma torch can be used for the decomposition of waste gases which are harmful and contribute to the global warming but are needed as etching gases in growing industry sectors like the semiconductor branch. Another application is the dissociation of CO2. Surplus electrical energy from renewable energy sources can be used to dissociate CO2 to CO and O2. The CO can be further processed to gaseous or liquid higher hydrocarbons thereby providing chemical storage of the energy, synthetic fuels or platform chemicals for the chemical industry. Applications of the afterglow of the plasma torch are the treatment of surfaces to increase the adhesion of lacquer, glue or paint, and the sterilization or decontamination of different kind of surfaces. The movie will explain how to ignite the plasma solely by microwave power without any additional igniters, e.g., electric sparks. The microwave plasma torch is based on a combination of two resonators &#8212; a coaxial one which provides the ignition of the plasma and a cylindrical one which guarantees a continuous and stable operation of the plasma after ignition. The plasma can be operated in a long microwave transparent tube for volume processes or shaped by orifices for surface treatment purposes.

This movie shows how an atmospheric plasma torch can be ignited by microwaves with no additional igniters and provides a stable and continuous plasma operation suitable for plenty of applications.

This movie shows how an atmospheric pressure plasma torch can be ignited by microwave power with no additional igniters. After ignition of the plasma, a ...

Methods for Measuring the Orientation and Rotation Rate of 3D-printed Particles in Turbulence

Experimental methods are presented for measuring the rotational and translational motion of anisotropic particles in turbulent fluid flows. 3D printing technology is used to fabricate particles with slender arms connected at a common center. Shapes explored are crosses (two perpendicular rods), jacks (three perpendicular rods), triads (three rods in triangular planar symmetry), and tetrads (four arms in tetrahedral symmetry). Methods for producing on the order of 10,000 fluorescently dyed particles are described. Time-resolved measurements of their orientation and solid-body rotation rate are obtained from four synchronized videos of their motion in a turbulent flow between oscillating grids with R&#955; = 91. In this relatively low-Reynolds number flow, the advected particles are small enough that they approximate ellipsoidal tracer particles. We present results of time-resolved 3D trajectories of position and orientation of the particles as well as measurements of their rotation rates.

We use 3D printing to fabricate anisotropic particles in the shapes of jacks, crosses, tetrads, and triads, whose alignments and rotations in turbulent fluid flow can be measured from multiple simultaneous video images.

Experimental methods are presented for measuring the rotational and translational motion of anisotropic particles in turbulent fluid flows. 3D printing ...

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 ...

Applying X-ray Imaging Crystal Spectroscopy for Use as a High Temperature Plasma Diagnostic

X-ray spectra provide a wealth of information on high temperature plasmas; for example electron temperature and density can be inferred from line intensity ratios. By using a Johann spectrometer viewing the plasma, it is possible to construct profiles of plasma parameters such as density, temperature, and velocity with good spatial and time resolution. However, benchmarking atomic code modeling of X-ray spectra obtained from well-diagnosed laboratory plasmas is important to justify use of such spectra to determine plasma parameters when other independent diagnostics are not available. This manuscript presents the operation of the High Resolution X-ray Crystal Imaging Spectrometer with Spatial Resolution (HIREXSR), a high wavelength resolution spatially imaging X-ray spectrometer used to view hydrogen- and helium-like ions of medium atomic number elements in a tokamak plasma. In addition, this manuscript covers a laser blow-off system that can introduce such ions to the plasma with precise timing to allow for perturbative studies of transport in the plasma.

X-ray spectra provide a wealth of information on high temperature plasmas. This manuscript presents the operation of a high wavelength resolution spatially imaging X-ray spectrometer used to view hydrogen- and helium-like ions of medium atomic number elements in a tokamak plasma.

X-ray spectra provide a wealth of information on high temperature plasmas; for example electron temperature and density can be inferred from line ...

Effect of Bending on the Electrical Characteristics of Flexible Organic Single Crystal-based Field-effect Transistors

The charge transport in an organic semiconductor depends highly on the molecular packing in the crystal, which influences the electronic coupling immensely. However, in soft electronics, in which organic semiconductors play a critical role, the devices will be bent or folded repeatedly. The effect of bending on the crystal packing and thus the charge transport is crucial to the performance of the device. In this manuscript, we describe the protocol to bend a single crystal of 5,7,12,16-tetrachloro-6,13-diazapentacene (TCDAP) in the field-effect transistor configuration and to obtain reproducible I-V characteristics upon bending the crystal. The results show that bending a field-effect transistor prepared on a flexible substrate results in nearly reversible yet opposite trends in charge mobility, depending on the bending direction. The mobility increases when the device is bent toward the top gate/dielectric layer (upward, compressive state) and decreases when bent toward the crystal/substrate side (downward, tensile state). The effect of bending curvature was also observed, with greater mobility change resulting from higher bending curvature. It is suggested that the intermolecular &#960;-&#960; distance changes upon bending, thereby influencing the electronic coupling and the subsequent carrier transport ability.

This manuscript describes the bending process of an organic single crystal-based field-effect transistor to maintain a functioning device for electronic property measurement. The results suggest that bending causes changes in the molecular spacing in the crystal and thus in the charge hopping rate, which is important in flexible electronics.

The charge transport in an organic semiconductor depends highly on the molecular packing in the crystal, which influences the electronic coupling ...

An Atmospheric Pressure Plasma Setup to Investigate the Reactive Species Formation

Non-thermal atmospheric pressure (&#39;cold&#39;) plasmas have received increased attention in recent years due to their significant biomedical potential. The reactions of cold plasma with the surrounding atmosphere yield a variety of reactive species, which can define its effectiveness. While efficient development of cold plasma therapy requires kinetic models, model benchmarking needs empirical data. Experimental studies of the source of reactive species detected in aqueous solutions exposed to plasma are still scarce. Biomedical plasma is often operated with He or Ar feed gas, and a specific interest lies in investigation of the reactive species generated by plasma with various gas admixtures (O2, N2, air, H2O vapor, etc.) Such investigations are very complex due to difficulties in controlling the ambient atmosphere in contact with the plasma effluent. In this work, we addressed common issues of &#39;high&#39; voltage kHz frequency driven plasma jet experimental studies. A reactor was developed allowing the exclusion of ambient atmosphere from the plasma-liquid system. The system thus comprised the feed gas with admixtures and the components of the liquid sample. This controlled atmosphere allowed the investigation of the source of the reactive oxygen species induced in aqueous solutions by He-water vapor plasma. The use of isotopically labelled water allowed distinguishing between the species originating in the gas phase and those formed in the liquid. The plasma equipment was contained inside a Faraday cage to eliminate possible influence of any external field. The setup is versatile and can aid in further understanding the cold plasma-liquid interactions chemistry.

An experimental setup was created for the helium-operated kHz frequency plasma jet. The setup includes a cage for the plasma power supply and jet and an in-house built reactor to monitor plasma-induced reactive species without the interference of the ambient atmosphere.

Non-thermal atmospheric pressure (&#39;cold&#39;) plasmas have received increased attention in recent years due to their significant biomedical potential. ...

Plasma-assisted Molecular Beam Epitaxy of N-polar InAlN-barrier High-electron-mobility Transistors

Plasma-assisted molecular beam epitaxy is well suited for the epitaxial growth of III-nitride thin films and heterostructures with smooth, abrupt interfaces required for high-quality high-electron-mobility transistors (HEMTs). A procedure is presented for the growth of N-polar InAlN HEMTs, including wafer preparation and growth of buffer layers, the InAlN barrier layer, AlN and GaN interlayers and the GaN channel. Critical issues at each step of the process are identified, such as avoiding Ga accumulation in the GaN buffer, the role of temperature on InAlN compositional homogeneity, and the use of Ga flux during the AlN interlayer and the interrupt prior to GaN channel growth. Compositionally homogeneous N-polar InAlN thin films are demonstrated with surface root-mean-squared roughness as low as 0.19 nm and InAlN-based HEMT structures are reported having mobility as high as 1,750 cm2/V&#8729;sec for devices with a sheet charge density of 1.7 x 1013 cm-2.

Molecular beam epitaxy is used to grow N-polar InAlN-barrier high-electron-mobility transistors (HEMTs). Control of the wafer preparation, layer growth conditions and epitaxial structure results in smooth, compositionally homogeneous InAlN layers and HEMTs with mobility as high as 1,750 cm2/V&#8729;sec.

Plasma-assisted molecular beam epitaxy is well suited for the epitaxial growth of III-nitride thin films and heterostructures with smooth, abrupt ...

Spark Plasma Sintering Apparatus Used for the Formation of Strontium Titanate Bicrystals

A spark plasma sintering apparatus was used as a novel method for diffusion bonding of two single crystals of strontium titanate to form bicrystals with one twist grain boundary. This apparatus utilizes high uniaxial pressure and a pulsed direct current for rapid consolidation of material. Diffusion bonding of strontium titanate bicrystals without fracture, in a spark plasma sintering apparatus, is possible at high pressures due to the unusual temperature dependent plasticity behavior of strontium titanate. We demonstrate a method for the successful formation of bicrystals at accelerated time scales and lower temperatures in a spark plasma sintering apparatus compared to bicrystals formed by conventional diffusion bonding parameters. Bond quality was verified by scanning electron microscopy. A clean and atomically abrupt interface containing no secondary phases was observed using transmission electron microscopy techniques. Local changes in bonding across the boundary was characterized by simultaneous scanning transmission electron microscopy and spatially resolved electron energy-loss spectroscopy.

A viable technique for the formation of strontium titanate bicrystals at high pressure and fast heating rate via the spark plasma sintering apparatus is developed.

A spark plasma sintering apparatus was used as a novel method for diffusion bonding of two single crystals of strontium titanate to form bicrystals with ...

Optimization, Test and Diagnostics of Miniaturized Hall Thrusters

Miniaturized spacecraft and satellites require smart, highly efficient and durable low-thrust thrusters, capable of extended, reliable operation without attendance and adjustment. Thermochemical thrusters which utilize thermodynamic properties of gases as a means of acceleration have physical limitations on their exhaust gas velocity, resulting in low efficiency. Moreover, these engines demonstrate extremely low efficiency at small thrusts and may be unsuitable for continuously operating systems which provide real-time adaptive control of the spacecraft orientation, velocity and position. In contrast, electric propulsion systems which use electromagnetic fields to accelerate ionized gases (i.e., plasmas) do not have any physical limitation in terms of exhaust velocity, allowing virtually any mass efficiency and specific impulse. Low-thrust Hall thrusters have a lifetime of several thousand hours. Their discharge voltage ranges between 100 and 300 V, operating at a nominal power of &lt;1 kW. They vary from 20 to 100 mm in size. Large Hall thrusters can provide fractions of millinewton of thrust. Over the past few decades, there has been an increasing interest in small mass, low power, and high efficiency propulsion systems to drive satellites of 50-200 kg. In this work, we will demonstrate how to build, test, and optimize a small (30 mm) Hall thruster capable of propelling a small satellite weighing about 50 kg. We will show the thruster operating in a large space environment simulator, and describe how thrust is measured and electric parameters, including plasma characteristics, are collected and processed to assess key thruster parameters. We will also demonstrate how the thruster is optimized to make it one of the most efficient small thrusters ever built. We will also address challenges and opportunities presented by new thruster materials.

Here, we present a protocol to test and optimize space propulsion systems based on miniaturized Hall-type thrusters.

Miniaturized spacecraft and satellites require smart, highly efficient and durable low-thrust thrusters, capable of extended, reliable operation without ...