Name: spark plasma sintering apparatus used for the formation of strontium titanate bicrystals
Uploaded: 2017-02-09T15:00:00
Description: Watch this Scientific Journal Video about Spark Plasma Sintering Apparatus Used for the Formation of Strontium Titanate Bicrystals at JoVE.com

LH gratefully acknowledges financial support by an US National Science Foundation Graduate Research Fellowship under Grant No. 1148897. Electron microscopy characterization and SPS processing at UC Davis was financially supported by a University of California Laboratory Fee award (#12-LR-238313). Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.

1. Sample Preparation of Single Crystal Strontium Titanate
NOTE: Single crystal STO is supplied with a (100) surface polished to a mirror finish.
<ol>
	<li>Section STO into 5x5 mm2 pieces using diamond wire saw.</li>
	<li>Ultrasonically clean samples at 50-60 Hz consecutively in baths of acetone, isopropanol, and methanol for fifteen minutes each.</li>
	<li>Remove STO from methanol bath to immediately place on hot plate held at a temperature of 200 &#176;C. Heating the sample afte...

<ol>
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Jpn. 109 (7), S110-S120 (2001).</li><li>Hutt, S., Kienzle, O., Ernst, F., Ruhle, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Processing+and+Structure+of+Grain+boundaries+in+Strontium+Titanate.">Processing and Structure of Grain boundaries in Strontium Titanate.</a> Z. Metallkd. 92 (2), 105-109 (2001).</li><li>Takahisa, Y., Ikuhara, Y., Sakuma, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Current-voltage+characteristics+across+45&#9702;+symmetric+tilt+boundary+in+highly+donor-doped+SrTiO3+bicrystal.">Current-voltage characteristics across 45&#9702; symmetric tilt boundary in highly donor-doped SrTiO3 bicrystal.</a> J. Mater. Sci. Lett. 20, 1827-1829 (2001).</li><li>Hill, A., Wallach, E. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modelling+Solid+State+Diffusion+Bonding.">Modelling Solid State Diffusion Bonding.</a> Acta Metall. 37 (9), 2425-2437 (1989).</li><li>Sato, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Non-linear+current-voltage+characteristics+related+to+native+defects+in+SrTiO3+and+ZnO+bicrystals.">Non-linear current-voltage characteristics related to native defects in SrTiO3 and ZnO bicrystals.</a> Sci. Technol. Adv. Mater. 4 (6), 605-611 (2003).</li><li>Hirose, S., Nishimura, H., Niimi, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Resistance+switching+effect+in+Nb-doped+SrTiO[sub+3]+(100)+bicrystal+with+(100)+&#8764;45&#176;+twist+boundary.">Resistance switching effect in Nb-doped SrTiO[sub 3] (100) bicrystal with (100) &#8764;45&#176; twist boundary.</a> J. App. Phys. 106 (4), 043711-043716 (2009).</li><li>Hutt, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Doctoral Thesis. , (2002).</li><li>Brunner, D., Taeri-Baghbadrani, S., Sigle, W., Ruhle, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Suprising+Results+of+a+Studay+on+the+Plasticity+in+Strontium+Titanate.">Suprising Results of a Studay on the Plasticity in Strontium Titanate.</a> J. Amer. Ceram. Soc. 84 (5), 1161-1163 (2001).</li><li>Gumbsch, P., Taeri-Baghbadrani, S., Brunner, D., Sigle, W., Ruhle, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Plasticity+and+an+inverse+brittle-to-ductile+transition+in+strontium+titanate.">Plasticity and an inverse brittle-to-ductile transition in strontium titanate.</a> Phys. Rev. Lett. 87 (8), 085501-085504 (2001).</li><li>Taeri, S., Brunner, D., Sigle, W., Ruhle, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Deformation+Behavior+of+Strontium+Titanate+between+Room+Temperature+and+1800K+under+Ambient+Pressure.">Deformation Behavior of Strontium Titanate between Room Temperature and 1800K under Ambient Pressure.</a> Z. Metallkd. 95, 433-446 (2004).</li><li>Takahashi, K., Ohtomo, A., Kawasaki, M., Koinuma, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Advanced+Processing+and+Characterization+of+SrTiO3+Single+Crystals+and+Bicrystals+for+High+Tc+Superconducting+Film+Substrate.">Advanced Processing and Characterization of SrTiO3 Single Crystals and Bicrystals for High Tc Superconducting Film Substrate.</a> Mater. Sci. Eng. B. 41, 152-156 (1996).</li><li>Rhodes, W. H., Kingery, W. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dislocation+Dependence+of+Cationic+Diffusion+in+SrTiO3.">Dislocation Dependence of Cationic Diffusion in SrTiO3.</a> J. Amer. Ceram. Soc. 49 (10), 521-526 (1966).</li><li>Yamamoto, T., Hayashi, K., Ikuhara, Y., Sakuma, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Grain+Boundary+Structure+and+Electrical+Properties+in+Nb-Doped+SrTiO&lt;sub&gt;3&lt;/sub&gt;+Bicrystals.">Grain Boundary Structure and Electrical Properties in Nb-Doped SrTiO&lt;sub&gt;3&lt;/sub&gt; Bicrystals.</a> Key Eng. Mater. 181-182, 225-230 (2000).</li><li>Fitting, L., Thiel, S., Schmehl, A., Mannhart, J., Muller, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Subtleties+in+ADF+imaging+and+spatially+resolved+EELS:+A+case+study+of+low-angle+twist+boundaries+in+SrTiO3.">Subtleties in ADF imaging and spatially resolved EELS: A case study of low-angle twist boundaries in SrTiO3.</a> Ultramicroscopy. 106 (11-12), 1053-1061 (2006).</li><li>Hughes, L. A., van Benthem, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Formation+of+SrTiO3+bicrystals+using+spark+plasma+sintering+techniques.">Formation of SrTiO3 bicrystals using spark plasma sintering techniques.</a> Scr. Mater. 118, 9-12 (2016).</li></ol>

The bonding temperature of 1,200 &#176;C was chosen to maximize diffusion as small changes in temperature can greatly impact the kinetics of all diffusion bonding mechanisms. A temperature of 1,200 &#176;C is outside the brittle-ductile transition temperature range of STO. However, the sample underwent brittle fracture at this temperature. The catastrophic failure of the STO bicrystal was not unexpected as STO has ~ 0.5% ductility at 1,200 &#176;C. Also, the sample was held at a pressure of 140 MPa throughout the heating...

Spark plasma sintering (SPS) is a technique in which application of high uniaxial pressure and pulsed direct current leads to the rapid densification of powder compacts1. This technique also leads to the successful formation of composite structures from various materials, including silicon nitride/silicon carbide, zirconium boride/silicon carbide, or silicon carbide, with no additional sintering aids required2,3,4,5. The synthesis of these composite structures by conventional hot-pressing had been challenging in the past. While application of a high uniaxial pressure and fast heating rate via the SPS technique enhances consolidation of powders and composites, the phenomenon causing this enhanced densification debated in the literature2,3,6,7. There also exists only limited information regarding the influence of electric fields on grain boundary formation and the resulting atomic structures of grain boundary cores8,9. These core structures determine the functional properties of SPS sintered materials, including electric breakdown of high voltage capacitors and the mechanical strength and toughness of ceramic oxides10. Therefore, understanding the fundamental grain boundary structure as a function of SPS processing parameters, such as applied current, is necessary for the manipulation of a material&#39;s overall physical properties. One method to systematically elucidate the fundamental physical mechanisms underpinning SPS is the formation of specific grain boundary structures, i.e., bicrystals. A bicrystal is created by manipulation of two single crystals, which are then diffusion bonded with specific misorientation angles11. This method provides a controlled way to investigate the fundamental grain boundary core structures as a function of processing parameters, dopant concentration, and impurity segregation12,13,14.
Diffusion bonding is dependent on four parameters: temperature, time, pressure, and bonding atmosphere15. Conventional diffusion bonding of strontium titanate (SrTiO3, STO) bicrystals typically occurs at a pressure below 1 MPa, within a temperature range of 1,400-1,500 &#176;C, and time scales ranging from 3 to 20 hours13,14,16,17. In this study, bonding in a SPS apparatus is achieved at significantly lower temperature and time scales in comparison to conventional methods. For polycrystalline materials, reduced temperature and time scales via SPS significantly limits grain growth, thereby providing advantageous control of a material&#39;s properties through manipulation of its microstructure.
The SPS apparatus, for a 5&#215;5 mm2 sample, exerts a minimum pressure of 140 MPa. Within the conventional diffusion bonding temperature range, Hutt et al. report instantaneous fracture of STO when the bonding pressure exceeds 10 MPa18. However, STO exhibits temperature dependent plasticity behavior, indicating bonding pressure can exceed 10 MPa at specific temperatures. Above 1,200 &#176;C and below 700 &#176;C, STO exhibits some ductility, at which stresses greater than 120 MPa can be applied without instantaneous fracture of the sample. Within the intermediate temperature range of 700-1,200 &#176;C, STO is brittle and experiences instantaneous fracture at stresses greater than 10 MPa. At 800 &#176;C, STO has minor deformability prior to fracture at stresses less than 200 MPa19,20,21. Hence, bonding temperatures for STO bicrystal formation via SPS apparatus must be selected according to the plasticity behavior of the material.

<table border="0" cellpadding="0" cellspacing="0" width="1429">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:373px;">Strontium titanate single crystal (100)</td>
			<td style="width:187px;">MTI Corporation</td>
			<td style="width:427px;">STOa101005S1-JP</td>
			<td style="width:443px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:373px;">Buffered oxide etch, hyrofluoric acid 6:1</td>
			<td style="width:187px;">JT Baker</td>
			<td style="width:427px;">&#160;MBI 1178-03</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:373px;">Scanning electron microscope (SEM)</td>
			<td style="width:187px;">FEI</td>
			<td>Model: 430 NanoSEM</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">SPS apparatus&#160;</td>
			<td>Sumitomo Coal Mining Co</td>
			<td>Model: Dr. Sinter 5000 SPS Apparatus</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">High Temperature Furnace</td>
			<td>Thermolyne</td>
			<td>Model: 41600</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Ultrasonic Cleaner</td>
			<td>Bransonic</td>
			<td>Model: 221</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:373px;">Mechanical polisher</td>
			<td style="width:187px;">Allied High Tech Products</td>
			<td>15-2100-TEM</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:373px;">Diamond lapping film</td>
			<td style="width:187px;">3M</td>
			<td>660XV&#160;</td>
			<td>1 um to 9 um Grit Size</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:373px;">Diamond lapping film</td>
			<td style="width:187px;">3M</td>
			<td style="width:427px;">661X</td>
			<td>0.5 um to 0.1 um Grit Size</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:373px;">Colloidal silica</td>
			<td style="width:187px;">Allied High Tech Products</td>
			<td>180-20000</td>
			<td>.05 um Grit Size</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:373px;">Sputter coater</td>
			<td style="width:187px;">QuorumTech</td>
			<td>Model: Q150RES</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Focused ion beam (FIB) instrument&#160;</td>
			<td style="width:187px;">FEI</td>
			<td>Model: Scios dual-beamed focused ion beam (FIB) instrument&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Nanomill TEM specimen preparation system</td>
			<td style="width:187px;">Fischione Instruments</td>
			<td>Model: 1040</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Transmission electron microscope (TEM)&#160;</td>
			<td style="width:187px;">JEOL</td>
			<td>Model: JEM2500 SE&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Scanning transmission electron microscope (STEM)</td>
			<td style="width:187px;">FEI</td>
			<td>Model: TEAM 0.5&#160;</td>
			<td></td>
		</tr>
	</tbody>
</table>

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.

Bonding temperature, time, and misorientation angle were all altered to determine optimum parameters needed for the maximum possible bonded interface fraction of the STO bicrystal (Table 1). The interface was considered &#39;bonded&#39; when the grain boundary was not visible during SEM imaging (Figure 2a). A &#39;non-bonded&#39; interface was exhibited when a dark image contrast or voids were present at the boundary location (Figure 2b)....

Watch this Scientific Journal Video about Spark Plasma Sintering Apparatus Used for the Formation of Strontium Titanate Bicrystals at JoVE.com

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

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 ...

The goal of this procedure is to form strontium titanate bicrystals using a Spark Plasma Sintering apparatus in order to create grain boundary structures with well defined misorientations as a function of processing parameters, such as high pressure and heating rate. We need to understand whether grain boundaries generated during SPS are different from those produced during more traditional ceramic processing techniques. This will then help us generate new ceramic materials with unprecedented properties.The main advantage of this technique is to form specific grain boundaries with well defined misorientations for the systematic understanding of microstructure formation during spark plasma sintering. To begin sample preparation, use a diamond wire saw to cut five millimeter by five millimeter pieces of a strontium titanate single crystal with a 1-0-0 plane surface polished to a mirror finish. Clean the samples with an ultrasonic cleaner in baths of acetone, isopropanol, and methanol for 15 minutes each at 50 to 60 Hertz.Heat a hot plate to 200 degrees Celsius during the cleaning. Upon completing the ultrasonic cleaning in methanol, immediately place the samples on the hot plate to dry. Etch the samples in a six to one solution of ammonium fluoride and 49%hydrofluoric acid for 10 minutes.Rinse the etched samples in deionized water and isopropanol in sequence. Dry the samples with filtered dry air. Discard any samples that developed a rainbow patina on the optically flat side.First, place a 30 millimeter circle of graphite paper on a 30 millimeter diameter graphite plunger. Then, stack two STO single crystal samples with their optically flat sides facing each other on the center of the paper covered plunger. Rotate the top single crystal around the 1-0-0 axis to the desired misorientation angle.Carefully slide a 30 millimeter diameter graphite die over the crystals and plunger. Insert another 30 millimeter circle of graphite paper and plunger into the die on top of the crystal stack. Place the assembly on the lower graphite spacer of the SPS apparatus.And then place the other graphite spacer on top of the assembly. Use the z-axis control buttons to bring the upper punch down to apply a three kilonewton uniaxial force to the assembly. Insert a K type thermocouple into the side of the graphite die to reach the sample.Set the chamber pressure to approximately 10 Pascal. Then on the instrument program control, set the bond temperature, time, and heating rates for the experiment. Select sinter conditions of a DC pulse of 12 seconds on, two seconds off, and then start the sintering program.Once the program ends, allow the sample to cool to 150 degrees Celsius. Transfer the gray black reduced sample to a high temperature furnace. Anneal the sample at 1200 degrees Celsius for 140 hours in air at ambient pressure to obtain the off-white oxidized bicrystal.Use a diamond wire saw to slice the bicrystal into five millimeter by one millimeter pieces. Polish the cross-sections with decreasing grit sizes of diamond lapping film until the scratches are uniform at the smallest grit size. Then start a two minute polish of the cross-sections with continuously poured colloidal silica and a matte cloth.15 seconds before polishing ends, switch from pouring colloidal silica to pouring DI water onto the platen. Immediately rinse the polish sample in DI water for one minute. Clean the polished sample in consecutive ultrasonic cleaning baths of acetone, isopropanol, and methanol for 15 minutes each.Immediately after cleaning, dry the sample on a hot plate at 200 degrees Celsius. Melt the clean sample polished side up on a sample stub coated with colloidal graphite. Sputter coat the sample surface with two to three nanometers of carbon.First, place the focused ion beam copper grid in consecutive ultrasonic cleaner baths of acetone and isopropanol for one hour. Then, plasma clean the copper grid for 10 minutes. Place the STO bicrystal sample and the clean copper grid in the FIB apparatus with the sample stage set at seven millimeters.In the FIB instrument software, identify a region of interest along the grain boundary. Navigate to patterning control and select the rectangle patterning tool with the CE depth surface application for electron beam deposition of carbon. Insert the carbon gas injection needle and deposit a 15 by two by two micrometers cubed protective layer of carbon over the region of interest.Then, retract the injection needle. Return to patterning control and choose the rectangle patterning tool with a W dep application for ion beam deposition of tungsten. Insert the tungsten gas injection needle and deposit a protective layer of tungsten of the same dimensions over the region of interest.Retract the injection needle. In patterning control, select the regular cross section patterning tool with the silicon application property. Mill a 22 by 27 by 15 micrometer cubed trench above the protected ROI and a 22 by 25 by 15 micrometer cubed trench below the ROI.Then, in patterning control, use the silicon clean cross section patterning tool to clean the trenched lamella surface. Next, use the silicon rectangle patterning tool to cut a two micrometer wide J pattern with two micrometer wide rectangles into the sample. Switch to the easy lift dialog box and set the micromanipulator to the park position.Lower the micromanipulator and weld the sample to the tip of the micromanipulator by tungsten deposition. Then, extend the J patten into a U pattern. Lift the lamella from the bulk sample and rotate the micromanipulator 180 degrees to set the grain boundary perpendicular to the ion beam.Tungsten welds with a lamella to the copper grid. Then, cut the micromanipulator free from the lamella using the rectangle patterning tool. Deposit a 15 by two by four micrometer cubed layer of carbon and a 15 by two by eight micrometer cubed layer of tungsten over the area of interest.Then, with the ion beam, thin the sample first to approximately 200 nanometers with a cleaning cross section pattern. And then, with a rectangle pattern, thin the sample to electron transparency. Remove the copper FIB grid from the FIB apparatus and place the grid onto a NanoMil sample holder.Then place the sample holder into the NanoMil apparatus. Using the NanoMil apparatus software, mil the sample at 500 electron volts for 10 minutes to remove amorphous damage caused by the FIB. Place the cleaned TEM sample in a sample holder and insert the sample and holder into the STEM.In the STEM software, use the capture tool to obtain an image of the sample grain boundary. Strontium titanate bicrystals were formed from single crystal pairs at various misorientation angles using a Spark Plasma Sintering apparatus. The interface was considered to be bonded wherever the grain boundary was not observable in SEM imaging.Areas of dark contrast in the images are either attributed to voids or colloidal graphite diffusion between the single crystals. The maximum bonded interface fraction was achieved with zero degrees of misorientation, a bonding temperature of 600 or 700 degrees Celsius, a bonding duration of 90 minutes, and an annealing time of 100 hours. Increasing the angle of misorientation to approximately 45 degrees necessitated a higher bonding temperature and a longer annealing time to achieve a 45%bonded interface.High resolution TEM and high angle annular dark field STEM show an atomically abrupt grain boundary with no observed second phases or intergranular film. Electron energy loss spectroscopy at the interface showed decreased crystal field splitting of the titanium L2 and L3 edges and decreased intensity in the oxygen K edge compared to the bulk crystal, suggesting a greater concentration of oxygen vacancies at the interface. Following the same procedure, we can also form doped grain boundaries using the SPS.This will help us to address whether the electric field will change grain boundary segregation. After watching this video, you should have a good understanding of how to form bicrystals with atomically abrupt interface structures using SPS. Don't forget that hydrofluoric acid can be extremely hazardous and precautions, such as personal protective wear, should be taken.

spark-plasma-sintering-apparatus-used-for-formation-strontium

Research

JoVE Journal

Engineering

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 ...

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.

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 ...

Characterization of Recombination Effects in a Liquid Ionization Chamber Used for the Dosimetry of a Radiosurgical Accelerator

Most modern radiation therapy devices allow the use of very small fields, either through beamlets in Intensity-Modulated Radiation Therapy (IMRT) or via stereotactic radiotherapy where positioning accuracy allows delivering very high doses per fraction in a small volume of the patient. Dosimetric measurements on medical accelerators are conventionally realized using air-filled ionization chambers. However, in small beams these are subject to nonnegligible perturbation effects. This study focuses on liquid ionization chambers, which offer advantages in terms of spatial resolution and low fluence perturbation. Ion recombination effects are investigated for the microLion detector (PTW) used with the Cyberknife system (Accuray). The method consists of performing a series of water tank measurements at different source-surface distances, and applying corrections to the liquid detector readings based on simultaneous gaseous detector measurements. This approach facilitates isolating the recombination effects arising from the high density of the liquid sensitive medium and obtaining correction factors to apply to the detector readings. The main difficulty resides in achieving a sufficient level of accuracy in the setup to be able to detect small changes in the chamber response.

A growing number of radiation therapy devices offer the advantage of delivering the dose through very small beams to the tumor, allowing for increased conformity and higher doses per fraction. Many different detectors can be used for the dosimetry of these small fields. In the present study, the effect of ion recombination is investigated for a liquid ionization chamber using a stereotactic radiation therapy system.

Most modern radiation therapy devices allow the use of very small fields, either through beamlets in Intensity-Modulated Radiation Therapy (IMRT) or via ...

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 ...

Capillary-based Centrifugal Microfluidic Device for Size-controllable Formation of Monodisperse Microdroplets

Here, we demonstrate a simple method for the rapid production of size-controllable, monodisperse, W/O microdroplets using a capillary-based centrifugal microfluidic device. W/O microdroplets have recently been used in powerful methods that enable miniaturized chemical experiments. Therefore, developing a versatile method to yield monodisperse W/O microdroplets is needed. We have developed a method for generating monodisperse W/O microdroplets based on a capillary-based centrifugal axisymmetric co-flowing microfluidic device. We succeeded in controlling the size of microdroplets by adjusting the capillary orifice. Our method requires equipment that is easier-to-use than with other microfluidic techniques, requires only a small volume (0.1-1 &#181;l) of sample solution for encapsulation, and enables the production of hundreds of thousands number of W/O microdroplets per second. We expect this method will assist biological studies that require precious biological samples by conserving the volume of the samples for rapid quantitative analysis biochemical and biological studies.

Here, we demonstrate a simple production method for size-controllable, monodisperse, water-in-oil (W/O) microdroplets using a capillary-based centrifugal microfluidic device. This method requires only a small sample volume and enables high-yield production. We expect this method will be useful for rapid biochemical and cellular analyses.

Here, we demonstrate a simple method for the rapid production of size-controllable, monodisperse, W/O microdroplets using a capillary-based centrifugal ...

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 ...

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. ...

In Situ Synthesis of Gold Nanoparticles without Aggregation in the Interlayer Space of Layered Titanate Transparent Films

Combinations of metal oxide semiconductors and gold nanoparticles (AuNPs) have been investigated as new types of materials. The in situ synthesis of AuNPs within the interlayer space of semiconducting layered titania nanosheet (TNS) films was investigated here. Two types of intermediate films (i.e., TNS films containing methyl viologen (TNS/MV2+) and 2-ammoniumethanethiol (TNS/2-AET+)) were prepared. The two intermediate films were soaked in an aqueous tetrachloroauric(III) acid (HAuCl4) solution, whereby considerable amounts of Au(III) species were accommodated within the interlayer spaces of the TNS films. The two types of obtained films were then soaked in an aqueous sodium tetrahydroborate (NaBH4) solution, whereupon the color of the films immediately changed from colorless to purple, suggesting the formation of AuNPs within the TNS interlayer. When only TNS/MV2+ was used as the intermediate film, the color of the film gradually changed from metallic purple to dusty purple within 30 min, suggesting that aggregation of AuNPs had occurred. In contrast, this color change was suppressed by using the TNS/2-AET+ intermediate film, and the AuNPs were stabilized for over 4 months, as evidenced by the characteristic extinction (absorption and scattering) band from the AuNPs.

In Situ Synthesis of Gold Nanoparticles without Aggregation in the Interlayer Space of Layered Titanate Transparent Films

Here, we present a protocol for the in situ synthesis of gold nanoparticles (AuNPs) within the interlayer space of layered titanate films without the aggregation of AuNPs. No spectral change was observed even after 4 months. The synthesized material has expected applications in catalysis, photo-catalysis, and the development of cost-effective plasmonic devices.

Combinations of metal oxide semiconductors and gold nanoparticles (AuNPs) have been investigated as new types of materials. The in situ synthesis of AuNPs ...

A Novel Biaxial Testing Apparatus for the Determination of Forming Limit under Hot Stamping Conditions

The hot stamping and cold die quenching process is increasingly used to form complex shaped structural components of sheet metals. Conventional experimental approaches, such as out-of-plane and in-plane tests, are not applicable to the determination of forming limits when heating and rapid cooling processes are introduced prior to forming for tests conducted under hot stamping conditions. A novel in-plane biaxial testing system was designed and used for the determination of forming limits of sheet metals at various strain paths, temperatures, and strain rates after heating and cooling processes in a resistance heating uniaxial testing machine. The core part of the biaxial testing system is a biaxial apparatus, which transfers a uniaxial force provided by the uniaxial testing machine to a biaxial force. One type of cruciform specimen was designed and verified for the formability test of aluminum alloy 6082 using the proposed biaxial testing system. The digital image correlation (DIC) system with a high-speed camera was used for taking strain measurements of a specimen during a deformation. The aim of proposing this biaxial testing system is to enable the forming limits of an alloy to be determined at various temperatures and strain rates under hot stamping conditions.

This protocol proposes a novel biaxial testing system used on a resistance heating uniaxial tensile test machine in order to determine the forming limit diagram (FLD) of sheet metals under hot stamping conditions.

The hot stamping and cold die quenching process is increasingly used to form complex shaped structural components of sheet metals. Conventional ...

New Application of an Atmospheric Pressure Plasma Jet as a Neuro-protective Agent Against Glucose Deprivation-induced Injury of SH-SY5Y Cells

The atmospheric pressure plasma jet (APPJ) has attracted the attention of many researchers from multiple disciplines in recent years because its emissions include multiple types of reactive nitrogen species (RNS) and reactive oxygen species (ROS). Our previous study has shown the cytoprotective effect of the APPJ against oxidative stress-induced injuries. The aim of the present study is to provide a detailed in vitro treatment protocol regarding the neuroprotective applications of helium APPJs on glucose deprivation-induced injury in SH-SY5Y cells. The SH-SY5Y human neuroblastoma-derived cell line was maintained in RPMI 1640 medium supplemented with 15% fetal calf serum. The culture medium was then changed to RPMI 1640 without glucose before APPJ treatment. After a 1 h incubation in a cell incubator, cell viability was determined using Cell Counting Kit 8. The results showed that, compared to the glucose deprivation group, cells treated with APPJ exhibited significantly increased cell viability in a dose-dependent manner, with 8 s/well observed as an optimal dose. Meanwhile, helium flow had no effect on the glucose deprivation-induced cell impairment. Our results indicated that APPJ could be potentially used as a treatment method for the diseases in the central nervous system related to glucose deprivation. This protocol could also be used as a cytoprotective application for other cells with different impairments, but the cell culture and APPJ treatment conditions should be readjusted, and the treatment dose must be relatively low.

A protocol for the neuroprotective application of low-dose atmospheric pressure plasma treatment on glucose deprivation-induced SH-SY5Y injuries.

The atmospheric pressure plasma jet (APPJ) has attracted the attention of many researchers from multiple disciplines in recent years because its emissions ...