Name: electrospray deposition of uniform thickness ge23sb7s70 and as40s60 chalcogenide glass films
Uploaded: 2016-08-19T14:00:00
Description: Watch this Scientific Journal Video about Electrospray Deposition of Uniform Thickness Ge23Sb7S70 and As40S60 Chalcogenide Glass Films at JoVE.com

Funding for this work was provided by Defense Threat Reduction Agency contracts HDTRA1-10-1-0073: HDTRA1-13-1-0001.

Caution: Please consult Material Safety Data Sheets (MSDS) when working with these chemicals, and be aware of the other hazards such as high voltage, mechanical motion of the deposition system, and high temperatures of the hotplate and furnaces utilized.
Note: Begin this protocol with bulk chalcogenide glass, which is prepared by well-known melt-quench techniques 2.
1. Preparation of ChG Solutions
Note: Two solutions are utilized in this study, Ge<su...

<ol>
	<li>Novak, J., 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=Evolution+of+the+structure+and+properties+of+solution-based+Ge23Sb7S70+thin+films+during+heat+treatment.">Evolution of the structure and properties of solution-based Ge23Sb7S70 thin films during heat treatment.</a> Mat. Res. Bull. 48, 1250-1255 (2013).</li><li>Musgraves, J. D., 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=Comparison+of+the+optical,+thermal+and+structural+properties+of+Ge-Sb-S+thin+films+deposited+using+thermal+evaporation+and+pulsed+laser+deposition+techniques.">Comparison of the optical, thermal and structural properties of Ge-Sb-S thin films deposited using thermal evaporation and pulsed laser deposition techniques.</a> Acta Materiala. 59, 5032-5039 (2011).</li><li>Zha, Y., Waldmann, M., Arnold, C. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+review+on+solution+processing+of+chalcogenide+glasses+for+optical+components.">A review on solution processing of chalcogenide glasses for optical components.</a> Opt. Mat. Exp. 3 (9), 1259-1272 (2013).</li><li>Chiles, J., 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=Low-loss,+submicron+chalcogenide+integrated+photonics+with+chlorine+plasma+etching.">Low-loss, submicron chalcogenide integrated photonics with chlorine plasma etching.</a> Appl. Phys. Lett. 106, 11110 (2015).</li><li>Hu, J., 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=Demonstration+of+chalcogenide+glass+racetrack+microresonators.">Demonstration of chalcogenide glass racetrack microresonators.</a> Opt. Lett. 38 (8), 761-763 (2008).</li><li>Singh, V., 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=Mid-infrared+materials+and+devices+on+a+Si+platform+for+optical+sensing.">Mid-infrared materials and devices on a Si platform for optical sensing.</a> Sci. Technol. Adv. Mater. 15, 014603 (2014).</li><li>Novak, S., Johnston, D. E., Li, C., Deng, W., Richardson, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Deposition+of+Ge23Sb7S70+chalcogenide+glass+films+by+electrospray.">Deposition of Ge23Sb7S70 chalcogenide glass films by electrospray.</a> Thin Solid Films. 588, 56-60 (2015).</li><li>Kovalenko, M. V., Schaller, R. D., Jarzab, D., Loi, M. A., Talapin, D. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inorganically+functionalized+PbS-CdS+colloidal+nanocrystals:+integration+into+amorphous+chalcogenide+glass+and+luminescent+properties.">Inorganically functionalized PbS-CdS colloidal nanocrystals: integration into amorphous chalcogenide glass and luminescent properties.</a> J. Am. Chem. Soc. 134, 2457-2460 (2012).</li><li>Novak, S., 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=Incorporation+of+luminescent+CdSe/ZnS+core-shell+quantum+dots+and+PbS+quantum+dots+into+solution-derived+chalcogenide+glass+films.">Incorporation of luminescent CdSe/ZnS core-shell quantum dots and PbS quantum dots into solution-derived chalcogenide glass films.</a> Opt. Mat. Exp. 3 (6), 729-738 (2013).</li><li>Lu, C., Almeida, J. M. P., Yao, N., Arnold, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fabrication+of+uniformly+dispersed+nanoparticle-doped+chalcogenide+glass.">Fabrication of uniformly dispersed nanoparticle-doped chalcogenide glass.</a> Appl. Phys. Lett. 105, 261906 (2014).</li><li>Zhao, X. -. 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=Enhancement+of+the+performance+of+organic+solar+cells+by+electrospray+deposition+with+optimal+solvent+system.">Enhancement of the performance of organic solar cells by electrospray deposition with optimal solvent system.</a> Sol. Energ. Mat. Sol. C. 121, 119-125 (2014).</li><li>Novak, 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> Electrospray deposition of chalcogenide glass films for gradient refractive index and quantum dot incorporation [dissertation]. , (2015).</li><li>Tolansky, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=New+contributions+to+interferometry,+with+applications+to+crystal+studies.">New contributions to interferometry, with applications to crystal studies.</a> J. Sci. Instrum. 22 (9), 161-167 (1945).</li><li>Archer, R. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determination+of+the+properties+of+films+on+silicon+by+the+method+of+ellipsometry.">Determination of the properties of films on silicon by the method of ellipsometry.</a> J. Opt. Soc. Am. 52 (9), 970-977 (1962).</li><li>Hu, J., 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=Optical+loss+reduction+in+high-index-contrast+chalcogenide+glass+waveguides+via+thermal+reflow.">Optical loss reduction in high-index-contrast chalcogenide glass waveguides via thermal reflow.</a> Opt. Exp. 18 (2), 1469-1478 (2010).</li><li>Hu, J., 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=Exploration+of+waveguide+fabrications+from+thermally+evaporated+Ge-Sb-S+glass+films.">Exploration of waveguide fabrications from thermally evaporated Ge-Sb-S glass films.</a> Opt. Mater. 30, 1560-1566 (2008).</li><li>Song, S., Dua, J., Arnold, C. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Influence+of+annealing+conditions+on+the+optical+and+structural+properties+of+spin-coated+As2S3+chalcogenide+glass+thin+films.">Influence of annealing conditions on the optical and structural properties of spin-coated As2S3 chalcogenide glass thin films.</a> Opt. Exp. 18 (6), 5472-5480 (2010).</li><li>Deng, W., Klemic, J. F., Li, X., Reed, M. A., Gomez, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Increase+of+electrospray+throughput+using+multiplexed+microfabricated+sources+for+the+scalable+generation+of+monodisperse+droplets.">Increase of electrospray throughput using multiplexed microfabricated sources for the scalable generation of monodisperse droplets.</a> J. Aerosol. Sci. 37 (6), 696-714 (2006).</li></ol>

At the beginning of a uniform thickness film deposited with serpentine motion of the spray relative to the substrate, the film thickness profile is increasing. Once the distance travelled in the y-direction exceeds the diameter of the spray (upon arrival at the substrate), the flow rate becomes approximately equivalent for every point on the substrate, and thickness uniformity is achieved. To determine the appropriate deposition parameters of a uniform thickness electrosprayed film, theoretical film thickness, T, is util...

Chalcogenide glasses (ChGs) are well-known for their broad infrared transmission and amenability to uniform thickness, blanket film deposition 1-3. On-chip waveguides, resonators, and other optical components can then be formed from this film by lithography techniques, and then subsequent polymer coating to fabricate microphotonic devices 4-5. One key application that we seek to develop is small, inexpensive, highly sensitive chemical sensing devices operating in the mid-IR, where many organic species have optical signatures 6. Microphotonic chemical sensors can be deployed in harsh environments, such as near nuclear reactors, where exposure to radiation (gamma and alpha) is likely. Hence an extensive study of the modification of optical properties of the ChG electrospray materials is critical and will be reported in another paper. In this article, electrospray film deposition of ChGs is exhibited, as it is a method only recently applied to ChGs 7.
The existing film deposition methods can be categorized into two classes: vapor deposition techniques, such as thermal evaporation of bulk ChG targets, and solution-derived techniques, such as by spin-coating a solution of ChG dissolved in an amine solvent. Generally, solution-derived films tend to result in higher loss of the light signal due to the presence of residual solvent in the film matrix 3, but a unique advantage of solution-derived techniques over vapor deposition is the simple incorporation of nanoparticles (e.g., quantum dots or QDs) prior to spin-coating 8-10. However, aggregation of nanoparticles has been observed in spin-coated films 10. In addition, while vapor deposition and spin-coating approaches are well-suited to the formation of uniform thickness, blanket films, they do not lend themselves well to localized depositions, or engineered non-uniform thickness films. Furthermore, scale-up of spin-coating is difficult because of high material waste due to run-off from the substrate, and because it is not a continuous process 11.
In order to overcome some of the limitations of current ChG film deposition techniques, we have investigated the application of electrospray to the ChG materials system. In this process, an aerosol spray can be formed of the ChG solution by applying a high voltage electric field 7. Because it is a continuous process which is compatible with roll-to-roll processing, near 100% use of material is possible, which is an advantage over spin-coating. In addition, we have proposed that isolation of single QDs in the individual ChG aerosol droplets could lead to better QD dispersion, due to the charged droplets being spatially self-dispersing by Coulombic repulsion, combined with the quicker drying kinetics of the high surface area droplets that minimize the movement of QDs due to the increasing viscosity of the droplets while in-flight 7, 12. Finally, localized deposition is an advantage that can be utilized to fabricate GRIN coatings. Explorations of both QD incorporation and GRIN fabrication of ChG with electrospray are currently underway to be submitted as a future article.
In this publication, the flexibility of electrospray is demonstrated by both localized depositions and uniform thickness films. To investigate the suitability of the films for planar photonic applications, transmission Fourier transform infrared (FTIR) spectroscopy, surface quality, thickness, and refractive index measurements are utilized.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Ethanolamine</td>
			<td>Sigma-Aldrich</td>
			<td>411000-100ML</td>
			<td>99.5% purity</td>
		</tr>
		<tr>
			<td>Si wafer</td>
			<td>University Wafer</td>
			<td>1708</td>
			<td>Double side polished, undoped</td>
		</tr>
		<tr>
			<td>Syringe</td>
			<td>Sigma-Aldrich</td>
			<td>20788</td>
			<td>Hamilton 700 series, 50 microliter volume</td>
		</tr>
		<tr>
			<td>Syringe pump</td>
			<td>Chemyx</td>
			<td>Nanojet</td>
			<td></td>
		</tr>
		<tr>
			<td>CNC milling machine</td>
			<td>MIB instruments</td>
			<td>CNC 3020</td>
			<td></td>
		</tr>
		<tr>
			<td>Power supply</td>
			<td>Acopian</td>
			<td>P015HP4</td>
			<td>AC-DC power supply, 15 kV, 4 mA</td>
		</tr>
	</tbody>
</table>

electrospray deposition of uniform thickness ge23sb7s70 and as40s60 chalcogenide glass films

Solution-based electrospray film deposition, which is compatible with continuous, roll-to-roll processing, is applied to chalcogenide glasses. Two chalcogenide compositions are demonstrated: Ge23Sb7S70 and As40S60, which have both been studied extensively for planar mid-infrared (mid-IR) microphotonic devices. In this approach, uniform thickness films are fabricated through the use of computer numerical controlled (CNC) motion. Chalcogenide glass (ChG) is written over the substrate by a single nozzle along a serpentine path. Films were subjected to a series of heat treatments between 100 &#176;C and 200 &#176;C under vacuum to drive off residual solvent and densify the films. Based on transmission Fourier transform infrared (FTIR) spectroscopy and surface roughness measurements, both compositions were found to be suitable for the fabrication of planar devices operating in the mid-IR region. Residual solvent removal was found to be much quicker for the As40S60 film as compared to Ge23Sb7S70. Based on the advantages of electrospray, direct printing of a gradient refractive index (GRIN) mid-IR transparent coating is envisioned, given the difference in refractive index of the two compositions in this study.

A schematic representation of the serpentine path utilized to obtain uniform thickness films with single nozzle electrospray is shown in Figure 2. Figure 3 shows an example transmission FTIR spectrum of a partially-cured As40S60 film made with serpentine motion of the spray, as well as the spectrum of pure ethanolamine solvent. From the information that can be obtained from the FTIR spectra such as shown in Figure 3,...

Watch this Scientific Journal Video about Electrospray Deposition of Uniform Thickness Ge23Sb7S70 and As40S60 Chalcogenide Glass Films at JoVE.com

Electrospray Deposition of Uniform Thickness Ge23Sb7S70 and As40S60 Chalcogenide Glass Films

A method of uniform thickness solution-derived chalcogenide glass film deposition is demonstrated using computer numerical controlled motion of a single-nozzle electrospray.

Electrospray Deposition of Uniform Thickness Ge23Sb7S70 and As40S60 Chalcogenide Glass Films

Solution-based electrospray film deposition, which is compatible with continuous, roll-to-roll processing, is applied to chalcogenide glasses. Two ...

The overall goal of this investigation is to develop electrospray film deposition of chalcogenide glasses for mid-infrared photonic applications, and to explore the unique flexibility of this deposition method. The main advantages of this technique are that it allows localized deposition of material with the ability to fabricate an engineered film thickness profile. This makes it possible to create a spatially-varying compositional gradient.Due to these advantages electrospray can advance the field of chip-based mid-infrared chemical sensing devices by allowing more flexible device design. To set up the deposition process, first place the end of the needle into the chalcogenide glass. Draw the solution into the syringe by setting the syringe pump to Extract Mode at a slow rate, such as 150 microliters per hour to prevent the formation of bubbles.Set the working distance between the end of the nozzle and the top of the silicon substrate by using the computer numerical control in Manual Movement Mode. Place the silicon substrate on an aluminum plate connected to the power supply ground return. Then, dispense some liquid from the syringe, utilizing the syringe pump, to allow a small volume of liquid to coat the outside surface of the nozzle.Turn the hot plate on at a surface temperature of about 75 to 100 degrees Celsius. Wait for approximately two hours to allow a film of glass to dry on the nozzle surface. Connect the direct current or DC power supply to the syringe nozzle with an electrical clip.Set the flow rate at 10 micro-liters per hour and tune the DC voltage to form a stable Taylor cone. View the spray with a high magnification camera. Once the spray is stable, start computer numerical controlled motion of the spray over the substrate to deposit the film.Use a serpentine path for uniform thickness. Use passes with a distance longer than the width of the substrate, such that the spray moves completely off of the substrate before making the next pass. This ensures that the flow rate of liquid is the same at every point on the substrate.Alternatively, use one-dimensional passes for a linear thickness profile. Subject the deposited film to a series of heat treatments under vacuum as described in the text protocol. Take a transmission Fourier Transform InfraRed, or FTIR spectrum, periodically throughout the annealing conditions.To measure the same location on the sample each time, draw an outline of the substrate on the sample stage and place it within the south line each time a measurement is taken. In the FTIR software, click Experiment Setup and type in the number of scans as 64. Click to the Bench tab and type in the scan range as 7, 000 to 500 inverse centimeters.Take a background scan with just the sample stage in the instrument by clicking on Collect Background, then place the sample on the stage and click Collect Sample to take the spectrum of the sample. To track the removal of the solvent, estimate the size of the organic absorptions in the film matrix. In the FTIR software, draw a baseline in the spectral range of interest of approximately 2, 300 to 3, 600 inverse centimeters.The software calculates the area beneath the transmission spectrum of the sample relative to the baseline designated by the user. Scratch the film with fine point tweezers until the dark substrate becomes visible amongst the lighter colored film, which typically occurs in one scratching motion with light pressure. Remove debris caused by scratching with compressed nitrogen.Load the sample into a contact profilometer and measure the thickness of the blanket films to determine the step height from film to substrate. Open Measurement Setup and type in a scan rate of 0.1 millimeters per second and a scan length of 500 microns. Locate the scratch and rotate the sample, such that the scratch is oriented in the left to right direction.Move the state, such that the crosshairs are just below the scratch, and begin the surface scan by clicking Measurement. Once the scan is finished, drag the R and M cursors so that they are both on the film surface, and click Level Two Point Linear to level the surface profile. Move one cursor to the bottom of the scratch and write down the distance between each cursor position in the Y dimension.Measure the thickness as multiple locations to obtain an average thickness and variance in the data. Determine the thickness profiles of the non-uniform thickness films by scanning the profilometer across the entire film. Use this surface profile to create a graph of film thickness versus position.Scan across the entire film by entering an appropriate scan length greater than the width of the film, usually 10 to 20 millimeters, in Measurement Setup. Place the crosshairs on the uncoated substrate on one side of the film and click Measurement, allowing the profilometer to complete the scan on the uncoated substrate on the other side of the film. Right click on the surface profile and export as a csv file.Next, measure the surface roughness with a white-light interferometer. Adjust the focus and stage tilt to generate interference fringes over the entire measurement area using the 5X objective. Take five measurements across the uniform thickness film to determine the average roughness and variance of the data.Load the sample into an ellipsometer and measure the refractive index in the range of 600 to 1, 700 nanometers wavelength. In this case, use an angle of incidence of 60 degrees, and focus the beam to a spot size of 35 microns. Representative results of electrosprayed film properties are shown here.FTIR transmission spectra of pure ethanolamine solvent and a partially cured arsenic trisulfide film with residual ethanolamine showed the transparency of the films in mid-infrared and also the method by which the solvent peak absorption area is characterized. By characterizing the solvent peak absorption area, and film thickness throughout heat treatments, the evolution of solvent removal and film densification is demonstrated. Minimal residual solvent is achieved by vacuum annealing.Following deposition and heat treatment, electrosprayed films have a generally smooth appearance. On the left is a film with a uniform thickness region deposited with a serpentine path of the spray. On the right are films made with one-dimensional motion in order to achieve controlled non-uniform thickness profiles.One-dimensional motion allows linearly-sloped film thickness profiles with film thickness and coverage area controlled by the working distance of the spray. In conclusion, electrospray is the most treated as a method of infrared transparent chalcogenide glass fume deposition with the ability to make localized depositions with engineered non-uniform thickness profiles. Electrospray of chalcogenized glass is a new tool for the field of mid-infrared microphotonics, and it is envisioned that the additional flexibility allowed by this process will lead to novel device designs.

electrospray-deposition-uniform-thickness-ge23sb7s70-as40s60

Research

JoVE Journal

Engineering

Fabrication of Nano-engineered Transparent Conducting Oxides by Pulsed Laser Deposition

Nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas allows the deposition of metal oxides with tunable morphology, structure, density and stoichiometry by a proper control of the plasma plume expansion dynamics. Such versatility can be exploited to produce nanostructured films from compact and dense to nanoporous characterized by a hierarchical assembly of nano-sized clusters. In particular we describe the detailed methodology to fabricate two types of Al-doped ZnO (AZO) films as transparent electrodes in photovoltaic devices: 1) at low O2 pressure, compact films with electrical conductivity and optical transparency close to the state of the art transparent conducting oxides (TCO) can be deposited at room temperature, to be compatible with thermally sensitive materials such as polymers used in organic photovoltaics (OPVs); 2) highly light scattering hierarchical structures resembling a forest of nano-trees are produced at higher pressures. Such structures show high Haze factor (&gt;80%) and may be exploited to enhance the light trapping capability. The method here described for AZO films can be applied to other metal oxides relevant for technological applications such as TiO2, Al2O3, WO3 and Ag4O4.

We describe the experimental method to deposit nanostructured oxide thin films by nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas. By using this method Al-doped ZnO (AZO) films, from compact to hierarchically structured as nano-tree forests, can be deposited.

Nanosecond Pulsed  Laser Deposition (PLD) in the presence of a background gas allows the deposition  of metal oxides with tunable morphology, structure, ...

In-situ Tapering of Chalcogenide Fiber for Mid-infrared Supercontinuum Generation

Supercontinuum generation (SCG) in a tapered chalcogenide fiber is desirable for broadening mid-infrared (or mid-IR, roughly the 2-20 &mu;m wavelength range) frequency combs1, 2 for applications such as molecular fingerprinting, 3 trace gas detection, 4 laser-driven particle acceleration, 5 and x-ray production via high harmonic generation. 6 Achieving efficient SCG in a tapered optical fiber requires precise control of the group velocity dispersion (GVD) and the temporal properties of the optical pulses at the beginning of the fiber, 7 which depend strongly on the geometry of the taper. 8 Due to variations in the tapering setup and procedure for successive SCG experiments-such as fiber length, tapering environment temperature, or power coupled into the fiber, in-situ spectral monitoring of the SCG is necessary to optimize the output spectrum for a single experiment.
	In-situ fiber tapering for SCG consists of coupling the pump source through the fiber to be tapered to a spectral measurement device. The fiber is then tapered while the spectral measurement signal is observed in real-time. When the signal reaches its peak, the tapering is stopped. The in-situ tapering procedure allows for generation of a stable, octave-spanning, mid-IR frequency comb from the sub harmonic of a commercially available near-IR frequency comb. 9 This method lowers cost due to the reduction in time and materials required to fabricate an optimal taper with a waist length of only 2 mm.
	The in-situ tapering technique can be extended to optimizing microstructured optical fiber (MOF) for SCG10 or tuning of the passband of MOFs, 11 optimizing tapered fiber pairs for fused fiber couplers12 and wavelength division multiplexers (WDMs), 13 or modifying dispersion compensation for compression or stretching of optical pulses.14-16

In-situ Tapering of Chalcogenide Fiber for Mid-infrared Supercontinuum Generation

We describe a method for in-situ tapering of As2S3 fibers to achieve efficient mid-infrared supercontinuum generation. By tapering while monitoring the supercontinuum&#x2019;s spectrum, the spectral width can be maximized for a fiber taper. In-situ fiber tapering can be applied to optimize the performance of other fiber-based devices.

Supercontinuum  generation (SCG) in a tapered chalcogenide fiber is desirable for broadening mid-infrared  (or mid-IR, roughly the 2-20 &mu;m wavelength ...

Fabrication of Uniform Nanoscale Cavities via Silicon Direct Wafer Bonding

Measurements of the heat capacity and superfluid fraction of confined 4He have been performed near the lambda transition using lithographically patterned and bonded silicon wafers. Unlike confinements in porous materials often used for these types of experiments3, bonded wafers provide predesigned uniform spaces for confinement. The geometry of each cell is well known, which removes a large source of ambiguity in the interpretation of data.
Exceptionally flat, 5 cm diameter, 375 &#181;m thick Si wafers with about 1 &#181;m variation over the entire wafer can be obtained commercially (from Semiconductor Processing Company, for example). Thermal oxide is grown on the wafers to define the confinement dimension in the z-direction. A pattern is then etched in the oxide using lithographic techniques so as to create a desired enclosure upon bonding. A hole is drilled in one of the wafers (the top) to allow for the introduction of the liquid to be measured. The wafers are cleaned2 in RCA solutions and then put in a microclean chamber where they are rinsed with deionized water4. The wafers are bonded at RT and then annealed at ~1,100 &#176;C. This forms a strong and permanent bond. This process can be used to make uniform enclosures for measuring thermal and hydrodynamic properties of confined liquids from the nanometer to the micrometer scale.

A method for permanently bonding two silicon wafers so as to realize a uniform enclosure is described. This includes wafer preparation, cleaning, RT bonding, and annealing processes. The resulting bonded wafers (cells) have uniformity of enclosure ~1%1,2. The resulting geometry allows for measurements of confined liquids and gasses.

Measurements of the heat capacity and superfluid fraction of confined 4He have been performed near the lambda transition using lithographically patterned ...

Formation of Thick Dense Yttrium Iron Garnet Films Using Aerosol Deposition

Aerosol deposition (AD) is a thick-film deposition process that can produce layers up to several hundred micrometers thick with densities greater than 95% of the bulk. The primary advantage of AD is that the deposition takes place entirely at ambient temperature; thereby enabling film growth in material systems with disparate melting temperatures. This report describes in detail the processing steps for preparing the powder and for performing AD using the custom-built system. Representative characterization results are presented from scanning electron microscopy, profilometry, and ferromagnetic resonance for films grown in this system. As a representative overview of the capabilities of the system, focus is given to a sample produced following the described protocol and system setup. Results indicate that this system can successfully deposit 11 &#181;m thick yttrium iron garnet films that are &#160;&#62; 90% of the bulk density during a single 5 min deposition run. A discussion of methods to afford better control of the aerosol and particle selection for improved thickness and roughness variations in the film is provided.

This report describes the use of a custom-built system to perform aerosol deposition of thick films of yttrium iron garnet onto sapphire substrates at RT. The deposited films are characterized using scanning electron microscopy, profilometry, and ferromagnetic resonance to give a representative overview of the capabilities of the technique.

Aerosol deposition (AD) is a thick-film deposition process that can produce layers up to several hundred micrometers thick with densities greater than 95% ...

Production of Synthetic Nuclear Melt Glass

Realistic surrogate nuclear debris is needed within the nuclear forensics community to test and validate post-detonation analysis techniques. Here we outline a novel process for producing bulk surface debris using a high temperature furnace. The material developed in this study is physically and chemically similar to trinitite (the melt glass produced by the first nuclear test). This synthetic nuclear melt glass is assumed to be similar to the vitrified material produced near the epicenter (ground zero) of any surface nuclear detonation in a desert environment. The process outlined here can be applied to produce other types of nuclear melt glass including that likely to be formed in an urban environment. This can be accomplished by simply modifying the precursor matrix to which this production process is applied. The melt glass produced in this study has been analyzed and compared to trinitite, revealing a comparable crystalline morphology, physical structure, void fraction, and chemical composition.

A protocol for the production of synthetic nuclear melt glass, similar to trinitite, is presented.

Realistic surrogate nuclear debris is needed within the nuclear forensics community to test and validate post-detonation analysis techniques. Here we ...

Fabrication of Ultra-thin Color Films with Highly Absorbing Media Using Oblique Angle Deposition

Ultra-thin film structures have been studied extensively for use as optical coatings, but performance and fabrication challenges remain.&#160; We present an advanced method for fabricating ultra-thin color films with improved characteristics. The proposed process addresses several fabrication issues, including large area processing. Specifically, the protocol describes a process for fabricating ultra-thin color films using an electron beam evaporator for oblique angle deposition of germanium (Ge) and gold (Au) on silicon (Si) substrates.&#160; Film porosity produced by the oblique angle deposition induces color changes in the ultra-thin film. The degree of color change depends on factors such as deposition angle and film thickness. Fabricated samples of the ultra-thin color films showed improved color tunability and color purity. In addition, the measured reflectance of the fabricated samples was converted into chromatic values and analyzed in terms of color. Our ultra-thin film fabricating method is expected to be used for various ultra-thin film applications such as flexible color electrodes, thin film solar cells, and optical filters. Also, the process developed here for analyzing the color of the fabricated samples is broadly useful for studying various color structures.

We present a detailed method for fabricating ultra-thin color films with improved characteristics for optical coatings. The oblique angle deposition technique using an electron beam evaporator allows improved color tunability and purity. Fabricated films of Ge and Au on Si substrates were analyzed by reflectance measurements and color information conversion.

Ultra-thin film structures have been studied extensively for use as optical coatings, but performance and fabrication challenges remain.&#160; We present ...

Production of Single Tracks of Ti-6Al-4V by Directed Energy Deposition to Determine the Layer Thickness for Multilayer Deposition

Directed Energy Deposition (DED), which is an additive manufacturing technique, involves the creation of a molten pool with a laser beam where metal powder is injected as particles. In general, this technique is employed to either fabricate or repair different components. In this technique, the final characteristics are affected by many factors. Indeed, one of the main tasks in building components by DED is the optimization of process parameters (such as laser power, laser speed, focus, etc.) which is usually carried out through an extensive experimental investigation. However, this sort of experiment is extremely lengthy and costly. Thus, in order to accelerate the optimization process, an investigation was conducted to develop a method based on the melt pool characterizations. In fact, in these experiments, single tracks of Ti-6Al-4V were deposited by a DED process with multiple combinations of laser power and laser speed. Surface morphology and dimensions of single tracks were analyzed, and geometrical characteristics of melt pools were evaluated after polishing and etching the cross-sections. Helpful information regarding the selection of optimal process parameters can be achieved by examining the melt pool features. These experiments are being extended to characterize the larger blocks with multiple layers. Indeed, this manuscript describes how it would be possible to quickly determine the layer thickness for the massive deposition, and avoid over or under-deposition according to the calculated energy density of the optimum parameters. Apart from the over or under-deposition, time and materials saving are the other great advantages of this approach in which the deposition of multilayer components can be started without any parameter optimization in terms of layer thickness.

In this research, a rapid method based on melt pool characterization is developed to estimate the layer thickness of Ti-6Al-4V components produced by directed energy deposition.

Directed Energy Deposition (DED), which is an additive manufacturing technique, involves the creation of a molten pool with a laser beam where metal ...

Atomic Layer Deposition of Vanadium Dioxide and a Temperature-dependent Optical Model

Vanadium dioxide is a material that has a reversible metal-insulator phase change near 68 &#176;C. To grow VO2 on a wide variety of substrates, with wafer-scale uniformity and angstrom level control of thickness, the method of atomic-layer deposition was chosen. This ALD process enables high-quality, low-temperature (&#8804;150 &#176;C) growth of ultrathin films (100-1000 &#197;) of VO2. For this demonstration, the VO2 films were grown on sapphire substrates. This low temperature growth technique produces mostly amorphous VO2 films. A subsequent anneal in an ultra-high vacuum chamber with a pressure of 7x10-4 Pa of ultra-high purity (99.999%) oxygen produced oriented, polycrystalline VO2 films. The crystallinity, phase, and strain of the VO2 were determined by Raman spectroscopy and X-ray diffraction, while the stoichiometry and impurity levels were determined by X-ray photoelectron spectroscopy, and finally the morphology was determined by atomic force microscopy. These data demonstrate the high-quality of the films grown by this technique. A model was created to fit to the data for VO2 in its metallic and insulating phases in the near infrared spectral region. The permittivity and refractive index of the ALD VO2 agreed well with the other fabrication methods in its insulating phase, but showed a difference in its metallic state. Finally, the analysis of the films&#39; optical properties enabled the creation of a wavelength- and temperature-dependent model of the complex optical refractive index for developing VO2 as a tunable refractive index material.

Thin films (100-1000 &#197;) of vanadium dioxide (VO2) were created by atomic-layer deposition (ALD) on sapphire substrates. Following this, the optical properties were characterized through the metal-insulator transition of VO2. From the measured optical properties, a model was created to describe the tunable refractive index of VO2.

Vanadium dioxide is a material that has a reversible metal-insulator phase change near 68 &#176;C. To grow VO2 on a wide variety of substrates, with ...

Plasma-Assisted Molecular Beam Epitaxy Growth of Mg3N2 and Zn3N2 Thin Films

This article describes a procedure for growing Mg3N2 and Zn3N2 films by plasma-assisted molecular beam epitaxy (MBE). The films are grown on 100 oriented MgO substrates with N2 gas as the nitrogen source. The method for preparing the substrates and the MBE growth process are described. The orientation and crystalline order of the substrate and film surface are monitored by the reflection high energy electron diffraction (RHEED) before and during growth. The specular reflectivity of the sample surface is measured during growth with an Ar-ion laser with a wavelength of 488 nm. By fitting the time dependence of the reflectivity to a mathematical model, the refractive index, optical extinction coefficient, and growth rate of the film are determined. The metal fluxes are measured independently as a function of the effusion cell temperatures using a quartz crystal monitor. Typical growth rates are 0.028 nm/s at growth temperatures of 150 &#176;C and 330 &#176;C for Mg3N2 and Zn3N2 films, respectively.

Plasma-Assisted Molecular Beam Epitaxy Growth of Mg3N2 and Zn3N2 Thin Films

This article describes the growth of epitaxial films of Mg3N2 and Zn3N2 on MgO substrates by plasma-assisted molecular beam epitaxy with N2 gas as the nitrogen source and optical growth monitoring.

This article describes a procedure for growing Mg3N2 and Zn3N2 films by plasma-assisted molecular beam epitaxy (MBE). The films are grown on 100 oriented ...

Procedure for the Transfer of Polymer Films Onto Porous Substrates with Minimized Defects

The fabrication of devices containing thin film composite membranes necessitates the transfer of these films onto the surfaces of arbitrary support substrates. Accomplishing this transfer in a highly controlled, mechanized, and reproducible manner can eliminate the creation of macroscale defect structures (e.g., tears, cracks, and wrinkles) within the thin film that compromise device performance and the usable area per sample. Here, we describe a general protocol for the highly controlled and mechanized transfer of a polymeric thin film onto an arbitrary porous support substrate for eventual use as a water filtration membrane device. Specifically, we fabricate a block copolymer (BCP) thin film on top of a sacrificial, water-soluble poly(acrylic acid) (PAA) layer and silicon wafer substrate. We then utilize a custom-designed, 3D-printed transfer tool and drain chamber system to deposit, lift-off, and transfer the BCP thin film onto the center of a porous anodized aluminum oxide (AAO) support disc. The transferred BCP thin film is shown to be consistently placed onto the center of the support surface due to the guidance of the meniscus formed between the water and the 3D-printed plastic drain chamber. We also compare our mechanized transfer-processed thin films to those that have been transferred by hand with the use of tweezers. Optical inspection and image analysis of the transferred thin films from the mechanized process confirm that little-to-no macroscale inhomogeneities or plastic deformations are produced, as compared to the multitude of tears and wrinkles produced from manual transfer by hand. Our results suggest that the proposed strategy for thin film transfer can reduce defects when compared to other methods across many systems and applications.

We present a procedure for highly controlled and wrinkle-free transfer of block copolymer thin films onto porous support substrates using a 3D-printed drain chamber. The drain chamber design is of general relevance to all procedures involving transfer of macromolecular films onto porous substrates, which is normally done by hand in an irreproducible fashion.

The fabrication of devices containing thin film composite membranes necessitates the transfer of these films onto the surfaces of arbitrary support ...