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...

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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.

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	<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 ...

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