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, Ge23Sb7S70 and As40S60, both dissolved in ethanolamine at a concentration of 0.05 g/ml. The preparation of the two solutions are identical. Perform all steps in this section inside of a fume hood.
<ol>
	<li>Crush the bulk glass into a fine powder using a mortar and pestle.</li>
	<li>Mix 0.25 g of the glass with 5 ml of ethanolamine solvent.</li>
	<li>Allow 1-2 days for complete dissolution of the glass. Expedite dissolution by heating the solution on a hotplate with a surface temperature of ~50-75 &#176;C. Increase the rate of dissolution by stirring the mixture, such as with a magnetic stirring bar.</li>
	<li>Filter solution into a vial with 0.45 &#181;m polytetrafluoroethylene (PTFE) filter to remove any large precipitates from the solution.</li>
</ol>
2. Setting up the Deposition Process
Note: The electrospray deposition system is depicted schematically in Figure 1. In this process, a 50 &#181;l glass syringe with PTFE-tipped plunger is utilized. The syringe is a removable needle style with a cone-tipped, 22 gauge outer diameter needle (0.72 mm outer diameter, 0.17 mm inner diameter), and is connected to the vertically oriented syringe pump of the electrospray system. The electrospray system is exposed to ambient atmosphere in these initial experiments, though the system is set-up inside of a glovebox. The system should be set-up in a location where it is isolated from the user, such as a fume hood.
<ol>
	<li>Place the end of the needle into the ChG solution. Draw the solution into the syringe by setting the syringe pump in extract mode at a slow rate, such as 150 &#181;l/hr, to prevent the formation of bubbles.</li>
	<li>Set the working distance (10 mm in this case) between the end of the nozzle and the top of the Si substrate by using the CNC in manual movement mode. Place the Si substrate, which is undoped and has a resistivity of 10,000 Ohm-cm, on an aluminum plate connected to the power supply ground return.</li>
	<li>Allow a small volume of liquid to coat the outside surface of the nozzle by dispensing some liquid from the syringe utilizing the syringe pump. Turn hotplate on at a surface temperature of about 75-100 &#176;C. Wait for ~2 hr to allow a film of glass to dry on the nozzle surface. This coating aids the stability of the spray.</li>
</ol>
3. Electrospray Deposition of ChG Films
<ol>
	<li>Connect the direct current (DC) power supply to the syringe nozzle with an electrical clip.</li>
	<li>Set flow rate at 10 &#181;l/hr, and tune DC voltage to form a stable Taylor cone (~4 kV at 10 mm working distance). View the spray with a high magnification camera.</li>
	<li>Start CNC motion of the spray over the substrate to deposit film, once the spray is stable.
	<ol>
		<li>Use a serpentine path for uniform thickness, or one-dimensional (1-D) passes for a linear thickness profile.</li>
		<li>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 is done so that the flow rate of liquid is the same at every point on the substrate.</li>
		<li>Control the CNC using LinuxCNC software. For an example, use the supplementary G-code for a serpentine path with 0.5 mm offset between passes, velocity of 20 mm/min, and 30 mm length of the passes. Figure 1 shows a schematic of a film made with the serpentine path and also defines the coordinate system.</li>
	</ol>
	</li>
	<li>Subject the deposited film to a series of heat treatments under vacuum for 1 hr each at 100, 125, 150 and 175 &#176;C, and 16 hr at 200 &#176;C. An optimization of the heat treatment parameters is presented in the Representative Results section of this article.</li>
</ol>
4. Characterization of the ChG Films
<ol>
	<li>Characterization of Residual Solvent Removal
	<ol>
		<li>Take a transmission FTIR spectrum periodically throughout the annealing conditions, measuring the same location on the sample each time. Draw an outline of the substrate on the sample stage, and place it within this outline each time a measurement is taken.
		<ol>
			<li>In the FTIR software, click &#34;Experiment Setup,&#34; and type in the number of scans as 64. Click to the &#34;Bench&#34; tab and type in the scan range as 7,000 cm-1 to 500 cm-1. Take a background scan with just the sample stage in the instrument by clicking on &#34;Collect Background.&#34; Then place the sample on the stage, and click &#34;Collect Sample&#34; to take the spectrum of the sample.</li>
		</ol>
		</li>
		<li>To track the removal of 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, approximately 2,300-3,600 cm-1. The software calculates the area beneath the transmission spectrum of the sample, relative to the baseline designated by the user.</li>
	</ol>
	</li>
	<li>Measurement of Film Thickness
	<ol>
		<li>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.
		<ol>
			<li>Measure the thickness of blanket films by using a contact profilometer to determine the step height from film to substrate. Open &#34;Measurement Setup,&#34; and type in scan rate of 0.1 mm/sec, and scan length of 500 &#181;m.</li>
			<li>Place sample on stage, locating the scratch and rotating the sample such that the scratch is oriented in the left-right direction. Move the stage such that the cross-hairs are just below the scratch, and begin the surface scan by clicking &#34;Measurement.&#34;</li>
			<li>Once the scan is finished, drag the R and M cursors so that they are both on the film surface, and click &#34;Level Two Point Linear&#34; 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 thickness at multiple locations to obtain an average thickness and variance in the data.</li>
		</ol>
		</li>
		<li>Determine the thickness profiles of the non-uniform thickness films by scanning the profilometer across the entire film (perpendicular to the 1-D motion used to deposit the film), and use this surface profile to create a graph of film thickness vs. position.
		<ol>
			<li>Scan across the entire film by entering an appropriate scan length greater than the width of the film, usually 10-20 mm, in &#34;Measurement Setup.&#34; Place the cross-hairs on uncoated substrate on one side of the film and click &#34;Measurement,&#34; allowing the profilometer to complete the scan on uncoated substrate on the other side of the film. Right click on the surface profile and export as a .csv file.</li>
			<li>Alternatively, if the substrate is not flat enough to obtain reliable thickness data, scratch the film down to the substrate with about 1 mm between scratches, and scan profilometer across entire film. Write down the thickness and horizontal position at each scratch, and create a graph of film thickness vs. position from these data points.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Measure surface roughness with a white-light interferometer 13. Adjust the focus and stage tilt to generate interference fringes over the entire measurement area, which in this case was 414 &#181;m x 414 &#181;m using the 5x objective. Take five measurements across the uniform thickness film to determine the average roughness and variance of the data.</li>
	<li>Measure the refractive index with an ellipsometer 14 in the range of 600-1,700 nm wavelength. In this case, use an angle of incidence of 60&#176;, and focus the beam to a spot size of 35 &#181;m.
	<ol>
		<li>Take a measurement on the uncoated substrate, fitting the data to determine the thickness of the native oxide layer. Use this information to model the sample as a three layer system: Si wafer + native oxide + deposited film. Take eight measurements at different locations on the sample to determine the average refractive index and variance, while using the Cauchy model to fit the data.</li>
	</ol>
	</li>
</ol>

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The authors have nothing to disclose.

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><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 ...

electrospray-deposition-uniform-thickness-ge23sb7s70-as40s60

Research

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Engineering

8.5K Views.  Clemson University. A method of uniform thickness solution-derived chalcogenide glass film deposition is demonstrated using computer numerical controlled motion of a single-nozzle electrospray.

Video: Electrospray Deposition of Uniform Thickness Ge23Sb7S70 and As40S60 Chalcogenide Glass Films

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% ...

Improved Heterojunction Quality in Cu2O-based Solar Cells Through the Optimization of Atmospheric Pressure Spatial Atomic Layer Deposited Zn1-xMgxO

Atmospheric pressure spatial atomic layer deposition (AP-SALD) was used to deposit n-type ZnO and Zn1-xMgxO thin films onto p-type thermally oxidized Cu2O substrates outside vacuum at low temperature. The performance of photovoltaic devices featuring atmospherically fabricated ZnO/Cu2O heterojunction was dependent on the conditions of AP-SALD film deposition, namely, the substrate temperature and deposition time, as well as on the Cu2O substrate exposure to oxidizing agents prior to and during the ZnO deposition. Superficial Cu2O to CuO oxidation was identified as a limiting factor to heterojunction quality due to recombination at the ZnO/Cu2O interface. Optimization of AP-SALD conditions as well as keeping Cu2O away from air and moisture in order to minimize Cu2O surface oxidation led to improved device performance. A three-fold increase in the open-circuit voltage (up to 0.65 V) and a two-fold increase in the short-circuit current density produced solar cells with a record 2.2% power conversion efficiency (PCE). This PCE is the highest reported for a Zn1-xMgxO/Cu2O heterojunction formed outside vacuum, which highlights atmospheric pressure spatial ALD as a promising technique for inexpensive and scalable fabrication of Cu2O-based photovoltaics.

Improved Heterojunction Quality in Cu2O-based Solar Cells Through the Optimization of Atmospheric Pressure Spatial Atomic Layer Deposited Zn1-xMgxO

Here we present a protocol for synthesizing Zn1-xMgxO/Cu2O heterojunctions in open-air at low temperature via atmospheric pressure spatial atomic layer deposition (AP-SALD) of Zn1-xMgxO on cuprous oxide. Such high quality conformal metal oxides can be grown on a variety of substrates including plastics by this cheap and scalable method.

Atmospheric pressure spatial atomic layer deposition (AP-SALD) was used to deposit n-type ZnO and Zn1-xMgxO thin films onto p-type thermally oxidized Cu2O ...

Chemistry

Preparation of Macroporous Epitaxial Quartz Films on Silicon by Chemical Solution Deposition

This work describes the detailed protocol for preparing piezoelectric macroporous epitaxial quartz films on silicon(100) substrates. This is a three-step process based on the preparation of a sol in a one-pot synthesis which is followed by the deposition of a gel film on Si(100) substrates by evaporation induced self-assembly using the dip-coating technique and ends with a thermal treatment of the material to induce the gel crystallization and the growth of the quartz film. The formation of a silica gel is based on the reaction of a tetraethyl orthosilicate and water, catalyzed by HCl, in ethanol. However, the solution contains two additional components that are essential for preparing mesoporous epitaxial quartz films from these silica gels dip-coated on Si. Alkaline earth ions, like Sr2+ act as glass melting agents that facilitate the crystallization of silica and in combination with cetyl trimethylammonium bromide (CTAB) amphiphilic template form a phase separation responsible of the macroporosity of the films. The good matching between the quartz and silicon cell parameters is also essential in the stabilization of quartz over other SiO2 polymorphs and is at the origin of the epitaxial growth.

A protocol is presented for the preparation of piezoelectric macroporous epitaxial films of quartz on silicon by solution chemistry using dip-coating and thermal treatments in air.

This work describes the detailed protocol for preparing piezoelectric macroporous epitaxial quartz films on silicon(100) substrates. This is a three-step ...

Epitaxial Growth of Perovskite Strontium Titanate on Germanium via Atomic Layer Deposition

Atomic layer deposition (ALD) is a commercially utilized deposition method for electronic materials. ALD growth of thin films offers thickness control and conformality by taking advantage of self-limiting reactions between vapor-phase precursors and the growing film. Perovskite oxides present potential for next-generation electronic materials, but to-date have mostly been deposited by physical methods. This work outlines a method for depositing SrTiO3 (STO) on germanium using ALD. Germanium has higher carrier mobilities than silicon and therefore offers an alternative semiconductor material with faster device operation. This method takes advantage of the instability of germanium's native oxide by using thermal deoxidation to clean and reconstruct the Ge (001) surface to the 2&#215;1 structure. 2-nm thick, amorphous STO is then deposited by ALD. The STO film is annealed under ultra-high vacuum and crystallizes on the reconstructed Ge surface. Reflection high-energy electron diffraction (RHEED) is used during this annealing step to monitor the STO crystallization. The thin, crystalline layer of STO acts as a template for subsequent growth of STO that is crystalline as-grown, as confirmed by RHEED. In situ X-ray photoelectron spectroscopy is used to verify film stoichiometry before and after the annealing step, as well as after subsequent STO growth. This procedure provides framework for additional perovskite oxides to be deposited on semiconductors via chemical methods in addition to the integration of more sophisticated heterostructures already achievable by physical methods.

This work details the procedures for the growth and characterization of crystalline SrTiO3 directly on germanium substrates by atomic layer deposition. The procedure illustrates the ability of an all-chemical growth method to integrate oxides monolithically onto semiconductors for metal-oxide semiconductor devices.

Atomic layer deposition (ALD) is a commercially utilized deposition method for electronic materials. ALD growth of thin films offers thickness control and ...

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 ...

Bulk and Thin Film Synthesis of Compositionally Variant Entropy-stabilized Oxides

Here, we present a procedure for the synthesis of bulk and thin film multicomponent (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (Co variant) and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O (Cu variant) entropy-stabilized oxides. Phase pure and chemically homogeneous (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (x = 0.20, 0.27, 0.33) and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O (x = 0.11, 0.27) ceramic pellets are synthesized and used in the deposition of ultra-high quality, phase pure, single crystalline thin films of the target stoichiometry. A detailed methodology for the deposition of smooth, chemically homogeneous, entropy-stabilized oxide thin films by pulsed laser deposition on (001)-oriented MgO substrates is described. The phase and crystallinity of bulk and thin film materials are confirmed using X-ray diffraction. Composition and chemical homogeneity are confirmed by X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy. The surface topography of thin films is measured with scanning probe microscopy. The synthesis of high quality, single crystalline, entropy-stabilized oxide thin films enables the study of interface, size, strain, and disorder effects on the properties in this new class of highly disordered oxide materials.

The synthesis of high quality bulk and thin film (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O entropy-stabilized oxides is presented.

Here, we present a procedure for the synthesis of bulk and thin film multicomponent (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (Co variant) and ...

Theoretical Calculation and Experimental Verification for Dislocation Reduction in Germanium Epitaxial Layers with Semicylindrical Voids on Silicon

Reduction of threading dislocation density (TDD) in epitaxial germanium (Ge) on silicon (Si) has been one of the most important challenges for the realization of monolithically integrated photonics circuits. The present paper describes methods of theoretical calculation and experimental verification of a novel model for the reduction of TDD. The method of theoretical calculation describes the bending of threading dislocations (TDs) based on the interaction of TDs and non-planar growth surfaces of selective epitaxial growth (SEG) in terms of dislocation image force. The calculation reveals that the presence of voids on SiO2 masks help to reduce TDD. Experimental verification is described by germanium (Ge) SEG, using an ultra-high vacuum chemical vapor deposition method and TD observations of the grown Ge via etching and cross-sectional transmission electron microscope (TEM). It is strongly suggested that the TDD reduction would be due to the presence of semicylindrical voids over the SiO2 SEG masks and growth temperature. For experimental verification, epitaxial Ge layers with semicylindrical voids are formed as the result of SEG of Ge layers and their coalescence. The experimentally obtained TDDs reproduce the calculated TDDs based on the theoretical model. Cross-sectional TEM observations reveal that both the termination and generation of TDs occur at semicylindrical voids. Plan-view TEM observations reveal a unique behavior of TDs in Ge with semicylindrical voids (i.e., TDs are bent to be parallel to the SEG masks and the Si substrate).

Theoretical calculation and experimental verification are proposed for a reduction of threading dislocation (TD) density in germanium epitaxial layers with semicylindrical voids on silicon. Calculations based on the interaction of TDs and surface via image force, TD measurements, and transmission electron microscope observations of TDs are presented.

Reduction of threading dislocation density (TDD) in epitaxial germanium (Ge) on silicon (Si) has been one of the most important challenges for the ...

Niobium Oxide Films Deposited by Reactive Sputtering: Effect of Oxygen Flow Rate

Reactive sputtering is a versatile technique used to form compact films with excellent homogeneity. In addition, it allows easy control over deposition parameters such as gas flow rate that results in changes on composition and thus in the film required properties. In this report, reactive sputtering is used to deposit niobium oxide films. A niobium target is used as metal source and different oxygen flow rates to deposit niobium oxide films. The oxygen flow rate was changed from 3 to 10 sccm. The films deposited under low oxygen flow rates show higher electrical conductivity and provide better perovskite solar cells when used as electron transport layer.

Here, we present a protocol for niobium oxide films deposition by reactive sputtering with different oxygen flow rates for use as an electron transport layer in perovskite solar cells.

Reactive sputtering is a versatile technique used to form compact films with excellent homogeneity. In addition, it allows easy control over deposition ...

Fabrication of Thin Film Silver/Silver Chloride Electrodes with Finely Controlled Single Layer Silver Chloride

This paper aims to present a protocol to form smooth and well-controlled films of silver/silver chloride (Ag/AgCl) with designated coverage on top of thin film silver electrodes. Thin film silver electrodes sized 80 &#181;m x 80 &#181;m and 160 &#181;m x 160 &#181;m were sputtered on quartz wafers with a chromium/gold (Cr/Au) layer for adhesion. After passivation, polishing and cathodic cleaning processes, the electrodes underwent galvanostatic oxidation with consideration of Faraday&#39;s Law of Electrolysis to form smooth layers of AgCl with a designated degree of coverage on top of the silver electrode. This protocol is validated by inspection of scanning electron microscope (SEM) images of the surface of the fabricated Ag/AgCl thin film electrodes, which highlights the functionality and performance of the protocol. Sub-optimally fabricated electrodes are fabricated as well for comparison. This protocol can be widely used to fabricate Ag/AgCl electrodes with specific impedance requirements (e.g., probing electrodes for impedance sensing applications like impedance flow cytometry and interdigitated electrode arrays).

This paper aims to present a method to form smooth and well-controlled films of silver chloride (AgCl) with designated coverage on top of thin film silver electrodes.

This paper aims to present a protocol to form smooth and well-controlled films of silver/silver chloride (Ag/AgCl) with designated coverage on top of thin ...

Epitaxial Nanostructured &alpha;-Quartz Films on Silicon: From the Material to New Devices

In this work, we show a detailed engineering route of the first piezoelectric nanostructured epitaxial quartz-based microcantilever. We will explain all the steps in the process starting from the material to the device fabrication. The epitaxial growth of &#945;-quartz film on SOI (100) substrate starts with the preparation of a strontium doped silica sol-gel and continues with the deposition of this gel into the SOI substrate in a thin film form using the dip-coating technique under atmospheric conditions at room temperature. Before crystallization of the gel film, nanostructuration is performed onto the film surface by nanoimprint lithography (NIL). Epitaxial film growth is reached at 1000 &#176;C, inducing a perfect crystallization of the patterned gel film. Fabrication of quartz crystal cantilever devices is a four-step process based on microfabrication techniques. The process starts with shaping the quartz surface, and then metal deposition for electrodes follows it. After removing the silicone, the cantilever is released from SOI substrate eliminating SiO2 between silicon and quartz. The device performance is analyzed by non-contact laser vibrometer (LDV) and atomic force microscopy (AFM). Among the different cantilever&#8217;s dimensions included in the fabricated chip, the nanostructured cantilever analyzed in this work exhibited a dimension of 40 &#181;m large and 100 &#181;m long and was fabricated with a 600 nm thick patterned quartz layer (nanopillar diameter and separation distance of 400 nm and 1 &#181;m, respectively) epitaxially grown on a 2 &#181;m thick Si device layer. The&#160;measured&#160;resonance frequency was&#160;267 kHz and the estimated quality factor, Q, of the whole mechanical structure was Q ~ 398 under low vacuum conditions. We observed the voltage-dependent linear displacement of cantilever with both techniques (i.e., AFM contact measurement and LDV). Therefore, proving that these devices can be activated through the indirect piezoelectric effect.

Epitaxial Nanostructured &#945;-Quartz Films on Silicon: From the Material to New Devices

This work presents a detailed protocol for the microfabrication of nanostructured &#945;-quartz cantilever on a Silicon-On-Insulator(SOI) technology substrate starting from the epitaxial growth of quartz film with the dip coating method and then nanostructuration of the thin film via nanoimprint lithography.

In this work, we show a detailed engineering route of the first piezoelectric nanostructured epitaxial quartz-based microcantilever. We will explain all ...

Electrospray Deposition of Uniform Thickness Ge₂₃Sb₇S₇₀ and As₄₀S₆₀ Chalcogenide Glass Films

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