Name: applying dynamic strain on thin oxide films immobilized on a pseudoelastic nickel-titanium alloy
Uploaded: 2020-07-28T14:30:00
Description: Watch this Scientific Journal Video about Applying Dynamic Strain on Thin Oxide Films Immobilized on a Pseudoelastic Nickel-Titanium Alloy at JoVE.com

This work was conducted by all co-authors, employees of the Alliance for Sustainable Energy, LLC, the manager and operator of the National Renewable Energy Laboratory for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. Funding provided by the U.S. DOE, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences, Solar Photochemistry Program.

1. Preparation of NiTi/TiO2 electrodes
<ol>
	<li>Chemical and mechanical polishing of NiTi substrates
	<ol>
		<li>Cut the superelastic NiTi foil (0.05-mm thickness) into 1 cm x 5 cm strips.</li>
		<li>Polish sample using 320-, 600- and 1200-grit sandpaper, and then rinse with ultrapure water (18.2 M&#937;).</li>
		<li>Polish sample with 1 &#956;m diamond, 0.25 &#956;m diamond, and 0.05 &#956;m alumina polish.</li>
		<li>After polishing, sonicate for 5 min in sequential baths of ultrapure water (18.2 M&#937;)...

<ol>
	<li>Li, J., Shan, Z., Ma, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Elastic+strain+engineering+for+unprecedented+materials+properties.">Elastic strain engineering for unprecedented materials properties.</a> MRS Bulletin. 39, 108-114 (2014).</li><li>Luo, M., Guo, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Strain-controlled+electrocatalysis+on+multimetallic+nanomaterials.">Strain-controlled electrocatalysis on multimetallic nanomaterials.</a> Nature Reviews Materials. 2, 17059 (2017).</li><li>Yang, S., Liu, F., Wu, C., Yang, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tuning+Surface+Properties+of+Low+Dimensional+Materials+via+Strain+Engineering.">Tuning Surface Properties of Low Dimensional Materials via Strain Engineering.</a> Small. 2016, 4028-4047 (2016).</li><li>Clark, E. 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Nitinol is a suitable elastic substrate for applying mechanical stress on thin films. It is commercially available, highly conductive and can be easily functionalized. Preparation of rutile TiO2 thin films by thermal treatment of nitinol, results in highly n-type doped TiO2. It is important to emphasize that NiTi/TiO2 is a unique system where TiO2 films are prepared by thermal treatment of NiTi rather than a deposition method. Our previous publications have shown that strain ap...

The ability to alter the surface reactivity of catalytic materials by introducing strain has been widely recognized1,2,3. Effects of strain in crystalline materials can be introduced either by adjusting material architecture (static strain) or by applying a variable external force (dynamic strain). In crystalline materials, static strain can be introduced by doping4, de-alloying5,6, annealing7, epitaxial growth on a mismatched crystal lattice2 or size confinement2,3. In polycrystalline materials, strain can occur within grain boundaries due to crystal twinning8. Determining the optimal degree of static strain with material architectures requires designing a new sample for each discrete level of strain, which can be time consuming and expensive. Furthermore, introducing static strain often introduces chemical or ligand effects9,10, making it difficult to isolate the strain contribution. Applying a dynamic strain precisely controlled by an external force allows systematic tuning of a material&#8217;s structure/function relationship in order to explore a dynamic range over the strain space without introducing other effects.
To study the effects of dynamic strain on electrocatalysis, metals or metal oxides are deposited on elastic shape or volume tunable substrates, such as organic polymers11,12,13,14,15 or alloys16,17. Applications of mechanical, thermal or electrical loading results in bending, compression, elongation or expansion of an elastic substrate, further inducing a stress-strain response on the deposited catalytic material. So far, catalyst engineering through dynamic strain has been exploited to tune electrocatalytic activities of various metallic and semiconducting materials. Examples include i) the hydrogen evolution reaction (HER) on MoS2, Au, Pt, Ni, Cu, WC11,12,13,14, ii) the oxygen evolution reaction (OER) on NiOx16, nickel-iron alloys18 and iii) the oxygen reduction reaction (ORR) on Pt, Pd12,15,19,20. In most of these reports, organic polymers, such as polymethyl methacrylate (PMMA), were used as elastic substrates. We previously demonstrated the application of elastic metallic substrates, such as stainless steel16 and a superelastic/shape-memory NiTi alloy (Nitinol17,21) for strain studies. Nitinol has also been used as an elastic substrate for deposition of platinum films for ORR19 and deposition of battery cathode materials for energy storage22,23. Due to its shape memory and pseudoelastic properties, NiTi alloys can be deformed by applying moderate heat19 or mechanical strain17, respectively. In contrast to organic elastic substrates, metallic substrates typically do not require deposition of adhesion promoters, are highly conductive and can easily be functionalized. Nitinol is used as a more elastic alternative to stainless steel (SS). While SS can be reversibly strained up to 0.2%, nitinol can be reversibly strained up to 7%. Nitinol owes its unique properties to a martensitic solid state crystal transformation that allows for large elastic deformations24,25. Both materials are commercially available in different geometries (e.g., foils, wires, and springs). When shaped into elastic springs, metallic substrates can be used to study effects of dynamic strain on electrocatalysis without the need for expensive instrumentation16; however, defining the stress-strain response is more challenging than for other geometries.
In previous experimental studies with transition metal catalysts, changes in activities of catalytic surfaces under strain have been attributed to changes in the energetics of the d orbitals colloquially known as d-band theory26. In contrast, the effects of strain on metal oxides is significantly more complex, as it can effect bandgap, carrier mobility, diffusion and distribution of defects and even direct/indirect transitions21,27,28,29,30,31. Herein we provide detailed protocols for the preparation and characterization of n-type doped TiO2 thin films, as well as protocols to study electrocatalytic activities of these films under tunable, tensile strain. The equivalent system can be applied to study electrocatalytic activities of different materials as a function of dynamic strain.

<table>
	<tbody>
		<tr>
			<td>2-Propanol</td>
			<td>Sigma Aldrich</td>
			<td>109634</td>
			<td></td>
		</tr>
		<tr>
			<td>Ag/AgCl (3M NaCl) Reference Electrode</td>
			<td>BASi</td>
			<td>MF-2052</td>
			<td></td>
		</tr>
		<tr>
			<td>Alkaline Reference Electrode</td>
			<td>Basi</td>
			<td>EF-1369</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethyl alcohol, Pure, 200 proof, anhydrous, =99.5%</td>
			<td>Sigma Aldrich</td>
			<td>459836</td>
			<td></td>
		</tr>
		<tr>
			<td>MT I I / F u l l am SEMTester Series</td>
			<td>MTI Instruments</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Nitinol foil, 0.05mm (0.002in) thick, superelastic, flat annealed, pickled surface</td>
			<td>Alfa Aesar</td>
			<td>45492</td>
			<td></td>
		</tr>
		<tr>
			<td>PK-4 Electrode Polishing Kit</td>
			<td>BASi</td>
			<td>MF-2060</td>
			<td></td>
		</tr>
		<tr>
			<td>Potentiostat 600D</td>
			<td>CHI instruments</td>
			<td>600D</td>
			<td></td>
		</tr>
		<tr>
			<td>Pt wire</td>
			<td>Sigma Aldrich</td>
			<td>267228-1G</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium hydroxide</td>
			<td>Sigma Aldrich</td>
			<td>221465</td>
			<td></td>
		</tr>
		<tr>
			<td>Sulfuric acid</td>
			<td>Sigma Aldrich</td>
			<td>30743</td>
			<td></td>
		</tr>
	</tbody>
</table>

applying dynamic strain on thin oxide films immobilized on a pseudoelastic nickel-titanium alloy

Direct alteration of material structure/function through strain is a growing area of research that has allowed for novel properties of materials to emerge. Tuning material structure can be achieved by controlling an external force imposed on materials and inducing stress-strain responses (i.e., applying dynamic strain). Electroactive thin films are typically deposited on shape or volume tunable elastic substrates, where mechanical loading (i.e., compression or tension) can affect film structure and function through imposed strain. Here, we summarize methods for straining n-type doped titanium dioxide (TiO2) films prepared by a thermal treatment of a pseudo-elastic nickel-titanium alloy (Nitinol). The main purpose of the described methods is to study how strain affects electrocatalytic activities of metal oxide, specifically hydrogen evolution and oxygen evolution reactions. The same system can be adapted to study the effect of strain more broadly. Strain engineering can be applied for optimization of a material function, as well as for design of adjustable, multifunctional (photo)electrocatalytic materials under external stress control.

Pre-treated NiTi foils are oxidized at 500 &#176;C under aerobic conditions (Figure 1). Due to the oxophilic nature of titanium, calcination at elevated temperatures results in a surface layer of rutile TiO2. The thickness of the layer and degree of n-type doping are affected by annealing time and temperature, which is reflected in color change from gray (untreated sample) to uniform blue/purple after 20 min heating (Figure 2). Longer heating time res...

Watch this Scientific Journal Video about Applying Dynamic Strain on Thin Oxide Films Immobilized on a Pseudoelastic Nickel-Titanium Alloy at JoVE.com

Applying Dynamic Strain on Thin Oxide Films Immobilized on a Pseudoelastic Nickel-Titanium Alloy

Dynamic, tensile strain is applied on TiO2 thin films to study the effects of strain on electrocatalysis, specifically proton reduction and water oxidation. TiO2 films are prepared by thermal treatment of the pseudo-elastic NiTi alloy (Nitinol).

Direct alteration of material structure/function through strain is a growing area of research that has allowed for novel properties of materials to ...

The ability to apply viable external forces to materials allow us to alter their surface properties at will, as well as find optimal catalytic activities and demonstrate new properties. This technique allows us to apply strains and study their effect on electro-catalytic activities without needing to prepare multiple materials for each discreet degree of strain. These methods can also be used to study a range of fin films and their electro-chemical properties such as electro-chemical activity and corrosion.For a chemical and mechanical polishing of nickel-titanium substrates, first, cut a 0.05 millimeter thick piece of super-elastic nickel-titanium into one-by-five centimeter strips, and sequentially polish the resulting samples with 320, 600 and 1200-grit sand paper. Rinse the sample with ultra-pure water between each polishing. After the last rinse, polish the sample with one micron diamond, 0.3 micron diamond, and 0.05 micron-alumina polish.After polishing, sonicate the samples with sequential five-minute baths in ultra-pure water, isopropanol, ethanol and ultra-pure water before drying the samples under nitrogen. To prepare 50-nanometer thick rutile-titanium dioxide films, after drying, place the polished nickel-titanium foils in a 500 degree celsius oven under aerobic conditions for 30 minutes. Heating will cause the surface color to change from gray to blue-purple.To apply tensile stress to the heated film samples, gently clamp one foil in a mechanical tester, leaving one centimeter of foil exposed at each end. Then, strain the nickel-titanium, titanium dioxide sample at a rate of two millimeters per minute, keeping the strain at zero to three percent. Before starting the electro-chemical measurements, pre-strain the foil to five Newtons.To conduct electro-chemical experiments under applied strain, assemble a custom-made electro-chemical cell loosely around the nickel-titanium, titanium dioxide foil. Carefully positioning the cell in the middle to ensure that the center of the foil is exposed. Tighten the cell gently onto the sample to create a solution-tight cell for the electro-chemical measurements and fill the cell with an electrolyte.After gently purging the solution with nitrogen, increase the strain from zero to 0.5 percent and conduct cyclic photometry or linear sweep photometry measurements. To perform a hydrogen evolution reaction experiment using 0.5 molar sulfuric acid as the electrolyte, silver, silver chloride as the reference electrode, and a ten centimeter length, 0.5 millimeter diameter coiled platinum wire as the counter-electrode. Scan the potentials between the open circuit voltage to 0.8 folds versus RHE, which is the reversible hydrogen electrode, starting with the highest potential value and a scan rate of five to fifty milli-volts per second.To perform an oxygen evolution reaction experiment using one molar sodium hydroxide as the electrolyte, mercury, mercuric oxygen as the reference electrode, and a coiled platinum wire as the counter electrode, scan the potential between the open circuit voltage to two volts versus RHE, starting with the lowest potential value and a scan rate of five to fifty milli-volts per second. After completing the measurements, loosen the electro-chemical cell around the nickel-titanium, titanium dioxide foil so that the sample can move freely and gently tighten the cell back onto the sample to realign the assembly around the foil. Then, refill and purge the electrolyte before increasing the strain from 0.5 to one percent, and repeating the electro-chemical experiments.To determine if increases in hydrogen evolution reaction activities are due to increases in the electro-active surface, run cyclic photometry at different scan rates at a potential range at which faradaic currents are negligible, so that the currents represent only the charge-discharge of the electric double layer and plot the scan rates versus the currents. For the characterization of cracked films, keep a fifty nanometer titanium oxide foil strained at seven percent for thirty minutes or longer, before analyzing the surface for cracking by scanning electro-chemical microscopy. Then, conduct any desired measurements with a proper sample holder for scanning electron microscopy or electro-chemical cell for electro-chemical measurement with pristine and purposely cracked titanium dioxide films at different incrementally, increased and decreased strain values.For surface characterization of a sample, after electro-chemical measurements, wash the sample with water to remove any residual solved and assemble the rinsed foils in the tensile stretcher. Secure the custom-made sample holders around the strained sample. The sample surfaces can then be assessed by scanning electron microscopy according to standard protocols.Oxidization of nickel-titanium foils at 500 degrees Celsius results in calcination and a surface layer of rutile titanium dioxide. The thickness of the layer and the degree of N-type doping are affected by the annealing time and the temperature, as indicated by a color change from gray to uniform blue-purple after thirty minutes of heating. Longer heating times, result in thicker titanium dioxide films, and are accompanied by a gradual loss of the blue-purple color.Nitinol behavior under thermal and mechanical stress, reflects a reversible solid state phase transformation between two different martensite crystal phases, making it a pseudo-elastic rather than an elastic material. Cyclic photometry and linear sweep photometry experiments are important for understanding the electro-chemical system such as faradaic versus non-faradaic ranges. Further electro-chemical characterization, can include electro-chemical impedance to study changes in electrode surface reactivities with strain.To determine if increases in hydrogen evolution reaction and oxygen evolution reaction activities are simply due to increases in electro-active surface. Capacitance measurements can be performed at different strain values. To further determine if the changes in electro activities with strain are due to elastic or inelastic deformation under applied tensile stress, experiments can be conducted with pristine and purposely cracked titanium dioxide films.The sample must be mounted properly to obtain and to produce more results. This stencil stretcher can be incorporated in many different characterizations and techniques, including spectroscopy, trans-reabsorption, confocal Raman or probe microscopy.

applying-dynamic-strain-on-thin-oxide-films-immobilized-on

Research

JoVE Journal

Chemistry

Manufacturing of Three-dimensionally Microstructured Nanocomposites through Microfluidic Infiltration

Microstructured composite beams reinforced with complex three-dimensionally (3D) patterned nanocomposite microfilaments are fabricated via nanocomposite in&#64257;ltration of 3D interconnected microfluidic networks. The manufacturing of the reinforced beams begins with the fabrication of microfluidic networks, which involves layer-by-layer deposition of fugitive ink filaments using a dispensing robot, filling the empty space between filaments using a low viscosity resin, curing the resin and finally removing the ink.&#160;Self-supported 3D structures with other geometries and many layers (e.g.&#160;a few hundreds layers) could be built using this method. The resulting tubular micro&#64258;uidic networks are then infiltrated with thermosetting nanocomposite suspensions containing nanofillers (e.g.&#160;single-walled carbon nanotubes), and subsequently cured. The infiltration is done by applying a pressure gradient between two ends of the empty network (either by applying a vacuum or vacuum-assisted microinjection). Prior to the infiltration, the nanocomposite suspensions are prepared by dispersing nanofillers into polymer matrices using ultrasonication and three-roll mixing methods. The nanocomposites (i.e.&#160;materials infiltrated) are then solidified under UV exposure/heat cure, resulting in a 3D-reinforced composite structure. The technique presented here enables the design of functional nanocomposite macroscopic products for microengineering applications such as actuators and sensors.

Three-dimensional (3D) microstructured composite beams are fabricated through the directed and localized infiltration of nanocomposites into 3D porous microfluidic networks. The flexibility of this manufacturing method enables the utilization of different thermosetting materials and nanofillers in order to achieve a variety of functional 3D reinforced nanocomposite macroscopic products.

Microstructured composite beams reinforced with complex three-dimensionally (3D) patterned nanocomposite microfilaments are fabricated via nanocomposite ...

Reductive Electropolymerization of a Vinyl-containing Poly-pyridyl Complex on Glassy Carbon and Fluorine-doped Tin Oxide Electrodes

Controllable electrode surface modification is important in a number of fields, especially those with solar fuels applications. Electropolymerization is one surface modification technique that electrodeposits a polymeric film at the surface of an electrode by utilizing an applied potential to initiate the polymerization of substrates in the Helmholtz layer. This useful technique was first established by a Murray-Meyer collaboration at the University of North Carolina at Chapel Hill in the early 1980s and utilized to study numerous physical phenomena of films containing inorganic complexes as the monomeric substrate. Here, we highlight a procedure for coating electrodes with an inorganic complex by performing reductive electropolymerization of the vinyl-containing poly-pyridyl complex onto glassy carbon and fluorine doped tin oxide coated electrodes. Recommendations on electrochemical cell configurations and troubleshooting procedures are included. Although not explicitly described here, oxidative electropolymerization of pyrrole-containing compounds follows similar procedures to vinyl-based reductive electropolymerization but are far less sensitive to oxygen and water.

A procedure for performing reductive electropolymerization of vinyl-containing compounds onto glassy carbon and fluorine doped tin-oxide coated electrodes is presented. Recommendations on electrochemical cell configurations and troubleshooting procedures are included. Although not explicitly described here, oxidative electropolymerization of pyrrole-containing compounds follows similar procedures to vinyl-based reductive electropolymerization.

Controllable electrode surface modification is important in a number of fields, especially those with solar fuels applications. Electropolymerization is ...

Atomically Defined Templates for Epitaxial Growth of Complex Oxide Thin Films

Atomically defined substrate surfaces are prerequisite for the epitaxial growth of complex oxide thin films. In this protocol, two approaches to obtain such surfaces are described. The first approach is the preparation of single terminated perovskite SrTiO3 (001) and DyScO3 (110) substrates. Wet etching was used to selectively remove one of the two possible surface terminations, while an annealing step was used to increase the smoothness of the surface. The resulting single terminated surfaces allow for the heteroepitaxial growth of perovskite oxide thin films with high crystalline quality and well-defined interfaces between substrate and film. In the second approach, seed layers for epitaxial film growth on arbitrary substrates were created by Langmuir-Blodgett (LB) deposition of nanosheets. As model system Ca2Nb3O10- nanosheets were used, prepared by delamination of their layered parent compound HCa2Nb3O10. A key advantage of creating seed layers with nanosheets is that relatively expensive and size-limited single crystalline substrates can be replaced by virtually any substrate material.

Various procedures are outlined to prepare atomically defined templates for epitaxial growth of complex oxide thin films. Chemical treatments of single crystalline SrTiO3 (001) and DyScO3 (110) substrates were performed to obtain atomically smooth, single terminated surfaces. Ca2 Nb3 O10- nanosheets were used to create atomically defined templates on arbitrary substrates.

Atomically defined substrate surfaces are prerequisite for the epitaxial growth of complex oxide thin films. In this protocol, two approaches to obtain ...

Dynamic Electrochemical Measurement of Chloride Ions

This protocol describes the dynamic measurement of chloride ions using the transition time of a silver silver chloride (Ag/AgCl) electrode. Silver silver chloride electrode is used extensively for potentiometric measurement of chloride ions concentration in electrolyte. In this measurement, long-term and continuous monitoring is limited due to the inherent drift and the requirement of a stable reference electrode. We utilized the chronopotentiometric approach to minimize drift and avoid the use of a conventional reference electrode. A galvanostatic pulse is applied to an Ag/AgCl electrode which initiates a faradic reaction depleting the Cl&#713; ions near the electrode surface. The transition time, which is the time to completely deplete the ions near the electrode surface, is a function of the ion concentration, given by the Nernst equation. The square root of the transition time is in linear relation to the chloride ion concentration. Drift of the response over two weeks is negligible (59 &#181;M/day) when measuring 1 mM [Cl&#713;]using a current pulse of 10 Am-2. This is a dynamic measurement where the moment of transition time determines the response and thus is independent of the absolute potential. Any metal wire can be used as a pseudo-reference electrode, making this approach feasible for long-term measurement inside concrete structures.

Dynamic measurement of chloride ions is presented. Transition time of an Ag/AgCl electrode, during a chronopotentiometric technique, can give the concentration of chloride ions in electrolyte. This method does not require a stable conventional reference electrode.

This protocol describes the dynamic measurement of chloride ions using the transition time of a silver silver chloride (Ag/AgCl) electrode. Silver silver ...

Cooling Rate Dependent Ellipsometry Measurements to Determine the Dynamics of Thin Glassy Films

This report aims to fully describe the experimental technique of using ellipsometry for cooling rate dependent Tg (CR-Tg) experiments. These measurements are simple high-throughput characterization experiments, which can determine the glass transition temperature (Tg), average dynamics, fragility and the expansion coefficient of the super-cooled liquid and glassy states for a variety of glassy materials. This technique allows for these parameters to be measured in a single experiment, while other methods must combine a variety of different techniques to investigate all of these properties. Measurements of dynamics close to Tg are particularly challenging. The advantage of cooling rate dependent Tg measurements over other methods which directly probe bulk and surface relaxation dynamics is that they are relatively quick and simple experiments, which do not utilize fluorophores or other complicated experimental techniques. Furthermore, this technique probes the average dynamics of technologically relevant thin films in temperature and relaxation time (&#964;&#945;) regimes relevant to the glass transition (&#964;&#945; &#62; 100 sec). The limitation to using ellipsometry for cooling rate dependent Tg experiments is that it cannot probe relaxation times relevant to measurements of viscosity (&#964;&#945; &#60;&#60; 1 sec). Other cooling rate dependent Tg measurement techniques, however, can extend the CR-Tg method to faster relaxation times. Furthermore, this technique can be used for any glassy system so long as the integrity of the film remains throughout the experiment.

Here, we present a protocol for cooling rate dependent ellipsometry experiments, which can determine the glass transition temperature (Tg), average dynamics, fragility and the expansion coefficient of the super-cooled liquid and glass for a variety of glassy materials.

This report aims to fully describe the experimental technique of using ellipsometry for cooling rate dependent Tg (CR-Tg) experiments. These measurements ...

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 ...

Photochemical Oxidative Growth of Iridium Oxide Nanoparticles on CdSe@CdS Nanorods

We demonstrate a procedure for the photochemical oxidative growth of iridium oxide catalysts on the surface of seeded cadmium selenide-cadmium sulfide (CdSe@CdS) nanorod photocatalysts. Seeded rods are grown using a colloidal hot-injection method and then moved to an aqueous medium by ligand exchange. CdSe@CdS nanorods, an iridium precursor and other salts are mixed and illuminated. The deposition process is initiated by absorption of photons by the semiconductor particle, which results with formation of charge carriers that are used to promote redox reactions. To insure photochemical oxidative growth we used an electron scavenger. The photogenerated holes oxidize the iridium precursor, apparently in a mediated oxidative pathway. This results in the growth of high quality crystalline iridium oxide particles, ranging from 0.5 nm to about 3 nm, along the surface of the rod. Iridium oxide grown on CdSe@CdS heterostructures was studied by a variety of characterization methods, in order to evaluate its characteristics and quality. We explored means for control over particle size, crystallinity, deposition location on the CdS rod, and composition. Illumination time and excitation wavelength were found to be key parameters for such control. The influence of different growth conditions and the characterization of these heterostructures are described alongside a detailed description of their synthesis. Of significance is the fact that the addition of iridium oxide afforded the rods astounding photochemical stability under prolonged illumination in pure water (alleviating the requirement for hole scavengers).

A protocol for the photochemical oxidative growth of small crystalline iridium oxide nanoparticles on the surface of CdSe@CdS seeded rod nanoparticles is presented.

We demonstrate a procedure for the photochemical oxidative growth of iridium oxide catalysts on the surface of seeded cadmium selenide-cadmium sulfide ...

Capillary Electrophoresis to Monitor Peptide Grafting onto Chitosan Films in Real Time

Free-solution capillary electrophoresis (CE) separates analytes, generally charged compounds in solution through the application of an electric field. Compared to other analytical separation techniques, such as chromatography, CE is cheap, robust and effectively requires no sample preparation (for a number of complex natural matrices or polymeric samples). CE is fast and can be used to follow the evolution of mixtures in real time (e.g., chemical reaction kinetics), as the signals observed for the separated compounds are directly proportional to their quantity in solution.
Here, the efficiency of CE is demonstrated for monitoring the covalent grafting of peptides onto chitosan films for subsequent biomedical applications. Chitosan&#39;s antimicrobial and biocompatible properties make it an attractive material for biomedical applications such as cell growth substrates. Covalently grafting the peptide RGDS (arginine - glycine - aspartic acid - serine) onto the surface of chitosan films aims at improving cell attachment. Historically, chromatography and amino acid analysis have been used to provide a direct measurement of the amount of grafted peptide. However, the fast separation and absence of sample preparation provided by CE enables equally accurate yet real-time monitoring of the peptide grafting process. CE is able to separate and quantify the different components of the reaction mixture: the (non-grafted) peptide and the chemical coupling agents. In this way the use of CE results in improved films for downstream applications.
The chitosan films were characterized through solid-state NMR (nuclear magnetic resonance) spectroscopy. This technique is more time-consuming and cannot be applied in real time, but yields a direct measurement of the peptide and thus validates the CE technique.

Free solution capillary electrophoresis is a fast, cheap and robust analytical method that enables the quantitative monitoring of chemical reactions in real time. Its utility for rapid, convenient and precise analysis is demonstrated here through analysis of covalent peptide grafting onto chitosan films for improved cell adhesion.

Free-solution capillary electrophoresis (CE) separates analytes, generally charged compounds in solution through the application of an electric field. ...

Reactive Vapor Deposition of Conjugated Polymer Films on Arbitrary Substrates

We demonstrate a method of conformally coating conjugated polymers on arbitrary substrates using a custom-designed, low-pressure reaction chamber. Conductive polymers, poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3,4-propylenedioxythiophene) (PProDOT), and a semiconducting polymer, poly(thieno[3,2-b]thiophene) (PTT), were deposited on unconventional highly-disordered and textured substrates with high surface areas, such as paper, towels and fabrics. This reported deposition chamber is an improvement of previous vapor reactors because our system can accommodate both volatile and nonvolatile monomers, such as 3,4-propylenedioxythiophene and thieno[3,2-b]thiophene. Utilization of both solid and liquid oxidants are also demonstrated. One limitation of this method is that it lacks sophisticated in situ thickness monitors. Polymer coatings made by the commonly used solution-based coating methods, such as spin-coating and surface grafting, are often not uniform or susceptible to mechanical degradation. This reported vapor phase deposition method overcomes those drawbacks and is a strong alternative to common solution-based coating methods. Notably, polymer films coated by the reported method are uniform and conformal on rough surfaces, even at a micrometer scale. This feature allows for future application of vapor deposited polymers in electronics devices on flexible and highly textured substrates.

This paper presents a protocol for reactive vapor deposition of poly(3,4-ethylenedioxythiophene), poly(3,4-propylenedioxythiophene), and poly(thieno[3,2-b]thiophene) films on glass slides and rough substrates, such as textiles and paper.

We demonstrate a method of conformally coating conjugated polymers on arbitrary substrates using a custom-designed, low-pressure reaction chamber. ...

Chemical Synthesis of Porous Barium Titanate Thin Film and Thermal Stabilization of Ferroelectric Phase by Porosity-Induced Strain

Barium titanate (BaTiO3, hereafter BT) is an established ferroelectric material first discovered in the 1940s and still widely used because of its well-balanced ferroelectricity, piezoelectricity, and dielectric constant. In addition, BT does not contain any toxic elements. Therefore, it is considered to be an eco-friendly material, which has attracted considerable interest as a replacement for lead zirconate titanate (PZT). However, bulk BT loses its ferroelectricity at approximately 130 &#176;C, thus, it cannot be used at high temperatures. Because of the growing demand for high-temperature ferroelectric materials, it is important to enhance the thermal stability of ferroelectricity in BT. In previous studies, strain originating from the lattice mismatch at hetero-interfaces has been used. However, the sample preparation in this approach requires complicated and expensive physical processes, which are undesirable for practical applications.
In this study, we propose a chemical synthesis of a porous material as an alternative means of introducing strain. We synthesized a porous BT thin film using a surfactant-assisted sol-gel method, in which self-assembled amphipathic surfactant micelles were used as an organic template. Through a series of studies, we clarified that the introduction of pores had a similar effect on distorting the BT crystal lattice, to that of a hetero-interface, leading to the enhancement and stabilization of ferroelectricity. Owing to its simplicity and cost effectiveness, this fabrication process has considerable advantages over conventional methods.

Here, we present a protocol for the synthesis of porous barium titanate (BaTiO3) thin film by a surfactant-assisted sol-gel method, in which self-assembled amphipathic surfactant micelles are used as an organic template.