Name: low pressure vapor-assisted solution process for tunable band gap pinhole-free methylammonium lead halide perovskite films
Uploaded: 2017-09-08T11:00:00
Description: Watch this Scientific Journal Video about Low Pressure Vapor-assisted Solution Process for Tunable Band Gap Pinhole-free Methylammonium Lead Halide Perovskite Films at JoVE.com

Perovskite process development, thin film synthesis, structural and morphological characterization were performed at the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under Award Number DE-SC0004993. C.M.S.-F. acknowledges financial support from the Swiss National Science Foundation (P2EZP2_155586).

Caution: Please consult all relevant material safety data sheets (MSDS) before use. Several of the chemicals used in these syntheses are acutely toxic, carcinogenic, and toxic to reproduction. Implosion and explosion risks are associated with the use of a Schlenk line. Please make sure to check the integrity of the glass apparatus before performing the procedure. Incorrect use of the Schlenk line in association with a liquid nitrogen cold trap may result in condensation of liquid oxygen (pale blue) that can become explos...

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In order to fabricate highly efficient organo-lead planar perovskite heterojunctions, the homogeneity of the active layer is a key requirement. With respect to existing solution2,16,17 and vacuum-based18,19 methodologies, our process is remarkably amenable to composition tunability of the active layer that can be synthesized over the full CH3NH3PbI<...

Hybrid organic-inorganic lead halide perovskites (CH3NH3PbX3, X = I, Br, Cl) are a new class of semiconductors that has emerged rapidly within the last few years. This material class shows excellent semiconductor properties, such as high absorption coefficient1, tunable bandgap2, long charge carrier diffusion length3, high defect tolerance4, and high photoluminescence quantum yield5,6. The unique combination of these characteristics makes lead halide perovskites very attractive for application in optoelectronic devices, such as single junction7,8 and multijunction photovoltaics9,10, lasers11,12, and LEDs13.
CH3NH3PbX3 films can be fabricated by a variety of synthetic methods14, which aim at improving the efficiency of this semiconducting material for energy applications15. However, optimization of photovoltaic devices relies on the quality of the halide perovskite active layer, as well as its interfaces with charge selective contacts (i.e. electron and hole transport layers), which facilitate photocarrier collection in these devices. Specifically, continuous, pinhole-free active layers are necessary to minimize shunt resistance, thereby improving device performance.
Among the most widespread methods for fabricating organo-lead halide perovskite thin films are solution-based and vacuum-based processes. The most common solution process uses equimolar ratios of lead halide and methylammonium halide dissolved in dimethylformamide (DMF), dimethylsulfoxide (DMSO), or &#947;-butyrolactone (GBL), or mixtures of these solvents.2,16,17 Precursor molarity and solvent type, as well as annealing temperature, time and atmosphere, must be precisely controlled to obtain continuous and pinhole-free films.16 For example, to improve surface coverage, a solvent-engineering technique was demonstrated to yield dense and extremely uniform films.17 In this technique, a non-solvent (toluene) is dripped onto the perovskite layer during the spinning of the perovskite solution.17 These approaches are usually well suited for mesoscopic heterojunctions, which employ mesoporous TiO2 as an electron selective contact with increased contact area and reduced carrier transport length.
However, planar heterojunctions, which use selective contacts based on thin (usually TiO2) films, are more desirable because they provide a simple and scalable configuration that can be more easily adopted in solar cell technology. Therefore, the development of organo-lead halide perovskite active layers that show high efficiency and stability under operation for planar heterojunctions may lead to technological advancements in this field. However, one of the main challenges to fabricate planar heterojunctions is still represented by the homogeneity of the active layer. A few attempts, based on vacuum processes, have been made to prepare uniform layers on thin TiO2 films. For example, Snaith and collaborators have demonstrated a dual evaporation process, which yield highly homogenous perovskite layers with high power conversion efficiencies for photovoltaic applications.18 While this work represents a significant advancement in the field, the use of high vacuum systems and the lack of tunability of the composition of the active layer limit the applicability of this method. Interestingly, extremely high uniformity has been achieved with the vapor-assisted solution process (VASP)19 and modified low pressure VASP (LP-VASP)6,20. While the VASP, proposed by Yang and collaborators19, requires higher temperatures and the use of a glove box, the LP-VASP is based on the annealing of a lead halide precursor layer in the presence of methylammonium halide vapor, at reduce pressure and relatively low temperature in a fumehood. These specific conditions enable access mixed perovskite compositions, and fabrication of pure CH3NH3PbI3, CH3NH3PbI3-xClx, CH3NH3PbI3-xBrx, and CH3NH3PbBr3 can be easily achieved. Specifically, CH3NH3PbI3-xBrx films over the full composition space can be synthesized with high optoelectronic quality and reproducibility6,20.
Herein, we provide a detailed description of the protocol for the synthesis of organic-inorganic lead halide perovskite layers via LP-VASP, including the procedure for synthesizing the methylammonium halide precursors. Once the precursors are synthesized, formation of CH3NH3PbX3 films consists of a two-step procedure that comprises i) the spin-coating of the PbI2/PbBr2 (PbI2, or PbI2/PbCl2) precursor on glass substrate or fluorine-doped tin oxide (FTO) coated glass substrate with planar TiO2, as electron transport layer, and ii) the low pressure vapor-assisted annealing in mixtures of CH3NH3I and CH3NH3Br that can be finely adjusted depending on the desired optical bandgap (1.6 eV&#160;&#8804; Eg &#8804; 2.3 eV). Under these conditions, the methylammonium halide molecules present in the vapor phase slowly diffuse into the lead halide thin film yielding continuous, pinhole-free halide perovskite films. This process yields a two-fold volume expansion from the starting lead halide precursor layer to the completed organic-inorganic lead halide perovskite. The standard thickness of the perovskite film is about 400 nm. It is possible to vary this thickness between 100-500 nm by changing the speed of the second spin coating step. The presented technique results in films of high optoelectronic quality, which translates to photovoltaic devices with power conversion efficiencies of up to 19% using a Au/spiro-OMeTAD /CH3NH3PbI3-xBrx/compact TiO2/ FTO/glass solar cell architecture.21

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Lead (II) bromide, 99.999%</td>
			<td>Sigma-Aldrich</td>
			<td>398853</td>
			<td>Acute toxicity, Carcinogenicity</td>
		</tr>
		<tr>
			<td>Lead (II) Iodide, 99.9985%</td>
			<td>Alfa Aesar</td>
			<td>12724</td>
			<td>Acute toxicity, light sensitive</td>
		</tr>
		<tr>
			<td>N, N-Dimethylformamide, &#62; 99.9%</td>
			<td>Sigma-Aldrich</td>
			<td>270547</td>
			<td>Acute toxicity, flamable; store in well ventilated place</td>
		</tr>
		<tr>
			<td>Isopropyl alcohol, 99.5%</td>
			<td>BDH</td>
			<td>BDH1133-4LP</td>
			<td>Flamable</td>
		</tr>
		<tr>
			<td>Methylamine ca. 40% in water</td>
			<td>TCI</td>
			<td>M0137</td>
			<td>Acute toxicity, flamable; Corrosive</td>
		</tr>
		<tr>
			<td>Hydrobromic acid 48 wt. % in H2O, &#8805;99.99%</td>
			<td>Sigma-Aldrich</td>
			<td>339245</td>
			<td>Acute toxicity, Corrosive; air and light sensitive; store in well ventilated place</td>
		</tr>
		<tr>
			<td>Hydroiodic acid 57 wt. % in H2O, distilled, stabilized, 99.95%</td>
			<td>Sigma-Aldrich</td>
			<td>210021</td>
			<td>Corrosive; air and light sensitive; store in well ventilated place 
			Recommended storage temperature 2/8 &#176;C; air and light sensitiv</td>
		</tr>
		<tr>
			<td>Ethyl Ether Anhydrous BHT Stabilized/Certified ACS</td>
			<td>Fisher Chemicals</td>
			<td>E 138-4</td>
			<td>Acute toxicity, flamable</td>
		</tr>
		<tr>
			<td>Ethanol Denatured (Reagent Alcohol), ACS</td>
			<td>BDH</td>
			<td>BDH1156-4LP</td>
			<td>Flamable</td>
		</tr>
		<tr>
			<td>Alconoxdetergent</td>
			<td>Sigma-Aldrich</td>
			<td>242985</td>
			<td>Soap utilized for substrate cleaning</td>
		</tr>
		<tr>
			<td>Milli-QIntegral 3 Water Purification System</td>
			<td>EMD Millipore</td>
			<td>ZRXQ003WW</td>
			<td>Dispenser of ultrapure water</td>
		</tr>
		<tr>
			<td>Fluorine-doped Thin Oxide (FTO) coated glass</td>
			<td>Thin Film Devices</td>
			<td>Custom</td>
			<td>Glass: dimensions 13.8mm x 15.8mm &#177; 0.2mm, thickness 2.3mm &#177; 0.1mm; FTO: dimensions 3000&#197; &#177; 100&#197;, resistivity 7-10 ohms/sq, transmission 82% @ 550nm)</td>
		</tr>
		<tr>
			<td>Glass substrates</td>
			<td>C &#38; A Scientific - Premiere</td>
			<td>9101-E</td>
			<td>Plain. Length: 75 mm, Width: 25 mm, Thickness: 1 mm</td>
		</tr>
		<tr>
			<td>Ultrasonic Cleaner with Digital Timer and Heater</td>
			<td>VWR</td>
			<td>97043-992</td>
			<td>2.8 L (0.7 gal.)24L x 14W x 10D cm (97/16x 51/2x 315/16&#34;)</td>
		</tr>
		<tr>
			<td>Nuclear Magnetic Resonance Advance 500</td>
			<td>Bruker</td>
			<td>Z115311</td>
			<td></td>
		</tr>
		<tr>
			<td>Quanta 250 FEG Scanning Electron Microscope</td>
			<td>FEI</td>
			<td>743202032141</td>
			<td>Equipped with a Bruker Xflash 5030 Energy-dispersive X-ray detector</td>
		</tr>
		<tr>
			<td>SmartLab X-ray diffractometer</td>
			<td>Rigaku</td>
			<td>2080B411</td>
			<td>Using Cu K&#945; radiation at 40 kV and 40 mA</td>
		</tr>
	</tbody>
</table>

low pressure vapor-assisted solution process for tunable band gap pinhole-free methylammonium lead halide perovskite films

Organo-lead halide perovskites have recently attracted great interest for potential applications in thin-film photovoltaics and optoelectronics. Herein, we present a protocol for the fabrication of this material via the low-pressure vapor assisted solution process (LP-VASP) method, which yields ~19% power conversion efficiency in planar heterojunction perovskite solar cells. First, we report the synthesis of methylammonium iodide (CH3NH3I) and methylammonium bromide (CH3NH3Br) from methylamine and the corresponding halide acid (HI or HBr). Then, we describe the fabrication of pinhole-free, continuous methylammonium-lead halide perovskite (CH3NH3PbX3 with X = I, Br, Cl and their mixture) films with the LP-VASP. This process is based on two steps: i) spin-coating of a homogenous layer of lead halide precursor onto a substrate, and ii) conversion of this layer to CH3NH3PbI3-xBrx by exposing the substrate to vapors of a mixture of CH3NH3I and CH3NH3Br at reduced pressure and 120 &#176;C. Through slow diffusion of the methylammonium halide vapor into the lead halide precursor, we achieve slow and controlled growth of a continuous, pinhole-free perovskite film. The LP-VASP allows synthetic access to the full halide composition space in CH3NH3PbI3-xBrx with 0&#160;&#8804; x&#160;&#8804; 3. Depending on the composition of the vapor phase, the bandgap can be tuned between 1.6 eV&#160;&#8804; Eg&#160;&#8804; 2.3 eV. In addition, by varying the composition of the halide precursor and of the vapor phase, we can also obtain CH3NH3PbI3-xClx. Films obtained from the LP-VASP are reproducible, phase pure as confirmed by X-ray diffraction measurements, and show high photoluminescence quantum yield. The process does not require the use of a glovebox.

Proton nuclear magnetic resonance (NMR) spectra were taken after the methylammonium halide synthesis to verify the molecule purity (Figure 1). Scanning electron microscopy (SEM) images were acquired before and after vapor annealing (Figure 2) to characterize the morphology and the homogeneity of both the mixed lead halide precursor and the CH3NH3PbI3-xBrx films. X-ray diffraction (XRD) ...

Watch this Scientific Journal Video about Low Pressure Vapor-assisted Solution Process for Tunable Band Gap Pinhole-free Methylammonium Lead Halide Perovskite Films at JoVE.com

Low Pressure Vapor-assisted Solution Process for Tunable Band Gap Pinhole-free Methylammonium Lead Halide Perovskite Films

Here, we present a protocol for the synthesis of CH3NH3I and CH3NH3Br precursors and the subsequent formation of pinhole-free, continuous CH3NH3PbI3-xBrx thin films for the application in high efficiency solar cells and other optoelectronic devices.

Organo-lead halide perovskites have recently attracted great interest for potential applications in thin-film photovoltaics and optoelectronics. Herein, ...

the overall goal of this process is to synthesize homogenous pinhole-free and high quality methylammonium lead halide perovskite films over the full halide composition space for application in optoelectronics such as solar cells, lasers and LEDs. This synthetic protocol is designed such that it can be adapted to different laboratories and it provides a synthesis route to make faster and reproducible lead halide perovskites over the full highlight composition space. The main advantage of this technique is the use of low processing temperature and standard equipment available in most laboratories such as, fume hoods and schlenk lines.Demonstrating the procedure will be Aya Buckley and Phuong Ngo, students from UC Berkeley. To begin this procedure, add 100 milliliters of ethanol to a 250 milliliter round bottom flask equipped with the stir bar. Add 16.5 milliliters of 40%methylamine in water.Using an ice bath, cool the flask to zero degree celsius. Add 10 milliliters of 76 millimolar hydroiodic acid drop wise, while stirring. Then, seal the flask with a septum.Stir the reaction for two hours at zero degree celsius. Then, remove the flask from the ice bath using a rotary evaporator equipped with a water bath, evaporate the solvent in unreacted volatile components at 50 Torr and 60 degree celsius for four hours or until the volatiles are removed. Once the solvent has evaporated, add 100 milliliters of warm ethanol to the flask to dissolve the residual material.Slowly add 200 milliliters of diethyl ether to induce the crystallization of a white solid. After this, vacuum filter the mixture over a 50 millimeter glass frit filter. Recover the supernatant and add 200 milliliters of diethyl ether to induce additional crystallization.Vacuum filter the mixture again over the 50 millimeter glass frit filter. While vacuum filtering, wash the solid three times with diethyl ether. Dry the washed solid under vacuum.When cleaning the apparatus, the quality of starting material is also important. Therefore, careful recrystallization of the material volume precursor is particularly important. Store the dried solid in the desiccator in the dark at room temperature, to minimize decomposition.To begin, preheat a silicone oil bath equipped with a magnetic stir bar to 120 degree celsius. Next, use a weighing paper cylinder to transfer 0.1 grams of methylammonium halide to a 50 milliliter schlenk tube. To precondition the methylammonium halide, attach the tube to a schlenk line equipped with the rotary pump and evacuate the tube.Adjust the pressure to 0.185 Torr. Then, immerse the tube in the silicone bath for two hours while stirring the bath at 600 rpm. After this, remove the schlenk tube from the oil bath.Leave the tube under an overpressure of flowing nitrogen gas, to prevent moisture intake. Then make the precursor solutions by dissolving 0.146 grams lead bromide in one milliliter DMF, and then 0.369 grams of lead iodide and 0.073 grams of lead bromide in one milliliter of DMF. Sonicate these for approximately five minutes at 35 kilohertz to fully dissolve the precursor.Using a 0.2 micron PTFE filter, filter the precursor solution. Heat the filtered solution to 110 degree celsius for five minutes. Using a micropipette, deposit 80 microliters of heated lead halide precursor solution onto the substrate.Then, spin the substrate at 500 rpm for five seconds with an acceleration rate of 500 rpm/s and at 1500 rpm, for three minutes with an acceleration rate 1500 rpm.s. Next, transfer the substrate onto a hot plate in a fume hood. Dry the precursor film at 110 degree celsius for 15 minutes under flowing nitrogen gas.Load the dried substrate into the prepared schlenk tube orienting the lead halide surface away from the methylammonium halide in the tube. Adjust the pressure in the schlenk tube to 0.185 Torr. Then, immerse the tube in the silicone oil bath heated to 120 degree celsius for two hours.After this, remove the tube from the oil bath. Remove the sample from the schlenk tube and quickly dip it into a beaker containing isopropyl alcohol. Use an N2 gun to immediately dry the rinsed sample.In this study, pinhole-free methylammonium lead halide thin films are synthesized by LP vasp and subsequently characterized. NMR analysis of the precursors shows methyl group shifts at delta 2.35 pbm and delta 2.37 pbm. An ammonium shift centered at delta 7.65 pbm and delta 7.45 pbm, for methylammonium bromide and methylammonium iodide respectively, confirming their identity and purity.Scanning electron microscopy is then used to analyze mixed flat halide films and kneeled in 100%50%and 30%methylammonium iodide. Each of the faceted films is seen to be pinhole free with grain size up to 700 nanometers. While the standard thickness of the perovskite films is about 400 nanometers, the thickness can be changed by varying the spin coating rotational speed with higher speeds yielding thinner films and vice versa.X ray diffraction patterns are then collected to confirm phase purity and conversion of the precursors to methylammonium lead halide perovskite films. Residual or not converted lead iodide phase is seen to show a peak at approximately 12.7 degrees. The methylammonium lead halide films are seen films to exhibit a shift to higher angles due to a gradual replacement of the larger iodine atoms by smaller bromide atoms.While attempting this procedure, please keep in mind that the use of a schlenk line includes explosion and implosion risks. So, before you perform this experiment, please check the integrity of the apparatus. The development of this technique paves the way for researchers in the field of thin film solar cells, as well as, optoelectronics to synthesize high quality organometal highlight perovskite thin films.With this process, you can make thin film solar cells in planar geometry, reaching efficiencies of up to 19%and they show enhanced long term stability. After watching this video, you should have a good understanding of how to synthesize homogenous, phenofree, high optoelectronic quality, material volume lead halide film by LP vasp.

low-pressure-vapor-assisted-solution-process-for-tunable-band-gap

Research

JoVE Journal

Chemistry

Template Directed Synthesis of Plasmonic Gold Nanotubes with Tunable IR Absorbance

A nearly parallel array of pores can be produced by anodizing aluminum foils in acidic environments1, 2. Applications of anodic aluminum oxide (AAO) membranes have been under development since the 1990's and have become a common method to template the synthesis of high aspect ratio nanostructures, mostly by electrochemical growth or pore-wetting. Recently, these membranes have become commercially available in a wide range of pore sizes and densities, leading to an extensive library of functional nanostructures being synthesized from AAO membranes. These include composite nanorods, nanowires and nanotubes made of metals, inorganic materials or polymers 3-10. Nanoporous membranes have been used to synthesize nanoparticle and nanotube arrays that perform well as refractive index sensors, plasmonic biosensors, or surface enhanced Raman spectroscopy (SERS) substrates 11-16, as well as a wide range of other fields such as photo-thermal heating 17, permselective transport 18, 19, catalysis 20, microfluidics 21, and electrochemical sensing 22, 23. Here, we report a novel procedure to prepare gold nanotubes in AAO membranes. Hollow nanostructures have potential application in plasmonic and SERS sensing, and we anticipate these gold nanotubes will allow for high sensitivity and strong plasmon signals, arising from decreased material dampening 15.

Solution-suspendable gold nanotubes with controlled dimensions can be synthesized by electrochemical deposition in porous anodic aluminum oxide (AAO) membranes using a hydrophobic polymer core. Gold nanotubes and nanotube arrays hold promise for applications in plasmonic biosensing, surface-enhanced Raman spectroscopy, photo-thermal heating, ionic and molecular transport, microfluidics, catalysis and electrochemical sensing.

A nearly parallel array of pores can be produced by anodizing aluminum foils in acidic environments1, 2. Applications of anodic aluminum oxide (AAO) ...

Towards Biomimicking Wood: Fabricated Free-standing Films of Nanocellulose, Lignin, and a Synthetic Polycation

Woody materials are comprised of plant cell walls that contain a layered secondary cell wall composed of structural polymers of polysaccharides and lignin. Layer-by-layer (LbL) assembly process which relies on the assembly of oppositely charged molecules from aqueous solutions was used to build a freestanding composite film of isolated wood polymers of lignin and oxidized nanofibril cellulose (NFC). To facilitate the assembly of these negatively charged polymers, a positively charged polyelectrolyte, poly(diallyldimethylammomium chloride) (PDDA), was used as a linking layer to create this simplified model cell wall. The layered adsorption process was studied quantitatively using quartz crystal microbalance with dissipation monitoring (QCM-D) and ellipsometry. The results showed that layer mass/thickness per adsorbed layer increased as a function of total number of layers. The surface coverage of the adsorbed layers was studied with atomic force microscopy (AFM). Complete coverage of the surface with lignin in all the deposition cycles was found for the system, however, surface coverage by NFC increased with the number of layers. The adsorption process was carried out for 250 cycles (500 bilayers) on a cellulose acetate (CA) substrate. Transparent free-standing LBL assembled nanocomposite films were obtained when the CA substrate was later dissolved in acetone. Scanning electron microscopy (SEM) of the fractured cross-sections showed a lamellar structure, and the thickness per adsorption cycle (PDDA-Lignin-PDDA-NC) was estimated to be 17 nm for two different lignin types used in the study. The data indicates a film with highly controlled architecture where nanocellulose and lignin are spatially deposited on the nanoscale (a polymer-polymer nanocomposites), similar to what is observed in the native cell wall.

The objective of this research was to form synthetic plant cell wall tissue using layer-by-layer assembly of nanocellulose fibrils and isolated lignin assembled from dilute aqueous suspensions.&#160; Surface measurement techniques of quartz crystal microbalance and atomic force microscopy were used to monitor the formation of the polymer-polymer nanocomposite material.

Woody materials are comprised of plant cell walls that contain a layered secondary cell wall composed of structural polymers of polysaccharides and ...

Fabrication of Large-area Free-standing Ultrathin Polymer Films

This procedure describes a method for the fabrication of large-area and ultrathin free-standing polymer films. Typically, ultrathin films are prepared using either sacrificial layers, which may damage the film or affect its mechanical properties, or they are made on freshly cleaved mica, a substrate that is difficult to scale. Further, the size of ultrathin film is typically limited to a few square millimeters. In this method, we modify a surface with a polyelectrolyte that alters the strength of adhesion between polymer and deposition substrate. The polyelectrolyte can be shown to remain on the wafer using spectroscopy, and a treated wafer can be used to produce multiple films, indicating that at best minimal amounts of the polyelectrolyte are added to the film. The process has thus far been shown to be limited in scalability only by the size of the coating equipment, and is expected to be readily scalable to industrial processes. In this study, the protocol for making the solutions, preparing the deposition surface, and producing the films is described.

We describe a method for the fabrication of large-area (up to 13 cm diameter) and ultrathin (as thin as 8 nm) polymer films. Instead of using a sacrificial interlayer to delaminate the film from its substrate, we use a self-limiting surface treatment suitable for arbitrarily large areas.

This procedure describes a method for the fabrication of large-area and ultrathin free-standing polymer films.  Typically, ultrathin films are prepared ...

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 ...

Low-energy Cathodoluminescence for (Oxy)Nitride Phosphors

Nitride and oxynitride (Sialon) phosphors are good candidates for the ultraviolet and visible emission applications. High performance, good stability and flexibility of their emission properties can be achieved by controlling their composition and dopants. However, a lot of work is still required to improve their properties and to reduce the production cost. A possible approach is to correlate the luminescence properties of the Sialon particles with their local structural and chemical environment in order to optimize their growth parameters and find novel phosphors. For such a purpose, the low-voltage cathodoluminescence (CL) microscopy is a powerful technique. The use of electron as an excitation source allows detecting most of the luminescence centers, revealing their luminescence distribution spatially and in depth, directly comparing CL results with the other electron-based techniques, and investigating the stability of their luminescence properties under stress. Such advantages for phosphors characterization will be highlighted through examples of investigation on several Sialon phosphors by low-energy CL.

Low-energy Cathodoluminescence for OxyNitride Phosphors

An excellent chemical and luminescence stabilities of (oxy)nitride phosphors present it as an promising alternative to currently used sulfide and oxide phosphors. In this paper, we present the way to investigate its local luminescence properties using low-energy cathodoluminescence (CL).

Nitride and oxynitride (Sialon) phosphors are good candidates for the ultraviolet and visible emission applications. High performance, good stability and ...

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 ...

The Synthesis of [Sn10(Si(SiMe3)3)4]2- Using a Metastable Sn(I) Halide Solution Synthesized via a Co-condensation Technique

The number of well-characterized metalloid tin clusters, synthesized by applying the disproportionation of a metastable Sn(I) halide in the presence of a sterically demanding ligand, has increased in recent years. The metastable Sn(I) halide is synthesized at&#160;&#34;outer space conditions&#34; via the preparative co-condensation technique. Thereby, the subhalide is synthesized in an oven at high temperatures, around 1,300 &#176;C, and at reduced pressure by the reaction of elemental tin with hydrogen halide gas (e.g., HCl). The subhalide (e.g., SnCl) is trapped within a matrix of an inert solvent, like toluene at -196 &#176;C. Heating the solid matrix to -78 &#176;C gives a metastable solution of the subhalide. The metastable subhalide solution is highly reactive but can be stored at -78 &#176;C for several weeks. On heating the solution to room temperature, a disproportionation reaction occurs, leading to elemental tin and the corresponding dihalide. By applying bulky ligands like Si(SiMe3)3, the intermediate metalloid cluster compounds can be trapped before complete disproportionation to elemental tin. Hence, the reaction of a metastable Sn(I)Cl solution with Li-Si(SiMe3)3 gives [Sn10(Si(SiMe3)3)4]2- 1 as black crystals in high yield. 1 is formed via a complex reaction sequence including salt metathesis, disproportionation, and degradation of larger clusters. Further, 1 can be analyzed by various methods like NMR or single crystal X-ray structure analysis.

The Synthesis of [Sn10SiSiMe334]2- Using a Metastable SnI Halide Solution Synthesized via a Co-condensation Technique

The disproportionation reaction of a metastable Sn(I) chloride solution, obtained via the preparative co-condensation technique, is used for the synthesis of a metalloid tin cluster compound.

The number of well-characterized metalloid tin clusters, synthesized by applying the disproportionation of a metastable Sn(I) halide in the presence of a ...

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. ...

Solution-Processed "Silver-Bismuth-Iodine" Ternary Thin Films for Lead-Free Photovoltaic Absorbers

Bismuth-based hybrid perovskites are regarded as promising photo-active semiconductors for environment-friendly and air-stable solar cell applications. However, poor surface morphologies and relatively high bandgap energies have limited their potential. Silver-bismuth-iodine (Ag-Bi-I) is a promising semiconductor for optoelectronic devices. Therefore, we demonstrate the fabrication of Ag-Bi-I ternary thin films using material solution processing. The resulting thin films exhibit controlled surface morphologies and optical bandgaps according to their thermal annealing temperatures. In addition, it has been reported that Ag-Bi-I ternary systems crystallize to AgBi2I7, Ag2BiI5, etc. according to the ratio of the precursor chemicals. The solution-processed AgBi2I7 thin films exhibit a cubic-phase crystal structure, dense, pinhole-free surface morphologies with grains ranging in size from 200 to 800 nm, and an indirect bandgap of 1.87 eV. The resultant AgBi2I7 thin films show good air stability and energy band diagrams, as well as surface morphologies and optical bandgaps suitable for lead-free and air-stable single-junction solar cells. Very recently, a solar cell with 4.3% power conversion efficiency was obtained by optimizing the Ag-Bi-I crystal compositions and solar cell device architectures.

Solution-Processed &quot;Silver-Bismuth-Iodine&quot; Ternary Thin Films for Lead-Free Photovoltaic Absorbers

Herein, we present detailed protocols for solution-processed silver-bismuth-iodine (Ag-Bi-I) ternary semiconductor thin films fabricated on TiO2-coated transparent electrodes and their potential application as air-stable and lead-free optoelectronic devices.

Bismuth-based hybrid perovskites are regarded as promising photo-active semiconductors for environment-friendly and air-stable solar cell applications. ...

Synthesis of Soft Polysiloxane-urea Elastomers for Intraocular Lens Application

This study discusses a synthesis route for soft polysiloxane-based urea (PSU) elastomers for their applications as accommodating intraocular lenses (a-IOLs). Aminopropyl-terminated polydimethylsiloxanes (PDMS) were previously prepared via the ring-chain equilibration of the cyclic siloxane octamethylcyclotetrasiloxane (D4) and 1,3-bis(3-aminopropyl)-tetramethyldisiloxane (APTMDS). Phenyl groups were introduced into the siloxane backbone via the copolymerization of D4 and 2,4,6,8-tetramethyl-2,4,6,8-tetraphenyl-cyclotetrasiloxane (D4Me,Ph). These polydimethyl-methyl-phenyl-siloxane-block copolymers were synthesized for increasing the refractive indices of polysiloxanes. For applications as an a-IOL, the refractive index of the polysiloxanes must be equivalent to that of a young human eye lens. The polysiloxane molecular weight is controlled by the ratio of the cyclic siloxane to the endblocker APTMDS. The transparency of the PSU elastomers is examined by the transmittance measurement of films between 200 and 750 nm, using a UV-Vis spectrophotometer. Transmittance values at 750 nm (upper end of the visible spectrum) are plotted against the PDMS molecular weight, and &#62; 90% of the transmittance is observed until a molecular weight of 18,000 g&#183;mol&#8722;1. Mechanical properties of the PSU elastomers are investigated using stress-strain tests on die-cut dog-bone-shaped specimens. For evaluating mechanical stability, mechanical hysteresis is measured by repeatedly stretching (10x) the specimens to 5% and 100% elongation. Hysteresis considerably decreases with the increase in the PDMS molecular weight. In vitro cytotoxicity of some selected PSU elastomers is evaluated using an MTS cell viability assay. The methods described herein permit the synthesis of a soft, transparent, and noncytotoxic PSU elastomer with a refractive index approximately equal to that of a young human eye lens.

This study describes synthetic routes for aminopropyl-terminated polydimethylsiloxanes and polydimethyl-methyl-phenyl-siloxane-block copolymers and for soft polysiloxane-based urea (PSU) elastomers. It presents the application of PSUs as accommodating an intraocular lens. An evaluation method for in vitro cytotoxicity is also described.

This study discusses a synthesis route for soft polysiloxane-based urea (PSU) elastomers for their applications as accommodating intraocular lenses ...