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 explosive. Please ensure to receive appropriate on the job training by experts before using vacuum-systems, Schlenk lines, and cryogenic liquids. Please use all appropriate safety practices when performing the synthesis including the use of engineering controls (fume hood) and personal protective equipment (safety glasses, gloves, lab coat, full length pants, closed-toe shoes). All of the following procedures described below are performed in a fume hood in air, unless stated differently.
1. Preparation of Methylammonium Halide
<ol>
	<li>To a 250 mL round bottom flask equipped with a stir bar, add ethanol (100 mL) and methylamine (190 mmol, 16.5 mL, 40%wt in H2O), and cool the flask to 0 &#176;C with an ice bath.</li>
	<li>While the methylamine solution is stirring (for about 5 min at 600 revolution per min (rpm)), add HI (76 mmol, 10 mL, 57%wt in H2O) or HBr (76 mmol, 8.6 mL, 48%wt in H2O) dropwise, and seal the flask with a septum.</li>
	<li>Allow the reaction to stir for 2 h at 0 &#730;C.</li>
	<li>Remove the reaction flask from the ice bath and evaporate the solvent and unreacted volatile components at reduced pressure (~50 Torr) with a rotary evaporator equipped with a water bath at 60 &#730;C for 4 h or until the volatiles are removed.</li>
	<li>To recrystallize the resulting solid, add warm (~50 &#176;C) ethanol (100 mL) and dissolve the residual material.</li>
	<li>Slowly add diethyl ether (200 mL) to induce crystallization of a white solid.</li>
	<li>Vacuum filter the mixture over a coarse 50 mm glass frit filter.</li>
	<li>Recover the supernatant and add diethyl ether (200 mL) to induce additional crystallization of white solid. Vacuum filter the mixture over a second coarse 50 mm glass frit filter.</li>
	<li>Combine the white solids on a coarse 50 mm glass frit filter and, while vacuum filtering, wash the resulting powder with diethyl ether three times (~30 mL each time).</li>
	<li>Dry the white solid under vacuum. This procedure yields (58.9 mmol, 9.360 g, 77%) of methylammonium iodide (CH3NH3I) and (55.5 mmol, 6.229 g, 73%) of methylammonium bromide (CH3NH3Br).</li>
	<li>Store in the dark and in a desiccator at room temperature in order to minimize decomposition over time.</li>
</ol>
2. Preparation of Methylammonium Lead Halide (CH3NH3PbI3-xBrx ) Thin Films6,20
<ol>
	<li>Pre-conditioning of the Schlenk tube
	<ol>
		<li>Load a 50 mL Schlenk tube (diameter 2.5 cm) with 0.1 g of methylammonium halide. To prevent the chemicals sticking to the walls of the test tube, use a weighing paper cylinder to transfer the methylammonium halide into the tube. 
		NOTE: The final ratio of I/(I+Br) in CH3NH3PbI3-xBrx is determined by the methylammonium halide composition in the test tube. For example, to achieve 30% I content, the Schlenk tube is loaded with 0.03 g CH3NH3I and 0.07 g CH3NH3Br. Actual obtained compositions may vary with experimental setup, so calibration of the synthesis conditions to yield specific target compositions is necessary. In the present case, this was accomplished by measuring halide content in the synthesized films via energy dispersive X-ray spectroscopy (EDX).</li>
		<li>Use a Schlenk line equipped with a rotary pump to connect and evacuate the tube. Adjust the pressure to 0.185 Torr. Then, immerse the test tube in a silicone oil bath pre-heated to 120&#176;C, with a magnetic stirrer (600 rpm) for 2 h (pre-conditioning of the Schlenk tube). 
		NOTE: This step allows for sublimation of the methylammonium precursor along the sides of the Schlenk tube. It is important to ensure the sublimation of the methylammonium precursor during the two hours of pre-conditioning. A thin layer of methylammonium precursor will condense along the sides of the Schlenk tube to cover the lower half of the tube. If sublimation of the methylammonium precursor is not observed or is happening too fast, check if the pressure of the Schlenk line and the temperature of the oil bath are correct, or try to use fresh methylammonium halide precursor.&#160;</li>
		<li>Remove Schlenk tube from the oil bath and leave methylammonium halide under an overpressure of flowing N2 to avoid moisture intake.</li>
	</ol>
	</li>
	<li>Substrate preparation
	<ol>
		<li>Sonicate one substrate (glass or FTO coated glass, 14 x 16 mm2) with water (~3 mL) containing detergent for 15 min in a test tube (diameter 1.5 cm and height 15 cm) at 35 KHz.</li>
		<li>Discard the detergent/water by rinsing with ultrapure water (~10 mL) 5 times.</li>
		<li>Discard the ultrapure water, add acetone (~3 mL), and sonicate for 15 min at 35 KHz.</li>
		<li>Discard the acetone, add isopropanol (~3 mL), and sonicate for 15 min at 35 KHz.</li>
		<li>Discard the isopropanol, recover the substrate from the test tube with tweezers, and dry it with a N2 gun for 15 s.</li>
		<li>Deposit TiO2 compact layer (100 nm) on FTO glass substrates by electron beam evaporation at a substrate temperature of 350 &#176;C, and a deposition rate of 0.5 &#197;/s using substrate rotation.21</li>
	</ol>
	</li>
	<li>Preparation of the lead halide precursor solution
	<ol>
		<li>For the preparation of MAPbI3-xBrx (0 &#60; x &#60; 3), dissolve PbI2 (0.8 mmol, 0.369 g) and PbBr2 (0.2 mmol, 0.073 g) in 1 mL DMF to achieve a final concentration of 0.8 M of PbI2 and 0.2 M of PbBr2. Sonicate for 5 min at 35 KHz to fully dissolve the precursor.
		<ol>
			<li>For the preparation of pure iodine or bromine films, dissolve PbI2 (1 mmol, 0.461 g) or PbBr2 (0.8 mmol, 0.294 g) in 1 mL DMF, to achieve a final concentration of 1 M and 0.8 M, respectively. Sonicate for 5 min at 35 KHz to fully dissolve the precursor.</li>
			<li>For the preparation of chlorine-doped methylammonium lead iodide perovskite films, dissolve PbI2 (0.369 g) and PbCl2 (0.056 g) in 1 mL DMF, to achieve a final concentration of 0.8 M of PbI2 and 0.2 M of PbCl2. Sonicate for 5 min at 35 KHz to fully dissolve the precursor.</li>
		</ol>
		</li>
		<li>Filter the precursor solution with a 0.2 &#956;m polytetrafluorethylene (PTFE) filter.</li>
	</ol>
	</li>
	<li>Lead halide deposition
	<ol>
		<li>Pre-heat the precursor solution on a hot plate set to 110 &#176;C for 5 min.</li>
		<li>With a micropipette, drop 80 &#956;L of the pre-heated lead halide precursor solution onto the non-rotating substrate (glass or TiO2 deposited on FTO coated glass; 14 x 16 mm2 size). Spin at 500 rpm for 5 s with an acceleration rate of 500 rpm s-1, and 1500 rpm for 3 min with an acceleration rate of 1,500 rpm s-1.</li>
		<li>In a fumehood, dry precursor film for 15 min at 110 &#176;C on a hot plate under flowing N2. 
		NOTE: A crystalizing dish is used and placed over the substrate to allow the precursor to dry in a N2 atmosphere. To vary the thickness of the resulting perovskite film, the speed of the second spin-coating step can be varied from 1,200 to 12,000 rpm to achieve film thickness in the range of 500 to 100 nm. To further decrease the film thickness, diluted precursor solution can be used.</li>
	</ol>
	</li>
	<li>Vapor-assisted annealing
	<ol>
		<li>Load sample into the Schlenk tube (prepared according to instructions in section 2.1.2). Adjust the pressure to 0.185 Torr. 
		NOTE: The sample sits in the test tube above the methylammonium halide without being in direct contact with it. To slow down incorporation of methylammonium, the lead halide surface is oriented to face away from the methylammonium halide.</li>
		<li>Immerse the Schlenk tube loaded with the sample in silicone oil bath heated to 120 &#176;C for 2 h.</li>
		<li>Take out the sample and quickly rinse it by dipping it in a beaker containing isopropyl alcohol. Immediately dry the rinsed sample with a N2 gun. 
		NOTE: To prepare pure CH3NH3PbI3 use PbI2 as the halide precursor and pure methylammonium iodide in the vapor-assisted annealing step. To prepare CH3NH3PbBr3 use PbBr2 as the halide precursor and pure methylammonium bromide in the vapor-assisted annealing step.</li>
	</ol>
	</li>
</ol>

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The authors have nothing to disclose.

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, ...

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

Research

JoVE Journal

Chemistry

9.5K Views.  Lawrence Berkeley National Laboratory. Hier presenteren we een protocol voor de synthese van33NH CH I en CH3NH3Br precursoren en de daaropvolgende vorming van pinhole-vrije, continue CH3NH3PbI3-xBrx dunne lagen voor de toepassing in hoge efficiëntie zonnecellen en andere opto-elektronische apparaten.

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

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 ...

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 ...

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.

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. ...

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

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