This work was financially supported of by the Ministry of Science and Technology and National Science Council of Republic of China (contract nos. NSC 101-2221-E-027-042 and NSC 101-2622-E-027-003-CC2). D. H. Wei thanks the National Taipei University of Technology (TAIPEI TECH) for the Dr. Shechtman Prize Award.

1. Substrate Preparation and Cleaning
<ol>
	<li>Cut 10 mm x 10 mm silicon substrates from Si(100) wafer.</li>
	<li>Cut 10 mm x 10 mm glass substrates.</li>
	<li>Use ultrasonic cleaner to clean the silicon and glass substrates with acetone for 10 min, alcohol for 10 min, and then isopropanol for 15 min.</li>
	<li>Rinse the substrates with deionized (DI) water three times.</li>
	<li>Blow-dry the substrates with a nitrogen gun.</li>
</ol>
2. DEZn Preparation and Preservation
Note: Diethylzinc (C2H5)2Zn, also called DEZn, is a highly pyrophoric organozinc compound consisting of a zinc center bound to two ethyl groups. Never work alone when using DEZn. DEZn is very toxic and sensitive to the oxygen and water, be sure not to place the DEZn near the water. Always wear protective masks and eye protection; all procedures must be performed in the hood. Most importantly, unused DEZn must be stored in a 5 oC environment.
Note: For the first use of DEZn, follow step 2. If not, start the experiment from step 3.
<ol>
	<li>Use syringe to draw out 30 ml&#160;DEZn from the bottle and then inject into a beaker placed in a steel cylinder.</li>
	<li>Use a galvanized iron pipe to connect the steel cylinder with the reaction chamber.</li>
	<li>Use mechanical pump and ball valve to pump down the steel cylinder in vacuum environment (to 6 Torr). 
	Note: DEZn will severely react with oxygen, it must be maintained in the vacuum environment.</li>
	<li>Store the unused DEZn in a 5 oC environment.</li>
</ol>
3. PECVD Chamber Preparation and Synthesis of ZnO Thin Films
Note: The schematic diagram of plasma enhanced chemical vapor deposition is depicted in Figure 1.
<ol>
	<li>Set the working distance between showerhead electrode and sample stage at 30 mm.</li>
	<li>Place the substrates on the sample stage of reaction chamber in proper location where there is a 3 cm distance from the DEZn inlet.</li>
	<li>Open the rotary pump and gradually open the gate valves and butterfly valve.</li>
	<li>Wait until the background pressure of the reactor chamber is lower than 30 mTorr.</li>
	<li>Close the gate valves and butterfly valve, which connects to the rotary pump.</li>
	<li>Then open the turbo pump and relative gate valves to reach high vacuum of 3 x 10-6 Torr.</li>
	<li>After reaching the necessary&#160;vacuum condition, open the heat controller and heat the sample stage to the synthesis temperature (200, 300, 400, 500, and 600 oC for different experiment parameters).</li>
	<li>When the temperature and the pressure reach the necessary condition, close the turbo pump and then open the gate valves and butterfly valve which connects to the rotary pump simultaneously.</li>
	<li>Next, open the gas inlet valves and turn on the argon gas flow controller simultaneously.</li>
	<li>Flow the argon gas (0.167 ml/sec) into the chamber.</li>
	<li>Set the chamber pressure to 500 mTorr.</li>
	<li>Turn on the RF (13.56 MHz) generator and matching network, then set the RF power at 100 W for purging the samples surface for 15 min.</li>
	<li>After finishing the purge of samples, turn the RF power down to 70 W.</li>
	<li>Next, turn on the carbon dioxide gas controller and gas inlet valve.</li>
	<li>Flow the carbon dioxide (0.5 ml/sec) into the chamber.</li>
	<li>Set the working pressure at 6 Torr.</li>
	<li>After the chamber pressure reaches 6 Torr, flow the high pure argon as carrier gas (0.167 ml/sec) for carrying diethylzinc (DEZn) into the chamber and open ball valve connected to the DEZn simultaneously. At the same time, start the synthesis of ZnO films.</li>
	<li>Continue the plasma synthesis of ZnO films for 5 min.</li>
	<li>After the ZnO films have been synthesized, seriatim turn off the RF generator, ball valve, heat controller and all of gas flow controllers along with gas inlet valves.</li>
	<li>Take out the sample when the sample stage temperature cools down to RT. Note: The cooling rate is approximately 1.8 oC/min.</li>
</ol>
4. Preparation of Interdigitated-like Pattern onto As-synthesized ZnO Thin Film
Note: The schematic of lithography process is depicted in Figure 3.
<ol>
	<li>Use a hot plate to bake the as-synthesized ZnO sample at 150 oC for 10 min.</li>
	<li>Place the sample on the spin coater, and then dispense the liquid solution of photoresist (S1813) with 100 &#181;l&#160;onto the ZnO sample.</li>
	<li>Run the spin coater at 800 rpm for 10 sec and then accelerate to 3,000 rpm for 30 sec to produce a uniformly thin layer.</li>
	<li>Soft bake the photoresist-coated ZnO sample at 105 oC for 90 sec.</li>
	<li>After the soft-baking, use UV light to expose the photoresist-coated sample trough a photomask by mask aligner. The exposure time is 2 sec and the power is 400 W. 
	Note: The pattern of photomask is designed as interdigitated-like, which is 0.03 mm wide and 4 mm long (14 pairs) and has an inter-electrode spacing of 0.15 mm as depicted in Figure 2. It is worth noting that the total photosensitive area is 84.32 mm2 for the detector.</li>
	<li>After the exposure procedure, use tweezers to clip the sample, and then immerse into the diluted developer (mix 50 ml&#160;of developer and 150 ml&#160;of deionized water) through actions of swinging from side to side for 35 s to obtain the developed sample.</li>
	<li>Rinse the developed sample with DI water and dry with nitrogen gas.</li>
	<li>Use the optical microscope to check the pattern intact. If not, use acetone to remove the photoresist and repeat steps 4.2 to 4.7 until the perfect pattern has been obtained.</li>
	<li>Hard bake the sample at 120 oC for 20 min.</li>
</ol>
5. Deposition of Pt Top Electrode and Chemical Lift-off
<ol>
	<li>Use the RF magnetron sputtering system to deposit a thin conductive Pt layer (100 nm) on the top of the developed sample before proceeding to chemical lift-off procedure.</li>
	<li>Set the distance between target and substrate at 13 mm.</li>
	<li>Use the mechanical pump to reach a rough vacuum of 5 mTorr.</li>
	<li>Then, use the turbo pump to obtain a high vacuum of 7 x 10-7 Torr.</li>
	<li>Wait until the chamber reaches the high vacuum, close the turbo pump and open the mechanical pump subsequently.</li>
	<li>Flow the argon gas at 0.3 ml/sec&#160;into the chamber by mas flow controller until the chamber pressure reach the working pressure of 100 mTorr.</li>
	<li>Turn on the direct current (DC) discharge power supply and set the DC power at 15 W for sputtering the Pt thin film electrode onto the sample for 25 min.</li>
	<li>After the Pt electrode layer has been deposited by magnetron sputtering method, take out the sample from the chamber.</li>
	<li>Immerse the sample into the acetone liquid for chemical lift-off process by ultrasonic cleaner to remove the photoresist.</li>
	<li>Set the cleaning time at 1 min to thoroughly remove photoresist, and then obtain the interdigitated-like Pt electrode onto the ZnO thin film.</li>
</ol>
6. RTA process
<ol>
	<li>Place the as-fabricated Pt/ZnO sample into the RTA system.</li>
	<li>Use the mechanical pump and gate valve to pump down the RTA chamber pressure to 20 mTorr.</li>
	<li>Wait until the chamber pressure reaches 20 mTorr, flow argon gas at 0.3 ml/sec into the chamber and set the working pressure of 5 Torr.</li>
	<li>Next, set the heating rate as 100 oC/min.</li>
	<li>Then, anneal the sample at 450 oC for 10 min.</li>
	<li>Once annealed, wait until the sample cools to RT, then take out the sample.</li>
</ol>

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The authors declare that they have no competing financial interests.

Critical steps and modifications
In step 1, the substrates should be thoroughly cleaned and steps 1.3 to 1.5 followed to make sure that there is no grease or organic and inorganic contaminations on the substrates. Any grease or organic and inorganic contaminations on the substrate surface will significantly reduce the adhesion of the film.
Step 2 is the most important procedure before the ZnO film preparation process. DEZn is very toxic and violently reacts with wat...

ZnO is a promising wide-band-gap functional semiconductor material due to its unique properties such as high chemical stability, low cost, non-toxicity, low power threshold for optical pumping, wide direct band gap (3.37 eV) at RT and large exciton binding energy of ~60 meV 1-2. Recently, ZnO thin films have been employed in many application fields including transparent conductive oxide (TCO) films, blue light emitting device, field-effect transistors, and gas sensor 3-6. On the other hand, ZnO is a candidate material to replace indium tin oxide (ITO) owing to indium and tin being rare and expensive. Moreover, ZnO possesses&#160;high optical transmittance in the visible wavelength region and low resistivity compared with ITO films 7-8. Accordingly, fabrication, characterization and application of ZnO has been extensively reported. This present study focuses on synthesizing high c-axis (0002) ZnO thin films by a simple and effectively method and its practical application towards a UV photodetector.
The recent research report findings indicate that the high quality ZnO thin film could be synthesized by various techniques such as sol-gel method, radio frequency magnetron sputtering, metal organic chemical vapor deposition (MOCVD), and so on 9-14. Each technique has its advantages and disadvantages. For example, a principal advantage of sputtering deposition is that target materials with very high melting point are effortlessly sputtered onto the substrate. In contrast, the sputtering process is difficult to combine with a lift-off for structuring the film. In our study, the plasma enhanced chemical vapor deposition (PECVD) system was employed to synthesize high quality c-axis ZnO thin films. Plasma bombardment is a key factor in the synthesizing process that can increase the thin film density and enhance the ion decomposition reaction rate 15. In addition, the high growth rate and large-area uniform deposition are other distinctive advantages for PECVD technique.
Except for the synthesis technique, the good adhesion on the substrate is another considered issue. In many studies, the c-plane sapphire has been widely used as the substrate to synthesize high c-axis ZnO thin films because the ZnO and sapphire have the same hexagonal lattice structure. However, the ZnO was synthesized on sapphire substrate exhibiting rough surface morphology and high residual (defect-related) carrier concentrations due to the large lattice misfits between the ZnO and c-plane sapphire (18%) oriented in the in-plane direction 16. Compared with the sapphire substrate, a Si wafer is another widely used substrate for the ZnO synthesis. Si wafers have been extensively used in semiconductor industry; and thus, growth of high quality ZnO thin films on Si substrates is very important and necessary. Unfortunately, the crystal structure and thermal expansion coefficient between the ZnO and Si are obviously different leading to deterioration of crystal quality. Over past decade, great efforts have been made to improve the quality of ZnO thin films onto Si substrates by using various methods including ZnO buffer layers 17, annealing in various gas atmosphere 18, and passivation of the Si substrate surface 19. The present study successfully offered a simple and effectively method to synthesize high c-axis ZnO thin film onto Si substrates without any buffer layer or pre-treatment. The experiment results indicated that the ZnO thin films synthesized under the optimal growth temperature showed the good crystal and optical qualities. The crystalline structure, RF plasma composition, surface morphology, and optical properties of ZnO thin films were investigated by X-ray diffraction (XRD), optical emission spectroscopy (OES), field emission scanning electron microscopy (FE-SEM), and RT photoluminescence (PL) spectra, respectively. Moreover, the transmittance of ZnO thin films was also confirmed and reported.
The as-synthesized ZnO thin film served as a sensing layer for UV photodetector application was also investigated in this study. The UV photodetector has great potential applications in UV monitoring, optical switch, flame alarm, and missile warming system 20-21. There are many types of photodetectors which have been carried out such as positive intrinsic negative (p-i-n) mode and metal-semiconductor-metal (MSM) structures including Ohmic contact and Schottky contact. Each type has its own advantages and drawbacks. Currently, MSM photodetector structures have attracted intensive interest due to their outstanding performance in responsivity, reliability and response and recovery time 22-24. The results presented here have shown that the MSM Ohmic contact mode was employed to fabricate ZnO thin film based UV photodetector. Such a kind of photodetector typically reveals a good responsivity and reliability, indicating that the high c-axis ZnO thin film is a suitable sensing layer for UV photodetector.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>RF power supply</td>
			<td>ADVANCED ENERGY</td>
			<td>RFX-600</td>
			<td></td>
		</tr>
		<tr>
			<td>Butterfly valve</td>
			<td>MKS</td>
			<td>253B-1-40-1</td>
			<td></td>
		</tr>
		<tr>
			<td>Mass flow conctroller</td>
			<td>PROTEC INSTRUMENTS</td>
			<td>PC-540</td>
			<td></td>
		</tr>
		<tr>
			<td>Pressure conctroller</td>
			<td>MKS</td>
			<td>600 series&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>Heater</td>
			<td>UPGRADE INSTRUMENT CO.</td>
			<td>UI-TC 3001</td>
			<td></td>
		</tr>
		<tr>
			<td>Sputter gun</td>
			<td>AJA INTERNATIONAL</td>
			<td>A320-HA</td>
			<td></td>
		</tr>
		<tr>
			<td>DEZn 1.5M</td>
			<td>ACROS ORGANIC USA, New Jersey</td>
			<td></td>
			<td>also called Diethylzinc (C2H5)2Zn</td>
		</tr>
		<tr>
			<td>Spin coater&#160;</td>
			<td>SWIENCO</td>
			<td>PW - 490</td>
			<td></td>
		</tr>
		<tr>
			<td>I-V measurement</td>
			<td>Keithley</td>
			<td>Model: 2400</td>
			<td></td>
		</tr>
		<tr>
			<td>Photocondutive measurement&#160;</td>
			<td>Home-built</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>UV light sourse</td>
			<td>Panasonic</td>
			<td>ANUJ 6160</td>
			<td></td>
		</tr>
		<tr>
			<td>Mask aligner</td>
			<td>Karl Suss</td>
			<td>MJB4</td>
			<td></td>
		</tr>
		<tr>
			<td>Photoresist</td>
			<td>Shipley a Rohm &#38; Haas company</td>
			<td>S1813</td>
			<td></td>
		</tr>
		<tr>
			<td>Developer</td>
			<td>Shipley a Rohm &#38; Haas company</td>
			<td>MF319</td>
			<td></td>
		</tr>
		<tr>
			<td>Silicon wafer</td>
			<td>E-Light Technology Inc</td>
			<td>12/0801</td>
			<td></td>
		</tr>
		<tr>
			<td>Glass substrate</td>
			<td>CORNING</td>
			<td>1737</td>
			<td>P-type / Boron</td>
		</tr>
	</tbody>
</table>

synthesis and characterization of high c-axis zno thin film by plasma enhanced chemical vapor deposition system and its uv photodetector application

In this study, zinc oxide (ZnO) thin films with high c-axis (0002) preferential orientation have been successfully and effectively synthesized onto silicon (Si) substrates via different synthesized temperatures by using plasma enhanced chemical vapor deposition (PECVD) system. The effects of different synthesized temperatures on the crystal structure, surface morphologies and optical properties have been investigated. The X-ray diffraction (XRD) patterns indicated that the intensity of (0002) diffraction peak became stronger with increasing synthesized temperature until 400 oC. The diffraction intensity of (0002) peak gradually became weaker accompanying with appearance of (10-10) diffraction peak as the synthesized temperature up to excess of 400 oC. The RT photoluminescence (PL) spectra exhibited a strong near-band-edge (NBE) emission observed at around 375 nm and a negligible deep-level (DL) emission located at around 575 nm under high c-axis ZnO thin films. Field emission scanning electron microscopy (FE-SEM) images revealed the homogeneous surface and with small grain size distribution. The ZnO thin films have also been synthesized onto glass substrates under the same parameters for measuring the transmittance.
For the purpose of ultraviolet (UV) photodetector application, the interdigitated platinum (Pt) thin film (thickness ~100 nm) fabricated via conventional optical lithography process and radio frequency (RF) magnetron sputtering. In order to reach Ohmic contact, the device was annealed in argon circumstances at 450 oC by rapid thermal annealing (RTA) system for 10 min. After the systematic measurements, the current-voltage (I-V) curve of photo and dark current and time-dependent photocurrent response results exhibited a good responsivity and reliability, indicating that the high c-axis ZnO thin film is a suitable sensing layer for UV photodetector application.

The ZnO (0002) thin films with high c-axis preferred orientation have been successfully synthesized onto the Si substrates by using the PECVD system. The carbon dioxide (CO2) and the diethylzinc (DEZn) were used as oxygen and zinc precursors, respectively. The crystal structure of ZnO thin films was characterized by X-ray diffraction (Figure 4), indicating that the ZnO thin film synthesized at 400 oC with the strongest (0002) diffraction peak. When the synthesized temperatu...

Watch this Scientific Journal Video about Synthesis and Characterization of High c-axis ZnO Thin Film by Plasma Enhanced Chemical Vapor Deposition System and its UV Photodetector Application at JoVE.c

Synthesis and Characterization of High c-axis ZnO Thin Film by Plasma Enhanced Chemical Vapor Deposition System and its UV Photodetector Application

We offered a method to directly synthesize high c-axis (0002) ZnO thin film by plasma enhanced chemical vapor deposition. The as-synthesized ZnO thin film combined with Pt interdigitated electrode was used as sensing layer for ultraviolet photodetector, showing a high performance through a combination of its good responsivity and reliability.

In this study, zinc oxide (ZnO) thin films with high c-axis (0002) preferential orientation have been successfully and effectively synthesized onto ...

synthesis-characterization-high-c-axis-zno-thin-film-plasma-enhanced

Research

JoVE Journal

Engineering

15.1K Views.  National Taipei University of Technology (TAIPEI TECH). We offered a method to directly synthesize high c-axis (0002) ZnO thin film by plasma enhanced chemical vapor deposition. The as-synthesized ZnO thin film combined with Pt interdigitated electrode was used as sensing layer for ultraviolet photodetector, showing a high performance through a combination of its good responsivity and reliability.

Video: Synthesis and Characterization of High c-axis ZnO Thin Film by Plasma Enhanced Chemical Vapor Deposition System and its UV Photodetector Application

Polycrystalline Silicon Thin-film Solar cells with Plasmonic-enhanced Light-trapping

One of major approaches to cheaper solar cells is reducing the amount of semiconductor material used for their fabrication and making cells thinner. To compensate for lower light absorption such physically thin devices have to incorporate light-trapping which increases their optical thickness. Light scattering by textured surfaces is a common technique but it cannot be universally applied to all solar cell technologies. Some cells, for example those made of evaporated silicon, are planar as produced and they require an alternative light-trapping means suitable for planar devices. Metal nanoparticles formed on planar silicon cell surface and capable of light scattering due to surface plasmon resonance is an effective approach.
The paper presents a fabrication procedure of evaporated polycrystalline silicon solar cells with plasmonic light-trapping and demonstrates how the cell quantum efficiency improves due to presence of metal nanoparticles.
To fabricate the cells a film consisting of alternative boron and phosphorous doped silicon layers is deposited on glass substrate by electron beam evaporation. An Initially amorphous film is crystallised and electronic defects are mitigated by annealing and hydrogen passivation. Metal grid contacts are applied to the layers of opposite polarity to extract electricity generated by the cell. Typically, such a ~2 &mu;m thick cell has a short-circuit current density (Jsc) of 14-16 mA/cm2, which can be increased up to 17-18 mA/cm2 (~25% higher) after application of a simple diffuse back reflector made of a white paint.
To implement plasmonic light-trapping a silver nanoparticle array is formed on the metallised cell silicon surface. A precursor silver film is deposited on the cell by thermal evaporation and annealed at 23&deg;C to form silver nanoparticles. Nanoparticle size and coverage, which affect plasmonic light-scattering, can be tuned for enhanced cell performance by varying the precursor film thickness and its annealing conditions. An optimised nanoparticle array alone results in cell Jsc enhancement of about 28%, similar to the effect of the diffuse reflector. The photocurrent can be further increased by coating the nanoparticles by a low refractive index dielectric, like MgF2, and applying the diffused reflector. The complete plasmonic cell structure comprises the polycrystalline silicon film, a silver nanoparticle array, a layer of MgF2, and a diffuse reflector. The Jsc for such cell is 21-23 mA/cm2, up to 45% higher than Jsc of the original cell without light-trapping or ~25% higher than Jsc for the cell with the diffuse reflector only.
Introduction
Light-trapping in silicon solar cells is commonly achieved via light scattering at textured interfaces. Scattered light travels through a cell at oblique angles for a longer distance and when such angles exceed the critical angle at the cell interfaces the light is permanently trapped in the cell by total internal reflection (Animation 1: Light-trapping). Although this scheme works well for most solar cells, there are developing technologies where ultra-thin Si layers are produced planar (e.g. layer-transfer technologies and epitaxial c-Si layers) 1 and or when such layers are not compatible with textures substrates (e.g. evaporated silicon) 2. For such originally planar Si layer alternative light trapping approaches, such as diffuse white paint reflector 3, silicon plasma texturing 4 or high refractive index nanoparticle reflector 5 have been suggested.
Metal nanoparticles can effectively scatter incident light into a higher refractive index material, like silicon, due to the surface plasmon resonance effect 6. They also can be easily formed on the planar silicon cell surface thus offering a light-trapping approach alternative to texturing. For a nanoparticle located at the air-silicon interface the scattered light fraction coupled into silicon exceeds 95% and a large faction of that light is scattered at angles above critical providing nearly ideal light-trapping condition (Animation 2: Plasmons on NP). The resonance can be tuned to the wavelength region, which is most important for a particular cell material and design, by varying the nanoparticle average size, surface coverage and local dielectric environment 6,7. Theoretical design principles of plasmonic nanoparticle solar cells have been suggested 8. In practice, Ag nanoparticle array is an ideal light-trapping partner for poly-Si thin-film solar cells because most of these design principle are naturally met. The simplest way of forming nanoparticles by thermal annealing of a thin precursor Ag film results in a random array with a relatively wide size and shape distribution, which is particularly suitable for light-trapping because such an array has a wide resonance peak, covering the wavelength range of 700-900 nm, important for poly-Si solar cell performance. The nanoparticle array can only be located on the rear poly-Si cell surface thus avoiding destructive interference between incident and scattered light which occurs for front-located nanoparticles 9. Moreover, poly-Si thin-film cells do not requires a passivating layer and the flat base-shaped nanoparticles (that naturally result from thermal annealing of a metal film) can be directly placed on silicon further increases plasmonic scattering efficiency due to surface plasmon-polariton resonance 10.
The cell with the plasmonic nanoparticle array as described above can have a photocurrent about 28% higher than the original cell. However, the array still transmits a significant amount of light which escapes through the rear of the cell and does not contribute into the current. This loss can be mitigated by adding a rear reflector to allow catching transmitted light and re-directing it back to the cell. Providing sufficient distance between the reflector and the nanoparticles (a few hundred nanometers) the reflected light will then experience one more plasmonic scattering event while passing through the nanoparticle array on re-entering the cell and the reflector itself can be made diffuse - both effects further facilitating light scattering and hence light-trapping. Importantly, the Ag nanoparticles have to be encapsulated with an inert and low refractive index dielectric, like MgF2 or SiO2, from the rear reflector to avoid mechanical and chemical damage 7. Low refractive index for this cladding layer is required to maintain a high coupling fraction into silicon and larger scattering angles, which are ensured by the high optical contrast between the media on both sides of the nanoparticle, silicon and dielectric 6. The photocurrent of the plasmonic cell with the diffuse rear reflector can be up to 45% higher than the current of the original cell or up to 25% higher than the current of an equivalent cell with the diffuse reflector only.

Polycrystalline silicon thin-film solar cells on glass are fabricated by deposition of boron and phosphorous doped silicon layers followed by crystallisation, defect passivation and metallisation. Plasmonic light-trapping is introduced by forming Ag nanoparticles on the silicon cell surface capped with a diffused reflector resulting in ~45% photocurrent enhancement.

One of major approaches to cheaper solar cells is reducing the amount of semiconductor material used for their fabrication and making cells thinner. To ...

Encapsulation and Permeability Characteristics of Plasma Polymerized Hollow Particles

In this protocol, core-shell nanostructures are synthesized by plasma enhanced chemical vapor deposition. We produce an amorphous barrier by plasma polymerization of isopropanol on various solid substrates, including silica and potassium chloride. This versatile technique is used to treat nanoparticles and nanopowders with sizes ranging from 37 nm to 1 micron, by depositing films whose thickness can be anywhere from 1 nm to upwards of 100 nm. Dissolution of the core allows us to study the rate of permeation through the film. In these experiments, we determine the diffusion coefficient of KCl through the barrier film by coating KCL nanocrystals and subsequently monitoring the ionic conductivity of the coated particles suspended in water. The primary interest in this process is the encapsulation and delayed release of solutes. The thickness of the shell is one of the independent variables by which we control the rate of release. It has a strong effect on the rate of release, which increases from a six-hour release (shell thickness is 20 nm) to a long-term release over 30 days (shell thickness is 95 nm). The release profile shows a characteristic behavior: a fast release (35% of the final materials) during the first five minutes after the beginning of the dissolution, and a slower release till all of the core materials come out.

We have used plasma enhanced chemical vapor deposition to deposit thin films ranging from a few nm to several 100 nm on nano-sized particles of various materials. We subsequently etch the core material to produce hollow nanoshells whose permeability is controlled by the thickness of the shell. We characterize the permeability of these coatings to small solutes and demonstrate that these barriers can provide sustained release of the core material over several days.

In this protocol, core-shell nanostructures are synthesized by plasma enhanced chemical vapor deposition. We produce an amorphous barrier by plasma ...

Nanomoulding of Functional Materials, a Versatile Complementary Pattern Replication Method to Nanoimprinting

We describe a nanomoulding technique which allows low-cost nanoscale patterning of functional materials, materials stacks and full devices. Nanomoulding combined with layer transfer enables the replication of arbitrary surface patterns from a master structure onto the functional material. Nanomoulding can be performed on any nanoimprinting setup and can be applied to a wide range of materials and deposition processes. In particular we demonstrate the fabrication of patterned transparent zinc oxide electrodes for light trapping applications in solar cells.

We describe a nanomoulding technique which allows low-cost nanoscale patterning of functional materials, materials stacks and full devices. Nanomoulding can be performed on any nanoimprinting setup and can be applied to a wide range of materials and deposition processes.

We describe a nanomoulding technique which  allows low-cost nanoscale patterning of functional materials, materials stacks  and full devices. Nanomoulding ...

Synthesis and Microdiffraction at Extreme Pressures and Temperatures

High pressure compounds and polymorphs are investigated for a broad range of purposes such as determine structures and processes of deep planetary interiors, design materials with novel properties, understand the mechanical behavior of materials exposed to very high stresses as in explosions or impacts. Synthesis and structural analysis of materials at extreme conditions of pressure and temperature entails remarkable technical challenges. In the laser heated diamond anvil cell (LH-DAC), very high pressure is generated between the tips of two opposing diamond anvils forced against each other; focused infrared laser beams, shined through the diamonds, allow to reach very high temperatures on samples absorbing the laser radiation. When the LH-DAC is installed in a synchrotron beamline that provides extremely brilliant x-ray radiation, the structure of materials under extreme conditions can be probed in situ. LH-DAC samples, although very small, can show highly variable grain size, phase and chemical composition. In order to obtain the high resolution structural analysis and the most comprehensive characterization of a sample, we collect diffraction data in 2D grids and combine powder, single crystal and multigrain diffraction techniques. Representative results obtained in the synthesis of a new iron oxide, Fe4O5 1 will be shown.

The laser heated diamond anvil cell combined with synchrotron micro-diffraction techniques allows researchers to explore the nature and properties of new phases of matter at extreme pressure and temperature (PT) conditions. Heterogeneous samples can be characterized in situ under high pressure by 2D mapping and combined powder, single-crystal and multigrain diffraction approaches.

High pressure compounds and polymorphs are investigated for a broad range of purposes such as determine structures and processes of deep planetary ...

Making Record-efficiency SnS Solar Cells by Thermal Evaporation and Atomic Layer Deposition

Tin sulfide (SnS) is a candidate absorber material for Earth-abundant, non-toxic solar cells. SnS offers easy phase control and rapid growth by congruent thermal evaporation, and it absorbs visible light strongly. However, for a long time the record power conversion efficiency of SnS solar cells remained below 2%. Recently we demonstrated new certified record efficiencies of 4.36% using SnS deposited by atomic layer deposition, and 3.88% using thermal evaporation. Here the fabrication procedure for these record solar cells is described, and the statistical distribution of the fabrication process is reported. The standard deviation of efficiency measured on a single substrate is typically over 0.5%. All steps including substrate selection and cleaning, Mo sputtering for the rear contact (cathode), SnS deposition, annealing, surface passivation, Zn(O,S) buffer layer selection and deposition, transparent conductor (anode) deposition, and metallization are described. On each substrate we fabricate 11 individual devices, each with active area 0.25 cm2. Further, a system for high throughput measurements of current-voltage curves under simulated solar light, and external quantum efficiency measurement with variable light bias is described. With this system we are able to measure full data sets on all 11 devices in an automated manner and in minimal time. These results illustrate the value of studying large sample sets, rather than focusing narrowly on the highest performing devices. Large data sets help us to distinguish and remedy individual loss mechanisms affecting our devices.

Tin sulfide (SnS) is a candidate material for Earth-abundant, non-toxic solar cells. Here, we demonstrate the fabrication procedure of the SnS solar cells employing atomic layer deposition, which yields 4.36% certified power conversion efficiency, and thermal evaporation which yields 3.88%.

Tin sulfide (SnS) is a candidate absorber material for Earth-abundant, non-toxic solar cells. SnS offers easy phase control and rapid growth by congruent ...

Preparation of ZnO Nanorod/Graphene/ZnO Nanorod Epitaxial Double Heterostructure for Piezoelectrical Nanogenerator by Using Preheating Hydrothermal

Well-aligned ZnO nanostructures have been intensively studied over the last decade for remarkable physical properties and enormous applications. Here, we describe a one-step fabrication technique to synthesis freestanding ZnO nanorod/graphene/ZnO nanorod double heterostructure. The preparation of the double heterostructure is performed by using thermal chemical vapor deposition (CVD) and preheating hydrothermal technique. In addition, the morphological properties were characterized by using the scanning electron microscopy (SEM). The utility of freestanding double heterostructure is demonstrated by fabricating the piezoelectric nanogenerator. The electrical output is improved up to 200% compared to that of a single heterostructure owing to the coupling effect of the piezoelectricity between the arrays of ZnO nanorods on the top and bottom of graphene. This unique double heterostructure have a tremendous potential for applications of electrical and optoelectrical devices where the high number density and specific surface area of nanorod are needed, such as pressure sensor, immuno-biosensor and dye-sensitized solar cells.

One-step fabrication method for obtaining freestanding epitaxial double heterostructure is presented. This approach could achieve ZnO coverage with a higher number density than that of the epitaxial single heterostructure, leading to a piezoelectric nanogenerator with an increased output electrical performance.

Well-aligned ZnO nanostructures have been intensively studied over the last decade for remarkable physical properties and enormous applications. Here, we ...

In Situ Monitoring of the Accelerated Performance Degradation of Solar Cells and Modules: A Case Study for Cu(In,Ga)Se2 Solar Cells

The levelized cost of electricity (LCOE) of photovoltaic (PV) systems is determined by, among other factors, the PV module reliability. Better prediction of degradation mechanisms and prevention of module field failure can consequently decrease investment risks as well as increase the electricity yield. An improved knowledge level can for these reasons significantly decrease the total costs of PV electricity. 
In order to better understand and minimize the degradation of PV modules, the occurring degradation mechanisms and conditions should be identified. This should preferably happen under combined stresses, since modules in the field are also simultaneously exposed to multiple stress factors. Therefore, two 'Combined Stress test with in situ measurement' setups have been designed and constructed. These setups allow the simultaneous use of humidity, temperature, illumination, and electrical biases as independently controlled stress factors on solar cells and minimodules. The setups also allow real-time monitoring of the electrical properties of these samples. This protocol presents these setups and describes the experimental possibilities. Moreover, results obtained with these setups are also presented: various examples about the influence of both deposition and degradation conditions on the stability of thin film Cu(In,Ga)Se2 (CIGS) as well as Cu2ZnSnSe4 (CZTS) solar cells are described. Results on the temperature dependency of CIGS solar cells are also presented.

In Situ Monitoring of the Accelerated Performance Degradation of Solar Cells and Modules: A Case Study for CuIn,GaSe2 Solar Cells

Two &#39;Combined Stress test with in situ measurement&#39; setups, which allow real-time monitoring of accelerated degradation of solar cells and modules, were designed and constructed. These setups allow the simultaneous use of humidity, temperature, electrical biases, and illumination as independently controlled stress factors. The setups and various experiments executed are presented.

The levelized cost of electricity (LCOE) of photovoltaic (PV) systems is determined by, among other factors, the PV module reliability. Better prediction ...

Well-aligned Vertically Oriented ZnO Nanorod Arrays and their Application in Inverted Small Molecule Solar Cells

This manuscript describes how to design and fabricate efficient inverted solar cells, which are based on a two-dimensional conjugated small molecule (SMPV1) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM), by utilizing ZnO nanorods (NRs) grown on a high quality Al-doped ZnO (AZO) seed layer. The inverted SMPV1:PC71BM solar cells with ZnO NRs that grew on both a sputtered and sol-gel processed AZO seed layer are fabricated. Compared with the AZO thin film prepared by the sol-gel method, the sputtered AZO thin film exhibits better crystallization and lower surface roughness, according to X-ray diffraction (XRD) and atomic force microscope (AFM) measurements. The orientation of the ZnO NRs grown on a sputtered AZO seed layer shows better vertical alignment, which is beneficial for the deposition of the subsequent active layer, forming better surface morphologies. Generally, the surface morphology of the active layer mainly dominates the fill factor (FF) of the devices. Consequently, the well-aligned ZnO NRs can be used to improve the carrier collection of the active layer and to increase the FF of the solar cells. Moreover, as an anti-reflection structure, it can also be utilized to enhance the light harvesting of the absorption layer, with the power conversion efficiency (PCE) of solar cells reaching 6.01%, higher than the sol-gel based solar cells with an efficiency of 4.74%.

This manuscript describes how to design and fabricate efficient inverted SMPV1:PC71BM solar cells with ZnO nanorods (NRs) grown on a high quality Al-doped ZnO (AZO) seed layer. The well-aligned vertically oriented ZnO NRs exhibit high crystalline properties. The power conversion efficiency of solar cells can reach 6.01%.

This manuscript describes how to design and fabricate efficient inverted solar cells, which are based on a two-dimensional conjugated small molecule ...

Fabrication of Ultra-thin Color Films with Highly Absorbing Media Using Oblique Angle Deposition

Ultra-thin film structures have been studied extensively for use as optical coatings, but performance and fabrication challenges remain.&#160; We present an advanced method for fabricating ultra-thin color films with improved characteristics. The proposed process addresses several fabrication issues, including large area processing. Specifically, the protocol describes a process for fabricating ultra-thin color films using an electron beam evaporator for oblique angle deposition of germanium (Ge) and gold (Au) on silicon (Si) substrates.&#160; Film porosity produced by the oblique angle deposition induces color changes in the ultra-thin film. The degree of color change depends on factors such as deposition angle and film thickness. Fabricated samples of the ultra-thin color films showed improved color tunability and color purity. In addition, the measured reflectance of the fabricated samples was converted into chromatic values and analyzed in terms of color. Our ultra-thin film fabricating method is expected to be used for various ultra-thin film applications such as flexible color electrodes, thin film solar cells, and optical filters. Also, the process developed here for analyzing the color of the fabricated samples is broadly useful for studying various color structures.

We present a detailed method for fabricating ultra-thin color films with improved characteristics for optical coatings. The oblique angle deposition technique using an electron beam evaporator allows improved color tunability and purity. Fabricated films of Ge and Au on Si substrates were analyzed by reflectance measurements and color information conversion.

Ultra-thin film structures have been studied extensively for use as optical coatings, but performance and fabrication challenges remain.&#160; We present ...

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

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

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

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