This work was supported by the Ministry of Science and Technology, Taiwan, Republic of China through Grant No. 101-2113-M-001-006-MY3.

1. Preparation of TCDAP12
<ol>
	<li>Synthesize TCDAP by following literature procedures13.</li>
	<li>Purify the TCDAP product by the temperature-gradient sublimation method, with the three temperature zones set at 340, 270, and 250 &#176;C, respectively, under a vacuum pressure of 10-6 Torr12,14.</li>
</ol>
2. Grow Single Crystals of TCDAP Using a Physical Vapor Transfer (PVT) System14
<ol>
	<li>Put the TCDAP sample at one end of a boat (5 cm long) and load the boat into a glass inner tube (15 cm long with a diameter of 1.2 cm).</li>
	<li>Load the inner tube into a longer glass tube (83 cm long and 2 cm in diameter) and push it in to about 17 cm from the opening.</li>
	<li>Load the long glass tube into a copper tube (60 cm long and 2.5 cm in diameter) horizontally fixed on a rack; make sure the boat of TCDAP is located in the middle of the heating area defined by a heating band around the copper tube.</li>
	<li>Purge the PVT system with helium gas at a flow rate of 30 cc/min, and then turn on the transformer to heat up the heating band to 310 &#176;C; maintain at this temperature for two days.</li>
	<li>After cooling the system to room temperature, collect the crystals from the inner tube.</li>
</ol>
3. Device Fabrication
<ol>
	<li>Put a 200-&#181;m-thick, transparent, pre-cut PET substrate (2 cm x 1 cm) into a vial and clean it by sonication in detergent solution, deionized water, and acetone, in sequence, for 30 min each. Dry the substrate by nitrogen flow.</li>
	<li>Place double-sided tape on the PET substrate.</li>
	<li>Examine the crystals under a stereomicroscope. Select good quality, shining crystals with a dimension of ~5 mm x ~0.03 mm for device fabrication. Place a needle-like TCDAP crystal parallel with the length of the PET substrate on the double-sided tape and fix it securely.</li>
	<li>Under a stereomicroscope, apply water-based colloidal graphite through a microliter syringe needle in a line (several mm) that extends from the two ends of the crystal acting as the source and drain. Wait for about 30 min for the colloidal graphite to dry and measure the distance between the two graphite spots under an optical microscope to determine the exact channel length (keep it at 0.6-1 mm).</li>
	<li>Use carbon conductive tape to fix the PET substrate on a microscopic slide. Place the slide near the end of the pyrolysis tube of the deposition chamber.</li>
	<li>Weigh 0.5 g of the precursor of the dielectric insulator, [2.2]paracyclophane, and place it near the inlet of the pyrolysis tube.</li>
	<li>Pump down the system to a vacuum of 10-2 Torr. Pre-heat the pyrolysis zone near the center of the tube up to a pre-set temperature of 700 &#176;C and maintain at this temperature.</li>
	<li>Heat up the [2.2]paracyclophane sample to 150 &#176;C. The vapors of the precursor will pass through the pyrolysis zone to give the monomers, which will condense near the end of the pyrolysis tube to polymerize.</li>
	<li>Let the pyrolysis/polymerization reaction continue for 2 hr.</li>
	<li>Cool down the system and take out the samples from the pyrolysis tube.</li>
	<li>Determine the thickness of the deposited dielectric layer by measuring the step height of the layer and substrate using a profilometer according to the manufacturer&#39;s instructions.</li>
	<li>Apply isopropanol-based colloidal graphite through a microliter syringe needle in a line on the back of the dielectric layer above the crystal to serve as the gate electrode.</li>
</ol>
4. Measure the Performance of the Device
<ol>
	<li>Use the scalpel to cut a hole through the polymeric dielectric film above the source/drain electrode area in order to expose the electrodes underneath for connection.</li>
	<li>With the help of a stand and clamps, bring the electrode probes from the Parameter Analyzer into contact with the source/drain/gate electrodes. Record the I-V characteristics at different gate potentials according to the manufacturer&#39;s instructions. 
	Note: Here, the gate potentials are set from -60 V to 60 V at 15 V steps.</li>
</ol>
5. Bending Experiments
<ol>
	<li>To measure the properties in the tensile state, wrap the backside of the flexible PET substrate around cylinders of different radii (14.0 mm, 12.4 mm, 8.0 mm, and 5.8 mm) and fix the PET substrate to the cylinder on four sides with vacuum tape.</li>
	<li>Connect the probes to the source/drain/gate electrodes and measure the I-V characteristics at different gate potentials as described in 4.2.</li>
	<li>To measure in the compressive state, wrap half of the front side of the PET substrate around the end of a cylinder, such that the crystal/source/drain/gate electrodes are facing the cylinder and yet are still exposed. Fix the PET substrate on the cylinder with vacuum tape (see Fig. 5).</li>
	<li>Connect the probes to the source/drain/gate electrodes and measure the I-V characteristics at different gate potentials as described in 4.2. 
	NOTE: A cross-sectional illustration of the device structure is shown in Fig. 1.</li>
</ol>

<ol>
	<li>Sekitani, T., Zschieschang, U., Klauk, H., Someya, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Flexible+Organic+Transistors+and+Circuits+with+Extreme+Bending+Stability.">Flexible Organic Transistors and Circuits with Extreme Bending Stability.</a> Nat. Mater. 9, 1015-1022 (2010).</li><li>Yang, Y., Ruan, G., Xiang, C., Wang, G., Tour, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Flexible+Three-Dimensional+Nanoporous+Metal-Based+Energy+Devices.">Flexible Three-Dimensional Nanoporous Metal-Based Energy Devices.</a> J. Am. Chem. Soc. 136, 6187-6190 (2014).</li><li>Zhan, Y., Mei, Y., Zheng, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Materials+Capability+and+Device+Performance+in+Flexible+Electronics+for+the+Internet+of+Things.">Materials Capability and Device Performance in Flexible Electronics for the Internet of Things.</a> J. Mater. Chem. C. 2, 1220-1232 (2014).</li><li>Zhang, L., Wang, H., Zhao, Y., Guo, Y., Hu, W., Yu, G., Liu, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Substrate-Free+Ultra-Flexible+Organic+Field-Effect+Transistors+and+Five-Stage+Ring+Oscillators.">Substrate-Free Ultra-Flexible Organic Field-Effect Transistors and Five-Stage Ring Oscillators.</a> Adv. Mater. 25, 5455-5460 (2013).</li><li>Jedaa, A., Halik, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Toward+Strain+Resistant+Flexible+Organic+Thin+Film+Transistors.">Toward Strain Resistant Flexible Organic Thin Film Transistors.</a> Appl. Phys. Lett. 95, (2009).</li><li>Nomura, K., Ohta, H., Takagi, A., Kamiya, T., Hirano, M., Hosono, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Room-Temperature+Fabrication+of+Transparent+Flexible+Thin-Film+Transistors+Using+Amorphous+Oxide+Semiconductors.">Room-Temperature Fabrication of Transparent Flexible Thin-Film Transistors Using Amorphous Oxide Semiconductors.</a> Nature. 432, 488-492 (2004).</li><li>Sekitani, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bending+Experiment+on+Pentacene+Field-Effect+Transistors+on+Plastic+Films.">Bending Experiment on Pentacene Field-Effect Transistors on Plastic Films.</a> Appl. Phys. Lett. 86, 073511 (2005).</li><li>Tseng, C. -. W., Huang, D. -. C., Tao, Y. -. 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A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Physical+Vapor+Growth+of+Centimeter-Sized+Crystals+of+&#913;-Hexathiophene.">Physical Vapor Growth of Centimeter-Sized Crystals of &#913;-Hexathiophene.</a> J. Cryst. Growth. 182, 416-427 (1997).</li></ol>

The authors have nothing to disclose.

In this experiment, a number of parameters affect the successful measurement of the field-effect mobility. Firstly, the single crystal should be large enough to be fabricated into a field-effect device for property measurement. The physical vapor transfer (PVT) method is the one that allows larger crystals to be grown. By adjusting the temperature and the flow rate of the carrier gas, crystals of sizes up to half a centimeter can be obtained. Secondly, the choice of a single crystal is important. An apparent single cryst...

Soft electronic devices, such as sensors, displays, and wearable electronics, are currently being designed and researched more actively, and many have even been launched in the market in recent years1,2,3,4. Organic semiconducting materials play an important role in these electronic devices due to their inherent advantages, including low development cost, the ability to be prepared in solution or at low temperatures, and, in particular, their flexibility when compared to inorganic semiconductors5,6. One special consideration for these electronics is that they will be subjected to frequent bending. Bending introduces strain in the components and the materials within the device. A stable and consistent performance is required as such devices are bent. Transistors are a vital component in most of these electronics, and their performance under bending is of interest. A number of studies have addressed this performance issue by bending organic thin film transistors7,8. While the changes in conductance upon bending may be attributed to the changes in spacing between the grains in a polycrystalline thin film, a more fundamental question to ask is whether the conductance may change within a single crystal upon bending. It is well accepted that charge transport between organic molecules depends strongly on electronic coupling between molecules and the reorganization energy involved in the interconversion between the neutral and charged states9. Electronic coupling is highly sensitive to the distance between neighboring molecules and to the overlap of frontier molecular orbitals. The bending of a well-ordered crystal introduces strain and may change the relative position of molecules within the crystal. This can be tested with a single crystal-based field-effect transistor. One report used single crystals of rubrene on a flexible substrate to study the effect of crystal thickness upon bending10. Devices with copper phthalocyanine nanowire crystals prepared on a flat substrate were shown to have a higher mobility upon bending11. However, the properties for an FET device bent in different directions have not been explored.
The molecule 5,7,12,16-tetrachloro-6,13-diazapentacene (TCDAP) is an n-type semiconductor material12. The crystal of TCDAP has a monoclinic packing motif with shifted&#160;&#960;-&#960; stacking between neighboring molecules along the a axis of the unit cell at a cell length of 3.911 &#197;. The crystal grows along this packing direction to give long needles. The maximum n-type field-effect mobility measured along this direction reached 3.39 cm2/V&#183;sec. Unlike many organic crystals that are brittle and fragile, TCDAP crystal is found to be highly flexible. In this work, we used TCDAP as the conducting channel and prepared the single crystal field-effect transistor on a flexible substrate of polyethylene terephthalate (PET). Mobility was measured for the crystal on a flat substrate, with the device bent toward the flexible substrate (downward) or bent toward the gate/dielectric side (upward). I-V data were analyzed based on changes in the stacking/coupling distance among the neighboring molecules.

<table border="0" cellpadding="0" cellspacing="0" width="999">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:411px;">Colloidal Graphite(water-based)</td>
			<td style="width:208px;">TED PELLA,INC</td>
			<td style="width:160px;">NO.16053</td>
			<td style="width:220px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:411px;">Colloidal Graphite(IPA-based)</td>
			<td style="width:208px;">TED PELLA,INC</td>
			<td style="width:160px;">NO.16051</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">[2,2]Paracyclophane,99%</td>
			<td style="width:208px;">Alfa Aesar</td>
			<td>1633-22-3</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">&#160;polyethylene terephthalate&#160;</td>
			<td>Uni-Onward</td>
			<td style="width:160px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Mini-Mite 1100&#176;C Tube Furnaces (Single Zone)</td>
			<td style="width:208px;">Thermo Scientific</td>
			<td>TF55030A</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Agilent 4156C Precision Semiconductor Parameter</td>
			<td style="width:208px;">Keysight</td>
			<td>HP4156</td>
			<td></td>
		</tr>
	</tbody>
</table>

effect of bending on the electrical characteristics of flexible organic single crystal-based field-effect transistors

The charge transport in an organic semiconductor depends highly on the molecular packing in the crystal, which influences the electronic coupling immensely. However, in soft electronics, in which organic semiconductors play a critical role, the devices will be bent or folded repeatedly. The effect of bending on the crystal packing and thus the charge transport is crucial to the performance of the device. In this manuscript, we describe the protocol to bend a single crystal of 5,7,12,16-tetrachloro-6,13-diazapentacene (TCDAP) in the field-effect transistor configuration and to obtain reproducible I-V characteristics upon bending the crystal. The results show that bending a field-effect transistor prepared on a flexible substrate results in nearly reversible yet opposite trends in charge mobility, depending on the bending direction. The mobility increases when the device is bent toward the top gate/dielectric layer (upward, compressive state) and decreases when bent toward the crystal/substrate side (downward, tensile state). The effect of bending curvature was also observed, with greater mobility change resulting from higher bending curvature. It is suggested that the intermolecular &#960;-&#960; distance changes upon bending, thereby influencing the electronic coupling and the subsequent carrier transport ability.

The single crystal XRD analysis reveals that TCDAP is an extended &#960; system with molecules packing along the a axis. Fig. 2 shows the scan pattern by powder XRD for a TCDAP crystal. A series of sharp peaks are observed, corresponding only to the family of (0,k,&#8467;) planes, by comparing with the powder diffraction pattern of the crystal. This would imply that the crystal structure is oriented as shown in Fig. 3.
<p class="jove_content"...

Watch this Scientific Journal Video about Effect of Bending on the Electrical Characteristics of Flexible Organic Single Crystal-based Field-effect Transistors at JoVE.com

Effect of Bending on the Electrical Characteristics of Flexible Organic Single Crystal-based Field-effect Transistors

This manuscript describes the bending process of an organic single crystal-based field-effect transistor to maintain a functioning device for electronic property measurement. The results suggest that bending causes changes in the molecular spacing in the crystal and thus in the charge hopping rate, which is important in flexible electronics.

The charge transport in an organic semiconductor depends highly on the molecular packing in the crystal, which influences the electronic coupling ...

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8.0K Views.  Academia Sinica. This manuscript describes the bending process of an organic single crystal-based field-effect transistor to maintain a functioning device for electronic property measurement. The results suggest that bending causes changes in the molecular spacing in the crystal and thus in the charge hopping rate, which is important in flexible electronics.

Video: Effect of Bending on the Electrical Characteristics of Flexible Organic Single Crystal-based Field-effect Transistors

Controlling the Size, Shape and Stability of Supramolecular Polymers in Water

For aqueous based supramolecular polymers, the simultaneous control over shape, size and stability is very difficult1. At the same time, the ability to do so is highly important in view of a number of applications in functional soft matter including electronics, biomedical engineering, and sensors. In the past, successful strategies to control the size and shape of supramolecular polymers typically focused on the use of templates2,3, end cappers4 or selective solvent techniques5. 
Here we disclose a strategy based on self-assembling discotic amphiphiles that leads to the control over stack length and shape of ordered, chiral columnar aggregates. By balancing electrostatic repulsive interactions on the hydrophilic rim and attractive non-covalent forces within the hydrophobic core of the polymerizing building block, we manage to create small and discrete spherical objects6,7. Increasing the salt concentration to screen the charges induces a sphere-to-rod transition. Intriguingly, this transition is expressed in an increase of cooperativity in the temperature-dependent self-assembly mechanism, and more stable aggregates are obtained. 
For our study we select a benzene-1,3,5-tricarboxamide (BTA) core connected to a hydrophilic metal chelate via a hydrophobic, fluorinated L-phenylalanine based spacer (Scheme 1). The metal chelate selected is a Gd(III)-DTPA complex that contains two overall remaining charges per complex and necessarily two counter ions. The one-dimensional growth of the aggregate is directed by &pi;-&pi; stacking and intermolecular hydrogen bonding. However, the electrostatic, repulsive forces that arise from the charges on the Gd(III)-DTPA complex start limiting the one-dimensional growth of the BTA-based discotic once a certain size is reached. At millimolar concentrations the formed aggregate has a spherical shape and a diameter of around 5 nm as inferred from 1H-NMR spectroscopy, small angle X-ray scattering, and cryogenic transmission electron microscopy (cryo-TEM). The strength of the electrostatic repulsive interactions between molecules can be reduced by increasing the salt concentration of the buffered solutions. This screening of the charges induces a transition from spherical aggregates into elongated rods with a length &gt; 25 nm. Cryo-TEM allows to visualise the changes in shape and size. In addition, CD spectroscopy permits to derive the mechanistic details of the self-assembly processes before and after the addition of salt. Importantly, the cooperativity -a key feature that dictates the physical properties of the produced supramolecular polymers- increases dramatically upon screening the electrostatic interactions. This increase in cooperativity results in a significant increase in the molecular weight of the formed supramolecular polymers in water.

The goal of this experiment is to determine and control the size, shape and stability of self-assembled discotic amphiphiles in water. For aqueous based supramolecular polymers such level of control is very difficult. We apply a strategy using both repulsive and attractive interactions. The experimental techniques applied to characterize this system are broadly applicable.

For aqueous based supramolecular polymers, the simultaneous control over shape, size and stability is very difficult1. At the same time, the ability to do ...

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 ...

Ultrahigh Density Array of Vertically Aligned Small-molecular Organic Nanowires on Arbitrary Substrates

In recent years &pi;-conjugated organic semiconductors have emerged as the active material in a number of diverse applications including large-area, low-cost displays, photovoltaics, printable and flexible electronics and organic spin valves. Organics allow (a) low-cost, low-temperature processing and (b) molecular-level design of electronic, optical and spin transport characteristics. Such features are not readily available for mainstream inorganic semiconductors, which have enabled organics to carve a niche in the silicon-dominated electronics market. The first generation of organic-based devices has focused on thin film geometries, grown by physical vapor deposition or solution processing. However, it has been realized that organic nanostructures can be used to enhance performance of above-mentioned applications and significant effort has been invested in exploring methods for organic nanostructure fabrication.	
A particularly interesting class of organic nanostructures is the one in which vertically oriented organic nanowires, nanorods or nanotubes are organized in a well-regimented, high-density array. Such structures are highly versatile and are ideal morphological architectures for various applications such as chemical sensors, split-dipole nanoantennas, photovoltaic devices with radially heterostructured "core-shell" nanowires, and memory devices with a cross-point geometry. Such architecture is generally realized by a template-directed approach. In the past this method has been used to grow metal and inorganic semiconductor nanowire arrays. More recently &pi;-conjugated polymer nanowires have been grown within nanoporous templates. However, these approaches have had limited success in growing nanowires of technologically important &pi;-conjugated small molecular weight organics, such as tris-8-hydroxyquinoline aluminum (Alq3), rubrene and methanofullerenes, which are commonly used in diverse areas including organic displays, photovoltaics, thin film transistors and spintronics.	
Recently we have been able to address the above-mentioned issue by employing a novel "centrifugation-assisted" approach. This method therefore broadens the spectrum of organic materials that can be patterned in a vertically ordered nanowire array. Due to the technological importance of Alq3, rubrene and methanofullerenes, our method can be used to explore how the nanostructuring of these materials affects the performance of aforementioned organic devices. The purpose of this article is to describe the technical details of the above-mentioned protocol, demonstrate how this process can be extended to grow small-molecular organic nanowires on arbitrary substrates and finally, to discuss the critical steps, limitations, possible modifications, trouble-shooting and future applications.

We report a simple method for fabricating an ultrahigh density array of vertically ordered small-molecular organic nanowires. This method allows for synthesis of complex heterostructured hybrid nanowire geometries, which can be inexpensively grown on arbitrary substrates. These structures have potential applications in organic electronics, optoelectronics, chemical sensing, photovoltaics and spintronics.

In  recent years &pi;-conjugated  organic semiconductors have emerged as the active material in a number of  diverse applications including large-area, ...

Casting Protocols for the Production of Open Cell Aluminum Foams by the Replication Technique and the Effect on Porosity

Metal foams are interesting materials from both a fundamental understanding and practical applications point of view. Uses have been proposed, and in many cases validated experimentally, for light weight or impact energy absorbing structures, as high surface area heat exchangers or electrodes, as implants to the body, and many more. Although great progress has been made in understanding their structure-properties relationships, the large number of different processing techniques, each producing material with different characteristics and structure, means that understanding of the individual effects of all aspects of structure is not complete. The replication process, where molten metal is infiltrated between grains of a removable preform material, allows a markedly high degree of control and has been used to good effect to elucidate some of these relationships. Nevertheless, the process has many steps that are dependent on individual &#8220;know-how&#8221;, and this paper aims to provide a detailed description of all stages of one embodiment of this processing method, using materials and equipment that would be relatively easy to set up in a research environment. The goal of this protocol and its variants is to produce metal foams in an effective and simple way, giving the possibility to tailor the outcome of the samples by modifying certain steps within the process. By following this, open cell aluminum foams with pore sizes of 1&#8211;2.36 mm diameter and 61% to 77% porosity can be obtained.

Replication is one of the processing techniques used for the production of porous metal sponges. In this paper one implementation of the method for the production of open celled porous aluminum is shown in detail.

Metal foams are interesting materials from both a fundamental understanding and practical applications point of view. Uses have been proposed, and in many ...

Silicon Metal-oxide-semiconductor Quantum Dots for Single-electron Pumping

As mass-produced silicon transistors have reached the nano-scale, their behavior and performances are increasingly affected, and often deteriorated, by quantum mechanical effects such as tunneling through single dopants, scattering via interface defects, and discrete trap charge states. However, progress in silicon technology has shown that these phenomena can be harnessed and exploited for a new class of quantum-based electronics. Among others, multi-layer-gated silicon metal-oxide-semiconductor (MOS) technology can be used to control single charge or spin confined in electrostatically-defined quantum dots (QD). These QD-based devices are an excellent platform for quantum computing applications and, recently, it has been demonstrated that they can also be used as single-electron pumps, which are accurate sources of quantized current for metrological purposes. Here, we discuss in detail the fabrication protocol for silicon MOS QDs which is relevant to both quantum computing and quantum metrology applications. Moreover, we describe characterization methods to test the integrity of the devices after fabrication. Finally, we give a brief description of the measurement set-up used for charge pumping experiments and show representative results of electric current quantization.

The fabrication process and experimental characterization techniques relevant to single-electron pumps based on silicon metal-oxide-semiconductor quantum dots are discussed.

As mass-produced silicon transistors have reached the nano-scale, their behavior and performances are increasingly affected, and often deteriorated, by ...

Scalable Solution-processed Fabrication Strategy for High-performance, Flexible, Transparent Electrodes with Embedded Metal Mesh

Here, the authors report the embedded metal-mesh transparent electrode (EMTE), a new transparent electrode (TE) with a metal mesh completely embedded in a polymer film. This paper also presents a low-cost, vacuum-free fabrication method for this novel TE; the approach combines lithography, electroplating, and imprint transfer (LEIT) processing. The embedded nature of the EMTEs offers many advantages, such as high surface smoothness, which is essential for organic electronic device production; superior mechanical stability during bending; favorable resistance to chemicals and moisture; and strong adhesion with plastic film. LEIT fabrication features an electroplating process for vacuum-free metal deposition and is favorable for industrial mass production. Furthermore, LEIT allows for the fabrication of metal mesh with a high aspect ratio (i.e., thickness to linewidth), significantly enhancing its electrical conductance without adversely losing optical transmittance. We demonstrate several prototypes of flexible EMTEs, with sheet resistances lower than 1 &#937;/sq and transmittances greater than 90%, resulting in very high figures of merit (FoM) &#8211; up to 1.5 x 104 &#8211; which are amongst the best values in the published literature.

This protocol describes a solution-based fabrication strategy for high-performance, flexible, transparent electrodes with fully-embedded, thick metal mesh. Flexible transparent electrodes fabricated by this process demonstrate among the highest reported performances, including ultra-low sheet resistance, high optical transmittance, mechanical stability under bending, strong substrate adhesion, surface smoothness, and environmental stability.

Here, the authors report the embedded metal-mesh transparent electrode (EMTE), a new transparent electrode (TE) with a metal mesh completely embedded in a ...

Preparation of Liquid Crystal Networks for Macroscopic Oscillatory Motion Induced by Light

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous light irradiation. The photo-excitation of dopants that can quickly dissipate light into heat, coupled with anisotropic thermal expansion and self-shadowing of the film, gives rise to the self-sustained deformation. The oscillations observed are influenced by the dimensions and the modulus of the film, and by the directionality and intensity of the light. The system developed offers applications in energy conversion and harvesting for soft-robotics and automated systems.
The general method described here consists of creating free-standing liquid crystalline films and characterizing the mechanical and thermal effects observed. The molecular alignment is achieved using alignment layers (rubbed polyimide), commonly used in the display manufacturing industry. To obtain actuators with large deformation, the mesogens are aligned and polymerized in a splay/bend configuration, i.e., with the director of the liquid crystals (LCs) going gradually from planar to homeotropic through the film thickness. Upon irradiation, the mechanical and thermal oscillations obtained are monitored with a high-speed camera. The results are further quantified by image analysis using an image processing program.

The goal of the protocol is to create liquid crystalline polymer films that can mechanically oscillate under continuous light irradiation. We describe in great detail the conception of free-standing films, from the liquid crystal alignment method to the photo-actuation. The experimental protocol applied to prepare this material is broadly applicable.

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous ...

Fabrication of Flexible Image Sensor Based on Lateral NIPIN Phototransistors

Flexible photodetectors have been intensely studied for the use of curved image sensors, which are a crucial component in bio-inspired imaging systems, but several challenging points remain, such as a low absorption efficiency due to a thin active layer and low flexibility. We present an advanced method to fabricate a flexible phototransistor array with an improved electrical performance. The outstanding electrical performance is driven by a low dark current owing to deep impurity doping. Stretchable and flexible metal interconnectors simultaneously offer electrical and mechanical stabilities in a highly deformed state. The protocol explicitly describes the fabrication process of the phototransistor using a thin silicon membrane. By measuring I-V characteristics of the completed device in deformed states, we demonstrate that this approach improves the mechanical and electrical stabilities of the phototransistor array. We expect that this approach to a flexible phototransistor can be widely used for the applications of not only next-generation imaging systems/optoelectronics but also wearable devices such as tactile/pressure/temperature sensors and health monitors.

We present a detailed method to fabricate a deformable lateral NIPIN phototransistor array for curved image sensors. The phototransistor array with an open mesh form, which is composed of thin silicon islands and stretchable metal interconnectors, provides flexibility and stretchability. The parameter analyzer characterizes the electrical property of the fabricated phototransistor.

Flexible photodetectors have been intensely studied for the use of curved image sensors, which are a crucial component in bio-inspired imaging systems, ...

Fabrication of Schottky Diodes on Zn-polar BeMgZnO/ZnO Heterostructure Grown by Plasma-assisted Molecular Beam Epitaxy

Heterostructure field effect transistors (HFETs) utilizing a two dimensional electron gas (2DEG) channel have a great potential for high speed device applications. Zinc oxide (ZnO), a semiconductor with a wide bandgap (3.4 eV) and high electron saturation velocity has gained a great deal of attention as an attractive material for high speed devices. Efficient gate modulation, however, requires high-quality Schottky contacts on the barrier layer. In this article, we present our Schottky diode fabrication procedure on Zn-polar BeMgZnO/ZnO heterostructure with high density 2DEG which is achieved through strain modulation and incorporation of a few percent Be into the MgZnO-based barrier during growth by molecular beam epitaxy (MBE). To achieve high crystalline quality, nearly lattice-matched high-resistivity GaN templates grown by metal-organic chemical vapor deposition (MOCVD) are used as the substrate for the subsequent MBE growth of the oxide layers. To obtain the requisite Zn-polarity, careful surface treatment of GaN templates and control over the VI/II ratio during the growth of low temperature ZnO nucleation layer are utilized. Ti/Au electrodes serve as Ohmic contacts, and Ag electrodes deposited on the O2 plasma pretreated BeMgZnO surface are used for Schottky contacts.

Attainment of high-quality Schottky contacts is imperative for achieving efficient gate modulation in heterostructure field effect transistors (HFETs). We present the fabrication methodology and characteristics of Schottky diodes on Zn-polar BeMgZnO/ZnO heterostructures with high-density two dimensional electron gas (2DEG), grown by plasma-assisted molecular beam epitaxy on GaN templates.

Heterostructure field effect transistors (HFETs) utilizing a two dimensional electron gas (2DEG) channel have a great potential for high speed device ...

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

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

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