Thanks to Michael Knutson, Paul Hamric, Greg Scott, and Chris Landes for helpful discussions and assistance related to the custom inert atmosphere sample holder and assistance in the University of Utah student machine shop. P.C. acknowledges the NSF GRFP under Grant No. 0750758. P.C. acknowledges the University of Utah Nanotechnology Training Fellowship. R.M. acknowledges a NSF CAREER Award No. 1054899 and funding from the USTAR Initiative.

NOTE: perform all the following steps under cleanroom class 100 conditions or better.
1. Sample Preparation
<ol>
	<li>Clean a 2&#8221; diameter silicon wafer with Buffered Oxide Etch (BOE) solution (6 parts 40% NH4F and 1 part 49% HF) for 2 min (Caution: Hazardous chemicals). Choose this etch time to remove any organics or contaminants on the surface. Rinse with deionized (DI) water for approximately 5 min. Dry wafer with dry N2. 
	NOTE: Never work alone when using HF. Always wears eye protection with face shield and personal protective equipment (PPE) in case of spills. Post guidelines for the use and handling of HF waste in the lab where the etching is performed. 
	NOTE: Steps 1.2 to 1.7 are for electrochemical locking only. If performing locking via dissolution proceed to Step 2.</li>
	<li>To lay down the working electrode, sputter 100 nm of Platinum (Pt) onto the clean 2&#8221; diameter silicon wafer.</li>
	<li>Before etching the platinum thin film, clean the RIE chamber of any impurities or leftover photoresist from previous dry etches.</li>
	<li>Pump down the chamber until a base pressure of 1 &#215; 10-5 Torr is achieved. Make sure that the RF power is set to 200 W and the flow rates for the oxygen and argon are set to 50 sccm and 10 sccm respectively. Ignite the Ar/O2 plasma and run for at least 1 hr.</li>
	<li>Turn off the Ar/O2 plasma and allow the chamber vent for approximately 10 min.</li>
	<li>To etch the platinum thin film surface, load the sample into the RIE chamber and pump the chamber down to a base pressure of 1 &#215; 10-5 Torr. This time set the argon flow rate to 0 sccm. Ignite the O2 plasma and let this process run for 30 min.</li>
	<li>Turn off the O2 plasma and let the chamber vent for 10 min.</li>
</ol>
2. Thermal Evaporation of Photochromic Molecule Using Custom Low Temperature Evaporator (LTE)
<ol>
	<li>Fill AlO2 boat with 30 mg of BTE and load into custom LTE source (Figure 6).</li>
	<li>Load silicon wafer into sample mount.</li>
	<li>Seal chamber ports and pump chamber down to a base pressure of 1 x 10-6 Torr.</li>
	<li>Evaporate the BTE at a setpoint temperature of 100 &#176;C, with a film thickness of 30 nm.</li>
	<li>Immediately after evaporation, flood illuminate the sample to 5 min of UV to transform the BTE material to the closed form, 1c.</li>
	<li>In order to define the sample size, cleave a small piece of the wafer using a diamond scribe to scratch a line from the edge of the silicon surface. Grab the wafer on both sides of the scratch line and bend the wafer downwards until it breaks along the crystal plane.</li>
	<li>Perform profilometer measurements to validate BTE thin film thickness. To do this, scratch the sample using a fine edge tweezers. Measure the step height from this scratch, which is the difference in height between the right and left cursor position. 
	NOTE: Inaccuracies in film thickness will result in discrepancies in exposure dose.</li>
	<li>Store remaining sample in N2 filled glovebox.</li>
</ol>
3. Exposures
NOTE: Perform all exposures under inert atmosphere conditions to prevent degradation of sample.
<ol>
	<li>Cleave the sample by following the same procedure as outlined in step 2.6.</li>
	<li>Load sample in inert atmosphere sample holder.</li>
	<li>Mount inert sample holder on stage. Purge sample with N2.</li>
	<li>Expose the sample to the desired exposure time using an interferometer, such as the one shown in Figure 8.</li>
</ol>
4. Electrochemical Oxidation Using Three Electrode Cell
NOTE: Perform electrochemistry under inert atmosphere conditions to prevent degradation of sample.
<ol>
	<li>Clamp a clean glass vial on top of the hot plate. Place a clean stirring bar in the vial. Turn on the stirrer.</li>
	<li>Clean a new copper clip with methanol. Clean the platinum counter electrode with methanol.</li>
	<li>Using a clean copper clip, clip the sample through one of the holes in the Teflon vial cap. Make sure to clip onto the exposed platinum only.</li>
	<li>Place the Teflon vial cap onto the vial. Clip the red lead onto the platinum counter electrode and the black lead onto the copper clip holding the sample.</li>
	<li>Using a clean syringe, fill the vial with filtered deionized (DI) water through the second hole in the Teflon vial cap. Fill as high without immersing any of the bare platinum on the sample.</li>
	<li>Bubble nitrogen through the water for 3-5 min. Turn off the nitrogen.</li>
	<li>Place the reference electrode in the second hole in the Teflon vial cap. Clip the white lead onto the reference electrode. Check to make sure none of the bare platinum on the sample is immersed.</li>
	<li>Using a voltammograph, set the oxidation voltage to 0.5 V/sec.</li>
	<li>After the desired oxidation time has elapsed, turn the power to the voltammograph off.</li>
	<li>Remove the red, black, and white clips from the platinum counter electrode, copper clip, and reference electrode.</li>
	<li>Expose the sample to UV for 5 min.</li>
</ol>
5. Sample Development &#8212; Electrochemical Locking
NOTE: Perform development under inert atmosphere conditions to prevent degradation of sample.
<ol>
	<li>Develop the sample in filtered 5 (wt%) isopropanol, 95 (wt%) ethylene glycol for the desired amount of time. Note: Typically 50 nm samples are developed for 30-60 sec while 80 nm samples are developed for 60-180 sec.</li>
	<li>Dry sample with dry N2.</li>
	<li>Immediately expose sample to 5 min of UV.</li>
</ol>
6. Sample Development &#8212; Dissolution Locking
NOTE: Perform development under inert atmosphere conditions to prevent degradation of sample.
<ol>
	<li>Using 100 ml of ethylene glycol in a clean glass beaker, develop the exposed sample for the desired development time.</li>
	<li>Dry sample with dry N2. Immediately expose sample to 5 min of UV.</li>
</ol>
7. Multiple Exposures
<ol>
	<li>If performing multiple exposures repeat steps 3-6 with a translation of the sample relative to the optics.</li>
</ol>

<ol>
	<li>Brimhall, N., Andrew, T. L., Manthena, R. V., Menon, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Breaking+the+far-field+diffraction+limit+in+optical+nanopatterning+via+repeated+photochemical+and+electrochemical+transitions+in+photochromic+molecules.">Breaking the far-field diffraction limit in optical nanopatterning via repeated photochemical and electrochemical transitions in photochromic molecules.</a> Physical Review Letters. 107 (20), 205501 (2011).</li><li>Cantu, P., 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=Subwavelength+nanopatterning+of+photochromic+diaryethene+films.">Subwavelength nanopatterning of photochromic diaryethene films.</a> Applied Physics Letters. 100 (18), 183103 (2012).</li><li>Cantu, P., Andrew, T. L., Menon, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanopatterning+of+diarylethene+films+via+selective+dissolution+of+one+photoisomer.">Nanopatterning of diarylethene films via selective dissolution of one photoisomer.</a> Applied Physics Letters. 103 (17), 173112 (2013).</li><li>Abbe, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Beitr&#228;ge+zur+Theorie+des+Mikroskops+und+der+mikroskopischen+Wahrnehmung.">Beitr&#228;ge zur Theorie des Mikroskops und der mikroskopischen Wahrnehmung.</a> Archiv f&#252;r mikroskopische Anatomie. 9 (1), 413-418 (1873).</li><li>Li, L., 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=Achieving+&#955;/20+resolution+by+one-color+initiation+and+deactivation+of+polymerization.">Achieving &#955;/20 resolution by one-color initiation and deactivation of polymerization.</a> Science. 324 (5929), 910-913 (2009).</li><li>Fischer, J., von Freymann, G., Wegener, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+materials+challenge+in+diffraction-unlimited+direct-laser-writing+optical+lithography.">The materials challenge in diffraction-unlimited direct-laser-writing optical lithography.</a> Advanced Materials. 22 (32), 3578-3582 (2010).</li><li>Mirkin, C. A., 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=Beam+pen+lithography.">Beam pen lithography.</a> Nature Nanotechnology. 5, 637-640 (2010).</li><li>Xie, X., 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=Manipulating+spatial+light+fields+for+micro-+and+nano-photonics.">Manipulating spatial light fields for micro- and nano-photonics.</a> Physica E: Low-dimensional Systems and Nanostructures. 44, 1109-1126 (2012).</li><li>Leroy, J., 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=High-speed+metal-insulator+transition+in+vanadium+dioxide+films+induced+by+an+electrical+pulsed+voltage+over+nano-gap+electrodes.">High-speed metal-insulator transition in vanadium dioxide films induced by an electrical pulsed voltage over nano-gap electrodes.</a> Applied Physics Letters. 100 (21), 213507 (2012).</li><li>Carr, D., Sekaric, L., Craighead, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measurement+of+nanomechanical+resonant+structures+in+single-crystal+silicon.">Measurement of nanomechanical resonant structures in single-crystal silicon.</a> Journal of Vacuum Science &amp; Technology B. 16 (6), 3821-3824 (1998).</li><li>Wilhelmi, O., 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=Rapid+prototyping+of+nanostructured+materials+with+a+focused+ion+beam.">Rapid prototyping of nanostructured materials with a focused ion beam.</a> Japanese Journal of Applied Physics. 47 (6), 2010-5014 (2008).</li><li>Hell, S. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Far-field+optical+nanoscopy.">Far-field optical nanoscopy.</a> Science. 316 (5828), 1153-1158 (2007).</li><li>Chou, S. Y., Krauss, P. R., Renstrom, P. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanoimprint+lithography.">Nanoimprint lithography.</a> Journal of Vacuum Science &amp; Technology B. 14, 4129 (1996).</li><li>Guillemette, M. D., 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=Surface+topography+induces+3D+self-orientation+of+cells+and+extracellular+matrix+resulting+in+improved+tissue+function.">Surface topography induces 3D self-orientation of cells and extracellular matrix resulting in improved tissue function.</a> Integrative Biology. 1 (2), 196-204 (2009).</li></ol>

The authors have nothing to disclose.

The fabrication, experimental setup and related operational procedures of Patterning via Optical Saturable Transitions (POST) have been described. By exploiting the linear switching properties of thermally stable photochromic molecules, POST offers new perspectives on circumventing the far-field diffraction limit.1-2,4
Previously long-term storage requirement of the samples was solved by storing the samples under N2, directly after the initial evaporation.2 How...

Optical lithography is of key importance in the fabrication of nanoscale structures and devices. Increased advancements in novel lithography techniques has the ability to enable new generations of novel devices.8-11 In this article, a review is presented of a class of optical lithographic techniques that achieve deep sub-wavelength resolution using novel photoswitchable molecules. This approach is called Patterning via Optical-Saturable Transitions (POST).1-3
POST is a novel nanofabrication technique that uniquely combines the ideas of saturating optical transitions of photochromic molecules, specifically (1,2-bis(5,5&#8217;-dimethyl-2,2&#8217;-bithiophen-yl))perfluorocyclopent-1-ene. Colloquially, this compound is referred to as BTE, Figure 1, such as those used in stimulated emission-depletion (STED) microscopy12, with interference lithography, which makes it a powerful tool for large-area parallel nanopatterning of deep subwavelength features onto a variety of surfaces with potential extension to 2- and 3-dimensions.
The photochromic layer is originally in one homogeneous state. When this layer is exposed to a uniform illumination of &#955;1, it converts into the second isomeric state (1c), Figure 2. Then the sample is exposed to a focused node at &#955;2, which converts the sample into the first isomeric state (1o) everywhere except in the near vicinity of the node. By controlling the exposure dose, the size of the unconverted region may be made arbitrarily small. A subsequent fixing step of one of the isomers may be selectively and irreversibly converted (locked) into a 3rd state (in black) to lock the pattern. Next, the layer is exposed uniformly to &#955;1, which converts everything except the locked region back to the original state. The sequence of steps may be repeated with a displacement of the sample relative to the optics, resulting in two locked regions whose spacing is smaller than the far-field diffraction limit. Therefore, any arbitrary geometry may be patterned in a &#8220;dot-matrix&#8221; fashion.1-3

<table border="0" cellpadding="0" cellspacing="0" width="778">
	<tbody>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Name of Material/ Equipment</td>
			<td style="width:205px;">Company</td>
			<td style="width:119px;">Catalog Number</td>
			<td style="width:239px;">Comments/Description</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Isopropanol</td>
			<td style="width:205px;">Fisher Scientific</td>
			<td style="width:119px;">P/7500/15</td>
			<td style="width:239px;">CAUTION: flammable, use good 
			ventilation and avoid all ignition 
			sources.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Buffered Oxide Etch</td>
			<td style="width:205px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Methanol</td>
			<td style="width:205px;">Ricca Chemical</td>
			<td style="width:119px;">48-293-2&#160;</td>
			<td style="width:239px;">CAUTION: flammable, use good 
			ventilation and avoid all ignition 
			sources.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Ethylene Glycol</td>
			<td style="width:205px;">Sigma-Aldrich</td>
			<td style="width:119px;">324558</td>
			<td>CAUTION: Harmful if swallowed</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Silicon wafer</td>
			<td style="width:205px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Diamond Scribe</td>
			<td style="width:205px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Glass Beakers</td>
			<td style="width:205px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Tweezers</td>
			<td style="width:205px;">Ted Pella</td>
			<td style="width:119px;">5226</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Reactive Ion Etching System</td>
			<td style="width:205px;">Oxford</td>
			<td style="width:119px;">Plasma Lab 80 Plus</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Inert Atmosphere Sample Holder</td>
			<td style="width:205px;">Proprietary In-house Designed</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Polarizing beamsplitter cube</td>
			<td style="width:205px;">Thorlabs</td>
			<td style="width:119px;">PBS052</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">HeNe Laser</td>
			<td style="width:205px;">Melles Griot</td>
			<td style="width:119px;">25-LHP-171</td>
			<td>CAUTION: Wear safety glasses</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Half-wave plates</td>
			<td style="width:205px;">Thorlabs</td>
			<td style="width:119px;">WPH05M-633</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Thermal Evaporator</td>
			<td style="width:205px;">Proprietary In-house Designed</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">TMV Super</td>
			<td style="width:205px;">TM Vacuum Products</td>
			<td style="width:119px;">TMV Super</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Voltammograph</td>
			<td style="width:205px;">Bioanalytical Systems</td>
			<td style="width:119px;">CV-37</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Shortwave UV lamp 365nm</td>
			<td style="width:205px;">UVP Analytik Jena Company</td>
			<td style="width:119px;">UVGL-25</td>
			<td>CAUTION: Wear UV safety glasses</td>
		</tr>
	</tbody>
</table>

patterning via optical saturable transitions - fabrication and characterization

This protocol describes the fabrication and characterization of nanostructures using a novel nanolithographic technique called Patterning via Optical Saturable Transitions (POST). In this technique the chemical properties of organic photochromic molecules that undergo single-photon reactions are exploited, enabling rapid top-down nanopatterning over large areas at low light intensities, thereby, allowing for the circumvention of the far-field diffraction barrier.4 Simple, cost-effective, high throughput and resolution alternatives to nanopatterning are being explored, such as, two-photon polymerization5,6, beam pen lithography (BPL)7, scanning electron beam lithography (SEBL), and focused ion beam (FIB) patterning. However, multi-photon approaches require high light intensities, which limit their potential for high throughput and offer low image contrast. Although, electron and ion beam lithographic processes offer increased resolution, the serial nature of the process is limited to slow writing speeds, which also prevents patterning of features over large areas. Beam-pen lithography is an approach towards parallel near-field optical lithography. However, the gap between the source of the beam and the surface of the photoresist needs to be controlled extremely precisely for good pattern uniformity and this is very challenging to accomplish for large arrays of beams. Patterning via Optical Saturable Transitions (POST) is an alternative optical nanopatterning technique for patterning sub-wavelength features1-3. Since this technique uses single photons instead of electrons, it is extremely fast and does not require high light intensities1-3, opening the door to massive parallelization.

Fabricated samples:
Different oxidation times were characterized as illustrated by the atomic-force micrographs in Figure 3 at an oxidation voltage of 0.85 V determined from cyclic voltammetry. The 50 nm-thick films were exposed to a standing wave at &#955; = 647 nm of period 400 nm for 60 sec at a power density of 0.95 mW/cm2. As the oxidation time is increased from 10 min&#160;to 25 min, one can clearly see a loss of contrast as some of the region...

Watch this Scientific Journal Video about Patterning via Optical Saturable Transitions - Fabrication and Characterization at JoVE.com

Patterning via Optical Saturable Transitions - Fabrication and Characterization

We report that the diffraction limit of conventional optical lithography can be overcome by exploiting the transitions of organic photochromic derivatives induced by their photoisomerization at low light intensities.1-3 This paper outlines our fabrication technique and two locking mechanisms, namely: dissolution of one photoisomer and electrochemical oxidation.

This protocol describes the fabrication and characterization of nanostructures using a novel nanolithographic technique called Patterning via Optical ...

patterning-via-optical-saturable-transitions-fabrication

Research

JoVE Journal

Engineering

6.8K Views.  The University of Utah. We report that the diffraction limit of conventional optical lithography can be overcome by exploiting the transitions of organic photochromic derivatives induced by their photoisomerization at low light intensities.1-3 This paper outlines our fabrication technique and two locking mechanisms, namely: dissolution of one photoisomer and electrochemical oxidation.

Video: Patterning via Optical Saturable Transitions - Fabrication and Characterization

Simulation, Fabrication and Characterization of THz Metamaterial Absorbers

Metamaterials (MM), artificial materials engineered to have properties that may not be found in nature, have been widely explored since the first theoretical1 and experimental demonstration2 of their unique properties. MMs can provide a highly controllable electromagnetic response, and to date have been demonstrated in every technologically relevant spectral range including the optical3, near IR4, mid IR5 , THz6 , mm-wave7 , microwave8 and radio9 bands. Applications include perfect lenses10, sensors11, telecommunications12, invisibility cloaks13 and filters14,15. We have recently developed single band16, dual band17 and broadband18 THz metamaterial absorber devices capable of greater than 80% absorption at the resonance peak. The concept of a MM absorber is especially important at THz frequencies where it is difficult to find strong frequency selective THz absorbers19. In our MM absorber the THz radiation is absorbed in a thickness of ~ &lambda;/20, overcoming the thickness limitation of traditional quarter wavelength absorbers. MM absorbers naturally lend themselves to THz detection applications, such as thermal sensors, and if integrated with suitable THz sources (e.g. QCLs), could lead to compact, highly sensitive, low cost, real time THz imaging systems.

This protocol outlines the simulation, fabrication and characterization of THz metamaterial absorbers. Such absorbers, when coupled with an appropriate sensor, have applications in THz imaging and spectroscopy.

Metamaterials (MM),  artificial materials engineered to have properties that may not be found in  nature, have been widely explored since the first ...

Fabrication And Characterization Of Photonic Crystal Slow Light Waveguides And Cavities

Slow light has been one of the hot topics in the photonics community in the past decade, generating great interest both from a fundamental point of view and for its considerable potential for practical applications. Slow light photonic crystal waveguides, in particular, have played a major part and have been successfully employed for delaying optical signals1-4 and the enhancement of both linear5-7 and nonlinear devices.8-11
Photonic crystal cavities achieve similar effects to that of slow light waveguides, but over a reduced band-width. These cavities offer high Q-factor/volume ratio, for the realization of optically12 and electrically13 pumped ultra-low threshold lasers and the enhancement of nonlinear effects.14-16 Furthermore, passive filters17 and modulators18-19 have been demonstrated, exhibiting ultra-narrow line-width, high free-spectral range and record values of low energy consumption.
To attain these exciting results, a robust repeatable fabrication protocol must be developed. In this paper we take an in-depth look at our fabrication protocol which employs electron-beam lithography for the definition of photonic crystal patterns and uses wet and dry etching techniques. Our optimised fabrication recipe results in photonic crystals that do not suffer from vertical asymmetry and exhibit very good edge-wall roughness. We discuss the results of varying the etching parameters and the detrimental effects that they can have on a device, leading to a diagnostic route that can be taken to identify and eliminate similar issues.
The key to evaluating slow light waveguides is the passive characterization of transmission and group index spectra. Various methods have been reported, most notably resolving the Fabry-Perot fringes of the transmission spectrum20-21 and interferometric techniques.22-25 Here, we describe a direct, broadband measurement technique combining spectral interferometry with Fourier transform analysis.26 Our method stands out for its simplicity and power, as we can characterise a bare photonic crystal with access waveguides, without need for on-chip interference components, and the setup only consists of a Mach-Zehnder interferometer, with no need for moving parts and delay scans.
When characterising photonic crystal cavities, techniques involving internal sources21 or external waveguides directly coupled to the cavity27 impact on the performance of the cavity itself, thereby distorting the measurement. Here, we describe a novel and non-intrusive technique that makes use of a cross-polarised probe beam and is known as resonant scattering (RS), where the probe is coupled out-of plane into the cavity through an objective. The technique was first demonstrated by McCutcheon et al.28 and further developed by Galli et al.29

Use of photonic crystal slow light waveguides and cavities has been widely adopted by the photonics community in many differing applications. Therefore fabrication and characterization of these devices are of great interest. This paper outlines our fabrication technique and two optical characterization methods, namely: interferometric (waveguides) and resonant scattering (cavities).

Slow light has been one of the hot topics in the photonics community in the past decade, generating great interest both from a fundamental point of view ...

Design, Fabrication, and Experimental Characterization of Plasmonic Photoconductive Terahertz Emitters

In this video article we present a detailed demonstration of a highly efficient method for generating terahertz waves. Our technique is based on photoconduction, which has been one of the most commonly used techniques for terahertz generation 1-8. Terahertz generation in a photoconductive emitter is achieved by pumping an ultrafast photoconductor with a pulsed or heterodyned laser illumination. The induced photocurrent, which follows the envelope of the pump laser, is routed to a terahertz radiating antenna connected to the photoconductor contact electrodes to generate terahertz radiation. Although the quantum efficiency of a photoconductive emitter can theoretically reach 100%, the relatively long transport path lengths of photo-generated carriers to the contact electrodes of conventional photoconductors have severely limited their quantum efficiency. Additionally, the carrier screening effect and thermal breakdown strictly limit the maximum output power of conventional photoconductive terahertz sources. To address the quantum efficiency limitations of conventional photoconductive terahertz emitters, we have developed a new photoconductive emitter concept which incorporates a plasmonic contact electrode configuration to offer high quantum-efficiency and ultrafast operation simultaneously. By using nano-scale plasmonic contact electrodes, we significantly reduce the average photo-generated carrier transport path to photoconductor contact electrodes compared to conventional photoconductors 9. Our method also allows increasing photoconductor active area without a considerable increase in the capacitive loading to the antenna, boosting the maximum terahertz radiation power by preventing the carrier screening effect and thermal breakdown at high optical pump powers. By incorporating plasmonic contact electrodes, we demonstrate enhancing the optical-to-terahertz power conversion efficiency of a conventional photoconductive terahertz emitter by a factor of 50 10.

We describe methods for the design, fabrication, and experimental characterization of plasmonic photoconductive emitters, which offer two orders of magnitude higher terahertz power levels compared to conventional photoconductive emitters.

In this video article we present a detailed demonstration of a highly efficient method for generating terahertz waves. Our technique is based on ...

Fabrication and Characterization of Disordered Polymer Optical Fibers for Transverse Anderson Localization of Light

We develop and characterize a disordered polymer optical fiber that uses transverse Anderson localization as a novel waveguiding mechanism. The developed polymer optical fiber is composed of 80,000 strands of poly (methyl methacrylate) (PMMA) and polystyrene (PS) that are randomly mixed and drawn into a square cross section optical fiber with a side width of 250 &mu;m. Initially, each strand is 200 &mu;m in diameter and 8-inches long. During the mixing process of the original fiber strands, the fibers cross over each other; however, a large draw ratio guarantees that the refractive index profile is invariant along the length of the fiber for several tens of centimeters. The large refractive index difference of 0.1 between the disordered sites results in a small localized beam radius that is comparable to the beam radius of conventional optical fibers. The input light is launched from a standard single mode optical fiber using the butt-coupling method and the near-field output beam from the disordered fiber is imaged using a 40X objective and a CCD camera. The output beam diameter agrees well with the expected results from the numerical simulations. The disordered optical fiber presented in this work is the first device-level implementation of 2D Anderson localization, and can potentially be used for image transport and short-haul optical communication systems.

We develop and characterize a disordered polymer optical fiber that uses transverse Anderson localization as a novel waveguiding mechanism. This microstructured fiber can transport a small localized beam with a radius that is comparable to the beam radius of conventional optical fibers.

We develop and characterize a disordered polymer optical fiber that uses transverse Anderson localization as a novel waveguiding mechanism. The developed ...

Fabrication of Uniform Nanoscale Cavities via Silicon Direct Wafer Bonding

Measurements of the heat capacity and superfluid fraction of confined 4He have been performed near the lambda transition using lithographically patterned and bonded silicon wafers. Unlike confinements in porous materials often used for these types of experiments3, bonded wafers provide predesigned uniform spaces for confinement. The geometry of each cell is well known, which removes a large source of ambiguity in the interpretation of data.
Exceptionally flat, 5 cm diameter, 375 &#181;m thick Si wafers with about 1 &#181;m variation over the entire wafer can be obtained commercially (from Semiconductor Processing Company, for example). Thermal oxide is grown on the wafers to define the confinement dimension in the z-direction. A pattern is then etched in the oxide using lithographic techniques so as to create a desired enclosure upon bonding. A hole is drilled in one of the wafers (the top) to allow for the introduction of the liquid to be measured. The wafers are cleaned2 in RCA solutions and then put in a microclean chamber where they are rinsed with deionized water4. The wafers are bonded at RT and then annealed at ~1,100 &#176;C. This forms a strong and permanent bond. This process can be used to make uniform enclosures for measuring thermal and hydrodynamic properties of confined liquids from the nanometer to the micrometer scale.

A method for permanently bonding two silicon wafers so as to realize a uniform enclosure is described. This includes wafer preparation, cleaning, RT bonding, and annealing processes. The resulting bonded wafers (cells) have uniformity of enclosure ~1%1,2. The resulting geometry allows for measurements of confined liquids and gasses.

Measurements of the heat capacity and superfluid fraction of confined 4He have been performed near the lambda transition using lithographically patterned ...

Fabrication and Operation of a Nano-Optical Conveyor Belt

The technique of using focused laser beams to trap and exert forces on small particles has enabled many pivotal discoveries in the nanoscale biological and physical sciences over the past few decades. The progress made in this field invites further study of even smaller systems and at a larger scale, with tools that could be distributed more easily and made more widely available. Unfortunately, the fundamental laws of diffraction limit the minimum size of the focal spot of a laser beam, which makes particles smaller than a half-wavelength in diameter hard to trap and generally prevents an operator from discriminating between particles which are closer together than one half-wavelength. This precludes the optical manipulation of many closely-spaced nanoparticles and&#160;limits the&#160;resolution of optical-mechanical systems. Furthermore, manipulation using focused beams requires beam-forming or steering optics, which can be very bulky and expensive. To address these limitations in the system scalability of conventional optical trapping our lab has devised an alternative technique which utilizes near-field optics to move particles across a chip. Instead of focusing laser beams in the far-field, the optical near field of plasmonic resonators produces the necessary local optical intensity enhancement to overcome the restrictions of diffraction and manipulate particles at higher resolution. Closely-spaced resonators produce strong optical traps which can be addressed to mediate the hand-off of particles from one to the next in a conveyor-belt-like fashion. Here, we describe how to design and produce a conveyor belt using a gold surface patterned with plasmonic C-shaped resonators and how to operate it with polarized laser light to achieve super-resolution nanoparticle manipulation and transport. The nano-optical conveyor belt chip can be produced using lithography techniques and easily packaged and distributed.

The scalability and resolution of conventional optical manipulation techniques are limited by diffraction. We circumvent the diffraction limit and describe a method of optically transporting nanoparticles across a chip using a gold surface patterned with a path of closely spaced C-shaped plasmonic resonators.

The technique of using focused laser beams to trap and exert forces on small particles has enabled many pivotal discoveries in the nanoscale biological ...

Compact Lens-less Digital Holographic Microscope for MEMS Inspection and Characterization

A micro-electro-mechanical-system (MEMS) is a widely used component in many industries, including energy, biotechnology, medical, communications, and automotive. However, effective inspection and characterization metrology systems are needed to ensure the functional reliability of MEMS. This study presents a system based on digital holography as a tool for MEMS metrology. Digital holography has gained increasing attention in the past 20 years. With the fast development and decreasing cost of sensor arrays, resolution of such systems has increased broadening potential applications. Thus, it has attracted attention from both research and industry sides as a potential reliable tool for industrial metrology. Indeed, by recording the interference pattern between an object beam (which contains sample height information) and a reference beam on a CCD camera, one can retrieve the quantitative phase information of an object. However, most of digital holographic systems are bulky and thus not easy to implement on industry production lines. The novelty of the system presented is that it is lens-less and thus very compact. In this study, it is shown that the Compact Digital Holographic Microscope (CDHM) can be used to evaluate several characteristics typically consider as criteria in MEMS inspections. The surface profiles of MEMS in both static and dynamic conditions are presented. Comparison with AFM is investigated to validate the accuracy of the CDHM.

We present a compact reflection digital holographic system (CDHM) for inspection and characterization of MEMS devices. A lens-less design using a diverging input wave providing natural geometrical magnification is demonstrated. Both static and dynamic studies are presented.

A micro-electro-mechanical-system (MEMS) is a widely used component in many industries, including energy, biotechnology, medical, communications, and ...

Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization

Polymer-based materials hold promise as low-cost, flexible efficient photovoltaic devices. Most laboratory efforts to achieve high performance devices have used devices prepared by spin coating, a process that is not amenable to large-scale fabrication. This mismatch in device fabrication makes it difficult to translate quantitative results obtained in the laboratory to the commercial level, making optimization difficult. Using a mini-slot die coater, this mismatch can be resolved by translating the commercial process to the laboratory and characterizing the structure formation in the active layer of the device in real time and in situ as films are coated onto a substrate. The evolution of the morphology was characterized under different conditions, allowing us to propose a mechanism by which the structures form and grow. This mini-slot die coater offers a simple, convenient, material efficient route by which the morphology in the active layer can be optimized under industrially relevant conditions. The goal of this protocol is to show experimental details of how a solar cell device is fabricated using a mini-slot die coater and technical details of running in situ structure characterization using the mini-slot die coater.

Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization

Here, we present a protocol to fabricate organic thin film solar cells using a mini-slot die coater and related in-line structure characterizations using synchrotron scattering techniques.

Polymer-based materials hold promise as low-cost, flexible efficient photovoltaic devices. Most laboratory efforts to achieve high performance devices ...

Fabrication and Characterization of Superconducting Resonators

Superconducting microwave resonators are of interest for a wide range of applications, including for their use as microwave kinetic inductance detectors (MKIDs) for the detection of faint astrophysical signatures, as well as for quantum computing applications and materials characterization. In this paper, procedures are presented for the fabrication and characterization of thin-film superconducting microwave resonators. The fabrication methodology allows for the realization of superconducting transmission-line resonators with features on both sides of an atomically smooth single-crystal silicon dielectric. This work describes the procedure for the installation of resonator devices into a cryogenic microwave testbed and for cool-down below the superconducting transition temperature. The set-up of the cryogenic microwave testbed allows one to do careful measurements of the complex microwave transmission of these resonator devices, enabling the extraction of the properties of the superconducting lines and dielectric substrate (e.g., internal quality factors, loss and kinetic inductance fractions), which are important for device design and performance.

Superconducting microwave resonators are of interest for detection of light, quantum computing applications and materials characterization. This work presents a detailed procedure for fabrication and characterization of superconducting microwave resonator scattering parameters.

Superconducting microwave resonators are of interest for a wide range of applications, including for their use as microwave kinetic inductance detectors ...

Fabrication of Polymer Microspheres for Optical Resonator and Laser Applications

This paper describes three methods of preparing fluorescent microspheres comprising &#960;-conjugated or non-conjugated polymers: vapor diffusion, interface precipitation, and mini-emulsion. In all methods, well-defined, micrometer-sized spheres are obtained from a self-assembling process in solution. The vapor diffusion method can result in spheres with the highest sphericity and surface smoothness, yet the types of the polymers able to form these spheres are limited. On the other hand, in the mini-emulsion method, microspheres can be made from various types of polymers, even from highly crystalline polymers with coplanar, &#960;-conjugated backbones. The photoluminescent (PL) properties from single isolated microspheres are unusual: the PL is confined inside the spheres, propagates at the circumference of the spheres via the total internal reflection at the polymer/air interface, and self-interferes to show sharp and periodic resonant PL lines. These resonating modes are so-called "whispering gallery modes" (WGMs). This work demonstrates how to measure WGM PL from single isolated spheres using the micro-photoluminescence (&#181;-PL) technique. In this technique, a focused laser beam irradiates a single microsphere, and the luminescence is detected by a spectrometer. A micromanipulation technique is then used to connect the microspheres one by one and to demonstrate the intersphere PL propagation and color conversion from coupled microspheres upon excitation at the perimeter of one sphere and detection of PL from the other microsphere. These techniques, &#181;-PL and micromanipulation, are useful for experiments on micro-optic application using polymer materials.

Protocols for the synthesis of microspheres from polymers, the manipulation of microspheres, and micro-photoluminescence measurements are presented.