This work is supported by the Engineering and Physical Sciences Research Council grant number EP/I017461/1. We also wish to acknowledge the contribution played by the technical staff of the James Watt Nanofabrication Centre.

1. Simulation of a Single Band THz Metamaterial Absorber
 A 3D view of the simulation set-up is shown in Figure 2.
 <ol>
 <li>Lumerical FDTD is used to optimize the transmission, reflection and absorption characteristics of the THz metamaterial absorber. All units are given in &mu;m.</li>
 <li>Define the THz polyimide material properties by left clicking Materials, Add (n,k) material and inputting 1.68 as the n and 0.06 as the k. Double left click on "new material 1" and rename it as "polyimide". Note that if theoretical or experimental refractive index data is available one can "add sampled data" to define the material properties.</li>
 <li>Draw the geometry of the device, starting with the 0.2 &mu;m thick metal ground plane. In the structures tab select rectangle and edit the properties by pressing the e key. Input "groundplane" in the name window, (0,0,0.1) as the structure centre co-ordinates and (31,31,0.2) as the span region. Move to the material tab and select Perfect Electrical Conductor (PEC). Repeat to define the 3 &mu;m thick polyimide dielectric layer typing "polyimide" in the name window, (0,0,1.7) as the centre co-ordinates and (31,31,3) as the span. Finally define the 0.2 &mu;m thick electric ring resonator by drawing two rectangular Perfect Electrical Conductor (PEC) regions called "ERR arm1" and "ERR arm2" with the same centre co-ordinates of (0,0,3.3) but different span regions of (10,26,0.2) and (26,10,0.2) respectively.</li>
 <li>Add the simulation region by left clicking on Simulation and press e to edit the properties. In the general tab input 20 psec as the simulation time. In the geometry tab choose (0,0,0) as the centre co-ordinates and (30,30,200) as the span regions. In the mesh settings tab select a mesh accuracy of 3 and keep the other default settings as they are. Set the simulation boundary conditions in the boundary conditions tab choosing "Anti-symmetric" for x min bc and x max bc, "symmetric" for y min bc and y max bc and "PML" for z min bc and z max bc (the "allow symmetry on all boundaries" must be ticked). Include a mesh override region by left clicking again on Simulation and edit by pressing e. In the general tab type 0.5 &mu;m for the dx and dy override and 0.05 &mu;m for the dz override. In the geometry tab enter the centre co-ordinates (0,0,1.7) and span regions (30,30,3.8). Note that a smaller mesh size of e.g. dx, dy 0.1 &mu;m, will increase simulation accuracy though this will come at the expense of significantly increased CPU memory and simulation time. It is best to simulate using a large mesh size until a structure with the desired properties is obtained and then re-simulate using the smaller mesh size.</li>
 <li>Define the source type by left clicking on the arrow next to sources and choosing plane wave. Press e to edit the source properties and in the general tab change the direction to backward. In the geometry tab enter the centre co-ordinates (0,0,90) and (35,35,0) for the span region. Note that you cannot modify the z span. Set the minimum and maximum frequency of the simulation in the frequency/wavelength tab. Choose a minimum of 1 THz and a maximum of 4 THz and ensure the pulse in the signal versus time graph in the bottom right corner of the window decays to zero well before 20 psec.</li>
 <li>Left click on the arrow next to Monitors and select frequency-domain field profile. Press e to edit the monitor properties and enter "r95" in the monitor name window. In the geometry tab enter the centre co-ordinates of (0,0,95) and span region (30,30,0). Repeat and create a second frequency-domain field profile monitor called "t95" with centre co-ordinates (0,0,-95) and spans (30,30,0). Left click on the arrow next to Monitors and select global properties. In the frequency/power profile tab enter 100 in the frequency points window. Figure 2 shows the perspective view displayed in Lumerical on completion of steps 1.1-1.6. Check the memory requirements are compatible with your computer by left clicking on the arrow next to the Check icon on the top toolbar and selecting check simulation memory requirements. Save the file giving it an appropriate name such as "Jove.sim".</li>
 <li>Run the simulation by left clicking on the Run icon.</li>
 <li>On completion of the simulation enter the following into the script prompt window. Note that one can also enter the following text in a text editor and save the file as a .lsf file. The script can then be run by left clicking on the arrow next to Run, selecting script and then locating the script file saved on your computer. Note that the # symbol indicates a comment. 
</li>
 </ol>

 load("Jove_sim"); # loads the simulation file 
f = getdata("r95","f"); # gets the reflection data and frequency data from the r95 monitor 
R = transmission("r95"); # defines R as a matrix containing the reflection data 
A = 1-R; # calculates the absorption 
fthz=f/1e12; # converts frequency to THz 
plot(fthz,A,R,"Frequency(THz)","Absorption","Reflection"); # plot data on a single graph 
legend("Absorption","Reflection"); 
filename = "Jove_sim.csv"; # export data for excel import 
rm(filename); # delete file if it already exists 
lambda = c/f; # converts frequency to wavelength 
for(i=1:length(lambda)) { 
 &nbsp;&nbsp;write(filename,num2str(f(i)) + "," + 
 num2str(fthz(i)) + "," + 
 num2str(R(i)) + "," +
 num2str(A(i)) + "," ); 
} # outputs a .csv file in column format of the frequency, reflection and absorption
2. Fabrication of a Single Band THz Metamaterial Absorber
 Figure 3 shows the most important fabrication steps.
 <ol>
 <li>Clean a 15 mm by 15 mm piece of silicon in sequential solutions of warm (50 &deg;C) opticlear, acetone and ispopropanol using ultrasonic agitation after initially heating the beaker containing the solvent for 10 min. Note that this protocol can also be used to fabricate several devices onto a 4 inch diameter wafer.</li>
 <li>Evaporate a metal bi-layer of 20 nm/100 nm Ti/Au onto the 15 mm by 15 mm using a Plassys 450 MEB electron beam evaporator (Figure 3, step 1). Note that the metal thickness must be greater than the skin depth at the desired operating frequency.</li>
 <li>Clean the sample as previously described in section 2.1</li>
 <li>Dispense VM651 primer onto the sample using a pipette and leave to relax for 20 sec. Spin sample at 4,000 rpm for 5 sec and then bake on a contact hotplate at 120 &deg;C for 60 sec.</li>
 <li>Remove Dupont PI2545 polyimide from the freezer. Allow 20 min for the bottle to reach room temperature. This is essential since opening the bottle directly after removal from the freezer will result in moisture condensing inside the bottle and degrading the polyimide film properties. Dispense PI2545 onto the sample using a pipette and allow 20 sec for it to relax. Spin sample using a 2 stage spin procedure with the following settings - (i) final spin speed 500 rpm, acceleration 100 rpms-1, final spin time 5 sec (ii) final spin speed 6,000 rpm, acceleration 500 rpms-1, final spin time 60 sec. Bake sample on a contact hotplate at 140 &deg;C for 5 min (Figure 3, step 2). If a thicker polyimide film is required then either spin multiple layers or reduce the final spin speed. To obtain a polyimide film thickness of 3 &mu;m with minimal edge bead three layers of PI2545 are spun using the above protocol.</li>
 <li>Cure the polyimide on a contact hotplate at 220 &deg;C for 10 min. After this cure procedure the PI2545 will be impervious to most solvents and acids and can only be removed using oxygen plasma. PI2545 can be spun onto a dummy piece of silicon, cured as above and the thickness of the film measured by scratching the polyimide and using a DEKTAK surface profilometer to measure the step height.</li>
 <li>Deposit 15% 2010 Poly(methyl methacrylate), known as PMMA, onto the sample. Spin at 5,000 rpm for 60 sec and bake in a convection oven at 180 &deg;C for 30 min. Before baking remove any excess resist that has crept on to the backside of the sample using acetone. Remove sample from the oven and leave to cool to room temperature (~5 min). Deposit 4% 2041 PMMA onto the sample, spin at 5,000 rpm for 60 sec and bake in a convection oven at 180 &deg;C for 60 min (Figure 3, step 3). Remove any excess resist that has crept on to the backside of the sample using acetone before baking.</li>
 <li>Write the desired job on a Vistec VB6 electron beam writer using a dose of 450 &mu;C/cm2. The job file is designed in Tanner L-Edit, fractured into polygons by Layout Beamer and finally submitted to the beam writer using the Java based BELLE software.</li>
 <li>Develop the sample in a solution of 1:1 MIBK:IPA at a temperature of 23 &deg;C for 60 sec (Figure 3, step 4). Rinse in a beaker of isopropanol. Inspect pattern fidelity on an optical microscope. If features are poorly resolved strip the resist in opticlear, acetone and isopropanol and start again from 2.2.</li>
 <li>Descum the sample with O2 using a Gala Plasmaprep5 barrel asher for 1 min at 0.1 mbar and 50 W RF power. Evaporate 20 nm Ti and 150 nm Au using a Plassys 450 MEB electron beam evaporator (Figure 3, step 5).</li>
 <li>Insert the sample into a beaker of warm acetone and place the beaker into a hot water bath kept at 50 &deg;C. After 4 hr remove the sample from the water bath and using a pipette suck up some of the warm acetone and spray liberally onto the sample (Figure 3, step 6). Inspect sample by eye to check that metal is lifting off from the areas where PMMA was present. If lift-off is progressing slowly place beaker in the ultrasonic water bath for 2 min. Inspect sample under the optical microscope.</li>
 <li>The protocol describes the fabrication of a single band THz absorber however multi-level dual band and broadband absorbers can be produced by repeating steps 2.3-2.11 and stacking several crosses on top of polyimide layers.</li>
 </ol>
 3. Characterization of a Single Band THz Metamaterial Absorber
 Figure 4 shows the basic FTIR instrument layout.
 <ol>
 <li>Turn on the nitrogen supply to the IFS 66V/S Fourier Transform Infra Red (FTIR) spectrometer. Press the "FIR" button on the front of the spectrometer control unit to turn on the Hg arc lamp. It takes around 15 min for the lamp power to stabilize. Insert the 6 &mu;m multilayer beam splitter into the appropriate slot in the interferometer unit.</li>
 <li>Vent the sample compartment of the spectrometer and insert the PIKE 30 &deg; reflection unit. Place the 4 mm aperture on top of the reflection unit aperture and on top of this put a gold mirror. The 4 mm aperture determines the area of the sample that will be interrogated while the gold mirror is necessary to make a background measurement.</li>
 <li>Evacuate the sample compartment and wait for the pressure to get down to 5 mbar. The spectrometer can be run in a purged nitrogen environment however the signal size typically drops to less than 20% compared to vacuum.</li>
 <li>Start the OPUS software and load the configuration file (set-up on installation of the unit) for taking measurements in the 30 cm-1 to 300 cm-1 range (1-9THz). This file sets numerous spectrometer parameters such as the scanner velocity, source aperture, source type, data collection method and Fourier transform execution mode. Ensure the LED on the front of the detector compartment is flashing green, indicating that the scanner is operating. Check that the shape of the interferogram is as expected.</li>
 <li>Run 100 background scans to obtain the background spectrum.</li>
 <li>Vent sample compartment, remove mirror and place sample face down onto the aperture. Ensure the centre of the sample is in the middle of the aperture. Evacuate the sample compartment.</li>
 <li>Run 1,000 sample scans to obtain the sample spectrum. The sample spectrum will be compared to the background reference spectrum and the final reflection spectrum of the sample obtained. Note that if the signal reaching the detector is low, a greater number of sample scans may be required to reduce the noise (e.g. 10,000 scans). Repeat sample scans should be made to ensure the measured data is reliable and consistent.</li>
 <li>Data from the completed scan can be converted into a text file and analyzed offline. The continuous ground plane of the sample means that there is no transmission ergo the absorption spectrum can be found by subtracting the reflection from 1.</li>
 </ol>

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No conflicts of interest declared.

This protocol describes the simulation, fabrication and characterization of THz metamaterial absorbers. It is essential such sub-wavelength structures are accurately simulated before any effort is committed to costly fabrication procedures. Lumerical FDTD simulations provide information on not only the MM absorption spectrum but also the location of the absorption, essential knowledge to aid placement of a transducer and obtain the maximum response. In addition the optimization algorithm in Lumerical can be implem...

This protocol describes the simulation, fabrication and characterization of single band and broadband THz MM absorbers. The device, shown in Figure 1, consists of a metal cross and a dielectric layer on top of a metal ground plane. The cross-shaped structure is an example of an electric ring resonator (ERR)20,21 and couples strongly to uniform electric fields, but negligibly to a magnetic field. By pairing the ERR with a ground plane, the magnetic component of the incident THz wave induces a current in the sections of the ERR that are parallel to the direction of the E-field. The electric and magnetic response can then be tuned independently and the impedance of the structure matched to free space by varying the geometry of the ERR and the distance between the two metallic elements. As shown in Figure 1(d), the symmetry of the structure results in a polarization insensitive absorption response.

<table border="1">
 <tbody>
 <tr>
 <td>Name of Reagent/Material</td>
 <td>Company</td>
 <td>Catalogue Number</td>
 <td>Comments</td>
 </tr>
 <tr>
 <td>Lumerical FDTD</td>
 <td>Lumerical</td>
 <td></td>
 <td></td>
 </tr>
 <tr>
 <td>Silicon wafer</td>
 <td>IDB technologies</td>
 <td></td>
 <td>Single sided polished</td>
 </tr>
 <tr>
 <td>Plassys 450 MEB evaporator</td>
 <td>Plassys Bestek</td>
 <td></td>
 <td></td>
 </tr>
 <tr>
 <td>VM651 Primer</td>
 <td>Dupont</td>
 <td></td>
 <td></td>
 </tr>
 <tr>
 <td>PI2545</td>
 <td>Dupont</td>
 <td></td>
 <td></td>
 </tr>
 <tr>
 <td>Methyl Isobutyl Ketone</td>
 <td>Sigma-Aldrich</td>
 <td></td>
 <td></td>
 </tr>
 <tr>
 <td>Isopropanol</td>
 <td>Sigma-Aldrich</td>
 <td></td>
 <td></td>
 </tr>
 <tr>
 <td>Plasmaprep5 barrel Asher</td>
 <td>Gala Instrumente</td>
 <td></td>
 <td></td>
 </tr>
 <tr>
 <td>VB6 UHR EWF electron beam writer</td>
 <td>Vistec</td>
 <td></td>
 <td></td>
 </tr>
 <tr>
 <td>Tanner L-Edit</td>
 <td>Tanner Inc.</td>
 <td></td>
 <td></td>
 </tr>
 <tr>
 <td>Layout Beamer</td>
 <td>GenISys Inc.</td>
 <td></td>
 <td></td>
 </tr>
 <tr>
 <td>Polymethyl methacrylate (PMMA)</td>
 <td>Sigma-Aldrich</td>
 <td>293261 Sigma-Aldrich</td>
 <td></td>
 </tr>
 <tr>
 <td>IFV 66v/s FTIR</td>
 <td>Bruker</td>
 <td></td>
 <td></td>
 </tr>
 <tr>
 <td>Pike 30spec reflection unit</td>
 <td>Pike Technologies</td>
 <td></td>
 <td></td>
 </tr>
 <tr>
 <td>Hg arc lamp</td>
 <td>Bruker</td>
 <td></td>
 <td></td>
 </tr>
 <tr>
 <td>Au mirror</td>
 <td>Thor Labs</td>
 <td>PF05-03-M01</td>
 <td></td>
 </tr>
 <tr>
 <td>Leica INM20 Optical Microscope</td>
 <td>Leica microsystems</td>
 <td></td>
 <td></td>
 </tr>
 <tr>
 <td>6 mm Mylar Beamsplitter</td>
 <td>Bruker</td>
 <td></td>
 <td></td>
 </tr>
 </tbody>
 </table>

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.

Figure 5(a) shows the experimentally obtained and simulated absorption spectra for a MM absorber with a 3.1 &mu;m thick polyimide dielectric spacer. This MM structure has a repeat-period of 27 &mu;m and dimensions K = 26 &mu;m, L = 20 &mu;m, M = 10 &mu;m and N = 5 &mu;m. Experimental measurements were also performed on samples with no ERR layer to confirm that absorption was a consequence of the MM structure and not of the dielectric. The 7.5 &mu;m thick polyimide sample with no ERR structur...

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Simulation, Fabrication and Characterization of THz Metamaterial Absorbers

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 ...

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15.2K Views.  University of Glasgow. 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.

Video: Simulation, Fabrication and Characterization of THz Metamaterial Absorbers

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 and Testing of Microfluidic Optomechanical Oscillators

Cavity optomechanics experiments that parametrically couple the phonon modes and photon modes have been investigated in various optical systems including microresonators. However, because of the increased acoustic radiative losses during direct liquid immersion of optomechanical devices, almost all published optomechanical experiments have been performed in solid phase. This paper discusses a recently introduced hollow microfluidic optomechanical resonator. Detailed methodology is provided to fabricate these ultra-high-Q microfluidic resonators, perform optomechanical testing, and measure radiation pressure-driven breathing mode and SBS-driven whispering gallery mode parametric vibrations. By confining liquids inside the capillary resonator, high mechanical- and optical- quality factors are simultaneously maintained.

Parametric optomechanical excitations have recently been experimentally demonstrated in microfluidic optomechanical resonators by means of optical radiation pressure and stimulated Brillouin scattering. This paper describes the fabrication of these microfluidic resonators along with methodologies for generating and verifying optomechanical oscillations.

Cavity optomechanics experiments that parametrically couple the phonon modes and photon modes have been investigated in various optical systems including ...

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.

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 ...

Ohmic Contact Fabrication Using a Focused-ion Beam Technique and Electrical Characterization for Layer Semiconductor Nanostructures

Layer semiconductors with easily processed two-dimensional (2D) structures exhibit indirect-to-direct bandgap transitions and superior transistor performance, which suggest a new direction for the development of next-generation ultrathin and flexible photonic and electronic devices. Enhanced luminescence quantum efficiency has been widely observed in these atomically thin 2D crystals. However, dimension effects beyond quantum confinement thicknesses or even at the micrometer scale are not expected and have rarely been observed. In this study, molybdenum diselenide (MoSe2) layer crystals with a thickness range of 6-2,700 nm were fabricated as two- or four-terminal devices. Ohmic contact formation was successfully achieved by the focused-ion beam (FIB) deposition method using platinum (Pt) as a contact metal. Layer crystals with various thicknesses were prepared through simple mechanical exfoliation by using dicing tape. Current-voltage curve measurements were performed to determine the conductivity value of the layer nanocrystals. In addition, high-resolution transmission electron microscopy, selected-area electron diffractometry, and energy-dispersive X-ray spectroscopy were used to characterize the interface of the metal&#8211;semiconductor contact of the FIB-fabricated MoSe2 devices. After applying the approaches, the substantial thickness-dependent electrical conductivity in a wide thickness range for the MoSe2-layer semiconductor was observed. The conductivity increased by over two orders of magnitude from 4.6 to 1,500 &#937;&#8722;1 cm&#8722;1, with a decrease in the thickness from 2,700 to 6 nm. In addition, the temperature-dependent conductivity indicated that the thin MoSe2 multilayers exhibited considerably weak semiconducting behavior with activation energies of 3.5-8.5 meV, which are considerably smaller than those (36-38 meV) of the bulk. Probable surface-dominant transport properties and the presence of a high surface electron concentration in MoSe2 are proposed. Similar results can be obtained for other layer semiconductor materials such as MoS2 and WS2.

We describe the approaches for the device fabrication and electrical characterization of molybdenum diselenide (MoSe2) layer semiconductor nanostructures with different thicknesses. In addition, the fabrication of ohmic contacts for MoSe2-layer nanocrystals by the focused-ion beam deposition method using platinum (Pt) as a contact metal is described.

Layer semiconductors with easily processed two-dimensional (2D) structures exhibit indirect-to-direct bandgap transitions and superior transistor ...

Visualizing Hyporheic Flow Through Bedforms Using Dye Experiments and Simulation

Advective exchange between the pore space of sediments and the overlying water column, called hyporheic exchange in fluvial environments, drives solute transport in rivers and many important biogeochemical processes. To improve understanding of these processes through visual demonstration, we created a hyporheic flow simulation in the multi-agent computer modeling platform NetLogo. The simulation shows virtual tracer flowing through a streambed covered with two-dimensional bedforms. Sediment, flow, and bedform characteristics are used as input variables for the model. We illustrate how these simulations match experimental observations from laboratory flume experiments based on measured input parameters. Dye is injected into the flume sediments to visualize the porewater flow. For comparison virtual tracer particles are placed at the same locations in the simulation. This coupled simulation and lab experiment has been used successfully in undergraduate and graduate laboratories to directly visualize river-porewater interactions and show how physically-based flow simulations can reproduce environmental phenomena. Students took photographs of the bed through the transparent flume walls and compared them to shapes of the dye at the same times in the simulation. This resulted in very similar trends, which allowed the students to better understand both the flow patterns and the mathematical model. The simulations also allow the user to quickly visualize the impact of each input parameter by running multiple simulations. This process can also be used in research applications to illustrate basic processes, relate interfacial fluxes and porewater transport, and support quantitative process-based modeling.

This manuscript describes how to create regular bedforms in a flume, visualize flow through the bedforms, and use computer simulations to simulate the hyporheic flow. The computer simulations compare well with the experimental observations. This coupled simulation and experiment is well-suited for both research and educational purposes.

Advective exchange between the pore space of sediments and the overlying water column, called hyporheic exchange in fluvial environments, drives solute ...

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 ...

Study of Siphon Breaker Experiment and Simulation for a Research Reactor

Under the design conditions of a research reactor, the siphon phenomenon induced by pipe rupture can cause continuous outward flow of water. To prevent this outflow, a control device is required. A siphon breaker is a type of safety device that can be utilized to control the loss of coolant water effectively.
To analyze the characteristics of siphon breaking, a real-scale experiment was conducted. From the results of the experiment, it was found that there are several design factors that affect the siphon breaking phenomenon. Therefore, there is a need to develop a theoretical model capable of predicting and analyzing the siphon breaking phenomenon under various design conditions. Using the experimental data, it was possible to formulate a theoretical model that accurately predicts the progress and the result of the siphon breaking phenomenon. The established theoretical model is based on fluid mechanics and incorporates the Chisholm model to analyze two-phase flow. From Bernoulli&#39;s equation, the velocity, quantity, undershooting height, water level, pressure, friction coefficient, and factors related to the two-phase flow could be obtained or calculated. Moreover, to utilize the model established in this study, a siphon breaker analysis and design program was developed. The simulation program operates on the theoretical model basis and returns the result as a graph. The user can confirm the possibility of the siphon breaking by checking the shape of the graph. Furthermore, saving the entire simulation result is possible and it can be used as a resource for analyzing the real siphon breaking system.
In conclusion, the user can confirm the status of the siphon breaking and design the siphon breaker system using the program developed in this study.

The siphon breaking phenomenon was investigated experimentally and a theoretical model was proposed. A simulation program based on the theoretical model was developed and the results of the simulation program were compared with experimental results. It was concluded that the results of the simulation program matched the experimental results well.

Under the design conditions of a research reactor, the siphon phenomenon induced by pipe rupture can cause continuous outward flow of water. To prevent ...