Name: determination of the excitation and coupling rates between light emitters and surface plasmon polaritons
Uploaded: 2018-07-21T12:30:00
Description: Watch this Scientific Journal Video about Determination of the Excitation and Coupling Rates Between Light Emitters and Surface Plasmon Polaritons at JoVE.com

This research was supported by the Chinese University of Hong Kong through the Direct Grants 4053077 and 4441179, RGC Competitive Earmarked Research Grants, 402812 and 14304314, and Area of Excellence AoE/P-02/12.

1. Setup of Interference Lithography
NOTE: Interference lithography is used to fabricate the periodic arrays12. The schematic setup, as is shown in Figure 1, is built up as follows:
<ol>
	<li>Focus the 325 nm laser from a HeCd multimode laser to a 13X UV objective lens and pass it through a 50 &#956;m pinhole based spatial filter for mode cleaning.</li>
	<li>Place two 2.5 cm diameter irises 30 cm apart to further filter the central region...

<ol>
	<li>Okamoto, K., 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-plasmon-enhanced+light+emitters+based+on+InGaN+quantum+wells.">Surface-plasmon-enhanced light emitters based on InGaN quantum wells.</a> Nature Materials. 3 (9), 601-605 (2004).</li><li>Akselrod, G. M., 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=Leveraging+Nanocavity+Harmonics+for+Control+of+Optical+Processes+in+2D+Semiconductors.">Leveraging Nanocavity Harmonics for Control of Optical Processes in 2D Semiconductors.</a> Nano Letters. 15 (5), 3578-3584 (2015).</li><li>Gontijo, I., 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=Coupling+of+InGaN+quantum-well+photoluminescence+to+silver+surface+plasmons.">Coupling of InGaN quantum-well photoluminescence to silver surface plasmons.</a> Physical Review B. 60 (16), 11564 (1999).</li><li>Huang, K. C. Y., 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=Antenna+electrodes+for+controlling+electroluminescence.">Antenna electrodes for controlling electroluminescence.</a> Nature Communications. 3, 1005 (2012).</li><li>Atwater, H. A., Polman, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Plasmonics+for+improved+photovoltaic+devices.">Plasmonics for improved photovoltaic devices.</a> Nature Materials. 9 (3), 205-213 (2010).</li><li>Anker, J. N., 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=Biosensing+with+plasmonic+nanosensors.">Biosensing with plasmonic nanosensors.</a> Nature Materials. 7 (6), 442-453 (2008).</li><li>Chen, Y., 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=Excitation+enhancement+of+CdSe+quantum+dots+by+single+metal+nanoparticles.">Excitation enhancement of CdSe quantum dots by single metal nanoparticles.</a> Applied Physics Letters. 93 (5), 053106 (2008).</li><li>Birowosuto, M. D., Skipetrov, S. E., Vos, W. L., Mosk, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Observation+of+Spatial+Fluctuations+of+the+Local+Density+of+States+in+Random+Photonic+Media.">Observation of Spatial Fluctuations of the Local Density of States in Random Photonic Media.</a> Physical Review Letters. 105 (1), 013904 (2010).</li><li>Cao, Z. L., Ong, H. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determination+of+coupling+rate+of+light+emitter+to+surface+plasmon+polaritons+supported+on+nanohole+array.">Determination of coupling rate of light emitter to surface plasmon polaritons supported on nanohole array.</a> Applied Physics Letters. 102 (24), 241109 (2013).</li><li>Lin, M., Cao, Z. L., Ong, H. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determination+of+the+excitation+rate+of+quantum+dots+mediated+by+momentum-resolved+Bloch-like+surface+plasmon+polaritons.">Determination of the excitation rate of quantum dots mediated by momentum-resolved Bloch-like surface plasmon polaritons.</a> Optics Express. 25 (6), 6029-6103 (2017).</li><li>Nikolaev, I. S., Lodahl, P., Driel, A. F. V., Koenderink, A. F., Vos, W. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Strongly+nonexponential+time-resolved+fluorescence+of+quantum-dot+ensembles+in+three-dimensional+photonic+crystals.">Strongly nonexponential time-resolved fluorescence of quantum-dot ensembles in three-dimensional photonic crystals.</a> Physical Review B. 75 (11), 115302 (2007).</li><li>Cao, Z. L., Lo, H. Y., Ong, H. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determination+of+absorption+and+radiative+decay+rates+of+surface+plasmon+polaritons+from+nanohole+array.">Determination of absorption and radiative decay rates of surface plasmon polaritons from nanohole array.</a> Optics Letters. 37 (24), 5166-5168 (2012).</li><li>Haus, H. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Waves and Fields in Optoelectronics. , (1984).</li></ol>

In this protocol, there are several critical steps. First, mechanical stability is crucial in sample preparation. The standing wave generated by Lloyd&#39;s setup is sensitive to the phase difference between two illumination beams. Therefore, any vibration during the exposure time will degrade the uniformity and edge sharpness of the nanohole. It is highly recommended to operate in a vibration-free environment, e.g., an optical table with vibration isolation supports. In addition, high power laser is also desire...

Surface plasmon mediated fluorescence (SPMF) has received considerable attention recently1,2,3,4,5,6. When light emitters are placed in close proximity to a plasmonic system, energy can be transferred between the emitters and surface plasmon polaritons (SPPs). In general, the strong plasmonic fields can strongly enhance the excitation of the emitters2. At the same time, the emission rate is also increased because of the large density-of-states created by SPPs, yielding the well-known Purcell effect3. These two processes work hand in hand in producing the SPMF. As SPMF has stimulated numerous applications in solid-state lighting1,4, energy harvesting5, and bio-detection6, it is currently under intensive investigation. In particular, the knowledge of the energy transfer rates from the SPPs to the emitters and vice versa, i.e., the excitation and coupling rates, is of great importance. However, the excitation and emission processes are usually entangled together, study on this aspect is still lacking. For example, most of the studies only determine the excitation efficiency ratio, which simply compares the emission with and without SPPs7. The exact measurement of the excitation rate is still missing. On the other hand, conventional time-resolved techniques such as fluorescence lifetime spectroscopy are routinely used for studying the dynamics of the emission process, but they are unable to separate the coupling rate from the total decay rate8. Here, we describe how one can determine them by combining the rate equation model and the temporal coupled mode theory9,10. Remarkably, we find that the excitation and coupling rates can be expressed in terms of measurable quantities, which can be accessed by performing angle- and polarization-resolved reflectivity and photoluminescence spectroscopy. We will first outline the formulation and then describe the instrumentation in detail. This approach is entirely frequency domain based and it does not require any time-resolved accessories such as ultra-fast lasers and time-correlated single-photon counters, which are expensive and sometimes difficult to implement8,11. We anticipate this technique to be an enabling technology for determining the excitation and coupling rates between light emitters and resonant cavities.
The SPMF in periodic systems is briefed here. For a periodic plasmonic system where Bloch-like SPPs can be generated, other than direct excitation and emission, which are characterized by the excitation efficiency&#160;&#951; and spontaneous emission rate &#915;r, the emitters can be excited by incoming SPPs and decay via outgoing SPPs. In other words, under resonance excitation, incoming SPPs are generated to create strong plasmonic fields that energize the emitters. Once the emitters are excited, energy from them can be transferred to outgoing SPPs, which subsequently radiatively dissipate to far-field, giving rise to enhanced emission. They define SPMF. For simple two-level emitters, the excitation refers to the increased transition of electrons from the ground to the excited states whereas the emission defines the decay of electrons back to the ground states, accompanied by photon emission at wavelengths defined by the energy difference between the excited and ground states. The excitation and emission conditions for the SPMF are required to fulfill the well-known phase matching equation to excite the incoming and outgoing SPPs9
<img alt="Equation 1" src="/files/ftp_upload/56735/56735eq1.jpg" /> (1)
where &#949;a and &#949;m are the dielectric constants of the dielectrics and the metal,&#160;&#952; and&#160;&#966; are the incident and azimuthal angles, P is the period of the array,&#160;&#955; is the excitation or emission wavelength, and m and n are the integers specifying the order of SPPs. For excitation, the in-plane wavevector of the laser beam will be Bragg scattered to momentum match with the incoming SPPs and the &#952; and&#160;&#966; together define the specified incident configuration for exciting the SPPs to enhance the electronic absorption at the excitation wavelength &#955;ex. Likewise, for the emission, the outgoing SPPs will be reversely Bragg scattered to match with the light line and the angles now represent the possible emission channels at the emission wavelength &#955;em. However, it is noted that as the emitters can couple their energy to vectorial propagating SPPs with <img alt="Equation 2" src="/files/ftp_upload/56735/56735eq2.jpg" /> that has the same magnitude <img alt="Equation 3" src="/files/ftp_upload/56735/56735eq3.jpg" /> but different directions, the SPPs can decay via various combination of (m,n) to far-field following Eq. (1).
By using the rate equation model and temporal coupled mode theory (CMT), we find that the excitation rate &#915;ex, i.e., the energy transfer rate from SPPs to emitters, can be expressed as9,12,13
<img alt="Equation 4" src="/files/ftp_upload/56735/56735eq4.jpg" /> (2)
where &#951; is the aforementioned direct excitation rate in the absence of the incoming SPPs, &#915;tot is the total decay rate of the incoming SPPs&#160;<img alt="Equation 5" src="/files/ftp_upload/56735/56735eq5.jpg" /> in which &#915;abs and &#915;rad are the Ohmic absorption and radiative decay rates of SPPs, and&#160;<img alt="Equation 6" src="/files/ftp_upload/56735/56735eq6.jpg" /> is the photoluminescence power ratio with and without the incoming SPPs. On the other hand, the coupling rate &#915;c, i.e., the energy transfer rate from emitters to SPPs, can be written as:
<img alt="Equation 7" src="/files/ftp_upload/56735/56735eq7.jpg" /> (3)
where &#915;r is the direct emission rate, <img alt="Equation 8" src="/files/ftp_upload/56735/56735eq8.jpg" /> is the photoluminescence power ratio between the &#945;th SPP mediated decay and direct ports, and &#915;rad&#945; and &#915;tot are the radiative decay rates for the &#945;th port and the total decay rates. We will see that while all the SPP decay rates can be measured by reflectivity spectroscopy, the emission power ratio can be determined by photoluminescence spectroscopy. Details of the formulations can be found in reference9,10.

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		<tr height="21">
			<td height="21" style="height:21px;width:319px;">SU-8</td>
			<td style="width:213px;">MicroChem</td>
			<td style="width:119px;">SU-8 2000.5</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Adhesion solution</td>
			<td style="width:213px;">MicroChem</td>
			<td style="width:119px;">Omnicoat</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:21px;width:319px;">SU-8 Thinner (Gamma-Butyrolactone)</td>
			<td style="width:213px;">MicroChem</td>
			<td style="width:119px;">SU-8 2000 Thinner</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">SU-8 Developer</td>
			<td style="width:213px;">MicroChem</td>
			<td style="width:119px;">SU-8 Developer</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">Spin Coater</td>
			<td style="width:213px;">Chemat Technology</td>
			<td style="width:119px;">KW-4A</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">HeCd laser</td>
			<td style="width:213px;">KIMMON KOHA CO., LTd</td>
			<td style="width:119px;">IK3552R-G</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">Shutter</td>
			<td style="width:213px;">Thorlabs</td>
			<td style="width:119px;">SH05</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">Objective for sample preparation</td>
			<td style="width:213px;">Newport</td>
			<td style="width:119px;">U-13X</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">Pinhole</td>
			<td style="width:213px;">Newport</td>
			<td style="width:119px;">PNH-50</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">Iris</td>
			<td style="width:213px;">Newport</td>
			<td style="width:119px;">M-DI47.50</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">Prism</td>
			<td style="width:213px;">Thorlabs</td>
			<td style="width:119px;">PS611</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">Rotation stage for sample preparation</td>
			<td style="width:213px;">Newport</td>
			<td style="width:119px;">481-A</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">Supttering Deposition System</td>
			<td style="width:213px;">Homemade</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">Rotation Stage 1</td>
			<td style="width:213px;">Newport</td>
			<td style="width:119px;">URM80ACC</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">Rotation Stage 2</td>
			<td style="width:213px;">Newport</td>
			<td style="width:119px;">RV120PP</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">Rotation Stage 3</td>
			<td style="width:213px;">Newport</td>
			<td style="width:119px;">SR50PP</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">Detection arm</td>
			<td style="width:213px;">Homemade</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">Quartz lamp</td>
			<td style="width:213px;">Newport</td>
			<td align="right" style="width:119px;">66884</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">Fiber Bundle</td>
			<td style="width:213px;">Newport</td>
			<td align="right" style="width:119px;">77578</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">Objective for measurement</td>
			<td style="width:213px;">Newport</td>
			<td style="width:119px;">M-5X &#38; M-60X</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">Polarizer &#38; Analyzer</td>
			<td style="width:213px;">Thorlabs</td>
			<td style="width:119px;">GT15</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">Multimode Fiber</td>
			<td style="width:213px;">Thorlabs</td>
			<td style="width:119px;">BFL105LS02</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">Spectrometer</td>
			<td style="width:213px;">Newport</td>
			<td style="width:119px;">MS260i</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">CCD</td>
			<td style="width:213px;">Andor</td>
			<td style="width:119px;">DV420-OE</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">514nm Argon Ion Laser</td>
			<td style="width:213px;">Spectra-Physics</td>
			<td style="width:119px;">177-G01</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">633nm HeNe Laser</td>
			<td style="width:213px;">Newport</td>
			<td style="width:119px;">R-32413</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">CdSeTe quantum dot</td>
			<td style="width:213px;">Thermo Fisher Scientific</td>
			<td style="width:119px;">q21061mp</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">Polyvinyl alcohol polymer (PVA)</td>
			<td style="width:213px;">SIGMA-ALDRICH</td>
			<td align="right" style="width:119px;">363073</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:319px;">Control program</td>
			<td style="width:213px;">National Instruments</td>
			<td style="width:119px;">LabVIEW</td>
			<td></td>
		</tr>
	</tbody>
</table>

determination of the excitation and coupling rates between light emitters and surface plasmon polaritons

We have developed a unique method to measure the excitation and coupling rates between the light emitters and surface plasmon polaritons (SPPs) arising from metallic periodic arrays without involving time-resolved techniques. We have formulated the rates by quantities that can be measured by simple optical measurements. The instrumentation based on angle- and polarization-resolved reflectivity and photoluminescence spectroscopy will be described in detail here. Our approach is intriguing due to its simplicity, which requires routine optics and several mechanical stages, and thus is highly affordable to most of the research laboratories.

An example of an Au periodic array is given in the inset of Figure 4a8. The plane view SEM image shows that the sample is a 2D square lattice circular hole array with a period of 510 nm, a hole depth of 280 nm, and a hole diameter of 140 nm. The p-polarized reflectivity mapping taken along the &#915;-X direction is shown in Figure 4a. The dash line is calculated by the phase matching equation Eq. (1) indic...

Watch this Scientific Journal Video about Determination of the Excitation and Coupling Rates Between Light Emitters and Surface Plasmon Polaritons at JoVE.com

Determination of the Excitation and Coupling Rates Between Light Emitters and Surface Plasmon Polaritons

This protocol describes the instrumentation for determining the excitation and coupling rates between light emitters and Bloch-like surface plasmon polaritons arising from periodic arrays.

We have developed a unique method to measure the excitation and coupling rates between the light emitters and surface plasmon polaritons (SPPs) arising ...

This method can help answer key questions in fluorescence enhancement, such as surface plasmon-mediated fluorescence. The main advantage of this technique is that it differentiates the excitation and the decay processes of surface plasmon-mediated fluorescence entirely in frequency domain. Prepare a substrate for the periodic array.For this experiment, use a one square centimeter piece of glass. Clean it in ultrasonic baths of methanol and acetone for 10 minutes each. When done, place it on a 200 degree Celsius hotplate for one hour.For the spin coating steps, dilute native photoresist with a thinner, and have adhesion solution ready. Move the glass substrate to a spin coater, and dispense three to five drops of adhesion solution onto it. Spin the substrate at 600 rpm for 10 seconds, then 3, 600 rpm for one minute.Next, place five to seven drops of diluted photoresist on the substrate. Spin coat the substrate at 600 rpm for 10 seconds, then 3, 600 rpm for one minute. When done, move the spin coated sample to a 65 degree Celsius hotplate, and leave it there for one minute.Then, transfer the sample to a 95 degree Celsius hotplate, and leave it for another minute. From the hotplate, take the sample to mount on a Lloyd's interferometer. The set-up has a prism for a sample holder, with a mirror perpendicular to it.Use a drop of refractive index matching oil on the sample to attach it to the prism. Position the sample as close to the mirror as possible. Expose the sample in this initial orientation.Then, to create a two dimensional square lattice, rotate the sample 90 degrees on the prism. Use the same exposure time for a second exposure. Return the sample to the 65 degree Celsius hotplate for two minutes.Then, place it on the 95 degree Celsius hotplate for two minutes. Next, immerse the sample in developer for two minutes with continuous agitation. Retrieve the sample and immerse it in isopropyl alcohol for one minute, to rinse residuals.Work with an RF sputtering deposition system to put a 100 nanometer gold film on the sample. Once the sample is ready, take it and a styryl 8 dye preparation to a spin coater. Dispense 0.2 milliliters, or three to five drops, of the solution onto the sample.Spin coat this to produce a thickness of about 80 nanometers. For the reflectivity measurements, use a goniometer. This system uses broadband white light from a quartz lamp.A multi-mode fiber bundle transmits the light to face-to-face objective lenses for collimation. A polarizer and shutter are next in the path. The light illuminates a sample on a sample stage with three independent rotation stages.A detection analyzer is after the sample stage. Another multi-mode fiber collects the specular reflection from the sample, to transmit it to a spectrometer and CCD camera. After aligning and calibrating the set-up, set up an automated system to collect data.Use the automation to step through different incident angles and collect the reflection spectra. For these measurements, the step size of the incident angle is 0.5 degrees. The wavelength resolution is 0.66 nanometers.To measure the orthogonal reflectivity, alter the set-up. Set the incident polarizer to 45 degrees with respect to the incident plane. Set the analyzer to negative 45 degrees with respect to the incident plane.Proceed with another automated measurement. Photoluminescence measurements require another change to the set-up. Replace the broadband light source with a 633 nanometer helium neon laser.Place a laser line filter before the polarizer. Also, place a half wave plate after the shutter. Complete the set-up by substituting a notch filter for the analyzer before the spectrometer.Conduct automated incident scans by fixing the detection angle, and varying the incident angle with respect to the sample normal. The surface plasmon polaritons are incident angle dependent, and are selectively excited. Next, conduct a detection scans by fixing the incident angle with respect to the sample normal, and varying the detection angle.This is the P-polarized reflectivity mapping taken along the gamma X direction of the gold array in the inset. The dashed line is calculated using the phase matching equation, and implies that the M equals negative one and N equals zero surface plasma polaritons are excited. This reflectivity map is from when the polarizer and analyser are at orthogonal positions.The background is now zero, as indicated by the blue of the color map. The reflectivity profiles have peaks in green, instead of dips, as only the surface plasma polaritons remain after removing the background. This is the P-polarized reflectivity mapping and the orthogonal reflectivity mapping along the gamma X for cadmium, selenium, telluride, quantum dot doped PVA polymer, spin coated on the array.In addition, here are data for the incident and detection angle photoluminescence measurements. The data can be used to determine the excitation and coupling rates between light emitters and resident cavities. Though this method can provide insight into fluorescence enhancement from periodic arrays, it can be also applied to other systems, such as metamaterials and photonic crystals.Once mastered, this technique can be done in three hours, if it is performed properly. While attempting this procedure, it is important to remember to check the alignment of the array set-up, and the polarization and angles of the reflectivity spectrography. After its development, this technique paved the way for researchers in the field of photoluminescences to explore surface plasma-enhanced fluorescence in the field of resins enhancement.After watching this video, you should have a good understanding of how to determine the excitation and the coupling rate between light emitters and the surface plasma polaritons arising from periodic arrays.

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Research

JoVE Journal

Engineering

Characterization of Surface Modifications by White Light Interferometry: Applications in Ion Sputtering, Laser Ablation, and Tribology Experiments

In materials science and engineering it is often necessary to obtain quantitative measurements of surface topography with micrometer lateral resolution. From the measured surface, 3D topographic maps can be subsequently analyzed using a variety of software packages to extract the information that is needed.
In this article we describe how white light interferometry, and optical profilometry (OP) in general, combined with generic surface analysis software, can be used for materials science and engineering tasks. In this article, a number of applications of white light interferometry for investigation of surface modifications in mass spectrometry, and wear phenomena in tribology and lubrication are demonstrated. We characterize the products of the interaction of semiconductors and metals with energetic ions (sputtering), and laser irradiation (ablation), as well as ex situ measurements of wear of tribological test specimens.
Specifically, we will discuss:
<ol class="lroman">
	<li>Aspects of traditional ion sputtering-based mass spectrometry such as sputtering rates/yields measurements on Si and Cu and subsequent time-to-depth conversion.</li>
	<li>Results of quantitative characterization of the interaction of femtosecond laser irradiation with a semiconductor surface. These results are important for applications such as ablation mass spectrometry, where the quantities of evaporated material can be studied and controlled via pulse duration and energy per pulse. Thus, by determining the crater geometry one can define depth and lateral resolution versus experimental setup conditions.</li>
	<li>Measurements of surface roughness parameters in two dimensions, and quantitative measurements of the surface wear that occur as a result of friction and wear tests.</li>
</ol>
Some inherent drawbacks, possible artifacts, and uncertainty assessments of the white light interferometry approach will be discussed and explained.

White light microscope interferometry is an optical, noncontact and quick method for measuring the topography of surfaces. It is shown how the method can be applied toward mechanical wear analysis, where wear scars on tribological test samples are analyzed; and in materials science to determine ion beam sputtering or laser ablation volumes and depths.

In materials science and engineering it is often necessary to obtain quantitative measurements of surface topography with micrometer lateral resolution. ...

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 ...

Real-Time DC-dynamic Biasing Method for Switching Time Improvement in Severely Underdamped Fringing-field Electrostatic MEMS Actuators

Mechanically underdamped electrostatic fringing-field MEMS actuators are well known for their fast switching operation in response to a unit step input bias voltage. However, the tradeoff for the improved switching performance is a relatively long settling time to reach each gap height in response to various applied voltages. Transient applied bias waveforms are employed to facilitate reduced switching times for electrostatic fringing-field MEMS actuators with high mechanical quality factors. Removing the underlying substrate of the fringing-field actuator creates the low mechanical damping environment necessary to effectively test the concept. The removal of the underlying substrate also a has substantial improvement on the reliability performance of the device in regards to failure due to stiction. Although DC-dynamic biasing is useful in improving settling time, the required slew rates for typical MEMS devices may place aggressive requirements on the charge pumps for fully-integrated on-chip designs. Additionally, there may be challenges integrating the substrate removal step into the back-end-of-line commercial CMOS processing steps. Experimental validation of fabricated actuators demonstrates an improvement of 50x in switching time when compared to conventional step biasing results. Compared to theoretical calculations, the experimental results are in good agreement.

The robust device design of fringing-field electrostatic MEMS actuators results in inherently low squeeze-film damping conditions and long settling times when performing switching operations using conventional step biasing. Real-time switching time improvement with DC-dynamic waveforms reduces the settling time of fringing-field MEMS actuators when transitioning between up-to-down and down-to-up states.

Mechanically underdamped electrostatic fringing-field MEMS actuators are well known for their fast switching operation in response to a unit step input ...

Quantification of Hydrogen Concentrations in Surface and Interface Layers and Bulk Materials through Depth Profiling with Nuclear Reaction Analysis

Nuclear reaction analysis (NRA) via the resonant 1H(15N,&#945;&#947;)12C reaction is a highly effective method of depth profiling that quantitatively and non-destructively reveals the hydrogen density distribution at surfaces, at interfaces, and in the volume of solid materials with high depth resolution. The technique applies a 15N ion beam of 6.385 MeV provided by an electrostatic accelerator and specifically detects the 1H isotope in depths up to about 2 &#956;m from the target surface. Surface H coverages are measured with a sensitivity in the order of ~1013 cm-2 (~1% of a typical atomic monolayer density) and H volume concentrations with a detection limit of ~1018 cm-3 (~100 at. ppm). The near-surface depth resolution is 2-5 nm for surface-normal 15N ion incidence onto the target and can be enhanced to values below 1 nm for very flat targets by adopting a surface-grazing incidence geometry. The method is versatile and readily applied to any high vacuum compatible homogeneous material with a smooth surface (no pores). Electrically conductive targets usually tolerate the ion beam irradiation with negligible degradation. Hydrogen quantitation and correct depth analysis require knowledge of the elementary composition (besides hydrogen) and mass density of the target material. Especially in combination with ultra-high vacuum methods for in-situ target preparation and characterization, 1H(15N,&#945;&#947;)12C NRA is ideally suited for hydrogen analysis at atomically controlled surfaces and nanostructured interfaces. We exemplarily demonstrate here the application of 15N NRA at the MALT Tandem accelerator facility of the University of Tokyo to (1) quantitatively measure the surface coverage and the bulk concentration of hydrogen in the near-surface region of a H2 exposed Pd(110) single crystal, and (2) to determine the depth location and layer density of hydrogen near the interfaces of thin SiO2 films on Si(100).

We illustrate the application of 1H(15N,&#945;&#947;)12C resonant nuclear reaction analysis (NRA) to quantitatively evaluate the density of hydrogen atoms on the surface, in the volume, and at an interfacial layer of solid materials. The near-surface hydrogen depth profiling of a Pd(110) single crystal and of SiO2/Si(100) stacks is described.

Nuclear reaction analysis (NRA) via the resonant 1H(15N,&#945;&#947;)12C reaction is a highly effective method of depth profiling that quantitatively and ...

Emission Spectroscopic Boundary Layer Investigation during Ablative Material Testing in Plasmatron

Ablative Thermal Protection Systems (TPS) allowed the first humans to safely return to Earth from the moon and are still considered as the only solution for future high-speed reentry missions. But despite the advancements made since Apollo, heat flux prediction remains an imperfect science and engineers resort to safety factors to determine the TPS thickness. This goes at the expense of embarked payload, hampering, for example, sample return missions. 
Ground testing in plasma wind-tunnels is currently the only affordable possibility for both material qualification and validation of material response codes. The subsonic 1.2MW Inductively Coupled Plasmatron facility at the von Karman Institute for Fluid Dynamics is able to reproduce a wide range of reentry environments. This protocol describes a procedure for the study of the gas/surface interaction on ablative materials in high enthalpy flows and presents sample results of a non-pyrolyzing, ablating carbon fiber precursor. With this publication, the authors envisage the definition of a standard procedure, facilitating comparison with other laboratories and contributing to ongoing efforts to improve heat shield reliability and reduce design uncertainties.
The described core techniques are non-intrusive methods to track the material recession with a high-speed camera along with the chemistry in the reactive boundary layer, probed by emission spectroscopy. Although optical emission spectroscopy is limited to line-of-sight measurements and is further constrained to electronically excited atoms and molecules, its simplicity and broad applicability still make it the technique of choice for analysis of the reactive boundary layer. Recession of the ablating sample further requires that the distance of the measurement location with respect to the surface is known at all times during the experiment. Calibration of the optical system of the applied three spectrometers allowed quantitative comparison. At the fiber scale, results from a post-test microscopy analysis are presented.

Development of new ablative materials and their numerical modeling requires extensive experimental investigation. This protocol describes procedures for material response characterization in plasma flows with the core techniques being non-intrusive methods to track the material recession along with the chemistry in the reactive boundary layer by emission spectroscopy.

Ablative Thermal Protection Systems (TPS) allowed the first humans to safely return to Earth from the moon and are still considered as the only solution ...

Measurement of Outgassing Rates of Steels

Steels are commonly used materials in the fabrication of vacuum systems because of their good mechanical, corrosion, and vacuum properties. A variety of steels meet the criterion of low outgassing required for high or ultrahigh vacuum applications. However, a given material can present different outgassing rates depending on its manufacturing process or the various pretreatment processes involved during the fabrication. Thus, the measurement of outgassing rates is highly desirable for a specific vacuum application. For this reason, the rate-of-pressure rise (RoR) method is often used to measure the outgassing of hydrogen after bakeout. In this article, a detailed description of the design and execution of the experimental protocol involved in the RoR method is provided. The RoR method uses a spinning rotor gauge to minimize errors that stem from outgassing or the pumping action of a vacuum gauge. The outgassing rates of two ordinary steels (stainless steel and mild steel) were measured. The measurements were made before and after the heat pretreatment of the steels. The heat pretreatment of steels was performed to reduce the outgassing. Extremely low rates of outgassing (on the order of 10&#8722;11 Pa m3 sec&#8722;1 m&#8722;2) can be routinely measured using relatively small samples.

A protocol for the measurement of outgassing rates of hydrogen from ordinary steel vacuum chambers using the rate-of-pressure rise method is presented.

Steels are commonly used materials in the fabrication of vacuum systems because of their good mechanical, corrosion, and vacuum properties. A variety of ...

Synchrotron X-ray Microdiffraction and Fluorescence Imaging of Mineral and Rock Samples

In this report, we describe a detailed procedure for acquiring and processing&#160;x-ray microfluorescence (&#956;XRF), and Laue and powder microdiffraction two-dimensional (2D) maps at beamline 12.3.2 of the Advanced Light Source (ALS), Lawrence Berkeley National Laboratory. Measurements can be performed on any sample that is less than 10 cm x 10 cm x 5 cm, with a flat exposed surface. The experimental geometry is calibrated using standard materials (elemental standards for XRF, and crystalline samples such as Si, quartz, or Al2O3 for diffraction). Samples are aligned to the focal point of the x-ray microbeam, and raster scans are performed, where each pixel of a map corresponds to one measurement, e.g., one XRF spectrum or one diffraction pattern. The data are then processed using the in-house developed software XMAS, which outputs text files, where each row corresponds to a pixel position. Representative data from moissanite and an olive snail shell are presented to demonstrate data quality, collection, and analysis strategies.

We describe a beamline setup meant to carry out rapid two-dimensional x-ray fluorescence and x-ray microdiffraction mapping of single crystal or powder samples using either Laue (polychromatic radiation) or powder (monochromatic radiation) diffraction. The resulting maps give information about strain, orientation, phase distribution, and plastic deformation.

In this report, we describe a detailed procedure for acquiring and processing&#160;x-ray microfluorescence (&#956;XRF), and Laue and powder ...

Excitation-Scanning Hyperspectral Imaging Microscopy to Efficiently Discriminate Fluorescence Signals

Several techniques rely on detection of fluorescence signals to identify or study phenomena or to elucidate functions. Separation of these fluorescence signals were proven cumbersome until the advent of hyperspectral imaging, in which fluorescence sources can be separated from each other as well as from background signals and autofluorescence (given knowledge of their spectral signatures). However, traditional, emission-scanning hyperspectral imaging suffers from slow acquisition times and low signal-to-noise ratios due to the necessary filtering of both excitation and emission light. It has been previously shown that excitation-scanning hyperspectral imaging reduces the necessary acquisition time while simultaneously increasing the signal-to-noise ratio of acquired data. Using commercially available equipment, this protocol describes how to assemble, calibrate, and use an excitation-scanning hyperspectral imaging microscopy system for separation of signals from several fluorescence sources in a single sample. While highly applicable to microscopic imaging of cells and tissues, this technique may also be useful for any type of experiment utilizing fluorescence in which it is possible to vary excitation wavelengths, including but not limited to: chemical imaging, environmental applications, eye care, food science, forensic science, medical science, and mineralogy.

Spectral imaging has become a reliable solution for identification and separation of multiple fluorescence signals in a single sample and can readily distinguish signals of interest from background or autofluorescence. Excitation-scanning hyperspectral imaging improves on this technique by decreasing the necessary image acquisition time while simultaneously increasing the signal-to-noise ratio.

Several techniques rely on detection of fluorescence signals to identify or study phenomena or to elucidate functions. Separation of these fluorescence ...

Accurate Determination of the Equilibrium Surface Tension Values with Area Perturbation Tests

We demonstrate two robust protocols for determining the equilibrium surface tension (EST) values with area perturbation tests. The EST values should be indirectly determined from the dynamic surface tension (DST) values when surface tension (ST) values are at steady-state and stable against perturbations. The emerging bubble method (EBM) and the spinning bubble method (SBM) were chosen, because, with these methods, it is simple to introduce area perturbations while continuing dynamic tension measurements. Abrupt expansion or compression of an air bubble was used as a source of area perturbation for the EBM. For the SBM, changes in the rotation frequency of the sample solution were used to produce area perturbations. A Triton X-100 aqueous solution of a fixed concentration above its critical micelle concentration (CMC) was used as a model surfactant solution. The determined EST value of the model air/water interface from the EBM was 31.5 &#177; 0.1 mN&#183;m-1 and that from the SBM was 30.8 &#177; 0.2 mN&#183;m-1. The two protocols described in the article provide robust criteria for establishing the EST values.

Two protocols for determining the equilibrium surface tension (EST) values using the emerging bubble method (EBM) and the spinning bubble method (SBM) are presented for a surfactant-containing aqueous phase against air.

We demonstrate two robust protocols for determining the equilibrium surface tension (EST) values with area perturbation tests. The EST values should be ...

Determination of Aggregate Surface Morphology at the Interfacial Transition Zone (ITZ)

Here, we present a comprehensive method to illustrate the uneven distribution of the interfacial transition zone (ITZ) around the aggregate and the effect of aggregate surface morphology on the formation of ITZ. First, a model concrete sample is prepared with a spherical ceramic particle in roughly the central part of the cement matrix, acting as a coarse aggregate used in common concrete/mortar. After curing until the designed age, the sample is scanned by X-ray computed tomography to determine the relative location of the ceramic particle inside the cement matrix. Three locations of the ITZ are chosen: above the aggregate, on the side of the aggregate, and below the aggregate. After a series of treatments, the samples are scanned with a SEM-BSE detector. The resultant images were further processed using a digital image processing method (DIP) to obtain quantitative characteristics of the ITZ. The surface morphology is characterized at the pixel level based on the digital image. Thereafter, K-means clustering method is used to illustrate the effect of surface roughness on ITZ formation.

Determination of Aggregate Surface Morphology at the Interfacial Transition Zone ITZ

Hereby, we proposed a protocol to illustrate the effect of aggregate surface morphology on the ITZ microstructure. The SEM-BSE image were quantitatively analyzed to obtain ITZ's porosity gradient via digital image processing and a K-means clustering algorithm was further employed to establish a relationship between porosity gradient and surface roughness.

Here, we present a comprehensive method to illustrate the uneven distribution of the interfacial transition zone (ITZ) around the aggregate and the effect ...