Name: characterization of nanocrystal size distribution using raman spectroscopy with a multi-particle phonon confinement model
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Description: Watch this Scientific Journal Video about Characterization of Nanocrystal Size Distribution using Raman Spectroscopy with a Multi-particle Phonon Confinement Model at JoVE.com

This work was part of the research programme of the Foundation for Fundamental Research on Matter (FOM), which is part of the Netherlands Organisation for Scientific Research (NWO). Authors of this work thank M. J. F. van de Sande for skillful technical assistance, M. A. Verheijen for TEM images, and the group of Tom Gregorkiewicz for PL measurements.

1. Planning of the Experiments
<ol>
	<li>Synthesize or obtain the nanocrystals of interest13 (Figure 1a).</li>
	<li>Avoid any confusion with the background signal by making sure that the substrate material does not have overlapping peaks in the Raman spectrum of the nanocrystals (Figure 1a).</li>
	<li>Turn on the laser of the Raman spectroscopy setup. Wait enough time (approximately 15 min) for the laser intensity to stabilize.</li>
	<li>Measure a bulk reference of the nanom...

<ol>
	<li>Goller, B., Polisski, S., Wiggers, H., Kovalev, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Freestanding+spherical+silicon+nanocrystals:+A+model+system+for+studying+confined+excitons.">Freestanding spherical silicon nanocrystals: A model system for studying confined excitons.</a> Appl Phys Lett. 97 (4), 041110 (2010).</li><li>Luo, J. -. W., Franceschetti, A., Zunger, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Carrier+multiplication+in+semiconductor+nanocrystals:+theoretical+screening+of+candidate+materials+based+on+band-structure+effects.">Carrier multiplication in semiconductor nanocrystals: theoretical screening of candidate materials based on band-structure effects.</a> Nano lett. 8 (10), 3174-3181 (2008).</li><li>Govoni, M., Marri, I., Ossicini, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Carrier+multiplication+between+interacting+nanocrystals+for+fostering+silicon-based+photovoltaics.">Carrier multiplication between interacting nanocrystals for fostering silicon-based photovoltaics.</a> Nat. Photonics. 6 (September), 672-679 (2012).</li><li>De Boer, W. D. A. M., Gregorkiewicz, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Step-like+enhancement+of+luminescence+quantum+yield+of+silicon+nanocrystals.">Step-like enhancement of luminescence quantum yield of silicon nanocrystals.</a> Nat nanotechnol. 6 (11), 1-4 (2011).</li><li>Sun, L., Choi, J. 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=Bright+infrared+quantum-dot+light-emitting+diodes+through+inter-dot+spacing+control.">Bright infrared quantum-dot light-emitting diodes through inter-dot spacing control.</a> Nat nanotechnol. 7 (6), 369-373 (2012).</li><li>Maier-Flaig, F., Rinck, 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=Multicolor+Silicon+Light-Emitting+Diodes+(SiLEDs).">Multicolor Silicon Light-Emitting Diodes (SiLEDs).</a> Nano lett. 13 (2), 1-6 (2013).</li><li>Patterson, A. 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V., 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=Determination+of+nanocrystal+sizes:+a+comparison+of+TEM,+SAXS,+and+XRD+studies+of+highly+monodisperse+CoPt3+particles.">Determination of nanocrystal sizes: a comparison of TEM, SAXS, and XRD studies of highly monodisperse CoPt3 particles.</a> Langmuir. 21 (5), 1931-1936 (2005).</li><li>Heitmann, J., M&#252;ller, F., Zacharias, M., G&#246;sele, U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Silicon Nanocrystals: Size Matters. Adv Mat. 17 (7), 795-803 (2005).</li><li>Faraci, G., Gibilisco, S., Russo, P., Pennisi, A., La Rosa, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modified+Raman+confinement+model+for+Si+nanocrystals.">Modified Raman confinement model for Si nanocrystals.</a> Phys Rev B. 73 (3), 1-4 (2006).</li><li>Zi, J., Bu&#776;scher, H., Falter, C., Ludwig, W., Zhang, K., Xie, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Raman+shifts+in+Si+nanocrystals.">Raman shifts in Si nanocrystals.</a> Applied Physics Letters. 69 (2), 200 (1996).</li><li>Do&#287;an, &. #. 3. 0. 4. ;., van de Sanden, M. C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+characterization+of+nanocrystal+size+distribution+using+Raman+spectroscopy.">Direct characterization of nanocrystal size distribution using Raman spectroscopy.</a> J. Appl. Phys. 114, 134310 (2013).</li><li>Dog&#774;an, I., Kramer, N. 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=Ultrahigh+throughput+plasma+processing+of+free+standing+silicon+nanocrystals+with+lognormal+size+distribution.">Ultrahigh throughput plasma processing of free standing silicon nanocrystals with lognormal size distribution.</a> J. Appl. Phys. 113, 134306 (2013).</li><li>Do&#287;an, &. #. 3. 0. 4. ;., Weeks, S. L., Agarwal, S., van de Sanden, M. C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nucleation+of+silicon+nanocrystals+in+a+remote+plasma+without+subsequent+coagulation.">Nucleation of silicon nanocrystals in a remote plasma without subsequent coagulation.</a> J Appl Phys. 115 (24), 244301 (2014).</li><li>Do&#287;an, &. #. 3. 0. 4. ;., Westermann, R. H. J., van de Sanden, M. C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Improved+size+distribution+control+of+silicon+nanocrystals+in+a+spatially+confined+remote+plasma.">Improved size distribution control of silicon nanocrystals in a spatially confined remote plasma.</a> Plasma Sources Sci. Technol. 24, 015030 (2015).</li><li>Delerue, C., Allan, G., Lannoo, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Theoretical+aspects+of+the+luminescence+of+porous+silicon.">Theoretical aspects of the luminescence of porous silicon.</a> Phys Rev B. 48 (15), 11024 (1993).</li><li>Boufendi, L., Jouanny, M. C., Kovacevic, E., Berndt, J., Mikikian, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dusty+plasma+for+nanotechnology.">Dusty plasma for nanotechnology.</a> J. Phys. D: Appl. Phys. 44 (17), 174035 (2011).</li><li>Wellner, A., Paillard, V., 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=Stress+measurements+of+germanium+nanocrystals+embedded+in+silicon+oxide.">Stress measurements of germanium nanocrystals embedded in silicon oxide.</a> J Appl Phys. 94 (2003), 5639-5642 (2003).</li><li>Faraci, G., Gibilisco, S., Pennisi, A. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantum+confinement+and+thermal+effects+on+the+Raman+spectra+of+Si+nanocrystals.">Quantum confinement and thermal effects on the Raman spectra of Si nanocrystals.</a> Phys. Rev. B. 80 (19), 1-4 (2009).</li><li>Roodenko, K., Goldthorpe, I. A., McIntyre, P. C., Chabal, Y. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modified+phonon+confinement+model+for+Raman+spectroscopy+of+nanostructured+materials.">Modified phonon confinement model for Raman spectroscopy of nanostructured materials.</a> Phys. Rev. B. 82 (11), 115210 (2010).</li><li>Die&#769;guez, A., Romano-Rodr&#305;&#769;guez, A., Vila&#768;, A., Morante, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+complete+Raman+spectrum+of+nanometric+SnO[sub+2]+particles.">The complete Raman spectrum of nanometric SnO[sub 2] particles.</a> J. Appl. Phys. 90 (3), 1550 (2001).</li><li>Bersani, D., Lottici, P. P., Ding, X. -. Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phonon+confinement+effects+in+the+Raman+scattering+by+TiO[sub+2]+nanocrystals.">Phonon confinement effects in the Raman scattering by TiO[sub 2] nanocrystals.</a> Appl. Phys. Lett. 72 (1), 73 (1998).</li><li>Lipp, M., Baonza, V. G., Evans, W. J., Lorenzana, H. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanocrystalline+diamond:+Effect+of+confinement,+pressure,+and+heating+on+phonon+modes.">Nanocrystalline diamond: Effect of confinement, pressure, and heating on phonon modes.</a> Phys. Rev. B. 56 (10), 5978-5984 (1997).</li></ol>

First discussion point is the critical steps within the protocol. In order not to have overlapping peaks with the material of interest, it is important to use another type of substrate material as mentioned in step 1.2. For instance, if Si-NCs are of interest, do not use silicon substrate for the Raman measurements. In Figure 1a, for instance, Si-NCs were synthesized on plexiglass substrates, which has completely flat signal roughly around the range of interest, i.e....

Semiconductor nanocrystals draw attention as their electronic and optical properties can be tuned by simply changing their size in the range compared to their respective exciton-Bohr radii.1 These unique size-dependent features make these nanocrystals relevant for various technological applications. For instance, carrier multiplication effects, observed when a high energy photon is absorbed by the nanocrystals of CdSe, Si, and Ge, can be used in the concept of spectrum conversion in solar cell applications;2&#8211;4 or size-dependent optical emission from PbS-NCs and Si-NCs can be used in the light emitting diode (LED) applications.5,6 A precise knowledge and control on the nanocrystal size distribution will therefore play a determinant role on the reliability and the performance of these technological applications based on nanocrystals.
The commonly used techniques for the size distribution and morphology analysis of nanocrystals can be listed as X-ray diffraction (XRD), transmission electron microscopy (TEM), photoluminescence spectroscopy (PL), and Raman spectroscopy. XRD is a crystallographic technique that reveals morphological information of the analyzed material. From the broadening of the diffraction peak, estimation of the nanocrystal size is possible,7 however, obtaining a clear data is usually time consuming. Moreover, XRD can only enable the calculation of average of the nanocrystal size distribution. In the existence of multi-modal size distributions, size analysis with XRD can be misleading and result in wrong interpretations. TEM is a powerful technique that enables imaging of the nanocrystals.8 Although TEM is able to reveal the presence of individual distributions in a multi-modal size distribution, sample preparation issue is always an effort to be spent before the measurements. In addition, working on densely packed nanocrystal ensembles with different sizes is challenging because of the difficulty of individual nanocrystal imaging. Photoluminescence spectroscopy (PL) is an optical analysis technique, and optically active nanocrystals can be diagnosed. Nanocrystal size distribution is obtained from the size-dependent emission.9 Due to their poor optical properties of indirect band gap nanoparticles, large nanocrystals that are not subject to confinement effects, and defect-rich small nanocrystals cannot be detected by PL and the observed size distribution is only limited to nanocrystals with good optical properties. Although each of these abovementioned techniques has its own advantages, none of them have the capability of meeting the expectations (that is, being fast, non-destructive, and reliable) from and idealized size analysis technique.
Another means of size distribution analysis of nanocrystals is Raman spectroscopy. Raman spectroscopy is widely available in most of the labs, and it is a fast and non-destructive technique. In addition, in most cases, sample preparation is not required. Raman spectroscopy is a vibrational technique, which can be used to obtain information on different morphologies (crystalline or amorphous), and size-related information (from the size-dependent shift in the phonon modes that appear in the frequency spectrum) of the analyzed material.10 The unique feature of Raman spectroscopy is that, while size-dependent changes are observed as a shift in the frequency spectrum, the shape of the phonon peak (broadening, asymmetry) gives information on the shape of the nanocrystal size distribution. Therefore it is in principle possible to extract the necessary information, i.e., the mean size and the shape factor, from Raman spectrum to obtain the size distribution of nanocrystals analyzed. In the case of multi-modal size distributions sub-distributions can also be separately identified via deconvolution of the experimental Raman spectrum.
In the literature, two theories are commonly referred to model the effect of nanocrystal size distribution on the shape of the Raman spectrum. The bond polarizability model (BPM)11 describes the polarizability of a nanocrystal from the contributions of all the bonds within that size. The one-particle phonon confinement model (PCM)10 uses size-dependent physical variables, i.e., crystal momentum, phonon frequency and dispersion, and the degree of confinement, to define the Raman spectrum of a nanocrystal with a specific size. Since these physical variables depend on the size, an analytical representation of the PCM that can be explicitly formulized as a function of nanocrystal size can be defined. Projecting this expression on a generic size distribution function will therefore be able to account for the effect of size distribution within the PCM, which can be used to determine the nanocrystal size distribution from the experimental Raman spectrum.12

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>Raman Spectroscopy</td>
			<td>Renishaw</td>
			<td>In Via</td>
			<td>Equipped with 514 nm Ar ion laser</td>
		</tr>
		<tr>
			<td>Wire 3.0</td>
			<td>Renishaw</td>
			<td></td>
			<td>Raman spectroscopy record tool</td>
		</tr>
		<tr>
			<td>Mathematica</td>
			<td>Wolfram</td>
			<td></td>
			<td>For fitting function and size determination</td>
		</tr>
		<tr>
			<td>Substrate</td>
			<td></td>
			<td></td>
			<td>Plexiglass (to avoid signal coincidence with Si-NCs)</td>
		</tr>
		<tr>
			<td>Si wafer</td>
			<td></td>
			<td></td>
			<td>Reference to Si-NC peak position</td>
		</tr>
		<tr>
			<td>Photoluminescence Spectroscopy</td>
			<td></td>
			<td></td>
			<td>334 nm Ar laser. For optical size distribution.</td>
		</tr>
		<tr>
			<td>Transmission Electron Microscopy</td>
			<td></td>
			<td></td>
			<td>Beam intensity 300 kV. For nanocrystal size and morphology determination.</td>
		</tr>
	</tbody>
</table>

characterization of nanocrystal size distribution using raman spectroscopy with a multi-particle phonon confinement model

Analysis of the size distribution of nanocrystals is a critical requirement for the processing and optimization of their size-dependent properties. The common techniques used for the size analysis are transmission electron microscopy (TEM), X-ray diffraction (XRD) and photoluminescence spectroscopy (PL). These techniques, however, are not suitable for analyzing the nanocrystal size distribution in a fast, non-destructive and a reliable manner at the same time. Our aim in this work is to demonstrate that size distribution of semiconductor nanocrystals that are subject to size-dependent phonon confinement effects, can be quantitatively estimated in a non-destructive, fast and reliable manner using Raman spectroscopy. Moreover, mixed size distributions can be separately probed, and their respective volumetric ratios can be estimated using this technique. In order to analyze the size distribution, we have formulized an analytical expression of one-particle PCM and projected it onto a generic distribution function that will represent the size distribution of analyzed nanocrystal. As a model experiment, we have analyzed the size distribution of free-standing silicon nanocrystals (Si-NCs) with multi-modal size distributions. The estimated size distributions are in excellent agreement with TEM and PL results, revealing the reliability of our model.

For using Raman spectroscopy as a size analysis tool, a model to extract the size-related information from a measured Raman spectrum is needed. Figure 2 summarizes the analytical multi-particle phonon confinement model.12 All-size-dependent phonon confinement function (Figure 2c) is projected onto a generic size distribution function (Figure 2b), which is chosen as a lognormal...

Watch this Scientific Journal Video about Characterization of Nanocrystal Size Distribution using Raman Spectroscopy with a Multi-particle Phonon Confinement Model at JoVE.com

Characterization of Nanocrystal Size Distribution using Raman Spectroscopy with a Multi-particle Phonon Confinement Model

We demonstrate how to determine the size distribution of semiconductor nanocrystals in a quantitative manner using Raman spectroscopy employing an analytically defined multi-particle phonon confinement model. Results obtained are in excellent agreement with the other size analysis techniques like transmission electron microscopy and photoluminescence spectroscopy.

Analysis of the size distribution of nanocrystals is a critical requirement for the processing and optimization of their size-dependent properties. The ...

characterization-nanocrystal-size-distribution-using-raman

Research

JoVE Journal

Engineering

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

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

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

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

Synthesis of Phase-shift Nanoemulsions with Narrow Size Distributions for Acoustic Droplet Vaporization and Bubble-enhanced Ultrasound-mediated Ablation

High-intensity focused ultrasound (HIFU) is used clinically to thermally ablate tumors. To enhance localized heating and improve thermal ablation in tumors, lipid-coated perfluorocarbon droplets have been developed which can be vaporized by HIFU. The vasculature in many tumors is abnormally leaky due to their rapid growth, and nanoparticles are able to penetrate the fenestrations and passively accumulate within tumors. Thus, controlling the size of the droplets can result in better accumulation within tumors. In this report, the preparation of stable droplets in a phase-shift nanoemulsion (PSNE) with a narrow size distribution is described. PSNE were synthesized by sonicating a lipid solution in the presence of liquid perfluorocarbon. A narrow size distribution was obtained by extruding the PSNE multiple times using filters with pore sizes of 100 or 200 nm. The size distribution was measured over a 7-day period using dynamic light scattering. Polyacrylamide hydrogels containing PSNE were prepared for in vitro experiments. PSNE droplets in the hydrogels were vaporized with ultrasound and the resulting bubbles enhanced localized heating. Vaporized PSNE enables more rapid heating and also reduces the ultrasound intensity needed for thermal ablation. Thus, PSNE is expected to enhance thermal ablation in tumors, potentially improving therapeutic outcomes of HIFU-mediated thermal ablation treatments.

Phase-shift nanoemulsions (PSNE) can be vaporized using high intensity focused ultrasound to enhance localized heating and improve thermal ablation in tumors. In this report, the preparation of stable PSNE with a narrow size distribution is described. Furthermore, the impact of vaporized PSNE on ultrasound-mediated ablation is demonstrated in tissue-mimicking phantoms.

High-intensity  focused ultrasound (HIFU) is used clinically to thermally ablate tumors. To  enhance localized heating and improve thermal ablation in ...

Scanning-probe Single-electron Capacitance Spectroscopy

The integration of low-temperature scanning-probe techniques and single-electron capacitance spectroscopy represents a powerful tool to study the electronic quantum structure of small systems - including individual atomic dopants in semiconductors. Here we present a capacitance-based method, known as Subsurface Charge Accumulation (SCA) imaging, which is capable of resolving single-electron charging while achieving sufficient spatial resolution to image individual atomic dopants. The use of a capacitance technique enables observation of subsurface features, such as dopants buried many nanometers beneath the surface of a semiconductor material1,2,3. In principle, this technique can be applied to any system to resolve electron motion below an insulating surface.
As in other electric-field-sensitive scanned-probe techniques4, the lateral spatial resolution of the measurement depends in part on the radius of curvature of the probe tip. Using tips with a small radius of curvature can enable spatial resolution of a few tens of nanometers. This fine spatial resolution allows investigations of small numbers (down to one) of subsurface dopants1,2. The charge resolution depends greatly on the sensitivity of the charge detection circuitry; using high electron mobility transistors (HEMT) in such circuits at cryogenic temperatures enables a sensitivity of approximately 0.01 electrons/Hz&frac12; at 0.3 K 5.

Scanning-probe single-electron capacitance spectroscopy facilitates the study of single-electron motion in localized subsurface regions. A sensitive charge-detection circuit is incorporated into a cryogenic scanning probe microscope to investigate small systems of dopant atoms beneath the surface of semiconductor samples.

The integration of low-temperature scanning-probe techniques and single-electron capacitance spectroscopy represents a powerful tool to study the ...

Quantum State Engineering of Light with Continuous-wave Optical Parametric Oscillators

Engineering non-classical states of the electromagnetic field is a central quest for quantum optics1,2. Beyond their fundamental significance, such states are indeed the resources for implementing various protocols, ranging from enhanced metrology to quantum communication and computing. A variety of devices can be used to generate non-classical states, such as single emitters, light-matter interfaces or non-linear systems3. We focus here on the use of a continuous-wave optical parametric oscillator3,4. This system is based on a non-linear &#967;2 crystal inserted inside an optical cavity and it is now well-known as a very efficient source of non-classical light, such as single-mode or two-mode squeezed vacuum depending on the crystal phase matching. 
Squeezed vacuum is a Gaussian state as its quadrature distributions follow a Gaussian statistics. However, it has been shown that number of protocols require non-Gaussian states5. Generating directly such states is a difficult task and would require strong &#967;3 non-linearities. Another procedure, probabilistic but heralded, consists in using a measurement-induced non-linearity via a conditional preparation technique operated on Gaussian states. Here, we detail this generation protocol for two non-Gaussian states, the single-photon state and a superposition of coherent states, using two differently phase-matched parametric oscillators as primary resources. This technique enables achievement of a high fidelity with the targeted state and generation of the state in a well-controlled spatiotemporal mode.

We describe the reliable generation of non-Gaussian states of traveling optical fields, including single-photon states and coherent state superpositions, using a conditional preparation method operated on the non-classical light emitted by optical parametric oscillators. Type-I and type-II phase-matched oscillators are considered and common procedures, such as the required frequency filtering or the high-efficiency quantum state characterization by homodyning, are detailed.

Engineering non-classical states of the electromagnetic field is a central quest for quantum optics1,2. Beyond their fundamental significance, such states ...

Surface Enhanced Raman Spectroscopy Detection of Biomolecules Using EBL Fabricated Nanostructured Substrates

Fabrication and characterization of conjugate nano-biological systems interfacing metallic nanostructures on solid supports with immobilized biomolecules is reported. The entire sequence of relevant experimental steps is described, involving the fabrication of nanostructured substrates using electron beam lithography, immobilization of biomolecules on the substrates, and their characterization utilizing surface-enhanced Raman spectroscopy (SERS). Three different designs of nano-biological systems are employed, including protein A, glucose binding protein, and a dopamine binding DNA aptamer. In the latter two cases, the binding of respective ligands, D-glucose and dopamine, is also included. The three kinds of biomolecules are immobilized on nanostructured substrates by different methods, and the results of SERS imaging are reported. The capabilities of SERS to detect vibrational modes from surface-immobilized proteins, as well as to capture the protein-ligand and aptamer-ligand binding are demonstrated. The results also illustrate the influence of the surface nanostructure geometry, biomolecules immobilization strategy, Raman activity of the molecules and presence or absence of the ligand binding on the SERS spectra acquired.

We describe the fabrication and characterization of nano-biological systems interfacing nanostructured substrates with immobilized proteins and aptamers. The relevant experimental steps involving lithographic fabrication of nanostructured substrates, bio-functionalization, and surface-enhanced Raman spectroscopy (SERS) characterization, are reported. SERS detection of surface-immobilized proteins, and probing of protein-ligand and aptamer-ligand binding is demonstrated.

Fabrication and characterization of conjugate nano-biological systems interfacing metallic nanostructures on solid supports with immobilized biomolecules ...

Resonance Raman Spectroscopy of Extreme Nanowires and Other 1D Systems

This paper briefly describes how nanowires with diameters corresponding to 1 to 5 atoms can be produced by melting a range of inorganic solids in the presence of carbon nanotubes. These nanowires are extreme in the sense that they are the limit of miniaturization of nanowires and their behavior is not always a simple extrapolation of the behavior of larger nanowires as their diameter decreases. The paper then describes the methods required to obtain Raman spectra from extreme nanowires and the fact that due to the van Hove singularities that 1D systems exhibit in their optical density of states, that determining the correct choice of photon excitation energy is critical. It describes the techniques required to determine the photon energy dependence of the resonances observed in Raman spectroscopy of 1D systems and in particular how to obtain measurements of Raman cross-sections with better than 8% noise and measure the variation in the resonance as a function of sample temperature. The paper describes the importance of ensuring that the Raman scattering is linearly proportional to the intensity of the laser excitation intensity. It also describes how to use the polarization dependence of the Raman scattering to separate Raman scattering of the encapsulated 1D systems from those of other extraneous components in any sample.

The paper describes a method for producing extreme nanowires by melt infiltration into carbon nanotubes and how 1D systems may be characterized and investigated using Resonance Raman Spectroscopy to determine vibrational and optical excitation energies.

This paper briefly describes how nanowires with diameters corresponding to 1 to 5 atoms can be produced by melting a range of inorganic solids in the ...

Characterization of Full Set Material Constants and Their Temperature Dependence for Piezoelectric Materials Using Resonant Ultrasound Spectroscopy

During the operation of high power electromechanical devices, a temperature rise is unavoidable due to mechanical and electrical losses, causing the degradation of device performance. In order to evaluate such degradations using computer simulations, full matrix material properties at elevated temperatures are needed as inputs. It is extremely difficult to measure such data for ferroelectric materials due to their strong anisotropic nature and property variation among samples of different geometries. Because the degree of depolarization is boundary condition dependent, data obtained by the IEEE (Institute of Electrical and Electronics Engineers) impedance resonance technique, which requires several samples with drastically different geometries, usually lack self-consistency. The resonant ultrasound spectroscopy (RUS) technique allows the full set material constants to be measured using only one sample, which can eliminate errors caused by sample to sample variation. A detailed RUS procedure is demonstrated here using a lead zirconate titanate (PZT-4) piezoceramic sample. In the example, the complete set of material constants was measured from room temperature to 120 &#176;C. Measured free dielectric constants <img alt="Equation 1" src="/files/ftp_upload/53461/image001.jpg" /> and&#160;<img alt="Equation 2" src="/files/ftp_upload/53461/image002.jpg" /> were compared with calculated ones based on the measured full set data, and piezoelectric constants d15 and d33 were also calculated using different formulas. Excellent agreement was found in the entire range of temperatures, which confirmed the self-consistency of the data set obtained by the RUS.

This protocol describes the procedure of measuring the temperature dependence of the full set material constants of piezoelectric materials using resonant ultrasound spectroscopy (RUS).

During the operation of high power electromechanical devices, a temperature rise is unavoidable due to mechanical and electrical losses, causing the ...

High Resolution Phonon-assisted Quasi-resonance Fluorescence Spectroscopy

High resolution optical spectroscopy methods are demanding in terms of either technology, equipment, complexity, time or a combination of these. Here we demonstrate an optical spectroscopy method that is capable of resolving spectral features beyond that of the spin fine structure and homogeneous linewidth of single quantum dots (QDs) using a standard, easy-to-use spectrometer setup. This method incorporates both laser and photoluminescence spectroscopy, combining the advantage of laser line-width limited resolution with multi-channel photoluminescence detection. Such a scheme allows for considerable improvement of resolution over that of a common single-stage spectrometer. The method uses phonons to assist in the measurement of the photoluminescence of a single quantum dot after resonant excitation of its ground state transition. The phonon&#39;s energy difference allows one to separate and filter out the laser light exciting the quantum dot. An advantageous feature of this method is its straight forward integration into standard spectroscopy setups, which are accessible to most researchers.

The manuscript describes a method of phonon-assisted quasi-resonant fluorescence spectroscopy that incorporates both laser-limited resolution and photoluminescence (PL) spectroscopy. This method utilizes optical phonons to provide linewidth-limited resolution spectra of atom-like semiconductor structures in the energy domain. The method is also easily realized with a single spectrometer optical spectroscopy setup.

High resolution optical spectroscopy methods are demanding in terms of either technology, equipment, complexity, time or a combination of these. Here we ...

Fabrication of Fully Solution Processed Inorganic Nanocrystal Photovoltaic Devices

We demonstrate a method for the preparation of fully solution processed inorganic solar cells from a spin and spray coating deposition of nanocrystal inks. For the photoactive absorber layer, colloidal CdTe and CdSe nanocrystals (3-5 nm) are synthesized using an inert hot injection technique and cleaned with precipitations to remove excess starting reagents. Similarly, gold nanocrystals (3-5 nm) are synthesized under ambient conditions and dissolved in organic solvents. In addition, precursor solutions for transparent conductive indium tin oxide (ITO) films are prepared from solutions of indium and tin salts paired with a reactive oxidizer. Layer-by-layer, these solutions are deposited onto a glass substrate following annealing (200-400 &#176;C) to build the nanocrystal solar cell (glass/ITO/CdSe/CdTe/Au). Pre-annealing ligand exchange is required for CdSe and CdTe nanocrystals where films are dipped in NH4Cl:methanol to replace long-chain native ligands with small inorganic Cl- anions. NH4Cl(s) was found to act as a catalyst for the sintering reaction (as a non-toxic alternative to the conventional CdCl2(s) treatment) leading to grain growth (136&#177;39 nm) during heating. The thickness and roughness of the prepared films are characterized with SEM and optical profilometry. FTIR is used to determine the degree of ligand exchange prior to sintering, and XRD is used to verify the crystallinity and phase of each material. UV/Vis spectra show high visible light transmission through the ITO layer and a red shift in the absorbance of the cadmium chalcogenide nanocrystals after thermal annealing. Current-voltage curves of completed devices are measured under simulated one sun illumination. Small differences in deposition techniques and reagents employed during ligand exchange have been shown to have a profound influence on the device properties. Here, we examine the effects of chemical (sintering and ligand exchange agents) and physical treatments (solution concentration, spray-pressure, annealing time and annealing temperature) on photovoltaic device performance.

This protocol describes the synthesis and solution deposition of inorganic nanocrystals layer by layer to produce thin film electronics on non-conductive surfaces. Solvent-stabilized inks can produce complete photovoltaic devices on glass substrates via spin and spray coating following post-deposition ligand exchange and sintering.

We demonstrate a method for the preparation of fully solution processed inorganic solar cells from a spin and spray coating deposition of nanocrystal ...

Measuring Spray Droplet Size from Agricultural Nozzles Using Laser Diffraction

When making an application of any crop protection material such as an herbicide or pesticide, the applicator uses a variety of skills and information to make an application so that the material reaches the target site (i.e., plant). Information critical in this process is the droplet size that a particular spray nozzle, spray pressure, and spray solution combination generates, as droplet size greatly influences product efficacy and how the spray moves through the environment. Researchers and product manufacturers commonly use laser diffraction equipment to measure the spray droplet size in laboratory wind tunnels. The work presented here describes methods used in making spray droplet size measurements with laser diffraction equipment for both ground and aerial application scenarios that can be used to ensure inter- and intra-laboratory precision while minimizing sampling bias associated with laser diffraction systems. Maintaining critical measurement distances and concurrent airflow throughout the testing process is key to this precision. Real time data quality analysis is also critical to preventing excess variation in the data or extraneous inclusion of erroneous data. Some limitations of this method include atypical spray nozzles, spray solutions or application conditions that result in spray streams that do not fully atomize within the measurement distances discussed. Successful adaption of this method can provide a highly efficient method for evaluation of the performance of agrochemical spray application nozzles under a variety of operational settings. Also discussed are potential experimental design considerations that can be included to enhance functionality of the data collected.

We present protocols to be used in the measurement of spray droplet size from agricultural nozzles used in both aerial and ground based agrochemical applications. These methods presented were developed to provide consistent and repeatable droplet size data both inter- and intra-laboratory, when using laser diffraction systems.

When making an application of any crop protection material such as an herbicide or pesticide, the applicator uses a variety of skills and information to ...