Name: characterization of nanocrystal size distribution using raman spectroscopy with a multi-particle phonon confinement model
Uploaded: 2015-08-22T14:00:00.000+00:00
Duration: 6 min 54 s
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 nanomaterial to be analyzed12 (Figure 1b), following the measurement steps described in Step 2. From the peak position of the bulk material, estimate the relative shift12.</li>
	<li>Estimate the required laser power for Raman measurements using different powers on the nanocrystals going to be measured. Start a measurement with the lowest possible power to get enough signal (the ratio of the peak intensity to the background noise should be at least 50) , and increase the laser power if needed, as long as the position and shape of the nanocrystal Raman peak stays same12,13.</li>
</ol>
2. Raman Spectroscopy of the Nanocrystal of Interest
<ol>
	<li>Load the sample with nanocrystal powder deposited on the substrate into the measurement chamber. 
	Note: The substrate dimensions are not critical (can be from millimeters to tens of centimeters) as long as it fits to the sample holder stage. The powder or thin film thickness should be at least tens of nanometers to have detectable signal from Raman spectroscope. For the planar substrate holder stage, simply lay the substrate under the optics (Figure 1b).
	<ol>
		<li>Make sure the &#8220;Laser&#8221; and &#8220;Active&#8221; lights are off before opening the door in order to be safe from the unwanted illumination of the operating laser. If these lights are not off, perform the actions in steps 2.5 and 2.6. The &#8220;Interlock&#8221; sign always stays on.</li>
		<li>Press &#8220;Door Release&#8221; and open the door of the measurement chamber, and put the sample onto the sample holder stage (Figure 1b).</li>
	</ol>
	</li>
	<li>Adjust the focusing of the sample to be measured to get the highest possible signal.
	<ol>
		<li>Select 50X objective and focus on the surface of the nanocrystal powder (Figure 1b).</li>
		<li>Bring the sample under focus using the z-direction manipulator of the sample holder. Check the clarity of the focused image from the live camera view on the computer screen.</li>
		<li>Close the door of the measurement chamber.</li>
		<li>Remove the shutter by clicking the &#8220;shutter-out&#8221; button from the Renishaw software, and let the laser light shine on the sample to be measured. Observe that the &#8220;Laser&#8221; and &#8220;Active&#8221; signs now flash green and blink red, respectively. In the live image from the screen, the laser will be visible (Figure 1c).</li>
		<li>From the live image, fine-tune the focusing of the sample using the wheel manipulator until the smallest laser spot, which is the best focus, is observed on the live image.</li>
	</ol>
	</li>
	<li>Set up a measurement from the Renishaw analysis software as described below (Figure 1d).
	<ol>
		<li>From &#8220;Measurement&#8221; select new spectral acquisition option.</li>
		<li>From the pop-up window, set the measurement range from 150 to 700 cm-1, set the time for the measurement as 30 sec, the total number of acquisition as 2x, and the percentage of the laser power as 0.5% (of a 25 mW laser) to be used during the measurement. Accept the parameters inserted, and the window will be closed.</li>
		<li>Start the measurement by clicking on the acquisition start button on the menu-bar. During the measurement the &#8220;Laser&#8221; and the &#8220;Active&#8221; lights will remain on.</li>
	</ol>
	</li>
	<li>Do not open the measurement chamber when these lights are on as the laser is in operation and measurement is being performed.</li>
	<li>After the measurement is finished, put the shutter in by clicking the &#8220;shutter in&#8221; button from the Renishaw software. Observe that the lights of the &#8220;Laser&#8221; and the &#8220;Active&#8221; are turned off. Press &#8220;Door Release&#8221; and then open the door of the measurement chamber.</li>
	<li>Before taking the sample out, lower the sample holder stage with the z-manipulator until there is a safe distance between the measured sample and the surface of the magnifying lens to remove the sample. Then, put the sample back to its container.</li>
	<li>Turn off the laser.</li>
	<li>Save the data in Renishaw software format, &#8220;.wxd&#8221;, and in the text file format, &#8220;.txt&#8221;. The latter will be used for the analysis of the experimental data.</li>
</ol>
3. Size Distribution Determination of the Nanocrystal of Interest
<ol>
	<li>Open the text files of the measurements for the nanocrystal measurement, and the bulk reference.</li>
	<li>Before plotting the data, smooth them using cubic spline, and normalize the data to 1 at their highest peak positions in order to have a good comparison of the relative peak shifts.</li>
	<li>Plot the silicon nanocrystal and reference silicon data, determine the peak position of reference silicon, and estimate the amount of the shift, if any, from the actual peak position of 521 cm-1.12 Then save the processed silicon nanocrystal data as .txt file.</li>
	<li>Start the fitting procedure.
	<ol>
		<li>For the fitting procedure, type the fitting function shown at Figure 2f into an analysis program such as Mathematica.</li>
		<li>Import the normalized and corrected data as the input for the non-linear fitting model using the &#34;Import&#34; command.</li>
		<li>Ensure that the interval for skewness is between 0.1 and 1.0, and the mean size interval is between 2 nm and 20 nm.</li>
		<li>If necessary, insert additional peak(s) under the measured peak using the fitting function and repeat the steps 3.4.2 and 3.4.3 to fit the other sub-distribution(s).</li>
		<li>Press &#8220;Shift+Enter&#8221; to perform the fitting procedure.</li>
		<li>After that, insert the obtained values for the mean size and the skewness in the pre-defined generic distribution function shown at Figure 2b.</li>
		<li>After that, insert the obtained values for the mean size, D0, and the skewness, &#963;, in the pre-defined generic distribution function shown in Figure 2b.</li>
		<li>Set the lower boundary of the of the integral as 1 nm. Set the upper limit of the integration to any size that does not exhibit any shift in the Raman spectrum (20 nm for Si-NCs)12.</li>
		<li>Integrate the distribution function in Figure 2b as a function of nanocrystal size using the integral function definition a data analysis and plotting program by setting the lower and higher sizes as integral boundaries (1-20 nm for Si-NCs). Plot &#934;(D) vs. D to give the size distribution. Alternatively, find a set of &#934;(D) values for each value of D (for instance, from 1 to 20 nm for Si-NCs with an increment of 1 nm) and plot &#934;(D) vs. D, which is the size distribution.</li>
		<li>If a multi-modal size distribution exists, first define the peaks to be fitted for other size distributions. Then, estimate their volume fractions of different size distributions with respect to each other by first finding the areas of each peaks obtained after deconvolution of the measurement data (with the size distribution determination procedure) and then calculating the areal ratio of each peak with respect to the total Raman peak.</li>
	</ol>
	</li>
</ol>

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The authors have nothing to disclose.

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><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 ...

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13.4K Views.  Eindhoven University of Technology.  We demonstreren hoe de grootteverdeling van halfgeleider nanokristallen bepalen kwantitatieve wijze met Raman spectroscopie toepassing van een analytisch gedefinieerde meerdere deeltjes fonon opsluiting model. De resultaten zijn in uitstekende overeenkomst met de andere grootte analyse technieken zoals transmissie-elektronenmicroscopie en fotoluminescentie spectroscopie. 

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

Measurement of Scattering Nonlinearities from a Single Plasmonic Nanoparticle

Plasmonics, which are based on the collective oscillation of electrons due to light excitation, involve strongly enhanced local electric fields and thus have potential applications in nonlinear optics, which requires extraordinary optical intensity. One of the most studied nonlinearities in plasmonics is nonlinear absorption, including saturation and reverse saturation behaviors. Although scattering and absorption in nanoparticles are closely correlated by the Mie theory, there has been no report of nonlinearities in plasmonic scattering until very recently. 
Last year, not only saturation, but also reverse saturation of scattering in an isolated plasmonic particle was demonstrated for the first time. The results showed that saturable scattering exhibits clear wavelength dependence, which seems to be directly linked to the localized surface plasmon resonance (LSPR). Combined with the intensity-dependent measurements, the results suggest the possibility of a common mechanism underlying the nonlinear behaviors of scattering and absorption. These nonlinearities of scattering from a single gold nanosphere (GNS) are widely applicable, including in super-resolution microscopy and optical switches. 
In this paper, it is described in detail how to measure nonlinearity of scattering in a single GNP and how to employ the super-resolution technique to enhance the optical imaging resolution based on saturable scattering. This discovery features the first super-resolution microscopy based on nonlinear scattering, which is a novel non-bleaching contrast method that can achieve a resolution as low as l/8 and will potentially be useful in biomedicine and material studies.

Saturable and reverse saturable scattering were discovered in isolated plasmonic particles and adopted as a novel non-bleaching contrast method in super-resolution microscopy. Here the experimental procedures of detecting and extracting nonlinear scattering are explained in detail, as well as how to enhance resolution with the aid of saturated excitation microscopy.

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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 ...

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 ...

Characterization of Ultra-fine Grained and Nanocrystalline Materials Using Transmission Kikuchi Diffraction

One of the challenges in microstructure analysis nowadays resides in the reliable and accurate characterization of ultra-fine grained (UFG) and nanocrystalline materials. The traditional techniques associated with scanning electron microscopy (SEM), such as electron backscatter diffraction (EBSD), do not possess the required spatial resolution due to the large interaction volume between the electrons from the beam and the atoms of the material. Transmission electron microscopy (TEM) has the required spatial resolution. However, due to a lack of automation in the analysis system, the rate of data acquisition is slow which limits the area of the specimen that can be characterized. This paper presents a new characterization technique, Transmission Kikuchi Diffraction (TKD), which enables the analysis of the microstructure of UFG and nanocrystalline materials using an SEM equipped with a standard EBSD system. The spatial resolution of this technique can reach 2 nm. This technique can be applied to a large range of materials that would be difficult to analyze using traditional EBSD. After presenting the experimental set up and describing the different steps necessary to realize a TKD analysis, examples of its use on metal alloys and minerals are shown to illustrate the resolution of the technique and its flexibility in term of material to be characterized.

This paper provides a detailed method to characterize the microstructure of ultra-fine grained and nanocrystalline materials using a scanning electron microscope equipped with a standard electron backscatter diffraction system. Metal alloys and minerals presenting refined microstructures are analyzed using this technique, showing the diversity of its possible applications.

One of the challenges in microstructure analysis nowadays resides in the reliable and accurate characterization of ultra-fine grained (UFG) and ...

Liquid-cell Transmission Electron Microscopy for Tracking Self-assembly of Nanoparticles

Drying a nanoparticle dispersion is a versatile way to create self-assembled structures of nanoparticles, but the mechanism of this process is not fully understood. We have traced the trajectories of individual nanoparticles using liquid-cell transmission electron microscopy (TEM) to investigate the mechanism of the assembly process. Herein, we present the protocols used for liquid-cell TEM studies of the self-assembly mechanism. First, we introduce the detailed synthetic protocols used to produce uniformly sized platinum and lead selenide nanoparticles. Next, we present the microfabrication processes used to produce liquid cells with silicon nitride or silicon windows and then describe the loading and imaging procedures of the liquid-cell TEM technique. Several notes are included to provide helpful tips for the entire process, including how to manage the fragile cell windows. The individual motions of nanoparticles tracked by liquid-cell TEM revealed that changes in the solvent boundaries caused by evaporation affected the self-assembly process of nanoparticles. The solvent boundaries drove nanoparticles to primarily form amorphous aggregates, followed by flattening of the aggregates to produce a 2-dimensional (2D) self-assembled structure. These behaviors are also observed for different nanoparticle types and different liquid-cell compositions.

Here we introduce experimental protocols for the real-time observation of a self-assembly process using liquid-cell transmission electron microscopy.

Drying a nanoparticle dispersion is a versatile way to create self-assembled structures of nanoparticles, but the mechanism of this process is not fully ...

Chemistry

Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses

We demonstrate the use of two nuclear-based analytical methods that can follow the modifications of microstructural arrangement of iron-based metallic glasses (MGs). Despite their amorphous nature, the identification of hyperfine interactions unveils faint structural modifications. For this purpose, we have employed two techniques that utilize nuclear resonance among nuclear levels of a stable 57Fe isotope, namely M&#246;ssbauer spectrometry and nuclear forward scattering (NFS) of synchrotron radiation. The effects of heat treatment upon (Fe2.85Co1)77Mo8Cu1B14 MG are discussed using the results of ex situ and in situ experiments, respectively. As both methods are sensitive to hyperfine interactions, information on structural arrangement as well as on magnetic microstructure is readily available. M&#246;ssbauer spectrometry performed ex situ describes how the structural arrangement and magnetic microstructure appears at room temperature after the annealing under certain conditions (temperature, time), and thus this technique inspects steady states. On the other hand, NFS data are recorded in situ during dynamically changing temperature and NFS examines transient states. The use of both techniques provides complementary information. In general, they can be applied to any suitable system in which it is important to know its steady state but also transient states.

Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses

Here, we present a protocol to describe ex situ and in situ investigations of structural transformations in metallic glasses. We employed nuclear-based analytical methods which inspect hyperfine interactions. We demonstrate the applicability of M&#246;ssbauer spectrometry and nuclear forward scattering of synchrotron radiation during temperature-driven experiments.

We demonstrate the use of two nuclear-based analytical methods that can follow the modifications of microstructural arrangement of iron-based metallic ...

Construction and Operation of a Light-driven Gold Nanorod Rotary Motor System

The possibility to generate and measure rotation and torque at the nanoscale is of fundamental interest to the study and application of biological and artificial nanomotors and may provide new routes towards single cell analysis, studies of non-equilibrium thermodynamics, and mechanical actuation of nanoscale systems. A facile way to drive rotation is to use focused circularly polarized laser light in optical tweezers. Using this approach, metallic nanoparticles can be operated as highly efficient scattering-driven rotary motors spinning at unprecedented rotation frequencies in water.
In this protocol, we outline the construction and operation of circularly-polarized optical tweezers for nanoparticle rotation and describe the instrumentation needed for recording the Brownian dynamics and Rayleigh scattering of the trapped particle. The rotational motion and the scattering spectra provides independent information on the properties of the nanoparticle and its immediate environment. The experimental platform has proven useful as a nanoscopic gauge of viscosity and local temperature, for tracking morphological changes of nanorods and molecular coatings, and as a transducer and probe of photothermal and thermodynamic processes.

Plasmonic gold nanorods can be trapped in liquids and rotated at kHz frequencies using circularly-polarized optical tweezers. Introducing tools for Brownian dynamics analysis and light scatteringspectroscopy leads to a powerful system for research and application in numerous fields of science.

The possibility to generate and measure rotation and torque at the nanoscale is of fundamental interest to the study and application of biological and ...

Assembly and Characterization of Polyelectrolyte Complex Micelles

Polyelectrolyte complex micelles (PCMs), core-shell nanoparticles formed by self-assembly of charged polymers in aqueous solution, provide a powerful platform for exploring the physics of polyelectrolyte interactions and also offer a promising solution to the pressing problem of delivering therapeutic oligonucleotides in vivo. Developing predictive structure-property relationships for PCMs has proven difficult, in part due to the presence of strong kinetic traps during nanoparticle self-assembly. This article discusses criteria for choosing polymers for PCM construction and provides protocols based on salt annealing that enable assembly of repeatable, low-polydispersity nanoparticles. We also discuss PCM characterization using light scattering, small-angle X-ray scattering, and electron microscopy.

We provide protocols and representative data for designing, assembling, and characterizing polyelectrolyte complex micelles, core-shell nanoparticles formed by polyelectrolytes and hydrophilic charged-uncharged block copolymers.

Polyelectrolyte complex micelles (PCMs), core-shell nanoparticles formed by self-assembly of charged polymers in aqueous solution, provide a powerful ...

Studying Soft-matter and Biological Systems over a Wide Length-scale from Nanometer and Micrometer Sizes at the Small-angle Neutron Diffractometer KWS-2

The KWS-2 SANS diffractometer is dedicated to the investigation of soft matter and biophysical systems covering a wide length scale, from nm to &#181;m. The instrument is optimized for the exploration of the wide momentum transfer Q range between 1x10-4 and 0.5 &#197;-1 by combining classical pinhole, focusing (with lenses), and time-of-flight (with chopper) methods, while simultaneously providing high-neutron intensities with an adjustable resolution. Because of its ability to adjust the intensity and the resolution within wide limits during the experiment, combined with the possibility to equip specific sample environments and ancillary devices, the KWS-2 shows a high versatility in addressing the broad range of structural and morphological studies in the field. Equilibrium structures can be studied in static measurements, while dynamic and kinetic processes can be investigated over time scales between minutes to tens of milliseconds with time-resolved approaches. Typical systems that are investigated with the KWS-2 cover the range from complex, hierarchical systems that exhibit multiple structural levels (e.g., gels, networks, or macro-aggregates) to small and poorly-scattering systems (e.g., single polymers or proteins in solution). The recent upgrade of the detection system, which enables the detection of count rates in the MHz range, opens new opportunities to study even very small biological morphologies in buffer solution with weak scattering signals close to the buffer scattering level at high Q.
In this paper, we provide a protocol to investigate samples with characteristic size levels spanning a wide length scale and exhibiting ordering in the mesoscale structure using KWS-2. We present in detail how to use the multiple working modes that are offered by the instrument and the level of performance that is achieved.

Here, we present a protocol to investigate soft matter and biophysical systems over a wide mesoscopic length scale, from nm to &#181;m that involves the use of the KWS-2 SANS diffractometer at high intensities and an adjustable resolution.

The KWS-2 SANS diffractometer is dedicated to the investigation of soft matter and biophysical systems covering a wide length scale, from nm to &#181;m. ...

Bioengineering

Exploring Multiphase Polymeric Systems by Nanoscale Infrared Spectroscopy

Advances in Nanoscale Infrared Spectroscopy to Explore Multiphase Polymeric Systems

Multiphase polymeric systems encompass local domains with dimensions that can vary from a few tens of nanometers to several micrometers. Their composition is commonly assessed using infrared spectroscopy, which provides an average fingerprint of the various materials contained in the volume probed. However, this approach does not offer any details on the arrangement of the phases in the material. Interfacial regions between two polymeric phases, often in the nanoscale range, are also challenging to access. Photothermal nanoscale infrared spectroscopy monitors the local response of materials excited by infrared light with the sensitive probe of an atomic force microscope (AFM). While the technique is suitable for interrogating small features, such as individual proteins on pristine gold surfaces, the characterization of three-dimensional multicomponent materials is more elusive. This is due to a relatively large volume of material undergoing photothermal expansion, defined by the laser focalization onto the sample and by the thermal properties of the polymeric constituents, compared to the nanoscale region probed by the AFM tip. Using a polystyrene (PS) bead and a polyvinyl alcohol (PVA) film, we evaluate the spatial footprint of photothermal nanoscale infrared spectroscopy for surface analysis as a function of the position of PS in the PVA film. The effect of the feature position on the nanoscale infrared images is investigated, and spectra are acquired. Some perspectives on the future advances in the field of photothermal nanoscale infrared spectroscopy are provided, considering the characterization of complex systems with embedded polymeric structures.

Author Spotlight: Advances in Nanoscale Infrared Spectroscopy to Explore Multiphase Polymeric Systems  

This protocol describes the application of atomic force microscopy and nanoscale infrared spectroscopy to evaluate the performance of photothermal nanoscale infrared spectroscopy in the characterization of three-dimensional multi-polymeric samples.

Multiphase polymeric systems encompass local domains with dimensions that can vary from a few tens of nanometers to several micrometers. Their composition ...

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

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