Spatial Modulation Spectroscopy Research Articles

Optically active cross-band transition in double-walled carbon nanotube and its impact on Raman resonances

Double-walled carbon nanotubes (DWNTs), often regarded as the simplest one-dimensional (1D) van der Waals moiré superlattices, are the ideal structures to explore the interlayer coupling, including mechanical and electronical coupling, at the nanoscale in 1D systems. By combining spatial modulation spectroscopy (SMS) and resonant Raman scattering (RRS) experiments on well-identified individual free-standing DWNTs with the calculations of their optical absorption by using the recursion method with non-orthogonal tight-binding (NTB) basis functions, we are able to unambiguously assign the nature, namely mirror transition or cross transition, of each optical transitions in DWNTs. Our study identifies and allows to determine the conditions of the mixing of the electronic states leading to the appearance of cross transitions in the optical absorption of DWNTs, beyond of the so-called Koshino's criteria previously derived. On the other hand, the striking behavior of the resonant excitation profile (REP) of the Raman active modes around the cross transition reveals the strong sensitivity of the modes intensity on the electronic interlayer coupling in DWNTs, emphasizing the relevance of Raman spectroscopy for studying the electronic and mechanical coupling at the nanoscale.

Progress and Application of Spatial Modulation Spectroscopy Technique for Detection of Extinction Cross Section of Single Nanoparticle

Progress and Application of Spatial Modulation Spectroscopy Technique for Detection of Extinction Cross Section of Single Nanoparticle

Highly stable measurement for nanoparticle extinction cross section by analyzing aperture-edge blurriness.

In order to stabilize the extinction cross section measurement of a single nanoparticle, we propose to analyze the blurriness parameter of aperture edge images in real time, which provides a feedback to lock the sample position. Unlike the conventional spatial modulation spectroscopy (SMS) technique, a probe beam experiences both the spatial modulation by a piezo stage and the temporal modulation by a chopper. We experimentally demonstrate that the measurement uncertainty is one order magnitude less than that in the previous report. The proposed method can be readily implemented in conventional SMS systems and can help to achieve high stability for sensing based on light extinction by a single nanoparticle, which alleviate the impact from laboratory environment and increase the experimental sensitivity.

Hybrid modes in a single thermally excited asymmetric dimer antenna.

The study of hybrid modes in a single dimer of neighboring antennas is an essential step to optimize the far-field electromagnetic (EM) response of large-scale metasurfaces or any complex antenna structure made up of subwavelength building blocks. Here we present far-field infrared spatial modulation spectroscopy (IR-SMS) measurements of a single thermally excited asymmetric dimer of square metal-insulator-metal (MIM) antennas separated by a nanometric gap. Through thermal fluctuations, all the EM modes of the antennas are excited, and hybrid bonding and anti-bonding modes can be observed simultaneously. We study the latter within a plasmon hybridization model, and analyze their effect on the far-field response.

Thermal emission from a single glass fiber

In this article, we study the thermal light emission from individual fibers of an industrial glass material, which are elementary building blocks of glass wool boards used for thermal insulation. Thermal emission spectra of single fibers of various diameters partially suspended on air are measured in the far field by means of infrared spatial modulation spectroscopy. These experimental spectra are compared with the theoretical absorption efficiency spectra of cylindrical shaped fibers calculated analytically in the framework of Mie theory taking as an input the measured permittivity of the industrial glass material. An excellent qualitative agreement is found between the measured thermal radiation spectra and the theoretical absorption efficiency spectra.

Forward and Backward Extinction Measurements on a Single Supported Nanoparticle: Implications of the Generalized Optical Theorem

In most conventional optical experiments on substrate-supported nanoparticles, detectors are located in the far-field space whereas their intrinsic properties (scattering, absorption cross sections) are commonly computed in the near-field by using numerical approaches. In this respect, a connection between experiment and theory can be usefully made on the basis of the generalized optical theorem (GOT) that gives access, from the far-field expansion of the scattered wave, to the total extinction cross section as the sum of “forward” and “backward” contributions related to the power changes of the waves respectively transmitted and reflected by the substrate. The purpose of this work is to address this issue as clearly as possible by performing quantitative measurements on individual objects and on both type of waves, as far a comprehensive description of the global extinction process is intended. We show that the spatial modulation spectroscopy technique applied to a single nanoparticle is especially well ...

High-Pressure Effect on the Optical Extinction of a Single Gold Nanoparticle.

When reducing the size of a material from bulk down to nanoscale, the enhanced surface-to-volume ratio and the presence of interfaces make the properties of nano-objects very sensitive not only to confinement effects but also to their local environment. In the optical domain, the latter dependence can be exploited to tune the plasmonic response of metal nanoparticles by controlling their surroundings, notably applying high pressures. To date, only a few optical absorption experiments have demonstrated this feasibility, on ensembles of metal nanoparticles in a diamond anvil cell. Here, we report a nontrivial combination between a spatial modulation spectroscopy microscope and an ultraflat diamond anvil cell, allowing us to quantitatively investigate the high-pressure optical extinction spectrum of an individual nano-object. A large tuning of the surface plasmon resonance of a gold nanobipyramid is experimentally demonstrated up to 10 GPa, in quantitative agreement with finite-element simulations and an analytical model disentangling the impact of metal and local environment dielectric modifications. High-pressure optical characterizations of single nanoparticles allow for the accurate investigation and modeling of size, strain, and environment effects on physical properties of nano-objects and also enable fine-tuned applications in nanocomposites, nanoelectromechanical systems, or nanosensing devices.

Optothermal response of a single silicon nanotip

The optical properties and thermal dynamics of conical single silicon nanotips are experimentally and theoretically investigated. The spectral and spatial dependencies of their optical extinction are quantitatively measured by spatial modulation spectroscopy (SMS). A nonuniform optical extinction along the tip axis and an enhanced near-infrared absorption, as compared to bulk crystalline silicon, are evidenced. This information is a key input for computing the thermal response of single silicon nanotips under ultrafast laser illumination, which is investigated by laser assisted atom probe tomography (La-APT) used as a highly sensitive temperature probe. A combination of these two experimental techniques and comparison with modeling also permits us to elucidate the impact of thermal effects on the laser assisted field evaporation process. Extension of this coupled approach opens up future perspectives for the quantitative study of the optical and thermal properties of a wide class of individual nano-objects, in particular elongated ones such as nanotubes, nanowires, and nanocones, which constitute promising nanosources for electron and/or ion emission.

Fourier-transform spatial modulation spectroscopy of single gold nanorods

AbstractSensing the scattered fields of single metallic nanostructures is a crucial step towards the applications of isolated plasmonic antennas, such as for the sensing of single molecules or nanoparticles. In the past, both near- and far-field spectroscopy methods have been applied to monitor single plasmonic resonances. So far, however, these spectral-domain techniques do not yet provide the femtosecond time resolution that is needed to probe the dynamics of plasmonic fields in the time domain. Here, we introduce a time-domain technique that combines broadband Fourier-transform spectroscopy and spatial modulation spectroscopy (FT-SMS) to quantitatively measure the extinction spectra of the isolated gold nanorods with a nominal footprint of 41×10 nm2. Using a phase-stable pulse pair for excitation, the technique is capable of rejecting off-resonant stray fields and providing absolute measurements of the extinction cross section. Our results indicate that the method is well suited for measuring the optical response of strongly coupled hybrid systems with high signal-to-noise ratio. It may form the basis for new approaches towards time-domain spectroscopy of single nanoantennas with few-cycle time resolution.

Robust raspberry-like metallo-dielectric nanoclusters of critical sizes as SERS substrates

Raspberry-like nano-objects made of large plasmonic satellites (>10 nm) covering a central dielectric particle have many potential applications as photonic materials, superlenses and (bio-) sensors, but their synthesis remains challenging. Herein, we show how to build stable and robust raspberry-like nano-systems with close-packed satellites, by combining monodisperse silica particles (80 or 100 nm diameter) and oppositely charged noble metal nanoparticles (Au or Ag) with well-defined sizes (10-50 nm). The spectral characteristics of their associated plasmonic resonances (wavelength, linewidth, extinction cross-section) and the electromagnetic coupling between satellites were observed using the spatial modulation spectroscopy technique and interpreted through a numerical model. The composite nano-objects exhibit numerous hot spots at satellite junctions, resulting in excellent surface-enhanced Raman scattering (SERS) performance. The SERS efficiency of the raspberry-like clusters is highly dependent on their structure.

Fano Transparency in Rounded Nanocube Dimers Induced by Gap Plasmon Coupling.

Homodimers of noble metal nanocubes form model plasmonic systems where the localized plasmon resonances sustained by each particle not only hybridize but also coexist with excitations of a different nature: surface plasmon polaritons confined within the Fabry-Perot cavity delimited by facing cube surfaces (i.e., gap plasmons). Destructive interference in the strong coupling between one of these highly localized modes and the highly radiating longitudinal dipolar plasmon of the dimer is responsible for the formation of a Fano resonance profile and the opening of a spectral window of anomalous transparency for the exciting light. We report on the clear experimental evidence of this effect in the case of 50 nm silver and 160 nm gold nanocube dimers studied by spatial modulation spectroscopy at the single particle level. A numerical study based on a plasmon mode analysis leads us to unambiguously identify the main cavity mode involved in this process and especially the major role played by its symmetry. The Fano depletion dip is red-shifted when the gap size is decreasing. It is also blue-shifted and all the more pronounced that the cube edge rounding is large. Combining nanopatch antenna and plasmon hybridization descriptions, we quantify the key role of the face-to-face distance and the cube edge morphology on the spectral profile of the transparency dip.

Spatial modulation spectroscopy imaging of nano-objects of different sizes and shapes.

Spatial modulation spectroscopy (SMS) is a powerful method for interrogating single nanoparticles. In these experiments optical extinction is measured by moving the particle in and out of a tightly focused laser beam. SMS is typically used for particles that are much smaller than the laser spot size. In this paper, we extend the analysis of the SMS signal to particles with sizes comparable to or larger than the laser spot, where the shape of the particle matters. These results are important for the analysis of polydisperse samples that have a wide range of sizes. The presented example images and analysis of a carbon microparticle sample show the utility of the derived expressions. In particular, we show that SMS can be used to generate extinction cross-section information about micrometer-sized particles with complex shapes.

Absorption Spectroscopy of Single Optically Trapped Gold Nanorods.

Extinction spectra of single gold nanorods optically trapped in water were measured by spatial modulation spectroscopy. Comparison of the extinction cross sections and resonance frequencies to finite element calculations allows us to determine the dimensions of the nanorod and estimate the contribution of radiation damping to the LSPR line width. Subtracting the radiation damping and bulk contributions from the measured line widths yields the electron-surface scattering contribution. The results show that the surfactant coating for the nanorods causes large electron-surface scattering effects with significant particle-to-particle variations. These effects are more pronounced than those seen for substrate-supported particles in previous single particle studies. Indeed, the measured line widths are only slightly narrower than that of the ensemble spectrum. These results show the importance of removing surfactant for sensing applications of these materials.

Imaging nano-objects by linear and nonlinear optical absorption microscopies

Absorption based microscopy measurements are emerging as important tools for studying nanomaterials. This review discusses the three most common techniques for performing these experiments: transient absorption microscopy, photothermal heterodyne imaging, and spatial modulation spectroscopy. The focus is on the application of these techniques to imaging and detection, using examples taken from the authors’ laboratory. The advantages and disadvantages of the three methods are discussed, with an emphasis on the unique information that can be obtained from these experiments, in comparison to conventional emission or scattering based microscopy experiments.

Spatial modulation spectroscopy for imaging and quantitative analysis of single dye-doped organic nanoparticles inside cells.

Imaging of non-fluorescent nanoparticles in complex biological environments, such as the cell cytosol, is a challenging problem. For metal nanoparticles, Rayleigh scattering methods can be used, but for organic nanoparticles, such as dye-doped polymer beads or lipid nanoparticles, light scattering does not provide good contrast. In this paper, spatial modulation spectroscopy (SMS) is used to image single organic nanoparticles doped with non-fluorescent, near-IR croconaine dye. SMS is a quantitative imaging technique that yields the absolute extinction cross-section of the nanoparticles, which can be used to determine the number of dye molecules per particle. SMS images were recorded for particles within EMT-6 breast cancer cells. The measurements allowed mapping of the nanoparticle location and the amount of dye in a single cell. The results demonstrate how SMS can facilitate efforts to optimize dye-doped nanoparticles for effective photothermal therapy of cancer.

Plasmonic coupling with most of the transition metals: a new family of broad band and near infrared nanoantennas.

In this article, we show for the first time, both theoretically and empirically, that plasmonic coupling can be used to generate Localized Surface Plasmon Resonances (LSPRs) in transition metal dimeric nano-antennas (NAs) over a broad spectral range (from the visible to the near infrared) and that the spectral position of the resonance can be controlled through morphological variation of the NAs (size, shape, interparticle distance). First, accurate calculations using the generalized Mie theory on spherical dimers demonstrate that we can take advantage of the plasmonic coupling to enhance LSPRs over a broad spectral range for many transition metals (Pt, Pd, Cr, Ni etc.). The LSPR remains broad for low interparticle distances and masks the various hybridized modes within the overall resonance. However, an analysis of the charge distribution on the surface of the nanoparticles reveals these modes and their respective contributions to the observed LSPR. In the case of spherical dimers, the transfer of the oscillator strengths from the "dipolar" mode to higher orders involves a maximum extinction cross-section for intermediate interparticle distances of a few nanometers. The emergence of the LSPR has been then experimentally illustrated with parallelepipedal NAs (monomers and dimers) made of various transition metals (Pt, Pd and Cr) and elaborated by nanolithography. Absolute extinction cross-sections have been measured with the spatial modulation spectroscopy technique over a broad spectral range (300-900 nm) for individual NAs, the morphology of which has been independently characterized by electron microscopy imaging. A clear enhancement of the LSPR has been revealed for a longitudinal excitation and plasmonic coupling has been clearly evidenced in dimers by an induced redshift and broadening of the LSPR compared to monomers. Furthermore, the LSPR has been shown to be highly sensitive to slight modifications of the interparticle distance. All the experimental results are well in agreement with finite element method (FEM) calculations in which the main geometrical parameters characterizing the NAs have been derived from electron microscopy imaging analysis. The main advantage of dimers as compared to monomers lies in the generation of a well-defined and highly enhanced electromagnetic field (the so-called "hot spots") within the interparticle gap that can be exploited in photo-catalysis, magneto-plasmonics or nano-sensing.

Imaging and Analysis of Single Optically Trapped Gold Nanoparticles Using Spatial Modulation Spectroscopy.

The extinction cross sections and spectra of single nanoparticles can be directly measured by moving the particle in and out of a tightly focused laser beam. This technique, known as spatial modulation spectroscopy, yields detailed information about the size, shape, and environment of the particles. These experiments are typically done on particles immobilized on a substrate. Here we demonstrate for the first time the use of spatial modulation spectroscopy to interrogate single, optically trapped nanoparticles in solution. Gold nanoparticles as small as 15 nm were trapped and imaged. The experiments were performed by modulating the position of the probe laser beam while scanning it over the trapped particle with a galvo-scanning mirror system. This technique opens up the possibility of precisely measuring the optical properties of single nanoparticles in liquid environments, free from the influence of a surface.

Invited Presentation: Direct Measurement of the Absolute Absorption Spectrum of Individual Carbon Nanotubes

The unique optical properties of single-wall carbon nanotubes (SWNTs) are very promising for the development of novel opto-electronic components and sensors with applications in many fields. Despite numerous studies performed using photoluminescence or Raman and Rayleigh scattering, knowledge of their optical response is still partial, in particular direct and quantitative access to the intrinsic absorption characteristics of SWNT is still challenging. Their precise investigation is made difficult by the large heterogeneities of the carbon nanotube structural parameters in most synthesized ensembles, leading to measurement of mean properties. This can be avoided by performing optical investigations on individual nanotubes. We show here that the spatial modulation spectroscopy (SMS) technique, initially developed to quantitatively study the optical response of single metal nanoparticles1, can be applied to the investigation of individual SWNTs2,3. As compared to other optical techniques, SMS has the key advantage of being sensitive to the nano-object absorption and to directly measure its absolute absorption cross-section. Using this approach, we have determined, over a broad optical spectral range, the absorption spectrum of semiconducting individual SWNTs and the oscillator strength of their different excitonic resonances. A non-resonant background is also identified and its cross-section comparable to the ideal graphene optical absorbance. Furthermore, investigation of the same SWNT either free-standing or lying on a substrate shows large broadening of the excitonic resonances, as well as strong weakening of polarization-dependent antenna effects, due to SWNT-substrate interaction. [1] A.Arbouet, D.Christofilos, N.Del Fatti and F.Vallée ; J-R.Huntzinger, L.Arnaud, P.Billaud and M. Broyer, Physical Review Letters 93, 127401 (2004).[2] D.Christofilos , J-C.Blancon , J.Arvanitidis, A.San Miguel, A.Ayari, N.Del Fatti and F.Vallée, Journal of Physical Chemistry Letters 3, 1176 (2012).[3] J.-C. Blancon, M. Paillet, H.N.Tran, X.T.Than, S. Aberra-Guebrou, A. Ayari, A. San Miguel, N-M. Phan, A-A. Zahab, J-L. Sauvajol, N. Del Fatti and F. Vallée, Nature Communications 4:2542 doi:10.1038/ncomms3542 (2013).

Spatial modulation spectroscopy of graphene sheets

Two different samples of graphene, multi-layer flakes on Si/SiO2 substrates and single layer graphene on glass, have been examined by reflectivity contrast and spatial modulation spectroscopy measurements. For the multi-layer graphene flakes, the reflectivity contrast and spatial modulation spectroscopy measurements are in good agreement, validating the application of spatial modulation spectroscopy to two-dimensional samples. The measurements for single layer graphene on glass show features that correspond to increases and decreases in reflectivity. The features with increased reflectivity are assigned to small regions of multilayer graphene or polymer, and the features with decreased reflectivity are assigned to holes in the graphene film. Using a model for thin film reflectivity we calculate the size dependent spatial modulation signal for the holes, and find that a significant number of holes have a larger than expected signal. This could arise from the presence of multi-layers of graphene in the sample, or because of optical resonance effects for the holes.

Detection of single gold nanoparticles using spatial modulation spectroscopy implemented with a galvo-scanning mirror system

The optical extinction of single nanoparticles can be sensitively detected by spatial modulation spectroscopy (SMS), where the particle is moved in and out of a tightly focused laser beam with a piezo-device. Here we show that high sensitivity can be obtained by modulating the beam with a galvo-mirror system, rather than by moving the sample. This work demonstrates an inexpensive method for making a SMS microscope, and shows how an existing laser scanning microscope can be adapted for SMS measurements. The galvo-mirror technique also allows SMS measurements to be performed in a liquid, which is difficult to do with piezo-modulation.