Single Nanostructures Research Articles

Excited states of neutral and charged excitons in single strongly asymmetric InP-based nanostructures emitting in the telecom C band

We investigate strongly asymmetric self-assembled nanostructures with one of dimensions reaching hundreds of nanometers. Close to the nanowire-like type of confinement, such objects are sometimes assigned as one-dimensional in nature. Here, we directly observe the spectrum of exciton excited states corresponding to longitudinal quantization. This is based on probing the optical transitions via polarization-resolved microphotoluminescence excitation ($\mu$PLE) measurement performed on single nanostructures combined with theoretical calculation of neutral and charged exciton optical properties. We successfully probe absorption-like spectra for individual bright states forming the exciton ground-state fine structure, as well as for the negatively charged exciton. Confronting the calculated spectrum of excitonic absorption with $\mu$PLE traces, we identify optical transitions involving states that contain carriers at various excited levels related to the longest dimension. Based on cross-polarized excitation-detection scheme, we show very well conserved spin configuration during orbital relaxation of the exciton from a number of excited states comparable to the quasi-resonant pumping via the optical phonon, and no polarization memory for the trion, as theoretically expected.

Circular Dichroism Measurement of Single Metal Nanoparticles Using Photothermal Imaging.

Circular dichroism (CD) spectroscopy is a powerful optical technique for the study of chiral materials and molecules. It gives access to an enantioselective signal based on the differential absorption of right and left circularly polarized light, usually obtained through polarization analysis of the light transmitted through a sample of interest. CD is routinely used to determine the secondary structure of proteins and their conformational state. However, CD signals are weak, limiting the use of this powerful technique to ensembles of many molecules. Here, we experimentally realize the concept of photothermal circular dichroism, a technique that combines the enantioselective signal from circular dichroism with the high sensitivity of photothermal microscopy, achieving a superior signal-to-noise ratio to detect chiral nano-objects. As a proof of principle, we studied the chiral response of single plasmonic nanostructures with CD in the visible range, demonstrating a signal-to-noise ratio better than 40 with only 30 ms integration time for these nanostructures. The high signal-to-noise ratio allows us to quantify the CD signal for individual nanoparticles. We show that we can distinguish relative absorption differences for right circularly and left circularly polarized light as small as gmin = 4 × 10–3 for a 30 ms integration time with our current experimental settings. The enhanced sensitivity of our technique extends CD studies to individual nano-objects and opens CD spectroscopy to numbers of molecules much lower than those in conventional experiments.

Size-Independent Transmembrane Transporting of Single Tetrahedral DNA Nanostructures.

DNA nanostructures have attracted considerable attention as drug delivery carriers. However, the transmembrane kinetics of DNA nanostructures remains less explored. Herein, the dynamic process of transporting single tetrahedral DNA nanostructures (TDNs) is monitored in real time using a force‐tracing technique based on atomic force microscopy. The results show that transporting single TDNs into living HeLa cells need ≈53 pN force and ≈25 ms duration with the average speed of ≈0.6 µm s−1. Interestingly, the dynamic parameters are irrelevant to the size of TDNs, while the larger TDNs rotated slightly during the transporting process. Meanwhile, both the results from single‐molecule force tracing and ensemble fluorescence imaging demonstrate that the different size TDNs transmembrane transporting depends on caveolin‐mediated endocytosis.

Nonlinear absorption and scattering of a single plasmonic nanostructure characterized by x-scan technique

Nonlinear nanoplasmonics is a largely unexplored research area that paves the way for many exciting applications, such as nanolasers, nanoantennas, and nanomodulators. In the field of nonlinear nanoplasmonics, it is highly desirable to characterize the nonlinearity of the optical absorption and scattering of single nanostructures. Currently, the common method to quantify optical nonlinearity is the z-scan technique, which yields real and imaginary parts of the permittivity by moving a thin sample with a laser beam. However, z-scan typically works with thin films, and thus acquires nonlinear responses from ensembles of nanostructures, not from single ones. In this work, we present an x-scan technique that is based on a confocal laser scanning microscope equipped with forward and backward detectors. The two-channel detection offers the simultaneous quantification for the nonlinear behavior of scattering, absorption and total attenuation by a single nanostructure. At low excitation intensities, both scattering and absorption responses are linear, thus confirming the linearity of the detection system. At high excitation intensities, we found that the nonlinear response can be derived directly from the point spread function of the x-scan images. Exceptionally large nonlinearities of both scattering and absorption are unraveled simultaneously for the first time. The present study not only provides a novel method for characterizing nonlinearity of a single nanostructure, but also reports surprisingly large plasmonic nonlinearities.

Tunable mid-infrared dual-band and broadband cross-polarization converters based on U-shaped graphene metamaterials.

We propose a tunable dual-band reflective cross-polarization converter composed of periodically arranged single layer U-shaped graphene nanostructures in mid-infrared region. The proposed dual-band reflective cross-polarization converter can convert the polarization state of an incident wave from the linear polarization state to its cross polarization state at the operating frequencies of 34.67 and 44.13 THz with the high-efficiency polarization conversion ratio (PCR) approaching 100%. Furthermore, as a complementary structure, a reflective cross-polarization converter with a hollow-carved U-shaped graphene sheet shows a broadband polarization conversion performance with a bandwidth of 1 THz and the PCR over 90%. The bandwidth of this broadband converter can be further extended to 2 THz after certain geometric parameter optimization. More importantly, both the dual-band and broadband cross-polarization converters not only can dynamically tune their PCR peak frequencies and magnitudes by adjusting the chemical potential and relaxation time of graphene without changing the geometric structure but also have good angular stability with high PCR in a wide range of incident angle up to 55°. These polarization converters may have great potential applications in mid-infrared spectroscopy, radiometer, sensor, and other photonic devices.

Influence of Thickness on Structural and optical properties of the CdS single crystal nano structure thin films Deposited Via Thermal evapovation

In this paper, the preparation of the harmful cadmium CdS on glass bases, prepared by thermal evaporation in the vacuum and study of optical and structural properties. The thickness and structural of the films were determined by (FESEM cross section). The results of the X-ray diffraction (XRD) showed that the films had a single crystal the hexagonal structure and the roughness and granular size were studied by using the (AFM) in two dimensions and three dimensions. The surface of the films was formed from clusters of granules called cluster and the roughness rate increased . The optical properties were studied through the (T) permeability spectrum of cadmium sulfide (CdS) prepared in wavelength range (400,650,750) nm. It was noted hat the permeability of cadmium sulfide was low and when the permeability decreased, the energy gap increased. And the value of the optical energy gap is(2.6eV) for cadmium sulfide. The optical properties were calculated as a function of the photon energy, which includes the absorption coefficient. The optical properties suggest that the prepared had a direct energy gap of 2.5,2.2,1.95eV where the energy gap was observed by increasing the thickness of the prepared the films was studied for the manufacture of electronic devices such as solar cells. The morphology of the surface was studied through (AFM) ,and the study of the optical properties of the films by UV-visible, and the CdS of the (PVD) thermal discharge were prepared in vacuum.

Wavelength-decoupled geometric metasurfaces by arbitrary dispersion control

Conventional multicolor metaholograms suffer from the fundamental limitations of low resolution and irreducible noise because the unit structure functionality is still confined to a single wavelength. Here, we propose wavelength-decoupled metasurfaces that enables to control chromatic phase responses independently in a full range from 0 to 2π for each wavelength. The propagation phase associated with the geometric phase of rectangular dielectric nanostructures plays a critical role to embed a dual phase response into a single nanostructure. A multicolor metahologram is also demonstrated to verify the feasibility of our method that breaks through the fundamental constraints of conventional multicolor metaholograms. Our approach can be extended to achieve complete control of chromatic phase responses in the visible for general dual-wavelength diffractive optical elements.

Surface and Interface Control in Nanoparticle Catalysis.

The surface and interfaces of heterogeneous catalysts are essential to their performance as they are often considered to be active sites for catalytic reactions. With the development of nanoscience, the ability to tune surface and interface of nanostructures has provided a versatile tool for the development and optimization of a heterogeneous catalyst. In this Review, we present the surface and interface control of nanoparticle catalysts in the context of oxygen reduction reaction (ORR), electrochemical CO2 reduction reaction (CO2 RR), and tandem catalysis in three sections. In the first section, we start with the activity of ORR on the nanoscale surface and then focus on the approaches to optimize the performance of Pt-based catalyst including using alloying, core-shell structure, and high surface area open structures. In the section of CO2 RR, where the surface composition of the catalysts plays a dominant role, we cover its reaction fundamentals and the performance of different nanosized metal catalysts. For tandem catalysis, where adjacent catalytic interfaces in a single nanostructure catalyze sequential reactions, we describe its concept and principle, catalyst synthesis methodology, and application in different reactions.

Carving Plasmon Modes in Silver Sierpiński Fractals

The surface plasmon resonance (SPR) modes of the first three generations of a Sierpinski fractal triangle are investigated using electron energy loss spectroscopy (EELS) complemented with finite difference time domain simulations. The Sierpinski fractal geometry is created in a subtractive manner, by carving triangular apertures into the triangular prism of the previous fractal generation. The ability of the fractal antenna to efficiently utilize space in coupling to long wavelength excitations is confirmed on the single nanostructure level via redshifting of the primary dipole mode as the fractal generation is increased. Through application of the Babinet principle, it is demonstrated that this spectral shift is caused by coupling of two degenerate orthogonal dipolar modes of a single triangle with two degenerate orthogonal dipole modes of the triangular aperture occupying the center of the first generation fractal. It is also shown that the spectral position and strength of the dipole mode can be tuned ...

Hybridized plasmon modes in a system of metal thin film–nanodisk array

Controlling the hybridization is a very powerful tool to manipulate the modes in a single nanostructure. We investigate the hybridization between localized and propagating surface plasmons in a nanostructure system where a thin metal layer strongly interacts with a nanodisk array. Hybrid plasmon resonances are observed in the reflection spectra obtained from finite-difference time domain simulations and experimental measurements in the visible-near-infrared region. We demonstrate how the geometrical parameters of the nanostructure can be utilized to bring these plasmon modes in the strong coupling regime. The hybrid plasmon modes exhibit anticrossing with a Rabi splitting of ∼0.1eV, which is the signature of strong coupling. Near-field profiles of the hybrid modes exhibit a mixture of localized and propagating plasmon characteristics, with propagating modes excited on both sides of the metal film. Our design promises richer implementations in light manipulation towards novel photonic applications compared to the systems with thick metal films.

Particle‐in‐a‐Frame Nanostructures with Interior Nanogaps

AbstractDesigning plasmonic hollow colloids with small interior nanogaps would allow structural properties to be exploited that are normally linked to an ensemble of particles but within a single nanoparticle. Now, a synthetic approach for constructing a new class of frame nanostructures is presented. Fine control over the galvanic replacement reaction of Ag nanoprisms with Au precursors gave unprecedented Au particle‐in‐a‐frame nanostructures with well‐defined sub‐2 nm interior nanogaps. The prepared nanostructures exhibited superior performance in applications, such as plasmonic sensing and surface‐enhanced Raman scattering, over their solid nanostructure and nanoframe counterparts. This highlights the benefit of their interior hot spots, which can highly promote and maximize the electric field confinement within a single nanostructure.

Particle-in-a-Frame Nanostructures with Interior Nanogaps.

Designing plasmonic hollow colloids with small interior nanogaps would allow structural properties to be exploited that are normally linked to an ensemble of particles but within a single nanoparticle. Now, a synthetic approach for constructing a new class of frame nanostructures is presented. Fine control over the galvanic replacement reaction of Ag nanoprisms with Au precursors gave unprecedented Au particle-in-a-frame nanostructures with well-defined sub-2 nm interior nanogaps. The prepared nanostructures exhibited superior performance in applications, such as plasmonic sensing and surface-enhanced Raman scattering, over their solid nanostructure and nanoframe counterparts. This highlights the benefit of their interior hot spots, which can highly promote and maximize the electric field confinement within a single nanostructure.

Nanostructuring Iridium Complexes into Crystalline Phosphorescent Nanoparticles: Structural Characterization, Photophysics, and Biological Applications.

One of the key challenges in materials science is to control the properties of a material by directing its supramolecular arrangement. Here we show that iridium complexes, such as FIrpic, Ir-PPY, and Ir-MDQ, can be organized into crystalline and phosphorescent nanoparticles through the nanoprecipitation method, which allows thorough modification of their functional properties. Moreover, we found that it is possible to combine different iridium complexes into a single multicomponent nanostructure, thus creating nanoparticles whose photonic properties derive from the close spatial proximity of the electronic excited states of the different Ir complexes. The morphology of all nanoparticles was fully characterized by microscopic and spectroscopic techniques, and their ordered arrangement was assessed by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (TEM) measurements. We demonstrate that the nanostructuring of the complexes influences their optical and redox properties-by promoting a fine-tuning of emission, photoluminescence quantum yield, excited state lifetime, HOMO/LUMO energy levels, and energy-transfer processes-as well as their interaction with living cells. Investigations on glioblastoma U-251 MG cells demonstrate that nanostructuring represents an effective tool to regulate the efficiency of cell loading, cell viability, colocalization, and penetration in 3D spheroids.

Recent Advances in Magnetic Upconversion Nanocomposites for Bioapplications.

The combination of magnetism and upconversion luminescent property into one single nanostructure is fascinating for biological fields, such as multimodal bioimaging, targeted drug delivery, and imaging-guided therapy. In this review, we will provide the state-of-the-art advances on magnetic upconversion nanocomposites towards their bioapplications. Their structure design, synthesis methods, surface engineering and applications in bioimaging, drug delivery, therapy as well as biodetection will be covered.

Manipulation of a Single Crystal Nanowire on an Atomic Level

In recent years, metal oxide nanostructures (MO) have been intensively studied due to a wide variety of applications on multiple fields, for example in optoelectronics, gas sensing, photovoltaics, field-effect transistors, UV lasers, field emission sources etc. [1]. However, for applications, other types of structures are also interesting such as sulfides and nitrides. Here the question that raises is can we manipulate nanomaterials like nanowires on an atomic level. Knowing the exact mechanism of sulfur-oxygen exchange in the metal oxide crystal lattice can be utilized for the synthesis of metal sulfides with specific morphologies. When compared to metal oxides, single-crystalline metal sulfide nanostructures of specific morphologies are usually harder to produce than MOs. Generally, metal sulfide nanostructures represent unconventional materials in areas such as batteries or photovoltaics with yet unexploited potential, where their efficiency is mainly limited by the purity of crystalline phases and structural defects [2]. A promising path for novel synthesis route is incorporation of the sulfur in the crystal structure of a metal oxide nanoparticle, while during this transition the morphology of the nanostructure does not change. In this way, it is possible to obtain single crystal metal sulfide nanostructures from metal oxide nanostructures in the single crystal to single crystal (SCSC) transformation. A promising method to achieve such transformation in a short period of time is a treatment of metal oxide nanostructures with the plasma of sulfur-containing gas. In this research, we studied the mechanism of sulfur incorporation in the metal oxide crystal structure. The procedure was carried out by synthesis of ultra-thin metal oxide nanowires, which were then treated with sulfur-containing gases under increased temperature (in thermodynamic equilibrium conditions) and in the plasma of the same gases (under thermodynamically non-equilibrium conditions). Experiments were conducted at different temperatures and pressures to evaluate the influence of plasma on transformation process. Mechanisms involved in the interaction of sulfur-containing species with metal oxides were studied on isolated single ultra-thin metal oxide nanowire. Furthermore, changes in crystal structures and their effect on the material properties before and after sulfurization were studied. [1] Umar A. & Hahn Y. B. (Eds.). (2010), Metal Oxide Nanostructures and their Applications. American Scientific Publishers, CA, USA [2] Zavašnik, J., & Rečnik, A. (2013). Electron microscopy study of CVT grown Fe-sulphides. Journal of Crystal Growth, 367, 18-23.

Combining Nanofocused X-Rays with Electrical Measurements at the NanoMAX Beamline

The advent of nanofocused X-ray beams has allowed the study of single nanocrystals and complete nanoscale devices in a nondestructive manner, using techniques such as scanning transmission X-ray microscopy (STXM), X-ray fluorescence (XRF) and X-ray diffraction (XRD). Further insight into semiconductor devices can be achieved by combining these techniques with simultaneous electrical measurements. Here, we present a system for electrical biasing and current measurement of single nanostructure devices, which has been developed for the NanoMAX beamline at the fourth-generation synchrotron, MAX IV, Sweden. The system was tested on single InP nanowire devices. The mechanical stability was sufficient to collect scanning XRD and XRF maps with a 50 nm diameter focus. The dark noise of the current measurement system was about 3 fA, which allowed fly scan measurements of X-ray beam induced current (XBIC) in single nanowire devices.

Synthesis and characterization of zinc oxide incorporated iron borate glass-ceramic

Here, zinc oxide (ZnO) incorporated iron borate (Fe3BO6) glass-ceramics have been synthesized using the traditional melt-quenching technique, and the role of ZnO has been investigated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) reveals that the prepared samples have a single crystalline phase and crystalline nanostructures, respectively. The orthorhombic crystal structure has been retained without the formation of a new crystalline phase. The addition of ZnO is found to distort the Fe3BO6 lattice by substituting Zn2+ in the Fe3+ sites, with the formation of ZnO6 structural units as revealed by Fourier transform infrared spectroscopy (FTIR). FTIR and Raman spectroscopy conducted to study the structure of glass-ceramic, have also revealed the formation of other structural units like ZnO4, BO3, BO4, and FeO6 in the system. Surface analysis conducted by X-ray photoelectron spectroscopy (XPS) reveals that the addition of ZnO diminishes the formation of surface B2O3 layer which forms over the Fe3BO6 phase in the Fe3BO6 iron borate glass-ceramic system. ZnO addition has also shown a remarkable difference in the volume of the crystallization in the system, thereby paving the way for controlled crystallization in the iron borate glass-ceramic system. The controlled crystallization was achieved through additive content, retaining the iron borate (Fe3BO6) glass-ceramic system without the evolution of any secondary phases even with large additive concentrations up to 10 mol%.

Dark Excitons: Dark‐Exciton‐Mediated Fano Resonance from a Single Gold Nanostructure on Monolayer WS2 at Room Temperature (Small 31/2019)

Dark Excitons: Dark‐Exciton‐Mediated Fano Resonance from a Single Gold Nanostructure on Monolayer WS₂ at Room Temperature (Small 31/2019)

The effect of in-situ and post deposition annealing towards the structural optimization studies of RF sputtered SnS and Sn2S3 thin films for solar cell application

Optimization studies towards the formation of single phase orthorhombic SnS and Sn2S3 thin films are independently achieved using SnS target in RF magnetron sputtering by varying the RF power, in-situ and post-deposition vacuum annealing temperature. Micro structural analyses confirmed the role of in-situ annealing at 400 °C for the columnar growth formation of single phase SnS nanostructures which is an important aspect towards the fabrication of SnS based thin film solar cells with improved efficiency. Further, SnS to Sn2S3 phase transition is observed at 500 °C. The observed variations in the optical properties such as band edge shift, direct energy band gap (Eg), absorption coefficient (α), extinction coefficient (K) and refractive index (n) of the films are correlated with the structural and morphological analysis. Electrical studies along with band gap measurement further confirmed the transition from p-type SnS phase having a band gap value of 1.55 eV with resistivity as 1280 Ω cm to n-type Sn2S3 with band gap value of 1.06 eV and resistivity of 0.864 Ω cm.

Conductometric Sensing with Individual InAs Nanowires.

In this work, we isolate individual wurtzite InAs nanowires and fabricate electrical contacts at both ends, exploiting the single nanostructures as building blocks to realize two different architectures of conductometric sensors: (a) the nanowire is drop-casted onto—supported by—a SiO2/Si substrate, and (b) the nanowire is suspended at approximately 250 nm from the substrate. We test the source-drain current upon changes in the concentration of humidity, ethanol, and NO2, using synthetic air as a gas carrier, moving a step forward towards mimicking operational environmental conditions. The supported architecture shows higher response in the mid humidity range (50% relative humidity), with shorter response and recovery times and lower detection limit with respect to the suspended nanowire. These experimental pieces of evidence indicate a minor role of the InAs/SiO2 contact area; hence, there is no need for suspended nanostructures to improve the sensing performance. Moreover, the sensing capability of single InAs nanowires for detection of NO2 and ethanol in the ambient atmosphere is reported and discussed.