Single Nanostructures Research Articles

CNT supported NiO hierarchal nanostructure on stainless steel substrate for efficient field emitters

The field emission application has recently focused on assembling nanoscale building blocks into three-dimensional (3D) hierarchical or hybrid nanostructure. The hierarchical nanostructure provides better field emission than a single nanostructure. In the present study, the chemical vapor deposition (CVD) method was used to synthesize 1D carbon nanotube (CNT) on stainless steel (SS) substrate. Nickel (Ni) was then sputtered on the synthesized CNT, and the sputtered substrate was treated hydrothermally in LiOH solution. The deposited Ni on CNT forms Ni(OH)2, and after oxidation, it was converted to NiO nanostructure. The structure, morphology, and chemical state of the samples were characterized by XRD, FESEM, Raman spectroscopy, and XPS. The SS-CNT exhibited a turn-on field and maximum emission current of 5.5 V/μm and 275 µA/cm2, respectively. However, SS-CNT-Ni demonstrated reduced field emission responses with turn-on field and maximum current 8.7 V/μm and 68 µA/cm2, respectively. The field emission response has been enhanced in the case of the SS-CNT-NiO sample as compared to the other structures. The turn-on field and maximum current densities were 5.1 V/µm and 719 µA/cm2 for the SS-CNT-NiO, respectively.

Direct visualization of the drug loading of single DNA origami nanostructures by AFM-IR nanospectroscopy.

The efficient loading of DNA nanostructures with intercalating or groove-binding drugs is an important prerequisite for various applications in drug delivery. However, unambiguous verification and quantification of successful drug loading is often rather challenging. In this work, AFM-IR nanospectroscopy is thus employed to directly visualize the loading of DNA origami nanostructures with the photosensitizer methylene blue (MB). Single MB-loaded DNA origami nanostructures can be clearly resolved in high-resolution infrared (IR) maps and the occurrence of MB-specific IR absorption correlates well with the topographic signals of the DNA origami nanostructures. The intensity of the recorded MB absorption bands furthermore scales with the MB concentration used for MB loading. By comparing single- and multilayer DNA origami nanostructures, it is also shown that the IR signal intensity of the loaded MB increases with the thickness of the DNA origami nanostructures. This indicates that also DNA double helices located in the core of bulky 3D DNA origami nanostructures are accessible for MB loading. AFM-IR nanospectroscopy thus has the potential to become an invaluable tool for quantifying drug loading of DNA origami nanostructures and optimizing drug loading protocols.

Controlled crystal growth of ZnO nanobelts by chemical vapor deposition method

With the development expansion of environmental sensors in recent years, nanogenerators utilizing small amounts of mechanical energy in surrounding environment to generate electricity have been frequently studied. In order to convert mechanical energy into electrical energy more efficiently, it is necessary to fabricate single crystal ZnO nanostructures with specific crystal facet that exhibits piezoelectricity in the direction of applied strain. Since ZnO nanobelts have three pairs of crystal facets, controlling crystal growth can increase the size of specific crystal facet and their piezoelectricity is greater than that of ZnO nanowires, which is advantageous for power generation using piezoelectricity. ZnO nanobelts have been fabricated by chemical vapor deposition method, and we attempted to control the crystal growth by changing the heating temperature and pressure. Morphologies were observed by field emission scanning electron microscopy. Diffraction patterns were observed by transmission electron microscopy. ZnO nanobelts with the growth direction of [0001] and [0110] have been successfully fabricated in this research.

Strong coupling of single plasmonic nanoparticles and nanogaps with quantum emitters

In cavity quantum electrodynamics, when the interaction between quantum emitter and cavity mode is strong enough to overcome the mean decay rate of the system, it will enter into a strong coupling regime, thereby forming part-light part-matter polariton states. Strong coupling can serve as a promising platform for room temperature Bose-Einstein condensation, polariton lasing, single photon nonlinearity, quantum information, etc. Localized surface plasmons supported by single metal nanostructures possess extremely small mode volume, which is favorable for realizing strong coupling. Moreover, the nanoscale dimensions of plasmonic structures can facilitate the miniaturization of strong coupling systems. Here, the research progress of strong plasmon-exciton coupling between single metal nanoparticles/nanogaps and quantum emitters is reviewed. The theory background of strong coupling is first introduced, including quantum treatment, classical coupled oscillator model, as well as the analytical expressions for scattering and photoluminescence spectra. Then, strong coupling between different kinds of plasmonic nanostructures and quantum emitters is reviewed. Single metal nanoparticles, nanoparticle dimers, and nanoparticle-on-mirror structures constitute the most typical plasmonic nanostructures. The nanogaps in the latter two systems can highly concentrate electromagnetic field, providing optical nanocavities with smaller mode volume than single nanoparticles. Therefore, the larger coupling strength can be achieved in the nanogap systems, which is conducive to strong coupling at the single-exciton level. In addition, the active tuning of strong coupling based separately on thermal, electrical and optical means are reviewed. The energy and oscillator strength of the excitons in transition metal dichalcogenide (TMDC) monolayers are dependent on temperature. Therefore, the strong coupling can be tuned by heating or cooling the system. The excitons in TMDC monolayers can also be tuned by electrical gating, enabling electrical control of strong coupling. Optically tuning the quantum emitters provides another way to actively control the strong coupling. Overall, the research on active tuning of strong plasmon-exciton coupling is still very limited, and more investigations are needed. Finally, this review is concluded with a short summary and the prospect of this field.

Single GaP nanowire nonlinear characterization with the aid of an optical trap.

Semiconductor nanowires exhibit numerous capabilities to advance the development of future optoelectronic devices. Among the III-V material family, gallium phosphide (GaP) is an attractive platform with low optical absorption and high nonlinear susceptibility, making it especially promising for nanophotonic applications. However, investigation of single nanostructures and their waveguiding properties remains challenging owing to typically planar experimental arrangements. Here we study the linear and nonlinear waveguiding optical properties of a single GaP nanowire in a special experimental layout, where an optically trapped structure is aligned along its major axis. We demonstrate efficient second harmonic generation in individual nanowires and unravel phase matching conditions, linking between linear guiding properties of the structure and its nonlinear tensorial susceptibility. The capability to pick up single nanowires, sort them with the aid of optomechanical manipulation and accurately position pre-tested structures opens a new avenue for the generation of optoelectronic origami-type devices.

Coupled Nanoring Resonators Based Reconfigurable and Multifunctional Platform for Photonic Integrated Circuits

A novel coupled nanoring resonators-based reconfigurable and multifunctional platform is designed with high-speed, low input power and ultra-compact size for scalable and high performance Photonic Integrated Circuits. This single nanostructure platform is used to realize five different optical components such as wavelength multiplexer, D-flip flop, power splitter, reconfigurable switch, and bandpass filter. The performance of these optical components is analyzed by Finite-Difference Time Domain (FDTD) method. The coupled resonator platform plays a very significant role in wavelength filtering, light signal routing, multiplexing, power dividing and logical operations. The multipurpose structure is numerically investigated and optimized to achieve a high data rate of 5.4 Tbps, high ON-OFF ratio of 36.98 dB, ultra-compact size of 186.48 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and low insertion loss of 0.0043 dB. Hence, this nanoscale structure is highly suitable for optical computing, wavelength division-based photonic communication systems and optical interconnects.

Toward high-performance refractive index sensor using single Au nanoplate-on-mirror nanocavity.

Refractive index sensors based on the localized surface plasmon resonance (LSPR) have emerged as powerful tools in various chemosensing and biosensing applications. However, owing to their limited decay length and strong radiation damping, LSPR sensors always suffer from low sensitivity and small figure of merit (FOM). Here, we fabricate a plasmonic nanocavity sensor consisting of a hexagonal Au nanoplate positioned over an ultrasmooth Au film. The strong coupling between the nanoplate and the lower metal film allows for the formation of a plasmonic gap mode that enhances the interaction of the local field with the ambient glycerol solution to increase the sensitivity. Meanwhile, the plasmonic gap mode has a trait of an antiphase charge oscillation in the gap region, imparting a strongly reduced radiative damping and a subsequently promoted FOM. The performance of our proposed refractive index sensor is further boosted by decreasing the gap size of the nanocavity, yielding an outstanding FOM of 11.2 RIU-1 that is the highest yet reported for LSPR sensing in a single nanostructure.

Modulation of electric dipoles inside electrospun BaTiO3@TiO2 core-shell nanofibers for enhanced piezo-photocatalytic degradation of organic pollutants

Ferroelectric materials can generate a built-in electric field under strain, which can produce reactive oxygen species (ROS) for in-situ piezocatalysis via a series of redox reactions, or enhance photocatalytic activities through the separation of the photoinduced electron and hole pairs. In this study, the synergistic piezo-phototronic effect is enhanced by increasing the inner piezopotential of ferroelectric nanofibers in fibrous piezoelectric/oxide semiconductor heterostructures. Ferroelectric BaTiO3 nanofibers are fabricated by a sol-gel assisted electrospinning and subsequent annealing at 700 ºC for 2 h, 4 h, and 6 h, respectively (denoted as BT2H, BT4H, and BT6H). Piezoelectric force microscopy results reveal that the necklace-like BT6H nanofibers demonstrate the highest local piezoelectric coefficient d33 (42.7 pm V−1) than BT2H (26.3 pm V−1) and BT4H (37.8 pm V−1) nanofibers because BT6H nanofibers are composed of highly crystallized electric dipoles with single domain nanostructures. Additionally, BT6H@TiO2 core-shell nanofibers are synthesized by a wet-chemical coating of TiO2 on BT6H nanofibers. Under both ultrasound and UV light irradiations, BT6H@TiO2 core-shell nanofibers exhibit a high piezo-photocatalytic degradation rate constant of 6 × 10−2 min−1 because of the enhancement of the piezotronic effect by the high piezoelectricity of electric dipoles that promote the separation of the photoinduced electron and hole pairs. The enhancement of the synergistic piezo-phototronic effect is ascribed to the highly active reaction sites that are confined into the high specific surface area of the one-dimensional fibrous boundary of BT6H@TiO2 core-shell nanofibers, beneficial for the migration of the interfacial charge carriers. This study presents a simple approach to improve the piezo-photocatalysis through modulating the crystallization and the size of electric dipoles, providing an efficient pathway for underpinning the coupling mechanism between the enhancement of local ferro/piezoelectricity and piezo-phototronic effect.

Resistively Detected NMR Lineshapes in a Local Filling ν&lt;1 Quantum Hall Breakdown

Resistively‐detected nuclear magnetic resonance (RDNMR) is a unique characterization method enabling highly sensitive NMR detection for a single quantum nanostructure, such as a quantum point contact (QPC). In many studies, dynamic nuclear polarization and RDNMR detection are used in a quantum Hall breakdown regime of a local QPC filling factor of 1 (νqpc = 1). However, the RDNMR lineshapes are complicated and still not fully understood yet. Herein, the nuclear spins are systematically polarized by current pumping from the close vicinity of the νqpc = 1 conductance plateau all the way down to pinch‐off point, providing clear evidence that the spin‐flip scattering between two edge channels at the lowest Landau level still occurs in the constriction even when it is close to the pinch off point. The collected RDNMR spectra reveal two sets of distinguished features. First, in a strong to intermediate tunneling regime, we observe an ordinary resistance dip lineshape with snake‐like transition frequencies, indicative of spatial modulation of electron density in the QPC. Second, in a weak tunneling regime, the spectrum turns into a dispersive lineshape, which is interpreted due to the build‐up of two sets of nuclear spin polarization that are in contact with different electron spin polarization.

Nonlinear heating and scattering in a single crystalline silicon nanostructure.

Silicon nanophotonics has attracted significant attention because of its unique optical properties such as efficient light confinement and low non-radiative loss. For practical applications such as all-optical switch, optical nonlinearity is a prerequisite, but the nonlinearity of silicon is intrinsically weak. Recently, we discovered a giant nonlinearity of scattering from a single silicon nanostructure by combining Mie resonance enhanced photo-thermal and thermo-optic effects. Since scattering and absorption are closely linked in Mie theory, we expect that absorption, as well as heating, of the silicon nanostructure shall exhibit similar nonlinear behaviors. In this work, we experimentally measure the temperature rise of a silicon nanoblock by in situ Raman spectroscopy, explicitly demonstrating the connection between nonlinear scattering and nonlinear heating. The results agree well with finite-element simulation based on the photo-thermo-optic effect, manifesting that the nonlinear effect is the coupled consequence of the red shift between scattering and absorption spectra. Our work not only unravels the nonlinear absorption in a silicon Mie-resonator but also offers a quantitative analytic model to better understand the complete photo-thermo-optic properties of silicon nanostructures, providing a new perspective toward practical silicon photonics applications.

STED microscopy reveals in-situ photoluminescence properties of single nanostructures in densely perovskite thin films.

All-inorganic perovskite nanomaterials have attracted much attention recently due to their prominent optical performance and potential application for optoelectronic devices. The carriers dynamics of all-inorganic perovskites has been the research focus because the understanding of carriers dynamics process is of critical importance for improving the fluorescence conversion efficiency. While photophysical properties of excited carrier are usually measured at the macroscopic scale, it is necessary to probe the in-situ dynamics process at the nanometer scale and gain deep insights into the photophysical mechanisms and their localized dependence on the thin-film nanostructures. Stimulated emission depletion (STED) nanoscopy with super-resolution beyond the diffraction limit can directly provide explicit information at a single particle level or nanometer scale. Through this unique technique, we firstly study the in-situ dynamics process of single CsPbBr3 nanocrystals(NCs) and nanostructures embedded inside high-dense samples. Our findings reveal the different physical mechanisms of PL blinking and antibunching for single CsPbBr3 NCs and nanostructures that correlate with thin-film nanostructural features (e.g. defects, grain boundaries and carrier mobility). The insights gained into such nanostructure-localized physical mechanisms are critically important for further improving the material quality and its corresponding device performance.

Large nonlinear absorption in single aggregate of silver nanoparticles observed with z-scan imaging technique

Although nonlinear optical spectroscopy of nanostructures, nanomaterials, and nanomedicines has been widely used to observe and study the nature of nonlinear optical (NLO) phenomena, the field has to improve for the single nanostructure system. However, it is extremely difficult to investigate the nonlinear optical behaviors of single nanostructure materials because the optical setup used in the experiment has to obligate a high resolution imaging arrangement and overcome the diffraction limit problem. This paper presents that a newly modified z-scan technique with imaging as a starting point for nonlinear optics measurement technology has been successfully implemented to investigate silver nanoparticle aggregation. Such single aggregation with a diameter of ∼1.56 µm made from silver nanoparticles has been precisely observed with an imaging profile on an aggregation target with a large nonlinear absorption coefficient of 8.90 × 109 cm/GW. This technique suggests a wide impact application for a better understanding and knowledge in conjunction with the origin of NLO behavior in any nanomaterials, including nanomedicines.

Preparation of chromium and sulfur single and co-doped TiO2 nanostructures for efficient photoelectrochemical water splitting: effect of aliphatic alcohols on their activity

Preparation of chromium and sulfur single and co-doped TiO2 nanostructures for efficient photoelectrochemical water splitting: effect of aliphatic alcohols on their activity

Thermoresponsive Fluorescence Switches Based on Au@pNIPAM Nanoparticles.

Despite numerous studies emphasizing the plasmonic impact on fluorescence, the design of a dynamic system allowing on-demand fluorescence switching in a single nanostructure remains challenging. The reversibility of fluorescence switching and the versatility of the approach, in particular its compatibility with a wide range of nanoparticles and fluorophores, are among the main experimental difficulties. In this work, we achieve reversible fluorescence switching by coupling metal nanoparticles with fluorophores through stimuli-responsive organic linkers. As a proof of concept, we link gold nanoparticles with fluorescein through thermoresponsive poly(N-isopropylacrylamide) at a tunable grafting density and characterize their size and optical response by dynamic light scattering, absorption, and fluorescence spectroscopies. We show that the fluorescence emission of these hybrid nanostructures can be switched on-demand using the thermoresponsive properties of poly(N-isopropylacrylamide). The described system presents a general strategy for the design of nanointerfaces, exhibiting reversible fluorescence switching via external control of metal nanoparticle/fluorophore distance.

Multistage Cooperative Nanodrug Combined with PD-L1 for Enhancing Antitumor Chemoimmunotherapy.

Combinatorial CpG oligonucleotide (CPG) and chemotherapy drug represent a promising approach to reactivate immune system. However, these two agents possess different physicochemical properties, hindering the application of direct self-assembly of these two cargos into a single nanostructure. Here, a multistage cooperative nanodrug is developed by the direct self-assembly of cis-platinum (CDDP, Pt), l-arginine (l-Arg, R), and CPG (defined as PtR/CPG) for antitumor chemoimmunotherapy. First, the CDDP can induce cell apoptosis. Meanwhile, CDDP also promotes the production of H2 O2 , catalyzing the conversion of l-Arg into nitric oxide (NO). The generated NO decreases the multidrug resistance of cells toward CDDP. Thus, the synergistic effects of CDDP and NO can trigger immunogenic cell death to produce tumor-associated antigens (TAAs). The TAAs and CPG will induce the maturation of dendritic cells (DCs) and enhance antigen presentation ability of DCs. In this way, the PtR/CPG can reverse the immunosuppressive microenvironment, sensitizing tumors to immune checkpoint inhibitors mediated by the programmed death-ligand 1 (PD-L1) antibody. Furthermore, the PtR/CPG combined with the PD-L1 antibody decreases the exhaustion and dysfunction of cytotoxic T lymphocytes to elicit durable systemic immune response. As a result, the prepared PtR/CPG nanodrug in combination with PD-L1 may be highly significant for cancer immunotherapy.

Crystallinity engineering of Au nanoparticles on graphene for in situ SERS monitoring of Fenton-like reaction

Fabrication of multifunctional nanoplatform to in situ monitor Fenton reaction is of vital importance to probe the underlying reaction process and design high-performance catalyst. Herein, a hybrid catalyst comprising of single-crystalline Au nanoparticles (SC Au NPs) on reduced graphene oxide (RGO) sheet was prepared, which not only exhibited an excellent 1O2 mediated Fenton-like catalytic activity in promoting rhodamine 6G (R6G) degradation by activating H2O2, but also displayed a sensitive surface-enhanced Raman spectroscopy (SERS) detection performance to R6G with a linear response range from 1.0 × 10−8 mol/L to 1.0 × 10−5 mol/L thus providing a powerful and versatile nanoplatform for in situ SERS monitoring Fenton-like catalytic reaction. The integration of catalytic and SERS activities into a single nanostructure are expected to provide great potentials for practical applications in environmental catalysis.

Synthesis of CaIn2S4/TiO2 heterostructures for enhanced UV–visible light photocatalytic activity

Semiconductor heterostructures are regarded as an efficient way to improve the photocatalytic activity. Herein, novel Z-scheme CaIn2S4 (CIS)/TiO2 heterostructures photocatalysts were synthesized by a simple two-step hydrothermal approach. Compared with single phase nanostructures of TiO2 and CIS, the CIS/TiO2-0.05 g nanocomposites exhibited efficient and stable photocatalytic activity, with 97% of methyl orange (MO) decomposed within 30 min under UV–visible light irradiation. In addition to increased broad light absorption, the outstanding photocatalytic performance is mainly attributed to intimate contact and matched energy band positions between CIS and TiO2, which efficiently produce more active electrons and holes, reduce the photogenerated electron-hole recombination, and boost photoinduced charge carrier transfer. The possible Z-scheme mechanism for the photocatalytic reaction in the system was reasonably proposed. This work would arouse an increasing interest in designing more Z-scheme heterojunction photocatalysts with high efficiency for the application of photodegradation.

Complementary switching in single Nb3O7(OH) nanowires

Single nanowires and networks are considered as promising candidates for miniaturized memristive devices for brain-inspired systems. Moreover, single crystalline nanostructures are useful model systems to gain a deeper understanding in the involved switching mechanism of the investigated material. Here, we report on hydrothermally grown single crystalline Nb3O7(OH) nanowires showing a complementary resistive switching (CRS) behavior. The CRS characteristics can be related to an oxygen vacancy migration at the electrode/metal hydroxide interface. Therefore, an oxygen plasma treatment is used to reduce the oxygen vacancy content, resulting in a total reduction of the device conductivity. Furthermore, temporal resolved current–voltage measurements demonstrate the dependence of the destructive readout process of the resistance states on the voltage amplitude and polarity.

Scalable synthesis of multicomponent multifunctional inorganic core@mesoporous silica shell nanocomposites

Integrating multiple materials with different functionalities in a single nanostructure enables advances in many scientific and technological applications. However, such highly sophisticated nanomaterials usually require complex synthesis processes that complicate their preparation in a sustainable and industrially feasible manner. Herein, we designed a simple general method to grow a mesoporous silica shell onto any combination of hydrophilic nanoparticle cores. The synthetic strategy, based on the adjustment of the key parameters of the sol-gel process for the silica shell formation, allows for the embedment of single, double, and triple inorganic nanoparticles within the same shell, as well as the size-control of the obtained nanocomposites. No additional interfacial adhesive layer is required on the nanoparticle surfaces for the embedding process. Adopting this approach, electrostatically stabilized, small-sized (from 4 to 15 nm) CeO2, Fe3O4, Gd2O3, NaYF4, Au, and Ag cores were used to test the methodology. The mean diameter of the resulting nanocomposites could be as low as 55 nm, with high monodispersity. These are very feasible sizes for biological intervention, and we further observed increased nanoparticle stability in physiological environments. As a demonstration of their increased activity as a result of this, the antioxidant activity of CeO2 cores was enhanced when in core-shell form. Remarkably, the method is conducted entirely at room temperature, atmospheric conditions, and in aqueous solvent with the use of ethanol as co-solvent. These facile and even “green” synthesis conditions favor scalability and easy preparation of multicomponent nanocomposite libraries with standard laboratory glassware and simple benchtop chemistry, through this sustainable and cost-effective fabrication process.

Web-above-a-Ring (WAR) and Web-above-a-Lens (WAL): Nanostructures for Highly Engineered Plasmonic-Field Tuning and SERS Enhancement.

Synthetic strategies of web-above-a-ring (WAR) and web-above-a-lens (WAL) nanostructures are reported. The WAR has a controllable gap between the nanoring core and a nanoweb with nanopores for the effective confinement of electromagnetic field in the nanogap and subsequent surface-enhanced Raman scattering (SERS) of Raman dyes inside the gap with high signal reproducibility, which are attributed to the generation of circular 3D hot zones along the rim of Pt@Au nanorings with wrapping nanoweb architecture. More specifically, Pt@Au nanorings are adopted as a plasmonic core for structural rigidity and built porous nanowebs above them through a controlled combination of galvanic exchange and the Kirkendall effect. Both nanoweb and nanolens structures are also formed on Pt@Au nanoring, which is WAL. structure. Remarkably, plasmonic hot zone, nanopores, and hot lens are formed inside a single WAL nanostructure, and these structural components are orchestrated to generate stronger SERS signals.