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Facilitating Tip-Enhanced Raman Scattering on Dielectric Substrates via Electrical Cutting of Silver Nanowire Probes
摘要： TERS is a powerful tool for nanoscale optical characterization of surfaces. However, even after 20 years of development, the parameters for optimal TERS tips are still up for debate. As a result, routine measurements on bulk or dielectric substrates remain exceptionally challenging. Herein we help to alleviate this by using electrical cutting to strategically modify silver nanowire TERS probes. Following cutting, the tips present a large, spherical apex and are often nanostructured with numerous nanoparticles, which we argue improve light collection and optical coupling. This doubles TERS signals on a highly-enhancing, gap-mode substrate compared to our standard nanowire tips, whilst maintaining a high reproducibility and resolution. More interestingly, on a dielectric substrate (graphene on SiO2) the tips give ~7x higher signals than our standard tips. Further investigations point to the non-local nature of the enhancement using standard, smooth, TERS probes without gap-mode, making such nanostructuring highly beneficial in these cases.
关键词： electrical cutting,silver nanowire,TERS,Tip-Enhanced Raman Scattering,nanoscale optical characterization,dielectric substrates
更新于2025-09-23 15:21:01
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Nanoscale virtual potentials using optical tweezers
摘要： We combine optical tweezers with feedback to impose arbitrary potentials on a colloidal particle. The feedback trap detects a particle’s position, calculates a force based on an imposed “virtual potential,” and shifts the trap center to generate the desired force. We create virtual harmonic and double-well potentials to manipulate particles. The harmonic potentials can be chosen to be either weaker or stiffer than the underlying optical trap. Using this ?exibility, we create an isotropic trap in three dimensions. Finally, we show that we can create a virtual double-well potential with ?xed well separation and adjustable barrier height. These are accomplished at length scales down to 11 nm, a feat that is dif?cult or impossible to create with standard optical-tweezer techniques such as time sharing, dual beams, or spatial light modulators.
关键词： optical tweezers,colloidal particle,virtual potential,nanoscale,feedback trap
更新于2025-09-23 15:21:01
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Epitaxial lateral overgrowth of GaN on nano-cavity patterned sapphire substrates
摘要： The epitaxial lateral overgrowth of GaN by metal-organic chemical vapor deposition using a nano-cavity patterned sapphire substrate (NCPSS) was investigated. The NCPSS, with a hexagonal non-close-packed nano-cavity pattern on the sapphire substrate, was fabricated by polystyrene sphere coating and size reduction by reactive ion etching, followed by deposition of alumina and thermal oxidation. The coalescence of GaN on the NCPSS was achieved by the formation of relatively large GaN islands and enhanced lateral overgrowth of the GaN islands over several nano-cavity pattern areas. The threading dislocation density (TDD) measured by cathodoluminescence measurement was significantly reduced from 2.4 108 cm-2 to 6.9 107 cm-2 by using the NCPSS. Dislocation behaviors that contribute to the reduction of TDD of the GaN layer were observed by transmission electron microscopy. Raman spectroscopy revealed that the compressive stress in the GaN layer was reduced by 21% due to the embedded nano-cavities. In addition, the diffuse reflectance of GaN on the NCPSS was enhanced by 54% ~ 62%, which is attributed to the increased probability of light extraction through effective light scattering by nano-cavities.
关键词： A1. Nanostructures,B1. Nitrides,A2. Single crystal growth,A3. Metalorganic chemical vapor deposition,A3. Nanoscale epitaxial lateral overgrowth
更新于2025-09-23 15:21:01
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Precession Electron Diffraction and Orientation Phase Mapping of Assembled Ag/ZnO Nanoantennas
摘要： The manipulation of the geometrical and structural arrangement of the constituent’s elements on devices at nanoscale level is highly desirable for a precise monitoring of the opto-electrical properties exhibited for these nanomaterials. In fact, a great effort has being made to understand the coupling mechanisms on metal-semiconductors systems, most precisely at interfaces nanoscale level. For instance, it is well known that the multidirectional radiation pattern generated by the active elements on nanoantenna applications is highly dependent on both the structural and orientation distribution of the receiver elements as well as the passive element on the nanoscale device. For example, Wang, et al [1] have synthesized high order nanostructures in a hierarchical configuration to study the photo-induced optical properties of these systems in function of the ZnO concentration distributed along the silver nanowires. However, few is known about the structural coupling mechanisms between this metal-semiconductor heterojunctions. Thus, to understand the dynamic coupling at the interface level in the Ag/ZnO metal-semiconductor heterojunctions we report the epitaxial growing of zinc oxide nanorods on the pentagonal exposes faces of Ag nanowires resembling a hierarchal nanoantenna. Moreover, the studied of the growth mechanism in the active/contact faces of the metal-semiconductor heterojunction has been done by mapping simultaneously the dynamical electron diffraction pattern under in-situ precession electron diffraction at the heterojunction interface Ag/ ZnO nanosystem. Indeed, by indexing the dynamical diffraction patterns using orientational/phase mapping from the precessed electron diffraction data collected an orientational mapping has been retrieved showing the interfacial growing polar planes (0002) of ZnO nanorods on the pentagonal planes of silver nanowires with a mismatch between planes along the coupling interface. For completeness, grazing angle x-ray diffraction measurements on prepared substrates Ag/ZnO systems shown well-defined peaks associated to the main phases of ZnO nanorods and Ag nanowires respectively. A full understanding of the fit faces mechanism between Ag/ZnO along the mismatch direction undoubtedly will allow elucidating the mechanism through which the contact metal-semiconductor behaves at the heterojunction interface.
关键词： Nanoscale Devices,Ag/ZnO Nanoantennas,Metal-Semiconductor Heterojunctions,Orientation Phase Mapping,Precession Electron Diffraction
更新于2025-09-23 15:19:57
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Fluorescent Sensors Based on a Novel Functional Design: Combination of an Environment-sensitive Fluorophore with Polymeric and Self-assembled Architectures
摘要： The fluorescence properties, e.g., fluorescence intensity, of fluorescent sensors can change due to covalent derivatization or noncovalent complexation with a target chemical species (i.e., molecules and ions) or by variations in circumstantial physical parameters (e.g., temperature and viscosity). The internal charge transfer (ICT) character and photoinduced electron transfer (PET) efficiency can be used to tune the fluorescence switching mechanism, facilitating the development of new fluorescent sensors. In addition, the utilization of an environment─ sensitive (i.e., polarity─ and hydrogen bonding─ sensitive) fluorophore in stimulus─ responsive macromolecules to design novel fluorescent sensors has been proposed. Based on this concept, highly sensitive fluorescent polymeric thermometers and (extremely sensitive) digital fluorescent pH sensors have been developed. These thermometers are being used to measure the temperature of live cells in biological and medical studies. This concept has also allowed nanoscale proton mapping near membranes, which exemplifies the downsizing of targets for fluorescent sensing from a micrometer─ scale to a nanometer─ scale.
关键词： digital fluorescent pH sensors,polymeric thermometers,nanoscale proton mapping,fluorescent sensors,environment─ sensitive fluorophore
更新于2025-09-23 15:19:57
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Highly Rectifying Heterojunctions Formed by Annealed ZnO Nanorods on GaN Substrates
摘要： We study the effect of thermal annealing on the electrical properties of the nanoscale p-n heterojunctions based on single n-type ZnO nanorods on p-type GaN substrates. The ZnO nanorods are prepared by chemical bath deposition on both plain GaN substrates and on the substrates locally patterned by focused ion beam lithography. Electrical properties of single nanorod heterojunctions are measured with a nanoprobe in the vacuum chamber of a scanning electron microscope. The focused ion beam lithography provides a uniform nucleation of ZnO, which results in a uniform growth of ZnO nanorods. The specific configuration of the interface between the ZnO nanorods and GaN substrate created by the focused ion beam suppresses the surface leakage current and improves the current-voltage characteristics. Further improvement of the electrical characteristics is achieved by annealing of the structures in nitrogen, which limits the defect-mediated leakage current and increases the carrier injection efficiency.
关键词： chemical bath deposition,nanoscale heterojunctions,ZnO nanorods,nanoprobe in the scanning electron microscope,current-voltage characteristics,annealing,focused ion beam patterning
更新于2025-09-23 15:19:57
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Smart Nanocontainers || Advanced spectroscopic technique for the study of nanocontainers: atomic force microscopy-infrared spectroscopy (AFM-IR)
摘要： Over the years, advances in the synthesis of nanostructures have enabled the appearance of a large number of nanocontainers. The materials constructing nanocontainers cover a wide range of compounds including small molecules, polymers, micelles, dendrimers, mesoporous silica nanoparticles, layered double hydroxides, halloysite nanotubes, and metal-organic frameworks (MOFs). The structure of nanocontainers based on them has an inner compartment that can be used for storage or encapsulation of guests including anticancer drugs, corrosion inhibitors, and water-treating absorbents. Because of this special structure, nanocontainers are of great interests in applications such as drug delivery system, corrosion prevention, and environment protection. For example, when nanocontainers are used as drug delivery devices, they are of great advantages to characterize the drug/device properties using spectroscopic techniques including Fourier transform infrared spectroscopy and Raman spectroscopy.
关键词： AFM-IR,nanoscale,spectroscopy,chemical imaging,nanocontainers
更新于2025-09-23 15:19:57
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Theoretical assessment of D-shaped optical fiber chemical sensor associated with nanoscale silver strip operating in near-infrared region
摘要： In present work, we propose a surface plasmon resonance based D-shaped fiber for the chemical sensor using nanoscale silver strip deposited over polished surface of single mode fiber. Various parameters of the designed sensors are optimized to achieve the maximum wavelength sensitivity. The sensing properties are investigated using finite element method based on COMSOL Multiphysics. An average wavelength sensitivity of 2100 nm/RIU is obtained for wide range of refractive index (RI) varying between 1.34 and 1.42 and a maximum wavelength and amplitude sensitivity of 3240 nm/RIU and 192 RIU?1 is achieved for RI range varying between 1.38 and 1.42 with 3.08 × 10?5 RIU resolution. The results indicate that our designed sensor perform effectively in high RI range and hence can be used in chemical and biological sensing.
关键词： Nanoscale,Surface plasmon resonance,Refractive index,D-shaped,Evanescent waves
更新于2025-09-23 15:19:57
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The fundamentals of harnessing the magneto-optics of quantum wires for designing optical amplifiers: Formalism
摘要： Quantum wires occupy a unique status among the semiconducting nanostructures with reduced dimensionality, no other system seems to have engaged researchers with as many appealing features to pursue. This paper aims at a core issue related with the magnetoplasmon excitations in the quantum wires characterized by the confining harmonic potential and subjected to a longitudinal electric field and a perpendicular magnetic field in the symmetric gauge. Despite the substantive complexity, we obtain the exact analytical expressions for the eigenfunction and eigenenergy, using the scheme of ladder operators, which fundamentally characterize the quantal system. Crucial to this inquiry is an intersubband collective excitation that evolves into a magnetoroton — above a threshold value of magnetic field — which observes a negative group velocity between the maxon and the roton. The evidence of negative group velocity implies anomalous dispersion in a gain medium with the population inversion that forms the basis for the lasing action of lasers. Thus, the technological pathway that unfolds is the route to devices exploiting the magnetoroton features for designing the novel optical amplifiers at nanoscale and hence paving the way to a new generation of lasers.
关键词： magnetorotons,Quantum wires,magnetoplasmons,optical amplifiers,nanoscale lasers,quantum optics
更新于2025-09-19 17:15:36
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Size effect-enhanced thermoelectric properties of nanoscale Cu2-xSe
摘要： As a promising thermoelectric material, copper selenides have attracted the interest of researchers owing to their low cost, abundance in earth, environmental friendliness, and low thermal conductivity. In this study, copper selenide (Cu2-xSe) powders with controllable sizes from nanoscale to mesoscale were obtained by a facile one-pot solvothermal method. After treatment with spark plasma sintering, the nanoscale Cu2-xSe pellets exhibited excellent thermoelectric properties such as sharply reduced thermal conductivity and enhanced Seebeck coefficient as well as a suppressed electrical conductivity. The figure of merit (ZT) of the nanoscale Cu2-xSe reached up to ~1.51 at 873 K, which is about 2.67 times higher than that of the meso-Cu2-xSe. This study confirms that thermoelectric properties can be enhanced by the size effect.
关键词： size effect,solvothermal method,thermoelectric property,Copper selenide,nanoscale
更新于2025-09-19 17:15:36