Au Nanodots Research Articles

Surface Potential Based Analytical Modeling of Double Gate MOSFET with Si and Au Nano-Dots Embedded Gate Dielectric for Non-Volatile Memory Applications

In this paper we present an analytical study of Double Gate (DG) MOSFET memory devices with Si and Au nanocrystal embedded gate dielectric stacks. We considered an undoped long channel DG MOSFET, having a multilayer SiO2 (5 nm)–Si/Au nc embedded Si3N4 (6 nm)–SiO2 (7 nm) gate dielectric. From a quasi-1-D analytic solution of the Poisson equation, the potential and the electric fields in the substrate and the different layers of the gate oxide stack were derived. Thereafter following a trap-like model using the WKB approximation, we have investigated the Fowler Nordheim tunneling currents from the Si inversion layer to the embedded nanocrystal states in such devices. We evaluated the write-erase characteristics, gate tunneling currents, threshold voltage shifts and the output characteristics of the NVM devices from our analytical model. The performance of the nanoparticle embedded DGMOS memory device was compared with that of a DG SONOS NVM of similar dimensions. From the studies, the nc embedded devices showed better performance than the conventional SONOS DGMOS NVM. Among the two ncs compared the nc-Au embedded device emerged as the better performer in terms of higher charge density, faster charging, higher threshold voltage shift and better charge retention.

Surface-Enhanced Raman Scattering on Ordered Metal Nanodot Array Obtained Using Anodic Porous Alumina

The fabrication of an ordered array of Au nanodots using anodic porous alumina as an evaporation mask, and its application to a substrate for the measurement of surface-enhanced Raman scattering (SERS) were studied. One of the advantageous points of using anodic porous alumina as a template to fabricate nanostructures is that the size, shape and arrangement of the obtained nanostructures can be controlled by changing the geometrical structures of the porous alumina. Au nanodot arrays were obtained by thermal evaporation method. The SERS signals of pyridine molecules adsorbed on the nanodots were detected. The intensity of the SERS signals was strongly dependent on the arrangement of the nanodots. The enhancement factor of the intensity of the incident light on Au nanodots was analyzed by numerical calculations based on finite-difference time-domain (FDTD) method. The obtained SERS substrates are expected to be used for Raman spectra measurement with high sensitivity.

Effective improvement in the distribution of single crystalline diamond nanorods fabricated from the randomly-oriented polycrystalline films

By using the bias-assisted reactive ion etching technique and the etching masks of Au nanodots, the high-density single crystalline diamond nanorods have been obtained from the polycrystalline diamond films with randomly-oriented grains grown on silicon substrates. The inhomogenous distribution of the nanorods mainly results from the existence of grain boundaries in the films, and can be effectively improved by adding the graphite sheet under the substrate. Furthermore, the fabrication mechanism of the nanorod array is carefully investigated in this paper. The morphological evolution is observed by using a scanning electron microscopy technique. Raman measurements are carried out to monitor the phase change during the etching process. It is found that the non-diamond phases are present during the experimental process, and then are completely removed away in the end.

Morphology Control of ZnO Nanowires Grown by Hydrothermal Methods Using Au Nanodots on Al doped ZnO Seed Layer

ZnO nanowires were synthesized by hydrothermal method using Au nanodots on Al doped ZnO (AZO) seed layer to control those density and morphology. Morphology of the synthesized ZnO nanowires could be modified effectively by controlling the feature of Au nanodots obtained from the thickness and post thermal treatment conditions of Au thin films prepared on AZO seed layer. The synthesized ZnO nanowires showed vertically grown features and long length despite relatively short synthesis time, while their density could be controlled effectively by the technique proposed in this study. In particular, the ZnO nanowires synthesized on Au nanodots formed after thermal treatment at 700 °C showed outstanding length and distinctively decreased density.

Photocatalytic nano-optical trapping using TiO2 nanosphere pairs mediated with Mie-scattered near field

The localized enhanced near field on nanostructures has been attracting much attention for a template for size-selective optical trapping (tweezers) beyond the diffraction limit. The near-field optical trapping has mainly been studied using metallic substrates such as Au nanodot pairs, periodic Al nanoslits, nanoapertures on an Au film, etc. In this paper, we newly propose a Mie-scattered-near-field optical trapping scheme for size-selective photocatalytic application using pairs of poly-rutile TiO2 nanospheres. The optical intensity distribution in a 3D-nanogap space between the nanospheres was simulated by a 3D FDTD method. The simulation system consists of the two TiO2 nanospheres placed on a silica substrate in water. The 400-nm excitation laser is used for both the near-field trapping and the photocatalyst excitation. The optical trapping forces were calculated based on the near-field optical intensity distribution. The trapping stiffness for 20-nm polystyrene sphere at a gap distance of 20 nm was 6.4 pN/nm/W. The optical force vector shows that the object like virus can be trapped with sufficient forces into the nanogap space and then is driven into the direct surface of the TiO2 sphere. This result suggests that this system works as a photocatalytic trapping for killing virus, protein, etc.

Facile synthesis of spherical nanoparticles with a silica shell and multiple Au nanodots as the core

Highly spherical nanoparticles with a core comprising multiple gold (Au) nanodots and a silica shell (multi-Au@SiO2 NPs) were successfully synthesized through a reverse (water-in-oil) microemulsion-based method. The microemulsion was prepared by mixing a surfactant (Brij35), cyclohexane, n-hexanol, and aqueous HAuCl4 solution. Multiple Au nanodots with a maximum diameter of ∼5 nm could be encapsulated within a silica matrix during the growth process. The size of the multi-Au@SiO2 NPs and the number of Au nanodots doped could be controlled by varying the water-to-Brij35 ratio and the amount of the precursor of cationic gold ions. This is a novel and simple synthetic approach for generating hybrid Au–silica nanomaterials by encapsulating multiple Au nanoparticles within a silica matrix.

Block copolymernanolithography to manufacture nanopatterned gold substrate for surface-initiated polymerization

The diblock copolymer polystyrene-block-polyethylene oxide forms phase-separated cylindrical nanopatterns with two oriented phases perpendicular to the substrates, which provides a great opportunity for directed flow/diffusion through one of the phases. This work aims to construct a nanopattern of nanoparticles on a surface using the directed diffusion of metal nanocrystals through hydrophilic polyethylene oxide (PEO) domains onto the surface, where specific bonding interactions between the nanocrystals and the surface chemical functionality occurs to immobilize the gold nanoparticles on the surface. Gold nanocrystals approximately 12 ± 3 nm in size are allowed to diffuse through about 21 ± 1 nm swollen PEO domains on aminopropyltrimethoxysilane-modified silicon and react with the amino groups via chelating or ion-pairing interactions, forming uniform Au nanodot patterns. The Au nanodot patterns can be used for further attachment, for example, grafting polymer brushes. The morphology of the Au nanopatterns evolves with polymer growth until the Au nanodots are completely masked by polymer brushes. The Au nanopatterns can also be used as substrates for microcontact printing initiators followed by polymer grafting, i.e., nanolithography (20–30 nm, block copolymer) and micropattern technology (2–20 μm, PDMS stamps), which are combined in this manner to construct a dual-patterned structure.

Atmospheric microplasma-functionalized 3D microfluidic strips within dense carbon nanotube arrays confine Au nanodots for SERS sensing

An atmospheric microplasma jet produces three-dimensional (3D) microfluidic channels on dense arrays of vertically aligned carbon nanotubes, which confines Au nanodot aqueous solution. The resulting hybrid 3D nanostructure is exploited as an effective microscopic area-selective sensing platform based on surface-enhanced Raman scattering.

Optical Properties of Multilayer Ordered Gold Nanodot Array Fabricated by a Thermal Dewetting Method

A new efficient and low-cost method to fabricate multilayer ordered nanodot array is developed. In this method, firstly, a 2D nanodot array is fabricated by combination of Nano Plastic Forming (NPF) patterning of Au layer coated on the substrate and thermal dewetting induced self-organization. Then, multilayer ordered Au nanodot array is fabricated by repeating SiO2 deposition and Au deposition followed by thermal dewetting. Feasibility of this process was verified experimentally. The absorbance spectra of the fabricated ordered Au nanodot arrays show strong localized surface plasmon resonance (LSPR) with narrow bandwidth. It is shown that the absorbance spectra of a 2D nanodot array can be tuned by controlling annealing temperature. It is also found that intensity of the absorbance spectrum increases linearly with the increase of the number of layers. This enhanced absorbance gives rise to great potential in biosensing devices.

SERS in Ordered Array of Geometrically Controlled Nanodots Obtained Using Anodic Porous Alumina

The fabrication of geometrically controlled nanodot arrays based on anodic porous alumina and their application as substrates used for surface-enhanced Raman scattering (SERS) measurements were studied. Ordered arrays of circular, square, and triangular Au nanodots were obtained using anodic porous alumina as an evaporation mask. The shape and arrangement of the nanodots were precisely controlled by adjusting the geometrical structure of the nanoholes in the anodic porous alumina. We also fabricated triangular nanodots that had sharp corners with a curvature radius of 15 nm. SERS spectra of pyridine molecules adsorbed on the Au nanodots were measured using the obtained nanodot arrays as substrates for measurements. The SERS intensity obtained from the triangular nanodot array was strongly enhanced compared with that obtained from the array of circular nanodots. The intensity of signals was dependent on the shape and arrangement of the nanodots. It is expected that nanodot arrays obtained by this fabricati...

In vivo Metabolic Imaging of Insulin with Multiphoton Fluorescence of Human Insulin–Au Nanodots

Functional human insulin-Au nanodots (NDs) are synthesized for the in vivo imaging of insulin metabolism. Benefiting from its efficient red to near infrared fluorescence, deep tissue subcellular uptake of insulin-Au NDs can be clearly resolved through a least-invasive harmonic generation and two-photon fluorescence (TPF) microscope. In vivo investigations on mice ear and ex vivo assays on human fat tissues conclude that cells with rich insulin receptors have higher uptake of administrated insulin. Interestingly, the insulin-Au NDs can even permeate into lipid droplets (LDs) of adipocytes. Using this newly discovered metabolic phenomenon of insulin, it is found that enlarged adipocytes in type II diabetes mice have higher adjacent/LD concentration contrast with small-sized ones in wild type mice. For human clinical samples, the epicardial adipocytes of patients with diabetes and coronary artery disease (CAD) also show elevated adjacent/LD concentration contrast. As a result, human insulin-Au nanodots provide a new approach to explore subcellular insulin metabolism in model animals or patients with metabolic or cardiovascular diseases.

Facile preparation of luminescent and intelligent gold nanodots based on supramolecular self-assembly

A new strategy for preparing luminescent and intelligent gold nanodots based on supramolecular self-assembly is described in this paper. The supramolecular self-assembly was initiated through electrostatic interactions and ion pairing between palmitic acid and hyperbranched poly(ethylenimine). The resulting structures not only have the dynamic reversible properties of supramolecules but also possess torispherical and highly branched architectures. Thus they can be regarded as a new kind of ideal nanoreactor for preparing intelligent Au nanodots. By preparing Au nanodots within this kind of supramolecular self-assembly, the environmental sensitivity of intelligent polymers and the optical, electrical properties of Au nanodots can be combined, endowing the Au nanodots with intelligence. In this paper, a supramolecular self-assembly process based on dendritic poly(ethylenimine) and palmitic acid was designed and then applied to prepare fluorescent and size-controlled Au nanodots. The pH response of Au nanodots embodied by phase transfer from oil phase to water phase was also investigated.

Nanopattern Fabrication of Gold on Hydrogels and Application to Tunable Photonic Crystal

Pattern fabrication was performed by transcribing Au nano-dots from Si to the hydrogel surface. The nano-dots exhibited excellent adhesion despite extensive hydrogel expansion and contraction. Au nano-dots on a hydrogel can produce iridescent color, and its spectral response can be finely modulated by controlling the nano-dot spacing. This is a novel tunable photonic crystal made from soft and wet matter.

Conductance Statistics from a Large Array of Sub-10 nm Molecular Junctions

Devices made of few molecules constitute the miniaturization limit that both inorganic and organic-based electronics aspire to reach. However, integration of millions of molecular junctions with less than 100 molecules each has been a long technological challenge requiring well controlled nanometric electrodes. Here we report molecular junctions fabricated on a large array of sub-10 nm single crystal Au nanodots electrodes, a new approach that allows us to measure the conductance of up to a million of junctions in a single conducting atomic force microscope (C-AFM) image. We observe two peaks of conductance for alkylthiol molecules. Tunneling decay constant (β) for alkanethiols, is in the same range as previous studies. Energy position of molecular orbitals, obtained by transient voltage spectroscopy, varies from peak to peak, in correlation with conductance values.

Synthesis, structure, and biocompatibility of pulsed laser-deposited TiN nanowires for implant applications

A bottom-up based pulsed laser deposition technique has been used to grow titanium nitride (TiN) nanowires on single crystalline substrates. The first step of this method is the dissolution of laser ablated gaseous TiN material in the nanodimensional catalytic gold (Au) liquid islands located on the substrate surfaces. The continuous dissolution of TiN results in the supersaturation of liquid Au with TiN followed by extrusion of solid TiN material in the nanowire form at the liquid/solid interface. The growth of TiN nanowires continues as long as its dissolution rate into the catalyst Au matches the extrusion rate of solid TiN. This bottom-up approach gives rise to a one-dimensional TiN nanowire structures (length: 200-300 nm and diameter: 20-30 nm) capped with Au. The ascent of Au nanodots to the top of TiN nanowires can be explained based on breaking of weaker bonds and building of stronger bonds. The TiN nanowires are provided vertical alignment by selecting a plane of the substrate that provides the least lattice mismatching to the (111) plane of TiN which has lower surface energy than its other planes: (100) or (110). After the successful formation and structural characterization, a lactate dehydrogenase (LDH) release assay has been used to confirm the biocompatibility and cytotoxicity of these nanowires.

Direct Nanoscale Observation of Resistance Switching with Au Nano-Dots Embedded Nb<SUB>2</SUB>O<SUB>5</SUB> by Scanning Tunneling Microscopy

Direct Nanoscale Observation of Resistance Switching with Au Nano-Dots Embedded Nb<SUB>2</SUB>O<SUB>5</SUB> by Scanning Tunneling Microscopy

Study on nano dots formation by thermal dewetting and transfer to plastic films

This paper proposes a method to fabricate ordered metal nano dot arrays by combination of nano plastic forming, coating, thermal dewetting, and transferring to plastic substrates. The shape and contact angle of the dots on master substrate are the key factors for successfully transferring to plastic substrates. The effects of process parameters such as indentation load, coating thickness, annealing temperature, etc. on the formation of nano dot arrays on master substrate and dots transfer to PDMS films are investigated. The results show that the ordered Au nano dots arrays are successfully formed on pre-patterned substrates and the transfer of ordered nano dot arrays to plastic films is feasible.

Bottom Electrode Modification of ZrO2 Resistive Switching Memory Device with Au Nanodots

The resistive switching properties of the ZrO2 memory devices with bottom electrode modification by using Au nanodots are investigated in this study. The regular arrays of Au nanodots are fabricated on Pt bottom electrode by nanosphere lithography. Due to the tip of the Au nanodots on the Pt bottom electrode, it causes the higher electric field within the ZrO2 film above the nanodots due to reduced effective film thickness and induces the localized conducting filaments easily. The operation parameters' variation for switching devices is, therefore, suppressed with lower operation voltage and resistance ratio. Long retention time (>106 s) and stubborn nondestructive readout test (>104 s) at room temperature and 150 °C are also demonstrated in this device.

Bottom Electrode Modification of ZrO2Resistive Switching Memory Device with Au Nanodots

Bottom Electrode Modification of ZrO₂Resistive Switching Memory Device with Au Nanodots

Fabrication, characterization, and mechanism of vertically aligned titanium nitride nanowires

Titanium nitride (TiN) nanowires have been grown on single crystal magnesium oxide (MgO) substrates using a bottom-up pulsed laser deposition method where Ti–N based gaseous reactants in the laser plume supersaturate the catalytic gold (Au) liquid located on the substrate surfaces. Growth of TiN continues as long as the dissolution rate of material into the catalyst matches the extrusion of solid material at the liquid/solid interface. This bottom-up approach gives rise to a one-dimensional TiN nanowire structure (length: 200–300nm and diameter: 20–30nm) capped with a catalytic Au seed. The ascent of Au nanodots to the top of TiN nanowires can be explained based on breaking of weaker bonds and formation of stronger bonds. From strength point of view, these bonds are listed here in order of decreasing strength as follows: Ti–O (672kJ/mol)>Ti–N (496kJ/mol)>Au–N (416kJ/mol)>Au–O (221kJ/mol). The TiN nanowires were provided vertical alignment by selecting a plane of the substrate that provides the least lattice mismatching to the (111) plane of TiN which has lower surface energy than its other planes: (100) or (110).