Nano Tips Research Articles

A comparison of optical properties of ZnO nanorods and ZnO nanotips for improving light absorption in rGO/ZnO nanostrctures

In this study, two types of ZnO nanostructures (ZnO nanotips and ZnO nanorods) were synthesized through a chemical bath deposition (CBD) method. These two structures were then compared by optical and structural analyses. The result showed the significant effect of ammonia concentration and the preferential etchings along the c axis on the formation of ZnO nanotips (NTs). To improve the absorption, nanostructures were optimized by reflectance analysis. To enhance the optical properties of the optimized sample, reduced graphene oxide (rGO) layers were transferred on the ZnO NTs surface by the electrophoretic deposition (EPD) method. The deposition of rGO layers on ZnO NTs can increment the optical absorption over a wide range of frequencies. The reflectance results showed enhanced adsorption capacity in the case of rGO/ZnO NTs.

Synthesis of mesoporous-silica coated multi-branched gold nanoparticles for surface enhanced Raman scattering evaluation of 4-bromomethcathinone

Mesoporous silica-coated multi-branched gold nanoparticles (bAu@mesoSiO2) aiming for enhanced Raman sensing for 4-bromomethcathinone (4-BMC) detection is reported. In this work, we present an effective strategy to probe the Raman signal of 4-MBC. Morphologies and optical properties of the synthesized materials with different [Au3+]/[Au0] ratios are characterized utilizing transmission electron microscopy (TEM), UV–vis and mid-infrared spectroscopy. Both experimental and theoretical (simulation) studies were investigated. Taking advantages of gold core branches that provide highly localized and strongly enhanced electromagnetic fields due to plasmon resonance, surface-enhanced Raman scattering (SERS) is observed. The experimental results show that the SERS intensity exhibits a 100-fold increase with the increased average length and quantity of gold branches (nano tips). The analytical performance yielded a detection limit of 0.1 mg/ml for the 4-MBC target within 5 mins. The sensing method will likely find further improvement and broad use in the forensic science. Besides rapid detection and portability, the combination of the Raman effect and enhanced materials imparts other notable advantages, such as its non-contact and free of reagents.

Selective Nucleation of GaAs on Si Nanofacets.

The early growth stage of GaAs by metal organic vapor phase epitaxy on a novel kind of Si substrate is investigated. The substrate consists of nanotips (NTs) fabricated on a Si(001) wafer by means of lithography and reactive ion etching. 3D GaAs nanocrystals are found to nucleate with a probability of 90% on the (n0m), (-n0m), (0nm), and (0-nm) facets (n, m integers) of these NTs. Additionally, in terms of nucleation yield, an average of 2 GaAs nanocrystals in each of those facets is observed. By contrast, facets of type {±nnm} remain virtually free of any 3D nuclei. A simple model based on the kinetics of the growth is used to explain the facet selective 3D nucleation. The model is consistent with a similar selectivity observed on micrometer-sized substrate features.

Bi-modal nanoheteroepitaxy of GaAs on Si by metal organic vapor phase epitaxy

Nano-heteroepitaxial growth of GaAs on Si(001) by metal organic vapor phase epitaxy was investigated to study emerging materials phenomena on the nano-scale of III–V/Si interaction. Arrays of Si nano-tips (NTs) embedded in a SiO2 matrix were used as substrates. The NTs had top Si openings of 50–90 nm serving as seeds for the selective growth of GaAs nano-crystals (NCs). The structural and morphological properties were investigated by high resolution scanning electron microscopy, atomic force microscopy, electron backscatter diffraction, x-ray diffraction, and high resolution scanning transmission electron microscopy. The GaAs growth led to epitaxial NCs featuring a bi-modal distribution of size and morphology. NCs of small size exhibited high structural quality and well-defined {111}–{100} faceting. Larger clusters had less regular shapes and contained twins. The present work shows that the growth of high quality GaAs NCs on Si NTs is feasible and can provide an alternate way to the integration of compound semiconductors with Si micro- and opto-electronics technology.

Structural and optical characterization of GaAs nano-crystals selectively grown on Si nano-tips by MOVPE

We present the nanoheteroepitaxial growth of gallium arsenide (GaAs) on nano-patterned silicon (Si) (001) substrates fabricated using a CMOS technology compatible process. The selective growth of GaAs nano-crystals (NCs) was achieved at 570 °C by MOVPE. A detailed structure and defect characterization study of the grown nano-heterostructures was performed using scanning transmission electron microscopy, x-ray diffraction, micro-Raman, and micro-photoluminescence (μ-PL) spectroscopy. The results show single-crystalline, nearly relaxed GaAs NCs on top of slightly, by the SiO2-mask compressively strained Si nano-tips (NTs). Given the limited contact area, GaAs/Si nanostructures benefit from limited intermixing in contrast to planar GaAs films on Si. Even though a few growth defects (e.g. stacking faults, micro/nano-twins, etc) especially located at the GaAs/Si interface region were detected, the nanoheterostructures show intensive light emission, as investigated by μ-PL spectroscopy. Achieving well-ordered high quality GaAs NCs on Si NTs may provide opportunities for superior electronic, photonic, or photovoltaic device performances integrated on the silicon technology platform.

Wavelength and shape dependent strong-field photoemission from silver nanotips

We study optical field emission from silver nanotips, showing the combined influence of the illumination wavelength and the exact shape of the nanotip on the strong-field response. This is particularly relevant in the case of FIB milled nano tips, where the nanotip fabrication capabilities could become a new ingredient for the study of strong-field physics. The influence of the thermal load on the nanotip and its effect on the emission is studied as well by switching the repetition rate of the laser source from 1 kHz to 62 MHz, showing a clear transition towards the quenching of the strong-field emission.

Site controlled red-yellow-green light emitting InGaN quantum discs on nano-tipped GaN rods.

We report a method of growing site controlled InGaN multiple quantum discs (QDs) at uniform wafer scale on coalescence free ultra-high density (>80%) nanorod templates by metal organic chemical vapour deposition (MOCVD). The dislocation and coalescence free nature of the GaN space filling nanorod arrays eliminates the well-known emission problems seen in InGaN based visible light sources that these types of crystallographic defects cause. Correlative scanning transmission electron microscopy (STEM), energy-dispersive X-ray (EDX) mapping and cathodoluminescence (CL) hyperspectral imaging illustrates the controlled site selection of the red, yellow and green (RYG) emission at these nano tips. This article reveals that the nanorod tips' broad emission in the RYG visible range is in fact achieved by manipulating the InGaN QD's confinement dimensions, rather than significantly increasing the In%. This article details the easily controlled method of manipulating the QDs dimensions producing high crystal quality InGaN without complicated growth conditions needed for strain relaxation and alloy compositional changes seen for bulk planar GaN templates.

The fabrication of high-aspect-ratio cylindrical nano tool using ECM

With the miniaturization of various types of components and devices, micro- and nanometer-scale tools are increasingly in demand. Electrochemical machining (ECM) is a well-established technique for the fabrication of micro tools and nano tips. This paper presents a machining method for the fabrication of a high-aspect-ratio cylindrical nano tool using liquid membrane ECM, in which a straight reciprocating motion is applied to the anodic electrode. The method is based on periodic machining of the anodic rod within the amplitude of the straight reciprocating motion. In this process, the machining rate within amplitude varies periodically, allowing nano tools with high aspect ratios to be obtained by the presented method. Experiments were conducted to verify the proposed method. The influences of applied voltage, electrolyte concentration, amplitude and velocity of the straight reciprocating motion on the fabrication of cylindrical nano-electrode were investigated. By using this method, nano-electrodes with average diameters of several hundred nanometers and aspect ratios up to 70 were successfully fabricated.

Fabrication of CoPt Ultra-Sharp Single Atom Tips

Two kinds of new nano tips with potential to magnetic application are fabricated. One is a PtCo alloy pyramidal tip formed by surface faceting, the other is a Pt based Co tip formed by the epitaxy with a proper growth mode. Ultra high vacuum-field ion microscopy with atomic resolution is used to investigate the atomic structures of the tip apex after various sharpen treatments.

Broadband and wide-angle antireflection subwavelength structures of Si by inductively coupled plasma etching using dewetted nanopatterns of Au thin films as masks

We report the broadband and wide-angle antireflection subwavelength structures (SWSs) on silicon (Si) substrate by inductively coupled plasma (ICP) etching using gold (Au) nanopatterns as etch masks. The reflectance depends strongly on the etched profile of Si SWSs which is influenced by both thermal dewetting and etching conditions. The size, shape, and array geometry of nano-sized patterns, which are produced via the thermal dewetting of Au thin films, are optimized under proper heat treatment. The etched depth and shape of Si nano tips are controlled additionally by ICP power, thus achieving the efficient antireflection characteristics. The optimized Si SWS with the tapered structure and sharp tips at high ICP power leads to a significantly low reflectance value of <1% at wavelengths of 350–1100nm. Furthermore, it exhibits a wide-angle antireflection property of <7.5% at incident angles of 8–70° over a wide wavelength range of 300–1100nm.

Nanofabrication based on MEMS technology

In this paper, a novel nanofabrication method that develops from the traditional microelectromechanical system (MEMS) technology of anisotropic etching, deep reaction ion etching, and sacrificial layer process has been reviewed based on our work. With such a technology, nano tips, nano wires, nano beams even nano devices can be fabricated in a batch process. Beams with thickness of only 12 nm, a nano tip with a heater on the beam, and a nano wire whose width and thickness is only 50 nm are demonstrated. The scale effect of the Young's modulus of silicon has been observed and the nano-electronic-mechanical data storage has been presented

P-97: Nano-Tip Enhanced Nanoplasma Devices for Plasma-Display Application

Nano-plasma devices with nano-tip enhanced electrodes have been fabricated and operated successfully in Neon gas. Combining the nano tips and the rear panel metal electrode of panel type nanoplasma device specifically heighten the device properties, such as ignition voltage, sustain voltage, brightness, etc. The current-voltage characteristics of nanoplasma devices have been examined by DC pulsed waveform with different frequencies from 2 to 20 kHz in 400 Torr of Neon gas.

EXTREMELY SHARP {111}-BOUND, SINGLE-CRYSTALLINE SILICON NANO TIPS

This paper presents (111) nano tips made using (111) single crystalline silicon. Many research efforts have reported on the fabrication methods of micro and nano tips in silicon. Most of the developed fabrication methods are based on (100) or (110) silicon. However, (111) silicon will give the sharpest {111}-bounded nano tips, and in addition, (111) silicon has the best mechanical properties compared with other types of silicon. In this paper, we use (111) silicon wafers to fabricate two type of nano tip. One type is the sharpest nano tip that can be fabricated by using only {111} silicon planes. The other type is a high aspect ratio nano tip, which is composed of one {111} plane and two vertical passivation planes. In the first case, the tip height is 5 μm and the total cone angle of the tip is 54.7°, which represents the sharpest angle for a nano tip bounded only by {111} planes on silicon. In the second case, the nano tip height is 15 μm, and the aspect ratio is greater than 3:1. The cone angle of the nano tip is only 19.5°. The tip radius is less then 10 nm, which is of the sharpest {111}-bound, single-crystalline-silicon nano tips.

DRY AND WET ETCHING WITH (111) SILICON FOR HIGH-PERFORMANCE MICRO AND NANO SYSTEMS

Etching with (111) silicon is relatively new, but it represents very exciting opportunities in micro and nano system applications. By combining wet and dry anisotropic etching, high-precision, actuatable micro and nano structures can be fabricated in single-crystalline silicon. This paper reviews several relevant (111) microfabrication results reported in the literature. Among these, a single-mask process that we call sacrificial bulk micromachining (SBM) is reviewed in detail. Various electrical isolation methods as well as a number of applications to micro and nano systems are presented.