Formation Of Au Nanostructures Research Articles

Formation of Au nanostructures on the surfaces of annealed [formula omitted] thin films

One of the promising methods for high-throughput fabrication of nanostructures is the spontaneous dewetting of an as-deposited thin film. The formation process of Au nanostructures (AuNS) on TiO2 thin films consisted of two steps: formation of Au thin films and post-deposition annealing at 500∘C temperature in Ar gas environment for 60 minutes. TiO2 thin films were deposited using reactive magnetron sputtering method on SiO2 and fused quartz substrates and soaked at 500∘C and 900∘C temperatures to understand the influence of crystalline structure and surface morphology of Au and TiO2 thin films on the formation of AuNS. Properties of the deposited thin films were investigated using XRD, SEM, AFM, and RAMAN. The mean diameter (Dmean), mean area of AuNS (Amean), and mean distance between centroids of nearest neighbor AuNS (NNDcentr) increased exponentially when thicker nanocrystalline Au films were annealed. Standard deviation from Dmean and coefficient of variation also increased indicating higher dispersion of AuNS diameter. It was found that the influence of surface roughness increased by annealing thicker nanocrystalline Au thin films. Dmean, Amean, and NNDcentr increased and the density of AuNS (n) decreased (hAu: 10 nm and 15 nm) with decreasing Rq of TiO2 thin films. The peaks of absorbance (500 nm- 750 nm) were broad and not symmetrical indicating multiple localized surface plasmon resonance (LSPR) from various size AuNS. The position of peak shifted to the longer wavelengths when Dmean and NNDcentr was larger.

One-Step and Spontaneous in Situ Growth of Popcorn-like Nanostructures on Stretchable Double-Twisted Fiber for Ultrasensitive Textile Pressure Sensor.

Highly conductive fibers play an essential role in the development of electronic textiles for wearable devices. Even though great progress has been made recently, big challenges of developing simple and rapid methods to prepare functional fibers with stretchability, high sustainability, and electrical conductivity still remain. Herein, we proposed a simple, rapid, and scalable approach to fabricate stretchable and conductive fibers by growing Au nanostructures on a double-twisted fiber coated with metallic MoS2 nanosheets. The formation of Au nanostructures with a unique "popcorn"-like shape (namely, Au "nanopopcorn", AuNPC) occurs instantaneously and spontaneously on the surface of MoS2-coated fiber, without any additional reducing reagents or heating conditions. Moreover, the overall fabrication process takes less than 5 min, demonstrating the realization of fast fabrication of functional conductive fibers. The obtained fiber with piezoresistive property can be fabricated into a pressure sensor. The unique morphology of AuNPC with a rough surface can significantly enhance the performance of the pressure sensor, with high sensitivity of up to 0.19 kPa-1 and a fast response time of 93 ms. Furthermore, the functional fiber can be woven into electronic textiles with sensing arrays, which has multiple two-dimensional (2D) force mapping properties. Therefore, we envision that this simple, rapid, and scalable method to fabricate conductive functional fibers would show great potential in the field of electronic textiles and wearable devices.

Nanostructuring and wettability of ion treated Au thin films

The formation of Au nanostructures (NSs) under 8 keV Ne+ ion treatment of Au thin film is investigated to explore the involved mechanism using experimental and theoretical approaches. This study is based on atomic force microscopy, Rutherford backscattering spectrometry, and contact angle measurements. The results are discussed in the light of the thermal spike model and tridyn simulation. It is observed in the simulations that Ne ion treatment results in ejection of atoms from the surface due to elastic collision induced transfer of energy and increase in lattice temperature due to the formation of thermal spikes. The effect of ion dose on the surface morphology is also explored using a two-dimensional detrended fluctuation analysis (DFA).The DFA gives information about the fractal dimension (Df) and Hurst exponent (H) of the surface. The fractal dimension (Df) shows that irregularity of a surface is significantly influenced by ion treatment. The contact angle of the water droplet with the surface is discussed with the interface width and fractal dimension. The competition among nuclear sputtering, de-wetting, and diffusion processes results in the formation of NSs. It also demonstrates that the experimental findings are in good agreement with the theoretical results.

Facile preparation of SERS and catalytically active Au nanostructures using furfuryl derivatives

Six different types of Au nanostructures with rough surfaces were readily prepared through the redox reactions between Au precursor, AuCl4−, and furfuryl derivatives without extra metal surface capping ligands, in deionized water at room temperature. Furfuryl alcohol (FA) or furfurylamine (FFA) was used as a sole reducing agent for the reduction of Au precursor. Both FA and FFA effectively polymerized during the redox reactions to form polyfuran polymers. These polymers are thought to act as surface capping ligands during the formation of Au nanostructures. Experiments were conducted with three different concentrations of each furfuryl derivative. Interestingly, Au particles prepared from the reaction with varying concentration of FA or FFA showed large differences in size, and revealed that the higher the ratios of [FA]/[AuCl4−] or [FFA]/[AuCl4−], the smaller the size of Au particles. The size of Au particles was in the range of 1μm to under 30nm. Among these samples, two nanostructured Au particles, AuFA-4 and AuFFA-1, deposited on a Si wafer by a simple drop-casting method, were revealed as highly active surface-enhanced Raman scattering (SERS) substrates for the detection of methylene blue (MB) and crystal violet (CV). High SERS enhancement factors (EFs) of 106∼108 for MB and CV were observed. Small size Au nanoparticles (AuFFA-2 and AuFFA-4) were also found to be very active for the catalytic hydrogenation of 4-nitrophenol to 4-aminophenol in the presence of NaBH4 at room temperature. AuFFA-2 could be recycled eight times, without losing its activity.

Electrodeposited gold nanostructures at Nafion–poly(o-phenylenediamine) modified electrode and its electrocatalytic application

A facile method to prepare gold (Au) nanostructures at the Nafion–poly(o-phenylenediamine) (Nf–PPD) composite film modified electrode (ITO or GC/Nf–PPD/Au) and its application toward the electrocatalytic reduction of oxygen in acidic medium are reported. The formation of Au nanostructures at the Nf–PPD composite film modified electrode was monitored by in-situ spectroelectrochemical method. The oPD monomer was oxidatively polymerized during the electrodeposition of Au nanostructures. The Nf–PPD/Au modified electrode was characterized by cyclic voltammetry, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses. The composite film formed on the electrode surface was dissolved in ethanol and the Au nanostructures were characterized by high resolution transmission electron microscopy (HRTEM) analysis. The HRTEM images showed the formation of ginger shaped Au nanostructures by a fusion growth process at the Nf–PPD film. The GC/Nf–PPD/Au modified electrode displayed a better electrocatalytic activity in terms of peak current density, mass activity and stability toward oxygen reduction reaction (ORR) in acidic medium than the other controlled modified electrodes investigated in this work. The presence of PPD and Au nanostructures in the Nf matrix at the modified electrode showed a synergistic catalytic activity in the ORR.

Creation of self-organized gold nanostructures by keV ion beam irradiation

We synthesized Au nanostructures on glass by low-energy ion irradiation of a thin Au film. The Au films, deposited on a glass substrate, were irradiated by 50 keV Si− ions with different fluences. The UV–vis absorption spectroscopy of irradiated samples indicates the surface plasmon resonance peak, which is a signature of the formation of Au nanostructures. The surface morphology of the films has been characterized by atomic force microscopy, which supports the UV–vis spectroscopy findings. The metal content or the film thickness of the samples, as measured by Rutherford backscattering spectroscopy, decreased with increasing fluence, showing sputtering by ion irradiation and tailing in the lower energy edge with irradiation, revealing recoil implantation. The formation of Au nanostructures by this method can be explained on the basis of an interplay between surface instability due to ion beam sputtering and surface diffusion.

Formation of Au Nanostructures through an Alumina Mask by Laser-Assisted Deposition

We report a new method to produce ordered arrays of metal nanostructures on substrates. The method employs a through-hole nanoporous alumina membrane as a mask that is attached onto the substrate, silicon in this study. The material of deposition, Au in this study, was provided by pulsed laser ablation of a target gold. At an early stage of the deposition, a significant portion of Au penetrated the alumina through-holes and formed an ordered nanodot array on the silicon surface. At the later stage, the through-hole deposition was blocked by the growth of Au film on the top surface of the alumina, so that the heights of the Au nanodots were limited to about 10 nm under current experimental conditions. Subsequent attempts to clean up the top surface of the alumina with a lower power laser illumination resulted in the formation of new nanostructures around the alumina pores, nanospheres, or nanorings, depending on the fluence of the laser and the duration of the cleanup. We will discuss the underlying mechanism of the formation of these nanostructures.