Au Doping Research Articles

Effect of Au Nanoparticles Doping on The Properties of TiO2 Thin Films

In this study, pure and gold (Au) nanoparticles doped TiO2 thin films (Au/Ti = 10, 20, 30, 40 and 50 at%) were prepared by sol-gel method and the impact of Au nanoparticles doping on the optical, structural and morphological properties of these thin films was examined. All thin films were characterized using ultraviolet-visible-near infrared (UV-Vis-NIR) spectrophotometry, X-ray diffraction (XRD), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The optical band gap of the thin films increases from 3.74 eV to 3.89 eV with the increase of Au nanoparticles concentrations due to the Moss-Burstein effect. XRD results show that all thin films have cubic poly-crystal structure and the intensities of peaks of the crystalline phase increased with the increase of Au nanoparticles concentrations. The AFM results indicate that the TiO2 thin films are formed from the nanoparticles and the grain size of the films is changed with Au doping level. Consequently, it is shown that the structural, morphological and optical properties of the TiO2 thin films could be changed by Au nanoparticles-doping. DOI: http://dx.doi.org/10.5755/j01.ms.20.1.3709

Electronic and optical properties of Au-doped Cu2O: A first principles investigation

The Cu2O and Au-doped Cu2O films are prepared on MgO (001) substrates by pulsed laser deposition. The X-ray photoelectron spectroscopy proves that the films are of Au-doped Cu2O. The optical absorption edge decreases by 1.6% after Au doping. The electronic and optical properties of pure and Au-doped cuprite Cu2O films are investigated by the first principles. The calculated results indicate that Cu2O is a direct band-gap semiconductor. The scissors operation of 1.64 eV has been carried out. After correcting, the band gaps for pure and Au doped Cu2O are about 2.17 eV and 2.02 eV, respectively, decreasing by 6.9%. All of the optical spectra are closely related to the dielectric function. The optical spectrum red shift corresponding to the decreasing of the band gap, and the additional absorption, are observed in the visible region for Au doped Cu2O film. The experimental results are generally in agreement with the calculated results. These results indicate that Au doping could become one of the more important factors influencing the photovoltaic activity of Cu2O film.

Synthesis and characterisations of Au-nanoparticle-doped TiO2 and CdO thin films

In the present study, pure and gold nanoparticle (Au NP)-doped titanium dioxide (TiO2) and cadmium oxide (CdO) thin film were prepared by the sol–gel method, and the effect of Au NP doping on the optical, structural and morphological properties of these thin films was investigated. The prepared thin films were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and ultraviolet–visible–near infrared (UV–Vis–NIR) spectra. While the optical band increases from 3.62 to 3.73 for TiO2 thin films, it decreases from 2.20 to 1.55 for CdO thin films with increasing Au doping concentration. Analysis of XRD indicates that the intensities of peaks of the crystalline phase have increased with the increasing Au NP concentrations in all thin films. SEM images demonstrate that the surface morphologies of the samples were affected by the incorporation of Au NPs. Consequently, the most significant results of the present study are that the Au NPs can be used to modify the optical, structural and morphological properties of TiO2 and CdO thin films.

Enhanced Mineralization of Gaseous Organic Pollutant by Photo-Oxidation Using Au-Doped TiO2/MCM-41

The synthesis, characterization, and photocatalytic evaluation of titania-loaded MCM-41 with and without Au doping are reported in the present study. The samples were characterized by powder XRD, TEM, low temperature N2 adsorption/desorption, UV–Vis, and FTIR. UV-induced vapor-phase photo-oxidation of acetone was used as a probe reaction to study the role of Au in mineralization of volatile organic compounds (VOCs), viz. acetone at different concentrations. The doping of Au in titania-loaded MCM-41 resulted in the decrease of BET surface area, total pore volume, and average pore size. UV–Vis diffuse reflectance spectra of Au-doped titania-loaded MCM-41 showed the red shift in their absorption bands compared to titania-loaded MCM-41. The activity of mineralization of acetone by photocatalysis for 2 % Au-doped titania-loaded MCM-41 was found to be ∼1.6 times higher than titania-loaded MCM-41. The presence of cocatalytic nanosized gold might be responsible for their enhanced activity on account of the delayed recombination of electron/hole pair. Although, almost complete mineralization of acetone was observed irrespective of the initial concentration of acetone in air (up to 3.72 mol%) by all the catalysts, 2 wt.% Au-doped titania-loaded MCM-41 has shown the most enhanced activity.

Gd doped Au nanoclusters: Molecular magnets with novel properties

The structural, magnetic, and optical properties of subnanometer AuN and AuN−1Gd1 gas phase clusters (N=2 to 8) are systematically investigated in the framework of (time-dependent) density functional theory, using the B3LYP hybrid exchange correlation functional. The size dependent evolution of the gap between the highest occupied and lowest unoccupied molecular orbitals, the magnetism, and the absorption spectra are studied. The simultaneous appearance of large magnetic moments, significant band gaps, and plasmon resonances in the visible spectral region leads to novel multi-functional nanomaterials for applications in drug delivery, magnetic resonance imaging, and photo-responsive agents.

Field emission performance enhancement of Au nanoparticles doped graphene emitters

Graphene (GP) field emitters fabricated by the electrophoretic deposition (EPD) and their field emission performance can be enhanced and tailed simultaneously by chemical doping Au nanoparticles (NPs). It was found that doped Au NPs could both decrease the resistance of GP emitters and increase the density of field emission sites. The Au-doped GP emitters showed lower turn-on voltage, lower threshold field, higher field enhancement factor, higher luminance intensity, and emitting uniformity, compared with that of pristine GP. This study will provide us to further understand the role of doping effect on the GP emitters used for the future display.

First-principles study of electrical structures and optical properties of Ag or Au doped MgF2 crystal

The geometric structure, electronic and optical properties of MgF2 crystal mixed with Ag, Au are obtained by adopting the first-principles calculation of plane wave ultra-soft pseudo-potential technology based upon the density function theory (DFT). The calculation results show that the doping of Ag and Au diminishes of the MgF2 system and the occurrence of half-metallic properties with a greater influence of Au than Ag. In addition, the refractive index and absorption coefficient of the MgF2 system are enhanced because of the doping. The modulation action on the refractive index of MgF2 indicates potential application of the forbidden bandwidth doping in optical devices.

Contour mapping 2D and 3D-photoluminescence of Au-doped one-dimensional Eu(III) and Tb(III) hydroxide and oxide nanostructures

Abstract Au nanoparticles were embedded in one-dimensional Eu(III) and Tb(III) hydroxide and oxide nanostructures, and the Au doping effect was understood by contour mapping 2D and 3D-photoluminscecne profiles. Photoluminescence intensity was commonly quenched by dipole–dipole coupling between Au NPs and luminescent centers. The 5 D 0 → 7 F J emission of Eu(III) was observed by a direct excitation of Eu(III), while the emission was further quenched upon annealing, and only observed by an indirect excitation. The 5 D 4 → 7 F J emission of Tb(III) was seen before annealing. Upon annealing, the emission was totally quenched, and a broad emission peak was observed at 550 nm.

Enhanced solar energy conversion in Au-doped, single-wall carbon nanotube-Si heterojunction cells

The power conversion efficiency (PCE) of single-wall carbon nanotube (SCNT)/n-type crystalline silicon heterojunction photovoltaic devices is significantly improved by Au doping. It is found that the overall PCE was significantly increased to threefold. The efficiency enhancement of photovoltaic devices is mainly the improved electrical conductivity of SCNT by increasing the carrier concentration and the enhancing the absorbance of active layers by Au nanoparticles. The Au doping can lead to an increase of the open circuit voltage through adjusting the Fermi level of SCNT and then enhancing the built-in potential in the SCNT/n-Si junction. This fabrication is easy, cost-effective, and easily scaled up, which demonstrates that such Au-doped SCNT/Si cells possess promising potential in energy harvesting application.

A DFT study of the NO dissociation on gold surfaces doped with transition metals

The NO dissociation on a series of doped gold surfaces (type TM(n)@Au(111) or TM(n)@Au(110), with TM(n) = Ni, Ir, Rh, or Ag and referring n to the number of dopant atoms per unit cell) was investigated through periodic density functional theory calculations. Generally, doping of Au(111) and Au(110) matrices was found to strengthen the interaction with NO species, with the exception of Ag, and was found to increase the energy barrier for dissociation, with the exception of Ni on Au(111). The calculations suggest that the NO dissociation is only possible in the case of the Ir@Au(110) bimetallic surface but only at high temperatures. The increase of the contents of Ir on Au(110) was found to improve significantly the catalytic activity of gold towards the NO dissociation (E(act) = ∼1 eV). Nevertheless, this energy barrier is almost the double of that calculated for NO dissociation on pure Ir(110). However, mixing the two most interesting dopant atoms resulted in a catalyst model of the type Ir@Ni(110) that was found to decrease the energy barrier to values close to those calculated for pure Ir surfaces, i.e., ∼0.4 eV, and at the same time the dissociation reaction became mildly exothermic.

Water adsorption and dissociation on Ni surface: Effects of steps, dopants, coverage and self-aggregation

Water-metal interaction has been receiving extensive attention due to its interdisciplinary application. In this paper, on the basis of first-principle calculations and slab models, the behavior of water adsorption and dissociation on planar, stepped and blocked Ni surfaces is investigated, the effects of steps, Au and Ag dopants, coverage and self-aggregation of water are also disclosed. The results show that: step not only strengthens water-substrate interaction but also facilitates water dissociation. With dopants modification, the adsorption and dissociation properties remain relatively unchanged at lower coverage (1/9 on facets and 1/12 ML on steps) while at higher coverage (1/4 on facets and 1/6 ML on steps) water adsorption is weakened and dissociation activity decreases dramatically. Water adsorption and dissociation properties on Ni surfaces are essentially unaffected with the increase of coverage. On doped surfaces, adsorption properties and dissociation activities are closely associated with the ligand effect, which is dependent on the dopant, dopant concentration and surface morphology. Water self-aggregation enhances water-surface interaction on all studied surfaces due to hydrogen bond (network) formation. Furthermore, investigation shows that it does not assist water dissociation.

Graphene electrodes transfer-printed with a surface energy-mediated wet PDMS stamp: impact of Au doped-graphene for high performance soluble oxide thin-film transistors

Unlike conventional dry stamp-based printing methodologies, the suggested wet PDMS stamping technique allows for the generation of well-patterned graphene source/drain electrode structures. It is clarified that the electrical characteristics of soluble In–Ga–Zn–O (IGZO) TFTs can be improved effectively by adjusting the work function of transfer-printed graphene electrodes with a simple, facile Au doping technique. By implementing the transfer-printed, Au-doped graphene layers as a source/drain electrode and the newly developed chemical structure-tailored IGZO semiconductors as a soluble channel layer, the high performance graphene/IGZO TFTs are demonstrated with a field-effect mobility of 3.2 cm2 V−1 s−1, which is far superior to the previously reported TFTs employing the printable electrode and a soluble oxide semiconductor.

Au doping of CdS polycrystalline films prepared by co-sputtering of CdS–Cd-Au targets

Au doped CdS polycrystalline films were grown on Corning glass substrates at room temperature by co-sputtering from a CdS–Cd–Au target. Elemental Cd and Au were placed onto the CdS target covering small areas. The electrical, structural, and optical properties were analyzed as a function of Au content. The Au doped CdS polycrystalline films showed a p-type semiconductor nature. It was found that the electrical resistivity drops and the carrier concentration increases as a consequence of Au incorporation within the CdS lattice. In both cases, the changes were of several orders of magnitude.

Singular response to a dopant of an evaporating crystal surface

Moving crystal surfaces can undergo step-bunching instabilities, when subject to an electric current. We show analytically that an infinitesimal quantity of a dopant may invert the stability, whatever the sign of the current. Our study is relevant for experimental results [S. S. Kosolobov et al., JETP Lett. 81, 117 (2005)] on an evaporating Si(111) surface, which show a singular response to Au doping, whose density distribution is related to inhomogeneous Si diffusion.

CO Oxidation at the Interface between Doped CeO2 and Supported Au Nanoclusters.

DFT+U calculations of CO oxidation by Au13 nanoclusters (NCs) supported on either CeO2 or doped (X-Ce)O2 (X = Au, Pt, Pd, Ti, Ru, Zr) show that doping the CeO2 support accelerates CO oxidation by the Mars-van Krevelen mechanism at the Au-(X-Ce)O2 interface. We find that Au, Pd, Pt, and Ti dopants significantly lower the vacancy formation energy of the CeO2 support and that electron donation from the supported Au13 NC shifts the vacancy formation energy of (X-Ce)O2 and determines the final vacancy formation energy of Au13@(X-Ce)O2. The vacancy formation energy of Au13@(X-Ce)O2 is a good reactivity descriptor for CO oxidation at the Au-(X-Ce)O2 interface and a screening factor for dopant selection. Our results confirm that the catalytic activity of oxide-supported Au catalysts can be modified by the chemical composition of the support and suggest that chemical modification of the oxide support is promising for the optimization of oxidation catalysis by supported Au NCs/nanoparticles.

Origin of the Increase of Activity and Selectivity of Nickel Doped by Au, Ag, and Cu for Acetylene Hydrogenation

Activity and selectivity are both important issues in heterogeneous catalysis and recent experimental results have shown that Ni catalysts doped by gold exhibit high activity for the hydrogenation of acetylene with good selectivity of ethylene formation. To unravel the underlying mechanism for this observation, the general trend of activity and selectivity of Ni surfaces doped by Au, Ag, and Cu has been investigated using density functional theory calculations. Complete energy profiles from C2H2 to C2H4 on Ni(111), Au/Ni(111), Ag/Ni(111) and Cu/Ni(111) are obtained and their turnover frequencies (TOFs) are computed. The results show that acetylene adsorption on Ni catalyst is strong which leads to the low activity while the doping of Au, Ag, and Cu on the Ni catalyst weakens the acetylene adsorption, giving rise to the increase of activity. The selectivity of ethylene formation is also quantified by using the energy difference between the hydrogenation barriers and the absolute value of the adsorption ene...

Direct Imaging of Single Au Atoms Within GaAs Nanowires

Incorporation of catalyst atoms during the growth process of semiconductor nanowires reduces the electron mean free path and degrades their electronic properties. Aberration-corrected scanning transmission electron microscopy (STEM) is now capable of directly imaging single Au atoms within the dense matrix of a GaAs crystal, by slightly tilting the GaAs lattice planes with respect to the incident electron beam. Au doping values in the order of 10(17-18) cm(3) were measured, making ballistic transport through the nanowires practically inaccessible.

Spray deposited localized surface plasmonic Au–ZnO nanocomposites for solar cell application

The Au–ZnO nanocomposites were deposited onto the glass and tin doped indium oxide (ITO) coated glass substrates by a simple and cost effective spray pyrolysis technique (SPT) at 450°C. The effect of Au concentration on the properties of ZnO thin films was investigated. The structural evolution of Au–ZnO nanocomposite films with Au doping concentrations is reflected in the X-ray diffraction patterns. The FESEM images reveal uniform and compact distribution of spherical grains/clusters of size ∼60–80nm. A clear indication of localized surface plasmon resonance (LSPR) is observed in optical studies. The band gap energy decreases with Au content. The overall photoelectrochemical (PEC) performance of the samples was investigated and discussed. Moreover, the Au–ZnO samples are more photoactive as compare to the pure ZnO sample and the sample ZnOAu15 shows the highest photocurrent. The photocurrent increases up to 279μAcm−2 and 379μAcm−2 in visible light and in UV illumination, respectively. An improvement in the PEC output parameters is observed because of the increased absorption as well as the energy transfer mechanism from the noble metal (Au) to ZnO.

Au doping effects on electrical and optical properties of vanadium dioxides

Vanadium dioxides were fabricated on normal glass substrates using reactive radio frequency (RF) magnetron sputtering. The oxygen flow volume and annealed temperatures as growth parameters are systematically investigated. The electrical and optical properties of VO2 and Au:VO2 thin films with different growth conditions are discussed. The semiconductor-metal phase transition temperature decreased by ∼10°C for the sample with Au doping compared to the sample without Au doping. However, the optical transmittance of Au:VO2 thin films is much lower than that of bare VO2. These results show that Au doping has a marked effect on the electrical and optical properties.

First-principles study of electronic structures and optical properties of Cu, Ag, and Au-doped anatase TiO2

We perform first-principles calculations to investigate the band structure, density of states, optical absorption, and the imaginary part of dielectric function of Cu, Ag, and Au-doped anatase TiO2 in 72 atoms systems. The electronic structure results show that the Cu incorporation can lead to the enhancement of d states near the uppermost of valence band, while the Ag and Au doping cause some new electronic states in band gap of TiO2. Meanwhile, it is found that the visible optical absorptions of Cu, Ag, and Au-doped TiO2, are observed by analyzing the results of optical properties, which locate in the region of 400–1000nm. The absorption band edges of Cu, Ag, and Au-doped TiO2 shift to the long wavelength region compared with the pure TiO2. Furthermore, according to the calculated results, we propose the optical transition mechanisms of Cu, Ag, and Au-doped TiO2. Our results show that the visible light response of TiO2 can be modulated by substitutional doping of Cu, Ag, and Au.