Au Deposition Rate Research Articles

Open Cross-gap Gold Nanocubes with Strong, Large-Area, Symmetric Electromagnetic Field Enhancement for On-Particle Molecular-Fingerprint Raman Bioassays.

Plasmonic nanoparticles with an externally open nanogap can localize the electromagnetic (EM) field inside the gap and directly detect the target via the open nanogap with surface-enhanced Raman scattering (SERS). It would be beneficial to design and synthesize the open gap nanoprobes in a high yield for obtaining uniform and quantitative signals from randomly oriented nanoparticles and utilizing these particles for direct SERS analysis. Here, we report a facile strategy to synthesize open cross-gap (X-gap) nanocubes (OXNCs) with size- and EM field-tunable gaps in a high yield. The site-specific growth of Au budding structures at the corners of the AuNC using the principle that the Au deposition rate is faster than the surface diffusion rate of the adatoms allows for a uniform X-gap formation. The average SERS enhancement factor (EF) for the OXNCs with 2.6 nm X-gaps was 1.2 × 109, and the EFs were narrowly distributed within 1 order of magnitude for ∼93% of the measured OXNCs. OXNCs consistently displayed strong EM field enhancement on large particle surfaces for widely varying incident light polarization directions, and this can be attributed to the symmetric X-gap geometry and the availability of these gaps on all 6 faces of a cube. Finally, the OXNC probes with varying X-gap sizes have been utilized in directly detecting biomolecules with varying sizes without Raman dyes. The concept, synthetic method, and biosensing results shown here with OXNCs pave the way for designing, synthesizing, and utilizing plasmonic nanoparticles for selective, quantitative molecular-fingerprint Raman sensing and imaging applications.

Study of the Heat‐Induced Degradation Mechanism in PbI2‐Excess Perovskite Solar Cells

The photodecomposition of PbI2 in the perovskite halide structure has been identified as a primary reason for the rapid degradation of metal halide perovskite solar cells (PSCs) under continuous illumination. In particular, excess PbI2 on the surface of perovskite films reduces the stability of PSCs via several mechanisms that are still unelucidated. Herein, the influence of excess PbI2 on PSCs is investigated by varying the Au deposition rate, which results in different temperatures during the fabrication of PSCs, and then they are compared with stoichiometric PSCs. It is demonstrated that the anion exchange of Br− in perovskite and I− in excess PbI2 occurs at the grain boundary and interface of the perovskite layers induced by the high heating temperature, leading to a photoluminescence peak redshift and lower power conversion efficiency. Light illumination accelerates the exchange of Br− and I− between the perovskite layer and excess PbI2 induced by carrier accumulation at the interface and grain boundary, leading to the poor stability of the PSCs.

Mechanism of Bismuth Stimulated Bottom-up Gold Feature Filling

The mechanism underlying -stimulated bottom-up Au filling and self-passivation in trenches and vias in slightly alkaline electrolytes is explored. The impacts of electrolyte components and and potential-dependent kinetic factors on the rate of Au electrodeposition are quantified experimentally. Derived parameters are applied within the surfactant conservation Curvature Enhanced Accelerator Coverage model to simulate the filling of high aspect ratio trenches. It is observed that Bi adsorption accelerates the Au deposition rate with a non-linear dependence occurring around a critical coverage. Further, the impact of electrolyte composition is such that gradients of and derived from reduction of during deposition accentuate deposition farther from the feature opening. These factors and surface area reduction result in Bi enrichment at the bottoms of filling features that localizes active deposition to feature bottoms. Ultimately, weakening of the concentration gradients and associated kinetics as bottom-up feature filling progresses reduces the Bi coverage on the growth front below the critical value and bottom-up growth terminates. Good agreement is observed with key experimental features including the incubation period of conformal deposition, transition to bottom-up growth, subsequent bottom-up filling and finally self-passivation as the growth front nears the field.

Controlled compositional gradients of electroformed gold and silver

Motivated by an interest in high-pressure research, thick (>1 mm) compositionally graded gold/silver (Au/Ag) films were electroformed. Systematic studies were performed to understand the role of processing temperature on the nucleation and growth kinetics and associated microstructure. Furthermore, as the electrolyte composition is continuously changing during the experiment, systematic studies were performed to correlate electrochemical parameters with film morphology and composition. The results showed that the nucleation pathways and relative deposition rate of Au and Ag are heavily dependent on the processing temperature. A procedure to ramp the temperature while continuously pumping an Au electrolyte into an initial Ag electrolyte to produce the graded film is presented. The obtained film is comprised of a segment of pure Au followed by a complete compositional gradient and ending with a segment of pure Ag across 1.5 mm. The results presented here describe a general framework to fabricate gradients of other materials through electrodeposition.

Nanofabrication of 30 nm Au zone plates by e-beam lithography and pulse voltage electroplating for soft x-ray imaging

High resolution Fresnel zone plates for nanoscale 3D imaging of materials by both soft and hard X-ray are growingly needed in broad applications in nanoscience and technology. When the outmost zone-width approaches 30 nm or even below, electro-deposition of gold into narrow trenches replicated by electron beam lithography in resist becomes increasingly difficult. Pulse electroplating instead of conventional direct-current one has been attempted in this work to overcome the problem in the au deposition in narrow trenches. Careful study of the au deposition rate as the function of adjustment parameters including the anodic bias, the pulse frequency and the deposition time has been systematically carried out. The optimized window of the parameters is adopted in the fabrication of 30 nm zone plates with the aspect ratio from 3:1 up to 7:1 and the duty cycle close to 0.5. Imaging of in-house made Siemens stars with 30 nm as the narrowest line-width has been successfully demonstrated in soft X-ray (706 eV). The origin of electroforming of well-structured au zones by pulse electroplating is discussed

Dynamics of Au-Ge liquid droplets on Ge(1 1 1) terraces: Nucleation, growth and dynamic coalescence

Nucleation, growth and coalescence of 3D Au-Ge droplets on Ge(1 1 1) surface have been studied in real time by low energy electron microscopy. The surface diffusion energy barrier of Au on Ge(1 1 1) is estimated as 1.8±0.2 eV from the dependence of the number of droplets per surface unit with temperature and Au deposition rate. At long time scale it is also shown that the droplets have a diffusive motion that results in dynamic coalescence events. From the decrease of the droplet number, the size-dependence of the diffusion coefficient of the droplets is shown to decay as R-1.9±0.5 where R is the droplet radius. This result indicates that the spontaneous motion of the droplets is controlled by an interfacial mass-transport phenomenon.

An origin of the irreproducibility of hole injection barrier from Au top-contact electrodes and its influence on device performance in top-contact organic field-effect transistors

Abstract To understand the origin of the irreproducibility of the hole injection barrier at the interface between Au top-contact electrodes and organic semiconductors, we performed a systematic study by focusing on the deposition rate of Au. As a benchmarking material system, we fabricated field-effect transistors with pentacene active layers and Au top-contact electrodes evaporated with the deposition rate from 0.5 to 10 A/s. From the contact potential differences (ΔCPDs) between Au and pentacene measured with Kelvin-probe force microscopy, cross-sectional structures with scanning transmission electron microscopy, crystallographic structures with X-ray diffraction, and Au depth profiles with secondary ion mass spectrometry, we concluded that the variation of ΔCPD is due to embedded Au nanoclusters in pentacene with the average diameter of 4–6 nm. These Au nanoclusters, of which depth significantly varies by the Au deposition rate, modulate the ΔCPD and interfere with the reproducibility of hole injection barrier. As a result, gate threshold voltage and field-effect mobility also become irreproducible.

Bottom-Up Gold Filling of High Aspect Ratio Trenches

Bottom-up superconformal Au filling of trenches as tall as seventeen micrometers, with aspect ratios of 26, is demonstrated. Deposition is conducted in a near-neutral Na3Au(SO3)2 electrolyte containing a micromolar concentration of Bi3+, known to accelerate the Au deposition and provide void-free, bottom-up filling of smaller trenches. Electroanalytical and X-ray photoelectron spectroscopy (XPS) measurements show that a Bi surface species is responsible for the accelerated Au deposition. The adsorbed Bi has a profound effect on the morphological evolution of the surface at the concentration and potentials of interests, transitioning from the growth of isolated (111) oriented trigonal pyramidal features in its absence to the growth of smooth epitaxial deposits once the fractional coverage of Bi reaches 0.15 ± 0.02 (1σ). A non-linear dependence of Au deposition rate on Bi coverage gives rise to extended incubation prior to the onset of bottom-up feature filling. For higher transport conditions, shearing of the interface limits Bi coverage to a value of approximately 0.05 or less, which correlates with a small leakage or passive current for Au deposition. The unusual correlation of Bi coverage with hydrodynamics is consistent with the inception and localization of deposition to the most recessed, and thereby quiescent, bottom surface of the patterned trench arrays.

Room temperature thermally evaporated thin Au film on Si suitable for application of thiol self-assembled monolayers in micro/nano-electro-mechanical-systems sensors

Gold is a standard surface for attachment of thiol-based self-assembled monolayers (SAMs). To achieve uniform defect free SAM coatings, which are essential for bio/chemical sensing applications, the gold surface must have low roughness and be highly orientated. These requirements are normally achieved by either heating during Au deposition or postdeposition Au surface annealing. This paper shows that room temperature deposited gold can afford equivalent gold surfaces, if the gold deposition parameters are carefully controlled. This observation is an important result as heating (or annealing) of the deposited gold can have a detrimental effect on the mechanical properties of the silicon on which the gold is deposited used in microsensors. This paper presents the investigation of the morphology and crystalline structure of Au film prepared by thermal evaporation at room temperature on silicon. The effect of gold deposition rate is studied, and it is shown that by increasing the deposition rate from 0.02 to 0.14 nm s−1 the gold surface root-mean-square roughness decreases, whereas the grain size of the deposited gold is seen to follow a step function decreasing suddenly between 0.06 and 0.10 nm s−1. The x-ray diffraction intensity of the preferentially [111] orientated gold crystallites is also seen to increase as the deposition rate increases up to a deposition rate of 0.14 nm s−1. The formation and characterization of 1-dodecanethiol on these Au coated samples is also studied using the contact angle. It is shown that by increasing the Au deposition rate, the contact angle hysteresis (CAH) decreases until it plateaus, for a deposition rate greater than 0.14 nm s−1, where the CAH is smaller than 9° which is an indication of homogeneous SAM formation, on a smooth surface.

Real-Time Dynamics of Galvanic Replacement Reactions of Silver Nanocubes and Au Studied by Liquid-Cell Transmission Electron Microscopy.

We study the galvanic replacement reaction of silver nanocubes in dilute, aqueous ethylenediaminetetraacetic acid disodium salt (EDTA)-capped gold aurate solutions using in situ liquid-cell electron microscopy. Au/Ag etched nanostructures with concave faces are formed via (1) etching that starts from the faces of the nanocubes, followed by (2) the deposition of an Au layer as a result of galvanic replacement, and (3) Au deposition via particle coalescence and monomer attachment where small nanoparticles are formed during the reaction as a result of radiolysis. Analysis of the Ag removal rate and Au deposition rate provides a quantitative picture of the growth process and shows that the morphology and composition of the final product are dependent on the stoichiometric ratio between Au and Ag.

In-Plane Si Nanowire Growth Mechanism in Absence of External Si Flux.

We report on a new mechanism of nanowire formation: during Au deposition on Si(110) substrates, Au-Si droplets grow, move spontaneously, and fabricate a Si nanowire behind them in the absence of Si external flux. Nanowires are formed by Si dissolved from the substrate at the advancing front of the droplets and transported backward to the crystallization front. The droplet shape is determined by the Si etching anisotropy. The nanowire formation can be tuned by changing experimental parameters like substrate temperature and Au deposition rate.

Performance of Au/Nafion/Pt electrodes in benzene–water electrochemical hydrogenation

Au/Nafion/Pt electrodes were used in the coupled reaction system of benzene hydrogenation and water electrolysis for hydrogen production and storage. Au/Nafion/Pt electrodes with the short electrode spacing reduce hydrogen evolution and increase current density and current efficiency. The morphology of metal layer surface of electrodes and electrochemistry hydrogenation reactions were studied. The results showed that the morphology and conductivity of metal layer surface of electrodes were related to the reduction reaction rate of metal complex in the electrode preparation process. The Au complex reduction reaction rate and Au deposition rate were lower than Pt complex reduction reaction rate, yielding a dense smooth Au surface which had low resistance and was not conducive to the diffusion of H+. Benzene hydrogenation reaction rate increased and current efficiency decreased with increased electrode potential. The effect of electrode potential on current efficiency was similar for all electrodes tested. Au/Nafion/Pt electrodes had the highest current efficiency and current density among the electrodes tested; the current density of benzene hydrogenation was higher than 100 mA/cm2 and 90% current efficiency.

Superfilling Damascene Trenches with Gold in a Sulfite Electrolyte

Superconformal Au deposition is demonstrated in a Na3Au(SO3)2 - Na2SO3 based electrolyte using underpotential deposited (upd) Pb to catalyze the reduction of Au(SO3)23−. Micromolar additions of Pb2+ to the electrolyte give rise to acceleration of the Au deposition rate as evidenced by hysteretic voltammetry and rising chronoamperometric transients that convolve the diffusion, adsorption kinetics and coverage isotherm of the upd Pb catalyst. The catalytic activity on the Au deposition reaction may be quenched, or reset, by stepping the potential to more positive values to deactivate or strip the Pb catalyst. Void-free Damascene trench superfilling at various fixed potentials and Pb2+ concentrations is demonstrated and shown to be congruent with the curvature enhanced accelerator model (CEAC) of superconformal growth. This includes enhanced deposition due to catalyst enrichment on concave surface segments at the bottom corners of the trenches, followed by rapid bottom-up growth and, for certain conditions, bump formation above the filled trenches.

Organic field-effect transistors with nearly non-injection barrier from source/drain electrodes to pentacene

Top contact pentacene field-effect transistors (OFETs) with or without MoO3 source/drain (S/D) electrodes buffer layers were fabricated by utilizing different deposition rates of Au S/D electrodes. The results showed that the characteristics of these OFETs have a strong dependence on the deposition rate of Au S/D electrodes. More importantly, single pentacene layer OFETs with optimized Au deposition process exhibits significantly improved performance, which is almost equal to the OFETs with MoO3 buffer layers. The high performance of OFETs with optimized Au deposition process was attributed to an improved contact of Au and pentacene caused by ordered dipole arrangement at the interface, leading to a nearly non-injection barrier of charge carriers from Au electrodes to pentacene.

VLS Growth of III-V Semiconductor Nanowires on Graphene Layers

ABSTRACTGaP, GaAs, and InP nanowires were grown on graphitic layers by the vapor-liquid-solid method in a metalorganic vapor phase epitaxy chamber. On graphene/SiC(0001), Au particles as catalyst were formed at the steps by controlling the Au deposition rate and the annealing temperature in a low-energy electron microscopy system. GaP nanowires were grown on this substrate, and it was found that vertical nanowires were formed at the steps of the surface. We also performed GaP, GaAs, and InP nanowire growth on graphite substrates. Free-standing nanowires were obtained for all three materials, although they were vertically, diagonally, and laterally-oriented at the same time. The results suggested that the growth at the steps is the key to growing nanowires vertically on graphene surface.

Contact resistance variation in top-contact organic thin-film transistors with the deposition rate of Au source/drain electrodes

We investigated the effect of the deposition rate of Au source/drain electrodes on the contact resistance of the top-contact organic thin-film transistors (OTFTs). For the formation of source/drain contacts, Au was thermally deposited at the different rates of 0.5, 1.0, 5.0, and 13.0 Å/s. With increasing the Au deposition rate, the contact resistance extracted at the gate voltage of − 30 V could be reduced from 14 × 10 6 to 2.4 × 10 6 Ω, resulting in the characteristic improvements of the top-contact OTFT. It is also found that the contact resistance significantly affects the off-state currents of the device having the short channel length of 10 μm. The control of the deposition rate of source/drain electrodes is suggested to optimize the contact properties of the top-contact OTFTs as well as the device performance.

Preparation and performance of thin-layered PdAu/ceramic composite membranes

Preparation of 3–5 μm thick, hydrogen-selective PdAu layers via sequential electroless plating of Pd and Au onto ceramic microfiltration membranes was investigated employing a cyanide-free Au plating bath. The Au deposition rate was strongly dependent on bath temperature and alkalinity reaching an optimum at 333 K and pH 10. Homogenous alloying of the separate metal layers under atmospheric H 2 proved to be a protracted process and required approximately a week at 873 K for a PdAu layer as thin as 3 μm. After 300 h annealing at 823 K the 5 μm thick PdAu layer of a composite membrane still exhibited a Au gradient declining from 7.4 at.% at the top surface to 5.5 at.% at the support interface despite that the H 2 permeation rate had become stable. Nonetheless, the membrane exhibited a very high H 2 permeability of e.g. 1.3 × 10 −8 mol m m −2 s −1 Pa −0.5 at 673 K, but it decreased much faster with temperature below 573 K than above, likely due to a change from bulk H diffusion-controlled to H 2 adsorption or desorption-limited transport. The composite membrane withstood cycling between 523 and 723 K in H 2 well showing that differing thermal expansion of the joined metallic and ceramic materials stayed within the tolerance range up to 723 K.

Effect of Au deposition rate on the performance of top-contact pentacene organic field-effect transistors

A study of the influence of the deposition rate of top-contact Au source and drain electrodes deposited by electron-beam evaporation on the electrical performance of pentacene organic field-effect transistors (OFETs) is presented. By adjusting the deposition rate of the Au electrodes to minimize metal diffusion into the semiconductor pentacene layer, the source/drain contact resistance could be reduced. At a Au deposition rate of 10 Å/s, high-performance pentacene p-channel OFETs were obtained with a field-effect mobility of 0.9 cm 2/Vs and a normalized channel width resistance of 23 kΩ cm in a device with a channel length of 25 μm.

Gold Superfill in Submicrometer Trenches: Experiment and Prediction

Bottom-up deposition of gold in fine trenches, also called “superfill,” was recently demonstrated using a submonolayer coverage of preadsorbed, deposition-rate-accelerating lead followed by gold electrodeposition. The present study has used experiments on planar substrates to quantify the effect of Pb adsorption on the Au deposition rate and the rate at which the adsorbed Pb was consumed during the Au deposition process. The values obtained have been incorporated into the curvature enhanced accelerator coverage mechanism of superfill where they were used to quantitatively predict the nonconformal, bottom-up deposition observed during filling of the patterned features. The results indicate the potential of the process for damascene interconnect fabrication in GaAs, GaN, and related technologies.

Interface Characteristics between Au Electrode and Pentacene Layer in Organic Thin-film Transistors

In order to investigate interfacial characteristics between top-Au and pentacene layers, devices with the structure of bottom-Au/pentacene/top-Au were fabricated on glass substrates at various deposition rates of top-Au of about 1.0, 3.0 and 15.0 Å/s. It was observed that electrical characteristics could be improved by increasing the deposition rate of top-Au, and the highest electrical conductivity value, 1.5×10-6 S/cm, was obtained for the device with top-Au deposited at 15.0 Å/s. Auger electron spectroscopy (AES) results showed that the atomic content of Au is substantially increased with the deposition rate of top-Au, but there is no marked difference in the depth profile of Au atoms regardless of the deposition rate of top-Au. Likewise, field-emission scanning electron microscopy (FE-SEM) images did not reveal structural defects that might cause short circuit. We also fabricated top-contact organic thin-film transistors (OTFTs) at various deposition rates of the Au layer for source/drain electrodes. As a result, the performance of the OTFTs can be modified by the deposition rate of Au. These results will be discussed.