Chemical vapor deposition of aluminum from methylpyrrolidine alane complex

Chemical vapor deposition of aluminum from a recently developed precursor, methylpyrrolidine alane complex, has been studied. Aluminum films deposited on conducting surfaces (titanium nitride, copper, gold), but not on insulating surfaces (silicon, silicon dioxide, glass) at low substrate temperatures, showing deposition selectivity, while the deposition selectivity was lost at high substrate temperatures (> 210 °C). Al deposition rates on TiN and Cu were very close, but much higher than on Au. Deposition rates on all conducting substrates increased with the temperature and reached maximum at 180 °C. Al films deposited on as-sputtered TiN or Cu have no preferred orientations. Al–Au alloys and intermetallics were observed in the films deposited on Au. Surface morphology observation revealed that the film growth on TiN or Cu is different from that on Au. The surface roughness of Al films increased with the deposition time or the film thickness.     

Electrochemical thinning of thicker gold film with qualified thickness for surface plasmon resonance sensing

To meet the requirement of surface plasmon resonance (SPR) sensing, controlling the thickness of the gold film is very important. Here, we report an efficient and simple approach to prepare a SPR-active substrate when the thickness of the gold film is larger than the optimizing 50 nm and smaller than 100 nm. This method is based on anodic electrodissolution of gold in electrolyte containing chloride ions. Using this method, the thickness of gold films can be easily changed at a nanometer scale by controlling the number of potential scans and the concentrations of chloride ions in the electrolyte. At the same time, the influence of gold film thickness on the SPR signal is recorded by SPR in real time. To assess the change of the surface roughness and morphology of gold film through anodic electrodissolution, atomic force microscopy was used. The surface roughness of the same Au film before and after anodic electrodissolution is 1.179 and 2.767 nm, respectively. The change of the surface roughness of Au film brings out a slight angle shift of SPR. This indicates that surface electrodissolution of the gold does not affect the character of the original bulk film and this film can be used for SPR experiments. To confirm our expectation, a simple adsorption experiment of cytochrome c (Cyt c) on the gold film treated with anodic electrodissolution modified by 11-mercaptoundecanic acid was carried out. The angle shift of SPR confirmed the adsorption of Cyt c, and the cyclic voltammetry of Cyt c provided a complementary confirmation for the adsorption of Cyt c. These results show that this approach provides a good way to change the thicker gold film to an optimized thickness of SPR sensing. The great advantage brought by this approach is in that it can convert the waste gold films with greater thicknesses fabricated by the vacuum deposition method or other methods into useful materials as active SPR substrates.     

Optimizing growth conditions for electroless deposition of Au films on Si(111) substrates

Electroless deposition of Au films on Si(111) substrates from fluorinated-aurate plating solutions has been carried out at varying concentrations, deposition durations as well as bath temperatures, and the resulting films were characterized by X-ray diffraction, optical profilometry, atomic force microscopy and scanning electron microscopy. Depositions carried out with dilute plating solutions (< 0.1 mM) at 28°C for 30 min produce epitaxial films exhibiting a prominent Au(111) peak in the diffraction patterns, while higher concentrations or temperatures, or longer durations yield polycrystalline films. In both epitaxial and polycrystalline growth regimes, the film thickness increases linearly with time, however, in the latter case, at a rate an order of magnitude higher. Interestingly, the surface roughness measured using atomic force microscopy shows a similar trend. On subjecting to annealing at 250°C, the roughness of the film decreases gradually. Addition of poly (vinylpyrrolidone) to the plating solution is shown to produce a X-ray amorphous film with nanoparticulates capped with the polymer as evidenced by the core-level photoelectron spectrum. Nanoindentation using AFM has shown the hardness of the films to be much higher (∼ 2.19 GPa) than the bulk value.     

电场对Au/SiO_2及Au-Ag/SiO_2表面结构与原子迁移特性的影响

利用扫描俄歇微探针（SAM）和原子力显微镜（AFM）研究了SiO2衬底上在外加直流电场作用下沉积的Au薄膜及Au－Ag复层薄膜的表面形貌、结构变化及电迁移扩散行为。结果表明：①在衬底表面施加水平方向电场辅助沉积制备的Au薄膜其表面显示出平整的椭球形晶粒，并沿外电场方向呈织构取向。与未加电场的热蒸发沉积膜相比，具有较为均匀、有序的表面微观结构。②SiO2表面Au-Ag复层薄膜在直流电场作用下，Au，Ag物种同时向负极方向作走向迁移扩散，这与Au－Ag复层薄膜在Si（111）表面电迁移时Au，Ag分别向两极扩散的特点不同，反映了衬底性质对表面原子电迁移的影响。③Au－Ag复膜在电迁移过程中还发生了表面原子聚集状态的变化，原来沉积排布的细小晶粒在电迁移扩散过程中出现不均匀长大，导致薄膜表面粗糙度显著增加。     

Surface properties of thin gold layers sputtered on polymers

Thin gold layers were sputtered on the foils of polypropylene-PP, polyethyleneterephthalate-PET, polystyrene-PS, polyethylene-PE and polytetrafluoroethylene-PTFE modified by Ar+ plasma. Surface properties of pristine, plasma treated and gold coated polymers were characterized by two-points method (sheet electrical resistance), electrokinetical analysis (zeta-potential, surface chemistry), goniometry (contact angle), electron paramagnetic resonance (concentration of radicals), atomic force microscopy (AFM, surface morphology and roughness) and scratch test (mechanical properties). Zeta potential and contact angle, as assumed, differ dramatically for plasma treated polymers and for the polymers deposited by Au layers. AFM images indicate that after gold deposition on polymers the surface roughness and the surface morphology change depending on pristine polymer surfaces (roughness and morphology) and sputtering time. Electrical measurements resulted in fact that with increasing layer thickness, the sheet resistance of the gold layer decreases for all polymers with increasing sputtering time. Lower adhesive destruction is observed on the gold layer deposited on plasma treated PE in comparison with pristine.     

Evolution of microstructure and electrical conductivity of electroless copper deposits on a glass substrate

This paper describes the evolution of the microstructure and conductivity of electroless copper deposition on a glass substrate for applications in electronics manufacture. The glass was activated using a (3-aminopropyl)trimethoxysilane pre-treatment followed by a Pd/Sn catalyst. Surface morphology of the deposited copper films was characterized using a dual beam focused ion beam field emission scanning electron microscope, and together with atomic force microscopy, showed clearly that the roughness and grain size tended to increase with the plating time. Film thickness measurements showed a high initial deposition rate, which slowed to a constant level as the thickness increased above 100 nm. This corresponded with the resistivity of the films which decreased rapidly as the thickness increased from 20 to 100 nm, but then remained largely stable at a level approximately twice that of bulk copper.     

Au thin films deposited on SnO2:In and glass: Substrate effects on the optical and electrical properties

We report on a detailed study on the optical and electrical properties of Au films made by sputter deposition onto glass substrates with and without transparent and electrically conducting layers of SnO₂:In. The Au films had thicknesses up to 10.7 nm and hence spanned the range for thin film growth from discrete islands, via large scale coalescence and formation of a meandering conducting network, to the formation of a more or less “holey” film. Scanning electron microscopy and atomic force microscopy demonstrated that the SnO₂:In films were considerably rougher than the glass itself, and this roughness influenced the Au film formation so that large scale coalescence set in at a somewhat larger thickness for films on SnO₂:In than on glass. Measurements of spectral optical transmittance and reflectance and of electrical resistance gave a fully consistent picture that could be reconciled with impeded Au film formation on the SnO₂:In layer; this led to pronounced “plateaus” in the near infrared optical spectra for Au films on SnO₂:In and a concomitant change from such two-layer films having a lower resistance than the single gold film at thicknesses below large scale coalescence to the opposite behavior for larger film thicknesses. Our work highlights the importance of the substrate roughness for transparent conductors comprising coinage metal films backed by wide band gap transparent conducting oxides.     

Effect of gold immersion time on the electrochemical migration property of electroless nickel/immersion gold surface finishing

In this study, the electrochemical performance of an electroless nickel/immersion gold (ENIG) surface finish was evaluated as a function of the Au immersion time by the water immersion migration test. As the Au plating time increased, the electroless nickel phosphorous (EN-P) changed from amorphous to crystalline and then increased in crystallinity. X-ray diffraction (XRD) was used to evaluate the crystallinity of the plating layer. The electrical resistance of the electrodes was tracked as the sample was immersed in water with a 5 V bias. The microstructures of the electrodes after the electrochemical migration test were observed by using secondary electron microscopy (SEM) and energy dispersive spectroscopy (EDS). As the Au immersion time increased, the EN-P's crystallinity and Au thickness increased. This enhanced the electrochemical migration protection of the surface finish layer.     

Low pressure annealing of gold nanostructures

Ultra-thin Au films sputtered on glass substrates were investigated. The samples were annealed in air and in an evacuated chamber. The dependence of the annealing process on ambient pressure during thermal treatment was studied. The thermally-induced changes in surface morphology were followed by atomic force microscopy. The changes have a great impact on dielectric, optical and physical properties of the prepared structures. UV–Vis absorption spectra were used to investigate optical parameters and showed the semiconducting characteristic of intrinsic Au clusters. It was found that reduced ambient pressure stabilizes the continuous structure of the thin gold film during the annealing process.     

Study of electroless copper plating on ABS resin surface modified by heterocyclic organosilane self-assembled film

6-(3-triethoxysilylpropyl)amino-1, 3, 5-triazine-2, 4-dithiol monosodium (TES) was used to fabricate self-assembled film on corona pretreated acrylonitrile–butadiene–styrene (ABS) resin surface. The self-assembled film modified ABS resin was treated by electroless copper plating. Orthogonal test was carried out to study optimal condition of the process. The surface appearance, plating rate and thickness of electroless copper films were investigated to determine the optimal time of corona-discharge, self-assembly and electroless copper plating. SEM results indicated that porous morphology appeared on ABS resin surface modified by TES self-assembled film and the surface roughness also increased. The adhesion test showed that the adhesion property between ABS resin and copper was excellent. The surface of electroless copper film had high brightness under the optimal condition of 1 min corona-discharge, 30 min self-assembly and 10 min electroless copper plating. The electroless-copper plating temperature was 55 ～ 60°C and pH was 13 ～ 13·5.     

Quantitative analysis of electrodeposited tin film morphologies by atomic force microscopy

This study of the electrodeposition of tin on steel substrates demonstrates that it is possible to obtain quantitative information on the thin film growth at industrially relevant substrates using atomic force microscopy (AFM) to monitor the film morphology and X-ray fluorescence (XRF) to measure the average film thickness. The effects of current density and electrolyte temperature on the film morphology, surface roughness, and grain size distribution (GSD) are reported. While the roughness of the substrates used in this study can vary by several hundred nanometers to a micrometer, we are interested in quantitative characterization of the tin films with thickness varying from a few tens of nanometers to several hundred nanometers. This study shows that for the range of film thickness and length scale studied, analysis of the AFM images can provide quantitative characterization of the thin film roughness and grain size distribution at various stages of growth with little interference from the substrate morphological inhomogeneities.     

Growth mechanism investigation of SnO2 thin films deposited by aerosol pyrolysis for biosensor applications: Importance of the thickness

Transparent conductive oxide films are suitable sensitive layers for gas sensors and biosensors, provided that their intrinsic properties are controlled, notably considering their thickness dependence. The present paper reports on a study of the variation of some physical properties of polycrystalline Sb doped SnO₂ films according to the film thickness. Films were deposited onto Si and glass substrates by aerosol pyrolysis. Their thickness was varied in a range of 20-280 nm. The electrical resistivity, the roughness, the optical constant, the microstructure and the texture were investigated. Correlated evolutions of the resistivity and the surface roughness are found in relation with the evolutions of both the microstructure and the texture. Two main successive growth steps were evidenced which are delimited by a critical film thickness. Below this thickness of approximately 100-120 nm, a strong dependence of physical properties with the thickness is evidenced whereas for thicker films no significant change is evidenced. A two-step growth model is proposed to explain this behaviour. This mechanism growth is to be considered in view of the integration of SnO₂ films as sensitive layers in biosensors. Notably, in the case of biosensors based on the label-free electrochemical detection of biomolecules, it is recommended to use films with thicknesses ranging above the critical thickness value of 100-120 nm in order to obtain optimized, reproducible and comparable responses of biosensors.     

Surface-enhanced Raman scattering dendritic substrates fabricated by deposition of gold and silver on silicon

This paper reports a study on the preparation of gold nanoparticles and silver dendrites on silicon substrates by immersion plating. Firstly, gold was deposited onto silicon wafer from HF aqueous solution containing HAuCl4. Then, the silicon wafer deposited gold was dipped into HF aqueous solution of AgNO3 to form silver coating gold film. Scanning electron microscopy reveals a uniform gold film consisted of gold nanoparticles and rough silver coating gold film containing uniform dendritic structures on silicon surface. By SERS (surface-enhanced Raman scattering) measurements, the fabricated gold and silver coating gold substrates activity toward SERS is assessed. The SERS spectra of crystal violet on the fabricated substrates reflect the different SERS activities on gold nanoparticles film and silver coating gold dendrites film. Compared with pure gold film on silicon, the film of silver coating gold dendrites film significantly increased the SERS intensity. As the fabrication process is very simple, cost-effective and reproducible, and the fabricated silver coating gold substrate is of excellent enhancement ability, spatial uniformity and good stability.     

Dewetting behavior of Au films on porous substrates

Understanding the stability of thin films and their spontaneous pattern formation upon dewetting is essential to a host of physical phenomena. In this paper, we study the dewetting phenomena of Au thin films deposited on anodic aluminum oxide (AAO) membranes to analyze the stability of the metal film on porous substrates. AAO membranes, as-sputtered and dewetted Au films are all characterized by scanning electronic microscopy and X-ray diffraction. We found that both the roughness of AAO surface and modification of AAO pores exhibit remarkable influences on the dewetting behavior of Au films. The observed dewetting phenomena are explained from an energetic point of view since dewetting is a process of minimization of the system free energy.     

Dendrimer-Mediated Adhesion between Vapor-Deposited Au and Glass or Si Wafers

Here, we report the use of amine-terminated poly(amidoamine) (PAMAM) dendrimers as adhesion promoters between vapor-deposited Au films and Si-based substrates. This method is relatively simple, requiring only substrate cleaning, dipping, and rinsing. Proof of concept is illustrated by coating glass slides and single-crystal Si wafers with monolayers of PAMAM dendrimers and then evaporating adherent, 150-nm-thick Au films atop the dendritic adhesion promoter. Scanning tunneling microscopy and cyclic voltammetry have been used to assess the surface roughness and electrochemical stability of the Au films. The effectiveness of the dendrimer adhesion layer is demonstrated using standard adhesive-tape peel tests.     

Investigation of quantum systems with surface plasmons and surface state electrons

We report on investigations of thin films of the quantum systems hydrogen and helium both in thermodynamic equilibrium and in metastable states. Information about the film thickness and surface roughness is obtained from the excitation of surface plasmons and mobility measurements of surface state electrons. The equilibrium studies show triple-point wetting for H ₂ on Au substrates, in agreement with earlier results for similar systems. Unexpectedly a distinct hysteretic behavior of the saturated film thickness is found near the triple-point. Superfluid ⁴ He films on as prepared Ag display complete wetting. Investigations of H ₂ films in metastable states prepared by quench-condensation at 1.5K reveal pronounced changes in the film structure upon annealing. These changes set in far below the desorption temperature and are ascribed to surface diffusion.     

Surface morphology and optical properties of magnetron - sputtered ultrathin Al films

Ultrathin Al films with different thicknesses were deposited on glass substrates by DC magnetron sputtering. The effects of film thickness on morphology and optical properties of the films were investigated in detail. When film thickness increases from 7.0 to 84.0 nm, the average grain size and surface roughness enlarges from 27.6 to 94.2 nm and from 0.25 to 1.87 nm, respectively. Below critical thickness of 28.0 nm, which is the thickness that Al films form continuous film, the optical properties vary significantly with thickness increasing and then tend to be stable. In the absorptance spectra, all films exhibit distinct broad peaks which can be attributed to the absorption due to the interband transition. The possible reasons for the shift in the peak position are due to the quantum size effects and internal stress in the ultrathin Al films.     

Electroplating of porous gold films for SERS analysis of heme derivatives

Gold porous films with an 2D inverse opal structure were prepared via electrochemical deposition for further application as SERS-active substrates for the on-chip analysis of heme B derivatives. The thickness of the deposited film was controlled through deposition charge while the grain size was dependent significantly on electrolyte content. A semiquantitative surface analysis of film composition and phase analysis of the gold films were performed by XPS and XRD methods while the observed local, Mie and Bragg plasmon resonance modes were discussed based on UV–vis reflectance data.     

Electrochemical fabrication of polyaniline films containing gold nanoparticles deposited on titanium electrode for electro-oxidation of ascorbic acid

Polyaniline films prepared on titanium were employed as substrate for the electrodeposition of gold. The modified electrode was used as anode for the electro-oxidation of ascorbic acid. The electrochemical behavior and electro-catalytic activity of Au/PAni/Ti electrode were characterized by cyclic voltammetry. The morphology of the polyaniline film and gold coating on PAni/Ti electrode were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) techniques, respectively. Results indicated that gold nanoparticles were homogeneously dispersed on the surface of polyaniline film. The electro-oxidation of ascorbic acid is found to proceed more facile on Au/PAni/Ti electrode than on bare gold electrode. The irreversible oxidation current of ascorbic acid exhibits a linear dependence on the ascorbic acid concentration in the range of 1–5 mM.     

Effect of film thickness and agglomerate size on the superwetting and fog-free characteristics of TiO2 films

The effect of TiO₂ film thickness and agglomerate size on the non-UV activated superhydrophilic wetting and antifogging characteristics of TiO₂ films was investigated. Evidence from Atomic Force Microscopy analysis showed that surface roughness is the key parameter requiring control so as to retain the superhydrophilic wetting and antifogging behaviour of the synthesised films. Surface roughness can be tuned by simple manipulation of the multilayer assembly of TiO₂ nanoparticles through varying the film thickness and agglomerate size. A film thickness of ~ 140 nm yielded the optimum roughness (root mean square = 23 nm) to give the best superhydrophilic wetting behaviour. Thicker films reduced the film roughness and were detrimental to their superhydrophilic wetting properties. Smaller agglomerate size was also found to be important in retaining film roughness.