Evaporated Gold Films Research Articles

Rough growth fronts of evaporated gold films, compared with self-affine and mound growth models

The power spectra, S( q, t), of evaporated gold films at room temperature are quantitatively compared with the Das Sarma Tamborenea model. The experimental curves fit the theory. However, the noise parameter, deduced from the fitting, disagrees with the predicted value. The two-dimensional (2D) experimental height–height correlation functions of scanning tunnelling microscope (STM) images present a hexagonal anisotropy. This fact agrees with the existence of a mound structure in the three-dimensional STM images. In addition the 2D Fourier transform module shows the predicted maxima for a mound model.

Nanocrystalline Domain Identification in Gold Films, by Backscattered Electron Imaging and Energy-Filtered Transmission Electron Microscopy

Gold nanocrystallites dispersed in an inhomogeneous gold matrix are detected by high-resolution scanning electron microscopy using a field emission source and backscattered electron detection in the composition mode, as well as by energy-filtered transmission electron microscopy in the plasmon energy region. The identity of the nanocrystalline domains was established by observing the same evaporated gold film samples but using bright-field, dark-field, electron diffractogram, and electron energy loss spectroscopy images in the transmission electron microscope. Comparison of these images shows that backscattered electron and plasmon energy detection can be used to identify crystalline domains in an otherwise chemically uniform sample.

Plasma polymerization using solid phase polymer reactants (non-classical sputtering of polymers)

Non-classical plasma sputtering of polymers was carried out using a reaction geometry in which the substrate (a supported evaporated gold film) was far (∼250 mean free paths) from the polymer target with no line of sight between the two surfaces (the target and substrate faced the same direction). An inductively coupled radio frequency argon plasma of 100 W at 200 mt and a flow rate of 1.8 sccm were used. The polymers studied are polyethylene, poly(isobutylene), poly(oxymethylene), poly(tetrahydrofuran), poly(tetrafluoroethylene), poly(chlorotrifluoroethylene), polystyrene, poly(α-methyl styrene), and poly(methyl methacrylate). Substrate-supported polymer films that formed were compared with samples of films prepared by plasma polymerizing monomer gases. Water contact angle, and X-ray photoelectron and infrared spectroscopy were used to characterize the films. Ablation rates of these and similar polymers were studied; factors that influence sputtering behavior are discussed.

Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry of self‐assembled monolayers of ruthenium complexes on gold

Self-assembled monolayers (SAMs) of three ruthenium complexes, [Ru(L)2](PF6)2, [Ru(L)(tpyPO3)](PF6)2, and [Ru(L18)(tpyPO3)](PF6)2, were prepared on evaporated gold films on glass or stainless steel plates; where L = 2,6-bis(benzimidazoyl)pyridine, tpyPO3 = 2,6-bis(2,2′:6′,2″-terpyridyl)pyridine phosphanate, and L18 = 2,6-bis(N-octadecylbenzimidazoyl)pyridine. Structures of these SAM complexes were studied by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). The SAMs were either prepared by direct binding of Ru-complexes to Au films by alkanethiol or by the multilayer method. In the multilayer method 1,4-thiobutylphosphate was used to form a base layer on an Au film, and the base layer was then chemically bridged to the Ru-complexes by zirconium phosphate. MALDI-TOFMS of SAM1, that had been prepared by direct binding of [Ru(L)2](PF6)2 to the Au film by an octanethiol group, showed cleavage at the S-Au linkages and elimination of the counter anion to yield a molecular ion and its dimeric ion. On the other hand, SAM2 and SAM3, which had been prepared by bridging Ru-complexes [Ru(L)(tpyPO3)](PF6)2 or [Ru(L18)(tpyPO3)](PF6)2 to the base layers with zirconium phosphate, showed dissociation from the base layers and elimination of the counter anion to give ions of the Ru complex molecules and their fragmentation ions. No molecular ion containing the base layer resulting from the S-Au bond cleavage was observed. Copyright © 2000 John Wiley & Sons, Ltd.

X-ray measurements of the depth dependence of stress in gold films

X-rays are used to determine the stress as a function of depth for five evaporated gold films of 0.8–2.5 μm thickness. The depth dependence is achieved by varying the incident angle of the X-rays, which affects the penetration depth of the X-rays into the film. The films, which have a different thermal expansion coefficient than the silicon substrate, are strained as a result of thermal cycling after deposition. We find essentially no stress variation as a function of depth for these films.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of self-assembled monolayers of ruthenium complexes on gold

Self-assembled monolayers (SAMs) of three ruthenium complexes, [Ru(L)(2)](PF(6))(2), [Ru(L)(tpyPO(3))](PF(6))(2), and [Ru(L18)(tpyPO(3))](PF(6))(2), were prepared on evaporated gold films on glass or stainless steel plates; where L = 2, 6-bis(benzimidazoyl)pyridine, tpyPO(3) = 2,6-bis(2,2':6', 2"-terpyridyl)pyridine phosphanate, and L18 = 2, 6-bis(N-octadecylbenzimidazoyl)pyridine. Structures of these SAM complexes were studied by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). The SAMs were either prepared by direct binding of Ru-complexes to Au films by alkanethiol or by the multilayer method. In the multilayer method 1,4-thiobutylphosphate was used to form a base layer on an Au film, and the base layer was then chemically bridged to the Ru-complexes by zirconium phosphate. MALDI-TOFMS of SAM1, that had been prepared by direct binding of [Ru(L)(2)](PF(6))(2) to the Au film by an octanethiol group, showed cleavage at the S-Au linkages and elimination of the counter anion to yield a molecular ion and its dimeric ion. On the other hand, SAM2 and SAM3, which had been prepared by bridging Ru-complexes [Ru(L)(tpyPO(3))](PF(6))(2) or [Ru(L18)(tpyPO(3))](PF(6))(2) to the base layers with zirconium phosphate, showed dissociation from the base layers and elimination of the counter anion to give ions of the Ru complex molecules and their fragmentation ions. No molecular ion containing the base layer resulting from the S-Au bond cleavage was observed. Copyright 2000 John Wiley & Sons, Ltd.

Subpicosecond excimer laser ablation of thick gold films of ultra-fine particles generated by a gas deposition technique

The results of UV laser ablation of gold nanoparticle films on glass substrates using femtosecond pulses are presented. Films of ultra-fine gold particles were prepared by an inert gas evaporation and deposition technique, resulting in a well-defined log-normal particle size distribution of (7±1) nm. The pulse length of the laser was 500 fs at a wavelength of 248 nm. Ablation thresholds, ablation rates at different fluxes, and the morphology of the ablated structures are presented. For the nanoparticle films studied an ablation rate five times higher than that of gold films prepared by the conventional evaporation technique was found. The ablation thresholds and rates are supposed to depend on the particle size and also on the evaporation pressure. These results are explained by taking into account the energy transport properties of nanocrystalline and conventionally evaporated gold films.

Extended statistical analysis of rough growth fronts in gold films prepared by thermal evaporation

The surface roughness of evaporated gold films has been studied by scanning tunneling microscopy and a frequency analysis method that uses the whole image. The power spectrum $\mathbf{S}(q,t)$ presents a clear ${q}^{\ensuremath{-}\ensuremath{\gamma}}$ dependence in the region of high frequencies and the interface width of the films follows a ${t}^{\ensuremath{\beta}}$ behavior. The values obtained for the two exponents $(\ensuremath{\gamma}=4.1$ and $\ensuremath{\beta}=0.26)$ agree with the theoretical predictions $(\ensuremath{\gamma}=4$ and $\ensuremath{\beta}=0.25)$ for a process controlled by pure surface diffusion in the thickness range studied. The power spectrum at high frequencies is similar for different film thickness describing a phenomenon free from anomalous scaling. We also conclude that dimensional analysis of profiles presents some practical problems in its application. On the other hand, frequency analysis of the whole image allows us to obtain a reliable determination of surface roughness.

Thermal conductivities of evaporated gold films on silicon and glass

We present four-point probe measurements of the in-plane electrical conductivities of electron beam-evaporated gold layers of thickness 20 nm to 2 μm deposited on Si(100), Si(111), and BK7 glass substrates. The values of thermal conductivities deduced from these measurements of gold films on glass samples agree well with prediction from the surface and grain-boundary scattering model, but not for gold films on silicon samples. Thermal conductivities of gold films are found to be different for samples on hydrofluoric acid etched Si(100) and Si(111) substrates, for which surface roughness and microstructures of the gold films have been examined to understand the difference in these thermal conductivity results.

Thin microstructured polymer films by surface-directed film formation

Evaporated gold films are hydrophilized within well defined areas of several micrometer size by microcontact printing of 11-mercapto-undecanoic acid. The localized hydrophilizing of the surface controls the formation of water microdroplets within these areas due to preferred condensation from a water saturated atmosphere. The preparation of regular well defined condensation patterns of water microdroplets is necessary to obtain structured thin polymer films from ordered liquid/liquid (water/organic polymer solution) two-phase systems by dip-coating. Through incomplete surface wetting of the hydrophobic polymer solution, the polymer is strictly excluded from the hydrophilic surface areas covered by water microdroplets. Different steps of water condensation and subsequent polymer film formation are characterized by microscopic methods. The microstructure of the film generated in this way is compared with predetermined microstructures used for surface heterogenization. It is demonstrated that the replication of well defined micropatterns from a given stamp structure to a polymer film is of high accuracy with respect to the long range order of the periodic features of the transferred structures. The reproducibility of the individual motif is shown to depend on its geometry and the condensation process. Microstructures in micrometer and submicrometer dimension could be prepared by the technique described.

Self-excited piezoelectric PZT microcantilevers for dynamic SFM—with inherent sensing and actuating capabilities

Currently three crucial components are necessary for the dynamic SFM, they are the microcantilever, oscillator, and cantilever deflection sensor. We demonstrate a piezoelectric microcantilever made of PZT thin films for SFM. This PZT microcantilever can perform the same functions which have to be done by the three crucial components. It is able to excite itself when an ac voltage is applied to it, and actuate itself in z-directional displacement by a superimposed dc voltage, while force sensing is executed concurrently. Since the motional admittance can be derived from the piezoelectric current output when the PZT microcantilever is vibrated at resonance frequency, the motional admittance will vary as the change of vibrational amplitude. Thus the topography of the sample can be recorded as the trace of the difference between output signals of motional admittance. The piezoelectric coefficient d 31 of the PZT layer is about −58 pC/N. The dimensions of piezoelectric microcantilevers used are 125×50×3.8 μm. The actuating ability is estimated as 75 nm/V. The vertical resolution of the self-excited PZT microcantilever can be derived as 1.2 Å at the bandwidth of 125 Hz. Very clear images of a 1.0 μm pitch Au coated SiO 2 grating and an evaporated gold film on a smooth glass plate are obtained by an SFM using this self-excited force sensing PZT microcantilever. The invention of this smart PZT microcantilever endows the possibility of constructing a stand-alone micro SFM system and a multiprobe SFM system.

Electrooxidation reactions on gas-diffusion electrodes catalyzed by DC sputtered Pt

A thin metallic film electrode deposited on a porous substrate, in this case a glass frit, in which electrolyte is entrained, may permit electrochemical effects with gas-phase reagents. Direct current sputtering is a convenient physical deposition method to prepare these electrode [1–3]and catalyst [4]materials. By using appropriate sputtering parameters (current density, voltage and time), metallic particles (Au, Pt, Pd, etc.) were deposited, forming continuous conducting films on rough, porous glass frit substrates. Supporting electrolyte was entrapped in the pores and the surface metallic films used as electrodes [5], the reagents being absorbed from the gas phase. In the present work sputtered Pt films, or Pt clusters sputtered on thin (350 nm) evaporated gold films were used as working electrodes. The morphology of these platinum films, as well as their modifications in service, were examined by scanning electron microscopy (SEM) and by atomic force microscopy (AFM). Various electrooxidations of gases such as CO, H 2 and methanol vapor demonstrated the electroactivity of Pt clusters as gas adsorption electrodes.

Increased Lateral Density in Alkanethiolate Films on Gold by Mercury Adsorption

We present a method for increasing the lateral chain density in self-assembled monolayers (SAMs) of alkanethiols on polycrystalline gold. This method relies on exposure of the alkanethiolate monolayers to mercury vapor and subsequent reimmersion into the thiol solution. Mercury adsorption on the gold surface induces a structural rearrangement in the alkanethiolate monolayers, as indicated by changes in dichroism in the Fourier transform infrared (FTIR) spectra, in line shape in the sum frequency generation (SFG) spectra, and in the macroscopic wetting behavior of the monolayers. X-ray photoelectron spectroscopy (XPS) data show that saturation of the thiolate samples with mercury occurs after 20−30 min of exposure to air saturated with mercury vapor. For 100 nm evaporated gold films a mercury bulk concentration of 14−16 atom % was determined by energy-dispersive X-ray analysis (EDX). Time-of-flight secondary ion mass spectroscopy (ToF-SIMS) data indicate that after mercury adsorption the monolayers consist of gold thiolate and mercury thiolate molecules. From the FTIR and XPS data we conclude that the mercury-exposed SAMs exhibit an inhomogeneous structure with differently tilted domains. As determined from the IR experiments, the average tilt angle of the alkyl chains in hexadecanethiolate monolayers decreases by ∼16° by mercury adsorption and by an additional ∼3° after reimmersion into the thiol solution. The corresponding changes obtained from near edge X-ray absorption fine structure (NEXAFS) spectra are ∼9° and ∼3°, respectively.

Evidence of pure diffusion process during growth of gold films

The surface roughness of evaporated gold films has been studied by scanning tunnelling microscopy and analysed by a Fourier transform method. The power spectrum S( q, t) presents a clear q − γ dependence in the high-frequency region and t β behaviour of the total interface width of the films. The values obtained for the two exponents, in the range of 300–18 000 Å thickness studied ( γ=4.1±0.1 and β=0.26±0.02), agree with the theoretical predictions ( γ=4 and β=0.25) for a pure diffusion-controlled process but not with a re-evaporation process. The power spectrum for high frequencies shows good correlation for different film thicknesses, describing scaling without anomalous behaviour.

Effects of polymer substrate surface energy on nucleation and growth of evaporated gold films

Discontinuous gold films with up to 4.0 nm nominal thickness were deposited on five different polymer substrates using a resistively-heated evaporation source. Images of gold particles from these films were created with low-voltage scanning electron microscopy and were analyzed with a digital camera and computer-processed image analysis. On all five substrates, growth was island-like, and the increase of surface coverage progressed at a similar rate, approximately proportional to the cube-root of nominal thickness. For a fixed amount of deposited gold, the size, shape and density of particles were characterized for each composition of polymer substrate. The rates of particle growth and coalescence were different on each polymer surface and were correlated to the surface energy of the polymer substrate.

Calculation of concentration depth profiles in electron probe microanalysis

AbstractBased on a multiple reflection model, the concentration depth profiles of gold diffused into a silver substrate are determined. To conclude the structure of the sample from the measured intensity of radiation, an accurate correction procedure is necessary. A new model was developed for this purpose. Since the new electron probe microanalysis (EPMA) correction procedure is also valid for tilted samples, measurements with different geometries could be performed. The different angles of incidence and take‐off angles allow for a better comparison of theory with experiment. One advantage of the applied multiple reflection model is that it can be extended comparatively easily with the analysis of layered specimens. Measurements of some specimens with one layer on a substrate are reported. The mean deviation of calculated thicknesses is about 10%. To calculate depth profiles, gold was evaporated with physical vapor deposition on silver foils. The thicknesses of evaporated gold films were 50 and 100 nm. Then the specimens were annealed at a temperature of approximately 400°C. Finally, the concentration depth profiles were quantified with EPMA. The shape of the profiles was derived from a simple diffusion model valid for the samples under consideration. To check the shape of the functions obtained, a comparison with measurements by secondary ion mass spectrometry was performed.

Sol–gel derived PNNZT thin films for micromachined piezoelectric force sensors

A novel piezoelectric thin film of Pb(Ni 1/3Nb 2/3) 0.2Zr 0.4Ti 0.4O 3 (PNNZT, 2/4/4) has been successfully deposited on Pt/Ti/SiO 2/Si substrates via a 2-methoxyethanol based sol–gel process. The pure perovskite phase was obtained after 600 °C, 30 min annealing. The optimized annealing condition was at 650 °C for 4 h, and the derived relative permittivity and dissipation factor were 1650 and 0.05. Free-standing piezoelectric PNNZT microcantilevers were sculpted from a Au/Cr/PNNZT/Pt/Ti/SiO 2/Si wafer by a microfabrication process. Then these PNNZT microcantilevers were used as the force sensors for a scanning force microscope (SFM). Force sensors were cantilever shapes with dimensions like 125–200(l)×50(w)×3.7(t) μm 3. An image of an evaporated gold film surface was obtained by SFM using the PNNZT force sensor. The PNNZT films have been proved to be an alternative sensing material for the force sensors of SFMs. © 1997 Elsevier Science S.A.

Measurement of Mechanical Properties of a Thermally Evaporated Gold Film Using Blister Test

Mechanical properties, including Young's modulus, residual stress and rupture strength, of a thermally evaporated gold film have been measured form a blister test. In a theoretical study, the priniple of minimum potential energy and that of virtual work have been applied to the pressurized circular membrane problem, and load-deflection relations have been derived for typical membrane deflection mode of spheroidal shape. In an experimental study, circular gold membranes of 4800 A-thickness and 3.5mm diameter were fabricated by the silicon electropolishing technique. Mecahnical properties of the thin gold films were deduced from the load-deflection curves obtained by the blister test, Young's moduli, obtianed from blister test, have been in the range of 45-70 GPa, while those of bulk gold have been in the range of 78-80 GPa. Residual stresses in the evaporated gold films have been measured as 28-110MPa in tension, The rupture strength of the gold film has turned out to be almost equal to that of dental gold alloy (310-380MPa). It has been demonstrated that the present specimen fabrication method and blister test apparatus have been effective for simultaneous measurement of Young's modulus, residual stress and repture strength of thin solid films. Especially, the electropolishing technique employed here has provided a simple and practical way to fabricate thin membranes in a circular or an arbitrary shape, which could not be obtained by the conventional anisotropic silicon mecromachining technique.

High-Pass Optical Filters Based on Gold-Coated Nanochannel Glass Materials

AbstractWe have fabricated high-pass optical filters from thin nanochannel glass (NCG) wafers coated with sputtered and evaporated gold films. The near-infrared (IR) transmission spectra of these filters have a sharp cutoff at a wavelength that scales linearly with the channel diameter, as expected for hollow metallic waveguides. Cutoff wavelengths approaching 1 μm have been achieved to date using NCG materials with sub-micron channel diameters. The spectra are dominated by a strongly resonant transmission peak just above the cutoff wavelength, where the peak transmission can be as much as twice that predicted based on the geometrical open area of the NCG structure. The NCG wafers were typically less than 20 μm thick, and the Au films ranged in thickness up to 600 nm.

Chain Length Dependence of the Structure and Wetting Properties in Binary Composition Monolayers of OH- and CH3-Terminated Alkanethiolates on Gold

Equimolar, binary-component, self-assembled monolayers (SAMs) of -S(CH 2 ) 15 CH 2 OH and -S(CH 2 ) (15+m) -CH 3 , with m varied systematically from -6 to +6, were prepared on evaporated gold films by self-assembly from ethanol solutions of the corresponding thiols. Single-wavelength ellipsometry, X-ray photoelectron spectroscopy, and infrared reflection spectroscopy (IRS) were used to monitor the coverage, composition, and chain conformational order, respectively, in the air/SAM structures, while liquid drop contact angle measurements with hydrogen-bonding and hydrocarbon liquids were used to probe the structural and chemical characteristics at the liquid/SAM interface. Both the IRS C-H stretching mode characteristics and the hydrocarbon liquid contact angles show sharp changes as m increases through the region of -4 to 0, while the hydrogen-bonding liquid contact angles remain essentially constant across the range of m values. The combined data lead to a general structural model in which monolayer structures shift from randomly placed, protruding HO-terminated chain segments which screen the underlying CH 3 surface at low m to contiguously placed, protruding CH 3 -terminated chains, organized in clusters and extending away from the underlying CH 2 OH surface at high m. These structures require that the monolayers approach random mixing at low m but be phase-segregated at high m.