Preparation of Surface Standards of Copper on Substrates of Platinum and Glass for X-Ray Photoelectron Spectroscopy in Adsorption Studies

Abstract

Changes in concentration of very dilute solutions of metals, due to adsorption on the walls of the container, are well known. Earlier studies, however, have been confined to follow the changes in trace metal concentration of the solution phase with time. Characterisation of the solid surface is equally important and for such a study are needed reproducible thin layers of the ions under consideration on the particular substrate. Deposition of thin layers of copper on platinum by electrodeposition and solution evaporation of CuCl₂ on platinum gave comparable results on examination of the Cu 2p peaks by XPS. Solution evaporation was found successfully for the sodium glass substrate as well. However, solution evaporation could not be applied to Teflon or PVC substrates.     

Polymer patterns in evaporating droplets on dissolving substrates

Self-organized polymer patterns resulting from the evaporation of an organic solvent drop on a soluble layer of polymer are investigated. The patterns can be modulated by changing the rate of evaporation and also the rate of substrate dissolution controlled by its solubility. Both of these affect the contact zone motion and its instabilities, leading to spatially variable rates of substrate etching and redeposition that result from a complex interplay of several factors such as Rayleigh-Benard cells, thermocapillary flow, solutal Marangoni flow, flow due to differential evaporation, osmotic-pressure-induced flow, and contact-line pinning-depinning events. The most complex novel pattern, observed at relatively low rates of evaporation, medium solubility, and without macroscopic contact-line stick-slip, consists of a regularly undulating ring made up of a bundle of parallel spaghetti-like threads or striations and radially oriented fingerlike ridges. Increased rate of evaporation obliterates the polymer threads, producing more densely packed fingers and widely separated multiple rings due to a frequent macroscopic pinning-depinning of the contact line. Near-equilibrium conditions such as slow evaporation or increased solubility of the substrate engender a wider and less undulating single ring.     

The influence of gravity on the distribution of the deposit formed onto a substrate by sessile, hanging, and sandwiched hanging drop evaporation

The focus of the present article is the study of the influence of gravity on the particle deposition profiles on a solid substrate during the evaporation of sessile, hanging and sandwiched hanging drops of colloidal particle suspensions. For concentrations of nanoparticles in the colloidal solutions in the range 0.0001-1 wt.%, highly diluted suspensions will preferentially form rings while concentrated suspensions will preferentially form spots in both sessile and hanging drop evaporation. For intermediary concentrations, the particle deposition profiles will depend on the nanoparticle aggregation dynamics in the suspension during the evaporation process, gravity and on the detailed evaporation geometry. The evaporation of a drop of toluene/carbon nanoparticle suspension hanging from a pendant water drop will leave on the substrate a circular spot with no visible external ring. By contrast, a clear external ring is formed on the substrate by the sessile evaporation of a similar drop of suspension sandwiched between a water drop and the substrate. From the application viewpoint, these processes can be used to create preferential electrical conductive carbon networks and contacts for arrays of self-assembled nanostructures fabricated on solid substrates as well as on flexible polymeric substrates.     

Modeling of drying in films of colloidal particles

The process of film formation on a solid substrate from polymer colloid dispersion during solvent evaporation has been investigated by means of the Monte Carlo simulation method. Colloid particles are modeled as hard spheres. Time evolution of the colloid density distribution and coverage of the solid substrate are studied. Both density and structure of colloid film is shown to depend strongly on the evaporation rate. At a low evaporation rate, the coexistence of hexagonal and tetragonal domains of dried colloid monolayer has been observed. The results of monolayer structure are in good agreement with the confocal scanning laser microscopy observations of Dullens et al. (2004).     

Carbon nanotube network formation from evaporating sessile drops

Fabrication of single-walled carbon nanotube (SWNT) networks using evaporation of SDS-SWNT sessile drops on a hydrophobized silicon substrate is reported. It is suggested that the organization of nanotubes during evaporation is controlled by aggregates (in the SDS-SWNT dispersion) and hydrophobicity of the substrate. On hydrophobic substrates, the evaporation of SDS-SWNT sessile drops proceeds through constant contact area. On hydrophilic substrates, nanotube aggregates in SDS-SWNT dispersion stop the contact line from moving, resulting in the formation of "coffee-stains". The (partial) removal of aggregates by centrifugation is essential for a freely moving contact line leading to the organization of nanotubes into a network of homogeneously distributed nanotubes on the most hydrophobic substrate. The evaporation of sessile drops was characterized by microscopic, spectroscopic, and topographical techniques.     

Evaporation of two solution droplets and a droplet located near a flat liquid surface

The mutual influence of two moderate-sized droplets of a dilute nonvolatile substance solution on the processes of their evaporation or condensation is theoretically analyzed under the assumption of a uniform concentration distribution inside the droplets. The conditions for the applicability of this approach are revealed. The evaporation or condensation of a droplet near a flat liquid surface is considered as a limiting case. The fluxes of water molecules to and from the surface of aqueous glycerol solution droplets occurring in air are numerically estimated depending on the droplet radii, distances between their surfaces, and air humidity. Analogous estimates are obtained for an aqueous glycerol solution droplet growing near a flat water surface.     

Diffusion,evaporation, and surface enrichment of a plasticizing additive in an annealed polymer thin film

We present the first measurements of the simultaneous diffusion, surface enhancement, and evaporation of a plasticizer from a polymer, thin-film matrix using neutron reflection techniques. The reflectivity profiles as a function of the annealing time at an elevated temperature yield the time-dependent, plasticizer volume fraction profiles in a polyester–polyurethane (Estane) film. Thin, plasticizer-enriched layers form at both the polymer/substrate and polymer/air interfaces for annealed and unannealed samples. The diffusion equations for a material diffusing through a film and then evaporating into a vacuum at the free surface describe the loss of the plasticizer from the film for annealed samples. The loss of the plasticizer from the film is not limited by the movement of the plasticizer through the polymer matrix but is dominated by the plasticizer's rate of evaporation from the surface. The rate of evaporation and the volume fraction profiles for the plasticizer at the substrate interface are both consistent with surface attractions dominating over bulk attractions between the miscible plasticizer and the polymer. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3258–3266, 2004     

Evaporation of pure liquid sessile and spherical suspended drops: a review

A sessile drop is an isolated drop which has been deposited on a solid substrate where the wetted area is limited by a contact line and characterized by contact angle, contact radius and drop height. Diffusion-controlled evaporation of a sessile drop in an ambient gas is an important topic of interest because it plays a crucial role in many scientific applications such as controlling the deposition of particles on solid surfaces, in ink-jet printing, spraying of pesticides, micro/nano material fabrication, thin film coatings, biochemical assays, drop wise cooling, deposition of DNA/RNA micro-arrays, and manufacture of novel optical and electronic materials in the last decades. This paper presents a review of the published articles for a period of approximately 120 years related to the evaporation of both sessile drops and nearly spherical droplets suspended from thin fibers. After presenting a brief history of the subject, we discuss the basic theory comprising evaporation of micrometer and millimeter sized spherical drops, self cooling on the drop surface and evaporation rate of sessile drops on solids. The effects of drop cooling, resultant lateral evaporative flux and Marangoni flows on evaporation rate are also discussed. This review also has some special topics such as drop evaporation on superhydrophobic surfaces, determination of the receding contact angle from drop evaporation, substrate thermal conductivity effect on drop evaporation and the rate evaporation of water in liquid marbles.     

Influence of substrate heating on the evaporation dynamics of pinned water droplets

The dynamics of evaporating water droplets deposited on a heated substrate is investigated numerically. Droplets are pinned with a contact line radius of R = 1 mm. Evaporative mass flow and convection occurring inside the droplets are studied for different heating substrate sizes L S and heating temperatures T S. A simplified model neglecting hydrodynamics in air and evaporative cooling and assuming droplets to be spherical caps is simulated with a finite element method. A toruslike convective cell appears inside the droplets as evaporation takes place. For L S/ R > 1, the contact line is warmer than the apex of the droplets, and convection generates a downstream flow in the vicinity of the symmetry axis of the droplets. For L S/ R < 1, it is the apex that is warmer. Convection then generates an upstream flow. The overall evaporation time is described. It slows when L S/ R > 1.     

Electroluminescence Characteristics of Card Anthracene-containing Polyimide: The Effect of the Cathode and Anode Materials

The effect of electrode materials on the characteristics of electroluminescence devices of the type transparent conductive substrate/polyimide/metallic electrode is studied. The reasons for variations in the electroluminescence spectra after replacing the substrate material and the metal of the top electrode are discussed. The applicability of the Fauler–Nordheim model for describing the injection of charge carriers in the electroluminescence devices under study is analyzed.     

Large-scale controllable patterning growth of aligned organic nanowires through evaporation-induced self-assembly

Organic one-dimensional nanostructures are attractive building blocks for electronic, optoelectronic, and photonic applications. Achieving aligned organic nanowire arrays that can be patterned on a surface with well-controlled spatial arrangement is highly desirable in the fabrication of high-performance organic devices. We demonstrate a facile one-step method for large-scale controllable patterning growth of ordered single-crystal C(60) nanowires through evaporation-induced self-assembly. The patterning geometry of the nanowire arrays can be tuned by the shape of the covering hats of the confined curve-on-flat geometry. The formation of the pattern arrays is driven by a simple solvent evaporation process, which is controlled by the surface tension of the substrate (glass or Si) and geometry of the evaporation surface. By sandwiching a solvent pool between the substrate and a covering hat, the evaporation surface is confined to along the edge of the solvent pool. The geometry of the formed nanowire pattern is well defined by a surface-tension model of the evaporation channel. This simple method is further established as a general approach that is applicable to two other organic nanostructure systems. The I-V characteristics of such a parallel, organic, nanowire-array device was measured. The results demonstrate that the proposed method for direct growth of nanomaterials on a substrate is a feasible approach to device fabrication, especially to the fabrication of the parallel arrays of devices.     

Formation of fractal structures upon the evaporation of nanoparticle dispersion droplets

The regularities of the self-organization of silver nanoparticles on solid substrates upon the evaporation of droplets of their aqueous dispersions were studied. The evaporation rate of the dispersion medium varied within a wide range. Upon a slow evaporation of the dispersion medium, a dense ring-like precipitate is formed around the droplet perimeter, where almost all particles are accumulated. In the vicinity of a rim, an ordered nanoparticle arrangement was observed. As the evaporation rate of the dispersion medium increases, most of the silver nanoparticles remain in the inner zone, limited by a rather dense rim, and form 2D fractal structures. At some regimes of droplet evaporation, 3D fractal structures were assembled whose shape depended on the substrate nature.Translated from Kolloidnyi Zhurnal, Vol. 66, No. 6, 2004, pp. 862–864.Original Russian Text Copyright © 2004 by Vysotskii, Roldughin, Uryupina.     

Diffusion-controlled evaporation of sodium dodecyl sulfate solution drops placed on a hydrophobic substrate

In this work, the effect of SDS anionic surfactant on the diffusion-controlled evaporation rate of aqueous solution drops placed on TEFLON-FEP substrate was investigated with 11 different SDS concentrations. Drop evaporation was monitored in a closed chamber having a constant RH of 54-57% by a video camera. The initial contact angle, θ(i) decreased from 104±2° down to 68±1° due to the adsorption of SDS both at the water-air and the solid-water interfaces. The adsorption of SDS on the solid surface was found to be 76% of that of its adsorption at the water-air interface by applying Lucassen-Reynders approach. An equation was developed for the comparison of the evaporation rates of drops having different θ(i) on the same substrate. It was found that the addition of SDS did not alter the drop evaporation rate considerably for the first 1200 s for all the SDS concentrations. The main difference was found to be the change of the mode of drop evaporation by varying the SDS concentration. The constant θ mode was operative up to 80 mM SDS concentration, whereas constant contact area mode was operative after 200 mM SDS concentrations due to rapid drop pining on the substrate.     

Effect of temperature on ring-shaped-deposit formated at evaporation of droplets of silver-nanoparticle dispersions

The effect of temperature is studied on the geometric parameters and conductivity of ring-shaped deposits formed at evaporation of droplets of dispersions of silver nanoparticles on hydrophilic (glass) and hydrophobic (copper) substrates. It has been shown that increasing temperature leads to substantial changes in the deposit profile. Therewith, the effects of temperature on droplet evaporation on glass and copper substrates are different. It has been found that the lateral conductivity of a ring-shaped deposit formed on a glass substrate increases stepwise similarly to a percolation transition at a droplet-evaporation temperature of 58°C. It has been suggested that the reason for the temperature effect is related to a change in the ratio between the rates of physicochemical processes occurring at different stages of droplet evaporation.     

Surface-enhanced Raman spectrometry on a silver-coated filter paper substrate

The production, morphology, and optical properties of silver-coated filter paper as a new active substrate for surface-enhanced Raman spectrometry (SERS) are reported. The procedure involves a simple, one-stage reduction of filter-paper-supported silver nitrate with sodium tetrahydroborate. Intense and reproducible spectra of a variety of ionic and molecular adsorbates including p-aminobenzoic acid, acridine, 9-aminoacridine, 2-aminoanthracene, 6-nitroquinoline and 5-aminoquinoline are obtained. Simplicity, low cost, speed and availability are salient features of the substrate, which extend the applicability of the SERS technique to more practical situations.     

Wetting and evaporation of binary mixture drops

Experimental results on the wetting behavior of water, methanol, and binary mixture sessile drops on a smooth, polymer-coated substrate are reported. The wetting behavior of evaporating water/methanol drops was also studied in a water-saturated environment. Drop parameters (contact angle, shape, and volume) were monitored in time. The effects of the initial relative concentrations on subsequent evaporation and wetting dynamics were investigated. Physical mechanisms responsible for the various types of wetting behavior during different stages are proposed and discussed. Competition between evaporation and hydrodynamic flow are evoked. Using an environment saturated with water vapor allowed further exploration of the controlling mechanisms and underlying processes. Wetting stages attributed to differential evaporation of methanol were identified. Methanol, the more volatile component, evaporates predominantly in the initial stage. The data, however, suggest that a small proportion of methanol remained in the drop after the first stage of evaporation. This residual methanol within the drop seems to influence subsequent wetting behavior strongly.     

Driving forces of the solute self-organization in an evaporating liquid microdroplet

A method is proposed for preparing solid phases of desired morphologies from microscopic droplets on solid substrates with a GMS 417 Arrayer, which is commonly used for biochip production. The initial droplet of an aqueous solution is about 100 pl (about 100 μm in diameter), and the evaporation time is about 0.5 s. Such small solution volumes are first considered from the viewpoint of the solute self-organization. Aqueous solutions of inorganic molecular and ionic substances, organic dyes, and latex colloid particles in the evaporating droplets are experimentally studied. Various substrates and solute concentrations are used. The morphology of the solid phase formed on the substrate after water evaporation is analyzed with the use of computer simulation of dynamics of the latex particles within the evaporating microdroplet. Elucidating the self-organization mechanisms will facilitate producing of the desired morphology of the solid phase, which can find an application in nanotechnology.     

Marangoni flow-induced self-assembly of hexagonal and stripelike nanoparticle patterns

We have developed a simple Marangoni flow-induced method for self-assembling nanoparticles (NPs) into both hexagonal and stripelike patterns. First, a NPs/ethanol suspension was spread on a slightly nonwettable and a wettable silicon oxide substrate. The Marangoni flow, induced by simultaneous evaporation of ethanol and condensation of water, leads to the formation of the corresponding hexagonal distributed circular NP rings and dotted stripes. The inter-ring spacing and ring size of the hexagonal patterns can be tuned by varying the relative humidity of the N2 stream blown over the slightly nonwettable substrate. Hexagonal patterns of circular NP patches can also be fabricated by lowering the evaporation of the condensed water droplets. On the wettable substrate, complex patterns result when the humidity of the N2 stream changes.     

Toward the growth of an aligned single-layer MoS2 film

Molybdenum disulfide (molybdenite) monolayer islands and flakes have been grown on a copper surface at comparatively low temperature and mild conditions through sulfur loading of the substrate using thiophenol (benzenethiol) followed by the evaporation of Mo atoms and annealing. The MoS(2) islands show a regular Moire? pattern in scanning tunneling microscopy, attesting to their atomic ordering and high quality. They are all aligned with the substrate high-symmetry directions providing for rotational-domain-free monolayer growth.