Preparing contamination-free mica substrates for surface characterization, force measurements, and imaging

Due to its perfect cleavage that provides large areas of molecularly smooth, chemically inert surfaces, mica is the most commonly used natural substrate in measurements with the surface forces apparatus (SFA), in atomic force microscopy (AFM), and in many adsorption studies. However, preparing mica surfaces that are truly clean is not easy since mica is a high-energy surface that readily adsorbs water, organic contaminants, and gases from the atmosphere. Mica can also become charged on cleaving, which makes it prone to picking up oppositely charged particles or mica flakes from the surroundings. High refractive index particles, such as metals, will adhere to mica through van der Waals forces. Recent articles have demonstrated that particle contamination is obtained when inappropriate cutting and handling procedures for the mica are used. In this paper, we show that both particle and other critical contamination is easy to detect and provide proper steps to take during the sample preparation process.     

Peptide Modified Electrodes as Electrochemical Metal Ion Sensors

Sensors for the detection of metal ions are of considerable importance for enabling the monitoring of environmental samples for metal ion contamination directly in the field. This review outlines the use of peptides and amino acids as the recognition element of electrochemical sensors for metal ion detection. Initially the complexation of metals by peptides is discussed followed by the immobilization of peptides on electrode surfaces. Subsequently, the application of peptide modified electrodes for detecting metals is reviewed and finally challenges and future prospects are outlined.     

Specimen transfer from the electrolyte to the UHV in a closed system and some examinations of the double layer on Cu

A transfer system is described which permits the electrochemical preparation of specimens in a purified argon atmosphere and their transport into the UHV for surface analysis. This transfer prevents contamination and oxide formation on semi-noble metals. Reactive metals from only a few monolayers of oxide. This permits examination of electrochemically prepared metal surfaces, which is otherwise not possible. For hydrophobic copper surfaces, the composition of the electrical double layer may be studied. The extraction of the electrode strips the electrolyte off in the vicinity of the Helmholtz layer. For NaClO₄ solutions, the amount of Na⁺ ions and the excess charge decrease linearly with the electrode potential in agreement with a constant electrode capacity. The formation of a prepassive and passive layer leads to a pronounced increase of adsorbed Na⁺ ions. For Cs₂SO₄, specific and co-adsorption of both ions is observed with a minimum in the region of the potential of zero charge.     

Molecular approaches to solar energy conversion with coordination compounds anchored to semiconductor surfaces

Strategies toward the realization of molecular control of interfacial charge transfer at nanocrystalline semiconductor interfaces are described. Light excitation of coordination compounds, based on (dpi)6 transition metals, anchored to wide band-gap semiconductors, such as TiO2, can initiate electron-transfer processes that ultimately reduce the semiconductor. Such photoinduced charge-separation processes are a key step for solar energy conversion. The thermodynamics and kinetic rate constants for three different interfacial charge separation mechanisms are discussed. Tuning the energetic position of the semiconductor conduction band relative to the molecular sensitizer has provided new insights into interfacial charge transfer. Supramolecular compounds that efficiently absorb light, promote interfacial electron transfer, and feature additional functions such as intramolecular electron transfer when bound to semiconductor surfaces have also been studied. New approaches for enhancing charge-separation lifetimes for solar energy conversion are presented.     

Effects of Electron Correlations in a Simple Model for Adiabatic Electrochemical Reactions: The General Relationships

General relationships for adiabatic free-energy surfaces (AFES) for electrochemical reactions of electron transfer are derived in the framework of exactly solvable model of the so-called surface molecule, which is a limiting case of Anderson's Hamiltonian and may be applied to transition metals. As opposed to earlier models for adiabatic reactions, the model exactly allows for the effects of electron–electron correlations. The obtained results constitute a basis for calculating AFES and plotting diagrams that correspond to different kinetic regimes of one- and two-electron processes.     

Soft-landing of peptide ions onto self-assembled monolayer surfaces: an overview

This review is focused on what has been learned in recent research studies concerned with fundamental aspects of soft-landing and reactive landing of peptide ions on self-assembled monolayer surfaces (SAMs). Peptide ions are particularly attractive model systems that provide important insights on the behavior of soft landed proteins, while SAMs provide a convenient and flexible platform for tailoring the interfacial properties of metals and semiconductor surfaces. Deposition of mass-selected ions on surfaces is accompanied by a number of processes including charge reduction, neutralization, covalent and non-covalent binding, and thermal desorption of ions and molecules from the substrate. Factors that affect the competition between these processes are discussed.     

Modeling drop shape on contaminated surfaces or surfaces with physical structures

Surface contaminants are commonly found on films. They get transferred to the surface from incompletely cured silicone liners on the films or owing to migration of additives to the surface from within the film. During the process of ink jet printing (a noncontact printing process), surface contamination affects the shape of the drops (causing the formation of fingers and crescents) and hence image quality. This study uses modeling methods to examine how such surface contamination affects the drops shapes. Subsequently, it models the effect of surface structures (pits) on the drop shape. This study explores how image quality can be controlled in the presence of surface contamination and surface structures.     

铅污染土壤的修复技术

综述了铅对土壤的污染及其修复技术。目前应用于污染土壤的修复技术可分为物理化学修复技术和生物修复技术。物理化学修复技术又可分为隔离包埋技术,固化稳定技术,Pyrometalluryical separation,化学稳定技术,电动修复技术等;生物修复技术可分为微生物修复技术和植物修复技术等。以期进一步推动铅污染土壤的治理和修复工作。     

On the HSAB based estimate of charge transfer between adsorbates and metal surfaces

The applicability of the HSAB based electron charge transfer parameter, ΔN, is analyzed for molecular and atomic adsorbates on metal surfaces by means of explicit DFT calculations. For molecular adsorbates ΔN gives reasonable trends of charge transfer if work function is used for electronegativity of metal surface. For this reason, calculated work functions of low Miller index surfaces for 11 different metals are reported. As for reactive atomic adsorbates, e.g., N, O, and Cl, the charge transfer is proportional to the adatom valence times the electronegativity difference between the metal surface and the adatom, where the electronegativity of metal is represented by a linear combination of atomic Mulliken electronegativity and the work function of metal surface. It is further shown that the adatom-metal bond strength is linearly proportional to the metal-to-adatom charge transfer thus making the ΔN parameter a useful indicator to anticipate the corresponding adsorption energy trends.     

Review of the heats of chemisorption of gases at metals in the context of the problem of ‘Heterogeneous’ <Emphasis Type="Italic">vs.</Emphasis> ‘Homogeneous’ catalytic surfaces

A critical review of available data on the heats of chemisorption of gases at metals is given. The effect of upward technical and procedural trends on measured results is demonstrated. The results for surfaces approached to their states occurring in catalytic processes are accentuated. Several tens of chemisorbent/gas systems are considered; a number of the results are confirmed by several independent measurements. The coverage-independence of heats of chemisorption for powders, supported catalysts, components of multi-component catalysts, and films is demonstrated; the better the techniques and procedures, the closer to zero the angle between the heat-coverage function and the abscissa. The principal conclusion on surface homogeneity of stabilized surfaces is made.     

Metals in biology: Electronic structure,properties and charge transfer for copper complexes of glyoxal and dithiene

Summary In an attempt to study the role of metals in biologyab initio SCF calculations have been performed on a model complex simulating the binding between metals and biological materials. There is a certain distinction between the copper complexes compared to the other transition metals and in many cases the copper complexes are more similar to the Li and Be complexes than to other transition metal complexes. One special feature of the copper complexes is their strong ability for an easy transfer between the Cu(I) and Cu(II) states, allowing for a very flexible charge transfer with small energies required for the redox processes. These processes have been described in terms of orbital energies and Mulliken populations.Dedicated to Professor Inga Fischer-Hjalmars on the occasion of her 75th birthday     

Kinetics of contact electrification between metals and polymers

Kinetics of charge transfer between metals and polymers was studied using an analytical rolling-sphere tool. The rates of charge transfer were related to the area of contact between contacting surfaces and the tunneling current between them. The derived rate equations accounted for the experimentally observed sigmoidal charging curves. Furthermore, for a model system of steel spheres rolling on modified polystyrene supports, it was shown that the magnitudes of separated charges can be varied by adjusting the polymer's surface properties and/or ambient conditions.     

Weak charge transfer between an acceptor molecule and metal surfaces enabling organic/metal energy level tuning

Evidence for charge transfer (CT) between the electron acceptor molecule octafluoroanthraquinone (FAQ) and the metal surfaces Ag(111) and polycrystalline Au is provided by ultraviolet photoelectron spectroscopy. The energy level alignment of subsequently deposited sexithienyl (6T) on FAQ-precovered metal substrates was investigated. Due to the metal work function change induced by the FAQ-metal CT, the hole injection barrier of 6T on FAQ-precovered metals could be reduced by up to 0.60 eV compared to that of 6T on pristine metal surfaces.     

Heavy Metals and Human Health: Possible Exposure Pathways and the Competition for Protein Binding Sites

Heavy metals enter the human body through the gastrointestinal tract, skin, or via inhalation. Toxic metals have proven to be a major threat to human health, mostly because of their ability to cause membrane and DNA damage, and to perturb protein function and enzyme activity. These metals disturb native proteins’ functions by binding to free thiols or other functional groups, catalyzing the oxidation of amino acid side chains, perturbing protein folding, and/or displacing essential metal ions in enzymes. The review shows the physiological and biochemical effects of selected toxic metals interactions with proteins and enzymes. As environmental contamination by heavy metals is one of the most significant global problems, some detoxification strategies are also mentioned.     

The effect of ion-conducting spacers on mass transfer — numerical analysis and concentration field visualization by means of laser interferometry

Mathematical model is developed for the study of mass transfer processes under the laminar stationary flow in the channels of electromembrane system formed by alternating cation- and anion-exchange membranes at whose surfaces the ion-conducting spacers are fixed. The results of calculations are given of velocity and concentration fields, of current density distribution along the channel length for some values of Reynolds number and the values of the applied voltage. The comparison is made between the calculated mass transfer characteristics and the experimental data obtained by means of laser interferometry.     

Electrochemical charge transfer mediated by metal nanoparticles and quantum dots

Electron transfer processes mediated by nanostructured materials assembled at electrode surfaces underpin fundamental processes in novel electrochemical sensors, light energy conversion systems and molecular electronics. Functionalisation of electrode surfaces with hierarchical architectures incorporating self-assembling molecular systems and materials, such as metal nanostructures, quantum dots, carbon nanotubes, graphene or biomolecules have been intensively studied over the last 20 years. Important steps have been made towards the rationalisation of the charge transfer dynamics from redox species in solution across molecular self-assembling systems to electrode surfaces. For instance, a unified picture has emerged describing the factors which determine the rate constant for electron transfer processes across rigid self-assembling molecular barriers. An increasing bulk of evidence has recently shown that the incorporation of nanomaterials into self-assembling monolayers leads to an entirely different electrochemical behaviour. This perspective rationalises some of the key observations associated with nanoparticle mediated charge transfer, such as the apparent distance independent charge transfer resistance observed for redox species in solution. This behaviour only manifests itself clearly in the case where the probability of direct charge transfer from the redox probe to the electrode is strongly attenuated by self-assembling molecular barriers. Here we will highlight specific issues concerning self-assembled monolayers as blocking barriers prior to discussing the effect of nanoparticles on the electrochemical response of the system. Selected examples will provide conclusive evidence that the extent of charge transfer mediation is determined by the overlap between the density of states of the nanostructures and the energy levels of redox species in solution. Only in the case where a strong overlap exists between the energy levels of the two components, the nanostructures behave as "electron launchers", allowing efficient charge transfer across insulating molecular layers.     

Semi-Automated Determination of Heavy Metals in Autopsy Tissue Using Robot-Assisted Sample Preparation and ICP-MS

The endoprosthetic care of hip and knee joints introduces multiple materials into the human body. Metal containing implant surfaces release degradation products such as particulate wear and corrosion debris, metal-protein complexes, free metallic ions, inorganic metal salts or oxides. Depending on the material composition of the prostheses, a systemic exposure occurs and may result in increasing metal concentrations in body fluids and tissues especially in the case of malfunctions of the arthroplasty components. High concentrations of Cr, Co, Ni, Ti and Al affect multiple organs such as thyroid, heart, lung and cranial nerves and may lead to metallosis, intoxications, poly-neuropathy, retinopathy, cardiomyopathy and the formation of localized pseudo tumors. The determination of the concentration of metals in body fluids and tissues can be used for predicting failure of hip or knee replacements to prevent subsequent severe intoxications. A semi-automated robot-assisted measurement system is presented for the determination of heavy metals in human tissue samples using inductively coupled plasma mass spectrometry (ICP-MS). The manual and automated measurement processes were similarly validated using certified reference material and the results are compared and discussed. The automation system was successfully applied in the determination of heavy metals in human tissue; the first results are presented.     

Multivariate geostatistical analysis of soil contaminations

Soil is one of the most endangered compartments of our environment. The input of pollutants into the soil caused by industrial production, agriculture, and other human activities is a problem of high relevance. A contour analysis of soil contamination is the first step to characterize the size and magnitude of pollution and to detect emission sources of heavy metals. The evaluation and assessment of the large number of measured samples and pollutants require the use of efficient statistical methods which are able to discover both spatial and multivariate relationships. The evaluation of the presented case study – soil contamination by heavy metals – is carried out by means of multivariate geostatistical methods, also described as theory of linear coregionalization. Multivariate geostatistics connects the advantages of common geostatistical methods (spatial correlation) and multivariate data analysis (multivariate relationships). In the given case study of soil pollution by heavy metal emissions it is excellently possible to detect multivariate spatial correlations between different heavy metals in the soil and to determine their common emission sources. These emission sources are located in the area under investigation. Received: 2 October 1997 / Revised: 22 January 1998 / Accepted: 27 January 1998     

Ultrafast charge transfer at surfaces accessed by core electron spectroscopies

Charge transfer at surfaces, which is very important for surface photochemistry and other processes, can be extremely fast. This tutorial review shows how high resolution correlated excitation/decay spectroscopies of core excitations can be used to obtain charge transfer times at surfaces around or below 1 fs. Some results are described in more detail, and their meaning and theoretical modelling are discussed. A brief comparison to laser methods shows that there are differences in the processes they look at.