bluuebunny/crossref_metadata_2025_split huggingface dataset:
Scanning Tunneling Microscopy/Spectroscopy in Analysis of Surfaces
Authors: Dharmadhikari C.V. 
Published: September 2006

Abstract
Scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS) and related techniques with their unique capability to resolve topological and electronic structures at atomic level have revolutionized the power of experimental techniques in high resolution imaging of surfaces. In STM, a sharp conducting tip is mechanically scanned over a conducting or semi‐conducting sample at the distance of few angstroms from the surface. A voltage bias applied between the tip and the sample leads to flow of tunnel current, which decreases exponentially as the gap increases. By keeping the tunnel current constant with an electronic feedback controller the tip is maintained at a fixed distance during the scanning by means of a 3‐D scanner made of a piezoelectric transducer. The trajectory of the tip then traces out a profile of the surface, including the bumps due to individual atoms. In the context of atomic resolution imaging capability, there are only a few techniques such as scanning transmission electron microscopy (STEM), transmission electron microscopy (TEM) and field ion microscopy (FIM) which perform as well as STM, but they do so under extremely special circumstances. The traditional spectroscopic techniques that can be compared with STS are those of conventional (elastic) electron tunneling spectroscopy (ETS) and inelastic electron tunneling spectroscopy (IETS), X‐ray photoelectron spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS) and inverse photoemission spectroscopy (IPS). But all these techniques detect and average the data from a relatively large area, a few microns to a few millimeters across. The STM/STS, in contrast, can take spectra localized to as small an area as an individual atom. The most important characteristic that distinguishes STM/STS from other techniques is ability to operate in a variety of different environments such as air, reactive gases, liquids, electrolytes and biological fluids, leading to its applications not only in basic research in surface science but also in such diverse fields as lithography, electrochemistry, biology and medicine. An inherent limitation of STM is that it always operates at high resolution and, therefore, works better for atomically flat surfaces.
SoftX‐Ray Photoelectron Spectroscopy in Analysis of Surfaces
Authors: Yarmoff Jory A. 
Published: September 2006

AbstractX‐ray photoelectron spectroscopy (XPS) is widely used to measure the composition and chemical states of species in the near‐surface region of a solid material in ultrahigh vacuum (UHV). In XPS, the core‐level, or inner‐shell, electrons that are emitted via the photoelectric effect are measured. The spectra provide information related to the electronic structure and chemical composition of the near‐surface region and to the bonding of adsorbates onto the surface. Because the mean free path for electrons traveling in solids is small, the spectra reflect the composition of the outermost few atomic layers. When synchrotron light is used as the excitation source, the technique is known as soft X‐ray photoelectron spectroscopy (SXPS). There are many advantages of synchrotron radiation over conventional XPS. For example, the photon energy is tunable over a wide range, which allows for the enhancement of particular spectral features and for unique types of spectroscopy in which the photon energy is continuously varied. The spectral resolution is also greatly enhanced, which allows for the observation of features not otherwise discernible. Also, the brightness of the beam is much greater than that of conventional X‐ray sources, thereby allowing for the detection of very small photoelectron signals. SXPS has been applied to a wide variety of materials, including metals, semiconductors, adsorbates on surfaces and nanoparticles. The information obtained from SXPS includes determining the core‐level binding energies of individual surface atoms, the position of the Fermi level within the gap of a semiconductor, and the surface work function. Shifts of the core‐level binding energy are observed for the outermost atoms on clean surfaces because they are in a different chemical environment than the atoms in the bulk. When an adsorbate attaches to a surface atom, there is a shift in binding energy that is related to the degree of charge transfer during bonding, i.e. the oxidation state. Analysis of the intensity of the shifted components provides the coverage and chemical state distribution of each adsorbate. Novel uses of SXPS include ultrahigh‐resolution spectroscopy, SXPS microscopy, photoelectron diffraction and spin‐polarized photoemission. The equipment utilized for SXPS includes an electron storage ring, an X‐ray monochromator, and an electron spectrometer.
Flow Injection Analysis Techniques in Atomic Spectroscopy
Authors: Pereiro Rosario , Sanz‐Medel Alfredo 
Published: September 2006

Abstract
Flow injection analysis (FIA), developed originally for the automation of serial assays, has become a powerful tool most adequate for performing on‐line any sample preparations before final measurement (e.g. sample dissolution, dilutions, matrix removal, preconcentration, etc.). It is not surprising that the combination of FIA with atomic spectrometric techniques has enlarged the analytical potential of atomic methods and expanded their wide field of applications. The collection of sample manipulation processes which can be covered today by flow operation procedures is amazing and therefore the general instrumentation required is reviewed in this contribution.
The description of the different flow strategies is carried out according to a hierarchy going from simple dilutions (including isotopic dilution of particular interest when using mass spectrometric detection), reagent mixing or standard additions, to more sophisticated flow manifolds such as those based on the use of two phases (e.g. gas–liquid, liquid–liquid or solid–liquid) for separation/preconcentration purposes. Modern approaches allowing for on‐line decomposition/dissolution of solid samples (e.g. on‐line chemical oxidation, photo‐oxidation and microwave heating) are also described. Finally, manifolds for the in situ uptake of the sample and its complete on‐line pretreatment are discussed.
The coupling of the above flow methodologies to a variety of atomization/excitation/ionization sources (flames, quartz tubes, graphite furnaces, inductively coupled plasmas (ICPs), microwave coupled plasmas, glow discharges (GDs), etc.) is detailed, in order to understand the usefulness of this combination both in atomic techniques based on photon measurements (absorption, emission and fluorescence spectrometry techniques) and on ions measurement mass spectrometry (MS).
Graphite Furnace Atomic Absorption Spectrometry
Authors: Holcombe James A. 
Published: September 2006

Abstract
Graphite furnace atomic absorption spectrometry (GFAAS) is an atomic spectroscopic technique in which a small sample is placed inside a graphite tube that is then resistively heated to accomplish sample desolvation (for liquid samples), ashing or charring (to decompose the sample and volatilize some of the matrix) and finally atomization. The light from a line source characteristic of the element being determined is passed longitudinally through the tube and the absorbance resulting from the presence of free analyte atoms in the gas phase is measured. The signal is transient in character, lasting approximately 1–5 s, and the area under this transient peak is generally used in the construction of a calibration curve. Modern instrumentation provides high levels of automation with capabilities of background correction as well as routine methods of sample analysis, for example quality assurance/quality control (QA/QC), standard additions, matrix modification, etc. Since the technique was first introduced in 1969, a lot of progress has been made in understanding the processes occurring within the graphite tube atomizer that ultimately produces the absorbance signal. An understanding of the free atoms formation process has facilitated the application of the technique to the analysis of a variety of complex samples.
Graphite furnace (also known as an electrothermal atomizer or ETA) atomic absorption (AA) is generally considered an ultratrace and microtrace analytical technique with limits of detection (LODs) in the low picogram range, precision of a few percent (relative standard deviation) and a dynamic range of about three orders of magnitude. In addition to its excellent sensitivity, it is unique in its ability to handle microsamples including aqueous solutions, viscous liquids, slurries and even solids. In general, there is considerable literature detailing methods and procedures for the determination of a variety of analytes in complex matrices that can be used by the analyst to apply the approach to new, complex analytical needs. When used correctly, this analytical tool can provide precise, accurate analysis for a wide range of sample types.
Laser‐Induced Breakdown Spectroscopy
Authors: Cremers David A. , Knight Andrew K. 
Published: September 2006

Abstract
Laser‐induced breakdown spectroscopy (LIBS) is a novel method of elemental analysis based on a laser‐generated plasma. Pulses from a laser are focused on a sample to atomize a small amount of material resulting in the formation of a microplasma. Because of the high plasma temperature, the resulting atoms are electronically excited to emit light. The plasma light is spectrallyresolved and detected to determine the elemental composition of the sample based on the unique emission spectrum of each element. Because of the simplicity of the method, it is suited for analyses that cannot be carried out using conventional methods of atomic emission spectroscopy (AES). This is particularly true for measurements that must be conducted outside of an analytical laboratory. A particular advantage of LIBS is the ability to analyze most types of samples without any preparation. This means that samples can be interrogated in situ, providing rapid measurement capability and permitting the method to be used in the analysis of gases, liquids, and solids in a variety of different sampling configurations. Although LIBS provides sensitive detection for many elements, it is not an ultrasensitive detection technique. In addition, under field conditions, the method typically does not provide the high accuracy and precision offered by laboratory‐based methods of AES.
Microwave‐Induced Plasma Systems in Atomic Spectroscopy
Authors: Broekaert José A.C. , Engel Ulrich 
Published: September 2006

AbstractThe use of microwave plasmas as radiation sources for optical atomic emission (AES), absorption (AAS) and fluorescence (AFS) spectroscopy and for laser ionization spectroscopy is treated and reference is also made to the use of microwave‐induced plasmas (MIPs) as ion sources for mass spectrometry (MS). Devices for producing both single‐electrode and electrodeless microwave plasmas are treated, in addition to methods for their diagnostics, and results for the analytically relevant plasma parameters are presented. Methods for sample introduction are discussed. They include dry aerosol generation techniques (hydride generation (HG), electrothermal evaporation, spark and laser ablation (LA)) and possibilities for the uptake of wet aerosols. Special reference is made to coupling with gas chromatography (GC) and also to the potential for coupling with high‐performance liquid chromatography (HPLC) Further, the use of microwave plasmas for cross‐excitation in the case of glow discharges (GDs) is treated. The analytical figures of merit in the case of AES with low‐power microwave plasmas, single‐electrode microwave plasmas, plasma torch sources and stabilized capacitively coupled plasmas are given also in the case of atomic absorption, fluorescence and laser ionization with these sources. The developments in MS in the case of both low‐power and high‐power microwave plasmas and in the case of various types of sample introduction are discussed.Applications of MIP atomic spectroscopy are in the fields of biological samples with special reference to microanalysis, and of environmental samples with special emphasis on metal speciation, on‐line monitoring and direct solids analysis. A critical comparison of the methodology with other methods for the determination of the elements and their species is given.
Classical and Nonclassical Optimization Methods
Authors: Wehrens Ron , Buydens Lutgarde M.C. 
Published: September 2006

Abstract
Optimization problems are abundant in analytical chemistry, examples being the determination of optimal conditions for experiments or optimal settings for instruments. In general, all the required information should be obtained from as few experiments as possible. Classical techniques such as response surface models or simplex optimization are often used. These techniques, which can be very efficient in cases where the underlying assumptions are fulfilled, are called “strong” methods.
With the advent of the computer in the laboratory, a new class of optimization problems arose which could not be tackled with the standard methodologies. For these search‐type problems, new strategies such as simulated annealing (SA) and genetic algorithms (GA) are applied. Although these are not guaranteed to give the optimal result, in almost all cases they are able to find very good solutions where other techniques fail completely. These methods find themselves in an intermediate position between the strong methods, mentioned above, and weak methods, where hardly any assumptions are made.
This article provides an overview of classical and nonclassical optimization techniques, and stresses the differences in their areas of application. The key ideas are highlighted and references to important publications are given.
Signal Processing in Analytical Chemistry
Authors: Wentzell Peter D. , Brown Christopher D. 
Published: September 2006

AbstractSignal processing refers to a variety of operations that can be carried out on a continuous (analog) or discrete (digital) sequence of measurements in order to enhance the quality of information it is intended to convey. In the analog domain, electronic signal processing can encompass such operations as amplification, filtering, integration, differentiation, modulation/demodulation, peakdetection, and analog‐to‐digital (A/D) conversion. Digital signal processing can include a variety of filtering methods (e.g. polynomial least‐squares smoothing, differentiation, median smoothing, matched filtering, boxcar averaging, interpolation, decimation, and Kalman filtering) and domain transformations (e.g. Fourier transform (FT), Hadamard transform (HT), and wavelet transform (WT)). Generally the objective is to separate the useful part of the signal from the part that contains no useful information (the noise) using either explicit or implicit models that distinguish these two components. Signal processing at various stages has become an integral part of most modern analytical measurement systems and plays a critical role in ensuring the quality of those measurements.
Infrared Spectro‐Electrochemistry
Authors: Anderson Mark R. , Taylor C. Douglas 
Published: September 2006

Abstract
The combination of infrared (IR) spectroscopy and electrochemistry in a single measurement has been an area of active research interest since the late 1960s. IR spectroelectrochemical experiments provide insight about interfacial electrochemical phenomena and/or oxidation–reduction reaction mechanisms that cannot be obtained using either technique individually. The power of the measurement is in the complementary nature of the spectroscopic and electrochemical information available when obtained simultaneously. The combination of measurements, however, requires compromise between the IR spectroscopy and the electrochemistry because of their different sampling requirements. The need for compromise illustrates the unique strengths and weaknesses of the combined spectroelectrochemical measurement. Three spectral sampling methods are commonly used: transmission, internal reflection, and specular reflection sampling of the electrochemical experiment. Additional experimental perturbations, such as polarization and electrode potential modulation, are frequently applied to increase the spectral sensitivity toward changes confined to the electrode interfacial region. This article presents the instrumental requirements for, and a theoretical background of, different types of IR spectroelectrochemical measurements.
Liquid/Liquid Interfaces, Electrochemistry at
Authors: Reymond Frédéric , Girault Hubert H. 
Published: September 2006

AbstractThis article outlines the electrochemical methodology at the interface between two electrolyte solutions (ITIES). The fundamental concepts of the thermodynamics in biphasic systems are presented in order to show how ions are distributed between the two adjacent phases, and hence how a Galvani potential difference is established at an ITIES. Polarizable and nonpolarizable ITIES are then characterized, and it is further evidenced that the classical electroanalytical methodology at a solid electrode can be directly transposed to the ITIES, thereby allowing reversible charge‐transfer reactions to be easily monitored and interpreted.This theoretical approach is completed by a review of the analytical methods used at ITIES, namely cyclic voltammetry, dropping electrolyte electrodes, optical techniques and microinterfaces (which are the biphasic analogs of microelectrodes). The last part deals with the practical applications that electrochemistry at ITIES has attracted during the last decade in the development of amperometric ion sensors and detectors, in the extraction of metal ions by interfacial formation of a complex and in the assessment of the lipophilicity of ionizable drugs.
Scanning Tunneling Microscopy, In Situ, Electrochemical
Authors: Itaya Kingo 
Published: September 2006

Abstract
This article describes the in situ scanning tunneling microscopy (STM) operated at electrode–electrolyte interfaces. It is demonstrated that in situ STM makes it possible to monitor with atomic resolution a wide variety of electrode processes such as the adsorption of inorganic and organic species and the dissolution and deposition of metals and semiconductors. Owing to limitations on space, the focus is on selected topics and mainly on our own experimental results.
Self‐Assembled Monolayers on Electrodes
Authors: Finklea Harry O. 
Published: September 2006

Abstract
Alkanethiols and related molecules spontaneously adsorb from solution or vapor phase onto oxide‐free metals, especially gold, to form close‐packed oriented monolayers. The ease and flexibility of the self‐assembly process provides a convenient method for altering the properties of the metal as an electrode. The close‐packed hydrocarbon layer blocks access of most solution species to the electrode surface. Consequently, interfacial capacitances are markedly reduced and most electron‐transfer reactions are strongly inhibited. The monolayers also provide a foundation for attachment of additional molecules or molecular layers to electrodes. Self‐assembled monolayers (SAMs) on electrodes have been used in voltammetric methods to improve the analytical sensitivity and to impart greater selectivity towards specific analytes. Redox molecules have been anchored at fixed and controllable distances from the electrode surface, thereby permitting the study of electron‐transfer kinetics over long distances and at large driving forces. The ability of SAMs to inhibit metal corrosion and to promote better adhesion of electroactive polymers has been demonstrated.
X‐Ray Methods for the Study of Electrode Interaction
Authors: Herrero Enrique 
Published: September 2006

Abstract
X‐ray methods provide an excellent tool for the determination of the structure and composition of the electrode/solution interphase. The possibility of carrying out in situ experiments, because of the low absorbability of the X‐rays by the solution, allows direct correlation to be made between the structural changes observed in the sample and the potential applied. Depending on the interaction of the X‐rays with matter, these techniques can be classified in two main groups: X‐ray absorption techniques and X‐ray scattering techniques. Within the absorption techniques, extended X‐ray absorption fine structure (EXAFS) and X‐ray absorption near edge structure (XANES) will be considered. EXAFS allows determination of the short‐range order of the sample, i.e. it provides information about the nature and distances of the closest neighbors to the absorbing atom. On the other hand, identification of the oxidation state of the absorbing atom can be done with XANES. Grazing incident X‐ray diffraction (GIXD) and crystal truncation rod (CTR) measurements belong to the scattering techniques. The information obtained from these measurements can be considered complementary since GIXD allows precise determination of the long‐range order structure of the interphase whereas CTR analysis gives information about the out‐of‐plane structure of the interphase. The last technique covered, X‐ray standing waves (XSW), is not a pure scattering technique, but rather one that combines X‐ray scattering and X‐ray interference. With this last technique, the exact position of a foreign atom in the interphase can be determined.
Circular Dichroism and Linear Dichroism
Authors: Rodger Alison 
Published: September 2006

AbstractCircular dichroism (CD) is the difference in absorption,A, of left and right circularly polarized light, Equation (1):For randomly oriented systems such as solutions of molecules, only chiral molecules will show any CD intensity corresponding to their absorption bands. Chiral molecules are those molecules that cannot be superposed on their mirror images.1Chiral is derived from the Greek word χɛιρ meaning hand, hence the alternate term for chirality, “handedness”. Two molecules that are mirror images of each other are often referred to as enantiomers and equimolar mixtures of two enatiomers form a racemic mixture which has no net CD intensity in solution.Linear dichroism (LD) is the difference in absorption of light linearly polarized parallel and perpendicular to an orientation axis, Equation (68):
Indirect Detection Methods in Capillary Electrophoresis
Authors: Shamsi Shahab A. 
Published: September 2006

Abstract
An overview is given of existing indirect detection methods of inorganic and organic anions in capillary zone electrophoresis (CZE). Kohlrausch's regulating function (KRF), used by several researchers to predict the detection sensitivity of ultraviolet (UV)‐inactive analytes in CZE, is reviewed. Sensitive indirect photometric detection (IPD) of ionic compounds in CZE is largely governed by the value of the change in absorbance in a solute zone. This in turn depends on a transfer ratio (TR), ratio of the charge, and ratio of the electrophoretic mobility of the analyte and IPD reagent. The influence of other experimental parameters, such as pH, type and concentration of the absorbing electrolyte, detection wavelength, and absorption pathlength, on detection sensitivity are also critically discussed. An extensive part of this review deals with the separation of various classes ofionic analytes using capillary zone electrophoresis/indirect photometric detection (CZE/IPD). Different approaches for simultaneous separation and indirect detection of nonabsorbing anions and cations are evaluated. From this evaluation, some rules of thumb as to when these approaches will be most effective are drawn. In addition, indirect fluorescence detection (IFD) in CZE and micellar electrokinetic chromatography (MEKC) are reviewed and possible application areas are highlighted. Some recent developments in other indirect detection modes, such as indirect chemiluminescence detection (ICLD) and indirect conductivity detection (ICD), are outlined.