bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interactive variable selection (IVS) for PLS. Part II: Chemical applications
Authors: Lindgren Fredrik , Geladi Paul , Berglund Anders , Sjöström Michael , Wold Svante 
Published: May 2005

AbstractWith the aim of developing PLS models with improved predictive properties, an interactive variable selection (IVS) approach for PLS regression was introduced in Part I of this series. IVS‐PLS is based on a dimension‐wise selective removal of single elements in the PLS weight vector w. IVS uses cross‐validation (CV) as a guiding tool. The present paper illustrates the use of IVS‐PLS on both simulated data and real examples from chemistry. In the first example, spectrophotometric data were simulated according to an experimental design. The objective was to see how IVS‐PLS was influenced by different levels of noise in X and Y and by the number of predictor variables (K). The results of the modelling are shown as response surfaces. In addition, four real examples were modelled by the IVS‐PLS technique. The real data sets were chosen to reflect different types of data from chemistry. For each example a comparison of ‘prediction error sum of squares’ (PRESS) between IVS‐PLS and classical PLS is madeFor most of the examples containing many predictor variables IVS‐PLS shows an improvement in predictive properties over classical PLS. Also, improvements for IVS‐PLS2 (modelling of more than one y‐variable) models were found. For data sets with a moderate number of variables the influence of the IVS method becomes less pronounced.
Orthogonal canonical variates for discrimination and classification
Authors: Krzanowski W. J. 
Published: May 2005

AbstractA new set of derived variables is proposed for exhibiting group separation in multivariate data on for preprocessing such data prior to discriminant analysis. The technique combines optimal features of canonical variate analysis and principal component analysis: the derived variables are linear combinations of the original variables that optimize the canonical variate criterion (ratio of between‐group to within‐group variance) but subject to the orthogonality constraints of principal components. In this formulation the canonical variates can be derived even when the within‐group matrix is singular (i.e. when there are more variables than objects in the data matrix). A simple computational algorithm for extraction of these variables is proposed. The methods are illustrated on several data sets and compared with alternative techniques such as principal component analysis and partial least squares.
Chemical vapor deposition of metals: Part 1. An overview of CVD processes
Authors: Hampden‐Smith Mark J. , Kodas Toivo T. 
Published: May 2005

AbstractThe chemical vapor deposition (CVD) of metals is a rapidly developing area in which metal‐containing compounds are being synthesized as new precursors. This article reviews this area and discusses precursor design, reaction pathways, reactor types, and the influence of reactor operating conditions on film growth. We have gathered recent results for precursor design and CVD chemistry and show how analysis of results from CVD experiments can be used to assist in the development of new CVD precursors.
Chemical vapor deposition of metals: Part 2. Overview of selective CVD of Metals
Authors: Hampden‐Smith Mark J. , Kodas Toivo T. 
Published: May 2005

AbstractThe Selective chemical vapor deposition (CVD) of metals from metal‐containing compounds is reviewed and the approaches taken are classified according to the different physicochemical phenomena which take place on the growth and non‐growth surfaces. These include: an intrinsic difference in reaction rates, sacrificial solid‐state co‐reactant, activation of the growth surface, radiation‐induced activation of the growth surface, passivation of non‐growth surfaces, and a physical nucleation barrier. The results from the literature suggest that surface modification, in which the growth surface is activated or the non‐growth surface is passivated, is a promising method to control selectivity. However, few results are available from experiments with well‐characterized surfaces, making meaningful comparisons of the origin of selective CVD difficult to interpret.
Atomic layer epitaxy of strontium sulfide thin films using in situ synthesized strontium precursors
Authors: Soininen Pekka , Nykänen Erja , Niinistö Lauri , Leskelä Markku 
Published: May 2005

AbstractSrS thin films were grown on uncoated or Al2O3‐coated soda lime glass substrates from hydrogen sulfide and Sr(thd)2 (thd = 2,2,6,6‐tetramethyl‐3,5‐heptanedionato) by the atomic layer epitaxy (ALE) process. Sr(thd)2 was prepared from Sr, SrO, Sr(OH)2 or SrCO3 and Hthd inside the reactor during the deposition process. Thicknesses of the thin films were measured by optical transmission spectroscopy while crystallinity and preferred orientation were evaluated by X‐ray diffraction. Under certain conditions strongly (200) oriented SrS was grown. The advantages of the in situ synthesis of the precursor are discussed.
Amine‐stabilized cyclopentadienyl diisobutyl aluminum complexes as new kinds of precursors for the deposition of thin aluminum films by CVD
Authors: Scherer Markus , Kruck Thomas 
Published: May 2005

Communication: The heteroepitaxy of diamond is of considerable scientific and technological interest. The significant lattice mismatch between diamond and silicon and the relatively high surface energy of a non‐terminated (100) diamond plane have prompted speculation that diamond nucleates on an aligned cubic silicon carbide interfacial layer. In this paper spectral and microscopic studies show that while formation of interfacial amorphous carbon and silicon carbide must be avoided, nevertheless an interfacial SiC layer is intimately involved in localized heteroepitaxial growth on (100) silicon.magnified image
Lead(II) dithiocarbamato complexes as precursors for the LP‐MOCVD of lead sulfide
Authors: Trindade Tito , Brien Paul O' 
Published: May 2005

Communication: Polycrystalline layers of PbS find wide application in IR detection. A simple and safe route to the IV‐VI material using a single precursor is described. The films obtained show cubic crystallites with columnar growth (see Figure) and X‐ray diffraction peak intensities suggest a strong [200] orientation. The approach has potential for the fabrication of IR detection devices.magnified image
Remote Plasma‐Enhanced CVD of Fluorinated Silicon Nitride Films
Authors: Alexandrov Sergei E. , Hitchman Michael L. 
Published: May 2005

AbstractAn investigation has been made of the effect of dilution of nitrogen with NF3 on the properties of silicon nitride deposited by remote plasma‐enhanced CVD (PECVD). For NF3/N2 mixtures with < 1.5% NF3, fluorinated films with the structure of silicon nitride are formed but the total concentration of bonded hydrogen in the films decreases with increasing NF3 flow rate, which leads to an improvement of the electrical properties of the films compared with unfluorinated films. Such films could be of interest for device applications. For NF3/N2 mixtures with NF3 > 1.5 %, films with the structure of silicon dioxide are formed, but they do not contain enough oxygen to give typical SiO2 IR spectra. It is suggested that the silicon dioxide structure arises because of isoelectronic substitution of oxygen by NF.
Boron Carbonitride Thin Films by PACVD of Single‐Source Precursors
Authors: Hegemann Dirk , Riedel Ralf , Dreßler Wolfgang , Oehr Christian , Schindler Bernd , Brunner Herwig 
Published: May 2005

AbstractThis work investigates the influence of the carrier gases N2, Ar, and He and the influence of the applied power density (about 1–4 W/cm2) on the chemical composition of boron carbonitride films deposited by a PACVD process. The plasma is activated via 13.56 MHz radio frequency. Si(100) wafers were used as substrates and pyridine‐borane (PB) and triazaborabicyclodecane (TBBD) as B‐C‐N‐forming single‐source precursors. Films that were either deposited in He using a low power density or in N2 using a high power density showed comparable properties. Analysis of these films showed their chemical composition to be BC4N. Moreover, they exhibited outstanding hardnesses of up to 64 GPa. A simple model describing the acceleration of B, C, and N ions in the plasma towards the substrate showed comparable ion momenta by use of the corresponding deposition parameters. Basically, it was found that, the higher the ion momentum, the higher the film hardness.
Origins of Texture in TTF‐TCNQ Thin Films Grown by Organic CVD from TTF and TCNQ Precursors
Authors: Caro Jaume , Fraxedas Jordi , Figueras Albert 
Published: May 2005

AbstractThe preparation and characterization of thin films of the organic molecular conductor TTF‐TCNQ formed by the donor TTF (tetrathiafulvalene) and the acceptor TCNQ (7,7,8,8‐tetracyano‐p‐quinodimethane) is presented. The layers were grown on KCl (001) substrates by OCVD (organic CHEMICAL VAPOR DEPOSITION). The experiments were carried out on a horizontal hotwall reactor using TTF and TCNQ as precursors and argon as carrier gas. The obtained films are polycrystalline, showing a different in‐plane texture depending on the substrate temperature. The existence, under very well defined experimental conditions, of new in‐plane textures in addition to the energetically most favorable has been interpreted in terms of a local minimum in the interaction energy between the first monolayer of a c‐oriented crystalline unit and the substrate. This interaction energy was calculated taking into account the van der Waals and electrostatic forces existing between the organic layer and the alkali halide substrate.
The use of chemically modified electrodes for liquid chromatography and flow‐injection analysis
Authors: Wang Erkang , Ji Huamin , Hou Weiying 
Published: May 2005

AbstractThe use of chemically modified electrodes (CMEs) for liquid chromatography and flow‐injection analysis is reviewed. Electrochemical detection with CMEs based on electrocatalsis, permselectivity, ion flow in redox films, and ion transfer across the water–solidified nitrobenzene interface is discussed in terms of improving the stability, selectivity, and scope of electrochemical detectors and the detection of electroinactive substances. More than 90 references are included.
Electrochemistry of conductive polymer X: Polyaniline‐based potentiometric sensor for dissolved oxygen
Authors: Shim Yoon‐Bo , Stilwell David E. , Park Su‐Moon 
Published: May 2005

AbstractA platinum electrode coated with polyaniline (PA) was examined as a Potentiometric or an optical sensor for dissolved oxygen, and the results are reported. While the polymer‐modified electrode behaved satisfactorily as a potentiometric sensor, its optical response (i.e., absorbance) gave a narrow linear region for varied oxygen concentrations. This conducting polymer‐coated electrode was characterized to give approximately 97 mV/decade of the oxygen concentration and a voltage signal range of about 400 mV, representing at least three orders of magnitudes of dynamic linearity over the dissolved oxygen concentration. The potentiometric sensing electrode showed reasonably short response times, excellent reproducibility, and good stability. A detection limit of about 5 × 10−7 mol/L of dissolved oxygen was estimated from the potentiometric response of PA‐coated electrodes.
Electroanalytical study of the hydrolysis of the thienodiazepine clotiazepam
Authors: Higelmo Fátima , Alonso Rosa M. , Jiménez Rosa M. 
Published: May 2005

AbstractThe hydrolysis reaction in an alkaline medium of the thiendodiazepine Clotiazepam has been studied by differential pulse polarography at various pH values at 25, 37, and 50°C. In an alkaline medium, Clotiazepam exhibits two well‐defined polarographic peaks, attributed to the azomethine group of the parent compound and the carboxylic group of the hydrolysis product, with a potential difference of 0.160 V, practically constant in the pH range studied. Kinetic studies of the reversible hydrolysis process based on the current changes with time of the first polarographic peak in indicate that the process is a pseudo‐first‐order reaction with a rate constant dependent on hydroxide ion concentration. Arrhenius parameters were also calculated. A voltammetric study of the hydrolysis product has been carried out, and determination methods have been developed by differential pulse voltammetry and differential pulse polarography.
Differential pulse polarographic determination of residual acrylic acid in sodium polyacrylate
Authors: Husain Sajid , Sastry G. S. R. , Prasad P. Ravi , Sarma G. V. 
Published: May 2005

AbstractA polarographic method has been developed for the estimation of acrylic acid monomer in polyacrylate. Polarograms of the polymer are recorded directly in N,N‐dimethylformamide side (DMF) solvent using 0.02 M tetrabutyl ammonium iodide as the supporting electrolyte. This solvent system was chosen because it avoids indirect measurements based on separation or reprecipitation procedures. The results obtained are found to be in good agreement with ultraviolet spectrophotometric results.
An amperometric glucose electrode based on carbon paste, chemically modified with glucose dehydrogenase, nicotinamide adenine dinucleotide, and a phenoxazine mediator, coated with a poly(ester sulfonic acid) cation exchanger
Authors: Bremle Gudrun , Persson Björn , Gorton Lo 
Published: May 2005

AbstractAn amperometric glucose electrode is described based on carbon paste chemically modified with glucose dehydrogenase, nicotinamide adenine dinucleotide, and a mediator, Meldola Blue. The surface of the chemically modified carbon paste electrode (CMCPE) is protected by coverage with a poly(ester sulfonic acid) cation exchanger to form a membrane, which prevents the aqueous soluble species from dissolving out of the CMCPE. The CMCPE was investigated in the flow‐injection analysis operation. Linear calibration curves for glucose were obtained between 100 μM and 20 mM glucose at +100 mV versus Ag/AgCl. The sample throughput was 40 h−1. The electrodes remained stable for about 2 weeks.
Novel STM‐EC center for in situ imaging under potentiostatic/galvanostatic control: Electrodeposition of copper and cadmium on carbon substrates
Authors: Yaniv Daphna R. , McCormick Larry D. 
Published: May 2005

AbstractAn electrochemical (EC) system, designed and incorporated into a scanning tunneling microscope (STM), is described. It has potentiostatic/galvanostatic capabilities for the sample and potentiostatic capabilities for the STM tip. The system permits imaging under potentiostatic (or galvanostatic) control. The STM‐EC center has been utilized to deposit metal films (Cu, Cd) on carbon substrates such as highly oriented pyrolytic graphite (HOPG) and glassy carbon (GC), and then used for in situ imaging under potentiostatic control. Tip‐induced electroplating on HOPG and its correlation to the bare graphite surface properties are also explored. Experimental considerations for in situ imaging under potentiostatic control are discussed.
Electrochemical oxidation and the quantitative determination of carbon monoxide on metal–solid polymer electrolyte (SPE) system
Authors: Xing Xue‐Kun , Liu Chung‐Chium 
Published: May 2005

AbstractThe electrochemical oxidation of carbon monoxide on a platinum–Nafion electrode was examined. It was found that the oxidation of CO on the Pt‐Nafion electrode is more favored in an acidic solution than in an alkaline medium. This is in contrast with what was reported for bulk metal electrodes, for which the oxidation rate of CO in acid is much smaller than in alkaline solutions. This phenomenon is believed to be directly related to the cation‐exchange capability of the Nafion membrane. The rest potential of the Pt–Nafion electrode was found to be dependent on the partial pressure of CO, which is also in contrast with the behavior of bulk metal electrodes. This result was attributed to a mixed potential phenomenon. A quantitative determination of CO concentration in the gas phase was carried out on the basis of the Pt–Nafion electrode system in a controlled‐potential mode. The results obtained showed a number of attractive properties, including a low detection limit, good reproducibility, and a fast response time.
Electrochemical behavior and determination of quinolinium and isoquinolinium oximes
Authors: Karljiković‐Rajić K. , Jovanović M. , Korićanac Z. , Stanković B. , Minić D. 
Published: May 2005

AbstractThe electrochemical behavior of 1‐(2‐phenyl‐2‐hydroxyiminoethyl)‐1‐quinolinium chloride (F‐1) and 1‐(2‐phenyl‐2‐hydroxyiminoethyl)‐1‐isoquinolinium chloride (F‐2) was investigated using dc and differential pulse polarography (DPP) and cyclic voltammetry. Well‐defined, diffusion‐controlled, cathodic waves were observed for F‐1 only in strong acidic solution (pH 1.25 HCl) and for F‐2 in the H range 1.25–5.33 (HCl and Britton–Robinson buffer). The overall reduction of the azomethine group to a primary amine, a process that involves the uptake of four electrons, is irreversible. For both oximes a mechanism of reduction has been proposed. The rapid and accurate determination of these quinolinium and isoquinolinium oximes is possible by dc polarography and by DPP. Limits of detection are 5 × 10−7 M for both oximes using DPP.
Electrocatalysis and flow detection at a glassy carbon electrode modified with a thin film of oxymanganese species
Authors: Taha Ziad , Wang Joseph 
Published: May 2005

AbstractA modified electrode prepared by dipping a glassy carbon substrate into a 0.027 M MnCl2/1.4 M NaOH solution and cycling the potential between −0.5 and +0.4 V(vs. AA/AgCl) greatly reduces the overvoltage for the oxidation of various hydrazines and hydrogen peroxide. The new electrocatalytic surfaces facilitate the amperometric detection of these compounds in flowing streams. Effects of pH, flow rate, operating potential, film thickness, concentration, and other variable on the catalytic response are explored. The electrode response is very stable. Detection limits at the femto‐ and picomole levels and relative standard deviations less than 1.3% are reported.
Nicardipine: Differential pulse polarography and photodecomposition
Authors: Squella J. A. , Borges Y. , Celedon C. , Peredo P. , Nuñez‐Vergara L. J. 
Published: May 2005

AbstractA new differential pulse polarographic method is proposed for the determination of nicardipine, based on the electroactivity of the nitroaromatic group of the molecule. The proposed method is applied in the determination of the drug in pharmaceutical formulations and in photodegradation studies.
Polarography and stripping voltammetry of metal–polycarboxylate complexes: Complexes of cadmium and zinc with polyacrylic and polymethacrylic acids
Authors: Díaz‐Cruz José M. , Ariño Cristina , Esteban Miquel , Casassas Enric 
Published: May 2005

AbstractComplex formation of Zn(II) and Cd(II) with polymethacrylic acid (PMA) and polyacrylic acid (PAA) is studied by sampled direct current, normal pulse, reverse pulse, and differential pulse polarography and by differential pulse anodic stripping voltammetry (DPASV). Titrations of Zn(II) or Cd(II) with partially neutralized PMA or PAA by DPASV allow the precise determination of the apparent formation constant K of the four systems. The two Zn(II) systems appear to be labile on the different time scales of the several techniques, without remarkable complications due to secondary phenomena. Their K values, determined by all techniques, agree satisfactorily. The two Cd(II) systems, and especially the Cd/PAA system, show rather involved behavior, which tends to normality when the degree of neutralization αn of the polycarboxylates increases. Both slow kinetics and ligand adsorption coupled with induced Cd(II) adsorption (evidenced by maxima on the normal pulse polarograms) seem to be present. For all αn values, DPASV yields higher estimates of K than do polarographic techniques.
Flow‐through pH‐ISFET as detector in automated determinations
Authors: Alegret S. , Bartrolí J. , Jiménez C. , del Valle M. , Domínguez C. , Cabruja E. , Merlos A. 
Published: May 2005

AbstractThe implementation of a pH‐ISFET (ion‐selective field effect transistor) planar chip in a flow‐injection system by means of a specially designed flow cell and the application of the sensor to the analysis of volatile compounds is described. Ammonia and sulfur dioxide are determined by exploiting the advantages of the flow techniques combined with continuous gas diffusion. Initial species are converted to gaseous compounds, which diffuse through a microporous hydrophobic membrane into an ammonium chloride or hydrogen sulfite recipient stream, producing a pH variation that is monitored by the semiconductor detector. The linear working range extends from 1 × 10−2 to 1 × 10−4 M for the ammonium system and from 4 × 10−3 to 7 × 10−5 for the sulfur dioxide system, with relative standard deviation of about 1 and 0.5%, respectively.
Adsorptive stripping voltammetry of phenylthiohydantoin and methylthiohydantoin derivatives of amino acids in the presence of copper(II) ions at a hanging mercury drop electrode
Authors: Moreira Josino C. , Miller Royston D. , Fogg Arnold G. 
Published: May 2005

AbstractIn the absence of Copper(II)—and even in its presence, if accumulation has been effected at positive potentials vs. Ag/AgCl—phenylthiohydantoin and methylthiohydantoin derivatives of amino acids gave a peak at −0.60 V (pH 8.0) owing to reduction of the mercury salt formed upon accumulation. At negative accumulation potentials, the presence of copper(II) affected the adsorptive stripping voltammograms markedly, including the lowering of the detection limits. When accumulation was effected at −0.3 V, the thiohydantoin derivatives gave single peaks in the range −0.4 to −0.6 V owing to reduction of copper(II) accumulated as copper(II) complexes. Determinations could be made readily at the 5 × 10−9 M level, accumulating at −0.3 V (pH 8.0) or −0.1 V (pH 4.5): calibration plots were rectilinear up to 8 × 10−8 M. Accumulation at −0.1 V (pH 8.0) in some cases gave additional minor peaks, but glycine derivatives were exceptional in giving a well‐defined peak at a considerably more negative potential. This peak appeared to be due to the accumulation of a different copper(II) complex, and evidence was obtained for the interconversion of these complexes in the surface. Mutual interferences by competitive adsorption were observed.
Simple and reliable fabrication of carbon fiber ultramicroelectrodes
Authors: Fernandez Avelino L. Suarez , Calzón Josefa A. Garcia , Garcia Agustin Costa , Blanco Paulino Tuñón 
Published: May 2005

AbstractA simple method for the fabrication of carbon fiber ultramicroelectrodes, using easily available materials (micropipette tips, metal rod, mercury, low viscosity inert epoxy resin, and carbon fiber of 7.5 μm diameter) and with no requirement for specialized instrumentation, is described. A high success rate is reported.
Electrochemical behavior of nitrofurantoin and assay of its formulations
Authors: Sridevi C. , Reddy S. Jayarama 
Published: May 2005

AbstractThe electrochemical behavior of nitrofurantoin was studied by employing do polarography, cyclic voltammetry, and differential pulse polarography in universal buffers of pH 2.0–12.0. Kinetic parameters such as transfer coefficients, diffusion coefficients, and heterogeneous forward rate constant values were evaluated using these techniques. Differential pulse polarography was employed for the estimation of this drug in several pharmaceutical formulations.