Electron Spectroscopy For Chemical Analysis Measurements Research Articles

Drying-Induced Variations in Physico-Chemical Properties of Amorphous Pharmaceuticals and Their Impact on Stability II: Stability of a Vaccine

To investigate the impact of drying method on the storage stability of dried vaccine formulations. A sucrose-based formulation of a live attenuated virus vaccine of a parainfluenza strain, with and without surfactant, was dried from by different methods; freeze drying, spray drying and foam drying. Dried powders were characterized by differential scanning calorimetry, specific surface area (SSA) analysis and by electron spectroscopy for chemical analysis (ESCA) to evaluate vaccine surface coverage in the dried formulations. Dried formulations were subjected to storage stability studies at 4, 25 and 37 degrees C. The vaccine was assayed initially and at different time points to measure virus-cell infectivity, and the degradation rate constant of the vaccine in different dried preparations was determined. SSA was highest with the spray dried preparation without surfactant (approximately 2.8 m(2)/g) and lowest in the foam dried preparations (with or without surfactant) (approximately 0.1 m(2)/g). Vaccine surface coverage was estimated based on ESCA measurements of nitrogen content. It was predicted to be highest in the spray dried preparation without surfactant and lowest in the foam with surfactant. Stability studies conducted at 25 degrees C and 37 degrees C showed that the vaccine was most stable in the foam dried preparation with surfactant and least stable in spray dried preparations without surfactant and in all freeze dried preparations regardless of the presence of surfactant. Addition of surfactant did lower the SSA and vaccine surface coverage in freeze dried preparations but still did not improve storage stability. In drying methods that did not involve a freezing step, good storage stability of Medi 534 vaccine in the dried form was found with low SSA and low vaccine surface accumulation, both of which integrate into low fraction of vaccine at the surface. Ice appears to be a major destabilizing influence.

Wettability and spectroscopic characterization of silylated wood samples

AbstractSurfaces of three European wood species (namely, English oak, Hungarian oak, and Scots pine) and two tropical wood species (namely, teak and cloves) were silylated with dichlorodimethylsilane (DDS), dichlorodiphenylsilane (DPS) and octadecyltrichlorosilane (OTS) in the first step, and with chlorotrimethylsilane (CTMS) as a monofunctional reagent in a second step. Attenuated total reflection‐Fourier transform infrared (ATR‐FT‐IR) and electron spectroscopy for chemical analysis (ESCA) measurements were performed in order to characterize the surface composition of the treated samples. The progress of surface modification was also monitored by contact angle measurements of different test liquids (water, formamide and diiodomethane). The water contact angles were found to be in the range of 80° to 145°. The most hydrophobic surface was obtained by two‐step silylation by OTS and CTMS (water contact angles were between 131° and 140°). Interestingly, the hydrophobicity of DDS‐treated samples showed a significant decrease after additional silylation by CTMS. The surface free energy values were evaluated in terms of the Lifshitz‐van der Waals/acid‐base theory. The results obtained by the surface analytical methods (i.e. FT‐IR and ESCA measurements) were compared with the contact angle data. These results suggest that in the case of DDS‐treated samples, CTMS molecules substitute partly the DDS molecules, thus only physisorption of the silylating agents is supposed at room temperature. Copyright © 2006 John Wiley & Sons, Ltd.

ESCA-thickness metrology and head-medium spacing impact of disk lubricant

Electron spectroscopy for chemical analysis (ESCA) has been commonly used as a metrology tool for lubricant film-thickness measurement on magnetic hard disks. The accuracy of the ESCA-thickness measurement rests solely with the calibration accuracy of the characteristic photoelectron attenuation length in the lubricant film. Several past studies on this subject yielded widely divergent results, due to the difficulty in obtaining an accurate, absolute lubricant film-thickness measurement. In this paper, we revisited the calibration issue and, instead of following the same paths pursued in the past, used a derivative method to yield an accurate calibration of the photoelectron attenuation length. We also compared the various methods for lubricant film-thickness calculation based on ESCA measurements and determined that the most accurate method is to use only the photoemission signal from the lubricant film. In addition, by studying the lubricant film-thickness effect on the electrical readback signal, we found that the lubricant film leads to an increase in the head-medium spacing by an amount greater than one times, but less than two times, its physical thickness.

Fabrication of a paraffin actuator using hot embossing of polycarbonate

Abstract In this paper a fabrication process for integrating paraffin-actuated structures in polycarbonate is outlined. A paraffin-actuated membrane with a diameter of 2.5 mm, where the volume expansion of 10–15% associated with the solid-to-liquid phase transition of paraffin is utilized, has been fabricated and evaluated. Microstructures fabricated in silicon have via an electroplated nickel mould been replicated in polycarbonate by hot embossing and the resulting structures have been sealed by thermal bonding. The bonding strength was measured by a pressurizing test, and the polycarbonate surfaces were characterized with electron spectroscopy for chemical analysis (ESCA). It was found that the bond strength increased when an oxygen plasma treatment was used prior to bonding. ESCA measurements showed a corresponding increase in oxygen content on the plasma treated surfaces. This procedure also improved the wetting properties. The contact angle between paraffin and polycarbonate decreased from 10° after embossing to about 5° after plasma treatment. The fabricated actuator had a total thickness of 1 mm and the membrane deflected about 140 μm when heating the actuator above the melting point of paraffin. Paraffin wax actuators are possible to integrate in plastic structures making them promising candidates in applications such as disposable microfluidic systems where inexpensive and robust valves and pumps are needed.

Surface characterization of four industrial spray-dried dairy powders in relation to chemical composition, structure and wetting property

The surface composition of powders is expected to play an important role during its end use. Understanding the mechanism of the powder surface formation in terms of the compositional aspect and the ability to control the surface composition will be highly useful in milk powder quality improvement and new product development. For a preliminary study, the surface compositions of four industrial spray-dried dairy powders (skim milk powder, whole milk powder, cream powder and whey protein concentrate) manufactured for consumer use, were studied by means of electron spectroscopy for chemical analysis (ESCA). It was found that all the powders have relatively high surface fat coverage. In order to verify these results and to demonstrate the usefulness of ESCA in analysing the surface composition of dairy powders, fresh powders and fat extracted powders were subjected to the following experiments: measurement of powder surface composition, surface structure studies, fat localization studies, wetting test and measurements of surface oxygen uptake during storage. The results obtained indicate that the ESCA measurements are very reliable and the surface composition of the industrial spray-dried dairy powders estimated by ESCA is also expected to be reliable. In addition, the results showed fat globules encapsulated by protein or proteins are preferentially located underneath the surface fat.

Copper Doped Waveguides in Glass Substrates

We have studied the fabrication and properties of the copper ion exchanged waveguides that were fabricated in special Na 2 O-rich soda-lime silicate glasses and in commercial BK7 optical glass substrates. The ion exchange was performed in melts containing either Cu I or Cu II at temperatures from 350°C to 500°C for times ranging from 5 min to 21 h. Optical properties of the fabricated waveguides were studied using mode spectroscopy and photoluminescence spectroscopy, and composition of the waveguides was determined by using Scanning Electron Microscope (SEM), Rutherford Backscattering Spectrometry (RBS), Electron Paramagnetic Resonance (EPR), and Electron Spectroscopy for Chemical Analysis (ESCA). After the ion exchange the refractive index increased, according to fabrication conditions, up to j n = +0.0693, and the guides supported up to 16 TE and TM modes. The Cu I 5 Cu II redox reaction during the fabrication depended strongly on the composition as well as the temperature of the reaction melts. In the Cu 2 Cl 2 :ZnCl 2 melts, the oxidation of Cu I to Cu II was strongly impeded, so that Cu I prevailed in the waveguiding region. These samples exhibited the most intensive blue-green luminescence in spite of those fabricated by using the Cu II -based reaction melts, where practically no blue-green luminescence was observed. ESCA measurement revealed an easy charge transfer between both oxidation states of copper in the very surface regions of the samples.

Interfacial Properties of a Model Polyampholyte Studied by Surface Force Measurements, ESCA, and Ellipsometry

The adsorption of a model polyampholyte, i.e., [acrylamide]−[sodium 2-(acrylamido)-2-methylpropanesulfonate]−[2-(methacryloyloxy)ethyltrimethylammonium chloride] ([AM]−[NaAMPS]−[MADQUAT]) at mica and silica surfaces was investigated by surface force measurements, electron spectroscopy for chemical analysis (ESCA), and ellipsometry. It was found that the adsorption isotherm of this polyampholyte on mica was of the high affinity type, yielding an adsorbed amount at saturation of 5.5 ± 0.5 mg/m2. By lowering the electron escape angle in the ESCA measurements (making the analysis more surface sensitive), it was found that the negatively charged groups in the polyampholyte are concentrated in the outer part of the adsorbed layer, i.e., away from the negatively charged mica surface. From ellipsometry studies with silica, it was found that the adsorption was relatively fast, reaching saturation after about 1000 s on adsorption from a 20 ppm solution. From both ellipsometry and ESCA it was found that the effect of electrolyte on the adsorbed amount of preadsorbed polyampholyte is relatively minor at concentrations up to 10 mM. At higher electrolyte concentrations, however, some desorption of the polyampholyte occurs. Surface force measurements showed that the extension of the polymer layer normal to the mica surface was small compared to the radius of gyration of the polymer in bulk. Upon addition of electrolyte the adsorbed layer was found to contract.

Thickness Measurements of Thin Perfluoropolyether Polymer Films on Silicon and Amorphous-Hydrogenated Carbon with X-Ray Reflectivity, ESCA and Optical Ellipsometry

Experimental techniques used to measure structural parameters of thin films such as thickness, density, and coverage provide important insights into the physical properties of these films. Structural parameters are also often used to predict the eventual performance of thin films. In this study, we use three different measurement techniques—X-ray reflectivity (XRR), electron spectroscopy for chemical analysis (ESCA), and optical ellipsometry—to measure the thickness of molecularly thin perfluoropolyether (PFPE) polymer films on silicon substrates and carbon overcoats. PFPE films are commonly used to lubricate surfaces in magnetic recording devices. Here, we use XRR to measure the absolute thickness of the films, which, in turn, is used to test the validity of ESCA and ellipsometry thickness measurements. Excellent agreement is found among the three methods, provided that a 25-Å electron mean-free path (MFP) is used for the PFPE film and the substrate in ESCA (single MFP model), that the bulk PFPE refractive index is used in ellipsometry, and that adventitiously adsorbed hydrocarbons are properly taken into account.

Surface composition and morphology of polyimidesiloxane copolymers with short polydimethylsiloxane segments studied by electron spectroscopy for chemical analysis and time-of-flight secondary ion mass spectrometry

A series of polyimidesiloxane (SIM) copolymers, based on α,ω-aminopropylpoly- (dimethylsiloxane) (PDMS), 2,2-bis(4-[4-aminophenoxyl]phenyl)propane and 4,4′- oxydiphthalicanhydride was synthesized in our laboratories. The effects of siloxane segment length (dimethylsiloxane repeat units=1, 2, 3, 4, 5, and 9) and PDMS bulk content (1–30 wt %) on the surface composition and free surface morphology of the copolymers were investigated. Experimentally, angle-dependent electron spectroscopy for chemical analysis (ESCA) was used to acquire composition information of the copolymer surface at various sampling depths. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used to describe ion formation mechanism of bulk SIM copolymers with variation of bulk composition or structure. In all cases, PDMS was segregated to the topmost 100 Å of the air (free) surface of ∼75 μm thick film, even with short siloxane segments and low PDMS contents. Angle-dependent ESCA measurements show that the dominant factor in defining the surface composition of these copolymers is not bulk composition, but in fact siloxane segment length. With the same PDMS content, a longer siloxane segment gives a surface richer in siloxane. For a given siloxane segment length, varying PDMS content does not significantly change the surface composition. TOF-SIMS measurements of bulk copolymers simulated by solvent-cast thin films show that a longer siloxane segment gives higher relative ion yields of fragment ions from siloxane versus imide segments even with the same 10 wt % PDMS content in the copolymers. For a given average siloxane segment length of 9 dimethylsiloxane repeat units, a higher PDMS content in the copolymers yields higher relative yields of fragment ions formed from siloxane versus imide segments.

Calibrating ESCA and ellipsometry measurements of perfluoropolyether lubricant thickness

X-ray reflectivity (XRR) has been used as an absolute measurement of the thickness of perfluoropolyether (PFPE) lubricant layers on silicon substrates to determine the validity of thickness measurements by electron spectroscopy for chemical analysis (ESCA) and ellipsometry. Excellent agreement is found between these three methods, provided that a 25 /spl Aring/ escape depth for the PFPE film is used in ESCA and the bulk refractive index of the PFPE is used in ellipsometry. It is also essential to properly account for adventitiously adsorbed hydrocarbons.

Surfaces coated with protein layers: a surface force and ESCA study

In this review article we discuss the types of non-specific forces that are of importance for the interactions between proteins and surfaces. Some of these forces are well understood theoretically, and their properties investigated in detail. The origin of other types of forces is less well understood, or even controversial, and here we will recapitulate the main experimental findings. Most of our knowledge of interfacial forces stems from the use of various surface force techniques. Two such techniques are described in this article. The typical experimental procedure is outlined and attention is drawn to the most common complications that we have met during our studies. In this article we have chosen to present data that illustrate the presence of some particular type of force, that illustrate a particular complication that occurs when evaluating the experimental findings, or that illustrate the advantage of using electron spectroscopy for chemical analysis (ESCA) in combination with surface force measurements. No system is discussed in detail, and for more detailed information we will refer the reader to the original literature. However, we present an estimate of the amount of small ions co-adsorbed with the protein calculated from a combination of the ESCA and surface force apparatus (SFA) results. This estimate is based on a simple charge balance which requires a knowledge of the adsorbed amount and the diffuse layer charge. The adsorbed amount is obtained from ESCA measurements using a quantification method that utilizes the known chemical composition of the mica surface. The diffuse layer charge is obtained from the magnitude of the double-layer force measured with a surface force technique.

Electron spectroscopic analysis of the SiO2/Si system and correlation with metal–oxide–semiconductor device characteristics

ESCA (electron spectroscopy for chemical analysis) measurement results on thin SiO2/Si samples are examined comprehensively, critically, and in detail to show that it is possible to correlate these results with MOS (metal–oxide–semiconductor) device characteristics such as flatband (threshold) voltage, oxide breakdown field, mobile-ion density, hole and electron trap density, and hot-carrier lifetime. Up to now, much effort has been made to detect SiOx phases at SiO2/Si interfaces since they are thought to have a significant effect on MOS device characteristics. However, correlating the SiOx phases with device characteristics is difficult and involves overcoming two problems. First, the chemical state is difficult to determine exactly due to x-ray irradiation effects. Second, the amount of defects and impurities which influence device characteristics is usually below the ESCA detection limit (1012–1013 cm−2) in device-quality SiO2/Si samples. Investigation of the first problem led to the conclusion that it is possible to correct for these effects from the x-ray intensity or oxide thickness dependence of the chemical shift. However, accurate (better than ±0.2 eV) chemical state determination is not easy. It is therefore necessary to approach this detection problem from a different viewpoint. Our first attempt involves measuring the ESCA thickness, which decreases when oxide defects like unoxidized Si or uneven thickness (or pinholes) are present, resulting in breakdown field degradation. Our second attempt started while we were studying how to interpret the measured chemical shift. The photoelectron peaks of the SiO2 and the Si can be observed to shift due to small amounts of charged defects and impurities, although they cannot be detected as peaks. This method is considered to be especially useful for characterizing ultrathin (a few nm thick) SiO2/Si samples which are difficult to characterize using conventional C-V (capacitance–voltage) measurements because of tunneling currents. Accordingly, we discuss the data obtained in steady-state and transient peak position measurements of SiO2/Si samples containing 1010–1012 cm−2 of Na (sodium) ions, 1012–1013 cm−2 of hole and electron traps, and 1014–1021 cm−3 of impurities such as P (phosphorus) (in the Si). It is shown that a correlation with MOS characteristics is possible. A close scrutiny of various results concerning x-ray irradiation time, intensity, and oxide thickness dependence of the above peak positions indicates that electric charging during ESCA measurements is correlated to the trap-capturing process. As MOS characteristics are also related to this process, more studies in this direction are needed and will certainly yield more information on the defects influencing the MOS characteristics and the trap-capturing mechanism.

Preparation and Characterization of Comb-like PEO Gradient Surfaces

Comb-like polyethylene oxide (PEO) gradient surfaces where the density of comb-like PEO chains changes gradually along the sample length were prepared on low density polyethylene (PE) sheets by corona discharge treatment with gradually increasing power and graft copolymerization of poly(ethylene glycol) monomethacrylate macromers (PEG-MA). Macromers with PEO chain lengths 1, 5, and 10 were used. The comb-like PEO gradient surfaces prepared were characterized by measurement of the water contact angle, Fourier transform infrared spectroscopy in the attenuated total reflectance mode (FTIR-ATR), and electron spectroscopy for chemical analysis (ESCA). The FTIR-ATR and ESCA measurements indicated that the PEO chains are grafted onto the PE surface with gradually increasing density of PEO. The gradient surfaces prepared can be used to systematically investigate the interactions of biological or other species in terms of PEO chain length and its surface density of polymeric materials.

ESCAによるSiO<SUB>2</SUB>/Si内の電子トラップ，正孔トラップの検出

Since very small amounts of defects or impurities influence Si MOS (Metal-Oxide-Semiconductor) device characteristics, it is usually difficult to detect them in the SiO2/Si structures used for these devices by ordinary surface characterization. We therefore tried to resolve this problem with a different approach. In an effort to detect electron and hole traps in SiO2/Si samples, the electric current that flows from the sample to the ground was measured as a function of the X-ray irradiation time during ESCA (Electron Spectroscopy for Chemical Analysis) measurements. The transient of this current was found to be due to electric charges supplied to the Si side of the SiO2/Si interface. The number of these charges increases as the electric charges of the opposite sign become trapped at oxide traps in the SiO2. This transient was found to be the sum of the exponential functions of the X-ray irradiation time with different time constants. Various types of traps can be distinguished by these time constants and the sign of the current. Our first experiment showed that traps whose concentration is of the order of 1014 m−2 can be detected by this method, whereas they cannot be easily detected with such sensitivity in an ESCA spectra because the ESCA detection limit is of the order of 1016 m−2. This new method was used to compare two different kinds of thermally oxidized silicon, namely, that oxidized in O2/N2 and that oxidized in pyrogenic steam. The present method is expected to be useful in the process development of MOS devices using ultra-thin SiO2 films.

Electron Spectroscopy for Chemical Analysis Study on Influence of Polymerization on Anisotropic Etching of Thick Silicon Oxide Using C 2F 6 Based ECR-RIBE

Anisotropic etching mechanism is investigated increasing the CF2 precursor in C2F6 plasma. The increasing of CF2 precursor is known from the ESCA (electron spectroscopy for chemical analysis) measurement of C/F elemental ratio of the deposited layer. It is found that the C/F ratio is increased from 0.28 to close to 1, when the microwave power of plasma is increased from 150 W to 350 W, respectively. The side wall angle of the deep SiO2 etching under the power of 350 W, is found to be close to 90°. The SiO2 etching selectivity with respect to the chromium (Cr) metal mask is also found to be enhanced considerably with the increasing of microwave power.

Antithrombogenicity of hydrophilic polyurethane-hydrophobic polystyrene IPNs. I. Synthesis and characterization.

A series of interpenetrating polymer networks (IPNs) composed of hydrophilic polyurethane (PU) and hydrophobic polystyrene (PS) were prepared by the simultaneous polymerization method. The PU network was synthesized via the isocyanate-terminated PU prepolymer based on polyethylene glycol (PEG), a highly hydrophilic oligomer, and hexamethylene diisocyanate (HDI). The bulk and surface characteristics of these materials were analyzed by differential scanning calorimetry (DSC), tensile testing, scanning electron microscopy (SEM), attenuated total reflectance-Fourier transform infrared (ATR-FTIR), electron spectroscopy for chemical analysis (ESCA), and contact angle measurement. The PU/PS IPNs prepared in this study exhibited phase separated structures, which had dispersed PS domains in the continuous PU matrix, in both the bulk and surface showing two transition temperatures. The IPN containing 50 wt% of PS showed good mechanical properties. The enrichment of PU phase in the surface was revealed by SEM, ATR-FTIR, ESCA, and contact angle measurement.

Influence of plasma treatment conditions on growth and electrical properties of oxides on InP

Abstract Plasma treatments are playing an increasing role in microelectronic technology. The present paper deals with the deposition of Ta 2 O 5 dielectric layers on n-InP by multipolar plasma technology for the fabrication of MISFET (metal-insulator-semiconductor field effect transistor) structures. Damage induced by plasma exposure is one of the major problems in such fabrication. Therefore the working conditions (sample bias, discharge power and oxygen pressure) have to be optimized so as to limit the ion energy on the substrate during treatment. After plasma treatment the oxide films are stabilized by post-annealing at 200°C in an N 2 atmosphere. The oxide thickness is determined by ellipsometric measurements. The growth condition of the dielectric in the plasma is also related to the basic electronic and interface properties of InP-oxide-Au structures using static I-V , dynamic C-V and ESCA (electron spectroscopy for chemical analysis) measurements. Equivalent Schottky barriers as high as 0.87 eV are obtained.

Analysis of the Wet Corrosion Mechanism of TbFeCoNb Magneto‐optical Recording Film

The wet corrosion mechanism on magneto‐optical recording film was analyzed by Auger electron spectroscopy (AES) and electron spectroscopy for chemical analysis (ESCA). The corrosion reaction rate of the film is slower as the Nb concentration is higher. From AES measurement, Tb is oxidized on the surface of the film; however, the oxide layer thickness is thinner with increasing Nb concentration. From ESCA measurement, Fe and Co are in the metallic state, and Nb is oxidized after exposure to 80°C at 95% RH for 100 h. These results show that when Nb oxide exists, the decrease in wet corrosion rate is effective for protection.

Physical characterization of E-glass fibres treated with alkylphenylpoly(oxyethylene)alcohol

The adsorption of a non-ionic surfactant, alkylphenylpoly(oxyelhylene)alcohol from aqueous solutions onte industrial E-glass fibres has been followed by measurements of their surface properties (electron spectroscopy for chemical analysis (ESCA) technique), streaming/zeta potential and wetting characteristics. All three techniques indicate substantial changes in the interaction between glass fibres and water as a consequence of surfactant adsorption, although it seems that only a fraction of the total surface is covered by the surfactant. The streaming/zeta potential has been found to reflect the processability of the fibres in a realistic way, whereas the wettability of the fibres provides indirect information concerning the surface coverage and polarity of the fibres. Although the ESCA measurements are performed in ultra-high vacuum, the results are shown to give semi-quantitative information about the amount adsorbed on the surface, and correlate well with the wetting properties. All methods indicate, as expected, an enhanced absorption with increased surfactant concentration.

Evidence for Degradation of Synthetic Polyurethanes by Staphylococcus epidermidis

The survival of Staphylococcus epidermidis strain KH 11 in the presence of synthetic high molecular polyurethanes was prolonged in comparison to control experiments performed in the absence of any nutrients. Investigations of the bacteria after contact with the polymers revealed changes in their surface properties and metabolism, in particular a marked induction of urease activity. ESCA (Electron Spectroscopy for Chemical Analysis) measurements detected a decrease in elementary nitrogen in the polyurethane surfaces after incubation with the bacteria. The alterations observed indicate an urease-induced degradation of synthetic polymers by Staphylococcus epidermidis KH 11.