Adventitious carbon

TEM observation and elemental analysis of the catalysts were performed by means of a transmission electron microscope (JEOL, JEM-201 OF) with energy dispersion spectrometer (EDS). The surface property of catalysts was analyzed by an X-ray photoelectron spectrometer (JEOL, JPS-90SX) using an A1 Ka radiation (1486.6 eV, 120 W). Carbon Is peak at binding energy of 284.6 eV due to adventitious carbon was used as an internal reference. Temperature programmed oxidation (TPO) with 5 vol.% 02/He was also performed on the catalyst after reaction, and the consumption of O2 was detected by thermal conductivity detector. The temperature was ramped at 10 K min to 1273 K. 

The XPS spectra of the freshly sulfided Co-Mo/NaY catalysts were measured on an XPS-7000 photoelectron spectrometer (Rigaku, A1 anode 1486.6 eV). The sample mounted on a holder was transferred from a glove bag into a pretreatment chamber attached to the spectrometer as possible as carefully not to be contacted with air. The binding energies (BE) were referenced to the Si2p band at 103.0 eV for the NaY zeolite, which had teen determined by the Cls reference level at 285.0 eV due to adventitious carbon. 

For insulating materials, on the contrary, the Fermi level lies in the gap, so that it is not detected on the photoelectron spectra. A possible calibration method stems from the gold decoration technique the binding energies can then be referred to the Au 4f doublet. This leads, however, to a poor reproducibility of the calibration Neither is the 1 s line of adventitious carbon a better energy standard. 

Actual joint preparation involved first acetone-degreasing the steel lap shear specimens for about 30 min (Independent evaluation via XPS found the metal surface to be 99% I C.O along with some adventitious carbon.) These joints coated with coupling agent underwent the following procedure ... 

The carbon surface concentration of 42.5% at 90° exit angle for water-sized fibers in Table 1 represents a high level of adventitious contamination, more typical of plant production than of fibers formed in a relatively clean laboratory environment, which typically show carbon levels of 25% to 35% on water-sized E glass [4, 7, 8]. This high level of adventitious carbon tends to obscure the... 

For amines of similar pKg activity increased along the series primary, secondary, tertiary. Changes in solvent, monomer concentration and amount of adventitious carbon... 

Some authors have used the emission of adventitious carbon at a fixed value of 285.0 eV. (Some others prefer 284.4, 284.5 or 284.6 eV without real justification). This practice is not recommended because of the complexity associated with the possible differential charging of carbon impurities. Moreover it is not unusual to observe multicomponent Cjs peaks in zeolite spectra [11] and the span in binding energy expands over 8 eV in the literature. 

These baths contain adventitious carbonate via absorption of CO2 from the air and via the anodic oxidative decomposition of cyanide. 

Stability of the acyl species Mn(COR) (CO)j, relative to the corresponding alkyl derivatives, decreased in the sequence Et > Me > Ph > CH2Ph (in 2,2 -diethoxydiethyl ether, T = 303 K). The acyl derivative is apparently favored by electron-releasing groups similar to the results obtained with platinum(II) (11.3.2.1.3). The propionyl derivative is so stable that attempts to purify the ethyl derivative led to Mn(COEt)(CO)5, from adventitious carbon monoxide. 

Fig. 4.21. Normalized XPS spectra of the Pt 4f region for (1) 130-nm Pt dots on ceria, (2) Pt film exposed to all the steps in the colloidal lithography process, (3) untreated Pt film, as reference. The samples were analyzed (a) as-prepared (b) after heating in vacuum to 400° C and cooled to room temperature (c) after reduction in H2 plasma (SOOmTorr, 250 W, 2min). The binding energies were referenced to adventitious carbon at 284.8eV (from [92])...

Table VI lists the relationship between the sample preparation and the amount of hydrocarbon (Cj) on the surface. Obviously, those samples with internal sizing added have an elevated hydrocarbon content. It is this hydrocarbon, in the form of rosin and rosin salts, that imparts the low surface energy and resistance to water penetration to the paper. In other cases, the hydrocarbon is probably in the form of lignin remaining from the pulping operation or adventitious carbon simply from the handling of the sample.

The binding energies were calculated taking as reference the C-(C,H) component of the C Is adventitious carbon peak fixed at 284.8 eV. The analyses of palladium, chlorine and aluminium were based on the following photopeaks Pd 3d, A12p and Cl 2p. 

The use of the adventitious carbon with 285 eV as internal reference is the most commonly used method for correcting charging. The energy scale of the measured data set is shifted such that the maximum of the C Is fine occurs at 285.0 eV assuming that elemental carbon and/or hydrocarbons are the source of... 

The sample surface is contaminated, e.g., with adventitious carbon (small signal in the figure with a height below the line thickness at 290 eV), with nitrogen compounds from templates, or with transition-metal impurities. Residual alkali ions from incomplete cation exchange or residual anions, e.g., from soUd-state ion exchange, are other sources of unexpected elements in the sample. 

On the basis of this crude picture a set of useful chemical shift data has been compiled as self-consistent data [18] which can be used for a qualitative first-sight interpretation of zeolitic materials. The list is given relative to a charge correction of adventitious carbon of C ls=285.0 eV (Table 1). 

Exposure of solid surfaces to ambient air invariably results in a modest overlayer of carbonaceous byproducts collectively labeled adventitious carbon (AC). The employment of the adventitious carbon to establish binding energy scales has been the standard in more ESCA analysis than all other referencing methods combined. In order to define the use of adventitious carbon (AC) [30-34], we must first try to describe what it is and how it behaves. Although each of these studies exhibits slight differences, the striking feature of the many thousands of XPS observations of adventitious carbon is their apparent chemical and physical similarity. Any attempt at analyzing the key details of AC requires a short review of the properties of the possible candidates. 

Adventitious Carbon in General. Having briefly described the ESCA characteristics of graphitic materials and hydrocarbon polymers, we must now see if we can use these features to provide a careful (and hopefully useful) chemical description of AC. 

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