Degree of surface sensitivity

The surface properties of polymers are important in many applications and they are dependent on the structure and composition of the ontermost molecular layers. The surface layer thickness involved is typically of the order of a few nanometers. Understanding surface structure-property relationships therefore requires analytical techniques which have this degree of surface sensitivity (or specificity). Two techniques stand out X-ray photoelectron spectroscopy (XPS) (1), also known as ESCA (electron spectroscopy for chemical analysis), and secondary ion mass spectrometry (SIMS) (2). The information provided by these methods is highly complementary and they are frequently used in combination. This article describes the physical bases and anal5dical capabilities of XPS and SIMS and illustrates their application in polymer surface characterization (3). 

Degree of Surface Sensitivity. Analysis of the (1 - exp(-l/(X sin 0))) term reveals that for AES both S and O over 80% of the observed signal originates from the first three layers below the surface (this calculation is based upon the equation, S(n) = exp(-n/ Xq s sin 30 ), where S(n) represents the relative signal contribution from species n layers below the surface (n=0) and Xq s =4.745 and 2.612 from (72) ). 

Acidified water surfaces degree of surface sensitivity, 111 experimental description, 107-109 stratospheric significance, 107 sulfuric acid, 109-111 surface composition, 111-113 surface vs. bulk composition, 113-114 Adsorption... 

Surface analytical techniques can be classified in terms of the excitating and emitted probe cfr. Table 4.4). The penetration of the physical probe increases fl om ions (ISS, RBS, SIMS) to electrons (XPS) and finally photons (UV/VIS, IR, XRF, etc.). Amongst the photon beam techniques which show some degree of surface sensitivity, in practice only XPS, total reflection X-ray fluorescence (TXRF) and laser-induced mass spectroscopic methods (LMMS),... 

For existing ships the only NDE method nominated by classification for the detection of fatigue cracks is close-up visual inspection - although all Surveyors have the option of requesting additional NDE when warranted. The sensitivity of visual inspection is influenced by the degree of surface preparation and the level of lighting at the inspected surface - which may not always meet the level of 500 lux nominated by some NDE specifications. 

The degree of surface cleanliness or even ordering can be determined by REELS, especially from the intense VEELS signals. The relative intensity of the surface and bulk plasmon peaks is often more sensitive to surface contamination than AES, especially for elements like Al, which have intense plasmon peaks. Semiconductor surfaces often have surface states due to dangling bonds that are unique to each crystal orientation, which have been used in the case of Si and GaAs to follow in situ the formation of metal contacts and to resolve such issues as Fermi-level pinning and its role in Schottky barrier heights. 

Electrode surface characteristics represent an important aspect in the construction of sensitive DNA electrochemical biosensors for rapid detection of DNA interaction and damage. A critical issue in the development of a DNA-electrochemical biosensor is the sensor material and the degree of surface coverage that influences directly the sensor response. 

Although the use of ionizing radiation has contributed to a definite picture of certain chemisorptions and catalyses, in other cases it has run into difficulties that have not yet been resolved. With several oxides, for example, water or some other poison is required for radiation sensitivity, and the role of the poison has not been clarified. Because this behavior seems to be fairly widespread, it is important to understand it more fully, and considerable attention could well be given to irradiation of such oxides in a high state of purity and with varying degrees of surface coverage. 

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