Near-edge X-ray absorption fine structure, NEXAFS, spectroscopy was used to investigate the relaxations of polystyrene, a typical amorphous polymer, near a free surface after the imposition of a small deformation. Using synchrotron radiation, the NEXAFS dichroic ratio was determined for both the Auger and total electron yield processes as a function of temperature to determine the orientation of the polymer in the first 1 and 10 nm from the free surface, respectively. Complete relaxation of the polymer was not seen for temperatures less than the bulk glass transition temperature. No evidence of enhanced mobility at the free surface was found. A planar relaxation of the polymer was found in the first nanometer from the free surface, whereas in the first 10 nm, the dominant relaxation was normal to the surface.

Surface-sensitive and polarization-dependent near-edge X-ray absorption fine structure (NEXAFS) measurements clearly reveal a preferred in-plane and out-of-plane orientation of phenyl and CO groups at the surface of rubbed polyimide films. The unidirectional molecular alignment at the surface is argued to provide the template for liquid crystal (LC) alignment of the films. Both the LC orientation along the rubbing direction as well as the direction of the out-of-plane LC pretilt are explained in a simple model. In this model the LC direction follows the preferential orientation of the phenyl rings at the surface. The preferred phenyl orientation is explained in terms of preferential chain segment alignment through a pulling action of the rubbing cloth fibers. The proposed LC alignment model is based on the existence of a statistically significant unidirectional bond asymmetry at the polymer surface, and it does not require the existence of crystalline order.

Articles you may be interested inStudy of surface cleaning methods and pyrolysis temperatures on nanostructured carbon films using x-ray photoelectron spectroscopy Influence of electron irradiation and heating on secondary electron yields from non-evaporable getter films observed with in situ x-ray photoelectron spectroscopy J. Vac. Sci. Technol. A 25, 675 (2007); 10.1116/1.2738491 X-ray photoelectron spectroscopy and secondary electron yield analysis of Al and Cu samples exposed to an accelerator environment Enhancement of secondary electron emission by annealing and microwave hydrogen plasma treatment of ionbeam-damaged diamond films Photoemission electron spectromicroscopy with synchrotron radiation has been used to study the correlation between the chemical surface composition and secondary electron yield from the surface of amorphous carbon films. Regions of about 4 m diam were found which exhibited up to ten times higher secondary electron emission than the rest of the film. Near edge x-ray absorption fine structure spectroscopy of these regions showed that they contained highly oxidized carbon in the form of carboxylic and carbonate groups. These observations might be linked to the field emission properties of these films.

X-ray photoelectron emission microscopy (X-PEEM) was used to study the surface orientation of stylized and rubbed polyimide thin films. Using soft X-rays produced by a synchrotron light source, this technique combines high spatial resolution imaging with near-edge X-ray absorption fine structure (NEXAFS) spectroscopy to yield information on the surface orientation of the films. Stylizing is an ideal model of the rubbing process since the local stress acting on the polyimide to orient the molecules can be calculated. The minimum normal stress necessary to orient the surface of BPDA-PDA films was found to be 45 MPa much lower than the bulk yield stress of 200-300 MPa. Studies of the polyimide films oriented by the conventional rubbing method showed lateral inhomogeneities in the orientation of the polymer at the surface.