Schematic illustration of the mechanism of hydrogen bombardment process for molecular cross-linking: generation of carbon radicals due to the low-energy hydrogen bombardment, formation of cross-link among molecular chains, and change of the height of the thin film due to the molecular cross-link.
XPS survey spectra of (a) virgin C32H66 monolayer; (b) the sample measured after immersion in hexane for 5 min; (c) C32H66 monolayer after 600 s bombardment; (d) the bombarded sample immersion in hexane for 5 min.
Topographic images (top) and height (bottom) of C32H66 perpendicular monolayer without bombardment (0 s) and after 700 s bombardment.
AFM measurements show that the height of C32H66 perpendicular monolayer decreases as the exposure time increases.
Roughness variance of C32H66 perpendicular monolayer with respect to the exposure time (measured by AFM). The error bars represent the standard deviations of roughness of surface of seven bombarded samples.
Phase contrast imaging of tapping AFM mode distinguishes virgin C32H66 perpendicular layer (exposure time = 0 s) from parallel layer: the bright region corresponds to C32H66 perpendicular layer and the dark region corresponds to the parallel layer.
Topographic (top) and phase (bottom) images of C32H66 monolayers after 700 s bombardment, where the phase image cannot effectively distinguish perpendicular layers from parallel layers because of the increased Young's moduli after hydrogen bombardment.
Large dynamic range of nanomechanical measurements on several reference samples by the HarmoniX™ mode: LDPE ∼100 MPa, PS ∼2 GPa, PP ∼1.2 GPa and mica ∼50 GPa.
Nanomechanical mapping of parallel and perpendicular layers of virgin C32H66 thin film in the HarmoniX™ mode. The upper figure shows the contrast of stiffness over the entire surface; the lower figure shows the Young's modulus profile along a section line, where the Young's modulus of perpendicular layer is ∼1.2 GPa and that of parallel layer is ∼0.2 GPa.
Amplitudes of the AFM cantilever in force modulation on virgin C32H66 perpendicular layer (dots) and perpendicular layer bombarded for 700 s (dashes) are 9.14 and 10.17 mV, respectively.
Maximum energy transferred from projectiles to target atoms.
Bond energy for typical chemical bonds.
Young's modulus of C32H66 thin films before and after bombardment.
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