Unusual kinematics-driven chemistry: cleaving C-H but not COO-H bonds with hyperthermal protons to synthesize tailor-made molecular films.
Unconventional reaction-design strategies have been developed to exploit the intriguing kinematics that occur when adsorbed organic molecules are bombarded by a beam of hyperthermal protons: kinematic energy transfer is only effective in H-->H collisions and thus only C-H bonds are cleaved. This process yields a cross-linked molecular film with its chemistry governed by the selection of appropriate precursor molecules. Unlike the conventional wet-chemistry synthesis of cross-linked polymeric films, this new route uses no chemical initiators, additives, nor catalysts, and only requires a proton beam with a kinetic energy of a few electron volts in a dry-process mode compatible with molecular-device fabrication. The reaction designs are expressed unconventionally: reaction energy is tuned by the kinetic energy of the proton beam and reactant supply is controlled precisely by the proton fluence. However, conventional considerations such as bond-strength effects on kinematic outcomes and branching-ratio statistics are also important and they can extend the reaction applicability of the kinematics concept. For example, taking advantage of the fact that COO-H bonds are stronger than C-H bonds, we show, with practical reaction conditions, synthesis results, and surface analysis using X-ray photoelectron spectroscopy and atomic force microscopy, that we can break C-H bonds without breaking COO-H and other bonds, in the production of cross-linked molecular layers with any desirable COOH concentration and with no ester nor other chemical contaminations. The new reaction-design strategies are also applicable to the synthesis of molecular layers with other functionalities such as OH, and to the synthesis of a mixture of functionalities, such as OH/COOH, with a controllable concentration ratio.
Zheng
Zhi
Z
Institute of Surface Micro and Nano Materials, Xuchang University, Henan Province, Xuchang, 461000, P.R. China.
Wong
Ka Wai
KW
Lau
Wai Cheung
WC
Kwok
Raymund Wai Man
RW
Lau
Woon Ming
WM
D001696:Biomechanical Phenomena; D002245:Carbon Dioxide; D006859:Hydrogen / Q000737:chemistry*; D008567:Membranes, Artificial; D018625:Microscopy, Atomic Force; D011522:Protons
D008567:Membranes, Artificial; D011522:Protons; D002245:Carbon Dioxide; C041069:carboxyl radical; D006859:Hydrogen