S. Kirkpatrick, M. Walsh, J. Khoury, D. Shashkov
Keywords: surface, nanotexture, atomic-level processing, etching, polishing, hydrophilic surface, oxidation resistance, coating adhesion, nanomembrane
Summary:It has long been recognized that nano-scale modifications of solid surfaces and thin films can result in multiple benefits and improved performance of the devices ranging from semiconductor structures to optical elements to medical implants. However, existing surface modification technologies fall short of the nano-scale requirements for such modifications due to high particle energy and electrically charged nature of traditional ion beam and plasma-based techniques. In this paper, we explore the use of Accelerated Neutral Atom Beam (ANAB) technique to impart beneficial functionality on metal, ceramic, glass, and polymer surfaces, without such detrimental impacts. ANAB provides intense, collimated beam of energetic neutral gas atoms with energy of 10-100eV per atom, an ideal range for many nanoscale surface modifications. We demonstrate ANAB impact in three distinct areas, namely modification of solid surfaces, improved properties of coatings, and creation and modification of thin films and nano-membranes. ANAB treatment of various glass and ceramic substrates common in optical applications, results in unprecedented level of surface smoothing combined with removal of sub-surface damage associated with most mechanical polishing methods. Roughness of 1-2Å is routinely achieved. TEM cross-sectional analysis of ANAB-treated Si surface reveals amorphization depth of 2.1 nm with an atomically abrupt interface, indicating highly controlled material removal. ANAB treatment of polycrystalline Cu surface results in greater resistance to atmospheric oxidation due to surface amorphization that results in inhibition of intergranular corrosion. Another demonstrated impact of ANAB on solid surfaces is an increase in surface area, energy, and hydrophilicity, with potential applications in microfluidics and medical implants, among others. Investigation of ANAB impact on coatings revealed significantly higher coating adhesion, with applications ranging from medical implants to high-power laser optics. Examples include Rapamycin coating on CoCr, epoxy adhesion to PEEK, and antireflective coatings on optical YAG crystals. In the latter case, we demonstrate a significant increase in laser-induced damage threshold (LIDT). Finally, ANAB interaction with thin films and membranes reveals novel forming and processing techniques. First, ultra-fragile SiN film is successfully thinned by ANAB from 200 to 80 nm, resulting in excellent EUV transparency. Second, we demonstrate formation of macroscopic, nanometer-thick freestanding carbon film using amorphization property of ANAB. Such films already find their applications in electron microscopy but can provide a platform for other uses, e.g. in molecular biology. Finally, we perforate freestanding graphene and molybdenum disulfide sheets to form nanomembranes with ~10 nm openings, with potential applications in chemical separation, desalination, and DNA research. In conclusion, ANAB technology demonstrates true nano-scale processing of solid surfaces, coatings, and thin films, enabling higher performance for a wide variety of applications and industries.