No abstract

Irrespective of the technology, we now rely on touch to interact with devices such as smart phones, tablet computers, and control panels. As a result, touch screen technologies are frequently in contact with body grease. Hence, surface deposition arises from localized inhomogeneous finger-derived contaminants adhering to a surface, impairing the visual/optical experience of the user. In this study, we examined the contamination itself in order to understand its static and dynamic behavior with respect to deposition and cleaning. A process for standardized deposition of fingerprints was developed. Artificial sebum was used in this process to enable reproducibility for quantitative analysis. Fingerprint contamination was shown to be hygroscopic and to possess temperature- and shear-dependent properties. These results have implications for the design of easily cleanable surfaces.

The properties of a thin film are, in part, governed by the nucleation or seeding of the material on a given substrate. Control over the seeding process is highly desirable, resulting in the ability to "dial up" desired film properties for the end application. In this study, we investigate the seeding process for thin films of Cr (thickness < 5 nm) sputtered onto polymeric substrates. These substrates are fabricated having Young's moduli spanning from the rubbery to the glassy state. Compliant substrates in the rubbery state display nanowrinkled structures during the early stages of film deposition (seeding). The combined chemical and morphological analysis of these films suggests implantation of Cr clusters within the polymeric substratethis implantation process is strongly influenced by substrate's mechanical properties. Understanding the seeding process, the resultant nanowrinkles, and the evolution to a continuous ultrathin film, will have an impact on the way these systems are engineered for practical applications.

Human interaction with touch screens requires physical touch and hence results in contamination of these surfaces, resulting in the necessity of cleaning. In this study we discuss the three bodies of this problem and how each component contributes and can be controlled. Utilizing a standard fingerprint machine and a standard cleanability test, this study examines the influence of parameters such as the wiping speed and pressure, the material and surface area of the cloths, and the surface energy of the contaminated surfaces. It was shown that fingerprint contamination undergoes shear banding and hence is not easily removed. The degree of material removal depends on the position of the shear plane, which is influenced by surface energies and shear rates.

Silicon is a leading candidate material to replace carbon/graphite, the commonly used anode material in lithium-ion batteries (LIBs), because it has an 11 times higher theoretical specific capacity. However, silicon anodes have two main issues, low electronic conductivity and large volume expansion during cycling, and these issues present challenges in the manufacture of mechanically stable high-electrochemical-performance Si electrodes. Physical vapor deposition (PVD) is an alternative fabrication process that can produce binderless compact Si thin films suitable for microbatteries and thin flexible devices. Despite numerous studies exploring the use of vacuum-based PVD silicon films, no definitive information has been recorded correlating how changes in process parameters affect the properties of the resulting deposited films and how this influences anode performance in Li-ion batteries. In this work, process parameters (i.e., deposition power and gas working pressure) were altered for various Si film deposition trials. Electronic resistivity, electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), residual film stress, X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) measurements were performed for a thorough physico/chemico analysis of the various films. This information was used to interpret the differences in discharge capacity and capacity retention obtained from the various Si anodes using galvanostatic charge/discharge cycling from assembled coin cells. CV measurements were used to corroborate performance outcomes, as well as to calculate Li-ion diffusion coefficients.