Development of ALD Coatings for Harsh Environment Applications.

Atomic layer deposition (ALD) is a well-known technique for the fabrication of ultrathin and highly conformal barrier coatings which have extensively been used for the protection of electronic devices in open atmospheric conditions. Here, we extend the scope for the application of low-temperature-deposited plasma-enhanced ALD barrier coatings for the protection of devices in a variety of chemical environments. The chemical stability tests were conducted in 3.5% NaCl, sea water, HCl (pH 4), and H2SO4 (pH 4) solutions for ALD Al2O3, HfO2, TiO2, and ZrO2, deposited at 100 °C on TiO2-coated Au and ALD ZnO (photoactive)-coated Si substrates. Using electrochemical impedance spectroscopy (EIS) and photoluminescence (PL) study, various aspects of the barrier properties and performance of ALD films in harsh chemical environments were explored. We demonstrate that the combined approach involving EIS and PL provides unique insights into the suitability of ALD films as barriers in harsh environments involving ionic solutions. The observations from EIS and PL tests are supported by the X-ray photoelectron spectroscopy analysis of ALD materials. Of the materials tested, ALD TiO2 and ZrO2 were found to be the most stable, chemically, in all four solutions, whereas TiO2 was a better permeation barrier.

Perspectives on the Growth of High Edge Density Carbon Nanostructures: Transitions from Vertically Oriented Graphene Nanosheets to Graphenated Carbon Nanotubes.

Insights into the growth of high edge density carbon nanostructures were achieved by a systematic parametric study of plasma-enhanced chemical vapor deposition (PECVD). Such structures are important for electrode performance in a variety of applications such as supercapacitors, neural stimulation, and electrocatalysis. A morphological trend was observed as a function of temperature whereby graphenated carbon nanotubes (g-CNTs) emerged as an intermediate structure between carbon nanotubes (CNTs) at lower temperatures and vertically oriented carbon nanosheets (CNS), composed of few-layered graphene, at higher temperatures. This is the first time that three distinct morphologies and dimensionalities of carbon nanostructures (i.e., 1D CNTs, 2D CNSs, and 3D g-CNTs) have been synthesized in the same reaction chamber by varying only a single parameter (temperature). A design of experiments (DOE) approach was utilized to understand the range of growth permitted in a microwave PECVD reactor, with a focus on identifying graphenated carbon nanotube growth within the process space. Factors studied in the experimental design included temperature, gas ratio, catalyst thickness, pretreatment time, and deposition time. This procedure facilitates predicting and modeling high edge density carbon nanostructure characteristics under a complete range of growth conditions that yields various morphologies of nanoscale carbon. Aside from the morphological trends influenced by temperature, a relationship between deposition temperature and specific capacitance emerged from the DOE study. Transmission electron microscopy was also used to understand the morphology and microstructure of the various high edge density structures. From these results, a new graphene foliate formation mechanism is proposed for synthesis of g-CNTs in a single deposition process.

A novel array chip to monitor in situ composite degradation using electrochemical impedance spectroscopy.

OBJECTIVES: This paper presents a novel array-chip technology used to monitor the physical properties of dental composites in situ. The DECAY chip (Degradation via Electrochemical Array) leverages microfabrication techniques to construct a uniform array of recessed wells that may be filled with dental restorative materials (e.g. composite or amalgam) and analyzed electrochemically in solution. METHODS: The array enables the uniform preparation of multiple specimens and reference controls on a common substrate, all of which may be simultaneously evaluated. The DECAY-chip presented here consists of a 3 × 3 array of 100 µm deep wells, and is used to monitor the degradation of a common dental composite as a function of time. RESULTS: The data correlate changes in the measured dielectric properties to surface and bulk changes as the composite is exposed to an ethanol:DI mixture (75% ethanol). A model for the system is presented, as are future plans to simplify the methodology for rapid materials screening and in vitro analyses. SIGNIFICANCE: This in situdiagnostic chip will enable evaluation of composite specimens, tested under a wide range of simulated oral environments. It may also serve as a screening platform for new composite formulations and aid in the study of materials degradation and failure mechanisms.