SiC is an extremely promising material for nanoelectromechanical systems given its large Young's modulus and robust surface properties. We have patterned nanometer scale electromechanical resonators from single-crystal 3C-SiC layers grown epitaxially upon Si substrates. A surface nanomachining process is described that involves electron beam lithography followed by dry anisotropic and selective electron cyclotron resonance plasma etching steps. Measurements on a representative family of the resulting devices demonstrate that, for a given geometry, nanometer-scale SiC resonators are capable of yielding substantially higher frequencies than GaAs and Si resonators. Silicon carbide is an important semiconductor for high temperature electronics due to its large band gap, high breakdown field, and high thermal conductivity. Its excellent mechanical and chemical properties have also made this material a natural candidate for microsensor and microactuator applications in microelectromechanical systems ͑MEMS͒. Recently, there has been a great deal of interest in the fabrication and measurement of semiconductor devices with fundamental mechanical resonance frequencies reaching into the microwave bands. Among technological applications envisioned for these nanoelectromechanical systems ͑NEMS͒ are ultrafast, high-resolution actuators and sensors, and high frequency signal processing components and systems.2 From the point of view of fundamental science, NEMS also offer intriguing potential for accessing regimes of quantum phenomena and for sensing at the quantum limit.SiC is an excellent material for high frequency NEMS for two important reasons. First, the ratio of its Young's modulus, E, to mass density, , is significantly higher than for other semiconducting materials commonly used for electromechanical devices, e.g., Si and GaAs. Flexural mechanical resonance frequencies for beams directly depend upon the ratio ͱ (E/). The goal of attaining extremely high fundamental resonance frequencies in NEMS, while simultaneously preserving small force constants necessary for high sensitivity, requires pushing against the ultimate resolution limits of lithography and nanofabrication processes. SiC, given its larger ͱ (E/), yields devices that operate at significantly higher frequencies for a given geometry, than otherwise possible using conventional materials. Second, SiC possesses excellent chemical stability.3 This makes surface treatments an option for higher quality factors ͑Q factor͒ of resonance. It has been argued that for NEMS the Q factor is governed by surface defects and depends on the device surface-to-volume ratio.
We report on the electrocatalytic properties of sputtered iridium oxide films (SIROF's) in acidic electrolytes. Long term stability (240 hr) is demonstrated. Typical steady‐state currents are 75 mA/cm2 at 1.85V (vs. RHE), which is 50% higher than previously reported. In addition, we introduce a new method of determining Tafel slopes based on the short‐time decay of the oxygen evolution reaction (OER) current, corrected for the capacitative component. Tafel plots are presented for samples of different thickness and degree of hydration. The high current density and absence of corrosion demonstrate the superior catalytic properties of SIROF's vs. iridium over the entire voltage range investigated.
We report the preparation and electrochromic properties of iridium oxide films deposited by reactively sputtering iridium in a humidified oxygen discharge. These sputtered iridium oxide films (SIROFs) have the fast coloring and bleaching kinetics and excellent stability previously observed for anodically grown iridium oxide films (AIROFs). SIROFs deposited on SnO2-coated glass can be modulated from clear to blue-gray with properties similar to those of AIROFs. In addition, SIROFs deposited on metal substrates exhibit a variety of colors which can be electrically altered. This adds a new dimension to the range of potential applications for iridium oxide displays.
Anodic iridium oxide films (AIROF’s) can be grown and operated on transparent substrates. Using SnO2-coated glass as the substrate we can monitor large, rapid, and persistent variations of the light intensity transmitted through the AIROF. The voltammogram of the AIROF on SnO2-coated glass is essentially identical to that of an AIROF on iridium. This proves that the electrochemistry producing the coloration does not involve the substrate.
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