Cyclic voltammetric response of boron-doped homoepitaxially grown single crystal and polycrystalline CVD diamond

Abstract Homoepitaxial single crystal and polycrystalline boron-doped CVD diamond films were grown by a microwave plasma process using a methane and hydrogen gas mixture at a pressure of 33 Torr over a Type IIa (orientation: 100) and mechanically damaged, cleaned molybdenum substrate, respectively. Doped diamond was grown on both substrates in a single experiment to maintain constant doping levels in the as-deposited films. Boron-doping of diamond was achieved in situ by using a solid disc source of B 2 O 3 . Doped diamond was evaluated for background response in 0.5 M NaCl and 0.5 M HCl solutions by cyclic voltammetry. We have observed a wide potential range over which negligible background current was observed for polycrystalline and single crystal diamond. Decomposition of water occurs electrochemically and evolves O 2 during positive (anodic) polarization and H 2 evolution during negative (cathodic) polarization. All experimental measurements were corrected for uncompensated IR drop and have been compared with the results obtained without the correction for uncompensated IR drop. Scanning electron microscopy has been used to study the morphology of diamond before and after electrochemical characterization and we conclude that the morphology was unchanged. We have investigated the redox kinetics of ferri-ferrocyanide (Fe(CN) 6 3 − + e − B == \ Fe(CN) 6 4 − ) in 0.5 M NaCl solution at the homoepitaxial boron-doped diamond electrode. The reaction is reversible at the diamond electrode, but the redox kinetics is sluggish. The heterogeneous electron transfer rate constant has been determined using the experimental data and COOL algorithm. The rate constant was found to be from 6.62 × 10 − 5 to 1.41× 10 − 4 cm s − 1 and the kinetics were considered to be sluggish at the diamond electrode/solution interface

Rover Low Gain Antenna Qualification for Deep Space Thermal Environments

A method to qualify the Rover Low Gain Antenna (RLGA) for use during the Mars Science Laboratory (MSL) mission has been devised. The RLGA antenna must survive all ground operations, plus the nominal 670 Martian sol mission that includes the summer and winter seasons of the Mars thermal environment. This qualification effort was performed to verify that the RLGA design, its bonding, and packaging processes are adequate. The qualification test was designed to demonstrate a survival life of three times more than all expected ground testing, plus a nominal 670 Martian sol missions. Baseline RF tests and a visual inspection were performed on the RLGA hardware before the start of the qualification test. Functional intermittent RF tests were performed during thermal chamber breaks over the course of the complete qualification test. For the return loss measurements, the RLGA antenna was moved to a test area. A vector network analyzer was calibrated over the operational frequency range of the antenna. For the RLGA, a simple return loss measurement was performed. A total of 2,010 (3 670 or 3 times mission thermal cycles) thermal cycles was performed. Visual inspection of the RLGA hardware did not show any anomalies due to the thermal cycling. The return loss measurement results of the RLGA antenna after the PQV (Package Qualification and Verification) test did not show any anomalies. The antenna pattern data taken before and after the PQV test at the uplink and downlink frequencies were unchanged. Therefore, the developed design of RLGA is qualified for a long-duration MSL mission

Use of Cumulative Degradation Factor Prediction and Life Test Result of the Thruster Gimbal Assembly Actuator for the Dawn Flight Project

The Dawn Ion Propulsion System is the ninth project in NASA s Discovery Program. The Dawn spacecraft is being developed to enable the scientific investigation of the two heaviest main-belt asteroids, Vesta and Ceres. Dawn is the first mission to orbit two extraterrestrial bodies, and the first to orbit a main-belt asteroid. The mission is enabled by the onboard Ion Propulsion System (IPS) to provide the post-launch delta-V. The three Ion Engines of the IPS are mounted on Thruster Gimbal Assembly (TGA), with only one engine operating at a time for this 10-year mission. The three TGAs weigh 14.6 kg

Motor Qualification for Long-Duration Mars Missions

Qualification of motors for deep space under extreme thermal environments to be encountered during the Mars Science Laboratory (MSL) mission is required to verify the reliability and validate mission assurance requirements. The motor assembly must survive all ground operations, plus the nominal 670 Martian-day (or sol) mission that includes summer and winter seasons of the Mars environment. The motor assembly was tested and characterized under extreme temperature conditions with reference to hardware requirements. The motor assembly has been proved to be remarkably robust and displayed no sign of degradation due to the 3 X (three times per JPL design principles) thermal environmental exposure to the punishing Mars surface operations cycles. The motor characteristics obtained before, during, and post-test comparisons for the surface operations cycles are within measurement error of one another. The motors withstood/survived 2,010 extreme temperature cycles with a Delta T of 190 C deep temperature cycles, representing three times the expected thermal cycling exposure during the MSL surface operations. The qualification test hardware elements (A200 motor assembly, encoders, and resolver) have not shown any signs of degradation due to the PQV (Package Qualification and Verification) testing. The test hardware has demonstrated sufficient life to survive the deep thermal cycles associated with MSL mission surface operations for three lives

Fabrication of a single sub-micron pore spanning a single crystal (100) diamond membrane and impact on particle translocation

The fabrication of sub-micron pores in single crystal diamond membranes, which span the entirety of the membrane, is described for the first time, and the translocation properties of polymeric particles through the pore investigated. The pores are produced using a combination of laser micromachining to form the membrane and electron beam induced etching to form the pore. Single crystal diamond as the membrane material, has the advantages of chemical stability and durability, does not hydrate and swell, has outstanding electrical properties that facilitate fast, low noise current-time measurements and is optically transparent for combined optical-conductance sensing. The resulting pores are characterized individually using both conductance measurements, employing a microcapillary electrochemical setup, and electron microscopy. Proof-of-concept experiments to sense charged polystyrene particles as they are electrophoretically driven through a single diamond pore are performed, and the impact of this new pore material on particle translocation is explored. These findings reveal the potential of diamond as a platform for pore-based sensing technologies and pave the way for the fabrication of single nanopores which span the entirety of a diamond membrane

Kinetics of corrosion of passive metals. Part II: Failure of linear polarization technique

To establish the degree of applicability of galvanostatic linear polarization technique to study the corrosion kinetics of passive metals, measurements were made with 6 typical passive metals which lead to the conclusion that no reliable or accurate data can be obtained in practice for such systems using the linear polarization technique. Shifts in the corrosion potential up to ±10 mV occur during polarization even when the quantity of electricity passed is negligibly small. The indeterminacy of corrosion potential arises from the absence of well-defined potential detg. reactions at the interface between a passive metal and solution. As a result, the exptl. values of polarization resistance may be highly misleading. Such a natural instability of corrosion potential on polarization tends to invalidate not only the linear polarization technique but also other small-signal perturbation technique and current or potential sweep techniques when applied to the detn. of the corrosion rate of passive metals

Kinetics of Corrosion of passive metals - part I: Concepts and Theory

A new electrochemical method was developed to overcome the problems met with in linear polarization and other small amplitude potential perturbation techniques for the evaluation of corrosion rates of passive metals. The method is based on an anal. of a galvanostatic polarization transient in the Tafel region and its decay on open circuit. Linear and Tafel polarization results for passive metals with conducting or insulating films were analyzed from a theorem viewpoint