Gas Phase And Surface Reactions In Organometallic Chemical Vapour Deposition Of Platinum

Organometallic chemical vapour deposition (OMCVD) films usually have carbon as an impurity. This comes from the decomposition of the ligands in the organometallic precursor. Understanding the chemical reactions in the decomposition will greatly enhance our ability to control the impurity level in these films and also the epitaxial growth of the films. Depending on the pressure in the reactor, the important reactions could be in the gas phase or on the surface.;Decomposition of the precursor, cis-dimethyl platinum diisocyanide in presence of hydrogen shows reduction in carbon impurity. The decomposition was carried out in an infrared gas cell so that infrared light could be used in a transmission experiment as an in-situ probe of the reaction. It was found that the methyl platinum groups reacted with the hydrogen to give an increased yield of methane. The isocyanide ligand appears to leave the complex in one piece in an initial reversible equilibrium step. Subsequently they reacted with hydrogen gas to give ammonia. Kinetic measurements demonstrate a heterogenous component to the reaction.;Surface reactions were carried out in an ultra high vacuum (UHV) chamber. The main surface tools used in the study were Infrared Reflection Absorption Spectroscopy (IRRAS) and Temperature Programmed Desorption (TPD). The interaction of acetonitrile with methyl isocyanide with Pt(111) was also studied to assist in the overall understanding of the decomposition mechanism of cis-dimethyl platinum diisocyanide. When the precursor is adsorbed on a Pt(111) surface at 110 K, it does so dissociatively to give terminally bonded methyl isocyanide and some platinum hydrocarbon fragments. Thermochemistry of the complex on Pt(111) involved decomposition to H{dollar}\sb2{dollar} and HCN. The effect of surface carbon on Pt(111) appears to turn off the reactivity of the surface. When it was sufficiently turned off, monolayer adsorption was molecular. The thermal chemistry was also changed as dehydrogenation was greatly reduced. Loss of methyl isocyanide at 525 K was turned on instead and is consistent with decomposition studies at 580 K in the infrared cell where methyl isocyanide loss was also observed

Four-probe thermal transport measurements of few-layer graphene and ultrathin graphite

The unique combination of mechanical, electrical, and thermal properties of graphite and its derivatives, such as graphene and carbon nanotubes, make graphitic materials desirable for a number of technological applications as well as a platform for studying various transport phenomena, especially at the nanoscale. Although it has been more than a decade since graphene was first successfully isolated, discrepancies between the results of theoretical and experimental studies have not yet been resolved and the answers to many fundamental questions concerning the details of thermal transport in graphene are still subject to debate. The presence of unknown contact thermal resistance has limited prior two-probe thermal transport measurements of suspended graphene samples. This work utilizes a four-probe thermal measurement technique to measure few-layer graphene and ultrathin graphite samples. This technique has the ability to measure the intrinsic thermal conductance of suspended samples and to isolate the contact thermal resistance between the sample and measurement device. By eliminating error due to contact thermal resistance and developing a clean method for transferring thin-film samples, the true intrinsic thermal properties of graphene can be realized, potentially leading to the observation of unique transport phenomena such as hydrodynamic phonon transport.Mechanical Engineerin

Four-probe thermal measurement of a carbon nanotube sheet

textAs advances are made in top-down nanofabrication and bottom-up syntheses of nanostructures, the characteristic length scales encountered in these structures are on the order of the mean free path of the heat carriers or smaller. Therefore, the thermal transport properties of these nanostructures can be different from the bulk counterparts. A number of experimental techniques have been developed for characterizing the size-dependent thermal transport properties of nanostructures. However, it is difficult to eliminate contact thermal resistance, an important error source, from the measurement results. Recently, a four-probe thermal measurement technique has been developed to measure the intrinsic thermal conductance of a suspended sample as well as isolate the values of contact resistance between the sample and measurement device. Here, the fabrication process of the four-probe measurement device is described. In addition, numerical heat conduction simulation is used to verify the analytical model of the measurement method. This method is further used to measure the thermal conductance of a carbon nanotube sheet.Mechanical Engineerin

Optomechanical guitar: reconfiguring metamaterials with sub-wavelength spatial resolution

Optomechanical metamaterials, where optical signals actuate unique elements of the nanostructure at their eigenfrequency, can be used to modulate metamaterials with sub-wavelength spatial resolution. We demonstrate the first all-optically addressable metadevice operating in the near infrared

Assessing Nozzle Geometry, Spacing and Height Effect on Pesticide Spray Characteristics and Swath from Ground and Aerial Sprayers

Nozzle is the basic aperture that controls pesticide spray jet onto targeted substrates. It is moulded from stainless steel, brass, ceramic and plastics at different wear rates. The efficiency of pesticide application is dependent on chemical efficacy and nozzle type. Both flat fan and hollow cone nozzles are commonly used to enhance pesticide spray characteristics and deposition. The surface coverage and spray distribution are influenced by nozzle spacing and spraying height. Therefore, using a nozzle type, spacing and spraying height that give pesticide spray-overlap is of interest to researchers. This review therefore analyses the effect of nozzle geometry, nozzle spacing and spraying height regimes on pesticide spray droplets characteristics from mechanical boom sprayers. To improve on uniformity of pesticides spray coverage on plant surfaces, a unitary relative span is reported suitable for application, but there had not been clearly defined nozzle type, spacing and height regime for effective spraying. The review further proposes an optimum parameters combination with specific nozzle type, spacing and spraying height for efficient application of pesticides

Random access actuation of nanowire grid metamaterial

While metamaterials offer engineered static optical properties, future artificial media with dynamic random-access control over shape and position of meta-molecules will provide arbitrary control of light propagation. The simplest example of such a reconfigurable metamaterial is a nanowire grid metasurface with subwavelength wire spacing. Recently we demonstrated computationally that such a metadevice with individually controlled wire positions could be used as dynamic diffraction grating, beam steering module and tunable focusing element. Here we report on the nanomembrane realization of such a nanowire grid metasurface constructed from individually addressable plasmonic chevron nanowires with a 230 nm × 100 nm cross-section, which consist of gold and silicon nitride. The active structure of the metadevice consists of 15 nanowires each 18 μm long and is fabricated by a combination of electron beam lithography and ion beam milling. It is packaged as a microchip device where the nanowires can be individually actuated by control currents via differential thermal expansion

Mitigating the Effects of Au-Al Intermetallic Compounds Due to High-Temperature Processing of Surface Electrode Ion Traps

Stringent physical requirements need to be met for the high performing surface-electrode ion traps used in quantum computing, sensing, and timekeeping. In particular, these traps must survive a high temperature environment for vacuum chamber preparation and support high voltage rf on closely spaced electrodes. Due to the use of gold wire bonds on aluminum pads, intermetallic growth can lead to wire bond failure via breakage or high resistance, limiting the lifetime of a trap assembly to a single multi-day bake at 200$^{\circ}$C. Using traditional thick metal stacks to prevent intermetallic growth, however, can result in trap failure due to rf breakdown events. Through high temperature experiments we conclude that an ideal metal stack for ion traps is Ti20nm/Pt100nm/Au250nm which allows for a bakeable time of roughly 86 days without compromising the trap voltage performance. This increase in the bakable lifetime of ion traps will remove the need to discard otherwise functional ion traps when vacuum hardware is upgraded, which will greatly benefit ion trap experiments.Comment: 9 Pages, 10 figure

Random access actuation of nanowire grid metamaterial

Dataset supporting: Cencillo Abad, Pablo, Ou, Jun-Yu, Plum, Eric, Valente, Jo&atilde;o and Zheludev, Nikolay (2016) Random access actuation of nanowire grid metamaterial. Nanotechnology, 27, 485206</span

Merging metamaterial and fiber technologies

We report on integration of plasmonic and all-dielectric metamaterials into active photonic devices on the fiber platform. These include all-optical and electro-optical phase change and nano-opto-mechanical switching devices, dispersion control solution and coherent control metadevices