Dc Plasma-enhanced Chemical Vapor Deposition Research Articles

Growth of Carbon Nanofibers on Tipless Cantilevers for High Resolution Topography and Magnetic Force Imaging

Carbon nanofibers are grown on tipless cantilevers as probe tips for scanning probe microscopy. A catalyst dot pattern for carbon nanofiber growth is formed on the surface of the tipless cantilevers using electron beam lithography, and the growth of carbon nanofibers is performed in a direct-current plasma-enhanced chemical vapor deposition reactor. Atomic force surface imaging and magnetic force-gradient imaging have been demonstrated using these probe tips.

Structural characterization of nanocomposite Ti–Si–N coatings prepared by pulsed dc plasma-enhanced chemical vapor deposition

Ti–Si–N coatings have been investigated widely in recent years due to their unique nanocomposite microstructure and attractive properties of superhardness, fairly good oxidation-resistance nearly to 1000 °C, etc. In this study, Ti–Si–N coatings have been prepared by pulsed dc plasma-enhanced chemical vapor deposition in an industrial-scale chamber. Structural characterization of Ti–Si–N coatings was examined by x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron micrograph, and transmission electron microscopy. The results show that: (1) The microstructure of Ti–Si–N coatings varies significantly with the processing parameters, (2) the microstructure can be confirmed as nanocomposite Ti–Si–N where nanocrystalline TiN and/or TiSi2 particles are embedded into an amorphous matrix of Si3N4, and (3) the nanocrystals have a multioriented microstructure. However, the silicon content in Ti–Si–N coatings and coating thickness as well as crystalline size all increase when the inlet gas ratio of X=[SiCl4/(TiCl4+SiCl4)]% increases. Whereas the microhardness of the coatings first increases with increased Si content, microhardness reaches a maximum value of about Hv5800 at 13 at. % Si and then decreases slightly.

Plasma nitrided and TiCN coated AISI H13 steel by pulsed dc PECVD and its application for hot-working dies

Pulsed direct current (dc) plasma-enhanced chemical-vapor deposition (PECVD) holds great advantages such as plasma permeation and deposition in the inner wall of holes and narrow cracks usually encountered in complex components. In this work, plasma nitriding and TiCN coatings on H13 steel have been developed using pulsed dc PECVD. The composite layer has been characterized with respect to its microhardness, adhesion, and microstructure. The results indicate that with the assistance of plasma nitriding, the composite layer improves the surface microhardness and interfacial adhesion between the coating and substrate. The application of this duplex-plasma processing on a hot-working die made of AISI H13 steel provides a significant increase in lifetime for the steel. This is a more-successful processing technique than conventional techniques, which usually do not improve the surface properties of dies, with complex shapes and demanding performance requirement conditions. However, extra hardening of this composite layer is not always advantageous. Microhardness (related to layer's strength) and adhesion, as well as the toughness of the coating system, should all be considered together.

Processing and Characterization of Functionally Graded Ti/Ti<sub>x</sub>C<sub>y</sub>/DLC Thin Film Coatings

In this study diamond-like carbon based functionally graded Ti/Ti xCy/DLC films were deposited by the hybrid technique of magnetron sputtering and DC plasma-enhanced chemical vapor deposition. The coating parameters investigated are; substrate bias (60-200 V), sputtering power (1.0-1.1 kW) and plasma booster current (1.7-2.5 A). The mechanical properties were investigated by calotest and scratch adhesion tests. The elemental depth profiling and the morphology of the coatings were examined by secondary ion mass spectrometer (SIMS) and electron probe micro analyzer (EPMA) which revealed that a functionally graded structure was successfully formed.

High growth rates and wall decoration of carbon nanotubes grown by plasma-enhanced chemical vapour deposition

DC plasma-enhanced chemical vapour deposition (PECVD) was used to grow films of aligned carbon nanotubes on a silicon wafer using Fe as catalyst and a C 2H 2/H 2 gas mixture. The films were of high quality and showed an exceptionally high growth rate compared with other plasma growth techniques. For long growth times, the upper parts of the nanotubes developed additional outer graphite flakes. The onset of the ‘tube decoration’ correlates with a decrease in linear growth rate and can be related to the gradient of plasma parameters in the cathode sheath.

The growth of freestanding single carbon nanotube arrays

Regular arrays of freestanding single carbon nanotubes (CNTs) were prepared on Ni dotarrays by dc plasma-enhanced chemical vapour deposition. The size of the Ni dot wasreduced for single CNT growth by means of conventional photolithography and a lateralwet-etch process. The vertical alignment of a single CNT was directly dependent on thelocation of the catalyst metals. Using this method, well-separated and well-defined regulararrays of freestanding CNTs can be fabricated and the process can be scaled up at a lowercost than electron beam lithography, which is encouraging for applications in field emittersand nanoelectrodes.

Individual free-standing carbon nanofibers addressable on the 50 nm scale

We report on the fabrication of arrays of free-standing carbon nanofibers (CNFs) individually addressable on the 50 nm scale. The template for CNF growth consists of a set of tungsten leads patterned with a catalyst dot at the tip of each terminal. The fabrication process involves electron-beam lithography, projection photolithography, reactive ion etching, and dc plasma-enhanced chemical vapor deposition. Discharge power is found to drastically influence the morphology of CNFs grown off single catalyst dots.

Effects of source gases on the growth of carbon nanotubes

We carry out the in situ analysis of chemical species for the growth of carbon nanotubes (CNTs) in direct current plasma enhanced chemical vapor deposition (DC-PECVD) with C 2H 2–NH 3, C 3H 4–NH 3 and CO–NH 3 mixtures by optical emission spectroscopy (OES). From OES analysis, it was shown that the hydrogen related radical was regarded as etching species in CNTs growth and the C 2 and CH radical as available carbon sources for the growth of CNTs irrespective of carbon source gas. As the NH 3 flow rate changed, different chemical species in plasma made effects on the growth of CNTs depending on the source gas.

Control Mechanisms for the Growth of Isolated Vertically Aligned Carbon Nanofibers

Isolated vertically aligned carbon nanofibers (VACNFs) have been grown using dc plasma-enhanced chemical vapor deposition, and the effects of the growth conditions on VACNF morphology and composition have been determined in substantial detail. The dependence of the growth rate, tip and base diameters, and chemical composition of isolated VACNFs on the growth parameters is described, including the effects of plasma power and gas mixture. Phenomenological models explaining the observed growth behavior are presented. The results indicate the importance of plasma control for the deterministic growth of isolated VACNFs, which are promising elements for the fabrication of practical nanoscale devices.

Sharpening of carbon nanocone tips during plasma-enhanced chemical vapor growth

In situ tip sharpening of vertically aligned carbon nanocones (VACNCs) was demonstrated. VACNCs were synthesized on patterned catalyst dots of 100 nm in diameter using dc plasma-enhanced chemical vapor deposition. The VACNC tip diameter was found to decrease with growth time. This enables synthesis of ultra-sharp VACNCs even for relatively large catalyst dot sizes, which is quite important for practical applications. We also find that for a given set of growth parameters the diameter of the initially formed catalyst nanoparticle determines the maximum length of the growing VACNC. The mechanism of VACNC growth and sharpening is discussed.

Growth of aligned carbon nanotubes by plasma-enhanced chemical vapor deposition: Optimization of growth parameters

Direct-current plasma-enhanced chemical vapor deposition (CVD) with mixtures of acetylene and ammonia was optimized to synthesize aligned carbon nanotubes (CNTs) on Co- or Ni-covered W wires with regard to wire temperature, wire diameter, gas pressure, and sample bias. A phase diagram of CNT growth was established experimentally in this optimization process. It was revealed by transmission electron microscopy that Co-catalyzed CNTs encapsulated a Co carbide nanoparticle at their tip, disagreeing with a previous report that Co particles were located at the base of CNTs CVD grown on Co-covered Si substrates [C. Bower et al., Appl. Phys. Lett. 77, 2767 (2000)]. This leads to the conclusion that the formation mechanism of aligned CNTs depends significantly on the catalyst support material as well as the catalyst material itself. Since the sample bias strongly affected the morphology of CNTs, the selective supply of positive ions to CNT tips was possibly responsible for the alignment of growing CNTs.

Low-temperature growth of Ti(C,N) thin films on D2 steel and Si(100) substrates by plasma-enhanced metalorganic chemical vapor deposition

We have deposited Ti(C,N) thin films on Si(100) and D2 steel substrates in the temperature range of 200–300 °C using tetrakis diethylamidotitanium (TDEAT) and titanium isopropoxide (TIP) by pulsed dc plasma-enhanced metalorganic chemical vapor deposition (PEMOCVD). Radical formation and ionization behaviors in plasma are analyzed in situ by optical emission spectroscopy at various pulsed bias voltages and gas conditions. H2 and He+H2 gases are used as carrier gases to compare plasma parameters, and the effect of N2 and NH3 as reactive gas is also evaluated by the reduction of the C content of the films. Polycrystalline Ti(C,N) thin films were successfully grown on either D2 steel or Si(100) surfaces with TDEAT at temperatures as low as 200 °C. For TIP, however, only TiOCN thin films were obtained on Si(100) substrates. The best deposition process is evident for H2 and N2 gas atmospheres and bias voltage of 600 V. The higher film hardness is about 1760 Hk 0.01, but depends on gas species and bias voltage. Compared to TiN films, the Ti(C,N) film grown by PEMOCVD has very good conformability; the step coverage exceeds 85%, with an aspect ratio of more than 3.

Laser Damage Threshold Of Diamond Films

Calculations indicate that the thermal stress resistance for diamond is significantly higher than for other materials, suggesting that diamond films may inhibit damage to optical components in laser systems. To assess this possibility we have begun to study laser-induced damage in diamond films. We have measured laser damage thresholds of free-standing diamond film windows, diamond films deposited on silicon substrates, and bare silicon substrate. Polycrystalline diamond films were deposited using a dc plasma-enhanced chemical vapor deposition process. As expected, the free-standing diamond films showed a high laser damage threshold. Melting or dielectric breakdown induced by laser radiation may be the damage mechanism. The film/substrate combination had a damage threshold lower than the calculated value, which is attributed to film stress and conditions of film deposition.