Role of carbon atoms in plasma-enhanced chemical vapor deposition for carbon nanotubes synthesis (original) (raw)
Related papers
Raman Characterisation of Carbon Nanotubes Grown by Plasma Enhanced Chemical Vapour Deposition
Materials Science Forum, 2012
Simple and up-scalable production of carbon nanotubes (CNTs) still remains difficult with current production methods. Plasma enhanced chemical vapour deposition (PECVD) provides an excellent method for producing high purity and large amounts of carbon nanotubes. This work demonstrates how PECVD can be used to tailor the required properties in the resultant nanotubes produced. By altering only one of the growth variables the resultant CNTs can be altered from single-walled to multi-walled. This was achieved by altering the growth temperature from 450-650°C, altering the growth time and altering the underlying catalyst and supporting layer. High purity SWCNT and MWCNT could be produced and easily distinguished leading to a wide range of applications.
Diamond and Related Materials, 2004
Effects of plasma pressure and the presence of nitrogen on growth of carbon nanotubes (CNTs) and their properties were studied by using microwave plasma chemical vapor deposition (MPCVD) (pressure=600-3300 Pa) and electron cyclotron resonance chemical vapor deposition (ECR-CVD) (pressure=0.3-0.6 Pa) systems. CH 4 /H 2 and CH 4 /N 2 were used as source gases, and Co as the catalyst. The structures and properties of CNTs were characterized by using field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Raman spectra, and field emission I-V measurements. The results show that CNTs made by higher plasma pressure system have a higher growth rate (typically 1-3 Am/min), smaller tube diameter, better field emission properties, and better tube quality. The growth rate is related to the availability of carbon source. The morphology change from spaghetti-like to well-aligned CNTs is discussed in terms of directed ions. The change in field emission properties is reasoned in terms of geometric enhancement factor and screening effect for different tube morphologies. The presence of nitrogen plasma can have the following effects: increasing tube diameter, increasing straightness of CNTs, forming of bamboo-like CNTs, deterioration of field emission properties, and shifting of Raman peak toward lowerfrequency side (or increasing residual tensile stress).
Materials Sciences and Applications, 2011
In this work, we studied the electro-optical properties of high-aligned carbon nanotubes deposited at room temperature. For this, we used the High Density Plasma Chemical Vapor Deposition system. This system uses a new concept of plasma generation: a planar coil is coupled to an RF system for plasma generation. This was used together with an electrostatic shield, for plasma densification, thereby obtaining high-density plasmas. The carbon nanotubes were deposited using pure methane plasmas. Three methods were used for the surface modification of the sample: reference substrate (silicon wafer only submitted to a chemical cleaning), silicon wafer with surface roughness generated by plasma etching, silicon wafer with a thin iron film and silicon wafer with diamond nano powder used as precursor materials. For each kind of silicon wafer surface, the carbon nanotubes were deposited with two different deposition times (two and three hours). The carbon nanotubes structural characteristics were analyzed by Atomic Force Microscope and Scanning Electronic Microscope. The carbon nanotubes electrical characteristics were observed by Raman Spectroscopy and the carbon nanotubes electro-optical properties were analyzed by current vs voltage electrical measurements and photo-luminescence spectroscopy measurements. The photoelectric effect in the carbon nanotubes were determined by photo-induced current measurements. In this work, we obtained carbon nanotubes with semiconductor properties and carbon nanotubes with metallic properties. The electro-optical effects depend strongly on the substrate preparation and the deposition parameters of the carbon nanotubes. The carbon nanotubes are high aligned and show singular properties that can be used for many applications.
Patterned growth of carbon nanotubes obtained by high density plasma chemical vapor deposition
Journal of Physics: Conference Series, 2015
Patterned growth of carbon nanotubes by chemical vapor deposition represents an assembly approach to place and orient nanotubes at a stage as early as when they are synthesized. In this work, the carbon nanotubes were obtained at room temperature by High Density Plasmas Chemical Vapor Deposition (HDPCVD) system. This CVD system uses a new concept of plasma generation, where a planar coil coupled to an RF system for plasma generation was used with an electrostatic shield for plasma densification. In this mode, high density plasmas are obtained. We also report the patterned growth of carbon nanotubes on full 4-in Si wafers, using pure methane plasmas and iron as precursor material (seed). Photolithography processes were used to pattern the regions on the silicon wafers. The carbon nanotubes were characterized by micro-Raman spectroscopy, the spectra showed very singlewalled carbon nanotubes axial vibration modes around 1590 cm-1 and radial breathing modes (RBM) around 120-400 cm-1 , confirming that high quality of the carbon nanotubes obtained in this work. The carbon nanotubes were analyzed by atomic force microscopy and scanning electron microscopy too. The results showed that is possible obtain high-aligned carbon nanotubes with patterned growth on a silicon wafer with high reproducibility and control.
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2006
Multiwall carbon nanotubes ͑CNTs͒ are synthesized using an atmospheric pressure rf plasma jet, with helium feed gas and acetylene gas as the precursor. The nanotubes are grown on a substrate with a thin catalyst ͑iron͒ film, with the substrate placed downstream from the plasma on a copper hot plate. In situ Fourier transformed infrared spectroscopy indicates an increase in gas temperature and a decrease in the density of the acetylene molecules at higher plasma powers. The helium metastables in the plasma break the C-H bonds in acetylene, causing molecular dissociation. It is apparent that the resultant formation of unsaturated carbon bonds causes taller and more graphitized CNT films to grow, as evident from scanning electron microscopy and Raman analyses of the samples. However, at higher substrate temperatures, taller and better quality films are obtained due to enhanced catalytic activity on the substrate surface.
Plasma Chemistry and Plasma Processing, 2008
A mixture of acetylene, hydrogen and ammonia (C 2 H 2 /H 2 /NH 3 ) is used to produce carbon nanotubes (CNTs) by a plasma-enhanced catalytic chemical vapor deposition process either without (PE CCVD) or with hot filaments-assistance (PE HF CCVD). A mathematical model based on Chemkin computer package is used for analyzing specific conditions of nanotube synthesis. Simulations are compared with optical emission spectroscopy (OES) measurements. Morphological and structural investigations on the grown carbon nanostructures are also performed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was shown that the significant change in the density and the morphology of the CNTs grown in the presence of NH 3 could be mainly explained by the gas phase formation of CN and HCN. Both species display a high etching activity, whereas the species C, CH, CH 2 , CH 2 (S), C 2 and C 2 H are expected to be the most probable carbon nanotube precursors.
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 2 H 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 Ôtube decorationÕ correlates with a decrease in linear growth rate and can be related to the gradient of plasma parameters in the cathode sheath.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2002
Plasma-enhanced chemical vapor deposition ͑PECVD͒ is a versatile technique for growing well-aligned, precisely patterned, multiwalled carbon nanotubes directly on substrates. We report on the characterization of PECVD deposited nanotubes using Auger Electron Spectroscopy ͑AES͒; we believe that this is the first comprehensive AES study of nanotubes and the effect of the deposition process on the substrate. The nanotubes contained well-crystallized graphitic carbon, in contrast to the amorphous/disordered carbon byproduct which is condensed on the substrate surface. By adjusting the deposition gas ratios, we show, using depth-profiled composition analysis, that it is possible to eliminate the unwanted amorphous carbon on the substrate surface. However, a 5 nm interfacial layer, which contained the plasma species, was always present on the substrate surface due to its exposure to the plasma. We could prevent the formation of this interfacial layer by shielding areas of the substrate from the plasma to achieve truly byproduct free deposition. This technique has allowed us to fabricate promising microelectronic field emission devices using vertically aligned carbon nanotubes.