Impact of Thermodiffusion on Carbon Nanotube Growth by Chemical Vapor Deposition

2010 ◽  
Vol 132 (8) ◽  
Author(s):  
Andrew C. Lysaght ◽  
Wilson K. S. Chiu
Keyword(s):  
Chemical Vapor Deposition ◽  
Thermal Diffusion ◽  
Vapor Deposition ◽  
Chemical Vapor ◽  
Scale Model ◽  
Single Wall Carbon Nanotubes ◽  
Heterogeneous Chemical Reaction ◽  
Energy Equations ◽  
The Impact ◽  
Swnt Growth

Thermal diffusion, the process by which a multicomponent mixture develops a concentration gradient when exposed to a temperature gradient, has been studied in order to understand if its inclusion is warranted in the modeling of single-wall carbon nanotubes (SWNTs) synthesis by thermal chemical vapor deposition (CVD). A fully coupled reactor-scale model employing conservation of mass, momentum, species, and energy equations with detailed gas phase and surface reaction mechanisms has been utilized to describe the evolution of hydrogen and hydrocarbon feed streams as they undergo transport, as well as homogeneous and heterogeneous chemical reaction within a CVD reactor. Steady state velocity, temperature, and concentration fields within the reactor volume are determined, as well as concentrations of adsorbed species and SWNT growth rates. The effect of thermodiffusion in differing reactor conditions has been investigated to understand the impact on SWNT growth. Thermal diffusion can have a significant impact on SWNT growth, and the first approximation of the thermal diffusion factor, based on the Chapman–Enskog molecular theory, is sufficient for modeling thermophoretic behavior within a CVD reactor. This effect can be facilitatory or inhibitory, based on the thermal and mass flux conditions. The results of this investigation are useful in order to optimize model and reactor designs to promote optimal SWNT deposition rates.

Impact of Thermophoresis on Carbon Nanotube Growth by Chemical Vapor Deposition

2008 ◽  
Author(s):  
Andrew C. Lysaght ◽  
Wilson K. S. Chiu
Keyword(s):  
Chemical Vapor Deposition ◽  
Vapor Deposition ◽  
Chemical Vapor ◽  
Scale Model ◽  
Reactor Wall ◽  
Flow Conditions ◽  
Energy Equations ◽  
Carbon Nanotube Growth ◽  
Nanotube Growth ◽  
Fully Coupled

Thermophoretic effect on the growth of carbon nanotubes (CNTs) by chemical vapor deposition (CVD) has been investigated using a fully coupled gas-phase and surface chemistry model. This reactor-scale model employs conservation of mass, momentum, species, and energy equations to describe the evolution of hydrogen and hydrocarbon feed streams as they undergo thermal transport and chemical reactions within the CVD reactor. The resulting CNT growth rates on individual catalytic iron nanoparticles located on the reactor wall is predicted by the model as well as steady state velocity, temperature, and concentration fields within the reactor volume and concentrations of species adsorbed onto the nanoparticle surfaces. The effect of thermophoresis on volumetric concentration fields and surface species adsorption for deposition occurring in differing reactor boundary and flow conditions has been investigated to understand the impacts on CNT growth. This investigation is useful in order to optimize reactor design and boundary conditions to promote optimal CNT deposition rates.

Hydrogen Concentration Analysis in Pecvd and Rtcvd Silicon Nitride Thin Films and It's Impact on Device Performance

2001 ◽  
Vol 664 ◽  
Author(s):  
C. Y. Wang ◽  
E. H. Lim ◽  
H. Liu ◽  
J. L. Sudijono ◽  
T. C. Ang ◽  
...  
Keyword(s):  
Chemical Vapor Deposition ◽  
Threshold Voltage ◽  
Vapor Deposition ◽  
Gas Flow ◽  
Chemical Vapor ◽  
Gate Oxide ◽  
Nitride Film ◽  
Device Performance ◽  
Gas Flow Ratio ◽  
The Impact

ABSTRACTIn this paper the impact of the ESL (Etch Stop layer) nitride on the device performance especially the threshold voltage (Vt) has been studied. From SIMS analysis, it is found that different nitride gives different H concentration, [H] in the Gate oxide area, the higher [H] in the nitride film, the higher H in the Gate Oxide area and the lower the threshold voltage. It is also found that using TiSi instead of CoSi can help to stop the H from diffusing into Gate Oxide/channel area, resulting in a smaller threshold voltage drift for the device employed TiSi. Study to control the [H] in the nitride film is also carried out. In this paper, RBS, HFS and FTIR are used to analyze the composition changes of the SiN films prepared using Plasma enhanced Chemical Vapor deposition (PECVD), Rapid Thermal Chemical Vapor Deposition (RTCVD) with different process parameters. Gas flow ratio, RF power and temperature are found to be the key factors that affect the composition and the H concentration in the film. It is found that the nearer the SiN composition to stoichiometric Si3N4, the lower the [H] in SiN film because there is no excess silicon or nitrogen to be bonded with H. However the lowest [H] in the SiN film is limited by temperature. The higher the process temperature the lower the [H] can be obtained in the SiN film and the nearer the composition to stoichiometric Si3N4.

CONTROLLABLE CHEMICAL VAPOR DEPOSITION SYNTHESIS OF SINGLE-WALL CARBON NANOTUBES USING MIST FLOW METHOD

NANO ◽  
2012 ◽  
Vol 07 (06) ◽  
pp. 1250045 ◽  
Author(s):  
YUN SUN ◽  
RYO KITAURA ◽  
TAKUYA NAKAYAMA ◽  
YASUMITSU MIYATA ◽  
HISANORI SHINOHARA
Keyword(s):  
Electron Microscopy ◽  
Carbon Nanotubes ◽  
Chemical Vapor Deposition ◽  
Vapor Deposition ◽  
Chemical Vapor ◽  
Single Wall Carbon Nanotubes ◽  
Flow Method ◽  
Mist Flow ◽  
Mean Diameter ◽  
The Mean

The influences of synthesis parameters on the mean diameter and diameter distribution of as-grown single-wall carbon nanotubes (SWCNTs) with chemical vapor deposition (CVD) using the mist flow method have been investigated in detail with Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). We found that CVD reaction temperature and flow rate play an essential role in controlling the mean diameter and the quality of as-grown SWCNTs. Furthermore, we found that the carbon supply kinetics can be a dominant factor to determine the diameter of as-grown SWCNTs in the present mist flow method. Under a different combination of various parameters, the mean diameter of SWCNTs can be varied from 0.9 nm to 1.5 nm controllably.

Impact of In Situ NH3 pre-treatment of LPCVD SiN passivation on GaN HEMT performance

2022 ◽  
Author(s):  
Ding-Yuan Chen ◽  
Axel R Persson ◽  
Kai Hsin Wen ◽  
Daniel Sommer ◽  
Jan Gruenenpuett ◽  
...  
Keyword(s):  
Chemical Vapor Deposition ◽  
Vapor Deposition ◽  
Chemical Vapor ◽  
Low Pressure ◽  
Untreated Sample ◽  
Pressure Chemical ◽  
Gan Hemts ◽  
Pre Treatment ◽  
The Impact

Abstract The impact on the performance of GaN HEMTs of in situ ammonia (NH3) pre-treatment prior to the deposition of silicon nitride (SiN) passivation with low-pressure chemical vapor deposition is investigated. Three different NH3 pre-treatment durations (0, 3, and 10 minutes) were compared in terms of interface properties and device performance. A reduction of oxygen at the interface between SiN and epi-structure is detected by Scanning Transmission Electron Microscopy-Electron Energy Loss Spectroscopy measurements in the sample subjected to 10 minutes of pre-treatment. The samples subjected to NH3 pre-treatment show a reduced surface-related current dispersion of 9 % (compared to 16% for the untreated sample), which is attributed to the reduction of oxygen at the SiN/epi interface. Furthermore, NH3 pre-treatment for 10 minutes significantly improves the current dispersion uniformity from 14.5 % to 1.9 %. The reduced trapping effects result in a high output power of 3.4 W/mm at 3 GHz (compared to 2.6 W/mm for the untreated sample). These results demonstrate that the in situ NH3 pre-treatment before low-pressure chemical vapor deposition of SiN passivation is critical and can effectively improves the large-signal microwave performance of GaN HEMTs.

Low temperature deposition of 2D WS2 layers from WF6 and H2S precursors: impact of reducing agents

2015 ◽  
Vol 51 (86) ◽  
pp. 15692-15695 ◽  
Author(s):  
A. Delabie ◽  
M. Caymax ◽  
B. Groven ◽  
M. Heyne ◽  
K. Haesevoets ◽  
...  
Keyword(s):  
Chemical Vapor Deposition ◽  
Low Temperature ◽  
Atomic Layer Deposition ◽  
Vapor Deposition ◽  
Chemical Vapor ◽  
Atomic Layer ◽  
Reducing Agents ◽  
Layer Deposition ◽  
Temperature Deposition ◽  
The Impact

We demonstrate the impact of reducing agents for Chemical Vapor Deposition (CVD) and Atomic Layer Deposition (ALD) of WS2 from WF6 and H2S precursors.

scholarly journals Chemical vapor deposition synthesis of near-zigzag single-walled carbon nanotubes with stable tube-catalyst interface

2016 ◽  
Vol 2 (5) ◽  
pp. e1501729 ◽  
Author(s):  
Qiuchen Zhao ◽  
Ziwei Xu ◽  
Yue Hu ◽  
Feng Ding ◽  
Jin Zhang
Keyword(s):  
Chemical Vapor Deposition ◽  
Vapor Deposition ◽  
Chemical Vapor ◽  
Catalyst Design ◽  
Chiral Angle ◽  
Single Walled Carbon ◽  
Cvd Growth ◽  
Elongation Process ◽  
Walled Carbon Nanotubes ◽  
Swnt Growth

Chemical vapor deposition (CVD) growth is regarded as the most promising method for realizing structure-specific single-walled carbon nanotube (SWNT) growth. In the past 20 years, many efforts dedicated to chirality-selective SWNT growth using various strategies have been reported. However, normal CVD growth under constant conditions could not fully optimize the chirality because the randomly formed cap structure allows the nucleation of all types of SWNTs and the chirality of an SWNT is unlikely to be changed during the following elongation process. We report a new CVD process that allows temperature to be periodically changed to vary SWNT chirality multiple times during elongation to build up the energetically preferred SWNT-catalyst interface. With this strategy, SWNTs with small helix angles (less than 10°), which are predicted to have lower interfacial formation energy than others, are enriched up to ~72%. Kinetic analysis of the process suggests a multiple redistribution feature whereby a large chiral angle SWNT tends to reach the near-zigzag chirality step by step with a small chiral angle change at each step, and hence, we named this method “tandem plate CVD.” This method opens a door to synthesizing chirality-selective SWNTs by rational catalyst design.

scholarly journals Single wall carbon nanotubes growth over cobalt-iron mesoporous MCM-41 bimetallic catalyst under methane chemical vapor deposition, an experimental and DFT evaluation

2020 ◽  
Vol 25 (2) ◽  
pp. 227-246
Author(s):  
Frank Ramírez-Rodríguez ◽  
Betty López
Keyword(s):  
Activation Energy ◽  
Carbon Nanotubes ◽  
Chemical Vapor Deposition ◽  
Vapor Deposition ◽  
Density Functional ◽  
Chemical Vapor ◽  
Photon Absorption ◽  
Single Wall Carbon Nanotubes ◽  
Single Wall Carbon ◽  
Mcm 41

Cobalt and iron MCM-41 catalysts were synthesized through an in-situ incorporation process starting from commercial iron and cobalt nitrates. The incorporation was confirmed by diffuse reflectance UV spectroscopy (DRS-UV) inspecting the cobalt and iron silicate-like photon absorption features and comparing with pure MCM-41-Co and MCM-41-Fe catalysts. Additionally it was found that the incorporation of cobalt and iron does not compromise the mesoporous structure of MCM-41 as confirmed by N2 adsorption isotherms. All catalysts showed high surface areas (∼1100 m2g−1). Catalysts performance was conducted in a simple methane chemical vapor deposition (CVD) set up at 800 °C to produce single wall carbon nanotubes (SWCNT) under a constant flow of methane for 30 min. CVD products were characterized by thermogravimetric analysis (TGA) and Raman spectroscopy, finding that the iron content in the catalysts favors the selectivity and yield of graphitic-like structures, and confirming the presence of SWCNT by the appearance of a characteristic radial breathing mode (RBM) signals. These results were supported by Density Functional Theory (DFT) simulations of the methane dissociation (CH4 +TM → H3C –TMH) over Con (n = 1–5) and ComFe (m = 1–4), finding a different activation energy trend where ComFe (m = 1–4) clusters have the lower activation energy. The DFT study also revealed a charge difference (δC − δTM) higher in the case of dissociation over ComFe (m = 1–4) which may lead to an electrostatic stabilization of the transition metal, diminishing the activation energy of those clusters and leading to a faster carbon uptake.

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