scholarly journals Prediction and Measurement of Thermal Transport Across Interfaces Between Isotropic Solids and Graphitic Materials

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
Pamela M. Norris ◽  
Justin L. Smoyer ◽  
John C. Duda ◽  
Patrick E. Hopkins
Keyword(s):  
Thermal Transport ◽  
Substrate Surface ◽  
Unit Length ◽  
Thermal Conductance ◽  
Thin Film Deposition ◽  
Film Deposition ◽  
Transport Models ◽  
Composite Systems ◽  
Graphene Flakes ◽  
Isotropic Solids

Due to the high intrinsic thermal conductivity of carbon allotropes, there have been many attempts to incorporate such structures into existing thermal abatement technologies. In particular, carbon nanotubes (CNTs) and graphitic materials (i.e., graphite and graphene flakes or stacks) have garnered much interest due to the combination of both their thermal and mechanical properties. However, the introduction of these carbon-based nanostructures into thermal abatement technologies greatly increases the number of interfaces per unit length within the resulting composite systems. Consequently, thermal transport in these systems is governed as much by the interfaces between the constituent materials as it is by the materials themselves. This paper reports the behavior of phononic thermal transport across interfaces between isotropic thin films and graphite substrates. Elastic and inelastic diffusive transport models are formulated to aid in the prediction of conductance at a metal-graphite interface. The temperature dependence of the thermal conductance at Au-graphite interfaces is measured via transient thermoreflectance from 78 to 400 K. It is found that different substrate surface preparations prior to thin film deposition have a significant effect on the conductance of the interface between film and substrate.

scholarly journals Prediction and Measurement of Thermal Transport Across Interfaces Between Isotropic Solids and Graphitic Materials

2010 ◽  
Author(s):  
Pamela M. Norris ◽  
Justin L. Smoyer ◽  
John C. Duda ◽  
Patrick E. Hopkins
Keyword(s):  
Thermal Transport ◽  
Substrate Surface ◽  
Unit Length ◽  
Thermal Conductance ◽  
Thin Film Deposition ◽  
Film Deposition ◽  
Transport Models ◽  
Composite Systems ◽  
Graphene Flakes ◽  
Isotropic Solids

Due to the high intrinsic thermal conductivity of carbon allotropes, there have been many attempts to incorporate such structures into existing thermal abatement technologies. In particular, carbon nanotubes (CNTs) and graphitic materials (i.e., graphite and graphene flakes or stacks) have garnered much interest due to the combination of both their thermal and mechanical properties. However, the introduction of these carbon-based nanostructures into thermal abatement technologies greatly increases the number of interfaces per unit length within the resulting composite systems. Consequently, thermal transport in these systems is governed as much by the interfaces between the constituent materials as it is by the materials themselves. This paper reports the behavior of phononic thermal transport across interfaces between isotropic thin films and graphite substrates. Elastic and inelastic diffusive transport models are formulated to aid in the prediction of conductance at a metal-graphite interface. The temperature dependence of the thermal conductance at Au-graphite interfaces is measured via transient thermoreflectance from 78 to 400 K. It is found that different substrate surface preparations prior to thin film deposition have a significant effect on the conductance of the interface between film and substrate.

Observations on the growth of YBa2Cu3O7-δ thin films on MgO by pulsed-laser ablation

1991 ◽  
Vol 49 ◽  
pp. 1068-1069
Author(s):  
M. Grant Norton ◽  
C. Barry Carter
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Laser Ablation ◽  
Substrate Surface ◽  
Pulsed Laser ◽  
Pulsed Laser Ablation ◽  
Thin Film Deposition ◽  
Film Deposition ◽  
Laser Ablation Process ◽  
Deposition Parameters

Pulsed-laser ablation has been widely used to produce high-quality thin films of YBa2Cu3O7-δ on a range of substrate materials. The nonequilibrium nature of the process allows congruent deposition of oxides with complex stoichiometrics. In the high power density regime produced by the UV excimer lasers the ablated species includes a mixture of neutral atoms, molecules and ions. All these species play an important role in thin-film deposition. However, changes in the deposition parameters have been shown to affect the microstructure of thin YBa2Cu3O7-δ films. The formation of metastable configurations is possible because at the low substrate temperatures used, only shortrange rearrangement on the substrate surface can occur. The parameters associated directly with the laser ablation process, those determining the nature of the process, e g. thermal or nonthermal volatilization, have been classified as ‘primary parameters'. Other parameters may also affect the microstructure of the thin film. In this paper, the effects of these ‘secondary parameters' on the microstructure of YBa2Cu3O7-δ films will be discussed. Examples of 'secondary parameters' include the substrate temperature and the oxygen partial pressure during deposition.

Fabrication of Periodic Arrays of Nanoscale Square Helices

2002 ◽  
Vol 728 ◽  
Author(s):  
Martin O. Jensen ◽  
Scott R. Kennedy ◽  
Michael J. Brett
Keyword(s):  
Photonic Band Gap ◽  
Substrate Surface ◽  
Three Dimensional ◽  
Thin Film Deposition ◽  
Film Deposition ◽  
Inorganic Materials ◽  
Periodic Arrays ◽  
Wide Range ◽  
Potential Applications ◽  
Third Dimension

AbstractWe demonstrate fabrication of periodic arrays of nanometre scale square helices, with potential applications in three-dimensional photonic bandgap (PBG) materials. Processing is performed using a thin film deposition method known as Glancing Angle Deposition (GLAD). Through advanced substrate motion, this technique allows for controlled growth of square helices in a variety of inorganic materials. Organization of the helices into periodic twodimensional geometries is achieved by prepatterning the substrate surface using electron beam lithography. The regular turns of the helices yield periodicity in the third dimension, perpendicular to the substrate. We present studies of tetragonal and trigonal arrays of silicon helices, with lattice constants as low as 300 nm. By deliberately adding or leaving out seeds in the substrate pattern, we have succeeded in engineering line defects. Our periodic nanoscale structure closely matches an ideal photonic band gap architecture, as recently proposed by Toader and John. While our fabrication technique is simpler than most suggested PBG schemes, it is highly versatile. A wide range of materials can be used for GLAD, manipulation of lattice constant and helix pitch ensures optical tunability, and the GLAD films are robust to micromachining.

The Plasma Deposition of Semiconductor Multilater Structures

1989 ◽  
Vol 165 ◽  
Author(s):  
Masataka Hirose ◽  
Seiichi Miyazaki
Keyword(s):  
Thin Film ◽  
Silicon Nitride ◽  
Amorphous Silicon ◽  
Plasma Deposition ◽  
Substrate Surface ◽  
Thin Film Deposition ◽  
Film Deposition ◽  
Atomic Scale ◽  
Layer By Layer ◽  
X Ray

AbstractThe early stages of thin film deposition from the rf glow discharge of SiH4 or SiH4 + NH3 have been studied by analysing the structure of silicon based multiiayers consisting of hydrogenated amorphous silicon (a-Si:H, 10 – 200 A thick) and stoichiometric silicon nitride (a-Si3N4:H, 25 – 250 A) alternating layers. The x-ray diffraction, its rocking curve and x-ray interference of the multilayers have shown that the amorphous silicon/silicon nitride interface is atomically abrupt and the surfaces of the respective layers are atomically flat regardless of substrate materials. This indicates that the precursors impinging onto a substrate from the gas phase homogeneously cover the growing surface and the layer by layer growth proceeds on atomic scale. In the plasma deposition of the covalently bonded semiconductors and insulators, the island formation on a substrate surface at the beginning of the thin film growth is very unlikely.

Laser-Reflectance Interferometry Measurements of Diamond-Film Growth

MRS Bulletin ◽  
1995 ◽  
Vol 20 (5) ◽  
pp. 29-31 ◽  
Author(s):  
Christopher D. Zuiker ◽  
Dieter M. Gruen ◽  
Alan R. Krauss
Keyword(s):  
Film Thickness ◽  
Film Growth ◽  
Substrate Surface ◽  
Diamond Films ◽  
Thin Film Deposition ◽  
Film Deposition ◽  
Index Of Refraction ◽  
Ex Situ ◽  
Laser Reflectance

The remarkable properties of diamond, including its hardness, chemical inertness, high thermal conductivity, low coefficient of friction, optical transparency, and semiconducting properties, have led to considerable research in the area of diamond thin-film deposition. Diamond films have been characterized ex situ by a large number of diagnostic techniques including Raman spectroscopy, x-ray diffraction, SEM, and TEM. In situ diagnostics, which can provide information in real time as the film is growing, are less common.Laser-reflectance interferometry (LRI) has been used to monitor the growth of diamond films in situ. The technique involves measuring the intensity of a laser beam reflected from the substrate surface on which the film is growing. The reflected beam is the sum of beams reflected by the gas-diamond interface and the diamond-silicon interface. Oscillations in the reflectivity are observed as the film grows because of interference between the reflected beams. Each oscillation indicates an increase in film thickness of λ/2n, where λ is the laser wavelength and n is the index of refraction of the film. If the index of refraction of the film is known, the thickness and growth rate can be determined in situ. For LRI measurements with 632.8-nm-wavelength HeNe lasers, the index of refraction of diamond films has been found to be within 10% of the bulk diamond value of 2.4. Each oscillation therefore indicates an increase in film thickness of 0.13 μm.The reflectivity measured by LRI is also affected by scattering because of surface roughness.

Thin film deposition and interface characterization of YBCO on LiNbO3 substrates

1995 ◽  
Vol 10 (12) ◽  
pp. 3009-3015 ◽  
Author(s):  
N.J. Wu ◽  
X.Y. Li ◽  
J. Li ◽  
H. Lin ◽  
H. Fredricksen ◽  
...  
Keyword(s):  
Thin Films ◽  
Photoelectron Spectroscopy ◽  
Substrate Surface ◽  
Thin Film Deposition ◽  
Film Deposition ◽  
Growth Surface ◽  
Force Microscopy ◽  
Atomic Force ◽  
Saw Devices ◽  
High Transition

High transition temperature superconducting YBa2Cu3O7−x (YBCO) thin films have been epitaxially grown on YZ-cut LiNbO3 (LNO) substrates by the pulsed laser deposition technique. The interface between YBCO and LNO has been systematically investigated by scanning electron microscopy, atomic force microscopy, Auger electron spectroscopy, and x-ray photoelectron spectroscopy. Off-stoichiometry LiNbOx phases are found to segregate on the substrate surface because of lithium and oxygen vacancies formed during the high temperature YBCO growth. These submicrometer particles are observed along the Z-axis on the X-Z plane of LNO with height of ∼30 nm above the LNO surface. This rough growth surface results in YBa2Cu3O7−x thin films grown on the LNO surface that have reduced Jc and Tc, possibly limiting the use of YBCO/LNO heterostructures for surface acoustic wave (SAW) devices.

Defect Analysis In Substrate Materials for High Tc Superconducting Thin Films

1994 ◽  
Vol 341 ◽  
Author(s):  
P. R. Fletcher ◽  
C. Leach ◽  
F. Wellhofer ◽  
P. Woodall
Keyword(s):  
Thin Films ◽  
Substrate Surface ◽  
Film Surface ◽  
Thin Film Deposition ◽  
Film Deposition ◽  
High Tc ◽  
Chemically Induced ◽  
Preparation Route ◽  
Induced Defects ◽  
Mgo Substrate

AbstractMany defects in high Tc superconducting films propagate from the substrate through to the film surface, disturbing the epitaxy at the interface and adversely affecting the physical properties of the film, particularly Jc. In this study the surface of Magnesium Oxide (100) single crystal substrates with different preparative treatments have been investigated using optical cathodoluminescence microscopy (CL), with a view to establishing its effect on the deposition of thin films of YBa2Cu3O7-δ superconductors.CL excitations due to mechanically and chemically induced defects in the MgO substrate crystals are observed by optical CL microscopy. Several pre-deposition treatments have been compared in this way to determine the best preparation route for the substrates. Jc measurements indicate that the substrate surface quality is an important parameter in the production of high quality thin films especially for the fabrication of devices.It is concluded that CL provides a powerful and rapid tool for MgO quality assessment before thin film deposition.

Impact of Contact Resistances on Electrical and Thermal Transport in Carbon Nanotube Network Transistors

2012 ◽  
Author(s):  
Man Prakash Gupta ◽  
David Estrada ◽  
Eric Pop ◽  
Satish Kumar
Keyword(s):  
Carbon Nanotube ◽  
Thermal Transport ◽  
Peak Power ◽  
Thermal Environment ◽  
Unit Length ◽  
Thermal Conductance ◽  
Network Density ◽  
Numerical Predictions ◽  
Breakdown Mechanism ◽  
Carbon Nanotube Network

The breakdown mechanism of carbon nanotube (CNT) networks is explored using a coupled electro-thermal model, which simulates both electrical and thermal transport in CNT network thin film transistors (CN-TFTs). The numerical results are validated against experimental observations on CN-TFTs with similar device geometry, network statistics, and thermal environment. We find the numerical predictions are in good agreement with experimental measurements of power and temperature of CN-TFT devices. Comparing the simulation results with experiments, we observe that the CNT-substrate thermal conductance per unit length is ∼0.1 Wm−1 K−1. This value represents high contact thermal resistance, but is very close to experimental estimations. The thermal profile and breakdown behavior of the CNT network is observed to be more sensitive to CNT-substrate interfacial thermal conductance compared to that of the CNT-CNT interface. The effect of CNT network density on breakdown behavior is also analyzed for relatively low densities of the network. The peak power dissipation in CN-TFTs before breakdown increases with network density, and this peak power is reached at the same source-to-drain bias (VSD) for all considered densities. The breakdown patterns in CN-TFTs of all considered densities are also observed to have similar characteristics.

Substrate surface effect on the laser-induced plasma characteristics for thin film deposition

1993 ◽  
Vol 1 (10-12) ◽  
pp. 1995-2003 ◽  
Author(s):  
M.R. Predtechensky ◽  
A.V. Bulgakov ◽  
A.P. Mayorov ◽  
A.V. Roshchin
Keyword(s):  
Thin Film ◽  
Surface Effect ◽  
Substrate Surface ◽  
Thin Film Deposition ◽  
Film Deposition ◽  
Laser Induced Plasma ◽  
Plasma Characteristics
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