The Effect of Buffer Layer on CNT Structure and CNT/Copper Interfacial Properties

MRS Advances ◽  
2016 ◽  
Vol 1 (20) ◽  
pp. 1447-1452
Author(s):  
Qiuhong Zhang ◽  
Levi Elston ◽  
James Scofield ◽  
Joseph Merrett ◽  
William Lanter ◽  
...  
Keyword(s):  
Carbon Nanotubes ◽  
Buffer Layer ◽  
Substrate Surface ◽  
High Surface ◽  
Interfacial Properties ◽  
Layer Growth ◽  
Buffer Layers ◽  
Mechanical And Thermal Properties ◽  
Cu Substrate ◽  
Cu Substrates

ABSTRACTCarbon nanotubes (CNTs), with exceptional thermal and mechanical properties as well as inherently high surface area, are an attractive candidate for integrating into thermal structures of advanced power electronics. Growth of vertically aligned carbon nanotubes (VACNTs) directly onto copper (Cu) substrates is a promising approach to apply CNTs as novel thermal interface materials (TIMs) in electronics packaging. However, compared to growing CNTs on conventional inert substrates such as SiO2, direct growth of controllable CNT arrays onto Cu substrates is significantly more challenging due to the diffusion of metallic catalyst into the substrate during growth. By depositing an appropriate buffer layer on the Cu substrate surface, VACNTs of good alignment and high quality were reproducibly synthesized on the Cu substrate via the chemical vapor deposition (CVD) method in this study. The effect of different buffer layers on the CNT growth, nanotube structure and quality was investigated (SEM, Raman), particularly in terms of the interfacial properties between the CNT array and Cu substrate (Tensile compression force tester, Laser Flash Analysis). Our experimental results indicated that the buffer layer material, deposition method, and thickness play a key role in regulating the CNT layer growth/structure, leading to variable mechanical and thermal properties. The fundamental understanding thus obtained allows the successful synthesis of VACNT on copper substrates with desired structure and properties.

Epitaxial GaN Layer Growth Using Nitrogen Enriched TiN Buffer Layers

2006 ◽  
Vol 916 ◽  
Author(s):  
Kazuhiro Ito ◽  
Yu Uchida ◽  
Sang-jin Lee ◽  
Susumu Tsukimoto ◽  
Yuhei Ikemoto ◽  
...  
Keyword(s):  
Buffer Layer ◽  
Light Emission ◽  
Chemical Vapor ◽  
Nucleation Site ◽  
Layer Growth ◽  
Buffer Layers ◽  
Organic Chemical ◽  
Nitrogen Enrichment ◽  
Threading Dislocation ◽  
Sapphire Substrates

AbstractAbout 20 years ago, the discovery of an AlN buffer layer lead to the breakthrough in epitaxial growth of GaN layers with mirror-like surface, using a metal organic chemical vapor deposition (MOCVD) technique on sapphire substrates. Since then, extensive efforts have been continued to develop a conductive buffer layer/substrate for MOCVD-grown GaN layers to improve light emission of GaN light-emitting diodes. In the present study, we produced MOCVD-grown, continuous, flat epitaxial GaN layers on nitrogen enriched TiN buffer layers with the upper limit of the nitrogen content of TiN deposited at room temperature (RT) on sapphire substrates. It was concluded that the nitrogen enrichment would reduce significantly the TiN/GaN interfacial energy. The RT deposition of the TiN buffer layers suppresses their grain growth during the nitrogen enrichment and the grain size refining must increase nucleation site of GaN. In addition, threading dislocation density in the GaN layers grown on TiN was much lower than that in the GaN layers grown on AlN.

scholarly journals Effect of Buffer Layer and III/V Ratio on the Surface Morphology of Gan Grown by MBE

1999 ◽  
Vol 4 (S1) ◽  
pp. 417-422 ◽  
Author(s):  
E. C. Piquette ◽  
P. M. Bridger ◽  
R. A. Beach ◽  
T. C. McGill
Keyword(s):  
Surface Morphology ◽  
Buffer Layer ◽  
Flux Ratio ◽  
Plasma Source ◽  
Growth Conditions ◽  
Nitrogen Plasma ◽  
Layer Growth ◽  
Buffer Layers ◽  
Flat Surfaces ◽  
Aln Buffer

The surface morphology of GaN is observed by atomic force microscopy for growth on GaN and AlN buffer layers and as a function of III/V flux ratio. Films are grown on sapphire substrates by molecular beam epitaxy using a radio frequency nitrogen plasma source. Growth using GaN buffer layers leads to N-polar films, with surfaces strongly dependent on the flux conditions used. Flat surfaces can be obtained by growing as Ga-rich as possible, although Ga droplets tend to form. Ga-polar films can be grown on AlN buffer layers, with the surface morphology determined by the conditions of buffer layer deposition as well as the III/V ratio for growth of the GaN layer. Near-stoichiometric buffer layer growth conditions appear to support the flattest surfaces in this case. Three defect types are typically observed in GaN films on AlN buffers, including large and small pits and “loop” defects. It is possible to produce surfaces free from large pit defects by growing thicker films under more Ga-rich conditions. In such cases the surface roughness can be reduced to less than 1 nm RMS.

scholarly journals Basic Potential of Carbon Nanotubes in Tissue Engineering Applications

2012 ◽  
Vol 2012 ◽  
pp. 1-10 ◽  
Author(s):  
Hisao Haniu ◽  
Naoto Saito ◽  
Yoshikazu Matsuda ◽  
Tamotsu Tsukahara ◽  
Yuki Usui ◽  
...  
Keyword(s):  
Carbon Nanotubes ◽  
Tissue Engineering ◽  
High Surface ◽  
High Surface Area ◽  
Volume Ratio ◽  
Medical Application ◽  
Mechanical And Thermal Properties ◽  
Biological Responses

Carbon nanotubes (CNTs) are attracting interest in various fields of science because they possess a high surface area-to-volume ratio and excellent electronic, mechanical, and thermal properties. Various medical applications of CNTs are expected, and the properties of CNTs have been greatly improved for use in biomaterials. However, the safety of CNTs remains unclear, which impedes their medical application. Our group is evaluating the biological responses of multiwall CNTs (MWCNTs)in vivoandin vitrofor the promotion of tissue regeneration as safe scaffold materials. We recently showed that intracellular accumulation is important for the cytotoxicity of CNTs, and we reported the active physiological functions CNTs in cells. In this review, we describe the effects of CNTsin vivoandin vitroobserved by our group from the standpoint of tissue engineering, and we introduce the findings of other research groups.

Annihilation of Threading Dislocations in Regrown GaN on Electrochemically Etched Nanoporous GaN Template with Optimization of Buffer Layer Growth

2007 ◽  
Vol 31 ◽  
pp. 227-229
Author(s):  
C.B. Soh ◽  
H. Hartono ◽  
S.Y. Chow ◽  
Soo Jin Chua
Keyword(s):  
Electron Microscopy ◽  
Buffer Layer ◽  
Electrochemical Etching ◽  
Layer Growth ◽  
Device Fabrication ◽  
Buffer Layers ◽  
Threading Dislocations ◽  
High Quality ◽  
Transmission Electron ◽  
Gan Buffer Layer

Nanoporous GaN template has been fabricated by electrochemical etching to give hexagonal pits with nano-scale pores of size 20-50 nm in the underlying grains. Electrochemical etching at The effect of GaN buffer layer grown at various temperatures from 650°C to 1015°C on these as-fabricated nano-pores templates are investigated by transmission electron microscopy. The buffer layer grown at the optimized temperature of 850°C partially fill up the pores and voids with annihilation of threading dislocations, serving as an excellent template for high-quality GaN growth. This phenomenon is, however not observed for the samples grown with other temperature buffer layers. The PL spectrum for the regrowth GaN on nanoporous GaN template also shows an enhancement of PL intensity for GaN peak compared to as-grown GaN template, which is indicative of its higher crystal quality. This makes it as a suitable template for subsequent device fabrication.

scholarly journals Effect of Buffer Layer and III/V Ratio on the Surface Morphology of Gan Grown by MBE

1998 ◽  
Vol 537 ◽  
Author(s):  
E. C. Piquette ◽  
P. M. Bridger ◽  
R. A. Beach ◽  
T. C. McGill
Keyword(s):  
Surface Morphology ◽  
Buffer Layer ◽  
Flux Ratio ◽  
Plasma Source ◽  
Growth Conditions ◽  
Nitrogen Plasma ◽  
Layer Growth ◽  
Buffer Layers ◽  
Flat Surfaces ◽  
Aln Buffer

AbstractThe surface morphology of GaN is observed by atomic force microscopy for growth on GaN and AlN buffer layers and as a function of III/V flux ratio. Films are grown on sapphire substrates by molecular beam epitaxy using a radio frequency nitrogen plasma source. Growth using GaN buffer layers leads to N-polar films, with surfaces strongly dependent on the flux conditions used. Flat surfaces can be obtained by growing as Ga-rich as possible, although Ga droplets tend to form. Ga-polar films can be grown on AlN buffer layers, with the surface morphology determined by the conditions of buffer layer deposition as well as the III/V ratio for growth of the GaN layer. Near-stoichiometric buffer layer growth conditions appear to support the flattest surfaces in this case. Three defect types are typically observed in GaN films on AlN buffers, including large and small pits and “loop” defects. It is possible to produce surfaces free from large pit defects by growing thicker films under more Ga-rich conditions. In such cases the surface roughness can be reduced to less than l nm RMS.

Fabrication and Properties of Epitaxial Buffer Layers on Nonmagnetic Textured Ni Based Alloy Substrates

1999 ◽  
Vol 13 (09n10) ◽  
pp. 1029-1034 ◽  
Author(s):  
G. Celentano ◽  
V. Boffa ◽  
L. Ciontea ◽  
F. Fabbri ◽  
V. Galluzzi ◽  
...  
Keyword(s):  
Buffer Layer ◽  
Ybco Film ◽  
Lattice Mismatch ◽  
Substrate Surface ◽  
Liquid Nitrogen Temperature ◽  
Metallic Substrate ◽  
Buffer Layers ◽  
X Ray Diffraction ◽  
Metallic Substrates ◽  
Layer Deposition

Biaxially aligned YBCO thick films on oxide buffered metallic substrates is a promising route toward the fabrication of superconducting tapes operating at liquid nitrogen temperature. The role of buffer layer is to reduce the lattice mismatch between the substrate and the YBCO film, to adapt the thermal expansion coefficient, to hamper the diffusion of Ni in YBCO film and to prevent the oxidation of the metallic substrate surface. This paper presents a study regarding CeO 2 buffer layer deposition on a new nonmagnetic (001)[100] textured Ni-V alloy substrates. The deposition of CeO 2 was performed by both pulsed laser ablation and e-beam evaporation techniques. The θ-2θ X-ray diffraction pattern mainly exhibits the (00l) peaks of CeO 2, indicating that the films are epitaxially grown with the c axis perpendicular to the substrate. Rocking curved through the CeO 2 (002) peak have a FWHM of about 6°. The SEM studies have shown that the surface is smooth, continuos and free of cracks. Texture analysis reveals a good in-plane orientation for the ablated CeO 2 film, whereas the electron beam evaporated CeO 2 shows two textures in the growth plane. Further efforts are focused on the deposition of YBCO thick film on the as buffered nonmagnetic metallic substrate.

Tem Investigation of Al0.5Ga0.5As1-y Sby Buffer Layer Systems

1997 ◽  
Vol 484 ◽  
Author(s):  
E. Chen ◽  
J. S. Ahearn ◽  
K. Nichols ◽  
P. Uppal ◽  
D. C. Paine
Keyword(s):  
Buffer Layer ◽  
Active Regions ◽  
Dark Field ◽  
Layer Growth ◽  
Buffer Layers ◽  
Growth Surface ◽  
Threading Dislocation ◽  
Misfit Dislocations ◽  
Plan View ◽  
Dark Field Imaging

AbstractWe report on a TEM study of Sb-adjusted quaternary Al0.5Ga0.5As1-y Sby buffer-layers grown on <001> GaAs substrates. A series of structures were grown by MBE at 470°C that utilize a multilayer grading scheme in which the Sb content of Al0.5Ga0.5As1-ySby is successively increased in a series of eight 125 nm thick layers. Post growth analysis using conventional bright field and weak beam dark field imaging of these buffer layers in cross-section reveals that the interface misfit dislocations are primarily of the 60° type and are distributed through out the interfaces of the buffer layer. Plan view studies show that the threading dislocation density in the active regions of the structure (approximately 2 μm from the GaAs substrate) is 105–6/cm2 which is comparable to equivalent InxGa1−x As buffers. Weak Sb-As compositional modulations with a period of 1.8 nm were observed that provide a marker for establishing the planarity of the growth process. These features reveal that the growth surface remains planar through out the buffer layer growth sequence.

Effect of Aluminum Nitride Buffer Layer Temperature on Gallium Nitride Grown by OMVPE

1994 ◽  
Vol 339 ◽  
Author(s):  
L. B. Rowland ◽  
K. Doverspike ◽  
D. K. Gaskill ◽  
J. A. Freitas
Keyword(s):  
Gallium Nitride ◽  
Buffer Layer ◽  
Growth Temperature ◽  
Growth Conditions ◽  
Layer Growth ◽  
Buffer Layers ◽  
Double Crystal ◽  
Relative Crystallinity ◽  
Excitonic Emission ◽  
Aln Buffer

ABSTRACTGallium nitride layers were grown by organometallic vapor phase epitaxy on AlN buffer layers deposited in the range of 450–650°C. The GaN growth conditions were kept constant so that changes in film properties were due only to changes in the buffer layer growth temperature. A monotonie improvement in relative crystallinity as measured by double-crystal X-ray diffraction corresponded with a decrease in buffer layer growth temperature. Improvements in GaN electron transport at 300 and 77 K were also observed with decreasing AlN buffer layer temperature. Photoluminescence spectra for the lowest temperatures studied were dominated by sharp excitonic emission, with some broadening of the exciton linewidth observed as the buffer layer growth temperature was increased. The full width at half maximum of the excitonic emission was 2.7 meV for GaN grown on a 450°C buffer layer. These results indicate that minimizing AlN buffer layer temperature results in improvements in GaN film quality.

Optimisation Of The Heteroepitaxy Of Ge On GaAs For Minority-Carrier Lifetime

1990 ◽  
Vol 198 ◽  
Author(s):  
R. Venkatasubramanian ◽  
M.L. Timmons ◽  
S. Bothra ◽  
J.M. Borrego
Keyword(s):  
High Temperature ◽  
Buffer Layer ◽  
Gaas Substrate ◽  
Carrier Lifetime ◽  
Minority Carrier ◽  
High Growth ◽  
Minority Carrier Lifetime ◽  
Layer Growth ◽  
Buffer Layers ◽  
Temperature Growth

ABSTRACTGrowth of Ge on GaAs at reasonably high temperatures, which produce better crystallinity in the Ge, presents serious difficulties due to the dissociation of the GaAs substrate. In this paper, we describe the growth of a lowtemperature buffer layer of Ge on GaAs that prevents decomposition of the GaAs during high-temperature growth of Ge. Using this approach, we present the first report of highly specular, mass-transport-limited high-temperature growth of Ge on GaAs that is comparable to the homoepitaxy of Ge. The factors affecting the minority-carrier lifetime of Ge on GaAs, using such an epitaxial growth technique, were studied with a non-invasive microwave technique. Lifetime variations, from very low values to about 0.45 μsec, were obtained as a function of the growth conditions. Significantly, the removal of the surface oxide on the GaAs substrate prior to low-temperature buffer-layer growth, terminating the flow of germane(GeH4) during the ramp to high growth temperatures, thinner buffer layers, and high-temperature growth of Ge were found to be important for obtaining long lifetimes.

A Study of the Effect of Growth Rate and Annealing on GaN Buffer Layers on Sapphire

1995 ◽  
Vol 395 ◽  
Author(s):  
J.C. Ramer ◽  
K. Zheng ◽  
C.F. Kranenberg ◽  
M. Banas ◽  
S.D Hersee
Keyword(s):  
Growth Rate ◽  
Buffer Layer ◽  
Layer Growth ◽  
Buffer Layers ◽  
Degree Of Crystallinity ◽  
X Ray Diffraction ◽  
X Ray ◽  
Force Microscopy ◽  
Atomic Force ◽  
Gan Buffer Layer

ABSTRACTUsing atomic force microscopy (AFM) and X-ray diffraction (XRD) we have determined that on [0001] oriented sapphire, the GaN buffer layer shows a degree of crystallinity that is dependent on growth rate. Annealing studies show evolution of the crystallinity and the emergence of a preferred orientation. Also, substrate orientation is found to influence the buffer layer crystallinity. Based on this work and previous results, we propose that the GaN buffer layer growth can be described by the Stranski-Krastanov growth process.

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