Science Current Events | Science News |

Nanotube forests grown on silicon chips for future computers, electronics

October 02, 2007
Engineers have shown how to grow forests of tiny cylinders called carbon nanotubes onto the surfaces of computer chips to enhance the flow of heat at a critical point where the chips connect to cooling devices called heat sinks.

The carpetlike growth of nanotubes has been shown to outperform conventional "thermal interface materials." Like those materials, the nanotube layer does not require elaborate clean-room environments, representing a possible low-cost manufacturing approach to keep future chips from overheating and reduce the size of cooling systems, said Placidus B. Amama, a postdoctoral research associate at the Birck Nanotechnology Center in Purdue's Discovery Park.

Researchers are trying to develop new types of thermal interface materials that conduct heat more efficiently than conventional materials, improving overall performance and helping to meet cooling needs of future chips that will produce more heat than current microprocessors. The materials, which are sandwiched between silicon chips and the metal heat sinks, fill gaps and irregularities between the chip and metal surfaces to enhance heat flow between the two.

The method developed by the Purdue researchers enables them to create a nanotube interface that conforms to a heat sink's uneven surface, conducting heat with less resistance than comparable interface materials currently in use by industry, said doctoral student Baratunde A. Cola.

Findings were detailed in a research paper that appeared in September's issue of the journal Nanotechnology. The paper was written by Amama; Cola; Timothy D. Sands, director of the Birck Nanotechnology Center and the Basil S. Turner Professor of Materials Engineering and Electrical and Computer Engineering; and Xianfan Xu and Timothy S. Fisher, both professors of mechanical engineering.

Better thermal interface materials are needed either to test computer chips in manufacturing or to keep chips cooler during operation in commercial products.

"In a personal computer, laptop and portable electronics, the better your thermal interface material, the smaller the heat sink and overall chip-cooling systems have to be," Cola said.

Heat sinks are structures that usually contain an array of fins to increase surface contact with the air and improve heat dissipation, and a fan often also is used to blow air over the devices to cool chips.

Conventional thermal interface materials include greases, waxes and a foil made of a metal called indium. All of these materials, however, have drawbacks. The greases don't last many cycles of repeatedly testing chips on the assembly line. The indium foil doesn't make good enough contact for optimum heat transfer, Fisher said.

The Purdue researchers created templates from branching molecules called dendrimers, forming these templates on a silicon surface. Then, metal catalyst particles that are needed to grow the nanotubes were deposited inside cavities between the dendrimer branches. Heat was then applied to the silicon chip, burning away the polymer and leaving behind only the metal catalyst particles.

The engineers then placed the catalyst particle-laden silicon inside a chamber and exposed it to methane gas. Microwave energy was applied to break down the methane, which contains carbon. The catalyst particles prompted the nanotubes to assemble from carbon originating in the methane, and the tubes then grew vertically from the surface of the silicon chip.

"The dendrimer is a vehicle to deliver the cargo of catalyst particles, making it possible for us to seed the carbon nanotube growth right on the substrate," Amama said. "We are able to control the particle size - what ultimately determines the diameters of the tubes - and we also have control over the density, or the thickness of this forest of nanotubes. The density, quality and diameter are key parameters in controlling the heat-transfer properties."

The catalyst particles are made of "transition metals," such as iron, cobalt, nickel or palladium. Because the catalyst particles are about 10 nanometers in diameter, they allow the formation of tubes of similar diameter.

The branching dendrites are tipped with molecules called amines, which act as handles to stick to the silicon surface.

"This is important because for heat-transfer applications, you want the nanotubes to be well-anchored," Amama said.

Researchers usually produce carbon nanotubes separately and then attach them to the silicon chips or mix them with a polymer and then apply them as a paste.

"Our direct growth approach, however, addresses the critical heat-flow path, which is between the chip surface and the nanotubes themselves," Fisher said. "Without this direct connection, the thermal performance suffers greatly."

Because the dendrimers have a uniform composition and structure, the researchers were able to control the distribution and density of catalyst particles.

The research team also has been able to control the number of "defect sites" in the lattice of carbon atoms making up the tubes, creating tubes that are more flexible. This increased flexibility causes the nanotube forests to conform to the surface of the heat sink, making for better contact and improved heat conduction.

"The tubes bend like toothbrush bristles, and they stick into the gaps and make a lot of real contact," Cola said.

The carbon nanotubes were grown using a technique called microwave plasma chemical vapor deposition, a relatively inexpensive method for manufacturing a thermal-interface material made of carbon nanotubes, Fisher said.

"The plasma deposition approach allows us great flexibility in controlling the growth environment and has enabled us to grow carbon nanotube arrays over a broad range of substrate temperatures," Fisher said.

The research has been funded by NASA through the Institute for Nanoelectronics and Computing, based at Purdue's Discovery Park. Cola also received support through a fellowship from Intel Corp. and Purdue.

Purdue University

Related Carbon Nanotubes Current Events and Carbon Nanotubes News Articles

Tiny carbon nanotube pores make big impact
A team led by the Lawrence Livermore scientists has created a new kind of ion channel based on short carbon nanotubes, which can be inserted into synthetic bilayers and live cell membranes to form tiny pores that transport water, protons, small ions and DNA.

Special UO microscope captures defects in nanotubes
University of Oregon chemists have devised a way to see the internal structures of electronic waves trapped in carbon nanotubes by external electrostatic charges.

Imaging electric charge propagating along microbial nanowires
The claim by UMass Amherst researchers that the microbe Geobacter produces tiny electrical wires has been mired in controversy for a decade, but a new collaborative study provides stronger evidence than ever to support their claims.

Beyond LEDs: Brighter, new energy-saving flat panel lights based on carbon nanotubes
Even as the 2014 Nobel Prize in Physics has enshrined light emitting diodes (LEDs) as the single most significant and disruptive energy-efficient lighting solution of today, scientists around the world continue unabated to search for the even-better-bulbs of tomorrow.

Fast, cheap nanomanufacturing
Luis Fernando Velásquez-García's group at MIT's Microsystems Technology Laboratories (MTL) develops dense arrays of microscopic cones that harness electrostatic forces to eject streams of ions.

Nanoparticles Accumulate Quickly in Wetland Sediment
A Duke University team has found that nanoparticles called single-walled carbon nanotubes accumulate quickly in the bottom sediments of an experimental wetland setting, an action they say could indirectly damage the aquatic food chain.

Future flexible electronics based on carbon nanotubes
Researchers from the University of Texas at Austin and Northwestern University have demonstrated a new method to improve the reliability and performance of transistors and circuits based on carbon nanotubes (CNT), a semiconductor material that has long been considered by scientists as one of the most promising successors to silicon for smaller, faster and cheaper electronic devices.

Nanotubes help healing hearts keep the beat
Carbon nanotubes serve as bridges that allow electrical signals to pass unhindered through new pediatric heart-defect patches invented at Rice University and Texas Children's Hospital.

Ultrasensitive Biosensor from Molybdenite Semiconductor Outshines Graphene
UC Santa Barbara researchers demonstrate atomically thin, ultrasensitive and scalable molybdenum disulfide field-effect transistor based biosensors and establish their potential for single-molecule detection

Ultrasensitive Biosensor from Molybdenite Semiconductor Outshines Graphene
Move over, graphene. An atomically thin, two-dimensional, ultrasensitive semiconductor material for biosensing developed by researchers at UC Santa Barbara promises to push the boundaries of biosensing technology in many fields, from health care to environmental protection to forensic industries.
More Carbon Nanotubes Current Events and Carbon Nanotubes News Articles

Physical Properties of Carbon Nanotubes

Physical Properties of Carbon Nanotubes
by Riichiro Saito (Author), R. Saito (Editor), M. S. Dresselhaus (Editor)

This text is intended for researchers who want to perform theoretical analysis of carbon nanotubes. It can be used by graduate students in a solid state physics to learn how to investigate the structure of carbon nanotubes, its electronic and vibrational properties.

Carbon Nanotube Science: Synthesis, Properties and Applications

Carbon Nanotube Science: Synthesis, Properties and Applications
by Peter J. F. Harris (Author)

Carbon nanotubes represent one of the most exciting research areas in modern science. These molecular-scale carbon tubes are the stiffest and strongest fibres known, with remarkable electronic properties, and potential applications in a wide range of fields. Carbon Nanotube Science is the most concise, accessible book for the field, presenting the basic knowledge that graduates and researchers need to know. Based on the successful Carbon Nanotubes and Related Structures, this new book focuses solely on carbon nanotubes, covering the major advances made in recent years in this rapidly developing field. Chapters focus on electronic properties, chemical and bimolecular functionalisation, nanotube composites and nanotube-based probes and sensors. The book begins with a comprehensive...

Carbon Nanotube and Graphene Device Physics

Carbon Nanotube and Graphene Device Physics
by H.-S. Philip Wong (Author), Deji Akinwande (Author)

Explaining the properties and performance of practical nanotube devices and related applications, this is the first introductory textbook on the subject. All the fundamental concepts are introduced, so that readers without an advanced scientific background can follow all the major ideas and results. Additional topics covered include nanotube transistors and interconnects, and the basic physics of graphene. Problem sets at the end of every chapter allow readers to test their knowledge of the material covered and gain a greater understanding of the analytical skill sets developed in the text. This is an ideal textbook for senior undergraduate and graduate students taking courses in semiconductor device physics and nanoelectronics. It is also a perfect self-study guide for professional...

Carbon Nanotubes and Graphene, Second Edition

Carbon Nanotubes and Graphene, Second Edition
by K. Tanaka (Editor), S. Iijima (Editor)

Carbon Nanotubes and Graphene is a timely second edition of the original Science and Technology of Carbon Nanotubes. Updated to include expanded coverage of the preparation, purification, structural characterization, and common application areas of single- and multi-walled CNT structures, this work compares, contrasts, and, where appropriate, unitizes CNT to graphene. This much expanded second edition reference supports knowledge discovery, production of impactful carbon research, encourages transition between research fields, and aids the formation of emergent applications. New chapters encompass recent developments in the theoretical treatments of electronic and vibrational structures, and magnetic, optical, and electrical solid-state properties, providing a vital base to research....

Carbon Nanotubes: Theoretical Concepts and Research Strategies for Engineers

Carbon Nanotubes: Theoretical Concepts and Research Strategies for Engineers
by A. K. Haghi (Author), Sabu Thomas (Author)

This book presents the diversity of recent advances in carbon nanotubes from a broad perspective that will be useful for scientists as well as for graduate students and engineers. Presenting leading-edge research in this dynamic field, this volume is an introduction to the physical concepts needed for investigating carbon nanotubes and other one-dimensional solid-state systems. Written for a wide scientific readership, each chapter consists of an instructive approach to the topic and sustainable ideas for solutions. Carbon nanotubes, with their extraordinary mechanical and unique electronic properties, have garnered much attention in recent years. With a broad range of potential applications, including nanoelectronics, composites, chemical sensors, biosensors, microscopy,...

The Carbon Nanotube Machine

The Carbon Nanotube Machine

This brief publication proposes an approach (actually several approaches) to manufacturing long carbon nanotubes on a commercial scale. I recently became interested in carbon nanotubes and apparently the field is dominated by inorganic and theoretical chemists. I happen to be an organic chemist and have been interested for some time in the structure of graphite and its potential. It appears to me that the current thinking concerning carbon nanotubes considered the carbide
ion associated with various metal cations as the basic building block of nanotubes. No wonder they are thinking about temperatures of thousands of degrees with vaporized carbon. I think the key here is not carbide, but rather polycarbyne.


In polycarbyne...

Carbon Nanotubes and Related Structures: Synthesis, Characterization, Functionalization, and Applications

Carbon Nanotubes and Related Structures: Synthesis, Characterization, Functionalization, and Applications
by Dirk M. Guldi (Editor), Nazario Martín (Editor)

Written by the most prominent experts and pioneers in the field, this ready reference combines fundamental research, recent breakthroughs and real-life applications in one well-organized treatise.
As such, both newcomers and established researchers will find here a wide range of current methods for producing and characterizing carbon nanotubes using imaging as well as spectroscopic techniques. One major part of this thorough overview is devoted to the controlled chemical functionalization of carbon nanotubes, covering intriguing applications in photovoltaics, organic electronics and materials design. The latest research on novel carbon-derived structures, such as graphene, nanoonions and carbon pea pods, round off the book.

Carbon Nanotubes: Science and Applications

Carbon Nanotubes: Science and Applications
by M. Meyyappan (Editor)

Carbon nanotubes, with their extraordinary mechanical and unique electronic properties, have garnered much attention in the past five years. With a broad range of potential applications including nanoelectronics, composites, chemical sensors, biosensors, microscopy, nanoelectromechanical systems, and many more, the scientific community is more motivated than ever to move beyond basic properties and explore the real issues associated with carbon nanotube-based applications.

Taking a comprehensive look at this diverse and dynamic subject, Carbon Nanotubes: Science and Applications describes the field's various aspects, including properties, growth, and processing techniques, while focusing on individual major application areas. Well-known authors who practice the craft of carbon...

  Defects and Diffusion in Carbon Nanotubes (Defect and Diffusion Forum)
by D. J. Fisher (Editor)

Carbon Nanotube and Related Field Emitters: Fundamentals and Applications

Carbon Nanotube and Related Field Emitters: Fundamentals and Applications
by Yahachi Saito (Editor)

Carbon nanotubes (CNTs) have novel properties that make them potentially useful in many applications in nanotechnology, electronics, optics and other fields of materials science. These characteristics include extraordinary strength, unique electrical properties, and the fact that they are efficient heat conductors. Field emission is the emission of electrons from the surface of a condensed phase into another phase due to the presence of high electric fields. CNT field emitters are expected to make a breakthrough in the development of field emission display technology and enable miniature X-ray sources that will find a wide variety of applications in electronic devices, industry, and medical and security examinations.
This first monograph on the topic covers all aspects in a concise yet...

© 2014