Thermal Energy Transfer in Nanomaterials: Interview with Professor Tim Fisher at Purdue University
March 18, 2013
Interview conducted by Kal Kaur
KK - What is the nanoHUB-U initiative?
TF - Our view is that the impact of nanoscience and technology will come by reshaping the way we think about traditional science and engineering disciplines, by providing new tools and approaches for those disciplines, and by promoting interdisciplinary research and development.
The open content that we have developed and disseminated through nanoHUB.org suggests a strong demand for such an approach.
Through the nanoHUB-U initiative, we offer online courses on nanoscience and nanotechnology that build on the open content on nanoHUB.org and are designed to be broadly accessible with few prerequisites.
Students gain access to a completely new set of pre-recorded video lectures not available on nanoHUB.org, extensive lecture notes, quizzes, exams, homework and exercises using nanoHUB.org simulation tools with video-recorded solutions, and Q&A forums for interacting with professors and other students.
Our goal is to help students at other institutions and working engineers and scientists acquire the knowledge they need to be successful in contemporary technology, which increasingly involves nanotechnology – no matter what the discipline.
KK - Why did you decide to run an online course on nanoscale thermal energy?
TF - Highly directed forms of energy found in a wide range of applications—from photovoltaics to thermoelectrics to microprocessors—convert ultimately to thermal energy.
Consequently, almost all modern technologies benefit from fundamental understanding of how heat flows.
KK - What topics will be covered in the course?
TF - The course will first identify the main carriers for heat conduction in solids—phonons and electrons—with some treatment of fluid molecules and their statistical profiles.
It will then develop thermal transport principles from the bottom up; introduce a common Landauer framework for heat flow; investigate realistic physical issues including quantum of thermal conductance, carrier scattering, and interface boundary resistances; and demonstrate extensions to confined and bulk thermal behavior.
Refer to the scientific overview video about thermal energy at the nanoscale.
KK - What are the basic principles of thermal energy management in nanoscale structures?
TF - All carrier types can be treated through a similar framework. Their statistical distributions drive net carrier movement when perturbed out of equilibrium. Then the carriers move with a given velocity, each carrying a certain amount of thermal energy, and are impeded in their progress by scattering events.
Nanoscale structure can affect each of these elements: speed, energy carrying ability, and scattering.
KK - What kind of nanomaterials can be used in heat management applications?
TF - Nanomaterials can extend the range of heat conduction on both sides of the ledger—allowing for ultra-high thermal conductivity in materials such as graphene, and ultra-low thermal conductivity in nanocomposites that are designed to block carrier flow.
KK - Why is heat flow important in the design of thermoelectric materials?
TF - In thermoelectrics, the goal is to enhance the flow of electrons within a certain energy range while suppressing other modes of heat transfer, by phonons for example. This is a tricky balance that requires detailed understanding of how carriers scatter at different energies and spatial scales.
KK - Why is heat management important in laser manufacturing?
TF - Laser manufacturing typically seeks to optimize the final microstructure and topography of a material’s surface, and both of these are strongly correlated to the time-temperature history of the material that can be precisely controlled with a laser.
KK - How can changes in electron distribution in a material impact thermal transport properties?
TF - Electrons are the primary thermal energy carriers in bulk metals, and their distribution can be altered by nanostructuring. For example, even in metallic-type carbon nanotubes, the free electron density is low because of spatial confinement, and phonons dominate their thermal transport behaviour.
KK - What consequences does quantum confinement have on thermal properties within a material?
TF - Quantum confinement changes the distribution of carriers by altering the availability of energy states. As a consequence, the carriers tend to be found in narrower energy bands that can be used to enhance or diminish thermal property magnitudes.
KK - What are the issues with measuring thermal properties in nanomaterials?
TF - This is a very active part of the discipline. In general, indirect measurements of thermal properties are required (e.g., measuring temperature through a change in a surrogate property). The major outstanding issues involve high levels of experimental uncertainty and unknown material details at the atomic level (i.e., sample-to-sample variations).
KK - Where can we find further information on this course and on your research?
TF - A link to the scientific overview video about the course can be found at nanoHUB.org.
For more information about the course and to register please go to the nanoHUB.org web page.
About Professor Tim Fisher
Timothy S. Fisher (PhD in Mechanical Engineering, 1998, Cornell) was born in Aurora, Illinois. He joined Purdue’s School of Mechanical Engineering and Birck Nanotechnology Center in 2002 after several years at Vanderbilt University.
Timothy is an adjunct professor in the International Centre for Materials Science at the Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore.
From 2009 to 2011, he served as a research scientist at the Air Force Research Laboratory’s newly formed Thermal Sciences and Materials Branch of the Materials and Manufacturing Directorate.
Prior to his graduate studies, Timothy was employed from 1991 to 1993 as a design engineer in Motorola’s Automotive and Industrial Electronics Group.
His research has included studies of nanoscale heat transfer, carbon nanomaterial synthesis, coupled electro-thermal effects in semi-conductor and electron emission devices, energy conversion and storage materials and devices, microfuidic devices, biosensing, and related computational methods ranging from atomistic to continuum scales.