Heat flow in nanomaterials is an important area of study, with both fundamental and technological... more Heat flow in nanomaterials is an important area of study, with both fundamental and technological implications. However, little is known about heat flow in two-dimensional devices or interconnects with dimensions comparable to the phonon mean free path. Here we find that short, quarter-micron graphene samples reach B35% of the ballistic thermal conductance limit up to room temperature, enabled by the relatively large phonon mean free path (B100 nm) in substrate-supported graphene. In contrast, patterning similar samples into nanoribbons leads to a diffusive heat-flow regime that is controlled by ribbon width and edge disorder. In the edge-controlled regime, the graphene nanoribbon thermal conductivity scales with width approximately as BW 1.8±0.3 , being about 100 W m À 1 K À 1 in 65-nm-wide graphene nanoribbons, at room temperature. These results show how manipulation of two-dimensional device dimensions and edges can be used to achieve full control of their heat-carrying properties, approaching fundamentally limited upper or lower bounds.
Abstract We investigate the influence of grain boundaries (GBs), line defects (LDs), and chiralit... more Abstract We investigate the influence of grain boundaries (GBs), line defects (LDs), and chirality on thermal transport in graphene using non-equilibrium Green's functions. At room temperature, the ballistic thermal conductance is∼ 4.2 GW m-2 K-1, and single GBs or LDs yield transmission from 50% to 80% of this value. LDs with carbon atom octagon defects have lower thermal transmission than that of GBs with pentagon and heptagon defects.
Abstract: One of the factors limiting electron mobility in supported graphene is remote phonon sc... more Abstract: One of the factors limiting electron mobility in supported graphene is remote phonon scattering. We formulate the theory of the coupling between graphene plasmon and substrate surface polar phonon (SPP) modes, and find that it leads to the formation of interfacial plasmon-phonon (IPP) modes, from which the phenomena of dynamic anti-screening and screening of remote phonons emerge.
Carbon nanotubes (CNTs) are a promising class of materials for nanoelectronic applications given ... more Carbon nanotubes (CNTs) are a promising class of materials for nanoelectronic applications given their high mobility as well as their ability to sustain large current densities. However, at large current densities Joule heating becomes an important issue, and the dissipation of waste heat must be taken into consideration to ensure optimal device performance. 1–4 Heat dissipation from the CNT depends on its thermal conductivity as well as the thermal boundary conductance (TBC) of its interface with the environment.
We directly image hot spot formation in functioning mono-and bilayer graphene field effect transi... more We directly image hot spot formation in functioning mono-and bilayer graphene field effect transistors (GFETs) using infrared thermal microscopy. Correlating with an electrical− thermal transport model provides insight into carrier distributions, fields, and GFET power dissipation. The hot spot corresponds to the location of minimum charge density along the GFET; by changing the applied bias, this can be shifted between electrodes or held in the middle of the channel in ambipolar transport.
As a result of its outstanding electrical 1, 2 and thermal properties, 3, 4 single-layer graphene... more As a result of its outstanding electrical 1, 2 and thermal properties, 3, 4 single-layer graphene (SLG) has become a promising nanomaterial for future electronics. In this context, graphene will be supported by and integrated with insulators such as SiO2, both for circuit and for heat-spreader applications. 5 Thus, thermal energy flow will be limited both by the thermal conductivity (TC) of the supported graphene 6–8 and by the thermal boundary conductance (TBC) at the graphene-SiO2 interface.
We study charged impurity scattering and static screening in a top-gated substrate-supported grap... more We study charged impurity scattering and static screening in a top-gated substrate-supported graphene nanostructure. Our model describes how boundary conditions can be incorporated into scattering, sheds light on the dielectric response of these nanostructures, provides insights into the effect of the top gate on impurity scattering, and predicts that the carrier mobility in such graphene heterostructures decreases with increasing top dielectric thickness and higher carrier density.
Abstract: The incorporation of graphitic compounds such as carbon nanotubes (CNTs) and graphene i... more Abstract: The incorporation of graphitic compounds such as carbon nanotubes (CNTs) and graphene into nano-electronic device packaging holds much promise for waste heat management given their high thermal conductivities. However, as these graphitic materials must be used in together with other semiconductor/insulator materials, it is not known how thermal transport is affected by the interaction.
Abstract Chemical vapor deposition growth of graphene on polycrystalline copper foil is a demonst... more Abstract Chemical vapor deposition growth of graphene on polycrystalline copper foil is a demonstrated technique for obtaining large-area, predominantly monolayer graphene. However, such growth results in grain boundaries between rotationally misoriented graphene grains.
We use scanning tunneling microscopy and spectroscopy to examine the electronic nature of grain b... more We use scanning tunneling microscopy and spectroscopy to examine the electronic nature of grain boundaries (GBs) in polycrystalline graphene grown by chemical vapor deposition (CVD) on Cu foil and transferred to SiO2 substrates. We find no preferential orientation angle between grains, and the GBs are continuous across graphene wrinkles and SiO2 topography.
Graphene, a mono-atomic layer of carbon atoms, has emerged as the basis for a possible alternativ... more Graphene, a mono-atomic layer of carbon atoms, has emerged as the basis for a possible alternative to modern Si-based semiconductor technology1. The hexagonally arranged carbon atoms in graphene result in a linear dispersion relation. Graphene's superior electronic, thermal, and mechanical properties provide a platform to test high mobility field-effect transistors (FET), novel heat sinks, and mechanical resonators2. In usual electronic devices, the input power needed to operate an electronic device generates a self-heating ...
We have employed thermal infrared microscopy to image temperature distributions in monolayer and ... more We have employed thermal infrared microscopy to image temperature distributions in monolayer and bilayer graphene transistors under high bias. The hot spot position is sensitive to device electrostatics, corresponding to the location of minimum charge density in unipolar ...
Heat flow in nanomaterials is an important area of study, with both fundamental and technological... more Heat flow in nanomaterials is an important area of study, with both fundamental and technological implications. However, little is known about heat flow in two-dimensional devices or interconnects with dimensions comparable to the phonon mean free path. Here we find that short, quarter-micron graphene samples reach B35% of the ballistic thermal conductance limit up to room temperature, enabled by the relatively large phonon mean free path (B100 nm) in substrate-supported graphene. In contrast, patterning similar samples into nanoribbons leads to a diffusive heat-flow regime that is controlled by ribbon width and edge disorder. In the edge-controlled regime, the graphene nanoribbon thermal conductivity scales with width approximately as BW 1.8±0.3 , being about 100 W m À 1 K À 1 in 65-nm-wide graphene nanoribbons, at room temperature. These results show how manipulation of two-dimensional device dimensions and edges can be used to achieve full control of their heat-carrying properties, approaching fundamentally limited upper or lower bounds.
Abstract We investigate the influence of grain boundaries (GBs), line defects (LDs), and chiralit... more Abstract We investigate the influence of grain boundaries (GBs), line defects (LDs), and chirality on thermal transport in graphene using non-equilibrium Green's functions. At room temperature, the ballistic thermal conductance is∼ 4.2 GW m-2 K-1, and single GBs or LDs yield transmission from 50% to 80% of this value. LDs with carbon atom octagon defects have lower thermal transmission than that of GBs with pentagon and heptagon defects.
Abstract: One of the factors limiting electron mobility in supported graphene is remote phonon sc... more Abstract: One of the factors limiting electron mobility in supported graphene is remote phonon scattering. We formulate the theory of the coupling between graphene plasmon and substrate surface polar phonon (SPP) modes, and find that it leads to the formation of interfacial plasmon-phonon (IPP) modes, from which the phenomena of dynamic anti-screening and screening of remote phonons emerge.
Carbon nanotubes (CNTs) are a promising class of materials for nanoelectronic applications given ... more Carbon nanotubes (CNTs) are a promising class of materials for nanoelectronic applications given their high mobility as well as their ability to sustain large current densities. However, at large current densities Joule heating becomes an important issue, and the dissipation of waste heat must be taken into consideration to ensure optimal device performance. 1–4 Heat dissipation from the CNT depends on its thermal conductivity as well as the thermal boundary conductance (TBC) of its interface with the environment.
We directly image hot spot formation in functioning mono-and bilayer graphene field effect transi... more We directly image hot spot formation in functioning mono-and bilayer graphene field effect transistors (GFETs) using infrared thermal microscopy. Correlating with an electrical− thermal transport model provides insight into carrier distributions, fields, and GFET power dissipation. The hot spot corresponds to the location of minimum charge density along the GFET; by changing the applied bias, this can be shifted between electrodes or held in the middle of the channel in ambipolar transport.
As a result of its outstanding electrical 1, 2 and thermal properties, 3, 4 single-layer graphene... more As a result of its outstanding electrical 1, 2 and thermal properties, 3, 4 single-layer graphene (SLG) has become a promising nanomaterial for future electronics. In this context, graphene will be supported by and integrated with insulators such as SiO2, both for circuit and for heat-spreader applications. 5 Thus, thermal energy flow will be limited both by the thermal conductivity (TC) of the supported graphene 6–8 and by the thermal boundary conductance (TBC) at the graphene-SiO2 interface.
We study charged impurity scattering and static screening in a top-gated substrate-supported grap... more We study charged impurity scattering and static screening in a top-gated substrate-supported graphene nanostructure. Our model describes how boundary conditions can be incorporated into scattering, sheds light on the dielectric response of these nanostructures, provides insights into the effect of the top gate on impurity scattering, and predicts that the carrier mobility in such graphene heterostructures decreases with increasing top dielectric thickness and higher carrier density.
Abstract: The incorporation of graphitic compounds such as carbon nanotubes (CNTs) and graphene i... more Abstract: The incorporation of graphitic compounds such as carbon nanotubes (CNTs) and graphene into nano-electronic device packaging holds much promise for waste heat management given their high thermal conductivities. However, as these graphitic materials must be used in together with other semiconductor/insulator materials, it is not known how thermal transport is affected by the interaction.
Abstract Chemical vapor deposition growth of graphene on polycrystalline copper foil is a demonst... more Abstract Chemical vapor deposition growth of graphene on polycrystalline copper foil is a demonstrated technique for obtaining large-area, predominantly monolayer graphene. However, such growth results in grain boundaries between rotationally misoriented graphene grains.
We use scanning tunneling microscopy and spectroscopy to examine the electronic nature of grain b... more We use scanning tunneling microscopy and spectroscopy to examine the electronic nature of grain boundaries (GBs) in polycrystalline graphene grown by chemical vapor deposition (CVD) on Cu foil and transferred to SiO2 substrates. We find no preferential orientation angle between grains, and the GBs are continuous across graphene wrinkles and SiO2 topography.
Graphene, a mono-atomic layer of carbon atoms, has emerged as the basis for a possible alternativ... more Graphene, a mono-atomic layer of carbon atoms, has emerged as the basis for a possible alternative to modern Si-based semiconductor technology1. The hexagonally arranged carbon atoms in graphene result in a linear dispersion relation. Graphene's superior electronic, thermal, and mechanical properties provide a platform to test high mobility field-effect transistors (FET), novel heat sinks, and mechanical resonators2. In usual electronic devices, the input power needed to operate an electronic device generates a self-heating ...
We have employed thermal infrared microscopy to image temperature distributions in monolayer and ... more We have employed thermal infrared microscopy to image temperature distributions in monolayer and bilayer graphene transistors under high bias. The hot spot position is sensitive to device electrostatics, corresponding to the location of minimum charge density in unipolar ...
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Papers by Zhun-Yong Ong