An electrochemical thermal transistor Sood, Aditya; Xiong, Feng; Chen, Shunda ...
Nature communications,
10/2018, Letnik:
9, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The ability to actively regulate heat flow at the nanoscale could be a game changer for applications in thermal management and energy harvesting. Such a breakthrough could also enable the control of ...heat flow using thermal circuits, in a manner analogous to electronic circuits. Here we demonstrate switchable thermal transistors with an order of magnitude thermal on/off ratio, based on reversible electrochemical lithium intercalation in MoS
thin films. We use spatially-resolved time-domain thermoreflectance to map the lithium ion distribution during device operation, and atomic force microscopy to show that the lithiated state correlates with increased thickness and surface roughness. First principles calculations reveal that the thermal conductance modulation is due to phonon scattering by lithium rattler modes, c-axis strain, and stacking disorder. This study lays the foundation for electrochemically-driven nanoscale thermal regulators, and establishes thermal metrology as a useful probe of spatio-temporal intercalant dynamics in nanomaterials.
We present a data-calibrated compact model of carbon nanotube (CNT) FETs (CNFETs), including contact resistance, direct source-to-drain, and band-to-band tunneling currents. The model captures the ...effects of dimensional scaling and performance degradations due to parasitic effects, and is used to study the tradeoffs between the drive current and the leakage current of CNFETs according to the selection of CNT diameter, CNT density, contact length, and gate length for a target contacted gate pitch. We describe a co-optimization study of CNFET device parameters near the limits of scaling with physical insight, and project the CNFET performance at the 5-nm technology node with an estimated contacted gate pitch of 31 nm. Based on the analysis, including parasitic resistance, capacitance, and tunneling leakage current, a CNT density of 180 CNTs/μm will enable the CNFET technology to meet the International Technology Roadmap for Semiconductors target of drive current (1.33 mA/μm), which is within reach of modern experimental capabilities.
Superlattice-like phase change memory (SL-PCM) promises lower switching current than conventional PCM based on Ge2Sb2Te5 (GST); however, a fundamental understanding of SL-PCM requires detailed ...characterization of the interfaces within such an SL. Here we explore the electrical and thermal transport of SLs with deposited Sb2Te3 and GeTe alternating layers of various thicknesses. We find up to an approximately four-fold reduction of the effective cross-plane thermal conductivity of the SL stack (as-deposited polycrystalline) compared with polycrystalline GST (as-deposited amorphous and later annealed) due to the thermal interface resistances within the SL. Thermal measurements with varying periods of our SLs show a signature of phonon coherence with a transition from wave-like to particle-like phonon transport, further described by our modeling. Electrical resistivity measurements of such SLs reveal strong anisotropy (∼2000×) between the in-plane and cross-plane directions due to the weakly interacting van der Waals-like gaps. This work uncovers electrothermal transport in SLs based on Sb2Te3 and GeTe for the improved design of low-power PCM.
We study the intrinsic transport properties of suspended graphene devices at high fields (≥1 V/μm) and high temperatures (≥1000 K). Across 15 samples, we find peak (average) saturation velocity of ...3.6 × 107 cm/s (1.7 × 107 cm/s) and peak (average) thermal conductivity of 530 W m–1 K–1 (310 W m–1 K–1) at 1000 K. The saturation velocity is 2–4 times and the thermal conductivity 10–17 times greater than in silicon at such elevated temperatures. However, the thermal conductivity shows a steeper decrease at high temperature than in graphite, consistent with stronger effects of second-order three-phonon scattering. Our analysis of sample-to-sample variation suggests the behavior of “cleaner” devices most closely approaches the intrinsic high-field properties of graphene. This study reveals key features of charge and heat flow in graphene up to device breakdown at ∼2230 K in vacuum, highlighting remaining unknowns under extreme operating conditions.
The performance and scaling of graphene-based electronics is limited by the quality of contacts between the graphene and metal electrodes. However, the nature of graphene-metal contacts remains ...incompletely understood. Here, we use atomic force microscopy to measure the temperature distributions at the contacts of working graphene transistors with a spatial resolution of ~ 10 nm (refs 5-8), allowing us to identify the presence of Joule heating, current crowding and thermoelectric heating and cooling. Comparison with simulation enables extraction of the contact resistivity (150-200 Ω µm²) and transfer length (0.2-0.5 µm) in our devices; these generally limit performance and must be minimized. Our data indicate that thermoelectric effects account for up to one-third of the contact temperature changes, and that current crowding accounts for most of the remainder. Modelling predicts that the role of current crowding will diminish and the role of thermoelectric effects will increase as contacts improve.
The thermal properties of a suspended metallic single-wall carbon nanotube (SWNT) are extracted from its high-bias (I − V) electrical characteristics over the 300−800 K temperature range, achieved by ...Joule self-heating. The thermal conductance is approximately 2.4 nW/K, and the thermal conductivity is nearly 3500 Wm-1K-1 at room temperature for a SWNT of length 2.6 μm and diameter 1.7 nm. A subtle decrease in thermal conductivity steeper than 1/T is observed at the upper end of the temperature range, which is attributed to second-order three-phonon scattering between two acoustic modes and one optical mode. We discuss sources of uncertainty and propose a simple analytical model for the SWNT thermal conductivity including length and temperature dependence.
Chemical vapor deposition of graphene on Cu often employs polycrystalline Cu substrates with diverse facets, grain boundaries (GBs), annealing twins, and rough sites. Using scanning electron ...microscopy (SEM), electron-backscatter diffraction (EBSD), and Raman spectroscopy on graphene and Cu, we find that Cu substrate crystallography affects graphene growth more than facet roughness. We determine that (111) containing facets produce pristine monolayer graphene with higher growth rate than (100) containing facets, especially Cu(100). The number of graphene defects and nucleation sites appears Cu facet invariant at growth temperatures above 900 °C. Engineering Cu to have (111) surfaces will cause monolayer, uniform graphene growth.
PDF
