More Like this

1. Thermal transport in graphene under large mechanical strains

   https://doi.org/10.1063/5.0223188  

   Wang, Yingtao; Zhang, Xian (August 2024, Journal of Applied Physics)

   Flexible electronic devices with skin-like properties are hailed as revolutionary for the development of next-generation electronic devices, such as electric-skin and humanoid robotics. Graphene is intrinsically flexible due to its structural thinness in nature and are considered next-generation materials for wearable electronics. These devices usually experience a large mechanical deformation in use so as to achieve intimate conformal contact with human skin and to coordinate complex human motions, while heat dissipation has been a major limitation when the device is under a large mechanical strain. Unlike the small deformation (<1%) induced by intrinsic material factors such as lattice mismatch between material components in devices, a large mechanical deformation (>1%) by an external loading condition could lead to apparent changes to global geometric shapes and significantly impact thermal transport. In this study, we investigated the thermal conductivities of graphene under several large mechanical strains: 2.9%, 4.3%, and 6.1%. We used a refined opto-thermal Raman technique to characterize the thermal transport properties and discovered the thermal conductivities to be 2092 ± 502, 972 ± 87, 348 ± 52, and 97 ± 13 W/(m K) for the relaxed state, 2.9%, 4.3%, and 6.1% tensile strain, respectively. Our results showed a significant decreasing trend in thermal conductivities with an increasing mechanical strain. The findings in this study reveal new thermal transport mechanisms in 2D materials and shed light on building novel flexible nanoelectronic devices with enhanced thermal management. 

   more » « less
2. Thermal rectification in thin film metalattice structures: A computational study

   https://doi.org/10.1063/5.0135963  

   Eichfeld, Devon A.; Chen, Weinan; Dabo, Ismaila; Foley, Brian M.; Ramos-Alvarado, Bladimir (March 2023, Journal of Applied Physics)

   Thermal rectification is an asymmetric heat transfer process where directionally dependent transport occurs along a given axis. In this work, geometric parameters that govern thermal rectification in solids composed of various semiconducting materials were investigated utilizing metalattice data for seven materials with pore sizes ranging between 2 and 30 nm. Using numerical simulation, thermal rectification was calculated at different thermal biases in single material systems, including silicon, cubic boron nitride, and diamond, among others. The largest thermal rectification for each material was exhibited in bilayer sample stacks that were thermally matched (i.e., the thermal resistance of each layer in the stack is equal in either forward or reverse direction). Of the materials tested, diamond provided the highest thermal rectification for all cases, with its best case achieving a thermal rectification of 57.2%. This novel thermal functionality will find application in advanced applications for temperature regulation, including resonator systems where thermal effects may significantly alter and/or degrade performance. 

   more » « less
3. Differences in water and vapor transport through angstrom-scale pores in atomically thin membranes

   https://doi.org/10.1038/s41467-022-34172-1  

   Cheng, Peifu; Fornasiero, Francesco; Jue, Melinda L.; Ko, Wonhee; Li, An-Ping; Idrobo, Juan Carlos; Boutilier, Michael S.; Kidambi, Piran R. (December 2022, Nature Communications)

   Abstract The transport of water through nanoscale capillaries/pores plays a prominent role in biology, ionic/molecular separations, water treatment and protective applications. However, the mechanisms of water and vapor transport through nanoscale confinements remain to be fully understood. Angstrom-scale pores (~2.8–6.6 Å) introduced into the atomically thin graphene lattice represent ideal model systems to probe water transport at the molecular-length scale with short pores (aspect ratio ~1–1.9) i.e., pore diameters approach the pore length (~3.4 Å) at the theoretical limit of material thickness. Here, we report on orders of magnitude differences (~80×) between transport of water vapor (~44.2–52.4 g m −2 day −1 Pa −1 ) and liquid water (0.6–2 g m −2 day −1 Pa −1 ) through nanopores (~2.8–6.6 Å in diameter) in monolayer graphene and rationalize this difference via a flow resistance model in which liquid water permeation occurs near the continuum regime whereas water vapor transport occurs in the free molecular flow regime. We demonstrate centimeter-scale atomically thin graphene membranes with up to an order of magnitude higher water vapor transport rate (~5.4–6.1 × 10 4  g m −2 day −1 ) than most commercially available ultra-breathable protective materials while effectively blocking even sub-nanometer (>0.66 nm) model ions/molecules. 

   more » « less
4. A Review of Scalable Hexagonal Boron Nitride ( h ‐BN) Synthesis for Present and Future Applications

   https://doi.org/10.1002/adma.202207374  

   Naclerio, Andrew_E; Kidambi, Piran_R (December 2022, Advanced Materials)

   Abstract Hexagonal boron nitride (h‐BN) is a layered inorganic synthetic crystal exhibiting high temperature stability and high thermal conductivity. As a ceramic material it has been widely used for thermal management, heat shielding, lubrication, and as a filler material for structural composites. Recent scientific advances in isolating atomically thin monolayers from layered van der Waals crystals to study their unique properties has propelled research interest in mono/few layeredh‐BN as a wide bandgap insulating support for nanoscale electronics, tunnel barriers, communications, neutron detectors, optics, sensing, novel separations, quantum emission from defects, among others. Realizing these futuristic applications hinges on scalable cost‐effective high‐qualityh‐BN synthesis. Here, the authors review scalable approaches of high‐quality mono/multilayerh‐BN synthesis, discuss the challenges and opportunities for each method, and contextualize their relevance to emerging applications. Maintaining a stoichiometric balance B:N = 1 as the atoms incorporate into the growing layered crystal and maintaining stacking order between layers during multi‐layer synthesis emerge as some of the main challenges forh‐BN synthesis and the development of processes to address these aspects can inform and guide the synthesis of other layered materials with more than one constituent element. Finally, the authors contextualizeh‐BN synthesis efforts along with quality requirements for emerging applications via a technological roadmap. 

   more » « less
5. Ultra‐High Interfacial Thermal Conductance via Double hBN Encapsulation for Efficient Thermal Management of 2D Electronics

   https://doi.org/10.1002/smll.202205726  

   Ye, Fan; Liu, Qingchang; Xu, Baoxing; Feng, Philip X. ‐L.; Zhang, Xian (February 2023, Small)

   Abstract Heat dissipation is a major limitation of high‐performance electronics. This is especially important in emerging nanoelectronic devices consisting of ultra‐thin layers, heterostructures, and interfaces, where enhancement in thermal transport is highly desired. Here, ultra‐high interfacial thermal conductance in encapsulated van der Waals (vdW) heterostructures with single‐layer transition metal dichalcogenides MX₂(MoS₂, WSe₂, WS₂) sandwiched between two hexagonal boron nitride (hBN) layers is reported. Through Raman spectroscopic measurements of suspended and substrate‐supported hBN/MX₂/hBN heterostructures with varying laser power and temperature, the out‐of‐plane interfacial thermal conductance in the vertical stack is calibrated. The measured interfacial thermal conductance between MX₂and hBN reaches 74 ± 25 MW m⁻²K⁻¹, which is at least ten times higher than the interfacial thermal conductance of MX₂in non‐encapsulation structures. Molecular dynamics (MD) calculations verify and explain the experimental results, suggesting a full encapsulation by hBN layers is accounting for the high interfacial conductance. This ultra‐high interfacial thermal conductance is attributed to the double heat transfer pathways and the clean and tight vdW interface between two crystalline 2D materials. The findings in this study reveal new thermal transport mechanisms in hBN/MX₂/hBN structures and shed light on building novel hBN‐encapsulated nanoelectronic devices with enhanced thermal management. 

   more » « less