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1. Non-volatile RF and mm-wave Switches Based on Monolayer hBN

   https://doi.org/10.1109/IEDM19573.2019.8993470  

   Kim, Myungsoo; Pallecchi, Emiliano; Ge, Ruijing; Wu, Xiaohan; Avramovic, Vanessa; Okada, Etienne; Lee, Jack C.; Happy, Henri; Akinwande, Deji (December 2019, IEEE IEDM)

   Non-volatile radio-frequency (RF) switches based on hexagonal boron nitride (hBN) are realized for the first time with low insertion loss (≤ 0.2 dB) and high isolation (≥ 15 dB) up to 110 GHz. Crystalline hBN enables the thinnest RF switch device with a single monolayer (~0.33 nm) as the memory layer owing to its robust layered structure. It affords ~20 dBm power handling, 10 dB higher compared to MoS 2 switches due to its wider bandgap (~6 eV). Importantly, operating frequencies cover the RF, 5G, and mm-wave bands, making this a promising low-power switch for diverse communication and connectivity front-end systems. Compared to other switch technologies based on MEMS, memristor, and phase-change memory (PCM), hBN switches offer a promising combination of non-volatility, nanosecond switching, power handling, high figure-of-merit cutoff frequency (43 THz), and heater-less ambient integration. Our pioneering work suggests that atomically-thin nanomaterials can be good device candidates for 5G and beyond. 

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2. On-Chip Integration of a Plasmonic FET Source and a Nano-Patch Antenna for Efficient Terahertz Wave Radiation

   https://doi.org/10.3390/nano13243114  

   Crabb, Justin; Cantos-Roman, Xavier; Aizin, Gregory; Jornet, Josep Miquel (December 2023, Nanomaterials)

   Graphene-based Field-Effect Transistors (FETs) integrated with microstrip patch antennas offer a promising approach for terahertz signal radiation. In this study, a dual-stage simulation methodology is employed to comprehensively investigate the device’s performance. The initial stage, executed in MATLAB, delves into charge transport dynamics within a FET under asymmetric boundary conditions, employing hydrodynamic equations for electron transport in the graphene channel. Electromagnetic field interactions are modeled via Finite-Difference Time-Domain (FDTD) techniques. The second stage, conducted in COMSOL Multiphysics, focuses on the microstrip patch antenna’s radiative characteristics. Notably, analysis of the S11 curve reveals minimal reflections at the FET’s resonant frequency of 1.34672 THz, indicating efficient impedance matching. Examination of the radiation pattern demonstrates the antenna’s favorable directional properties. This research underscores the potential of graphene-based FETs for terahertz applications, offering tunable impedance matching and high radiation efficiency for future terahertz devices. 

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3. Guided Mid‐IR and Near‐IR Light within a Hybrid Hyperbolic‐Material/Silicon Waveguide Heterostructure

   https://doi.org/10.1002/adma.202004305  

   He, Mingze; Halimi, Sami I.; Folland, Thomas G.; Sunku, Sai S.; Liu, Song; Edgar, James H.; Basov, D. N.; Weiss, Sharon M.; Caldwell, Joshua D. (February 2021, Advanced Materials)

   Abstract Silicon waveguides have enabled large‐scale manipulation and processing of near‐infrared optical signals on chip. Yet, expanding the bandwidth of guided waves to other frequencies will further increase the functionality of silicon as a photonics platform. Frequency multiplexing by integrating additional architectures is one approach to the problem, but this is challenging to design and integrate within the existing form factor due to scaling with the free‐space wavelength. This paper demonstrates that a hexagonal boron nitride (hBN)/silicon hybrid waveguide can simultaneously enable dual‐band operation at both mid‐infrared (6.5–7.0 µm) and telecom (1.55 µm) frequencies, respectively. The device is realized via the lithography‐free transfer of hBN onto a silicon waveguide, maintaining near‐infrared operation. In addition, mid‐infrared waveguiding of the hyperbolic phonon polaritons (HPhPs) supported in hBN is induced by the index contrast between the silicon waveguide and the surrounding air underneath the hBN, thereby eliminating the need for deleterious etching of the hyperbolic medium. The behavior of HPhP waveguiding in both straight and curved trajectories is validated within an analytical waveguide theoretical framework. This exemplifies a generalizable approach based on integrating hyperbolic media with silicon photonics for realizing frequency multiplexing in on‐chip photonic systems. 

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4. Highly efficient deoxydehydration and hydrodeoxygenation on MoS2-supported transition metal atoms through a C-H activation mechanism

   https://doi.org/10.1021/acscatal.0c02669  

   Xi, Yongjie; Heyden, Andreas (July 2020, ACS Catalysis)

   Deoxydehydration (DODH) is an efficient process for the removal of vicinal OH groups of a diol or polyol. Conventional DODH reactions usually take place at a single-site MOx (M=Re, Mo, V etc.) active center, which proceed through a diol condensation step, an alkene extrusion step and a catalyst regeneration (or reduction) step. Here, we suggest that MoS2-supported transition metal atoms allow for the DODH reaction to occur through an alternative mechanism, whereby the C-H bond of a diol is activated first, which facilitates the C-OH bond cleavage on a neighboring carbon. The removal of the second OH group is also facile over the proposed catalysts. Our kinetic studies suggest that the DODH of ethylene glycol on Ru2/MoS2, Ir2/MoS2 and Ru3/MoS2 are highly active with predicted turnover frequencies of over 1/s. Thus, our study suggests a possible approach for the design of highly active DODH catalysts. Apart from being a DODH catalyst, the proposed MoS2-supported catalysts are also highly active as hydrodeoxygenation catalyst for the removal of alcohol OH groups. 

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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. 

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