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Modeling Thermal Properties of Graphene and Graphene-Based Nanostructures
Published in Kun Zhou, Carbon Nanomaterials, 2020
The availability of various types of 2-D materials, such as GE, SE, and MoS2, provides a fertile ground for the design and fabrication of the novel van der Waals heterostructures. Different from the SE/GE bilayer heterostructure, which is still in their theoretical stage, the GE/MoS2 bilayer heterostructure has already been successfully synthesized and proved to work well in practical applications. In this section, the thermal transport in the GE/MoS2 bilayer heterostructure is discussed. Both the in-plane thermal conductivity and the out-of-plane interfacial thermal conductance are considered.
Heterostructures Based on 2D Xenes Materials
Published in Zongyu Huang, Xiang Qi, Jianxin Zhong, 2D Monoelemental Materials (Xenes) and Related Technologies, 2022
Considering the combination mode of heterostructure, two types of heterostructure could be classified, van der waals heterostructure and lateral heterostructure. The van der Waals heterostructure usually exhibits anisotropic characteristics, with covalent bonds' interaction within the layer and van der Waals interactions between the layers. However, the lateral heterostructure is formed by combining two materials into a planar structure, and the interaction inside is covalent bond interaction, as shown in Figure 6.2.
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Published in Vladimir Mitin, Taiichi Otsuji, Victor Ryzhii, Graphene-Based Terahertz Electronics and Plasmonics, 2020
V. Ryzhii, M. Ryzhii, V. Leiman, V. Mitin, M. S. Shur, T. Otsuji
The gapless energy spectrum of graphene layers (GLs) enables their use in the interband detectors of infrared radiation (see, for example, Refs. [1–5]). The incorporation of the GLs into the van der Waals (vdW) heterostructures based on such materials as hBN, WS2, InSe, GaSe, and similar materials [6–15] can enable the creation of novel GL infrared photodetectors (GLIPs) with improved characteristics. As discussed in the recent review [16], mixed-dimensional van der Waals heterostructures have already shown considerable promise with expectations for more improvements in material quality and reproducibility in the near future. In particular, the feasibility of the exfoliation/transfer/sampling technique including doping techniques in vdW heterostructures was demonstrated [11–19]. Recently, we proposed and evaluated the IR detectors using the vdW heterostructures with the GLs clad by the widegap barrier layers—GL infrared photodetectors (GLIPs) [20, 21]. The GLs serve as photosensitive elements, in which electron-hole pairs are generated due to the interband absorption of IR radiation. The photogenerated electrons tunnel from the GLs through the barrier top to the continuum states in the barrier layers and support the terminal current. The photogenerated holes, which are confined in the GLs, form the space charge. The space charge is determined by the balance of the photogeneration and capture of the electrons propagating above the barriers. Figures 50.1 and 50.2 show the GLIP schematic view and the fragment of the device band diagram with the indicated main electron processes (the photoexcitation and the tunneling from and capture into the GLs). The space charge affects the electric field at the device emitter and, therefore, controls the injected electron current. In the devices based on the heterostructures with a low efficiency of the electron capture into the GLs, the injected current can markedly exceed the current created by the photoexcited electrons. This provides a relatively high photoelectric gain and detector responsivity. The rates of the escape of the photoexcited and thermalized electrons from the GLs and the capture of the electrons propagating across the barrier layers strongly depend of the potential profile near the GLs. The doping of the barrier layers, in particular, the selective doping using the delta layers of donors and acceptors as shown in Figs. 50.1 and 50.2 (which is called the “dipole” doping [22]) can markedly modify this profile resulting in the appearance of the “tooth” adjacent to each inner GL at the donor sheet side. The barrier doping was also effectively used in the unitravelling-carrier (UTC) photodiodes to reinforce the injection of the electrons photogenerated in the emitter of these devices [23]. The doping of the GLs can also lead to shift of the Fermi level in the GLs with respect to the Dirac level. The latter affects the spectrum of the electron photoexcitation, the escape rate of the thermalized electrons, and the capture processes.
Thermoelectric transport in graphene and 2D layered materials
Published in Nanoscale and Microscale Thermophysical Engineering, 2019
Finally, we discussed 2DLMs for thermionic applications. These materials are made out of dissimilar 2D atomic layers stacked on top of each other to form van der Waals heterostructure. In general, thermal conductivity of these materials is very low, while electrical transport in the out-of-plane direction is ballistic. Therefore, theoretically, they are promising candidates for solid-state thermionic applications. There are several theoretical works at different levels of accuracy that all point out to the promise of 2DLMs for thermionic applications. However, there has not been any successful experimental demonstration of high performance solid-state thermionic power generators. The biggest challenge is the fabrication of these small devices with proper metal contacts. Engineering of the interfaces to be clean and oxygen free for the purpose of good electronic transport with minimum thermal conductance is not an easy task. If successful, theoretical figure of merits as large as 3 are predicted for these structures.
Recent progress in neuromorphic and memory devices based on graphdiyne
Published in Science and Technology of Advanced Materials, 2023
Zhi-Cheng Zhang, Xu-Dong Chen, Tong-Bu Lu
Two-dimensional (2D) materials have attracted numerous attentions due to their unique properties, which provide promising candidates for the development of neuromorphic devices. The atomic thickness and atomically sharp interface without surface dangling bonds facilitate the stacking of arbitrary 2D materials to construct van der Waals heterostructures with rich properties [15]. Up to now, the preparation techniques of wafer-scale 2D materials, for example, graphene [62,63], hexagonal boron nitride (hBN) [64], and MoS2 [65], are gradually mature, and 2D materials also have great compatibility with mainstream silicon-based complementary metal-oxide-semiconductor (CMOS) technologies [66], facilitating the fabrication of large-scale integrated circuits based on 2D materials. Graphdiyne (GDY), an emerging two-dimensional (2D) carbon allotrope material, has fascinating physical and chemical properties due to its highly π-conjugated structure and abundant electrons [67–72], demonstrating extensive potential applications in catalysis [73–84], biomedicine [85–91], energy storage [92–94], etc. In addition, GDY has a layer-dependent natural band gap and theoretically highly carrier mobility [95–98], and thus its applications in electronic and optoelectronic devices have attracted tremendous attentions. With the recent breakthroughs in the synthesis of large-area and high-quality GDY ultrathin films [99–102], a variety of GDY-based novel devices have been developed in recent years, such as artificial synapses [103–106], memories [100,107–109], memristors [110,111] and photodetectors [112–114]. In these devices, GDY always acts as a key functional layer that absorbs light and traps charge carriers, which is crucial for device performance. These results demonstrate that GDY holds considerable promise for advancing the next-generation high-speed low-energy electronic/optoelectronic devices.