Article
Optics
Susobhan Das, Yadong Wang, Yunyun Dai, Shisheng Li, Zhipei Sun
Summary: This study reports the ultrafast transient absorption of monolayer molybdenum disulfide in its sub-bandgap region, revealing significant absorbance enhancement below the bandgap. The different rise times at different wavelengths indicate various contributions of carrier states, providing insights into optical properties and carrier dynamics for potential photonic and optoelectronic applications beyond intrinsic bandgap limitations.
LIGHT-SCIENCE & APPLICATIONS
(2021)
Article
Nanoscience & Nanotechnology
Lang Zhu, Zongpeng Song, Ran Li, Haiou Zhu
Summary: TMDs based heterostructures, which can achieve rapid and effective carrier separation and ultra-long interlayer exciton lifetime, have potential applications in photoelectric devices. However, current studies mainly focus on the transfer process of photo-generated carriers across the interface and the lifetime of interlayer exciton, neglecting the dynamics of hot carriers.
Article
Chemistry, Physical
Fabio Caruso
Summary: The coupled nonequilibrium dynamics of electrons and phonons in monolayer MoS2 are studied, with strict phase-space constraints in electron-phonon scattering significantly influencing the decay path of excited electrons and holes. The momentum selectivity in phonon emission results in highly anisotropic population of phonons in reciprocal space, persisting for up to 10 ps until thermal equilibrium is restored by phonon-phonon scattering. Achieving control of the nonequilibrium dynamics of the lattice may offer unexplored opportunities to selectively enhance the phonon population of two-dimensional crystals and tailor electron-phonon interactions over subpicosecond time scales.
JOURNAL OF PHYSICAL CHEMISTRY LETTERS
(2021)
Article
Multidisciplinary Sciences
Wenyu Zhao, Sihan Zhao, Hongyuan Li, Sheng Wang, Shaoxin Wang, M. Iqbal Bakti Utama, Salman Kahn, Yue Jiang, Xiao Xiao, SeokJae Yoo, Kenji Watanabe, Takashi Taniguchi, Alex Zettl, Feng Wang
Summary: The study demonstrates the direct observation of the plasmonic Doppler effect in biased monolayer graphene, showing a non-reciprocal plasmon propagation due to fast drifting Dirac electron medium hosting the plasmon polariton. Cryogenic near-field infrared nanoscopy was used to measure the Doppler-shifted plasmon wavelength, showing a significant difference between plasmons moving with and against the drifting electron media. These findings open up opportunities for electrical control of non-reciprocal surface plasmon polaritons in non-equilibrium systems.
Article
Chemistry, Physical
Ashish Soni, Dushyant Kushavah, Li-Syuan Lu, Wen-Hao Chang, Suman Kalyan Pal
Summary: Utilizing the excess energy from photoexcitation to improve the efficiency of next-generation light-harvesting devices is possible. Multiple exciton generation (MEG) in semiconducting materials can break the conversion efficiency limit of photovoltaic devices. Monolayer transition metal dichalcogenides (TMDs) have high absorption coefficients and show efficient MEGs with low threshold energy and high (86%) efficiency in MoS2. The results suggest that van der Waals layered materials could be a potential candidate for flexible and efficient next-generation solar cells and photodetectors.
JOURNAL OF PHYSICAL CHEMISTRY LETTERS
(2023)
Article
Chemistry, Multidisciplinary
Jin Yang, Shaolong Jiang, Jiafeng Xie, Huachao Jiang, Shujuan Xu, Kai Zhang, Yuping Shi, Yanfeng Zhang, Zhi Zeng, Guangyou Fang, Tianwu Wang, Fuhai Su
Summary: By fabricating large-scale vertically stacked heterostructures with MoS2 and ReSe2 monolayers, this study thoroughly investigated carrier dynamics using various ultrafast spectroscopies, revealing charge separation and transport processes at different stages. The results provide insights into photocarrier dynamics and may aid in developing optoelectronic devices based on ReSe2-MoS2 heterostructures.
Article
Chemistry, Physical
Wenyan Wang, Ning Sui, Xiaochun Chi, Zhihui Kang, Qiang Zhou, Li Li, Hanzhuang Zhang, Jianbo Gao, Yinghui Wang
Summary: The hot carrier cooling dynamics in monolayer MoS2 C-excitonic state is affected by the hot phonon bottleneck and Auger heating effects, and can be prolonged by increasing the excitation photon energy or absorbed photon flux. The combination of these effects weakens the hot phonon bottleneck and extends the hot carrier lifetime, which has implications for various applications in advanced energy conversion and quantum technology.
JOURNAL OF PHYSICAL CHEMISTRY LETTERS
(2021)
Article
Chemistry, Multidisciplinary
Rongjie Zhang, Yongjue Lai, Wenjun Chen, Changjiu Teng, Yujie Sun, Liusi Yang, Jingyun Wang, Bilu Liu, Hui-Ming Cheng
Summary: The use of wrinkles in monolayer 2D semiconductors as controllable carrier trapping centers enables multilevel storage capability, high on/off ratios, and long retention times in memory devices. The study also reveals a wrinkle-based carrier trapping mechanism, offering a new approach for controlling carriers in ultra-thin memory devices and for in-memory calculations.
Article
Materials Science, Multidisciplinary
Hong Liu, Anny Pau, Dmitry K. Efimkin
Summary: Transition metal dichalcogenides have a diverse exciton landscape, with both bright and dark states. The dark excitons in MoS2, referred to as hybrid excitons, consist of a Dirac electron and a Schrodinger hole. The chiral nature of the Dirac electron introduces asymmetry and generates an additional Berry curvature contribution in hybrid excitons, which is substrate dependent and significant in suspended samples.
Article
Engineering, Electrical & Electronic
Weifeng Jin
Summary: In recent years, the high electric field transport characteristics in monolayer/few-layer MoS2 FETs have been a focus of research. However, there is a lack of comprehensive reviews on this topic. In this article, the recent advancements in numerical simulation and experimental investigation of high electric field transport in monolayer/few-layer MoS2 FETs are analyzed. Promising research directions to improve the characteristics are discussed, and important parasitic effects, such as self-heating, are briefly introduced. This article provides valuable guidance for future design of high-performance monolayer/few-layer MoS2 FETs.
IEEE TRANSACTIONS ON ELECTRON DEVICES
(2023)
Article
Physics, Condensed Matter
Durga Prasad Khatua, Asha Singh, Sabina Gurung, Salahuddin Khan, Manushree Tanwar, Rajesh Kumar, J. Jayabalan
Summary: This article presents a comprehensive study on the charge carrier dynamics of a monolayer MoS2 flake using the transient transmission technique. The dissociation and formation of excitons and their impact on the optical response are investigated.
JOURNAL OF PHYSICS-CONDENSED MATTER
(2022)
Article
Optics
Wenyan Wang, Ning Sui, Zhihui Kang, Qiang Zhou, Li Li, Xiaochun Chi, Hanzhuang Zhang, Xing He, Bing Zhao, Yinghui Wang
Summary: This study investigates the hot carrier dynamics in the C excitonic state of monolayer WS2 using transient absorption spectroscopy. The hot carrier cooling lifetime increases with the absorbed photon flux, exhibiting a distinct spectral feature compared to normal carriers. The results provide insights into the behavior of hot carriers in 2D TMDCs and offer guidance for designing high-performance TMDC-based electronic devices.
Article
Multidisciplinary Sciences
Amritanand Sebastian, Rahul Pendurthi, Tanushree H. Choudhury, Joan M. Redwing, Saptarshi Das
Summary: The study benchmarks device-to-device variation in FETs based on MoS2 and WS2, showing consistent performance and record high carrier mobility in WS2 FETs.
NATURE COMMUNICATIONS
(2021)
Article
Physics, Applied
Yuanzheng Li, Xianxin Wu, Weizhen Liu, Haiyang Xu, Xinfeng Liu
Summary: The study reveals that in monolayer WS2, band edge A-excitons can effectively generate high-energy C-excitons through a many-body process, and the relaxation of hot carriers from C-excitons to band edge states can compensate for and slow the decay of A-excitons. This comprehensive understanding of the interrelation between C-exciton and A-exciton dynamics in monolayer TMDs may lead to potential applications for future TMD-based light-harvesting devices.
APPLIED PHYSICS LETTERS
(2021)
Article
Chemistry, Physical
Meizhen Jiang, Zhen Wu, Qing Yang, Yuanyuan Zhang, Yumeng Men, Tianqing Jia, Zhenrong Sun, Donghai Feng
Summary: Compared with itinerant electrons, localized electrons in monolayer transition-metal dichalcogenides exhibit longer spin relaxation times and coherent spin precession in transverse magnetic fields. In this study, the intrinsic spin dephasing processes of localized electrons are uncovered in monolayer MoS2. Four subensembles of localized electrons with different g-factor values and inhomogeneous broadening are found. The spin dephasing rates of these subensembles are influenced by factors such as g-factor inhomogeneity, electron-nuclear hyperfine interaction, and anisotropic exchange interaction.
JOURNAL OF PHYSICAL CHEMISTRY LETTERS
(2022)
Article
Chemistry, Multidisciplinary
Timothy D. Brown, Stephanie M. Bohaichuk, Mahnaz Islam, Suhas Kumar, Eric Pop, R. Stanley Williams
Summary: This study presents a model of VO2/SiN Mott threshold switches constructed using the principle of local activity. The model is refined to measurable material properties by considering a minimal set of quasistatic and dynamic electrical and thermal data. It accurately predicts electrical and thermal conductivities and capacitances, as well as locally active dynamics.
ADVANCED MATERIALS
(2023)
Article
Chemistry, Multidisciplinary
Asir Intisar Khan, Heshan Yu, Huairuo Zhang, John R. Goggin, Heungdong Kwon, Xiangjin Wu, Christopher Perez, Kathryn M. Neilson, Mehdi Asheghi, Kenneth E. Goodson, Patrick M. Vora, Albert Davydov, Ichiro Takeuchi, Eric Pop
Summary: Phase-change memory (PCM) is a promising candidate for data-intensive artificial intelligence applications, and achieving simultaneous attributes such as resistance changes and low resistance drift remains a challenge. In this study, nanoscale PCM devices based on a new phase-change nanocomposite material (Ge4Sb6Te7) demonstrated bi-directional gradual resistance changes with a large resistance window using low energy pulses. These devices showed multiple resistance levels with low resistance drift, high on/off ratio, and low variability, enabled by the unique properties of Ge4Sb6Te7. These findings advance the development of energy-efficient analog computing using PCM.
ADVANCED MATERIALS
(2023)
Article
Engineering, Electrical & Electronic
Cagil Koroglu, Eric Pop
Summary: As physical transistor scaling nears its limits and memory bandwidth becomes a bottleneck for many applications, three-dimensional (3D) integration offers a promising solution to continue Moore's law. Effective thermal management is essential to maximize the performance benefits of 3D integrated circuits (ICs), and using high thermal conductivity insulators like AlN and hBN can significantly reduce thermal resistance and overcome thermal challenges. In addition, highly anisotropic insulators such as hBN can be utilized as heat spreaders in memory-on-logic architectures to keep both memory and logic dies cool.
IEEE ELECTRON DEVICE LETTERS
(2023)
Article
Multidisciplinary Sciences
Weisheng Li, Xiaoshu Gong, Zhihao Yu, Liang Ma, Wenjie Sun, Si Gao, Cagil Koroglu, Wenfeng Wang, Lei Liu, Taotao Li, Hongkai Ning, Dongxu Fan, Yifei Xu, Xuecou Tu, Tao Xu, Litao Sun, Wenhui Wang, Junpeng Lu, Zhenhua Ni, Jia Li, Xidong Duan, Peng Wang, Yuefeng Nie, Hao Qiu, Yi Shi, Eric Pop, Jinlan Wang, Xinran Wang
Summary: By hybridizing with semi-metallic antimony (0112) through strong van der Waals interactions, the electrical contact of monolayer molybdenum disulfide is improved, meeting the requirements for the development of next-generation electronics.
Article
Engineering, Electrical & Electronic
Emanuel Ber, Ryan W. Grady, Eric Pop, Eilam Yalon
Summary: This article explores the issue of contact resistance in atomically thin 2-D semiconductors, which hinders the integration of these materials into mainstream technology. The resistance is found to be influenced by the height and width of the Schottky barrier, as well as the number of transport modes for carrier injection. To reduce the contact resistance, a large number of transport modes can be achieved by increasing the number of channel carriers through heavy doping or gating.
IEEE TRANSACTIONS ON ELECTRON DEVICES
(2023)
Article
Chemistry, Multidisciplinary
Victoria Chen, Hye Ryoung Lee, Cagil Koroglu, Connor J. McClellan, Alwin Daus, Eric Pop
Summary: In this study, we characterized the electrical and thermoelectric properties of layered WSe2 with thicknesses ranging from 10 to 96 nm at temperatures between 300 and 400 K. By electrostatically gating the devices with an ion gel, we were able to investigate both electron and hole behavior over a wide range of carrier densities. The highest n- and p-type Seebeck coefficients for thin-film WSe2 at room temperature, -500 and 950 μV/K respectively, were obtained in this study. We also highlighted the significance of low substrate thermal conductivity for lateral thermoelectric measurements, which improves the platform for future studies on other nanomaterials.
Article
Chemistry, Multidisciplinary
Jie Zhao, Asir Intisar Khan, Mikhail Y. Efremov, Zichao Ye, Xiangjin Wu, Kangsik Kim, Zonghoon Lee, H. -S. Philip Wong, Eric Pop, Leslie H. Allen
Summary: The phase transition of Sb2Te3/Ge2Sb2Te5 superlattices was studied using nanocalorimetry, providing insights into the thermodynamics of superlattice-based PCM and enabling low-power switching.
Article
Physics, Applied
Stephanie M. Bohaichuk, Suhas Kumar, Mahnaz Islam, Miguel Munoz Rojo, R. Stanley Williams, Gregory Pitner, Jaewoo Jeong, Mahesh G. Samant, Stuart S. P. Parkin, Eric Pop
Summary: Oscillatory devices are important in biomimetic neuronal spiking computing systems, but understanding their time scales is challenging due to the influence of external circuitry. In this study, we demonstrate the challenges using a sub-100-nm VO2 Mott oscillator with a nanogap cut in a metallic carbon nanotube electrode. Despite its nanoscale thermal volume, external parasitics result in orders-of-magnitude slower dynamics. We discuss methods for determining when measurements are dominated by extrinsic factors and the conditions for observing intrinsic oscillation frequencies.
PHYSICAL REVIEW APPLIED
(2023)
Article
Nanoscience & Nanotechnology
Emanuel Ber, Ryan W. Grady, Eric Pop, Eilam Yalon
Summary: Achieving good electrical contacts is a major challenge in devices based on atomically thin 2D semiconductors. This study experimentally examines the classical transmission line model description of contacts to 2D materials and proposes a modification based on an additional lateral resistance component. It finds that the additional lateral resistance component dominates the contact resistance in atomically thin semiconductor devices and is responsible for the back-gate bias and temperature dependence.
ADVANCED ELECTRONIC MATERIALS
(2023)
Article
Nanoscience & Nanotechnology
Il-Kwon Oh, Asir Intisar Khan, Shengjun Qin, Yujin Lee, H. -S. Philip Wong, Eric Pop, Stacey F. Bent
Summary: This study explores the application of area-selective atomic layer deposition (AS-ALD) technique in the fabrication of RRAM devices and finds that AS-ALD can improve the reliability and accuracy of RRAM, regardless of device size. The application of this technique will contribute to the improvement of other data storage technologies.
ACS APPLIED MATERIALS & INTERFACES
(2023)
Article
Optics
Qitong Li, Jung-Hwan Song, Fenghao Xu, Jorik van de Groep, Jiho Hong, Alwin Daus, Yan Joe Lee, Amalya C. Johnson, Eric Pop, Fang Liu, Mark L. Brongersma
Summary: A general pathway to reduce the detrimental impact of dephasing and non-radiative decay processes in quantum devices is illustrated through photonic design of device electrodes. The design enables large Purcell enhancement, convenient electrical gating, and high modulation efficiencies.
Article
Multidisciplinary Sciences
Joel Martis, Sandhya Susarla, Archith Rayabharam, Cong Su, Timothy Paule, Philipp Pelz, Cassandra Huff, Xintong Xu, Hao-Kun Li, Marc Jaikissoon, Victoria Chen, Eric Pop, Krishna Saraswat, Alex Zettl, Narayana R. Aluru, Ramamoorthy Ramesh, Peter Ercius, Arun Majumdar
Summary: Four-dimensional scanning transmission electron microscopy (4D-STEM) was used to determine the electron charge density in monolayer MoS2 by combining center of mass (CoM) images and annular dark field (ADF) images. The contribution of core electrons and valence electrons to the charge density was evaluated, with the core electrons mainly responsible for the spatial modulation and the valence electrons forming a featureless background. This study highlights the importance of probe shape in interpreting charge densities derived from 4D-STEM and suggests the need for smaller electron probes.
NATURE COMMUNICATIONS
(2023)
Article
Nanoscience & Nanotechnology
Aviv Schwarz, Hadas Alon-Yehezkel, Adi Levi, Rajesh Kumar Yadav, Koushik Majhi, Yael Tzuriel, Lauren Hoang, Connor S. Bailey, Thomas Brumme, Andrew J. Mannix, Hagai Cohen, Eilam Yalon, Thomas Heine, Eric Pop, Ori Cheshnovsky, Doron Naveh
Summary: Recent research on 2D transition metal dichalcogenides (TMDCs) has led to important discoveries in fundamental phenomena and device applications. In this study, a two-step treatment with organic molecules was used to heal native defects in CVD-grown WSe2 and WS2. The adsorption of thiols was found to only partially passivate defects, but molecular trimming and release of atomic sulfur significantly improved semiconductor quality. Time-dependent XPS and first-principles calculations were used to characterize defects and their healing.
NPJ 2D MATERIALS AND APPLICATIONS
(2023)
Article
Chemistry, Multidisciplinary
Timm Swoboda, Nicolas Wainstein, Sanchit Deshmukh, Cagil Koroglu, Xing Gao, Mario Lanza, Hans Hilgenkamp, Eric Pop, Eilam Yalon, Miguel Munoz Rojo
Summary: Heat dissipation is a major concern for electronic devices, especially at the nanoscale. Scanning thermal microscopy (SThM) is a versatile tool for measuring device temperature with nanoscale resolution but quantifying thermal features is challenging. This study calibrates a thermo-resistive SThM probe using metal lines of different widths and evaluates its sensitivity under different conditions. The results provide new insights for accurately determining the temperature of scanned devices.
Article
Materials Science, Multidisciplinary
Hon-Loen Sinn, Aravindh Kumar, Eric Pop, Akm Newaz
Summary: Researchers demonstrated a bismuth-1L-MoS2-bismuth device with ohmic electrical contacts and extraordinary optoelectronic properties by suppressing metal-induced gap states (MIGS) at the metal-monolayer MoS2 interface. This overcomes Fermi-level pinning and expands the application range of optoelectronic devices based on 2D transition metal dichalcogenides.
ADVANCED PHOTONICS RESEARCH
(2023)