skip to main content


Title: Autonomous scanning probe microscopy investigations over WS2 and Au{111}
Abstract

Individual atomic defects in 2D materials impact their macroscopic functionality. Correlating the interplay is challenging, however, intelligent hyperspectral scanning tunneling spectroscopy (STS) mapping provides a feasible solution to this technically difficult and time consuming problem. Here, dense spectroscopic volume is collected autonomously via Gaussian process regression, where convolutional neural networks are used in tandem for spectral identification. Acquired data enable defect segmentation, and a workflow is provided for machine-driven decision making during experimentation with capability for user customization. We provide a means towards autonomous experimentation for the benefit of both enhanced reproducibility and user-accessibility. Hyperspectral investigations on WS2sulfur vacancy sites are explored, which is combined with local density of states confirmation on the Au{111} herringbone reconstruction. Chalcogen vacancies, pristine WS2, Au face-centered cubic, and Au hexagonal close-packed regions are examined and detected by machine learning methods to demonstrate the potential of artificial intelligence for hyperspectral STS mapping.

 
more » « less
Award ID(s):
2011839
PAR ID:
10379960
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;
Publisher / Repository:
Nature Publishing Group
Date Published:
Journal Name:
npj Computational Materials
Volume:
8
Issue:
1
ISSN:
2057-3960
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Tunable Fano resonances and plasmon–exciton coupling are demonstrated at room temperature in hybrid systems consisting of single plasmonic nanoparticles deposited on top of the transition metal dichalcogenide monolayers. By using single Au nanotriangles (AuNTs) on monolayer WS2as model systems, Fano resonances are observed from the interference between a discrete exciton band of monolayer WS2and a broadband plasmonic mode of single AuNTs. The Fano lineshape depends on the exciton binding energy and the localized surface plasmon resonance strength, which can be tuned by the dielectric constant of surrounding solvents and AuNT size, respectively. Moreover, a transition from weak to strong plasmon–exciton coupling with Rabi splitting energies of 100–340 meV is observed by rationally changing the surrounding solvents. With their tunable plasmon–exciton interactions, the proposed WS2–AuNT hybrids can open new pathways to develop active nanophotonic devices.

     
    more » « less
  2. Abstract

    The field of photovoltaics is revolutionized in recent years by the development of two–dimensional (2D) type‐II heterostructures. These heterostructures are made up of two different materials with different electronic properties, which allows for the capture of a broader spectrum of solar energy than traditional photovoltaic devices. In this study, the potential of vanadium (V)‐doped WS2is investigated, hereafter labeled V‐WS2, in combination with air‐stable Bi2O2Se for use in high‐performance photovoltaic devices. Various techniques are used to confirm the charge transfer of these heterostructures, including photoluminescence (PL) and Raman spectroscopy, along with Kelvin probe force microscopy (KPFM). The results show that the PL is quenched by 40%, 95%, and 97% for WS2/Bi2O2Se, 0.4 at.% V‐WS2/Bi2O2Se, and 2 at.% V‐WS2/Bi2O2Se, respectively, indicating a superior charge transfer in V‐WS2/Bi2O2Se compared to pristine WS2/Bi2O2Se. The exciton binding energies for WS2/Bi2O2Se, 0.4 at.% V‐WS2/Bi2O2Se and 2 at.% V‐WS2/Bi2O2Se heterostructures are estimated to be ≈130, 100, and 80 meV, respectively, which is much lower than that for monolayer WS2. These findings confirm that by incorporating V‐doped WS2, charge transfer in WS2/Bi2O2Se heterostructures can be tuned, providing a novel light‐harvesting technique for the development of the next generation of photovoltaic devices based on V‐doped transition metal dichalcogenides (TMDCs)/Bi2O2Se.

     
    more » « less
  3. Abstract

    2D materials have been of considerable interest as new materials for device applications. Non‐volatile resistive switching applications of MoS2and WS2have been previously demonstrated; however, these applications are dramatically limited by high temperatures and extended times needed for the large‐area synthesis of 2D materials on crystalline substrates. The experimental results demonstrate a one‐step sulfurization method to synthesize MoS2and WS2at 550 °C in 15 min on sapphire wafers. Furthermore, a large area transfer of the synthesized thin films to SiO2/Si substrates is achieved. Following this, MoS2and WS2memristors are fabricated that exhibit stable non‐volatile switching and a satisfactory large on/off current ratio (103–105) with good uniformity. Tuning the sulfurization parameters (temperature and metal precursor thickness) is found to be a straightforward and effective strategy to improve the performance of the memristors. The demonstration of large‐scale MoS2and WS2memristors with a one‐step low‐temperature sulfurization method with simple strategy to tuning can lead to potential applications such as flexible memory and neuromorphic computing.

     
    more » « less
  4. Wafer-scale synthesis of p-type TMD films is critical for its commercialization in next-generation electro/optoelectronics. In this work, wafer-scale intrinsic n-type WS2films and in situ Nb-doped p-type WS2films were synthesized through atomic layer deposition (ALD) on 8-inchα-Al2O3/Si wafers, 2-inch sapphire, and 1 cm2GaN substrate pieces. The Nb doping concentration was precisely controlled by altering cycle number of Nb precursor and activated by postannealing. WS2n-FETs and Nb-doped p-FETs with different Nb concentrations have been fabricated using CMOS-compatible processes. X-ray photoelectron spectroscopy, Raman spectroscopy, and Hall measurements confirmed the effective substitutional doping with Nb. The on/off ratio and electron mobility of WS2n-FET are as high as 105and 6.85 cm2 V-1 s-1, respectively. In WS2p-FET with 15-cycle Nb doping, the on/off ratio and hole mobility are 10 and 0.016 cm2 V-1 s-1, respectively. The p-n structure based on n- and p- type WS2films was proved with a 104rectifying ratio. The realization of controllablein situNb-doped WS2films paved a way for fabricating wafer-scale complementary WS2FETs.

     
    more » « less
  5. Abstract

    2D dilute magnetic semiconductors have been recently reported in transition metal dichalcogenides doped with spin‐polarized transition metal atoms, for example vanadium‐doped WS2monolayers, which exhibit room‐temperature ferromagnetic ordering. However, a broadband characterization of the electronic band structure of these doped WS2monolayers and its dependence on vanadium concentration is still lacking. Therefore, power‐dependent photoluminescence, resonant four‐wave mixing, and differential reflectance spectroscopies are performed here to study optical transitions close to the A exciton energy of vanadium‐doped WS2monolayers at three different doping levels. Instead of a single A exciton peak, vanadium‐doped samples exhibit two photoluminescence peaks associated with transitions from a donor‐like level and the conduction band minima. Moreover, resonant Raman and second‐harmonic generation experiments reveal a blueshift in the B exciton energy but no energy change in the C exciton after vanadium doping. Density functional theory calculations show that the band structure is sensitive to the HubbardUcorrection for vanadium, and several scenarios are proposed to explain the two photoluminescence peaks around the A exciton energy region. This work provides the first broadband optical characterization of these 2D dilute magnetic semiconductors, shedding light on the novel and tunable electronic features of V‐doped WS2 monolayers.

     
    more » « less