Out-of-plane polarization induces a picosecond photoresponse in rhombohedral stacked bilayer WSe₂

• Guixian Liu,
• Yufan Wang,
• Zhoujuan Xu,
• Zhouxiaosong Zeng,
• Lanyu Huang,
• Cuihuan Ge and
• Xiao Wang

Beilstein J. Nanotechnol. 2024, 15, 1362–1368, doi:10.3762/bjnano.15.109

• spontaneous polarization on ultrafast carrier dynamics in rhombohedral stacked bilayer WSe2. Using precise stacking techniques, a 3R WSe2-based vertical heterojunction was successfully constructed and confirmed by polarization-resolved second harmonic generation measurements. Through output characteristics

• and the scanning photocurrent map under zero bias, we reveal a non-zero short-circuit current in the graphene/3R WSe2/graphene heterojunction region, demonstrating the bulk photovoltaic effect. Furthermore, the out-of-plane polarization enables the 3R WSe2 heterojunction region to achieve an ultrafast

• photodetectors. Keywords: broken inversion symmetry; out-of-plane polarization; picosecond photoresponse; time-resolved photocurrent measurement (TRPC); WSe2; Introduction Two-dimensional (2D) van der Waals (vdW) ferroelectrics with dangling-bond-free surfaces exhibit ferroelectricity by effectively resisting

Quantum-to-classical modeling of monolayer Ge₂Se₂ and its application in photovoltaic devices

• Anup Shrivastava,
• Shivani Saini,
• Dolly Kumari,
• Sanjai Singh and
• Jost Adam

Beilstein J. Nanotechnol. 2024, 15, 1153–1169, doi:10.3762/bjnano.15.94

• extensive applications in photodevices. This is mainly because of the exceptional optoelectronic behavior of the TMDCs, especially the layer-dependent bandgap and the high absorption of incident sunlight [22][23][24][25]. Motivated by this, various TMDCs, including MoS2, WS2, WSe2, and TiS2, have been used

Classification and application of metal-based nanoantioxidants in medicine and healthcare

• Nguyen Nhat Nam,
• Nguyen Khoi Song Tran,
• Tan Tai Nguyen,
• Nguyen Ngoc Trai,
• Nguyen Phuong Thuy,
• Hoang Dang Khoa Do,
• Nhu Hoa Thi Tran and
• Kieu The Loan Trinh

Beilstein J. Nanotechnol. 2024, 15, 396–415, doi:10.3762/bjnano.15.36

• Co-doped Fe3O4 nanozymes [108], WS2, MoSe2, WSe2 nanosheets [109], carbogenic nanozymes [110], and Pt/CeO2 nanozymes [111][112] also showed excellent RNS scavenging capability. Table 2 gives an overview of experiments using antioxidant nanomaterials for the treatment of oxidative stress-related

Revealing local structural properties of an atomically thin MoSe₂ surface using optical microscopy

• Lin Pan,
• Peng Miao,
• Anke Horneber,
• Alfred J. Meixner,
• Pierre-Michel Adam and
• Dai Zhang

Beilstein J. Nanotechnol. 2022, 13, 572–581, doi:10.3762/bjnano.13.49

• , in the AFM image in Figure 2c, one can clearly see the presence of particle aggregates, which were reported to be oxidation products (MoOxSey or MoO3) either through the CVD growth process or through aging in air. Sahoo et al. have reported that the aging of WSe2 flakes by exposure to air produces

Theoretical understanding of electronic and mechanical properties of 1T′ transition metal dichalcogenide crystals

• Seyedeh Alieh Kazemi,
• Sadegh Imani Yengejeh,
• Vei Wang,
• William Wen and
• Yun Wang

Beilstein J. Nanotechnol. 2022, 13, 160–171, doi:10.3762/bjnano.13.11

• comparatively weak van der Waals (vdW) interactions [7]. The most extensively studied TMDs, including MoS2, MoSe2, WS2, and WSe2, can display different structural polytypes (e.g., 2H, 3R, 1T, and 1T′) [8]. Previous studies have revealed that the structures significantly affected the properties and physical

• . For instance, the 1T′ WSe2 nanosheets exhibit metallic nature demonstrated by an enhanced electrostatic activity for hydrogen evolution reaction (HER) as compared to other nanosheets [9]. In addition, 1T′ WSe2 nanosheets can be produced in high yield and in a reproducible and controlled manner, which

• ability to predict the mechanical characteristics of 1T′ TMD materials [33]. In this comparative study, the electronic and mechanical properties including shear modulus (G), bulk modulus (B), Young’s modulus (Y), Poisson’s ratio (ν), and microhardness (H), of MoS2, MoSe2, WS2, and WSe2 crystals with the

A review of defect engineering, ion implantation, and nanofabrication using the helium ion microscope

• Frances I. Allen

Beilstein J. Nanotechnol. 2021, 12, 633–664, doi:10.3762/bjnano.12.52

• study, field-effect transistors based on monolayer MoS2 were irradiated with helium ions over the transistor channel and the effect of varying the size and position of the irradiated area on the electrical performance of the device was characterized [28]. Complimentary work on few-layer WSe2 by Stanford

• irradiating just one side of a portion of WSe2 bridging two metal contacts to create semiconducting (pristine) and insulating (irradiated) halves contacted by the source and drain electrodes (Figure 2b). Direct-write of further logic circuits into single flakes of WSe2 and WS2 has also been demonstrated [26

• , irradiation-induced changes in the optical response of this class of materials has also been investigated using the HIM. This was first performed for few-layer WSe2 [29] and monolayer MoSe2 [30] (for the latter, changes in nanomechanical properties were also probed). In subsequent work on monolayer MoS2 by

Effect of localized helium ion irradiation on the performance of synthetic monolayer MoS₂ field-effect transistors

• Jakub Jadwiszczak,
• Pierce Maguire,
• Conor P. Cullen,
• Georg S. Duesberg and
• Hongzhou Zhang

Beilstein J. Nanotechnol. 2020, 11, 1329–1335, doi:10.3762/bjnano.11.117

• exploration of nanometer-scale structural modifications of TMD devices [6][7][8]. The localized formation of defects by focused ion beam irradiation has been shown to induce unusual electronic properties in monolayer TMDs, such as pseudo-metallic phase transitions in MoS2 and WSe2 [9][10], resistive switching

• in MoS2 [11], as well as enhanced out-of-plane charge transfer in 2D graphene/WSe2 heterostructures [12]. Energetic light ions are known to preferentially sputter chalcogen atoms from TMDs while retaining an adequate micrometer-scale structural integrity for irradiation doses up to approx. 1016 ions

Light–matter interactions in two-dimensional layered WSe₂ for gauging evolution of phonon dynamics

• Avra S. Bandyopadhyay,
• Chandan Biswas and
• Anupama B. Kaul

Beilstein J. Nanotechnol. 2020, 11, 782–797, doi:10.3762/bjnano.11.63

• of Electrical and Computer Engineering, University of Texas, El Paso, TX 79968, United States 10.3762/bjnano.11.63 Abstract Phonon dynamics is explored in mechanically exfoliated two-dimensional WSe2 using temperature-dependent and laser-power-dependent Raman and photoluminescence (PL) spectroscopy

• . From this analysis, phonon lifetime in the Raman active modes and phonon concentration, as correlated to the energy parameter E0, were calculated as a function of the laser power, P, and substrate temperature, T. For monolayer WSe2, from the power dependence it was determined that the phonon lifetime

• oscillator model to explain the damping mechanism in WSe2. From this it was determined that the damping coefficient increases with the number of layers. The work reported here sheds fundamental insights into the evolution of phonon dynamics in WSe2 and should help pave the way for designing high-performance

Hexagonal boron nitride: a review of the emerging material platform for single-photon sources and the spin–photon interface

• Stefania Castelletto,
• Faraz A. Inam,
• Shin-ichiro Sato and
• Alberto Boretti

Beilstein J. Nanotechnol. 2020, 11, 740–769, doi:10.3762/bjnano.11.61

• (TMD) materials, such as WSe2 and WS2 [38][39][40][41], hexagonal boron nitride (h-BN) [42][43][44][45][46][47] and WO3 [48]. A summary of quantum point defects identified in various emerging materials is provided in Table 1 for a quick comparison. Details of h-BN are then discussed in the specific

Exfoliation in a low boiling point solvent and electrochemical applications of MoO₃

• Matangi Sricharan,
• Bikesh Gupta,
• Sreejesh Moolayadukkam and
• H. S. S. Ramakrishna Matte

Beilstein J. Nanotechnol. 2020, 11, 662–670, doi:10.3762/bjnano.11.52

• researchers to look into other layered materials, such as metal dichalcogenides (MoS2, WS2, WSe2), hexagonal boron nitride (h-BN), layered double hydroxides, metal hydroxides (Ni(OH)2, Co(OH)2), metal oxides (MoO3, WO3) and phyllosilicates, for various applications in different fields [2][3][4][5]. Among the

First principles modeling of pure black phosphorus devices under pressure

• Ximing Rong,
• Zhizhou Yu,
• Zewen Wu,
• Junjun Li,
• Bin Wang and
• Yin Wang

Beilstein J. Nanotechnol. 2019, 10, 1943–1951, doi:10.3762/bjnano.10.190

• the magnitude and the orientation of the applied strain due to the strong anisotropic atomic structure of BP. Based on first principles calculations, Koda et al. studied the electric behavior of BP-MoSe2 and BP-WSe2 heterobilayers, and analyzed the effect of long-range structural bending on the

Tungsten disulfide-based nanocomposites for photothermal therapy

• Tzuriel Levin,
• Hagit Sade,
• Rina Ben-Shabbat Binyamini,
• Maayan Pour,
• Iftach Nachman and
• Jean-Paul Lellouche

Beilstein J. Nanotechnol. 2019, 10, 811–822, doi:10.3762/bjnano.10.81

• [19], or dermal application [20]. More recent studies conducted on rhenium-doped MoS2 nanoparticles showed no acute toxic risk, neither by oral administration nor by dermal application [21][22]. A few years ago, Teo et al. compared the cytotoxicity of exfoliated MoS2, WS2, and WSe2 to that of their

Temperature-dependent Raman spectroscopy and sensor applications of PtSe₂ nanosheets synthesized by wet chemistry

• Mahendra S. Pawar and
• Dattatray J. Late

Beilstein J. Nanotechnol. 2019, 10, 467–474, doi:10.3762/bjnano.10.46

• found to be −0.014 and −0.008, respectively. The nature of the temperature dependence of the Raman spectra of PtSe2 nanosheets is found to be similar in nature to that of graphene and other 2D materials such as MoS2, WS2, MoSe2, WSe2, BP, TiS3, multilayer graphene, and MoTe2 [29][31][32][33][34]. A

Valley-selective directional emission from a transition-metal dichalcogenide monolayer mediated by a plasmonic nanoantenna

• Haitao Chen,
• Mingkai Liu,
• Lei Xu and
• Dragomir N. Neshev

Beilstein J. Nanotechnol. 2018, 9, 780–788, doi:10.3762/bjnano.9.71

• WSe2 as a chiral point-dipole emitter, we demonstrate numerically that the emission from different valleys is directed into opposite directions when coupling to a double-bar plasmonic nanoantenna. The directionality derives from the interference between the dipole and quadrupole modes excited in the

• dipole and quadrupole will have a phase difference of π/2. Note that we have fine-tuned the geometry of the antennas in order to have them resonate around 715 nm, which matches the experimentally measured emission wavelength of monolayer WSe2. The parameters of the two bars are also optimized such that

• , such as WSe2 in its entire emission range. Thus, the simple nanoantenna we propose here could effectively enhance the emission intensity and simultaneously tune the valley-based emission directionality from the TMDCs. As discussed, the modes excited in the plasmonic nanoantenna depend on the position

Ab initio study of adsorption and diffusion of lithium on transition metal dichalcogenide monolayers

• Xiaoli Sun and
• Zhiguo Wang

Beilstein J. Nanotechnol. 2017, 8, 2711–2718, doi:10.3762/bjnano.8.270

• 2H-WSe2, which have large bandgaps of 1.66 and 1.96 eV, respectively. The diffusion energy barrier is in the range between 0.17 and 0.64 eV for lithium on MX2 monolayers, while for most of the materials it was found to be around 0.25 eV. Therefore, this work illustrated that most of the MX2

• ]. The 2H phase is the stable structure for MoS2, MoSe2, WS2 and WSe2 monolayers, which has also been predicted by other simulations [36][37][38][39][40]. 1T'-VTe2, 1T'-MoTe2 and 1T'-WTe2 are the energetically favourable phases. It is also can be seen from Table 1 that 1T'-MoTe2 is 0.06 eV/f.u. more

• monolayers is shown in Figure 4. The adsorption energy has positive values for Li adsorbed on 2H-WS2 and 2H-WSe2, which indicates that Li cannot be adsorbed on these two compounds and they are not ideal anodes for LIBs. The other compounds have negative values of adsorption energy. The adsorption energy of

Intercalation of Si between MoS₂ layers

• Rik van Bremen,
• Qirong Yao,
• Soumya Banerjee,
• Deniz Cakir,
• Nuri Oncel and
• Harold J. W. Zandvliet

Beilstein J. Nanotechnol. 2017, 8, 1952–1960, doi:10.3762/bjnano.8.196

• are dealing with the same material, i.e., MoS2. Both these points provide compelling evidence that the deposited Si intercalates between the MoS2 layers. For a comparable system, namely Si on WSe2, we recently arrived at a similar conclusion [45]. XPS measurements have been performed to obtain insight

Orientation of FePt nanoparticles on top of a-SiO₂/Si(001), MgO(001) and sapphire(0001): effect of thermal treatments and influence of substrate and particle size

• Martin Schilling,
• Paul Ziemann,
• Zaoli Zhang,
• Johannes Biskupek,
• Ute Kaiser and
• Ulf Wiedwald

Beilstein J. Nanotechnol. 2016, 7, 591–604, doi:10.3762/bjnano.7.52

• diffusion [22]. On WSe2(0001) supports, epitaxial FePt nanostructures were grown epitaxially with three possible azimuthal orientations [23]. FePt NPs have been prepared by different approaches mainly using colloidal chemistry [5][24], gas-phase preparation techniques [25][26], or thin films of few