Correction: Interlayer exciton emission in a MoS2/VOPc inorganic/organic van der Waals heterostructure.

Correction for 'Interlayer exciton emission in a MoS2/VOPc inorganic/organic van der Waals heterostructure' by Yuhan Kong et al., Mater. Horiz., 2022, DOI: 10.1039/d1mh01622a.

Interlayer exciton emission in a MoS2/VOPc inorganic/organic van der Waals heterostructure.

Heterostructures built from two-dimensional (2D) materials and organic semiconductors offer a unique platform for addressing many fundamental physics and construction of functional devices by taking advantage of both the 2D materials and organic semiconductors. We report interlayer exciton emission in the near infrared range around 1.54 eV (∼805 nm) from the heterostructure of pyramidal VOPc (p-type) and transition metal dichalcogenide monolayer MoS2 (VOPc/MoS2). This contrasts the observation of photoluminescence (PL) from the SnCl2Pc/MoS2 heterostructure despite both being type-II heterostructures. We attribute the exciton emission to the carrier transition from the generated interface mid-gap states of VOPc to the ground states of MoS2 in the heterostructure system as predicted from density functional theory (DFT) calculations. Furthermore, the observed PL signal of the VOPc/MoS2 heterostructure shows blue shift, while the PL peak of the SnCl2Pc/MoS2 heterostructure shows red shift. Our finding opens up a new avenue to tune the optoelectronic properties of the van der Waals heterojunctions consisting of 2D materials and organic semiconductors for optoelectronic applications.

Electronic properties of polymorphic two-dimensional layered chromium disulphide.

Two-dimensional (2D) Cr-based layered and non-layered materials such as CrI3, Cr2Ge2Te6, Cr2S3, CrSe, and CrOX (X = Cl and Br) have attracted considerable attention due to their potential application in spintronics. Despite few experimental studies, theoretical studies reported that 2D chromium dichalcogenide (CrS2) materials show unique properties such as valley polarization, piezoelectric coupling, and phase dependent intrinsic magnetic properties. Here, we report for the first time the synthesis of 2D layered CrS2 flakes down to the monolayer via the chemical vapor deposition (CVD) method, its phase structures and electronic properties. We observed the 2H, 1T, and 1T' phases coexisting in CVD grown monolayer CrS2. The formation of 1T' phases from 1T phases is described by dimerization of metal atoms at room temperature according to our molecular dynamics studies. The coexistence of 1T and 1T' phases with 2H phases is referred to as the 1T and 1T' puddling phenomenon. We theoretically showed that the monolayer 2H-CrS2 is a direct bandgap semiconductor with a gap of approximately 0.95 eV predicted by the PBE functional, while the 1T- and 1T'-CrS2 are metallic and semi-metallic with approximately 10 meV gap, respectively. Furthermore, 2H CrS2 exhibits nonmagnetic semiconducting properties while for ferromagnetic spin configuration, the 1T and 1T' CrS2 show magnetic characteristics with 0.531µB and 2.206µB magnetic moment per Cr atom respectively, for ferromagnetic spin configuration as predicted from DFT+U calculation. Importantly, CrS2-based field-effect transistors exhibit a p-type behavior. Our study would stimulate further exploration of 2D layered CrS2 with astonishing properties and open up a whole new avenue for the urgent need for developing multifunctional 2D materials for nanoelectronics, valleytronics, and spintronics.

Tunable photoluminescence in a van der Waals heterojunction built from a MoS2 monolayer and a PTCDA organic semiconductor.

We report the photoluminescence (PL) characteristics of a van der Waals (vdW) heterojunction constructed by simply depositing an organic semiconductor of 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) onto a two-dimensional MoS2 monolayer. The crystallinity of PTCDA on MoS2 is significantly improved due to the vdW epitaxial growth. We observe an enhanced PL intensity and PL peak shift of the MoS2/PTCDA heterojunction compared with the solo MoS2 and PTCDA layer. The synergistic PL characteristics are believed to originate from the hybridization interaction between the MoS2 and the PTCDA as evidenced by density functional theory calculations and Raman measurements. The hybridization interfacial interaction is found to be greatly influenced by the crystalline ordering of the PTCDA film on the 2D MoS2. Our study opens up a new avenue to tune the PL of vdW heterojunctions consisting of TMDs and organic semiconductors for optoelectronic applications.

A review of theoretical study of graphene chemical vapor deposition synthesis on metals: nucleation, growth, and the role of hydrogen and oxygen.

Graphene has attracted intense research interest due to its extraordinary properties and great application potential. Various methods have been proposed for the synthesis of graphene, among which chemical vapor deposition has drawn a great deal of attention for synthesizing large-area and high-quality graphene. Theoretical understanding of the synthesis mechanism is crucial for optimizing the experimental design for desired graphene production. In this review, we discuss the three fundamental steps of graphene synthesis in details, i.e. (1) decomposition of carbon feedstocks and formation of various active carbon species, (2) nucleation, and (3) attachment and extension. We provide a complete scenario of graphene synthesis on metal surfaces at atomistic level by means of density functional theory, molecular dynamics (MD), Monte Carlo (MC) and their combination and interface with other simulation methods such as quantum mechanical molecular dynamics, density functional tight binding molecular dynamics, and combination of MD and MC. We also address the latest investigation of the influences of the hydrogen and oxygen on the synthesis and the quality of the synthesized graphene.