Charge density wave states in phase-engineered monolayer VTe_(2)

Charge density wave(CDW)strongly affects the electronic properties of two-dimensional(2D)materials and can be tuned by phase engineering.Among 2D transitional metal dichalcogenides(TMDs),VTe_(2)was predicted to require small energy for its phase transition and shows unexpected CDW states in its T-phase.However,the CDW state of H-VTe_(2)has been barely reported.Here,we investigate the CDW states in monolayer(ML)H-VTe_(2),induced by phase-engineering from T-phase VTe_(2).The phase transition between T-and H-VTe_(2)is revealed with x-ray photoelectron spectroscopy(XPS)and scanning transmission electron microscopy(STEM)measurements.For H-VTe_(2),scanning tunneling microscope(STM)and low-energy electron diffraction(LEED)results show a robust 2√3×2√3CDW superlattice with a transition temperature above 450 K.Our findings provide a promising way for manipulating the CDWs in 2D materials and show great potential in its application of nanoelectronics.

High quality PdTe_2 thin films grown by molecular beam epitaxy

PdTe2, a member of layered transition metal dichalcogenides （TMDs）, has aroused significant research interest due to the coexistence of superconductivity and type-II Dirac fermions. It provides a promising platform to explore the inter- play between superconducting quasiparticles and Dirac fermions. Moreover, PdTe2 has also been used as a substrate for monolayer antimonene growth. Here in this paper, we report the epitaxial growth of high quality PdTe2 films on bilayer graphene/SiC（0001） by molecular beam epitaxy （MBE）. Atomically thin films are characterized by scanning tunneling microscopy （STM）, X-ray photoemission spectroscopy （XPS）, low-energy electron diffraction （LEED）, and Raman spec- troscopy. The band structure of 6-layer PdTe2 film is measured by angle-resolved photoemission spectroscopy （ARPES）. Moreover, our air exposure experiments show excellent chemical stability of epitaxial PdTe2 film. High-quality PdTe2 films provide opportunities to build antimonene/PdTe2 heterostructure in ultrahigh vacuum for future applications in electronic and optoelectronic nanodevices.

Electronic states and molecular orientation of ITIC film

ITIC is the milestone of non-fullerene small molecule acceptors used in organic solar cells. We study the electronic states and molecular orientation of ITIC film using photoelectron spectroscopy and x-ray absorption spectroscopy. The negative integer charge transfer energy level is determined to be 4.00 ± 0.05 eV below the vacuum level, and the ionization potential is 5,75 ±0.10 eV. The molecules predominantly have the face-on orientation on inert substrates as long as the surfaces of the substrates are not too rough. These results provide the physical understanding of the high performance of ITIC-based solar ceils, which also afford implications to design more advanced photovoltaic small molecules.

Experimental Synthesis of Strained Monolayer Silver Arsenide on Ag(111)Substrates

Two-dimensional(2 D)materials are playing more and more important roles in both basic sciences and industrial applications.For 2 D materials,strain could tune the properties and enlarge applications.Since the growth of 2 D materials on substrates is often accompanied by strain,the interaction between 2 D materials and substrates is worthy of careful attention.Here we demonstrate the fabrication of strained monolayer silver arsenide(AgAs)on Ag(111)by molecular beam epitaxy,which shows one-dimensional stripe structures arising from uniaxial strain.The atomic geometric structure and electronic band structure are investigated by low energy electron diffraction,scanning tunneling microscopy,x-ray photoelectron spectroscopy,angle-resolved photoemission spectroscopy and first-principle calculations.Monolayer AgAs synthesized on Ag(111)provides a platform to study the physical properties of strained 2 D materials.

Epitaxial fabrication of monolayer copper arsenide on Cu(111)

We report the epitaxial growth of monolayer copper arsenide(CuAs)with a honeycomb lattice on Cu(111)by molecular beam epitaxy(MBE).Scanning tunneling microscopy(STM),low energy electron diffraction(LEED),x-ray photoelectron spectroscopy(XPS),and density functional theory(DFT)verify the√3×√3 superlattice of monolayer CuAs on Cu(111)substrate.Angle-resolved photoemission spectroscopy(ARPES)measurements together with DFT calculations demonstrate the electronic band structures of monolayer CuAs and reveal its metallic nature.Further calculations show that charge transfer from Cu(111)substrate to monolayer CuAs lifts the Fermi level and tunes the band structure of the monolayer CuAs.This high-quality epitaxial monolayer CuAs with potential tunable band gap holds promise on the applications in nano-electronic devices.

Batch synthesis of rare-earth nickelates electronic phase transition perovskites via rare-earth processing intermediates

The rare-earth nickelates(RENiO_(3)) exhibit an exceptional complex electronic phase diagram and multiple electronic phase transitions that enrich promising applications in correlated electronic devices beyond conventional semiconductors.Nevertheless,the practical applications of RENiO_(3) are challenged by their intrinsic thermodynamic metastability in material synthesis and high material cost.Therefore,developing an economical strategy to achieve the batch synthesis of RENiO_(3) is of vital importance.In this work,we enlarged the synthesis amount of RENiO_(3) up to 20 g per batch using chloride(KCI) assisted molten salt reaction.By optimizing the reaction conditions,the powder of RENiO_(3) with the cubic shape and average size of ~2μm was effectively synthesized,while their phase purity exceeded 95%.In addition,the cost to synthesize RENiO_(3) was further reduced by using rare-earth extraction intermediate products as the raw materials,instead of using the pure rare-earth precursors.It also achieved wide adjustments in the metal-to-insulator-transition temperature from160 to 420 K without significantly reducing the transition sharpness.By enlarging the synthesis amount and the reducing the cost,it paves the way to the device application of RENiO_(3).

Epitaxially grown monolayer VSe2： an air-stable magnetic two-dimensional material with low work function at edges

Recent experimental breakthroughs open up new opportunities for magnetism in few-atomic-layer twodimensional(2 D) materials, which makes fabrication of new magnetic 2 D materials a fascinating issue.Here, we report the growth of monolayer VSe_2 by molecular beam epitaxy(MBE) method. Electronic properties measurements by scanning tunneling spectroscopy(STS) method revealed that the asgrown monolayer VSe_2 has magnetic characteristic peaks in its electronic density of states and a lower work-function at its edges. Moreover, air exposure experiments show air-stability of the monolayer VSe_2. This high-quality monolayer VSe_2, a very air-inert 2 D material with magnetism and low edge work function, is promising for applications in developing next-generation low power-consumption, high efficiency spintronic devices and new electrocatalysts.