A gate-free MoS2 phototransistor assisted by ferroelectrics

During the past decades,transition metal dichalcogenides(TMDs) have received special focus for their unique properties in photoelectric detection.As one important member of TMDs,MoS2 has been made into photodetector purely or combined with other materials,such as graphene,ionic liquid,and ferroelectric materials.Here,we report a gate-free MoS2 phototransistor combined with organic ferroelectric material poly(vinylidene fluoride-trifluoroethylene)(P(VDF-TrFE)).In this device,the remnant polarization field in P(VDF-TrFE) is obtained from the piezoelectric force microscope(PFM) probe with a positive or negative bias,which can turn the dipoles from disorder to be the same direction.Then,the MoS2 channel can be maintained at an accumulated state with downward polarization field modulation and a depleted state with upward polarization field modulation.Moreover,the P(VDF-TrFE) segregates MoS2 from oxygen and water molecules around surroundings,which enables a cleaner surface state.As a photodetector,an ultra-low dark current of 10^–11 A,on/off ration of more than 10^4 and a fast photoresponse time of 120 μs are achieved.This work provides a new method to make high-performance phototransistors assisted by the ferroelectric domain which can operate without a gate electrode and demonstrates great potential for ultra-low power consumption applications.

Two-Dimensional Electron Gas in MoSi_(2)N_(4)/VSi_(2)N_(4)Heterojunction by First Principles Calculation

Van der Waals(vdW)layered two-dimensional(2D)materials,which may have high carrier mobility,valley polarization,excellent mechanical properties and air stability,have been widely investigated before.We explore the possibility of producing a spin-polarized two-dimensional electron gas(2DEG)in the heterojunction composed of insulators MoSi_(2)N_(4)and VSi_(2)N_(4)by using first-principles calculations.Due to the charge transfer effect,the 2DEG at the interface of the MoSi_(2)N_(4)/VSi_(2)N_(4)heterojunction is found.Further,for different kinds of stacking of heterojunctions,lattice strain and electric fields can effectively tune the electronic structures and lead to metal-to-semiconductor transition.Under compressive strain or electric field parallel to c axis,the 2DEG disappears and band gap opening occurs.On the contrary,interlayer electron transfer enforces the system to become metallic under the condition of tensile strain or electric field anti-parallel to c axis.These changes are mainly attributed to electronic redistribution and orbitals’reconstruction.In addition,we reveal that MoSi_(2)N_(4)/VSi_(2)N_(4)lateral heterojunctions of armchair and zigzag edges exhibit different electronic properties,such as a large band gap semiconductor and a metallic state.Our findings provide insights into electronic band engineering of MoSi_(2)N_(4)/VSi_(2)N_(4)heterojunctions and pave the way for future spintronics applications.

Large-area high quality PtSe2 thin film with versatile polarity

Two-dimensional(2D)materials have attracted increasing attention for their outstanding structural and electrical properties.However,for mass-production of field effect transistors(FETs)and potential applications in integrated circuits,large-area and uniform 2D thin films with high mobility,large on-off ratio,and desired polarity are needed to synthesize firstly.Here,a transfer-free growth method for platinum diselenide(PtSe2)films has been developed.The PtSe2 films have been synthesized with various thicknesses in centimeter-sized scale.Typical FET made from a few layer PtSe2 show p-type unipolar,with a high field-effect hole mobility of 6.2 cm^(2) V^(−1) s^(−1) and an on-off ratio of 5×10^(3).The versatile semimetal-unipolar-ambipolar transition in synthesized PtSe2 films is also firstly observed as the thickness thinning.This work realizes the large-scale preparation of PtSe2 with prominent electrical properties and provides a new strategy for polarity's modulation.

A versatile photodetector assisted by photovoltaic and bolometric effects

The advent of low-dimensional materials with peculiar structure and superb band properties provides a new canonical form for the development of photodetectors.However,the limited exploitation of basic properties makes it difficult for devices to stand out.Here,we demonstrate a hybrid heterostructure with ultrathin vanadium dioxide film and molybdenum ditelluride nanoflake.Vanadium dioxide is a classical semiconductor with a narrow bandgap,a high temperature coefficient of resistance,and phase transformation.Molybdenum ditelluride,a typical two-dimensional material,is often used to construct optoelectronic devices.The heterostructure can realize three different functional modes:(i)the p-n junction exhibits ultrasensitive detection(450 nm-2μm)with a dark current down to 0.2 pA and a response time of 17μs,(ii)the Schottky junction works stably under extreme conditions such as a high temperature of 400 K,and(iii)the bolometer shows ultrabroad spectrum detection exceeding 10μm.The flexible switching between the three modes makes the heterostructure a potential candidate for next-generation photodetectors from visible to longwave infrared radiation(LWIR).This type of photodetector combines versatile detection modes,shedding light on the hybrid application of novel and traditional materials,and is a prototype of advanced optoelectronic devices.

Preparation of La0.67Ca0.23Sr0.1MnO3 thin films with interesting electrical and magnetic properties via pulsed-laser deposition

Manganese oxides with a perovskite-type Re_(1-x)D_xMnO_3(Re:heavy rare-earth elements,D:divalent alkali metal)structure have attracted interest because of the complex interaction between their electrons,lattices,and spins[1-5].Generally,manganese oxides with the structure Re_(1-x)D_xMnO_3 have special properties.For example,the half-metallic manganites,such as La_(2/3)Sr_(1/3)MnO_3 and La_(2/3)Ca_(1/3)MnO_3,wherein the conduction electrons are completely spin polarized。

Pd3 cluster catalysis: Compelling evidence from in operando spectroscopic, kinetic, and density functional theory studies

Identification of metal cluster catalysis is a topic that is being investigated since a long time. Here, we report a Pd3 metal cluster catalytic reaction investigated by means of operando studies. We discovered that atomically defined tri-nuclear palladium (Pd3) is a surprisingly active catalyst for the cycloisomerization of 2-phenylethynylaniline. Operando1H NMR spectroscopy and X-ray extended absorption fine structure (EXAFS) measurements have indicated that the structural integrity of such a catalyst remains intact throughout the reaction, which has also been confirmed by an ex situ X-ray photoelectron spectroscopy (XPS) study and catalyst recycling experiments. Kinetic data derived from operando IR spectroscopy measurements have shown that Pd3is the active catalytic species. Density functional theory calculations have revealed a reaction pathway consistent with the kinetic data, further supported by NMR titration and X-ray crystal structure studies. Overall, the present study presents a clear example of metal cluster catalysis. [Figure not available: see fulltext.] © 2016, Tsinghua University Press and Springer-Verlag Berlin Heidelberg.