We observe subpicosecond charge separation and formation of indirect excitons a van der Waals heterostructure formed by molybdenum disulfide diselenide monolayers. The sample is fabricated manually stacking monolayer MoS2 MoSe2 flakes prepared mechanical exfoliation. Photoluminescence measurements confirm the an effective heterojunction. In transient absorption measurements, ultrafast laser pulse resonantly injects in layer heterostructure. Differential reflection probe tuned to exciton...

Atomically thin molybdenum disulfide is emerging as a new nanomaterial with potential applications in the fields of electronic and photonics. Charge carrier dynamics plays an essential role determining its optical properties. We report spatially temporally resolved pump-probe studies charge carriers atomically samples fabricated by mechanical exfoliation. Carriers are injected interband absorption 390-nm pump pulse detected measuring differential reflection time-delayed scanned probe that...

We report a van der Waals heterostructure formed by monolayers of MoS2 and ReS2 with type-I band alignment. First-principle calculations show that in this heterostructure, both the conduction minimum valence maximum are located layer. This configuration is different from previously accomplished type-II heterostructures where electrons holes reside layers. The nature evident photocarrier dynamics observed transient absorption measurements. found carriers injected transfer to about 1 ps, while...

One key challenge in developing postsilicon electronic technology is to find ultrathin channel materials with high charge mobilities and sizable energy band gaps. Graphene can offer extremely mobilities; however, the lack of a gap presents significant barrier. Transition metal dichalcogenides possess thickness-tunable gaps; their are relatively low. Here we show that black phosphorus has room-temperature on order 10(4) cm(2) V(-1) s(-1), which about 1 magnitude larger than silicon. We also...

Two-dimensional transition metal dichalcogenides provide a unique platform to study excitons in confined structures. Recently, several important aspects of these materials have been investigated detail. However, the formation process from free carriers has yet be understood. Here we report time-resolved measurements on exciton monolayer samples MoS2, MoSe2, WS2, and WSe2. The electron–hole pairs, injected by an ultrashort laser pulse, immediately induce transient absorption signal probe...

We report the observation of trions at room temperature in a van der Waals heterostructure composed MoSe2 and WS2 monolayers. These are formed by excitons excited layer electrons transferred from layer. Recombination results peak photoluminescence spectra, which is absent monolayer that not contact with MoSe2. The trion origin this further confirmed linear dependence position on excitation intensity. deduced zero-density binding energy 62 meV. formation facilitates electrical control exciton...

Anisotropic optical and transport properties of monolayer ReS2 fabricated by mechanical exfoliation are reported. Transient absorption measurements with different polarization configurations sample orientations reveal that the coefficient transient both anisotropic, maximal minimal values occurring when light is parallel perpendicular to Re atomic chains, respectively. The about a factor 2.5 values. By resolving spatiotemporal dynamics excitons, it found diffusion excitons moving along...

Charge transfer excitons are observed in a van der Waals heterostructures formed by monolayer transition metal dichalcogenides.

We fabricated transistors formed by few layers to bulk single crystal WS2 quantify the factors governing charge transport. established a capacitor network analyze full-range electrical characteristics of channel, highlighting role quantum capacitance and interface trap density. find that transfer are mainly determined interplay between oxide capacitances. In OFF-state, density (<1012 cm–2) is limiting factor for subthreshold swing. Furthermore, superior crystalline quality low enabled...

High quality and stable electrical contact between metal two-dimensional materials, such as transition dichalcogenides, is a necessary requirement that has yet to be achieved in order successfully exploit the advantages these materials offer electronics optoelectronics. MoTe2, owing its phase changing property, can potentially solution. A recent study demonstrated metallic of MoTe2 connects semiconducting with very low resistance. To utilize this property connect other it important achieve...

We report synthesis and time-resolved transient absorption measurements of TiS3 nanoribbons. nanoribbons were fabricated by direct reaction titanium sulfur. Dynamics the photocarriers in these samples studied measurements. It was found that following ultrafast injection nonequilibrium hot photocarriers, thermalization, energy relaxation, exciton formation all occur on a subpicosecond time scale. Several key parameters describing dynamical properties including their recombination lifetime,...

We report a combined theoretical and experimental study on photocarrier dynamics in monolayer phosphorene bulk black phosphorus.

In-plane heterojuctions formed from two monolayer semiconductors represent the finest control of electrons in condensed matter and have attracted significant interest. Various device studies shown effectiveness such structures to electronic processes, illustrating their potentials for optoelectronic applications. However, information about physical mechanisms charge carrier transfer across junctions is still rare, mainly due lack adequate experimental techniques. Here we show that transient...

We present a joint theoretical/experimental study of van der Waals heterobilayer with type-I band alignment formed by monolayers WSe2 and MoTe2. Our first-principles computation suggests that both the valence maximum conduction minimum WSe2/MoTe2 reside in MoTe2 layer. The allows efficient transfer excitons from to Since monolayer is direct semiconductor bandgap infrared range, this attractive for light emission applications. Time-resolved measurements photocarrier dynamics were conducted...

Exciton transport in a two-dimensional semiconductor is controlled by placing top dielectric layer.

Transient absorption measurement reveals ultrafast charge transfer from crystalline to amorphous two-dimensional semiconductors.

Recently, two-dimensional materials have been extensively studied. Due to the reduced dielectric screening and confinement of electrons in two dimensions, these show dramatically different electronic optical properties from their bulk counterparts. So far, studies on mainly focused crystalline materials. Here we report atomically thin amorphous black phosphorus, as first material. Spatially temporally resolved pump-probe measurements that large-area uniform atomic layers synthesized at low...

Femtosecond optical pump-probe technique is used to study charge carrier dynamics in few-layer MoS2 samples fabricated by mechanical exfoliation. An ultrafast pump pulse excites carriers and differential reflection of a probe tuned an excitonic resonance detected. We find that the spectrum signal similar derivative resonance. The decay time range 150 400 ps, increasing with wavelength. With fixed wavelength, magnitude proportional fluence, while independent it.

We show that black phosphorus has room-temperature charge mobilities on the order of 10$^4$ cm$^2$V$^{-1}$s$^{-1}$, which are about one magnitude larger than silicon. also demonstrate strong anisotropic transport in phosphorus, where along armchair direction zigzag direction. A photocarrier lifetime as long 100 ps is determined. These results illustrate a promising candidate for future electronic and optoelectronic applications.

As the efficiency of mid-infrared LEDs has advanced, they have assumed increasing importance in sensitive gas optical sensors, most prominently for methane and carbon, LED arrays defense-related projection systems. While cascading superlattice quantum design advanced efficiency, a key limiting mechanism these devices is heavy loss from total internal reflection due to very high index refraction (~3.8). Here we report on substantial enhancement spectral radiance one- two-color emitters using...