Optical properties of two-dimensional tin nanosheets epitaxially grown on graphene

Heterostacks formed by combining two-dimensional materials show novel properties which are of great interest for new applications in electronics, photonics and even twistronics, the new emerging field born after the outstanding discoveries on twisted graphene. Here, we report the direct growth of tin nanosheets at the two-dimensional limit via molecular beam epitaxy on chemical vapor deposited graphene on Al2O3(0001). The mutual interaction between the tin nanosheets and graphene is evidenced by structural and chemical investigations. On the one hand, Raman spectroscopy indicates that graphene undergoes compressive strain after the tin growth, while no charge transfer is observed. On the other hand, chemical analysis shows that tin nanosheets interaction with sapphire is mediated by graphene avoiding the tin oxidation occurring in the direct growth on this substrate. Remarkably, optical measurements show that the absorption of tin nanosheets show a graphene-like behavior with a strong absorption in the ultraviolet photon energy range, therein resulting in a different optical response compared to tin nanosheets on bare sapphire. The optical properties of tin nanosheets therefore represent an open and flexible playground for the absorption of light in a broad range of the electromagnetic spectrum and technologically relevant applications for photon harvesting and sensors.Comment: 14 pages, 7 figure

A horvát–magyar együttélés fordulópontjai. Intézmények, társadalom, gazdaság, kultúra / Prekretnice u suživotu Hrvata i Mađara. Ustanove, društvo, gospodarstvo i kultura, ur. Pál Fodor – Dinko Šokčević – Jasna Turkalj – Damir Karbić, Institut za povijesne znanosti Istraživačkog centra za humanističke znanosti Mađarske akademije znanosti – Hrvatski institut za povijest, Budimpešta 2015., 772 str.

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Characterizing temporary hydrological regimes at a European scale

Monthly duration curves have been constructed from climate data across Europe to help address the relative frequency of ecologically critical low flow stages in temporary rivers, when flow persists only in disconnected pools in the river bed. The hydrological model is 5 based on a partitioning of precipitation to estimate water available for evapotranspiration and plant growth and for residual runoff. The duration curve for monthly flows has then been analysed to give an estimate of bankfull flow based on recurrence interval. The corresponding frequency for pools is then based on the ratio of bank full discharge to pool flow, arguing from observed ratios of cross-sectional areas at flood 10 and low flows to estimate pool flow as 0.1% of bankfull flow, and so estimate the frequency of the pool conditions that constrain survival of river-dwelling arthropods and fish. The methodology has been applied across Europe at 15 km resolution, and can equally be applied under future climatic scenarios

Optical Pump - Terahertz Probe Measurement of the Electron Dynamics in Ga1−x\text{}_{1-x}Mnx\text{}_{x}As

An optical pump - terahertz probe technique was used for measuring electron lifetime in various Ga$\text{}_{1-x}$Mn$\text{}_{x}$As epitaxial layers with the subpicosecond temporal resolution. The measurements were performed on the samples with x up to 2%, which had large resistivities and were transparent in a THz frequency range. It has been found that an induced THz absorption relaxation is the fastest and electron lifetimes are the shortest for the samples with the smallest Mn content. For the samples with x=0.3% and x=2% this relaxation becomes much slower; its rate is comparable to the carrier recombination rate in Ga$\text{}_{1-x}$Mn$\text{}_{x}$As substrate

Terahertz time-domain-spectroscopy system based on 1.55 μm fiber laser and photoconductive antennas from dilute bismides

We describe a terahertz time-domain-spectroscopy system that is based on photoconductive components fabricated from (GaIn)(AsBi) epitaxial layers and activated by femtosecond 1.55 μm pulses emitted by an Er-doped fiber laser. (GaIn)(AsBi) alloy grown on GaAs substrates contained 12.5%In and 8.5%Bi – a composition corresponding to a symmetrical approach of the conduction and valence band edges to each other. The layers were photosensitive to 1.55 μm wavelength radiation, had relatively large resistivities, and subpicosecond carrier lifetimes – a set of material parameters necessary for fabrication of efficient ultrafast photoconductor devices. The frequency limit of this system was 4.5 THz, its signal-to-noise ratio 65 dB. These parameters were comparable to their typical values for much bulkier solid-state laser based systems

TRANSIENT PHOTOCONDUCTIVITY AND PHOTOLUMINESCENCE IN InP:Cu

Nonequilibrium photoexcited carrier dynamics in InP:Cu was investigated by two experimental techniques: the time-resolved photoluminescence up-conversion and the transient photoconductivity measurement. Both measurements show that dopmg with copper significantly modifies the photoexcited carrier relaxation in indium phosphide. There are several strong indications that this effect originates from the carrier trapping at metallic precipitates. PACS numbers: 72.40.+w, 78.47.+p, 78.55.-m Semi-insulating Α3B5 semiconduction have numerous important applications as substrates for integrated circuits, microwave and optoelectronic devices. Usually, such materials are obtained by utilizing deep, near-midgap levels compensating shallow impurities. It has been proposed [1] that semi-insulating Α 3 B 5 materials can be created also by introduction of metallic precipitates into the semiconductor, at sufficiently large densities. Originally proposed for explaining unique properties of well-known GaAs 1ayers grown by a low-temperature molecular-beam epitaxy (LT GaAs) the precipitate model is still far from being commonly accepted for that material. In contrary, the latest investigations indicate that the high resistivity and ultrashort carrier lifetimes in LT GaAs can be better explained by the presence of deep, excess-arsenic-related defects [2], a model alternative to the precipitate model. However, it has been observed recently The samples studied were prepared using as-grown nominally undoped, n-type (5 x 10 15 /cm3) InP wafers. Cu was evaporated on both sides of the samples, diffused in clean quartz ampoules and sealed. After diffusion, the samples were rapidly quenched by dropping the ampoules into liquid nitrogen. Any residual Cu was removed from the samples surfaces by a mechanical polishing followed by an etchin

Photo-patterning of highly efficient state-of-the-art phosphorescent OLEDs using orthogonal hydrofluoroethers

Photolithography offers a scalable solution for large area pixel patterning of organic light-emitting diode (OLED) displays. It has been limited due to the incompatibility of traditional processing steps with the majority of organic materials. In this work, photolithographic structuring of state-of-the-art phosphorescent red p-i-n OLEDs is demonstrated using fluorinated polymers in combination with hydrofluoroether solvents. This is the first report on photolithographically patterned OLEDs with state-of-the-art efficiency and good long-term stability