79 research outputs found
Light Generation and Harvesting in a Van der Waals Heterostructure
Two-dimensional (2D) materials are a new type of materials under intense
study because of their interesting physical properties and wide range of
potential applications from nanoelectronics to sensing and photonics.
Monolayers of semiconducting transition metal dichalcogenides MoS2 or WSe2 have
been proposed as promising channel materials for field-effect transistors
(FETs). Their high mechanical flexibility, stability and quality coupled with
potentially inexpensive production methods offer potential advantages compared
to organic and crystalline bulk semiconductors. Due to quantum mechanical
confinement, the band gap in monolayer MoS2 is direct in nature, leading to a
strong interaction with light that can be exploited for building
phototransistors and ultrasensitive photodetectors. Here, we report on the
realization of light-emitting diodes based on vertical heterojunctions composed
of n-type monolayer MoS2 and p-type silicon. Careful interface engineering
allows us to realize diodes showing rectification and light emission from the
entire surface of the heterojunction. Electroluminescence spectra show clear
signs of direct excitons related to the optical transitions between the
conduction and valence bands. Our pn diodes can also operate as solar cells,
with typical external quantum efficiency exceeding 4%. Our work opens up the
way to more sophisticated optoelectronic devices such as lasers and
heterostructure solar cells based on hybrids of two-dimensional (2D)
semiconductors and silicon.Comment: Submitted versio
Optospintronics in graphene via proximity coupling
The observation of micron size spin relaxation makes graphene a promising
material for applications in spintronics requiring long distance spin
communication. However, spin dependent scatterings at the contact/graphene
interfaces affect the spin injection efficiencies and hence prevent the
material from achieving its full potential. While this major issue could be
eliminated by nondestructive direct optical spin injection schemes, graphenes
intrinsically low spin orbit coupling strength and optical absorption place an
obstacle in their realization. We overcome this challenge by creating sharp
artificial interfaces between graphene and WSe2 monolayers. Application of a
circularly polarized light activates the spin polarized charge carriers in the
WSe2 layer due to its spin coupled valley selective absorption. These carriers
diffuse into the superjacent graphene layer, transport over a 3.5 um distance,
and are finally detected electrically using BN/Co contacts in a non local
geometry. Polarization dependent measurements confirm the spin origin of the
non local signal
Valley Polarization by Spin Injection in a Light-Emitting van der Waals Heterojunction
The band structure of transition metal dichalcogenides (TMDCs) with valence
band edges at different locations in the momentum space could be harnessed to
build devices that operate relying on the valley degree of freedom. To realize
such valleytronic devices, it is necessary to control and manipulate the charge
density in these valleys, resulting in valley polarization. While this has been
demonstrated using optical excitation, generation of valley polarization in
electronic devices without optical excitation remains difficult. Here, we
demonstrate spin injection from a ferromagnetic electrode into a heterojunction
based on monolayers of WSe2 and MoS2 and lateral transport of spin-polarized
holes within the WSe2 layer. The resulting valley polarization leads to
circularly polarized light emission which can be tuned using an external
magnetic field. This demonstration of spin injection and magnetoelectronic
control over valley polarization provides a new opportunity for realizing
combined spin and valleytronic devices based on spin-valley locking in
semiconducting TMDCs.Comment: in Nano Letters (2016
Ultrasensitive photodetectors based on monolayer MoS2
Two-dimensional materials are an emerging class of new materials with a wide range of electrical properties and potential practical applications. Although graphene(1) is the most well-studied two-dimensional material, single layers of other materials, such as insulating BN (ref. 2) and semiconducting MoS2 (refs 3,4) or WSe2 (refs 5,6), are gaining increasing attention as promising gate insulators and channel materials for field-effect transistors. Because monolayer MoS2 is a direct-bandgap semiconductor(7,8) due to quantum-mechanical confinement(7,9,10), it could be suitable for applications in optoelectronic devices where the direct bandgap would allow a high absorption coefficient and efficient electron-hole pair generation under photo-excitation. Here, we demonstrate ultrasensitive monolayer MoS2 phototransistors with improved device mobility and ON current. Our devices show a maximum external photoresponsivity of 880 AW(-1) at a wavelength of 561 nm and a photoresponse in the 400-680 nm range. With recent developments in large-scale production techniques such as liquid-scale exfoliation(11-13) and chemical vapour deposition-like growth(14,15), MoS2 shows important potential for applications in MoS2-based integrated optoelectronic circuits, light sensing, biomedical imaging, video recording and spectroscopy
Large-area MoS2 grown using H2S as the sulphur source
We report on the growth of molybdenum disulphide (MoS2) using H2S as a gas-phase sulfur precursor that allows controlling the domain growth direction of domains in both vertical (perpendicular to the substrate plane) and horizontal (within the substrate plane), depending on the H2S:H2 ratio in the reaction gas mixture and temperature at which they are introduced during growth. Optical and atomic force microscopy measurements on horizontal MoS2 demonstrate the formation of monolayer triangular-shape domains that merge into a continuous film. Scanning transmission electron microscopy of monolayer MoS2 shows a regular atomic structure with a hexagonal symmetry. Raman and photoluminescence spectra confirm the monolayer thickness of the material. Field-effect transistors fabricated on MoS2 domains that are transferred onto Si/Si2 substrates show a mobility similar to previously reported exfoliated and chemical vapor deposition-grown materials. © 2015 IOP Publishing Ltd
Phenotypic, transcriptomic, and genomic features of clonal plasma cells in light-chain amyloidosis
Immunoglobulin light-chain amyloidosis (AL) and multiple myeloma (MM) are 2 distinct monoclonal gammopathies that involve the same cellular compartment: clonal plasma cells (PCs). Despite the fact that knowledge about MM PC biology has significantly increased in the last decade, the same does not apply for AL. Here, we used an integrative phenotypic, molecular, and genomic approach to study clonal PCs from 24 newly diagnosed patients with AL. Through principal-component-analysis, we demonstrated highly overlapping phenotypic profiles between AL and both monoclonal gammopathy of undetermined significance and MM PCs. However, in contrast to MM, highly purified fluorescence-activated cell-sorted clonal PCs from AL (n = 9) showed almost normal transcriptome, with only 38 deregulated genes vs normal PCs; these included a few tumor-suppressor (CDH1, RCAN) and proapoptotic (GLIPR1, FAS) genes. Notwithstanding, clonal PCs in AL (n=11) were genomically unstable, with a median of 9 copy number alterations (CNAs) per case, many of such CNAs being similar to those found in MM. Whole-exome sequencing (WES) performed in 5 AL patients revealed a median of 15 nonrecurrent mutations per case. Altogether, our results show that in the absence of a unifying mutation by WES, clonal PCs in AL display phenotypic and CNA profiles similar to MM, but their transcriptome is remarkably similar to that of normal PCs
Interplay between gonadal hormones and postnatal overfeeding in defining sex-dependent differences in gut microbiota architecture
Aging is associated with a decline in sex hormones, variable between sexes, that has an impact on many different body systems and might contribute to age-related disease progression. We aimed to characterize the sex differences in gut microbiota; and. to explore the impact of depletion of gonacial hormones, alone or combined with postnatal overfeeding, in rats. Many of the differences in the gut microbiota between sexes persisted after gonadectomy, but removal of gonadal hormones shaped several gut microbiota features towards a more deleterious profile, the effect being greater in females than in males, mainly when animals were concurrently overfed. Moreover, we identified several intestinal miRNAs as potential mediators of the impact of changes in gut microbiota on host organism physiology. Our study points out that gonadal hormones contribute to defining sex-dependent differences of gut microbiota, and discloses a potential role of gonadal hormones in shaping gut microbidta, OS consequence of the interaction between sex and nutrition. Our data suggest that the changes in gut microbion, observed in conditions of sex hormone decline, as those caused by ageing in men and menopause in women, might exert different effects on the host organism, which are putatively mediated by gut microbiota-intestinal miRNA cross-talk
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