and (A.C-G.) andres.castellanos@imdea.org KEYWORDS. Black phosphorus, strain engineering, uniaxial strain, local strain, periodic deformation, quantum confinement, optical absorption. This is the post-peer reviewed version of the following article: J. Quereda et al. "Strong modulation of optical properties in black phosphorus through strain-engineered rippling" Nano Letters (2016) DOI:10.1021/acs.nanolett.5b04670 Which has been published in final form at: http://pubs.acs.org/doi/abs/10.1021/acs.nanolett.5b04670 2 ABSTRACT Controlling the bandgap through local-strain engineering is an exciting avenue for tailoring optoelectronic materials. Two-dimensional crystals are particularly suited for this purpose because they can withstand unprecedented non-homogeneous deformations before rupture: one can literally bend them and fold them up almost like a piece of paper. Here, we study multi-layer black phosphorus sheets subjected to periodic stress to modulate their optoelectronic properties. We find a remarkable shift of the optical absorption band-edge of up to ~0.7 eV between the regions under tensile and compressive stress, greatly exceeding the strain tunability reported for transition metal dichalcogenides. This observation is supported by theoretical models which also predict that this periodic stress modulation can yield to quantum confinement of carriers at low temperatures. The possibility of generating large strain-induced variations in the local density of charge carriers opens the door for a variety of applications including photovoltaics, quantum optics and two-dimensional optoelectronic devices. TEXT.The recent isolation of black phosphorus has unleashed the interest of the community working on 2D materials because of its interesting electronic and optical properties: narrow intrinsic gap, ambipolar field effect and high carrier mobility. [1][2][3][4][5][6][7][8][9][10][11][12] Black phosphorus is composed of phosphorus atoms held together by strong bonds forming layers that interact through weak van der Waals forces holding the layers stacked on top of each other. This structure, without surface dangling This is the post-peer reviewed version of the following article: J. Quereda et al. "Strong modulation of optical properties in black phosphorus through strain-engineered rippling" Nano Letters (2016) DOI:10.1021/acs.nanolett.5b04670 Which has been published in final form at: http://pubs.acs.org/doi/abs/10.1021/acs.nanolett.5b04670 3 bonds, allows black phosphorus susceptible to withstand very large localized deformations without breaking (similarly to graphene and MoS2). [13][14][15] Its outstanding mechanical resilience makes black phosphorus a prospective candidate for strain engineering, i.e. the modification of a material's optical/electrical properties by means of mechanical stress. 16 This is in contrast to conventional 3D semiconductors that tend to break for moderate deformations. Very recent theoretical works explore the effect of strain on the band structure and optical properties of black phosp...

This is the post-peer reviewed version of the following article: A.J. Molina-Mendoza et al. "Centimeter-scale synthesis of ultrathin layered MoO3 by van der Waals epitaxy" Chem. Mater., 2016, 28 (11) ABSTRACTWe report on the large-scale synthesis of highly oriented ultrathin MoO3 layers using a simple and low-cost atmospheric pressure, van der Waals epitaxy growth on muscovite mica substrates. By this method we are able to synthetize high quality centimeter-scale MoO3 crystals with thicknesses ranging from 1.4 nm (two layers) up to a few nanometers. The crystals can be easily transferred to an arbitrary substrate (such as SiO2) by a deterministic transfer method and be extensively characterized to demonstrate the high quality of the resulting crystal. We also study the electronic band structure of the material by density functional calculations. Interestingly, the calculations demonstrate that bulk MoO3 has a rather weak electronic interlayer interaction and thus it presents a monolayer-like band structure. Finally, we demonstrate the potential of this synthesis method for optoelectronic applications by fabricating large-area field-effect devices (10 µm by 110 µm in lateral dimensions), finding responsivities of 30 mA·W -1 for a laser power density of 13 mW·cm -2 in the UV region of the spectrum and also as an electron acceptor in a MoS2-based field-effect transistor.This is the post-peer reviewed version of the following article: A.J. Molina-Mendoza et al. "Centimeter-scale synthesis of ultrathin layered MoO3 by van der Waals epitaxy"

Abstract:We explore the use of Si3N4/Si substrates as a substitute of the standard SiO2/Si substrates employed nowadays to fabricate nanodevices based on 2D materials. We systematically study the visibility of several 2D semiconducting materials that are attracting a great deal of interest in nanoelectronics and optoelectronics: MoS2, MoSe2, WSe2 and black-phosphorus. We find that the use of Si3N4/Si substrates provides an increase of the optical contrast up to a 50%-100% and also the maximum contrast shifts towards wavelength values optimal for human eye detection, making optical identification of 2D semiconductors easier. OPEN ACCESSElectronics 2015, 4 848

When a two-dimensional material, adhered onto a compliant substrate, is subjected to compression it can undertake a buckling instability yielding to a periodic rippling.Interestingly, when black phosphorus flakes are compressed along the zig-zag crystal direction the flake buckles forming ripples with a 40% longer period than that obtained when the compression is applied along the armchair direction. This anisotropic buckling stems from the puckered honeycomb crystal structure of black phosphorus and a quantitative analysis of the ripple period allows us to determine the Youngs's modulus of few-layer black phosphorus along the armchair direction (EbP_AC = 35.1 ± 6.3 GPa) and the zig-zag direction (EbP_ZZ = 93.3 ± 21.8 GPa).Since its isolation in 2014, 1-6 few-layer black phosphorus (bP) keeps attracting the interest of scientific community because of its remarkable electronic (i.e. ultrahigh charge carrier mobility, ambipolar field effect, etc) 7-10 and optical (i.e. narrow direct gap, strong quantum confinement effect, large band gap electrical tunability, etc) 11-20 that has motivated its application in many electronic and optoelectronic devices. 5,21-23 Strikingly, although the electronic and optical properties have been thoroughly characterized its mechanical properties, that have a crucial role in its applicability in flexible electronics and nanoelectromechanical systems, have been barely studied experimentally and these works do not provide a good consensus in their results, especially in the value of the elastic modulus of black phosphorus along the zig-zag direction. 24-28 One possible explanation for the scattering of results in the literature is the environmental instability of black phosphorus: few-layer black phosphorus flakes degrade upon atmospheric exposure within hours. [29][30][31][32][33][34][35][36][37][38] have deduced that the degradation most likely occurs as a result of photo-induced oxidation, forming phosphorus oxide species, from oxygen absorbed in the accumulated water at the surface of exfoliated flakes exposed to This is the authors' version (post peer-review) of the manuscript:Luis Vaquero-Garzon et al. Nanoscale, 2019,11, 12080-12086 https://doi.org/10.1039/C9NR03009C That has been published in its final form:https://pubs.rsc.org/en/content/articlelanding/2019/nr/c9nr03009c#!divAbstract ambient conditions. 32,39,40 In the previous works, the mechanical testing methods used require exposing the flakes to air for relatively long periods of time and in some cases the studied flakes have been even subjected to several wet-chemistry microfabrication steps 28 or exposed to electron beam irradiation. 24 Therefore, there is a need for a technique that allows to study the intrinsic mechanical properties of pristine black phosphorus flakes right after their exfoliation.

We present an easy drop-casting based functionalization of MoS2-based photodetectors that results in an enhancement of the photoresponse of about four orders of magnitude, reaching responsivities up to 100 A·W -1 . The functionalization is technologically trivial, air-stable, fully reversible and reproducible, and opens the door to the combination of 2D-materials with molecular dyes for the development of high performance photodetectors.Among the novel two-dimensional (2D) materials, 1-8 transition metal dichalcogenides (TMDCs) [9][10][11][12] show particularly promising electronic and optoelectronic properties. 13 In particular, their intrinsic bandgap within the visible part of the spectrum, makes them highly interesting materials for optoelectronic applications.14 In fact, the presence of a bandgap has allowed for the construction of a wealth of prototype electronic devices based on TMDCs. [15][16][17][18][19][20][21][22][23][24] In the last years, there has been a significant effort to modulate the optical properties of TMDCs in order to optimize the performance of the corresponding devices. Most of the strategies investigated so far rely on physical methods, such as strain-engineering, 25,26 fieldeffect doping, 12,27 or artificial stacking of different 2D materials. 28,29 In comparison, the chemical modification of TMDCs is still rather underexplored, despite the appealing combination of low-cost and high degree of control offered by synthetic chemistry. Examples of doping of TMDCs through surface charge-transfer using metal atoms, 30 gases, 31 and a few organic molecules has already been demonstrated. 32,33 Responsivities of just a few A·W -1 have been reported for MoS2 photodetectors functionalized with a rhodamine dye, 34 a rather modest value for MoS2-based photodetectors. Among the readily available organic dyes, perylenediimides (PDIs) and porphyrins show remarkable optical properties, including large molar absorptivity -ca. 10 5 M −1 cm −1 for PDIs and 10 6 M −1 cm −1 for porphyrins-, and outstanding photostability under ambient conditions. These intrinsic properties have made them two of the most popular families of organic dyes, particularly in the frame of photovoltaics. [35][36][37][38][39][40][41][42][43][44] However, their use for the modulation of the optoelectronic properties of TMDC-based devices has not been yet described. Considering this, we decided to investigate the effects of the noncovalent functionalization of MoS2 This is the post-peer reviewed version of the following article: A.J. Molina-Mendoza et al. "Engineering the optoelectronic properties of MoS2 photodetectors through reversible noncovalent functionalization" Chem. Comm., 2016 DOI: 10.1039/C6CC07678E Which has been published in final form at: http://pubs.rsc.org/en/content/articlelanding/2016/cc/c6cc07678e#!divAbstract photodetectors with the soluble PDI and tetraphenyl porphyrin (TPP) depicted in Chart 1. Here, we describe that the supramolecular functionalization of mechanically exfoliated MoS2-based photodetector...