Atomic layer deposition of stable 2D materials

2018-10-22T18:33:47+00:00 October 22nd, 2018|Categories: Publications|Tags: |

Following the graphene isolation, strong interest in two dimensional (2D) materials has been driven by their outstanding properties. Their typical intrinsic structure, including strong in-plane covalent bonding and weak out-of-plane Van der Waals interaction, makes them highly promising in diverse areas such as electronics, catalysis, and environment. Growth of 2D materials requires a synthesis approach able to control the deposition onto a support at the atomic scale. Thanks to their simplicity, versatility and ability to control thickness at the angstrom level, atomic layer deposition (ALD) and its variant atomic layer etching (ALET) appear as ones of the most suited techniques to synthesize 2D materials. The development of ALD technique for fabricating 2D materials in the last ten years justifies reviewing its most recent groundbreaking discoveries and progresses. Particular attention will be paid to stable 2D materials especially graphene, h-BN, Mo and W dichalcogenides and …

Published in: "2DMaterials".

2D material printer: a deterministic cross contamination-free transfer method for atomically layered materials

2018-10-22T16:34:16+00:00 October 22nd, 2018|Categories: Publications|

Precision and chip contamination-free placement of two-dimensional (2D) materials is expected to accelerate both the study of fundamental properties and novel device functionality. Current deterministic transfer methods of 2D materials onto an arbitrary substrate deploy viscoelastic stamping. However, these methods produce (a) significant cross-contamination of the substrate inherent from typical dense sources of 2D material flakes and (b) are challenged with respect to spatial alignment, and (c) multi-transfer at a single step. Here, we demonstrate a novel method of transferring 2D materials resembling the functionality known from printing; utilizing a combination of a sharp micro-stamper and viscoelastic polymer, we show precise placement of individual 2D materials resulting in vanishing cross-contamination to the substrate. Our 2D printer-method results in an aerial cross-contamination improvement of two to three orders of magnitude relative to state-of-the-art transfer metho…

Published in: "2DMaterials".

STM study of exfoliated few layer black phosphorus annealed in ultrahigh vacuum

2018-10-22T16:34:15+00:00 October 22nd, 2018|Categories: Publications|Tags: |

Black phosphorus (bP) has emerged as an interesting addition to the category of two-dimensional materials. Surface-science studies on this material are of great interest, but they are hampered by bP’s high reactivity to oxygen and water, a major challenge to scanning tunneling microscopy (STM) experiments. As a consequence, the large majority of these studies were performed by cleaving a bulk crystal in situ . Here we present a study of surface modifications on exfoliated bP flakes upon consecutive annealing steps, up to 550 °C, well above the sublimation temperature of bP. In particular, our attention is focused on the temperature range 375 °C–400 °C, when sublimation starts, and a controlled desorption from the surface occurs alongside with the formation of characteristic well-aligned craters. There is an open debate in the literature about the crystallographic orientation of these craters, whether they align along the zigzag or the armchair direction. Thanks to the atom…

Published in: "2DMaterials".

Reply to “Comment on ‘Piezoelectricity in planar boron nitride via a geometric phase’ ”

2018-10-22T16:33:57+00:00 October 22nd, 2018|Categories: Publications|Tags: |

Author(s): Matthias Droth, Guido Burkard, and Vitor M. PereiraIn relation to our original paper [M. Droth et al., Phys. Rev. B 94, 075404 (2016)], the Comment by Li et al. [Phys. Rev. B 98, 167403 (2018)] claims to have identified a “mistake in constructing the adiabatic process of the piezoelectricity.” More specifically, they write that in our original wor…[Phys. Rev. B 98, 167404] Published Mon Oct 22, 2018

Published in: "Physical Review B".

Comment on “Piezoelectricity in planar boron nitride via a geometric phase”

2018-10-22T16:33:55+00:00 October 22nd, 2018|Categories: Publications|Tags: |

Author(s): Jie Li, Yunhua Wang, Zongtan Wang, Jie Tan, Biao Wang, and Yulan LiuUsing the strain-dependent effective Hamiltonian and the geometric phase, Droth et al. [Phys. Rev. B 94, 075404 (2016)] obtain an analytical expression for the electronic contribution to the piezoelectricity of planar hexagonal boron nitride (h-BN). Their analytical results of piezoelectric constant…[Phys. Rev. B 98, 167403] Published Mon Oct 22, 2018

Published in: "Physical Review B".

Structure sensitivity of electronic transport across graphene grain boundaries

2018-10-22T16:33:53+00:00 October 22nd, 2018|Categories: Publications|Tags: |

Author(s): Delwin Perera and Jochen RohrerGraphene grown by large-scale synthesis methods usually contains grain boundaries. They can strongly affect the electronic and mechanical properties of graphene and it is promising to exploit them for the design of electronic components and sensors. Here, we consider semiconducting graphene bicrysta…[Phys. Rev. B 98, 155432] Published Mon Oct 22, 2018

Published in: "Physical Review B".

Electronic structure and optical properties of twisted multilayer graphene

2018-10-22T16:33:51+00:00 October 22nd, 2018|Categories: Publications|Tags: |

Author(s): Adriana Vela, M. V. O. Moutinho, F. J. Culchac, P. Venezuela, and Rodrigo B. CapazWe study the electronic and optical properties of twisted trilayer and tetralayer graphene structures using a combination of tight-binding and density-functional theory methods. Band structures, densities of states, and optical absorption spectra are calculated for a variety of layer stackings and t…[Phys. Rev. B 98, 155135] Published Mon Oct 22, 2018

Published in: "Physical Review B".

Organic semiconductor/graphene oxide composites as a photo-anode for photo-electrochemical applications

2018-10-22T16:32:38+00:00 October 22nd, 2018|Categories: Publications|Tags: , |

RSC Adv., 2018, 8,35959-35965DOI: 10.1039/C8RA06546B, Paper Open Access &nbsp This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.Farheen Khurshid, M. Jeyavelan, M. Sterlin Leo Hudson, Samuthira NagarajanNew organic materials with longer life-times of the charge carrier and enhancement of photocurrent

Published in: "RSC Advances".

Graphene Oxide-Phenalenyl Composite: Transition Metal Free Recyclable and Catalytic C-H Functionalization

2018-10-22T14:32:44+00:00 October 22nd, 2018|Categories: Publications|Tags: , |

Chem. Commun., 2018, Accepted ManuscriptDOI: 10.1039/C8CC05941A, CommunicationSwadhin K Mandal, Bhagat Singh, Rupankar Paira, Goutam Biswas, Bikash ShawAn efficient route towards a heterogeneous transition metal free catalytic C-H functionalization using a covalently linked graphene oxide-phenalenyl conjugate has been described herein (28 examples, which includes core of some…The content of this RSS Feed (c) The Royal Society of Chemistry

Published in: "Chemical Communications".

Quasi-free-standing monolayer hexagonal boron nitride on Ni. (arXiv:1810.08341v1 [cond-mat.mes-hall])

2018-10-22T04:30:24+00:00 October 22nd, 2018|Categories: Publications|Tags: |

The electronic structure of monolayer hexagonal boron nitride grown on Ni by the diffusion and precipitation method was studied by x-ray absorption spectroscopy, emission spectroscopy, x-ray photoelectron spectroscopy and micro-ultraviolet photoemission spectroscopy. No indication of hybridization between h-BN pi and Ni 3d orbitals was observed. That is, the monolayer h-BN was found to be in the quasi-free-standing state. These results are in striking contrast to those of previous studies in which h-BN was strongly bound to the Ni surface by the orbital hybridization. The absence of hybridization is attributed to absence of a Ni(111) surface in this study. The lattice-matched Ni(111) surface is considered to be essential to orbital hybridization between h-BN and Ni.

Published : "arXiv Mesoscale and Nanoscale Physics".

Design of Atomically Precise Nanoscale Negative Differential Resistance Devices. (arXiv:1810.08354v1 [cond-mat.mes-hall])

2018-10-22T04:30:23+00:00 October 22nd, 2018|Categories: Publications|Tags: |

Down-scaling device dimensions to the nanometer range raises significant challenges to traditional device design, due to potential current leakage across nanoscale dimensions and the need to maintain reproducibility while dealing with atomic-scale components. Here we investigate negative differential resistance (NDR) devices based on atomically precise graphene nanoribbons. Our computational evaluation of the traditional double-barrier resonant tunneling diode NDR structure uncovers important issues at the atomic scale, concerning the need to minimize the tunneling current between the leads while achieving high peak current. We propose a new device structure consisting of multiple short segments that enables high current by the alignment of electronic levels across the segments while enlarging the tunneling distance between the leads. The proposed structure can be built with atomic precision using a scanning tunneling microscope (STM) tip during an intermediate stage in the synthesis of an armchair nanoribbon. An experimental evaluation of the band alignment at the interfaces and an STM image of the fabricated active part of the device are also presented. This combined theoretical-experimental approach opens a new avenue for the design of nanoscale devices with atomic precision.

Published : "arXiv Mesoscale and Nanoscale Physics".

Field theoretic study of electron-electron interaction effects in Dirac liquids. (arXiv:1810.08428v1 [cond-mat.mes-hall])

2018-10-22T04:30:20+00:00 October 22nd, 2018|Categories: Publications|Tags: , |

The aim of this habilitation thesis is to present recent results, obtained during the period 2012-2017, related to interaction effects in condensed matter physics systems such as planar Dirac liquids, e.g., graphene and graphene-like systems, the surface states of some topological insulators and possibly half-filled fractional quantum Hall systems (for their Dirac composite fermions). These liquids are characterized by gapless bands, strong electron-electron interactions and emergent Lorentz invariance deep in the infra-red. We address a number of important issues raised by experiments on these systems covering subjects of wide current interest in low-energy (condensed matter) as well as high-energy (particle) physics. We shall consider in particular the subtle influence of interactions on transport properties and their supposedly crucial influence on a potential dynamical mass generation. The resolution of these problems will guide us from the thorough examination of the perturbative structure of gauge field theories to the development and application of non-perturbative approaches known from quantum electro/chromo-dynamics to address strong coupling issues.

Published : "arXiv Mesoscale and Nanoscale Physics".

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