Matheus J. S. Matos

Martins LGP, Matos MJS, Paschoal AR, Freire PTC, Andrade NF, Aguiar A??sio L, Kong J, Neves BRA, de Oliveira AB, Mazzoni M??rio SC, et al. Raman evidence for pressure-induced formation of diamondene. Nature Communications [Internet]. 2017;8 (1) :96. Publisher's VersionAbstract
Despite the advanced stage of diamond thin-film technology, with applications ranging from superconductivity to biosensing, the realization of a stable and atomically thick two-dimensional diamond material, named here as diamondene, is still forthcoming. Adding to the outstanding properties of its bulk and thin-film counterparts, diamondene is predicted to be a ferromagnetic semiconductor with spin polarized bands. Here, we provide spectroscopic evidence for the formation of diamondene by performing Raman spectroscopy of double-layer graphene under high pressure. The results are explained in terms of a breakdown in the Kohn anomaly associated with the finite size of the remaining graphene sites surrounded by the diamondene matrix. Ab initio calculations and molecular dynamics simulations are employed to clarify the mechanism of diamondene formation, which requires two or more layers of graphene subjected to high pressures in the presence of specific chemical groups such as hydroxyl groups or hydrogens.
Gonçalves JA, Nascimento R, Matos MJS, de Oliveira AB, Chacham H, Batista RJC. Edge-Reconstructed, Few-Layered Graphene Nanoribbons: Stability and Electronic Properties. The Journal of Physical Chemistry C [Internet]. 2017;121 (10) :5836-5840. Publisher's VersionAbstract

J. Phys. Chem. C, 2017, 121 (10), pp 5836–5840

We report a first-principles study of edge-reconstructed, few-layered graphene nanoribbons. We find that the nanoribbon stability increases linearly with increasing width and decreases linearly with increasing number of layers (from three to six layers). Specifically, we find that a three-layer 1.3 nm wide ribbon is energetically more stable than the C60 fullerene, and that a 1.8 nm wide ribbon is more stable than a (10,0) carbon nanotube. The morphologies of the reconstructed edges are characterized by the presence of five-, six-, and sevenfold rings, with sp3 and sp2bonds at the reconstructed edges. The electronic structure of the few-layered nanoribbons with reconstructed edges can be metallic or semiconducting, with band gaps oscillating between 0 and 0.28 eV as a function of ribbon width.

Chagas T, Cunha THR, Matos MJS, dos Reis DD, Araujo KAS, Malachias A, Mazzoni MSC, Ferlauto AS, Magalhaes-Paniago R. Room temperature observation of the correlation between atomic and electronic structure of graphene on Cu(110). RSC Adv. [Internet]. 2016;6 :98001-98009. Publisher's VersionAbstract
In this work we have used atomically-resolved scanning tunneling microscopy and spectroscopy to study the interplay between the atomic and electronic structure of graphene formed on copper via chemical vapor deposition. Scanning tunneling microscopy directly revealed the epitaxial match between a single layer of graphene and the underlying copper substrate in different crystallographic orientations. Using scanning tunneling spectroscopy we have directly measured the electronic density of states of graphene layers near the Fermi level, observing the appearance of a series of peaks in specific cases. These features were analyzed in terms of substrate-induced perturbations in the structural and electronic properties of graphene by means of atomistic models supported by density functional theory calculations.
Coelho PM, dos Reis DD, Matos MJS, Mendes-de-Sa TG, Goncalves AMB, Lacerda RG, Malachias A, Magalhaes-Paniago R. Near-edge X-ray absorption spectroscopy signature of image potential states in multilayer epitaxial graphene. Surface Science [Internet]. 2016;644 :135-140. Publisher's VersionAbstract
Single layer behavior in multilayer epitaxial graphene has been a matter of intense investigation. This is due to the layer decoupling that occurs during growth of graphene on some types of substrates, such as carbon-terminated silicon carbide. We show here that near-edge X-ray absorption spectroscopy can be used to observe the signature of this decoupling. To this end, samples of multilayer graphene from silicon carbide sublimation were grown with different degrees of decoupling. Raman spectroscopy was used to infer the degree of structural decoupling. X-ray grazing-incidence diffraction and scanning tunneling microscopy showed that growth initiates with the presence of bilayer graphene commensurate structures, while layer decoupling is associated to the formation of incommensurate structures observed for longer sublimation time. Near-edge X-ray absorption spectroscopy was used to probe the electronic states above the Fermi energy. Besides the σ* and π* empty states, image potential states are observed and show a clear change of intensity as a function of incident angle. These image potential states evolve from a graphite- to graphene-like behavior as a function of growth time and can be used to infer the degree of structural coupling among layers.
Prado MC, Nascimento R, Faria BEN, Matos MJS, Chacham H, Neves BRA. Nanometre-scale identification of grain boundaries in MoS 2 through molecular decoration. Nanotechnology [Internet]. 2015;26 (47) :475702. Publisher's VersionAbstract
In this paper, we address the challenge of identifying grain boundaries on the molybdenum disulphide (MoS 2 ) surface at the nanometre scale using a simple self-assembled monolayer (SAM) decoration method. Combined with atomic force microscopy, octadecylphosphonic acid monolayers readily reveal grain boundaries in MoS 2 at ambient conditions, without the need of atomic resolution measurements under vacuum. Additional ab initio calculations allow us to obtain the preferred orientation of the SAM structure relative to the MoS 2 beneath, and therefore, together with the experiments, the MoS 2 crystalline orientations at the grain boundaries. The proposed method enables the visualization of grain boundaries with sub-micrometer resolution for nanodevice investigation and failure analysis.
de Pauli M, Matos MJS, Siles PF, Prado MC, Neves BRA, Ferreira SO, Mazzoni MSC, Malachias A. Chemical Stabilization and Improved Thermal Resilience of Molecular Arrangements: Possible Formation of a Surface Network of Bonds by Multiple Pulse Atomic Layer Deposition. Journal of Physical Chemistry B. 2014;118 (32) :9792-9799.
Matos MJS, Mazzoni MSC, Chacham H. Graphene-boron nitride superlattices: the role of point defects at the BN layer. Nanotechnology. 2014;25 (16).
Carozo V, Almeida CM, Fragneaud B, Bede PM, Moutinho MVO, Ribeiro-Soares J, Andrade NF, Souza Filho AG, Matos MJS, Wang B, et al. Resonance effects on the Raman spectra of graphene superlattices. Physical Review B. 2013;88 (8).
Oliveira CK, Matos MJS, Mazzoni MSC, Chacham H, Neves BRA. Anomalous response of supported few-layer hexagonal boron nitride to DC electric fields: a confined water effect?. Nanotechnology. 2012;23 (17).
Mendes-de-Sa TG, Goncalves AMB, Matos MJS, Coelho PM, Magalhaes-Paniago R, Lacerda RG. Correlation between (in)commensurate domains of multilayer epitaxial graphene grown on SiC(000(1)over-bar) and single layer electronic behavior. Nanotechnology. 2012;23 (47).
de Pauli M, Prado MC, Matos MJS, Fontes GN, Perez CA, Mazzoni MSC, Neves BRA, Malachias A. Thermal Stability and Ordering Study of Long- and Short-Alkyl Chain Phosphonic Acid Multilayers. Langmuir. 2012;28 (43) :15124-15133.
Prado MC, Nascimento R, Moura LG, Matos MJS, Mazzoni MSC, Cancado LG, Chacham H, Neves BRA. Two-Dimensional Molecular Crystals of Phosphonic Acids on Graphene. Acs Nano. 2011;5 (1) :394-398.
Matos MJS, Azevedo S, Kaschny JR. On the structural properties of B-C-N nanotubes. Solid State Communications. 2009;149 (5-6) :222-226.