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Orientador: Douglas Soares Galvão Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin Resumo: A nanotecnologia teve seu início simbólico na apresentação de 1959 do Prêmio Nobel Richard Feynman: \"Há muito espaço lá embaixo\". Nesta palestra Feynman destaca as possibilidades de criação de novos materiais, desenhados para possuírem determinadas propriedades eletrônicas e estruturais. Desde então, grandes avanços têm sido feitos e estruturas antes nunca imaginadas têm sido observadas e produzidas. Estas são compostas dos mais diferentes materiais, desde os metais até carbono. Como exemplo de compostos de metais temos os nanofios, as cadeias atômicas lineares e mais atualmente o menor nanotubo de prata. Compostos por carbono também têm recebido grande atenção, como o grafeno. Assim a busca por novas estruturas com propriedades únicas tem se tornado incessante nas últimas décadas. Isso tem tornado cada vez mais importantes às ferramentas teóricas, uma vez que elas podem tanto ajudar na caracterização de novas estruturas, como também as prever, como poderiam ser formadas, qual seria a sua geometria, quais condições seriam necessárias para a sua formação ou demais características eletrônicas. Neste contexto, apresentamos nesta tese, o estudo destas novas nanoestruturas iniciando pelos fatores que influenciam na formação de cadeias atômicas lineares cm nanofios de platina e como a temperatura pode ser essencial para a presença de distâncias anômalas em nanofios de ouro. Cálculos de transporte também foram efetuados para nanofios de ouro e prata, com o fim de correlacionar possíveis geometrias encontradas em experimentos de HRTEM com os perfis de condutância obtidos em experimentos MCBJ. Estudos da evolução do estiramento de nanofios de prata prosseguem com a análise da formação e transporte transporte do menor nanotubo de seção quadrada formada por prata. Formação e estrutura eletrônica de estrutura de carbono topologicamente idêntica a este tubo de prata foi também proposta. Por fim, estudamos as formações do grafano e do fluorografano, a partir da hidrogenação e fluoração de membranas de grafeno, respectivamente Abstract: Nanotechnology had its symbolical beginning at the 1959\'s Nobel Prize awarder Richard Feynman\'s lecture: \"There is Plenty of Roam at the Bottom\". In this lecture, Feynman highlights the possibilities of creating new materials, designed to have specific electronic and structural properties. Ever since, great advances have been made and structures never dreamed before have been detected and synthesized. These are composed of very many different materials, from metals to carbon. As an example of metal made compounds, we have the nanowires, the linear atomic chains and more recently the smallest silver nanotube. Carbon made compounds have also received great attention; a great example is the graphene. This made the theoretical tools become increasingly important, since they can help both in the characterization of the new structures and in forecasting new ones, how could them be produced, what would its geometry be, which conditions would be necessary for its formation and the other electronic properties. ln this context, we present in this thesis the study of new nanostructures, beginning with the factors that influence in the atomic linear chains formation in platinum nanowires stretching and how the temperature can be essential to explain the presence of anomalous distances in gold nanowires. Transport calculations have also been made to gold and silver nanowires, in arder to correlate possible geometries found in HRTEM experiments with the conductance profiles obtained in MCBJ experiments. Studies in the stretch evolution of silver nanowires proceed with the analysis of formation and electronic transport in the smallest square section nanotube made of silver. Formation and electronic structure if a carbon topologically identical to this silver nanotube was also suggested. Lastly, we studied the formation of graphane and fluorographane respectively by the hydrogenation and fluorination of graphene membranes Doutorado Física Doutor em Ciências

Agradecimentos: We would like to thank the Brazilian agency FAPESP (Grant 2016/18499-0) forfinancial support. Computational andfinancial supportfrom the Center for Computational Engineering and Sciences atUnicamp through the FAPESP/CEPID Grant No. 2013/08293-7 is alsoacknowledged. We also acknowledge support from Brazilian agenciesCAPES and CNPq Abstract: Joining different parts is one of the crucial components of designing/engineering of materials. Presently, the current energy efficient low weight automotive and aerospace components consist of a different class of materials, such as metals, polymers, ceramics, etc. Joining these components remains a challenge. Here, we demonstrate metal (aluminum) and polymer (Polypropylene, pp) joining using mechanical friction. The detailed characterization clearly demonstrates that atomically locked interfaces are formed in such joining and no chemical bonds are formed during the joining. Also, a waterproof and strong interface is formed in such a process. Fully atomistic molecular dynamics simulations were also carried out in order to further gain insights on the joining process COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Fechado

Agradecimentos: The authors would like to acknowledge the electron microscopy facilities available at the Advanced Facility for Microscopy and Microanalysis, India Institute of Science (IISc), Bangalore, India. We want to thank the Brazilian agency FAPESP (Grant Nos. 2013/08293-7 and 2016/18499-0) for financial support. This research was also supported by resources supplied by the Center for Scientific Computing (NCC/GridUNESP) of the São Paulo State University (UNESP). Support from the Brazilian Agencies CNPq and CAPES is also acknowledged Abstract: In two-component metallic systems, thermodynamic immiscibility leads to phase separation such as in two-phase eutectic compositional alloys. The limit of the immiscibility of component elements under non-equilibrium conditions have been explored, but achieving complete miscibility and formation of single phase microstructures in eutectic alloys would be unprecedented. Here, we report that during the low-temperature ball milling that provides high energy impact, complete mixing of phases can occur in immiscible Ag-Cu eutectic alloys. From combined theoretical and experimental studies, we show that impact can produce solid solutions of Ag-Cu nanoparticles of eutectic composition. Our results show that phase diagrams of low dimensional materials under non-equilibrium conditions remain unexplored and could lead to new alloy microstructures drastically different from their bulk counterparts CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Fechado

Agradecimentos: We want to thank the Brazilian agency FAPESP (Grants 2013/08293-7, 2014/24547-1 and 2016/18499-0) for financial support. Computational and financial support from the Center for Computational Engineering and Sciences at Unicamp through the FAPESP/CEPID Grant No. 2013/08293-7 is also acknowledged. Support from the Brazilian Agencies CNPq and CAPES is also acknowledged Abstract: We report a detailed study through fully atomistic molecular dynamics simulations and DFT calculations on the mechanical properties of protomene. Protomene is a new carbon allotrope composed of a mixture of sp(2) and sp(3) hybridized states. Our results indicate that protomene presents an anisotropic behavior about tensile deformations. At room temperature, protomene presents an ultimate strength of similar to 100 GPa and Young's modulus of similar to 600 GPa, lower than the same for other carbon allotropes. Despite that, protomente presents the highest ultimate strain along the z-direction (similar to 24.7%). Our results also show that stretching the protomene along the z-direction or heating it can induce a semiconductor-metallic phase transition, due to a high amount of sp(3) bonds that are converted to sp(2) ones FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES Fechado

Agradecimentos: This work was supported in part by the Brazilian Agencies CAPES, CNPq and FAPESP. The authors also thank the Center for Computational Engineering and Sciences at Unicamp for financial support through the FAPESP/CEPID Grant # 2013/08293-7. DDB thanks FAPESP gr # 2015/14703-9 for financial support. CFW thanks São Paulo Research Foundation (FAPESP) Grant No. 2014/24547-1 for financial support Abstract: Experimental evidence has shown that graphene oxide (GO) can be impermeable to liquids, vapors and gases, while it allows a fast permeation of water molecules. Theoretical studies to understand the filtration mechanisms come mostly from water desalination, while very few works have been dedicated to alcohol dehydration. In this work, we have investigated the molecular level mechanism underlying the alcohol/water separation inside GO membranes. A series of Molecular Dynamics and Grand-Canonical Monte Carlo simulations were carried out to probe the ethanol/water and methanol/water separation through GO membranes composed of multiple layered graphene-based films with different interlayer distance values and number of oxygen-containing functional groups. Our results show that the size exclusion and membrane affinities are not sufficient to explain the selectivity. Besides that, the favorable water molecular arrangement inside GO 2D-channels forming a robust H-bond network and the fast water permeation are crucial for an effective separation mechanism. In other words, the separation phenomenon is not only governed by membrane affinities (enthalpic mechanisms) but mainly by the geometry and size factors (entropic mechanisms). Our findings are consistent with the available experimental data and contribute to clarify important aspects of the separation behavior of confined alcohol/ water in GO membranes COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Aberto

Agradecimentos: We would like to thank the Brazilian agency FAPESP (Grants 2013/08293-7 and 2016/18499-0) for financial support. This research was also supported by resources supplied by the Center for Scientific Computing (NCC/GridUNESP) of the São Paulo State University (UNESP). Computational support from the Center for Computational Engineering and Sciences at Unicamp is also acknowledged Abstract: Gradient nanograins (GNG) creation in metals has been a promising approach to obtain ultra-strong materials. Recently, R. Thevamaran et al. (Science 354:312 in 2016) proposed a single-step method based on high-velocity impacts of silver nanocubes (SNC) to produce almost perfect GNG. However, after certain time, these grains spontaneously coalesce, which compromises the induced hardening and other mechanical properties. To better understand these processes, a detailed investigation at the atomic scale of the deformation/hardening mechanisms are needed, which is one of the objectives of the present work. We carried out fully atomistic molecular dynamics (MD) simulations of silver nanocubes at high impact velocity values using realistic structural models. Our MD results suggest that besides the GNG mechanisms, the observed SNC hardening could be also the result of the existence of polycrystalline arrangements formed by HCP domains encapsulated by FCC ones in the smashed SNC. This can be a new way to design ultra-strong materials, even in the absence of GNG domains FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Fechado

Agradecimentos: We would like to thank the Brazilian agency FAPESP (Grants 2013/08293–7, 2014/24547–1 and 2016/18499–0) for financial support. Computational and financial support from the Center for Computational Engineering and Sciences at Unicamp through the FAPESP/CEPID Grant No. 2013/08293–7 is also acknowledged. Support from the Brazilian Agencies CNPq and CAPES is also acknowledged Abstract: We have investigated through fully atomistic reactive molecular dynamics and density functional theory simulations, the mechanical properties and fracture dynamics of single-ringed novamene (1R-novamene), a new 3D carbon allotrope structure recently proposed. Our results showed that 1R-novamene is an anisotropic structure with relation to tensile deformation. Although 1R-novamente shares some mechanical features with other carbon allotropes, it also exhibits distinct ones, such as, extensive structural reconstructions. 1R-novamene presents ultimate strength (similar to 100 GPa) values lower than other carbon allotropes, but it has the highest ultimate strain along the z-direction (similar to 22.5%). Although the Young's modulus (similar to 600 GPa) and ultimate strength values are smaller than for other carbon allotropes, they still outperform other materials, such as for example silicon, steel or titanium alloys. With relation to the fracture dynamics, 1R-novamene is again anisotropic with the fracture/crack propagation originating from deformed heptagons and pentagons for x and y directions and broken sp(3) bonds connecting structural planes. Another interesting feature is the formation of multiple and long carbon linear chains in the final fracture stages FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES Aberto

Agradecimentos: We would like to thank the Brazilian agency FAPESP (Grants 2013/08293-7 and 2016/18499-0) for financial support and Center for Computational Engineering and Sciences (CCES) for the computational support Abstract: Graphene is a very promising material for nanoelectronics applications due to its unique and remarkable electronic and thermal properties. However, when deposited on metallic electrodes the overall thermal conductivity is significantly decreased. This phenomenon has been attributed to the mismatch between the interfaces and contact thermal resistance. Experimentally, one way to improve the graphene/metal contact is thorough high-temperature annealing, but the detailed mechanisms behind these processes remain unclear. In order to address these questions, we carried out fully atomistic reactive molecular dynamics simulations using the ReaxFF force field to investigate the interactions between multi-layer graphene and metallic electrodes (nickel) under (thermal) annealing. Our results show that the annealing induces an upward-downward movement of the graphene layers, causing a pile-driver-like effect over the metallic surface. This graphene induced movements cause a planarization (thermal polishing-like effect) of the metallic surface, which results in the increase of the effective graphene/metal contact area. This can also explain the experimentally observed improvements of the thermal and electric conductivities FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Aberto

Agradecimentos: Work supported in part by the Brazilian Agencies CAPES and CNPq. The authors acknowledge the Sao Paulo Research Foundation (FAPESP) Grant No. 2014/24547-1 for financial support. Computational and financial support from the Center for Computational Engineering and Sciences at Unicamp through the FAPESP/CEPID Grant No. 2013/08293-7 is also acknowledged Abstract: The advent of graphene created a revolution in materials science. Because of this there is a renewed interest in other carbon-based structures. Graphene is the ultimate (just one atom thick) membrane. It has been proposed that graphene can work as impermeable membrane to standard gases, such argon and helium. Graphene-like porous membranes, but presenting larger porosity and potential selectivity would have many technological applications. Biphenylene carbon (BPC), sometimes called graphenylene, is one of these structures. BPC is a porous twodimensional (planar) allotrope carbon, with its pores resembling typical sieve cavities and/or some kind of zeolites. In this work, we have investigated the hydrogenation dynamics of BPC membranes under different conditions (hydrogenation plasma density, temperature, etc.). We have carried out an extensive study through fully atomistic molecular dynamics (MD) simulations using the reactive force field ReaxFF, as implemented in the well-known Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) code. Our results show that the BPC hydrogenation processes exhibit very complex patterns and the formation of correlated domains (hydrogenated islands) observed in the case of graphene hydrogenation was also observed here. MD results also show that under hydrogenation BPC structure undergoes a change in its topology, the pores undergoing structural transformations and extensive hydrogenation can produce significant structural damages, with the formation of large defective areas and large structural holes, leading to structural collapse COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Fechado

Agradecimentos: This work has been supported by the U.S. Department of Defense: U.S. Air Force Office of Scientific Research for the Project MURI: "Synthesis and Characterization of 3-D Carbon Nanotube Solid Networks" Award No. FA9550-12-1-0035. L.D.M., P.A.S.A., and D.S.G. thank the Center for Computational Engineering and Sciences at Unicamp for financial support through the FAPESP/CEPID Grant No. 2013/08293-7. E.V.B. thanks the Johnson Space Center for financial support through the "Advance Transparent Materials for Shielding and Produce Self-Healing Materials for Pressure Wall Use", Award No. NNX16AC36G. L.D.M. acknowledges financial support from the Brazilian Federal Agency CAPES via its PNPD program Abstract: Advanced materials with multifunctional capabilities and high resistance to hypervelocity, impact are of great interest to the designers of aerospace structures. Carbon nanotubes (CNTs) with their lightweight and high strength properties are alternative-to metals and/or metallic alloys conventionally used in aerospace-applications. Here we report, a detailed study on the ballistic fracturing of CNTs for different velocity ranges. Our-results show that the highly energetic impacts cause bond breakage and carbon atom rehybridizations, and sometimes extensive structural reconstructions were also observed Experimental,, observations Show the formation of nanoribbons,, nanodiamonds, and covalently interconnected nanostructures, depending On impact conditions. Fully atotnistic reactive molecular dynamics simulations were also carried out in order to gain further insights into the mechanism behind the transformation of CNTs. The simulations show that the velocity and relative-orientation of the multiple colliding :nanotubes are critical to determine the impact outcome FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES Fechado

Agradecimentos: This work has been supported by US Department of Defense: US Air Force of Scientific Research for the Project MURI: ‘Synthesis and Characterization of 3-D Carbon Nanotube Solid Networks’ Award No. FA9550-12-1-0035. P.A.S.A. acknowledge financial support from the Brazilian Agencies CNPq, CAPES and FAPESP and also thanks the Center for Computational Engineering and Sciences at Unicamp for financial support through the FAPESP/CEPID Grant #2013/08293-7. Work at IIT Madras was supported by a grant through the Nano Mission, Government of India. Part of work was done while MAK was a visiting student at IIT Madras. P.M.A thanks IIT Madras for a Distinguished Visiting Professorship Abstract: Carbon nanotubes can be chemically modified by attaching various functionalities to their surfaces, although harsh chemical treatments can lead to their break-up into graphene nanostructures. On the other hand, direct coupling between functionalities bound on individual nanotubes could lead to, as yet unexplored, spontaneous chemical reactions. Here we report an ambient mechano-chemical reaction between two varieties of nanotubes, carrying predominantly carboxyl and hydroxyl functionalities, respectively, facilitated by simple mechanical grinding of the reactants. The purely solid-state reaction between the chemically differentiated nanotube species produces condensation products and unzipping of nanotubes due to local energy release, as confirmed by spectroscopic measurements, thermal analysis and molecular dynamic simulations CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Aberto

Agradecimentos: This work was supported in part by the Brazilian Agencies FAPESP, CAPES and CNPq. The authors thank the Center for Computational Engineering and Sciences at Unicamp for financial support through the FAPESP/CEPID Grant #2013/08293-7. Authors would like to thank Drs. L. G. Cançado and C. Fantini (UFMG, Brazil) for help in performing Stokes/anti- Stokes Raman measurements Abstract: Graphene, in single layer or multi-layer forms, holds great promise for future electronics and high-temperature applications. Resistance to oxidation, an important property for high-temperature applications, has not yet been extensively investigated. Controlled thinning of multi-layer graphene (MLG), e.g., by plasma or laser processing is another challenge, since the existing methods produce non-uniform thinning or introduce undesirable defects in the basal plane. We report here that heating to extremely high temperatures (exceeding 2000 K) and controllable layer-by-layer burning (thinning) can be achieved by low-power laser processing of suspended high-quality MLG in air in "cold-wall" reactor configuration. In contrast, localized laser heating of supported samples results in non-uniform graphene burning at much higher rates. Fully atomistic molecular dynamics simulations were also performed to reveal details of oxidation mechanisms leading to uniform layer-by-layer graphene gasification. The extraordinary resistance of MLG to oxidation paves the way to novel high-temperature applications as continuum light source or scaffolding material FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Aberto

Agradecimentos: P. C. Silva is acknowledged for assistance during HRTEM and sample preparation work. We acknowledge financial support from LNLS, FAPESP, and CNPq. The authors thank the Center for Computational Engineering and Sciences at Unicamp for financial support through the FAPESP/CEPID Grant No. 2013/08293-7 Abstract: We report here an atomistic study of the mechanical deformation of AuxCu(1- x ) atomic-size wires (nanowires (NWs)) by means of high resolution transmission electron microscopy experiments. Molecular dynamics simulations were also carried out in order to obtain deeper insights on the dynamical properties of stretched NWs. The mechanical properties are significantly dependent on the chemical composition that evolves in time at the junction, some structures exhibit a remarkable de-alloying behavior. Also, our results represent the first experimental realization of mixed linear atomic chains (LACs) among transition and noble metals, in particular, surface energies induce chemical gradients on NW surfaces that can be exploited to control the relative LAC compositions (different number of gold and copper atoms). The implications of these results for nanocatalysis and spin transport of one-atom-thick metal wires are addressed FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Aberto

Agradecimentos: The authors acknowledge N.M. Barbosa Neto for technical support and A.C.T. van Duin for discussions. This work was supported in part by the Brazilian Agencies CAPES and CNPq (Rede Brasileira de Pesquisa e Instrumentação em NanoEspectroscopia Óptica, MCTI-CNPq). The authors thank the Center of Microscopy at the Universidade Federal de Minas Gerais (www.microscopia.ufmg.br) for providing the means for the microscopy work and the Center for Computational Engineering and Sciences at Unicamp for financial support through the FAPESP/CEPID Grant #2013/08293-7. RP acknowledges FAPESP for Grants #2011/17253-3 and #2013/09536-0 Abstract: Gold is a noble metal that, in comparison with silver and copper, has the advantage of corrosion resistance. Despite its high conductivity, chemical stability and biocompatibility, gold exhibits high plasticity, which limits its applications in some nanodevices. Here, we report an experimental and theoretical study on how to attain enhanced mechanical stability of gold nanotips. The gold tips were fabricated by chemical etching and further encapsulated with carbon nanocones via nanomanipulation. Atomic force microscopy experiments were carried out to test their mechanical stability. Molecular dynamics simulations show that the encapsulated nanocone changes the strain release mechanisms at the nanoscale by blocking gold atomic sliding, redistributing the strain along the whole nanostructure. The carbon nanocones are conducting and can induce magnetism, thus opening new avenues on the exploitation of transport, mechanical and magnetic properties of gold covered by sp(2) carbon at the nanoscale COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Aberto

Agradecimentos: This work has been supported by U.S. Department of Defense: U.S. Air Force Office of Scientific Research for the Project MUM: "Synthesis and Characterization of 3-D Carbon Nanotube Solid Networks" Award No. FA9550-12-1-0035. PASA, L.D.M., and D.S.G. acknowledge financial support from the Brazilian Agencies CNPq, CAPES, and FAPESP and also thank the Center for Computational Engineering and Sciences at Unicamp for financial support through the FAPESP/CEPID Grant 2013/08293-7. C.S.T. is thankful to IISc for support Abstract: The way nanostructures behave and mechanically respond to high impact collision is a topic of intrigue. For anisotropic nanostructures, such as carbon nanotubes, this response will be complicated based on the impact geometry. Here we report the result of hypervelocity impact of nanotubes against solid targets and show that impact produces a large number of defects in the nanotubes, as well as rapid atom evaporation, leading to their unzipping along the nanotube axis. Fully atomistic reactive molecular dynamics simulations are used to gain further insights of the pathways and deformation and fracture mechanisms of nanotubes under high energy mechanical impact. Carbon nanotubes have been unzipped into graphene nanoribbons before using chemical treatments but here the instability of nanotubes against formation, fracture, and unzipping is revealed purely through mechanical impact. defect CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Fechado

Agradecimentos: The authors would like to thank Prof. van Duin, Dr. Luiz H. G. Tizei and Dr. Vitor T. A. Oiko for helpful discussions for helpful discussions and Prof. Alexandru T. Balaban for a critical reading of the manuscript. This work was supported in part by the Brazilian Agencies CNPq and FAPESP. The authors thank the Center for Computational Engineering and Sciences at Unicamp for financial support through the FAPESP/CEPID Grant # 2013/08293-7. RP also acknowledges FAPESP Grant # 2011/17253-3 Abstract: By means of ab initio calculations, we investigate the possibility of existence of a boron nitride (BN) porous two-dimensional nanosheet, which is geometrically similar to the carbon allotrope known as biphenylene carbon. The proposed structure, which we called inorganic graphenylene (IGP), is formed spontaneously after selective dehydrogenation of the porous boron nitride (BN) structure proposed by Ding et al. We study the structural and electronic properties of both porous BN and IGP, and it is shown that, by selective substitution of B and N atoms with carbon atoms in these structures, the band gap can be significantly reduced, changing their behavior from insulators to semiconductors, thus opening the possibility of band gap engineering for this class of two-dimensional materials CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Aberto

Agradecimentos: This research was supported by the Science and technology innovation fund of Shenzhen (JCYJ20130401170306832); National Natural Science Foundation of China (grant no. 31100567); start-up grant from the First Institute of Oceanography (GY02-2011T10) and the MOHRSS (Ministry of Human Resources and Social Security of China), Taishan Scholar Fund, and the National Natural Science Foundation of China (grant no. 81071249, 81171446, 20905050, and 61205203). Douglas S. Galvao, Pedro A. S. Autreto and Eric Perim acknowledge partial support from the Brazilian agencies CNPq and Fapesp Abstract: We have developed a microwave assisted one-pot approach to fabricate a novel hybrid nano-composite composed of two-dimensional chemically exfoliated layered hexagonal boron nitride (h-BN) and embedded silver nanoparticles (SNP). Atomic layered h-BN exfoliated using chemical liquid showed strong in-plane bonding and weak van der Waals interplanar interactions, which is utilized for chemically interfacing SNP, indicating their ability to act as excellent nano-scaffolds. The SNP/h-BN optical response, in particular band gap, is strongly dependent on the concentration of the metallic particles. In order to gain further insight into this behavior we have also carried out ab initio density functional theory (DFT) calculations on modeled structures, demonstrating that the bandgap value of SNP/h-BN hybrids could be significantly altered by a small percentage of OH- groups located at dangling B and N atoms. Our results showed that these novel SNP/h-BN nanohybrid structures exhibited excellent thermal stability and they are expected to be applied as devices for thermal oxidation-resistant surface enhanced Raman spectroscopy (SERS). The SNP/h-BN membrane showed remarkable antibacterial activity, suggesting their potential use in water disinfection and food packaging CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Aberto

Agradecimentos: We acknowledge the funding support from U.S. Department of Defense: U.S. Air Force Office of Scientific Research for the Project MURI: 'Synthesis and Characterization of 3-D Carbon Nanotube Solid Networks' Award No. FA9550-12-1-0035. We also acknowledge the support by EAGER-NSF ECCS-1327093, CONACYT (213780) and INDO-US: IUSSTF/JC/22-2012/2013-14 Abstract: Low-density nanostructured foams are often limited in applications due to their low mechanical and thermal stabilities. Here we report an approach of building the structural units of three-dimensional (3D) foams using hybrid two-dimensional (2D) atomic layers made of stacked graphene oxide layers reinforced with conformal hexagonal boron nitride (h-BN) platelets. The ultra-low density (1/400 times density of graphite) 3D porous structures are scalably synthesized using solution processing method. A layered 3D foam structure forms due to presence of h-BN and significant improvements in the mechanical properties are observed for the hybrid foam structures, over a range of temperatures, compared with pristine graphene oxide or reduced graphene oxide foams. It is found that domains of h-BN layers on the graphene oxide framework help to reinforce the 2D structural units, providing the observed improvement in mechanical integrity of the 3D foam structure Aberto

Agradecimentos: This work was supported in part by the Brazilian Agencies, CAPES, CNPq and FAPESP. The authors thank the Center for Computational Engineering and Sciences at Unicamp for financial support through the FAPESP/CEPID Grant #2013/08293-7. RP acknowledges FAPESP for Grant No. 2013/09536-0. ACTvD acknowledges funding from the U.S. Army Research Laboratory through the Collaborative Research Alliance (CRA) for Multi Scale Multidisciplinary Modeling of Electronic Materials (MSME) and from AFOSR grants No. FA9550-10-1-0563 and No. FA9550-11-1-0158 Abstract: As graphene has become one of the most important materials, there is renewed interest in other similar structures. One example is silicene, the silicon analogue of graphene. It shares some of the remarkable graphene properties, such as the Dirac cone, but presents some distinct ones, such as a pronounced structural buckling. We have investigated, through density functional based tight-binding (DFTB), as well as reactive molecular dynamics (using ReaxFF), the mechanical properties of suspended single-layer silicene. We calculated the elastic constants, analyzed the fracture patterns and edge reconstructions. We also addressed the stress distributions, unbuckling mechanisms and the fracture dependence on the temperature. We analysed the differences due to distinct edge morphologies, namely zigzag and armchair COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Aberto

Agradecimentos: This work was supported in part by the Brazilian Agencies CNPq and FAPESP. The authors thank the Center for Computational Engineering and Sciences at Unicamp for financial support through the FAPESP/CEPID Grant #2013/08293-7. RP also acknowledges FAPESP Grant #2011/17253-3 Abstract: Boron nitride nanoribbons (BNNRs) exhibit very interesting magnetic properties, which could be very useful in the development of spintronic based devices. One possible route to obtain BNNRs is through the unzipping of boron nitride nanotubes (BNNTs), which have been already experimentally realized. In this work, different aspects of the unzipping process of BNNTs were investigated through fully atomistic molecular dynamics simulations using a classical reactive force field (ReaxFF). We investigated multiwalled BNNTs of different diameters and chiralities. Our results show that chirality plays a very important role in the unzipping process, as well as the interlayer coupling. These combined aspects significantly change the fracturing patterns and several other features of the unzipping processes in comparison to the ones observed for carbon nanotubes. Also, similar to carbon nanotubes, defective BNNTs can create regions of very high curvature which can act as a path to the unzipping process FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Fechado

Agradecimentos: This work was supported in part by the Brazilian Agencies CNPq, CAPES, FAPESP. Ricardo Paupitz is grateful for the financial support of Fapesp (grant 2011/17253-3) and Fundunesp (grant 01409/11). The authors wish to thank M Z S Flores for very useful discussions. ACTvD and SGS acknowledge funding from the Air Force Office of Scientific Research under AFOSR-MURI Grant FA9550-10-1-0563 Abstract: We report here a fully reactive molecular dynamics study on the structural and dynamical aspects of the fluorination of graphene membranes (fluorographene). Our results show that fluorination tends to produce defective areas on the graphene membranes with significant distortions of carbon-carbon bonds. Depending on the amount of incorporated fluorine atoms, large membrane holes were observed due to carbon atom losses. These results may explain the broad distribution of the structural lattice parameter values experimentally observed. We have also investigated the effects of mixing hydrogen and fluorine atoms on the graphene functionalization. Our results show that, when in small amounts, the presence of hydrogen atoms produces a significant decrease in the rate of fluorine incorporation onto the membrane. On the other hand, when fluorine is the minority element, it produces a significant catalytic effect on the rate of hydrogen incorporation. We have also observed the spontaneous formation of new hybrid structures with different stable configurations (chair-like, zigzag-like and boat-like) which we named fluorographane CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Fechado

Agradecimentos: The authors are grateful to FAPESP, CNPq, and LNLS for financial support Abstract: We have studied the effect of thermal effects on the structural and transport response of Ag atomic-size nanowires (NWs) generated by mechanical elongation. Our study involves both time-resolved atomic resolution transmission electron microscopy imaging and quantum conductance measurement using an ultra-high-vacuum mechanically controllable break Junection. We have observed drastic changes in conductance and structural properties of Ag nanowires generated at different temperatures (150 and 300 K). By combining electron microscopy images, electronic transport measurements, and quantum transport calculations, we have been able to obtain a consistent correlation between the conductance and structural properties of Ag NWs. In particular, our study has revealed the formation of metastable rectangular rod-like Ag wire (3/3) along the [001] crystallographic direction, whose formation is enhanced. These results illustrate the high complexity of analyzing structural and quantum conductance behaviour of metal atomic-size wires; also, they reveal that it is extremely difficult to compare NW conductance experiments performed at different temperatures due to the fundamental modifications of the mechanical behavior FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Aberto

Agradecimentos: This work was supported in part by the Brazilian Agencies CNPq, CAPES, and FAPESP Abstract: Graphene is considered one of the most promising materials for future electronics. However, in its pristine form, graphene is a gapless material, which imposes limitations to its use in some electronic applications. To solve this problem, many approaches have been tried, such as physical and chemical functionalizations. These processes compromise some of the desirable graphene properties. In this work, based on ab initio quantum molecular dynamics, we showed that a two-dimensional carbon allotrope, named biphenylene carbon (BPC), can be obtained from selective dehydrogenation of porous graphene. BPC presents a nonzero bandgap and well-delocalized frontier orbitals. Synthetic routes to BPC are also addressed CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Aberto

Agradecimentos: This work was supported by the Brazilian agencies CNPq, CAPES and FAPESP. We would like to thank Professor B I Yakobson and Dr V I Artyukhov for helpful discussions regarding fracture mechanisms of carbon-based materials. R P B dos Santos also acknowledges support from UNESP Abstract: Graphene nanoribbons (GNRs) are very interesting structures which can retain graphene's high carrier mobility while presenting a finite bandgap. These properties make GNRs very valuable materials for the building of nanodevices. Unzipping carbon nanotubes (CNTs) is considered one of the most promising approaches for GNR controlled and large-scale production, although some of the details of the CNT unzipping processes are not completely known. In this work we have investigated CNT unzipping processes through fully atomistic molecular dynamics simulations using reactive force fields (ReaxFF). Multiwalled CNTs of different dimensions and chiralities under induced mechanical stretching were considered. Our results show that fracture patterns and stress profiles are highly CNT chirality dependent. Our results also show that the 'crests' (partially unzipped CNT regions presenting high curvature), originating from defective CNT areas, can act as a guide for the unzipping processes, which can explain the almost perfectly linear cuts frequently observed in unzipped CNTs CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Fechado