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We report on the hydrogenation of (3×3)/(4×4) silicene epitaxially grown on Ag(111) studied by in situ Raman spectroscopy and state-of-the-art ab initio calculations. Our results demonstrate that hydrogenation of (3×3)/(4×4) silicene leads to the formation of two different atomic structures which exhibit distinct spectral vibrational modes. Raman selection rules clearly show that the Si atoms undergo a rehybridization in both cases from a mixed sp2-sp3 to a dominating sp3 state increasing the distance between the two silicene sublattices. This results in a softening of the in-plane and a stiffening of the out-of-plane phonon modes. Nevertheless, hydrogenated epitaxial silicene retains a two-dimensional nature and hence can be considered as epitaxial silicane. The level of hydrogenation can be determined by the intensity ratio of the Raman modes with different symmetries., Deutsche Forschungsgemeinschaft (VO1261/4-1); ESF Nachwuchsforschergruppe "E-PISA"; TUBITAK (116C073); The Science Academy, Turkey, under the BAGEP program

Rubio, Angel/0000-0003-2060-3151, WOS: 000400260500007, [No abstract available]

Recent studies show that several metal oxides and dichalcogenides (MX2), which exist in nature, can be stable in two-dimensional (2D) form and each year several new MX2 structures are explored. The unstable structures in H (hexagonal) or T (octahedral) forms can be stabilized through Peierls distortion. In this paper, we propose new 2D forms of RuS2 and RuSe2 materials. We investigate in detail the stability, electronic, magnetic, optical, and thermodynamic properties of 2D RuX2 (X = S, Se) structures from first principles. While their H and T structures are unstable, the distorted T structures (T'-RuX2) are stable and have a nonmagnetic semiconducting ground state. The molecular dynamic simulations also confirm that T'-RuX2 systems are stable even at 500 K without any structural deformation. T'-RuS2 and T'-RuSe2 have indirect band gaps with 0.745 eV (1.694 eV with HSE) and 0.798 eV (1.675 eV with HSE) gap values, respectively. We also examine their bilayer and trilayer forms and find direct and smaller band gaps. We find that AA stacking is more favorable than the AB configuration. The new 2D materials obtained can be good candidates with striking properties for applications in semiconductor electronic, optoelectronic devices, and sensor technology.

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY)., The growth of the √3 × √3 reconstructed silicene on Ag substrate has been frequently observed in experiments while its atomic structure and formation mechanism is poorly understood. Here, by first-principles calculations, we show that √3 × √3 reconstructed silicene is constituted by dumbbell units of Si atoms arranged in a honeycomb pattern. Our model shows excellent agreement with the experimentally reported lattice constant and STM image. We propose a new mechanism for explaining the spontaneous and consequential formation of √3 × √3 structures from 3×3 structures on Ag substrate. We show that the √3 × √3 reconstruction is mainly determined by the interaction between Si atoms and have weak influence from Ag substrate. The proposed mechanism opens the path to understanding of multilayer silicon, S.C. and A.R. acknowledge financial support from the Marie Curie Grant FP7-PEOPLE-2013-IEF project ID 628876, the European Research Council Advanced Grant DYNamo (ERC-2010-AdG-267374), Spanish Grant (FIS2010-21282-C02-01), Grupos Consolidados UPV/EHU del Gobierno Vasco (IT578-13), Ikerbasque and the European Commission projects CRONOS (Grant No. 280879-2). V.O.O. and S.C. acknowledge the support from TUBA.

Trabajo presentado a la International Conference on Mathematical Modeling in Physical Sciences, celebrado en Madrid (España) del 28 al 31 de Agosto de 2014., Theoretical calculations by Kyozaburo Takeda and Kenji Shiraishi predicted 20 years ago the possible existence and properties of 2D- new materials, later called : graphene, silicene and germanene. For the experimental discovery of graphene in 2004, Andrei Geim and Konstantin Novoselov were awarded the Nobel Prize in Physics; since then, many experiments by the international community developed different forms of preparation and isolation of this material and their use in nanoelectronic devices. Later, the discovery of silicene by a team of researchers from Germany, Italy and France, with Drs Patrick Vogt, Paola de Padova and Prof. Guy Le Lay occured in 2012. In the last two years, scientists around the world have demonstrated that this material can be obtained on a few substrates. Now, we will show evidence of the two-dimensional epitaxial growth of germanium in in a honeycomb arrangement, most likely, single layer germanene, a novel synthetic germanium allotrope that does not exist in nature. If true, this will complete the theoretical predictions presented years ago, offering 2D-new materials with exciting properties, with the potential to replace the silicon based traditional CMOS for a number of electronic applications., GLL gratefully acknowledge financial support from the “2D-NANOLATTICES" project of the Future and Emerging Technologies (FET) program within the 7th framework program for research of the European Commission under FET Grant No. 270749. L.X., S.V. and A.R. acknowledge financial support from the European Research Council Advanced Grant DYNamo (ERC-2010- AdG-267374), Spanish Grant (FIS2010-21282-C02-01), Grupos Consolidados UPV/EHU del Gobierno Vasco (IT578-13), Ikerbasque and the European Commission projects CRONOS (Grant number 280879-2 CRONOS CP-FP7).

Trabajo presentado a la 4th edition of Graphene Conference series (Parallel Workshop 3: Theory & Simulation), celebrada en Toulouse (Francia) del 6 al 9 de Mayo de 2014., Silicene, a monolayer of silicon atoms arranged in a honeycomb structure, received an enormous interest for being a candidate two-dimensional material that could bring the exotic electronic structure of graphene to the well-developed silicon-based technology. Experiments have shown that silicene synthesized on Ag substrates can acquire various reconstructions. In particular, structures having √3x√3 reconstruction have been frequently observed but yet poorly understood. Here we provide a compelling high-resolution angle resolved photoemission (ARPES) study together with first-principles calculations and scanning tunneling microscopy (STM), which unambiguously prove the existence of a particular two-dimensional arrangement of silicon atoms that, gives rise to two different phases with √3x√3 periodicity. We propose a new mechanism for explaining the spontaneous and consequential formation of both phases. We show that unlike others the √3x√3 reconstruction is intrinsic and is not dictated by the interaction with the Ag substrate. The proposed mechanism opens the path to the understanding of multilayer silicon.

Düşük boyutlu nanomalzemelerin sürtünme ve titreşimsel özellikleri ilk prensiplere dayanan en gelişmiş hesaplama yöntemleriyle incelendi.Fonon eğrilerinin hesaplanmasıyla nanobilim ve nanoteknolojide önemli uygulama potansiyeli taşı yan malzemelerin kararlılıkları test edildi. Bunlardan birisi grafin'in silisyum atomlarından oluşan analoğu olan silisen'dir. Silisen, günümüzün silikon teknolojisine uyumunun yanında, sahip olduğu eksantrik elektronik yapısıyla da önem taşımaktadır. Silisen'deki atomlar yukarı ve aşağı hareket ederek titreşimsel spektrumu sanal frekanslardan arındırmakta ve bununla birlikte kütlesiz Dirac Fermiyon'larının oluşumu için gerekli olan simetriyi korumaktadır. Silisen nanoşeritlerin ve atomik karbon zincirlerin titreşimsel özelliklerinin incelenmesi sonucu dördüncü akustik mod ve Friedel salınımlarından kaynaklı uzun mesafeli etkileşim gibi yeni fiziksel olgular ortaya konmuştur.Sürtünme biliminin temel kavramları olan enerji yayımı, adiyabatik ve ani olgularla birlikte sürtünmenin anlaşılması için kullanılan birkaç basit model özetlenmiştir. Katmanlı yağlama malzemelerinin sabit basınç altında korugasyon potansiyelinin hesaplanması için yeni bir yöntem geliştirilmiştir. Bu malzemelerin yapışma kayma rejiminden düzenli kayma rejimine geçişi sürtünmesel başarım katsayısının tanımlanmasıyla kantitatif hale getirilmiştir. Bu ölçüt kullanılarak, oksitlenmeye dayanıklı olan tungsten oksit malzemesinin süperyağlama malzemesi olarak molibden disulfat malzemesinden daha yüksek performans gösterebileceği öne sürülmüştür. Nikel yüzeyleri arasına konulan grafin tabakaların sürtünmeyi düşürdüğü ve bu etkinin tabaka sayısıyla birlikte arttığı gözlemlenmiştir. Frictional and vibrational properties of low-dimensional nanostructures have been investigated using the state-of-the-art ab-initio calculations.Stringent test of stability based on calculation of phonon dispersions have been performed for various materials having important potential applications in nanoscience and nanotechnology. Silicene, a counterpart of graphene composed of silicon atoms, is one of such materials with its suitability to well established silicon technology together with eccentric electronic structure due to its honeycomb symmetry. Vibrational spectrum of silicene is found to be exempt from imaginary frequencies upon the puckering of atoms in adjacent sublattices while preserving the symmetry necessary for occurrence of massless Dirac Fermions. Analyses of vibrational properties of silicene nanoribbons and carbon atomic chains revealed new interesting physics like fourth acoustical mode and long-ranged interactions due to Friedel oscillations.Basic concepts of friction science like dissipation phenomena, adiabatic and sudden processes together with several simple models of friction have been summarized. A new method for calculation of corrugation potential between layered lubricants under constant loading pressure is introduced. Transition from stick-slip to continuous sliding regime is quantified through definition of frictional figure of merit for layered lubricants. Using this measure tungsten oxide is proposed as an oxidation resistant material which can outperform molybdenum disulfide as a superlubricant. It was found that, the corrugation strengths of graphene layers sandwiched between Ni slabs decrease as the number of layers increase. 106