Nanofils de silici : com més llargs, millors

Investigadors de la UAB han estudiat un dels més prometedors sistemes unidimensionals per a futures aplicacions en el camp de la nanoelectrònica: els nanofils de silici. Els científics han aconseguit estudiar sistemes més llargs que els analitzats fins ara i han conclòs que són més realistes i tenen una física molt més rica.Investigadores de la UAB han estudiado uno de los más prometedores sistemas unidimensionales para futuras aplicaciones en el campo de la nanoelectrónica: los nanohilos de silicio. Los científicos han conseguido estudiar sistemas más largos que los analizados hasta ahora y han llegado a la conclusión de que son más realistas y tienen una física mucho más rica.UAB researchers have studied one of the most promising unidimensional systems for future applications in the nanoelectronics field: the silicon nanowires. The scientists have studied silicon nanowires longer than those analyzed until now, and have concluded that are more realistic systems and with a much richer physics

Band gap engineering of MoS2_2 upon compression

Molybdenum disulfide (MoS$_2$) is a promising candidate for 2D nanoelectronic devices, that shows a direct band-gap for monolayer structure. In this work we study the electronic structure of MoS$_2$ upon both compressive and tensile strains with first-principles density-functional calculations for different number of layers. The results show that the band-gap can be engineered for experimentally attainable strains (i.e. $\pm 0.15$). However compressive strain can result in bucking that can prevent the use of large compressive strain. We then studied the stability of the compression, calculating the critical strain that results in the on-set of buckling for free-standing nanoribbons of different lengths. The results demonstrate that short structures, or few-layer MoS$_2$, show semi-conductor to metal transition upon compressive strain without bucking

Spin transport in dangling-bond wires on doped H-passivated Si(100)

New advances in single-atom manipulation are leading to the creation of atomic structures on H passivated Si surfaces with functionalities important for the development of atomic and molecular based technologies. We perform total-energy and electron-transport calculations to reveal the properties and understand the features of atomic wires crafted by H removal from the surface. The presence of dopants radically change the wire properties. Our calculations show that dopants have a tendency to approach the dangling-bond wires, and in these conditions, transport is enhanced and spin selective. These results have important implications in the development of atomic-scale spintronics showing that boron, and to a lesser extent phosphorous, convert the wires in high-quality spin filters.Comment: 11 pages, 4 figure

Thermal conductivity and phonon hydrodynamics in transition metal dichalcogenides from first-principles

We carry out a systematic study of the thermal conductivity of four single-layer transition metal dichalcogenides, MX$_2$ (M = Mo, W; X = S, Se) from first-principles by solving the Boltzmann Transport Equation (BTE). We compare three different theoretical frameworks to solve the BTE beyond the Relaxation Time Approximation (RTA), using the same set of interatomic force constants computed within density functional theory (DFT), finding that the RTA severely underpredicts the thermal conductivity of MS$_2$ materials. Calculations of the different phonon scattering relaxation times of the main collision mechanisms and their corresponding mean free paths (MFP) allow evaluating the expected hydrodynamic behaviour in the heat transport of such monolayers. These calculations indicate that despite of their low thermal conductivity, the present TMDs can exhibit large hydrodynamic effects, being comparable to those of graphene, especially for WSe$_2$ at high temperatures.Comment: 16 pages, 9 figure

Tuning thermal transport in Si nanowires by isotope engineering

We study thermal transport in isotopically disordered Si nanowires, discussing the feasibility of phonon engineering for thermoelectric applications within these systems. To this purpose, we carry out atomistic molecular dynamics and nonequilibrium Green's function calculations to characterize the dependence of the thermal conductance as a function of the isotope concentration, isotope radial distribution and temperature. We show that a reduction of the conductivity of up to 20% can be achieved with suitable isotope blends at room temperature and approximately 50% at low temperature. Interestingly, precise control of the isotope composition or radial distribution is not needed. An isotope disordered nanowire roughly behaves like a low-pass filter, as isotope impurities are transparent for long wave-length acoustic phonons, while only mid- and high-frequency optical phonons undergo significant scattering.We acknowledge financial support from the Ministerio de Economía y Competitividad (MINECO) under grant FEDER-MAT2013-40581-P and the Severo Ochoa Centres of Excellence Program under Grant SEV-2015-0496 and from the Generalitat de Catalunya under grants no. 2014 SGR 301 and through the Beatriu de Pinós fellowship program (2014 BP_B 00101). The calculations were performed at the Barcelona Supercomputing Center (BSC-CNS) within the project “Thermal transport in isotopically disordered Si nanowires (FI-2016-1-0022)”. We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI) ReferencesPeer Reviewe