Atomic discreteness and the nature of structural equilibrium in conductance histograms of electromigrated Cu-nanocontacts

We investigate the histograms of conductance values obtained during controlled electromigration thinning of Cu thin films. We focus on the question whether the most frequently observed conductance values, apparent as peaks in conductance histograms, can be attributed to the atomic structure of the wire. To this end we calculate the Fourier transform of the conductance histograms. We find all the frequencies matching the highly symmetric crystallographic directions of fcc-Cu. In addition, there are other frequencies explainable by oxidation and possibly formation of hcp-Cu. With these structures we can explain all peaks occurring in the Fourier transform within the relevant range. The results remain the same if only a third of the samples are included. By comparing our results to the ones available in the literature on work-hardened nanowires we find indications that even at low temperatures of the environment, metallic nanocontacts could show enhanced electromigration at low current densities due to defects enhancing electron scattering

Near-equilibrium measurement of quantum size effects using Kelvin probe force microscopy

In nano-structures such as thin films electron confinement results in the quantization of energy levels in the direction perpendicular to the film. The discretization of the energy levels leads to the oscillatory dependence of many properties on the film thickness due to quantum size effects. Pb on Si(111) is a specially interesting system because a particular relationship between the Pb atomic layer thickness and its Fermi wavelength leads to a periodicity of the oscillation of two atomic layers. Here, we demonstrate how the combination of scanning force microscopy (SFM) and Kelvin probe force microscopy (KPFM) provides a reliable method to monitor the quantum oscillations in the work function of Pb ultra-thin film nano-structures on Si(111). Unlike other techniques, with SFM/KPFM we directly address single Pb islands, determine their height while suppressing the influence of electrostatic forces, and, in addition, simultaneously evaluate their local work function by measurements close to equilibrium, without current-dependent and non-equilibrium effects. Our results evidence even-odd oscillations in the work function as a function of the film thickness that decay linearly with the film thickness, proving that this method provides direct and precise information on the quantum states.Comment: This document is the unedited author's version of a Submitted Work that was subsequently accepted for publication in Nanoscale, copyright Royal Society of Chemistry after peer review. To access the final edited and published work see doi belo

Atomically resolved scanning force studies of vicinal Si(111)

Well-ordered stepped semiconductor surfaces attract intense attention owing to the regular arrangements of their atomic steps that makes them perfect templates for the growth of one- dimensional systems, e.g. nanowires. Here, we report on the atomic structure of the vicinal Si(111) surface with 10 degree miscut investigated by a joint frequency-modulation scanning force microscopy (FM-SFM) and ab initio approach. This popular stepped surface contains 7 x 7-reconstructed terraces oriented along the Si(111) direction, separated by a stepped region. Recently, the atomic structure of this triple step based on scanning tunneling microscopy (STM) images has been subject of debate. Unlike STM, SFM atomic resolution capability arises from chemical bonding of the tip apex with the surface atoms. Thus, for surfaces with a corrugated density of states such as semiconductors, SFM provides complementary information to STM and partially removes the dependency of the topography on the electronic structure. Our FM-SFM images with unprecedented spatial resolution on steps confirm the model based on a (7 7 10) orientation of the surface and reveal structural details of this surface. Two different FM-SFM contrasts together with density functional theory calculations explain the presence of defects, buckling and filling asymmetries on the surface. Our results evidence the important role of charge transfers between adatoms, restatoms, and dimers in the stabilisation of the structure of the vicinal surface

O exercício profissional do Assistente Social nos CRAS/PAIF do município de São José (SC): entre desafios e possibilidades

TCC (Graduação) - Universidade Federal de Santa Catarina. Centro Socioeconômico. Serviço Social.Neste Trabalho de Conclusão de Curso, elaboram-se reflexões acerca do exercício profissional dos Assistentes Sociais nos Serviços de Proteção e Atendimento Integral à Família - PAIF do município de São José (SC). A metodologia empregada, além da pesquisa bibliográfica, foi a pesquisa empírica com os assistentes sociais. A pesquisa promove o debate a respeito desse espaço do exercício profissional; dessa forma, os sujeitos da pesquisa apontam que, na grande maioria dos CRAS implantados no referido município, o Serviço PAIF ainda não é consolidado. Simultaneamente, sua efetivação esbarra nas atuais condições de trabalho dos profissionais quanto à precarização dos postos de trabalho e a interferência por parte da gestão em sua autonomia, ou seja, por meio da fala das profissionais fica clara a necessidade de uma gestão participativa. Ainda evidenciamos a importância por parte da categoria quanto à apropriação dos instrumentais do Serviço Social, bem como dos princípios do Código de Ética da profissão para identificar os mecanismos inerentes às amarras institucionais e encontrar meios para trabalhar rumo à coletivização das demandas. O debate ora proposto não cessa aqui, muito pelo contrário, suscita a continuidade do processo investigativo

AQI na rua: repassado informações, experiências e novas tecnologias aquícolas à população

Anais do 35º Seminário de Extensão Universitária da Região Sul - Área Temática: ComunicaçãoO projeto AQI na Rua teve origem a partir de uma iniciativa dos egressos em levar o curso de Engenharia de Aquicultura para a comunidade, por se tratar de um curso novo, pouco conhecido e ser muito confundido com outras atividades. Essa ideia tomou forma e foi para as ruas, levando informações, experiências e proporcionando aos graduandos uma rica forma de repassar o conhecimento para pessoas leigas. Durante as mostras eram montadas tendas onde ficavam expostos os materias e animais, para que os participantes pudessem explicar para o público como é o curso e suas aplicações. O projeto foi considerado um sucesso em todas as suas cinco edições pelo grande número de pessoas que não conheciam as funções do Engenheiro de Aquicultura e tão poucos sabiam da existência da aquicultur

STM-induced surface aggregates on metals and oxidized silicon

We have observed an aggregation of carbon or carbon derivatives on platinum and natively oxidized silicon surfaces during STM measurements in ultra-high vacuum on solvent-cleaned samples previously structured by e-beam lithography. We have imaged the aggregated layer with scanning tunneling microscopy (STM) as well as scanning electron microscopy (SEM). The amount of the aggregated material increases with the number of STM scans and with the tunneling voltage. Film thicknesses of up to 10 nm with five successive STM measurements have been obtained

Shell effects and free-electrons in electromigrated oxidized Cu-nanocontacts

Electromigration in interconnects continues to be an important field of study in integrated circuits as the interconnects are planned to shrink in size at comparable pace as the semiconductor functional elements. Through shrinking the interconnects approach the regime where quantum size effects become important. The observation of quantum size and shell effects is usually restricted either to low-temperatures or vacuum conditions or to chemically inert materials such as Au. Here, we show that in electromigrated Cu nanocontacts such effects can be observed at room temperature and room pressure even in the presence of oxidation. Our data provide evidence that the nanocontacts are nearly spherical objects with a triangular-cylindrical symmetry of their electronic wave functions with a stronger free-electron-like character compared to previous results. We do not observe a detrimental effect of oxygen. The presence of shell effects has implications for the technological use of Cu nanocontacts as interconnects in integrated circuits and could lead to the use of electronic wave functions of shells in such interconnects