Nanoindentation unidirectional sliding and lateral force microscopy: evaluation of experimental techniques to measure friction at the nanoscale

CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPERG - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DO RIO GRANDE DO SULFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOLateral force microscopy (LFM) is an established technique to assess friction forces at the nanoscale. Nanoindentation followed by unidirectional sliding (NUS) is also used to evaluate friction forces at the micro/nanoscale. However, comparative studies between NUS and LFM evaluating the experimental results at different scales are still missing. In this work, a-C:D/H and a-C:H thin films with different [D]/[C] and [H]/[C] contents were used to analyze the friction forces by NUS and LFM. The results show that the friction behavior assessed by these two techniques in different scales is the same. The correlation between friction forces measured by NUS and LFM depends mainly on a contact area factor that makes invariant the friction force from nanoscale to microscale. Such behavior suggests a similar damping mechanism, probably phonon-coupling phenomena, for the friction force origin.812110CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPERG - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DO RIO GRANDE DO SULFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPERG - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DO RIO GRANDE DO SULFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO465423/2014-0sem informação2012/10127-

On the phonon dissipation contribution to nanoscale friction by direct contact

CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DO RIO GRANDE DO SUL - FAPERGSFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPThe friction phenomenon is a ubiquitous manifestation of nature. Models considering phononic, electronic, magnetic, and electrostatic interactions are invoked to explain the fundamental forces involved in the friction phenomenon. In order to establish the incidence of the phonon prompting at the nanoscale friction by direct contact, we study a diamond spherical dome sliding on carbon thin films containing different amount of deuterium and hydrogen. The friction coefficient decreases by substituting hydrogen by deuterium atoms. This result is consistent with an energy dissipation vibration local mechanism from a disordered distribution of bond terminators.718CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DO RIO GRANDE DO SUL - FAPERGSFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DO RIO GRANDE DO SUL - FAPERGSFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP554336/2010-3087/113189032012/10127-5The authors are grateful to UCS, INCT-INES-CNPq (Grant #554336/2010-3), CAPES (Grant #Brafitec 087/11, FAPERGS and SUMA2 Network Project - 7th Framework Program of the European Commission (IRSES Project #318903) for financial support. SRSM is FAPERGS fellow. CMM is CAPES fellow. MEHMC, FLF, FA, and CAF are CNPq fellows. FA was supported by FAPESP project 2012/10127-5

Pulsar Timing and its Application for Navigation and Gravitational Wave Detection

Pulsars are natural cosmic clocks. On long timescales they rival the precision of terrestrial atomic clocks. Using a technique called pulsar timing, the exact measurement of pulse arrival times allows a number of applications, ranging from testing theories of gravity to detecting gravitational waves. Also an external reference system suitable for autonomous space navigation can be defined by pulsars, using them as natural navigation beacons, not unlike the use of GPS satellites for navigation on Earth. By comparing pulse arrival times measured on-board a spacecraft with predicted pulse arrivals at a reference location (e.g. the solar system barycenter), the spacecraft position can be determined autonomously and with high accuracy everywhere in the solar system and beyond. We describe the unique properties of pulsars that suggest that such a navigation system will certainly have its application in future astronautics. We also describe the on-going experiments to use the clock-like nature of pulsars to "construct" a galactic-sized gravitational wave detector for low-frequency (f_GW ~1E-9 - 1E-7 Hz) gravitational waves. We present the current status and provide an outlook for the future.Comment: 30 pages, 9 figures. To appear in Vol 63: High Performance Clocks, Springer Space Science Review

Phase Structure and Compactness

In order to study the influence of compactness on low-energy properties, we compare the phase structures of the compact and non-compact two-dimensional multi-frequency sine-Gordon models. It is shown that the high-energy scaling of the compact and non-compact models coincides, but their low-energy behaviors differ. The critical frequency $\beta^2 = 8\pi$ at which the sine-Gordon model undergoes a topological phase transition is found to be unaffected by the compactness of the field since it is determined by high-energy scaling laws. However, the compact two-frequency sine-Gordon model has first and second order phase transitions determined by the low-energy scaling: we show that these are absent in the non-compact model.Comment: 21 pages, 5 figures, minor changes, final version, accepted for publication in JHE

Gravitational Waves From Known Pulsars: Results From The Initial Detector Era

We present the results of searches for gravitational waves from a large selection of pulsars using data from the most recent science runs (S6, VSR2 and VSR4) of the initial generation of interferometric gravitational wave detectors LIGO (Laser Interferometric Gravitational-wave Observatory) and Virgo. We do not see evidence for gravitational wave emission from any of the targeted sources but produce upper limits on the emission amplitude. We highlight the results from seven young pulsars with large spin-down luminosities. We reach within a factor of five of the canonical spin-down limit for all seven of these, whilst for the Crab and Vela pulsars we further surpass their spin-down limits. We present new or updated limits for 172 other pulsars (including both young and millisecond pulsars). Now that the detectors are undergoing major upgrades, and, for completeness, we bring together all of the most up-to-date results from all pulsars searched for during the operations of the first-generation LIGO, Virgo and GEO600 detectors. This gives a total of 195 pulsars including the most recent results described in this paper.United States National Science FoundationScience and Technology Facilities Council of the United KingdomMax-Planck-SocietyState of Niedersachsen/GermanyAustralian Research CouncilInternational Science Linkages program of the Commonwealth of AustraliaCouncil of Scientific and Industrial Research of IndiaIstituto Nazionale di Fisica Nucleare of ItalySpanish Ministerio de Economia y CompetitividadConselleria d'Economia Hisenda i Innovacio of the Govern de les Illes BalearsNetherlands Organisation for Scientific ResearchPolish Ministry of Science and Higher EducationFOCUS Programme of Foundation for Polish ScienceRoyal SocietyScottish Funding CouncilScottish Universities Physics AllianceNational Aeronautics and Space AdministrationOTKA of HungaryLyon Institute of Origins (LIO)National Research Foundation of KoreaIndustry CanadaProvince of Ontario through the Ministry of Economic Development and InnovationNational Science and Engineering Research Council CanadaCarnegie TrustLeverhulme TrustDavid and Lucile Packard FoundationResearch CorporationAlfred P. Sloan FoundationAstronom