arXiv subjects

Luiz Gustavo Cançado

Publications and source records attributed to Luiz Gustavo Cançado.

3 recordsLinked to original sources

arXiv2026

Anomalous Tip-Sample Distance Behavior on the Tip-Enhanced Raman Spectroscopy of Graphene in Ambient Conditions

Tip-Enhanced Raman Spectroscopy (TERS) combines Raman spectroscopy with scanning probe microscopy to overcome the spatial resolution limitation imposed by light diffraction, offering a primary optical technique for the comprehensive study of two-dimensional (2D) materials. In this work, we investigate an anomalous decay profile of the TERS intensity of the graphene 2D band as the tip-sample separation changes, observations enabled by high TERS efficiency and accuracy in tip-approach and tip-retract procedures. The anomalous results can be properly described by the addition of an ad hoc deformation to the effective tip-sample distance, rationalized here as due to the presence of a liquid meniscus formed via capillary forces.

physics.optics↗

arXiv2014

Theory of spatial coherence in near-field Raman scattering

A theoretical study describing the coherence properties of near-field Raman scattering in two- and one-dimensional systems is presented. The model is applied to the Raman modes of pristine graphene and graphene edges. Our analysis is based on the tip-enhanced Raman scheme, in which a sharp metal tip located near the sample surface acts as a broadband optical antenna that transfers the information contained in the spatially-correlated (but non-propagating) near-field to the far-field. The dependence of the scattered signal on the tip-sample separation is explored, and the theory predicts that the signal enhancement depends on the particular symmetry of a vibrational mode. The model can be applied to extract of the correlation length $L_{\rm c}$ of optical phonons from experimentally recorded near-field Raman measurements. Although the coherence properties of optical phonons have been broadly explored in the time and frequency domains, the spatially-resolved approach presented here provides an alternative probe for the study of local material properties at the nanoscale.

cond-mat.mes-hall↗

arXiv2010

Optical Measurement of the Phase-Breaking Length in Graphene

In mesoscopic physics, interference effects play a central role on the transport properties of conduction electrons, giving rise to exotic phenomena such as weak localization, Aharonov-Bohm effect, and universal conduction fluctuations. Mesoscopic objects have a size on the order of the {\em phase-breaking length} $L_ϕ$, the length conduction electrons travel while keeping phase coherence. In this letter, we use vibrational spectroscopy in combination with a novel optical defocusing method to measure $L_ϕ$ of photo-excited electrons in graphene which undergo inelastic scattering by optical phonons. We extract $L_ϕ$ from the spatial confinement of the defect-induced Raman D band near the edges of graphene. Temperature dependent measurements in the range of 1.55\,K to 300\,K yield $L_ϕ \propto 1/\sqrt{T}$, in agreement with previous magneto-transport measurements.

cond-mat.mes-hall↗