Tip-Enhanced Raman spectroscopy for Nanoelectronics.

Nicklaus, Mischa (2013). Tip-Enhanced Raman spectroscopy for Nanoelectronics. Thèse. Québec, Université du Québec, Institut national de la recherche scientifique, 164 p.

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Résumé

The technological progress of electronics through miniaturization has reached the nanoscale while new materials with high performance and functional properties gain importance. Quality control and the scientific understanding of expected size effects in electronic nanostructures are required more than ever to consolidate existing technologies and to determine scaling limits of new materials. Conventional techniques, including scanning electron and scanning probe microscopy, provide topographic information but only very limited chemical information to analyze the physical properties of nanomaterials, especially without a priori knowledge about the sample. Chemical and structural sensitivity is accessible by Raman or infrared spectroscopy, but with a spatial resolution limited to the microscale by the diffraction limit of light. Tip-enhanced Raman spectroscopy (TERS) combines the virtues of scanning probe microscopy with those of optical spectroscopy to overcome the diffraction limit through the excitation of surface plasmons on a scanning probe tip to confine light to nanometers. TERS has been applied primarily to molecules and organic samples. Nanoelectronic devices, which are typically composed of metallic or semiconducting substrates and nanostructures with considerable variations in permittivity, are yet to be investigated systematically. First and foremost, this requires a reliable TERS system for operation on non-transparent and non-conductive samples. In this work, a TERS system is installed to operate on opaque samples by employing optical side access. TERS probes are fabricated by electrochemical etching and operated in scanning tunneling microscopy and atomic force microscopy with quartz tuning forks to enable scanning on various surfaces. The chemical sensitivity and lateral resolution of the system is evaluated on carbon nanotubes as reference sample. TERS is successfully applied to ferroelectric, lead titanate nano-crystals on a platinized silicon substrate as a model system for nanostructured, charge-based memory devices at the onset of finite size effects. TERS allows for the chemical identification of the lead titanate (PbTiO₃) and the verification of the ferroelectric phase of the crystals with a lateral resolution as small as 4 nm under ambient conditions. Furthermore, the TERS spectra indicate the close proximity of the crystals to their paraelectric phase transition. A detailed analysis identifies the combination of local heat introduced by the laser and the finite size of the crystal to be at the origin of this transition. Considerable variations in permittivity across the sample and between sample and substrate cause a modulation of the surface plasmon resonance frequency and thus variations in the enhancement factor of the tip. A quantitative analysis of the TERS spectra relates the plasmon frequency shift to the sample’s composition, morphology, and atomic structure. Small variations of the sample’s refractive index are imaged with nanoscale resolution and confirm the presence of grain boundaries in individual crystals. These results provide a deeper understanding of nucleation during the growth process of the sample. Our experimental findings and the interpretation of the plasmon frequency modulation are confirmed by a time-domain simulation.

Type de document:	Thèse Thèse
Directeur de mémoire/thèse:	Ruediger, Andreas
Mots-clés libres:	système TERS; systèmes nanoélectroniques; nanotubes de carbone; nanocristaux ferroélectriques de titanate de plomb; Tip-Enhanced Raman spectroscopy
Centre:	Centre Énergie Matériaux Télécommunications
Date de dépôt:	15 sept. 2021 17:31
Dernière modification:	21 janv. 2022 17:05
URI:	https://espace.inrs.ca/id/eprint/2158

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