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In this chapter, we describe the determination of the stress profile in 150-nm-wide SiGe nano-stripes embedded into a Si matrix by using oblique incidence tip-enhanced Raman spectroscopy (TERS) with a spatial resolution of ~20 nm. The TERS spectra of the stripes exhibit a number of locally enhanced phonon modes that are absent when the tip is positioned out of the stripes. The hydrostatic stress component across the nano-stripe width is evaluated from the strain-induced frequency shift of the Si-Ge mode at ~380 cm -1. The stress magnitude is found to be largest in the nano-stripe center and decreases monotonously on each side down to zero at the boundaries. This behavior is quantitatively described by a classic continuous medium model. These results demonstrate the applicability of the TERS technique to stress determination in novel semiconductor structures at the nanometer scale.

International audience; Tip enhanced Raman spectroscopy (TERS) and imaging experiments in tunnelling (gap) mode were performed on a 2 nm thick azobenzene thiol monolayer grafted on Au(111). A strong dependence on the tunnelling parameters, regulating the gold tip-gold surface gap distance,was observed for the intensity of the enhanced Raman signal. The influence of the incident light polarization is also discussed.

International audience; We present the theory underlying the large numerical aperture objective micro-Raman backscattering experiment and apply it to the elaboration of a characterization methodology for the determination of the stress tensor in strained cubic semiconductor structures. The presented stress characterization technique consists in monitoring the variations of the stress-sensitive optical phonon peak position and linewidth while rotating stepwise the sample about its normal. The practical application of the technique is illustrated on a silicon-on-insulator (SOI) microelectronic structure demonstrating a plane stress-tensor determination.

* * * ## Title, Contents and abstract * * * 1 Introduction 6 2 Fundamentals 14 2.1 Raman spectroscopy 14 2.2 Surface enhanced Raman spectroscopy 16 2.3 Tip enhanced Raman spectroscopy 25 2.4 Scanning tunneling microscopy 35 2.5 Light emission from tunneling junctions 37 3 Experimental 46 3.1 The set-up 46 3.2 The optics 48 3.3 Film preparation 49 3.4 Tip preparation 51 3.5 Chemicals and reagents 55 3.6 Optics for STM-emitted light detection 56 4 Tip Enhanced Raman Spectroscopy 60 4.1 Brilliant Cresyl Blue 60 4.2 Cyanide 73 4.3 Overview on literature data concerning TERS 85 4.4 Carbon fluctations 87 5 STM light emission 96 5.1 Gold-gold junctions 96 6 Conclusions 113 References 118 Ringraziamenti 129, Silver and gold colloids, but also other metal nanostructures show specific optical resonances due to the excitation of localized surface plasmons (LSP). They are confined to small spatial regions and create there high electromagnetic fields. This is also the basis of the surface enhanced Raman scattering (SERS), where the rough metal surface acts simultaneously as support for the molecules and as Raman enhancer. Thus, adsorbate-substrate interaction and enhancing processes are nearly inseparably interconnected. A new concept decouples adsorption and enhancing processes. A STM tunneling tip serves as external enhancer, since localized surface plasmons can also be excited in the tip apex, providing a high near-field enhancement. For molecules in the close vicinity of the tip, but adsorbed at the metal, a tip- enhanced Raman scattering (TERS) can be observed. This approach can lead to the development of spectroscopic tools with high spatial resolution, ultimately permitting single molecule spectroscopy. TERS experiments have been conducted at two different Raman scatterers, the dye Brilliant Cresyl Blue (BCB) and the cyanide ion. If a illuminated silver tip is brought into tunneling contact with a smooth, BCB covered Au-surface, a substantial rise of the Raman intensity can be observed. The high enhancement of about 104, centered underneath the tip apex, means that only a few thousand molecules contribute to TERS. At rough Au surfaces combined SERS and TERS spectra were recorded for adsorbed cyanide ions. Their analyses prove also for this case that TERS is a local spectroscopy, averaging over a rather small ensemble of molecules. Localized surface plasmons (LSP) can also be excited by electrons tunneling through the gap between the tip apex and the metal surface. Their light emission shows a number of discrete modes extending into the near IR region. Their energies depend on the parameters of the tip and the tunnel junction including the local topography of the metal surface, information that is useful for further optimizing the TERS experiments., Silber oder Gold-Kolloide, aber auch andere Metall-nano-Strukturen zeigen charakteristische optische Resonanzen durch Anregung lokalisierter Ober flachen Plasmonen (LSP). Diese sind auf kleine raeumliche Bereiche beschraenkt und erzeugen dort hohe elektromagnetische Felder. Darauf beruht auch die oberflaechenverstaerkte Ramanstreuung (SERS), wobei die rauhe Metalloberflaeche gleichzeitig als Traeger der Molekuele und als Raman- Verstaerker agiert. Dabei sind Adsorbat- Substrat Wechselwirkung und Verstaerkung nahezu unseparierbar miteinander verknuepft. Ein neues experimentelles Konzept entkoppelt Adsorptions- und Verstaerkungsprozesse. Eine STM Tunnelspitze (aus Ag oder Au) dient als externer Verstaerker, da dort ebenfalls lokalisierte Ober flaechenplasmonen angeregt werden koennen und dort hohe Nahfelder erzeugen. Fuer Molekuele direkt unterhalb der Tunnelspitze, aber adsorbiert auf dem Metall, findet eine hohe Nahfeld-Verstaerkung der Raman Prozesse statt (TERS). Dieser Ansatz kann zur Entwicklung spektroskopischer Werkzeuge mit hoher raeumlicher Aufloesung fuehren bis hin zur Spektroskopie einzelner Molekuele. TERS Experimente wurden an zwei verschiedenen Ramanstreuern durchgefuehrt, dem Farbstoff Brilliant Cresyl Blue (BCB), sowie dem Cyanidion. Bringt man eine Ag-Spitze in Tunnelkontakt mit einer glatten mit BCB bedeckten Au-Ober flaeche, so beobachtet man einen vielfachen Anstieg der Ramanintensitaet. Die hohen lokalen Verstaerkungsfaktoren von 104 bedeuten, dass nur einige tausend Molek�ule an TERS beteiligt sind. An rauhen Au- Oberflaechen wurden kombinierte SERS und TERS Spektren von adsorbierten CN