Équipe 104 : NanomatériauxInternational audienceThe improved phonon confinement model developed previously [11] is applied for definition of germanium nanocrystal sizes from the analysis of its Raman scattering spectra. The calculations based on the model allow determining the sizes of germanium nanocrystals more precisely from the analysis of their Raman spectra. In some cases, the comparative analysis of Raman data and electron microscopy data is carried out, and good agreement is observed

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An original technology for fabricating nano-objects as small as several nanometers in width using a new class of lithographic masks is described. Glassy films such as Si02, SiN(H), and others deposited from vapor onto semiconductor substrates and capable of changing their volume and, hence, the internal stress during specific treatments, are used as a mask material. Using these film's features, a technology of mask formation is developed. Its originality consists of (i) making openings in the masks by controlled introduction of cracks into the mask coating in prior prescribed places of the substrate and (ii) gradual controlled variation of the crack width, thus achieving self-alignment of the initial and final mask patterns. Using controlled cracking, narrow openings -300 to -17 nm wide have been formed in single-and double-layer mask films. Narrow electrodes on silicon have been produced by electrolytic deposition of Ni into the openings. It is also shown that the crack width can be controlled and sequentially varied at a nanometer scale using special successive treatments. Thus, high precision repeatable self-alignment of mask pattern can be achieved, which can be used in fabricating complex nanoscale devices.

Germanium nanocrystals in Ge02 films have been obtained with the use of two methods and have been studied. The first method of Ge nanocrystal formation is a film deposition from supersaturated GeO vapor with subsequent dissociation of metastable GeO on heterophase system Ge:Ge02. The second method is growth of anomalous thick native germanium oxide layers with chemical composition GeO(H2O) during catalytically enhanced Ge oxidation, x is close to 1 . The obtained films were studied with the use of photoluminescence, Raman scattering spectroscopy, highresolution electron microscopy. Strong photoluminescence signals were detected in Ge02 films with Ge nanocrystals at room temperature. "Blue-shift" of the photoluminescence maximum was observed with reducing of Ge nanocrystal size in anomalous thick native germanium oxide films. So, the correlation between reducing of the Ge nanoerystal sizes (estimated from position of Raman peaks) and photoluminescence "blue-shift" was observed. The Ge nanocrystals presence was confirmed by high-resolution electron microscopy data. The optical gap in Ge nanocrystals was calculated with taking into account quantum size effects and compared with the position of the experimental photoluminescence peaks. It can be concluded that a Ge nanocrystal in Ge02 matrix is a quantum dot of type I. It was shown, that "band gap engineering" approaches can lead to creation of Ge:Ge02 heterostructures with required properties. This heterostructures can be perspective for using in opto-electronics, for creation of elements of quasi-nonvolatile MOS memory using Ge nanocrystals as traps for electrons or holes, e.t.c.

The dislocation structure of germanium covered by a SiO2 pyrolitic film has been studied by X‐ray topography. The dislocations gliding in the Ge bulk are accompanied by the formation of steps on the optically smooth interface GeSiO2. Dislocations and steps are shown to be connected with a bending of the GeSiO2 system which is due to the densification of the film during its synthesis. In the germanium bulk a neutral surface N arises with dislocations accumulated near this surface. The interaction of dislocations with equal sign results in their symmetric distribution respective to N, if they lie in the same slip plane, while those ones lying in the intersecting slip planes interact with the formation of L‐type prismatic dislocations. A study of dislocation interaction near N gives estimates of the structural stresses in the film and in germanium.

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