O. Marty

Application of 3C-SiC quantum dots for living cell imaging

Highly luminescent, stable, and biocompatible 3C-SiC quantum dots (QDs) with no protective shells have been applied for fluorescence imaging of biological living cells. Structural and luminescent properties of the 3C-SiC QDs are described. Marking of the living cells with such QDs highlights the penetration, accumulation, and heterogeneous distribution of the QDs inside the intracellular space.

Characterization of the thermal conductivity of insulating thin films by scanning thermal microscopy

This paper reports on the abilities of a Scanning Thermal Microscopy (SThM) method to characterize the thermal conductivity of insulating materials and thin films used in microelectronics and microsystems. It gives a review of the previous works on the subject and gives new results allowing showing the performance of a new method proposed for reducing the thermal conductivity of meso-porous silicon by swift heavy ion irradiation. Meso-porous silicon samples were prepared by anodisation of silicon wafers and underwent irradiation by 845MeV ^2^0^8Pb ions, with fluences of 4x10^1^1 and 7x10^1^1cm^-^2. Thermal measurements show that irradiation reduced thermal conductivity by a factor of up to 2.

Extraction of ultraviolet emitting silicon species from strongly hydrogenated nanoporous silicon

Ultraviolet emitting silicon species were extracted from strongly hydrogenated porous silicon nanostructures. Their photoluminescence spectra depend on size distribution of the species and can be tuned by centrifugation. Molecular structure of the extracted Si species is assumed to be very similar to some kinds of polysilanes which were theoretically described earlier by Allan et al. [Phys. Rev. B 48, 7951 (1993)]. Absence of photoluminescence signal coming from the polysilanes in the initial porous nanostructures is supposed to be due to the competitive absorption and to the energy transfer between the polysilanes and Si red emitting porous nanoparticles.

Temperature dependence of the indirect bandgap in ultrathin strained silicon on insulator layer

Photoluminescence spectroscopy is applied on tensely strained silicon on insulator layer in order to evaluate the temperature dependence of the indirect energy bandgap. The strained silicon indirect bandgap follows a similar behaviour to bulk silicon at high temperature (from 80 K up to 300 K) which was described from the Varshni [Physica 34, 149 (1967)] and Bose-Einstein equations. Nevertheless, at low temperature (from 9 K to 80 K), an unusual blueshift of the bandgap is evidenced. The latter can be modelled considering band-tail states of density of states which are related to the strain fluctuation.

Optical characterization of a strained silicon quantum well on SiGe on insulator

An 8nm thick strained silicon layer embedded in relaxed Si0.8Ge0.2 has been grown on SiGe on insulator substrate in order to reduce the optical response of dislocations present in the SiGe virtual substrate. Photoreflectance measurement shows bandgap shrinkage at Γ point of 0.19eV which corresponds to a 0.94% strain value close to the one measured in Raman spectroscopy. The luminescence arising only from the strained Si quantum well in high injection conditions reveals clearly two optical transitions observed at 0.959 and 1.016eV.

SiC as a Biocompatible Marker for Cell Labeling

This chapter focuses on the application of SiC quantum dots (QDs) for fluorescent cell labeling. Two different top-down processes are investigated to produce SiC QDs from bulk or polycrystalline SiC substrates: electrochemical etching and laser ablation. In both cases, a broad size distribution of crystalline SiC nanoparticles is obtained (ranging from few tens of nanometers down to 2nm in diameter). In electrochemical etching, the original polytype is conserved, whereas in laser ablation, some stacking faults are found in the naoparticles. The mechanism of photoluminescence has been investigated as a function of QD spatial and chemical configuration, i.e., interconnected QDs in a freestanding nanoporous layer, dry and wetted nanopowder obtained from the nanoporous layer, dispersion of QDs in various solvents (with different dielectric constants) and with various surfactants, and centrigugated solutions of QDs to keep the smallest ones. From all these experiments, both surface-related photoluminescence, probably due to C═O double bonds, and photoluminescence, due to discrete levels of quantum-confined carriers, have been evidenced.

Straining of SiGe ultrathin films with mesoporous Si substrates

We report on the fabrication and characterization of ultrathin (down to 50 nm) tensile strained SiGe films on mesoporous Si substrates. Low temperature oxidation of the porous substrate relaxes the compressive strain in the as grown monocrystalline (mc) SiGe. Applying this method to a 50 nm thick mc-Si0.72Ge0.28 film, a tensile strain >0.78% can be achieved without compromising crystalline quality and up to 1.45 % without the appearance of cracks.

Thin film growth using hetero embryo: demonstration on pyrochlore phase.

The paper reports the possible use of nanoparticles embedded in amorphous host as hetero embryos in order to grow complex crystalline phases as thin film. Demonstration is performed in the prototypical case of pyrochlore phase Gd(2)Ti(2)O(7) grown from Gd(2)O(3) nanoparticles embedded in TiO(2) matrix at low temperature. As embryos, two kinds of nanoparticles are compared: clusters deposited by low energy cluster beam deposition (LECBD) and nanostructured films elaborated by sol-gel process. The growth has been analyzed by X-ray diffraction and transmission electron microscopy. Furthermore, the nanoparticles have been doped with Eu(3+) luminescence probes in order to follow the nucleation mechanisms at the atomic scale. It is shown that the size, shape, and composition of hetero embryos and as well their interfaces are of paramount importance to enhance the formation of complex materials, such as pyrochlore. By this mean, the first step in classical nucleation science, controlling the height of the energetic barrier, is skipped and the synthesis conditions can be eased.

Thickness dependence of photoluminescence for tensely strained silicon layer on insulator

Strain and crystalline quality of tensely strained silicon on insulator with thickness ranging from 8 to 100 nm have been evaluated by low temperature photoluminescence (PL). The strain conservation in the strained Si layers was checked by Raman spectroscopy. The PL clearly shows the emission related to the strained silicon optical band gap even for strained layers as much as seven times thicker than critical thickness (hc∼15 nm). For very thin layers (9 nm), a 21 meV blueshift is observed in the PL spectra, which corresponds to a 17 meV calculated one coming from quantum confinement in the sSi layer.