Julien L. Colaux

High accuracy traceable Rutherford backscattering spectrometry of ion implanted samples

There are few techniques capable of the non-destructive and model-free measurement at 1% absolute accuracy of quantity of material in thin films without the use of sample-matched standards. We demonstrate that Rutherford backscattering spectrometry can achieve this robustly, reliably and conveniently. Using 1.5 MeV He+, a 150 keV ion implant into silicon with a nominal fluence of 5 × 1015 As cm−2 has been independently measured repeatedly over a period of 2 years with a mean total combined standard uncertainty of 0.9 ± 0.3% relative to an internal standard given by the silicon stopping power (a coverage factor k = 1 is used for all uncertainties given). The stopping power factor of this beam in silicon is determined absolutely with a mean total combined standard uncertainty of 0.8 ± 0.1%, traceable to the 0.6% uncertainty of the Sb-implanted certified reference material (CRM) from IRMM, Geel. The uncertainty budget highlights the need for the accurate determination of the electronic gain of the detection system and the scattering angle, parameters conventionally regarded as trivial. This level of accuracy is equally applicable to much lower fluences since it is not dominated by any one effect; but it cannot be reached without good control of all of these effects. This analytical method is extensible to non-Rutherford scattering. The stopping power factor of 4.0 MeV lithium in silicon is also determined at 1.0% absolute accuracy traceable to the Sb-implanted CRM. This work used SRIM2003 stopping powers which are therefore demonstrated correct at 0.8% for 1.5 MeV He in Si and 1% for 4 MeV Li in Si.

Building Materials from Colloidal Nanocrystal Arrays: Preventing Crack Formation during Ligand Removal by Controlling Structure and Solvation

Crack-free, ligand-free, phase-pure nanostructured solids, using colloidal nanocrystals as precursors, are fabricated by a scalable and facile approach. Films produced by this approach have conductivities comparable to those of bulk crystals over more than 1 cm (1.370 S cm-1 for PbS films).

Bioactivity and hemocompatibility study of amorphous hydrogenated carbon coatings produced by pulsed magnetron discharge.

Literature contains very few data about the potential biomedical application of amorphous hydrogenated carbon (a-C:H) thin films deposited by reactive pulsed magnetron discharge even so it is one of the most scalable plasma deposition technique. In this article, we show that such a C2H2 pulsed magnetron plasma produces high quality coating with good hemocompatibility and bioactive response: no effect on hemolysis and hemostasis were observed, and proliferation of various cell types such as endothelial, fibroblast, and osteoblast-like cells was not affected when the deposition conditions were varied. Cell growth on a-C:H coatings is proposed to take place by a two-step process: the initial cell contact is affected by the smooth topography of the a-C:H coatings, whereas the polymeric-like structure, together with a moderate hydrophilicity and a high hydrogen content, directs the posterior cell spreading while preserving the hemocompatible behavior.

Accurate electronics calibration for particle backscattering spectrometry

Rutherford backscattering spectrometry (RBS) is a non-destructive thin film analytical technique of the highest absolute accuracy which, when used for elemental depth profiling, depends at first order on the gain of the pulse-height spectrometry system. We show here for the first time how this gain can be reliably and robustly determined at about 0.1%.

Building Materials from Colloidal Nanocrystal Arrays: Evolution of Structure, Composition, and Mechanical Properties upon the Removal of Ligands by O2 Plasma

The mechanical properties of colloidal nanocrystal superlattices can be tailored through exposure to low-pressure plasma. The elastic modulus and hardness of the ligand-free 3.7 nm ZrO2 superlattice are found to be similar to bulk yttria-stabilized tetragonal polycrystals of the same relative density but without any doping.

Solid phase epitaxial re-growth of Sn ion implanted germanium thin films

Doping of Ge with Sn atoms by ion implantation and annealing by solid phase epitaxial re-growth process was investigated as a possible way to create Ge1−xSnx layers. Ion implantation was carried out at liquid nitrogen to avoid nano-void formation and three implant doses were tested: 5×1015, 1×1015 and 5×1014 at/cm2, respectively. Implant energy was set to 45 keV and implants were carried out through an 11 nm SiNxOy film to prevent Sn out-diffusion upon annealing. This was only partially effective. Samples were then annealed in inert atmosphere either at 350°C varying anneal time or for 100 s varying temperature from 300 to 500°C. SPER was effective to anneal damage without Sn diffusion at 350° for samples implanted at medium and low fluences whereas the 5×1015 at/cm2 samples remained with a ∼15 nm amorphous layer even when applying the highest thermal budget.

Optics-free, plasma-based lithography in inorganic resists made up of nanoparticles

Abstract. We describe a lithographic approach—nanocrystal plasma polymerization-based lithography—in which colloidal nanocrystal assemblies (CNAs) are used as the inorganic resist and, potentially, the active material. The patterning process is based on a change in the dispersibility of the CNAs in solvents as a result of the exposure to plasmas. Plasmas can etch the capping ligands from the exposed area. During the development step, the unexposed area of CNAs is redispersed, leaving behind the patterned area, similar to what is expected from negative photoresist.

Electrical properties of amorphous chalcogenide/silicon heterojunctions modified by ion implantation

Doping of amorphous chalcogenide films of rather dissimilar bonding type and resistivity, namely, Ga-La-S, GeTe, and Ge-Sb-Te by means of ion implantation of bismuth is considered. To characterize defects induced by ionbeam implantation space-charge-limited conduction and capacitance-voltage characteristics of amorphous chalcogenide/silicon heterojunctions are investigated. It is shown that ion implantation introduces substantial defect densities in the films and their interfaces with silicon. This comes along with a gradual decrease in the resistivity and the thermopower coefficient. It is shown that conductivity in GeTe and Ge-Sb-Te films is consistent with the two-type carrier conduction model. It is anticipated that ion implantation renders electrons to become less localized than holes leading to electron conductivity in certain cases as, for example, in GeTe.

Accurate experimental determination of Gallium K- and L3-shell XRF fundamental parameters

The fluorescence yield of the K- and L3-shell of gallium was determined using the radiometrically calibrated (reference-free) X-ray fluorescence instrumentation at the BESSY II synchrotron radiation facility. Simultaneous transmission and fluorescence signals from GaSe foils were obtained, resulting in K- and L3-shell fluorescence yield values consistent with existing database values(omega_Ga_K=0.515 +- 0.019, omega_Ga_L3=0.013 +- 0.001). For the first time, these standard combined uncertainties are obtained from a properly constructed Uncertainty Budget. These K-shell fluorescence yield values support Bambyneks semi-empirical compilation from 1972: these and other measurements yield a combined recommended value of omega_Ga_K=0.514 +- 0.010. Using the measured fluorescence yields together with production yields from reference Ga-implanted samples where the quantity of implanted Ga was determined at 1.3% traceable accuracy by Rutherford backscattering spectrometry, the K-shell and L3-subshell photoionization cross sections at selected incident photon energies were also determined and compared critically with the standard databases.

Optics-free lithography on colloidal nanocrystal assemblies

We describe a lithographic approach – Nanocrystal Plasma Polymerization (NPP)-based lithography (Figure 1) – where colloidal nanocrystal assemblies (CNAs) are used as the resist and, potentially, the active material. The patterning process is based on a change in the dispersibility of the CNAs in solvents as a result of the exposure to plasmas. Plasmas can etch the capping ligands from the exposed area. During the development step, the unexposed area of CNAs are redispersed leaving behind the patterned area.