Marc Jobin

Structural characterization of oxidized titanium surfaces

Oxidized titanium surfaces resulting from various processes have been structurally characterized by means of scanning force microscopy, x‐ray photoemission spectroscopy (XPS), x‐ray diffraction, and electron energy‐loss spectroscopy (EELS) with losses in the 0–100 eV range. It has been found that the surface morphology has a granular structure for electropolished titanium and for titanium evaporated on mica at low substrate temperature (570 K), but changes to flat terraces for the films evaporated at higher temperature (770 K). Angular‐dependent XPS has revealed the presence of a Ti2O3 suboxide at the Ti/TiO2 interface for electropolished titanium. Dry oxidation has been performed at 770 and 970 K on both weakly and highly crystallized evaporated titanium films oriented along (0001). In the case of underlying crystallized metallic titanium, the resulting TiO2 films are crystallized with the anatase (004) orientation for oxidation at 770 K and with rutile (200) orientation for oxidation at 970 K. EELS spec...

Versatile force–feedback manipulator for nanotechnology applications

A nanoscale manipulation system has been designed and built through the integration of a force–feedback haptic device and a commercial atomic force microscope. The force–feedback interaction provides a very intuitive, efficient and reliable way for quick manipulation of nanoscale objects. Unlike other nanomanipulators, ours allows the user to feel the actual tip–sample interaction during the manipulation process. Various modes of manipulation have been implemented and evaluated. As a proof of concept, we show a contact-mode nanomanipulation of a carbon nanotube and a noncontact manipulation of silicon beads. In addition to nanomanipulation itself, all relevant signals can be recorded during the manipulation process which allows quantitative interpretation of nanomechanics experiments.

Local dynamic mechanical analysis.

While new materials with tailored properties appear every day, the need of appropriate characterization tools is still an important concern. Analyses of thin films on thick substrate are often highly influenced by the substrate properties. A dynamical nanoindentation system has been designed and built through the integration of a nanoindenter head equipped with capacitive displacement sensing, scanning probe microscope with related XYZ scanning electronics and an additional transducer for sample actuation. Our Local-Dynamic Mechanical Analysis (L-DMA) setup allows for both, tip and sample modulation mode what somehow contrasts with commercially available systems. This issue allows for direct comparison between both techniques and therefore for consistent quantitative mechanical measurements. The system offers two distinctive measurement techniques, local mechanical spectroscopy and mechanical imaging modes. Bulk materials as well as thin films of ceramics and polymers have been used for testing and validating the setup. The instrument has been modeled in sample modulation mode and experimental results obtained for different materials were compared with simulation data.

Nanometrology for MEMS : combination of optical interference, atomic force microscopy and nanoindentor-based actuator

We show the integration of a home-made interference optical microscope (IOM) with an Atomic force microscope, as well as the combination of IOM with a nanoindentor. Such combined instruments have many applications in the characterisation of MEMS/NEMS. As an illustrative example, we have used a MEMS accelerometer with capacitive read-out. Surface topography and defects have been measured with an IOM/AFM setup, as well as the bending and the torsion of the inertial mass while a calibrated force is applied with the nanoindentor probe on an off-axis location of the inertial mass.

Geometry of Chemical Beam Vapor Deposition System for Efficient Combinatorial Investigations of Thin Oxide Films: Deposited Film Properties versus Precursor Flow Simulations

An innovative deposition system has been developed to construct complex material thin films from single-element precursors by chemical beam vapor deposition (CBVD). It relies on well distributed punctual sources that emit individually controlled precursor beams toward the substrate under high vacuum conditions combined with well designed cryo-panel surfaces that avoid secondary precursor sources. In this configuration the impinging flows of all precursors can be calculated at any substrate point considering the controlled angular distribution of the emitted beams and the ballistic trajectory of the molecules. The flow simulation is described in details. The major advantage of the deposition system is its ability to switch between several possible controlled combinatorial configurations, in which the substrate is exposed to a wide range of flow compositions from the different precursors, and a uniform configuration, in which the substrate is exposed to a homogeneous flow, even on large substrates, with high precursor use efficiency. Agreement between calculations and depositions carried out in various system configurations and for single, binary, or ternary oxides in mass transfer limited regime confirms that the distribution of incoming precursors on the substrate follows the theoretical models. Additionally, for some selected precursors and in some selected conditions, almost 100% of the precursor impinging on the substrate is incorporated to the deposit. The results of this work confirm the potentialities of CBVD both as a research tool to investigate efficiently deposition processes and as a fabrication tool to deposit on large surfaces.

Nano‐scale Force Feedback Manipulator

A description of the instrumental requirements for AFM‐based nanomanipulation system is presented, as well as the design, the features and the benefits of our force feedback nano‐scale manipulator. The description covers as well some software aspects for quick and successful nano‐manipulation. As an illustration, cross sectioning of carbon nanotube (CNT) and WS2 nanotubes are shown.

Organic solar cells improvement with quantum dots, up-converters and MoO3 hole transport layers

We report on the power conversion efficiency (PCE) enhancement for organic solar cells (OSCs) based on several approaches. A standard cell composed of an indium tin oxide (ITO) anode, P3HT/ PCBM active layer, PEDOT:PSS hole transport layer and an aluminum cathode is used as a reference. We investigate the effects of the following three modifications. We first incorporate CdSe quantum dots (QDs) in the photo-optically active P3HT/PCBM blend in order to enhance the optical absorption. In opposite to other studies, QDs are not used here to replace the donor material (PCBM), and we always measured an enhanced PCE compared to the standard cell with a QDs:P3HTPCBM volume ratio up to 1:5. As a second modification, NaYF4:Yb,Er up conversion (UC) microcrystals are incorporated into a TiO2-x sol-gel to form an additional layer used to convert IR photons to blue and green photons. Again, OSCs with UC layer showed an improved PCE compared to the reference cell. The PCE enhancement is both attributed to the IR light absorption and to a better electron transport between the active layer and the cathode due to the electron transport layer capabilities of TiO2-x. Finally, MoO3 layer is used to replace the PEDOT:PSS layer as hole transport layer (HTL). This layer is deposed either by thermal evaporation or by spin coating from a sol-gel solution. We found evaporation better in terms of thickness control and reproducibility. It has been demonstrated that the PEDOT:PSS HTL can be replaced by MoO3, and the thickness of this MoO3 layer strongly affects the PCE of the cell. The maximum PCE was obtained with a thickness of 40nm, and again is better that the reference cell.

Force Modulation and Dynamic NanoIndentation Microscopy

We have made a Dynamic Nanoindentation Microscope (DNM) setup based on sample modulation, in order to allow a direct comparison between various dynamical mechanical measurement techniques such as Force Modulation Microscopy (FMM) and Dynamic Mechanical Analysis (DMA). The microscope is integrated to a standard Atomic Force Microscope (AFM) and uses a commercial nanoindentation system. Instead of the standard bimorph and force modulation configuration, we used a stacked ceramic sample actuator in displacement modulation. Both DMA measurements and DNM imaging were performed on each sample for the determination of the reduced, storage and loss modules, and a good agreement between the techniques have been found. Compared to FMM, we show that DNM has the advantage of always keeping the same contrast in the viscoelastic images as a function of the frequency.

Dielectric impedance and optical performance of quantum dots doped OLEDs

We investigate the effect of the incorporation of CdSe quantum dots (QD) in the standard ITO/TPD/Alq3/Al organic light emitting diodes (OLEDs). The OLEDs structures have been prepared in a double glove box coupled to a vacuum chamber containing both low and high temperature evaporators. For the standard (undoped) OLEDs, the hole transport layer (HTL) consisting of 50nm of TPD is deposited by spin coating (8000rpm during 60 sec) and the 40nm of Alq3 were deposited at 2A/sec (organic crucible Radak-I). 150nm of Al were finally evaporated at 5A/s. For the CdSe-doped OLEDs, the procedure was the same expect that the QDs were mixed with TPD in toluene before spin coating. During the thermal processing if the film, the QDs are expected to segregate to the surface, and then will be located at the TPD/Alq3 interface. The various layers were imaged by Atomic Force Microscopy (AFM) at each phase of the structure deposition, and we could indeed visualize the segregated QDs above the TPD film. AFM was systematically used to monitor the homogeneity and the thickness of the various films. The impedance of the non-encapsulated films structures were measured in air in the 40-40MHz frequency range, with bias at 0V (non-emitting), 2V (low emission) and 8V (strong emission). The corresponding dielectric spectra were analyzed with the standard Havriliak-Negami (HV) formula, where the conductive term has been subtracted from the data in case of light emission. We have measured a relaxation ranging from 100kHZ for the unbiased structure to 1MHz for 8V (strong emission). Apart from this expected relaxation, we found a second relaxation mechanism around 10 MHz. The origin of this second peak will be discussed. To monitor the optical emission of the OLEDs, we have built a specific bench which allows for the quantitative measurement of the emission spectra and the dynamics behavior of the OLEDs (raising and falling time). We found that the incorporation of the QDs unfortunately results in the decrease of the light emission but with a favorable modification of the light spectrum (around 700nm).

Concept of a split tandem photovoltaic window

We present a concept of a split tandem photovoltaic window, where the larger wavelengths solar radiations are sent towards horizontal silicon solar cells while short wavelength solar radiations are directed on transparent large band gap solar cells, either dye-sensitized or organic solar cells (DSSC and OSC respectively). We first evaluate the expected enhancement in them of conversion efficiency and then describe the construction of a mini module of this window.