Christian Bergaud

High-Spatial-Resolution Surface-Temperature Mapping Using Fluorescent Thermometry**

The characterization of temperature and thermal properties is of particular importance in micro- and nanotechnology. Considering the highly increased density of structures and the increased power dissipation per unit area associated with miniaturization, good thermal design is of great importance for device reliability and performance. Locating hot spots, for example, on a microelectronic circuit, can be of great value in evaluating a design, optimizing the performance, and performing failure analysis. [1,2] Apart from the industrial applications of micro- and nanoscale thermometry, fundamental questions of the thermal behavior, for example, thermal transfer at a scale comparable to the phonon wavelength, [3] could be more effectively addressed with improved characterization tools. The common approach for mapping temperature on the microscale is based on infrared microscopy, which relies on the analysis of the thermal radiation that is emitted from any material. IR microscopy is a well-established technique and can be used with relative ease for temperature mapping on large scales. However, the technique suffers from a diffractionlimited resolution, giving it an optimal spatial resolution of around 5 mm. [2,4,5] Nanoscale scientists typically use scanning thermal microscopy (SThM) for high-resolution measurements. Since the invention of the scanning probe microscope at the beginning of the 1980s, [6] several scanning probes for thermal characterization have been developed. The thermal probes used are generally based on either thermocouple or thermistor elements. [7–11] Other approaches have proposed bimaterial cantilevers or fluorescent particles as temperaturesensing probes. [12–14] The highest spatial resolution obtained

A novel approach for fluorescent thermometry and thermal imaging purposes using spin crossover nanoparticles

Temperature plays a fundamental role in all fields of science; hence the development of methods for measuring this property remains in vogue. Within this vast field, fluorescent thermometry appears as a simple, noninvasive and cost-effective method for providing good spatial, temporal and thermal resolution in both solid and liquid phases, even in distant or inaccessible environments. Here we describe the properties of a two-component fluorescent thermometry system comprised of Fe(II)-triazole type spin-crossover nanoparticles (temperature sensor) and an appropriate fluorophore (signal transducer). The primary advantage of this system is that the nanoparticles are modified easily, which enables fine control of the thermometric properties, while the optical properties (i.e. the signal detection) remain virtually unchanged. This system could thus be adapted in a straightforward manner to various problems where the use of fluorescent thermometry would be beneficial.

Fabrication of biological microarrays using microcantilevers

Arrays of silicon-based microcantilevers with properly designed passivated aluminum electrodes have been used to generate microarrays by depositing microspots of biological samples using a direct contact deposition technique. The approach proposed here can be compared to the dip-pen technique but with the noticeable difference that electrostatic fields are generated onto the cantilevers to increase the height of liquid rise on the cantilever surface when dipping them into the liquid to be deposited. Both electrowetting through the reduction of the contact angle and dielectrophoresis through electrostatic forces can be used to favor the loading efficiency. These phenomena are particularly pronounced on the microscale due to the fact that physical scaling laws favor electrostatic forces. Moreover, at this scale, conductive heat dissipation is enhanced and therefore joule heating can be minimized. Using this approach, with a single loading, arrays of more than a hundred spots, from the femtoliter to the pico...

Viscosity measurements based on experimental investigations of composite cantilever beam eigenfrequencies in viscous media

Experimental investigations have been conducted to study the multimode dynamic response of composite cantilever beams in various viscous media and to determine their viscosity. Theoretical eigenfrequencies are computed using the analytical model proposed by Sader [J. Appl. Phys. 84, 64 (1998)] based on the analysis of the hydrodynamic function of cantilever beams. A good agreement is found between theory and experiment for the first two resonant frequencies of composite beams operated in air and in water. The same experimental approach is used to determine the viscosity of ultrapure ethanol. Thus, it is established that Sader’s model represents an accurate alternative for the determination of liquid viscosity in small volumes (about 50 μl) which might be of great importance for microfluidics applications. Finally, the limits of the method are underlined by monitoring the dynamic response of cantilever beams in silicon oil.

Scanning thermal imaging by near-field fluorescence spectroscopy

A scanning thermal microscope that uses a fluorescent particle as a temperature probe has been developed. The particle, made of a rare-earth ion-doped fluoride glass, is glued at the extremity of a sharp tungsten tip and scanned on the surface of an electronic device. The temperature of the device is determined by measuring the fluorescence spectrum of the particle at every point on the surface and by comparing the intensity variations of two emission lines. As an example, we will show some images obtained on a nickel stripe 1 microm wide, heated by an electrical current. A good agreement is observed with a simulation of the temperature field on the device.

Piezoelectric properties of PZT films for microcantilever

The investigation of piezoelectric properties of materials in the thin layer form has become an important task because of the increased range of their applications as actuators and sensors. The sensor magnitude, is a direct function of the e31 piezoelectric constant. Pb(Zr,Ti)O3 thin films and the modified compositions have attracted great attention in recent years as promising for use in microelectromechanical systems. To determine this constant we use an unusual experimental method. A remanent piezoelectric constant of −4.7 C/m2 was obtained. The parameters as, coercive field, saturation field, curve of first polarization, and self polarization of the remanent piezoelectric hysteresis loop are presented for 1.6 μm thick PZT thin film. We will associate also dielectric results. To show the possible integration of the piezoelectric films in microelectromechanical systems, we have deposited PZT thin film on a 100 μm long, 20 μm wide, 1 μm thick silicon oxide beam to control the z actuation.

Identification of EOR defects due to the regrowth of amorphous layers created by ion bombardment

Abstract In this paper TEM investigations have been carried out on typical EOR defects found in Ge-amorphized (001) wafers (Ge → Si, 150 keV, 2×1015 ions/cm2) after thermal annealing (RTA, 1000°C, 10 s). These defects consist of medium sized (10–50 nm) dislocation loops that have been characterized by conventional electron microscopic techniques. Most of them (~ 75%) are circular faulted Frank loops with b = a 3〈111〉 vectors. The remaining (~ 25%) loops are perfect elongated hexagon-shaped loops: they have nearly t(111⊃ habit planes, with b = a 2〈101〉 vectors. Hence, it is possible to deduce from only one TEM image the number of Si atoms available in the loops as well as the density of the loops for different implantation or annealing conditions. This is needed for optimization of process conditions.

Parylene-based flexible neural probes with PEDOT coated surface for brain stimulation and recording

Implantable neural prosthetics devices offer a promising opportunity for the restoration of lost functions in patients affected by brain or spinal cord injury, by providing the brain with a non-muscular channel able to link machines to the nervous system. Nevertheless current neural microelectrodes suffer from high initial impedance and low charge-transfer capacity because of their small-feature geometry (Abidian et al., 2010; Cui and Zhou, 2007). In this work we have developed PEDOT-modified neural probes based on flexible substrate capable to answer to the three critical requirements for neuroprosthetic device: efficiency, lifetime and biocompatibility. We propose a simple procedure for the fabrication of neural electrodes fully made of Parylene-C, followed by an electropolymerization of the active area with the conductive polymer PEDOT that is shown to greatly enhance the electrical performances of the device. In addition, the biocompatibility and the very high SNR exhibited during signal recording make our device suitable for long-term implantation.

Soft lithographic patterning of spin crossover complexes. Part 1: fluorescent detection of the spin transition in single nano-objects

The investigation of size-reduction effects on the spin crossover properties of a class of transition metal complexes has recently become an area of intensive research. However, to avoid inter-particle interactions, ensemble averaging and matrix effects it is necessary to develop methods for the systematic study of individual nano-objects. To this aim thin films and nano-patterns of the compound [FeII(hptrz)3](OTs)2 doped with acridine orange were elaborated by spin coating and soft-lithography, respectively. The luminescence intensity was found to change significantly upon the spin transition even in isolated nano-objects of ca. 150 nm size, allowing us to monitor in a massively parallel way the spin crossover phenomenon in large arrays viafluorescence microscopy.

On the relation between dopant anomalous diffusion in Si and end-of-range defects

Abstract The goal of this paper is to answer questions regarding the relation between “anomalous” diffusion and EOR defects. Knowing the type and origin of these defects allows one to understand why and how they affect dopant diffusion. Hence, it is possible to find out under which experimental conditions their density can be minimized and most importantly to develop physical models for dopant diffusion taking into account the behaviour of EOR defects during annealing. Indeed, these dislocations loops are efficient trapping sites for boron and this cannot be neglected in realistic simulations. Upon annealing, these defects increase in size and reduce their density and this through the emission and capture of Si interstitials. Thus, EOR defects can be seen as reservoirs able to maintain a high supersaturation of free self-interstitials during their dissolution. This point defect supersaturation induces a strong increase of boron diffusivity through the formation of excess Si(1)-B pairs. Thus, the experimentally observed macroscopic motion of dopant is the result of the two competing phenomena.