Eric Bourillot

Effects of temperature and pressure on microcantilever resonance response

The variation in resonance response of microcantilevers was investigated as a function of pressure (10(-2)-10(6)Pa) and temperature (290-390K) in atmospheres of helium (He) and dry nitrogen (N(2)). Our results for a silicon cantilever under vacuum show that the frequency varies in direct proportion to the temperature. The linear response is explained by the decrease in Youngs modulus with increasing the temperature. However, when the cantilever is bimaterial, the response is nonlinear due to differential thermal expansion. Resonance response as a function of pressure shows three different regions, which correspond to molecular flow regime, transition regime, and viscous regime. The deflection in flow transition regime resulting from thermal variation has minimal effect on frequency. The frequency variation of the cantilever is caused mainly by changes in the mean free path of gas molecules.

Performance of interdigitated nanoelectrodes for electrochemical DNA biosensor

An electrochemical methodology for bio-molecule sensing using an array of well-defined nanostructures is presented. We describe the fabrication by e-beam lithography of nanoelectrodes consisting of a 100 micro m x 50 micro m area containing interdigitated electrodes of 100 nm in width and interelectrode distance of 200 nm. Sensitivity and response time of the nanoelectrodes are compared to the responses of macro- and microelectrodes. The specificity of the sensor is studied by modifying the gold electrodes with DNA. The technique enables to characterize both single and double-stranded DNA of 15 nucleotides. A special electrochemical cell is adapted to control the temperature and measure the DNA concentration by UV analysis. The electrochemical method requires no label on the DNA, only redox mediators were used.

Detection of defects buried in metallic samples by scanning microwave microscopy

This paper reports the local detection of buried calibrated metal defects in metal samples by a new experimental technique, scanning microwave microscopy. This technique combines the electromagnetic measurement capabilities of a microwave vector network analyzer with the subnanometer-resolution capabilities of an atomic force microscope. The network analyzer authorizes the use of several frequencies in the range 1-6 GHz, allowing three-dimensional tomographical investigation, which is useful for the detection of bulk defects in metal materials.

Resolution of the photon scanning tunneling microscope: influence of physical parameters

Abstract The photon scanning tunneling microscope (PSTM) is the photon analogue of the electron scanning tunneling microscope (ESTM). It uses the evanescent field due to total internal reflection (TIR) of a light beam in a prism modulated by a sample placed on the base of the prism. Our experimental results shown details which present a lateral size as small as 200 A. The PSTM axial resolution is more difficult to evaluate. It is a function of the roughness of the sample. For very smooth samples, images shown an axial resolution of about 10 A. At last we discuss how both lateral and axial resolution can be affected by several parameters such as the tip surface distance and the roughness of the sample itself. This paper shows the necessity to find for each sample a good working distance where the profile follows as close as possible the shape of the sample.

Analysis of photon-scanning tunneling microscope images of inhomogeneous samples: determination of the local refractive index of channel waveguides

Channel waveguides are imaged by a photon-scanning tunneling microscope (PSTM). The polarization of the light and its orientation with respect to the guide axis are shown to be very important parameters in the analysis of the images of such samples. We simulated image formation for the plane of incidence parallel to the axis of the guide. Our theoretical results are qualitatively in agreement with our measurements. These results show the ability of the PSTM to give information about the local refractive-index variations of a sample.

Observation of optical waveguides by using a photon scanning tunneling microscope

The photon scanning tunneling microscope (PSTM) is based on the frustration of total internal reflection by the apex of an optical fiber placed near the surface of reflection. It has so far been used to obtain topographic information. This article shows that it also allows one to reach local variations of the refractive index of the sample. The PSTM, like many local probes, is operated on a constant intensity level. In that case a theoretical analysis based on a simple model shows that a change of the refractive index can actually be seen with the PSTM. The authors find that the corrugation height depends on the distance between the tip and the sample surface. The local refractive index of microguides diffused in glass has been studied experimentally with the PSTM. Relative variations in the order of 10-3 have been observed.

Combining infrared and mode synthesizing atomic force microscopy: Application to the study of lipid vesicles inside Streptomyces bacteria

We propose a new analytical approach combining vibrational spectroscopy and acoustic tomography for the detection and characterization of vesicles inside Streptomyces bacteria. Using atomic force microscopy and infrared spectroscopy (AFM-IR), we detect the presence of triglyceride vesicles. Their sizes in depth are measured with high accuracy using mode synthesizing atomic force microscopy (MS-AFM). We conducted a comparative study of AFM-IR and MS-AFM, and highlighted the advantages of the coupling of these techniques in having a full characterization (chemical, topographical, and volumetric) of a biological sample. With these complementary techniques, a complete access to the vesicle size distribution has been achieved with an accuracy of less than 50 nm. A 3D reconstruction of bacteria showing the in-depth distribution of vesicles is given to underline the great potential of the acoustic method.

Imaging of test quartz gratings with a photon scanning tunneling microscope. Experiment and theory

We use the differential formalism of the electromagnetic theory of gratings to interpret the images of test sinusoidal or lamellar quartz gratings obtained with a photon scanning tunneling microscope. The period of the grating is 0.5 μm, and the height of the rule is 0.2 μm. It is shown that the images depend strongly on several parameters, such as polarization or angle of incidence, with respect to the ruling direction. A systematic study of the isointensity lines above the gratings as a function of polarization is presented, and it is shown that the image contrast can be increased or decreased depending on the sample–probe distance. To model the interaction of the fiber probe with the electromagnetic field, we consider a second grating facing the grating under study, and by varying the periodicity of the second grating we calculate the intensity of the collected light and compare it with the experimental results.

Detection of the optical magnetic field by circular symmetry plasmons

We report on the influence of coating a sharpened optical fiber tip with Au when observing nanofabricated dielectric structures with a Photon Scanning Tunneling Microscope (PSTM) in constant-height mode. For well-defined incident wavelengths and coating thicknesses, we found that such tips detect the distribution of the magnetic field associated with the optical wave in the near-field zone. A simple tip model indicates that this phenomenon is related to the excitation of circular symmetry plasmons in Au coated tips.

A dark field photon scanning tunneling microscope under incoherent light illumination

Abstract A new kind of photon scanning tunneling microscope which reduces the asymmetrical effects due to the illumination is described. The evanescent electromagnetic field is produces through a conventional dark field optical microscope condensor with a white incoherent light source. Images of quartz crossed grating are presented and compared to the spatial distribution of the calculated iso-intensity lines.