G. Pandraud

Atomic-scale electron-beam sculpting of near-defect-free graphene nanostructures.

In order to harvest the many promising properties of graphene in (electronic) applications, a technique is required to cut, shape, or sculpt the material on the nanoscale without inducing damage to its atomic structure, as this drastically influences the electronic properties of the nanostructure. Here, we reveal a temperature-dependent self-repair mechanism that allows near-damage-free atomic-scale sculpting of graphene using a focused electron beam. We demonstrate that by sculpting at temperatures above 600 °C, an intrinsic self-repair mechanism keeps the graphene in a single-crystalline state during cutting, even though the electron beam induces considerable damage. Self-repair is mediated by mobile carbon ad-atoms that constantly repair the defects caused by the electron beam. Our technique allows reproducible fabrication and simultaneous imaging of single-crystalline free-standing nanoribbons, nanotubes, nanopores, and single carbon chains.

Atomic Imaging of Phase Transitions and Morphology Transformations in Nanocrystals

A newly developed SiN microhotplate allows specimens to be studied at temperatures up to 1000 K at a resolution of 100 picometer. Aberration-corrected transmission electron microscopy has become a commonplace tool to investigate stable crystals; however, imaging transient nanocrystals is much more demanding. Morphological transformations in gold nanoparticles and layer-by-layer sublimation of PbSe nanocrystals is imaged with atomic resolution.

Etching methodologies in -oriented silicon wafers

New methodologies in anisotropic wet-chemical etching of -oriented silicon, allowing useful process designs combined with smart mask-to-crystal-orientation-alignment are presented in this paper. The described methods yield smooth surfaces as well as high-quality plan-parallel beams and membranes. With a combination of pre-etching and wall passivation, structures can be etched at different depths in a wafer. Designs, using the -crystal orientation, supplemented with pictures of fabricated devices, demonstrate the potential of using -oriented wafers in microsystem design.

Evanescent wave sensing: new features for detection in small volumes

The association by aligned direct bonding of an evanescent wave optical sensor and small-volume flow cells for visible absorption detection is demonstrated. We show that for sample volumes ranging from 760 to 190 nl and a sensor interaction length of 1 mm, very small cross-sectional dimensions of fluid channels are no more a serious obstacle for optical detection. The lowest limit for the channel depth is the penetration depth of the

In-situ TEM on (de)hydrogenation of Pd at 0.5–4.5 bar hydrogen pressure and 20–400°C

We have developed a nanoreactor, sample holder and gas system for in-situ transmission electron microscopy (TEM) of hydrogen storage materials up to at least 4.5 bar. The MEMS-based nanoreactor has a microheater, two electron-transparent windows and a gas inlet and outlet. The holder contains various O-rings to have leak-tight connections with the nanoreactor. The system was tested with the (de)hydrogenation of Pd at pressures up to 4.5 bar. The Pd film consisted of islands being 15 nm thick and 50-500 nm wide. In electron diffraction mode we observed reproducibly a crystal lattice expansion and shrinkage owing to hydrogenation and dehydrogenation, respectively. In selected-area electron diffraction and bright/dark-field modes the (de)hydrogenation of individual Pd particles was followed. Some Pd islands are consistently hydrogenated faster than others. When thermally cycled, thermal hysteresis of about 10-16°C between hydrogen absorption and desorption was observed for hydrogen pressures of 0.5-4.5 bar. Experiments at 0.8 bar and 3.2 bar showed that the (de)hydrogenation temperature is not affected by the electron beam. This result shows that this is a fast method to investigate hydrogen storage materials with information at the nanometer scale.

Characterization of low temperature deposited atomic layer deposition TiO2 for MEMS applications

TiO2 is an interesting and promising material for micro-/nanoelectromechanical systems (MEMS/NEMS). For high performance and reliable MEMS/NEMS, optimization of the optical characteristics, mechanical stress, and especially surface smoothness of TiO2 is required. To overcome the roughness issue of the TiO2 films due to crystallization during deposition at high temperatures (above 250?°C), low temperature (80–120?°C) atomic layer deposition (ALD) is investigated. By lowering the deposition temperature, the surface roughness significantly decreases from 3.64?nm for the 300?°C deposited crystalline (anatase phase) TiO2 to 0.24?nm for the 120?°C amorphous TiO2. However, the layers deposited at low temperature present different physical behaviors comparing to the high temperature ones. The refractive index drops from 2.499 to 2.304 (at 633?nm) and the stress sharply decreases from 684 to 133?MPa. Superhydrophilic surface is obtained for the high temperature deposited TiO2 under ultraviolet illumination, while little changes are found for the low temperature TiO2. The authors demonstrate that by suitable postdeposition annealing, all the properties of the low temperature deposited films recover to that of the 300?°C deposited TiO2, while the smooth surface profile (less than 1?nm roughness) is maintained. Finally, micromachining of the low temperature ALD TiO2 by dry etching is also studied.

A novel method for nanoprecision alignment in wafer bonding applications

Wafer bonding has been identified as a promising technique to enable fabrication of many advanced semiconductor devices such as three-dimensional integrated circuits (3D IC) and micro/nano systems. However, with the device dimensions already in the nanometre range, the lack of approaches to achieve high precision bonding alignment has restricted many applications. With this increasing demand for wafer bonding applications, a novel mechanical passive alignment technique is described in this work aiming at nanoprecision alignment based on kinematic and elastic averaging effects. A number of cantilever-supported pyramid and V-pit microstructures have been incorporated into the outer circumference area of the to-be-bonded Si chips, respectively. The engagement between the convex pyramids and concave V-pits and the compliance of the support cantilever flexures result in micromechanical passive alignment which is followed by direct bonding between the Si chips. The subsequent infrared (IR) and scanning electron microscopy (SEM) inspections repeatedly confirmed the achievement of alignment accuracy of better than 200 nm at the bonding interface with good bonding quality. The impact and potential applications of the developed alignment technique are also discussed.

Femto-molar sensitive field effect transistor biosensors based on silicon nanowires and antibodies

This article presents electrically-based sensors made of high quality silicon nanowire field effect transistors (SiNW-FETs) for high sensitive detection of vascular endothelial growth factor (VEGF) molecules. SiNW-FET devices, fabricated through an IC/CMOS compatible top-down approach, are covalently functionalized with VEGF monoclonal antibodies in order to sense VEGF. Increasing concentrations of VEGF in the femto molar range determine increasing conductance values as proof of occurring immuno-reactions at the nanowire (NW) surface. These results confirm data in literature about the possibility of sensing pathogenic factors with SiNW-FET sensors, introducing the innovating aspect of detecting biomolecules in dry conditions.

Miniature 10 kHz thermo-optic delay line in silicon

The scanning delay line is a key component of time-domain optical coherence tomography systems. It has evolved since its inception toward higher scan rates and simpler implementation. However, existing approaches still suffer from drawbacks in terms of size, cost, and complexity, and they are not suitable for implementation using integrated optics. In this Letter, we report a rapid scanning delay line based on the thermo-optic effect of silicon at λ = 1.3 μm manufactured around a generic planar lightwave circuit technology. The reported device attained line scan rates of 10 kHz and demonstrated a scan range of 0.95 mm without suffering any observable loss of resolution (15 µm FWHM) owing to depth-dependent chromatic dispersion.

Micro-fabricated channel with ultra-thin yet ultra-strong windows enables electron microscopy under 4-bar pressure

Transmission electron microscopy (TEM) of (de-)hydrogenation reactions is crucial to characterize efficiency of hydrogen storage materials. The nanoreactor, a micromachined channel with 15-nm-thick windows, effectively confines the gas flow to an electron-transparent chamber during TEM of reactions. Realistic experiments require very high pressures to be sustained by the device. Nanomechanical bulge tests and simulations show that due to a very strong size effect, ultra-thin device components can reliably withstand tensile stresses as high as 19.5 GPa enabling high pressure operation. We use the device to characterize Pd particles under a 4-bar H2 pressure within the ultra-high-vacuum of the TEM.