Anke Sanz-Velasco

Room Temperature Wafer Bonding Using Oxygen Plasma Treatment in Reactive Ion Etchers With and Without Inductively Coupled Plasma

The effects of oxygen plasma treatment on silicon surface topography and the properties of bonded interfaces formed using the oxygen plasma pretreatment were investigated. Bonded samples of silicon or oxidized silicon wafers using oxygen plasma pretreatment in reactive ion etchers with and without inductively coupled plasma were characterized in terms of surface energies obtained at room temperature. Annealing experiments at 1000°C were made to study the origin of thermally generated voids. Atomic force microscopy was used to study how the surface roughness of plasma-treated silicon wafers evolved over time. Furthermore, the influence of water dipping on the roughness of plasma-treated silicon surfaces was investigated. The results showed that plasma treatment of one wafer results in a surface energy of approximately I J m 2 at room temperature. The role of water in the increase of surface energy was found to be crucial. From annealing experiments it is concluded that water present at the wafer surfaces before bonding has a pronounced influence on void generation upon annealing. A dramatic change in the topography of silicon surfaces treated in oxygen plasma was observed during storage at room temperature, while water dipping the wafers after plasma treatment appeared to stabilize the surface topography.

A micro direct methanol fuel cell demonstrator

The demand for compact power sources with high energy density is increasing. A direct methanol fuel cell (DMFC) is a renewable energy source which works at near room temperature, and allows for easier liquid fuel storage, which makes it a potential candidate. We report the design, fabrication and characterization of a self-driven DMFC made by micromachining techniques and macro-assembly. Several designs were created on the basis of state-of-the-art DMFCs. A simplified mathematical model was used mainly to design the flow channels and verify the polarization curves, which reveal the output power of a cell. Silicon was used as a substrate for the fabrication of electrodes, and the membrane electrode assembly was provided by Ion Power, Inc. A 0.25 cm2 cell showed a performance of 0.29 mW cm−2 and an open circuit voltage of 0.7 V. Ten microliters of 6 M methanol solution is sufficient to operate the cell for more than 1 h.

Motion of nanometer sized magnetic particles in a magnetic field gradient

Using magnetic particles with sizes in the nanometer range in biomedical magnetic separation has gained much interest recently due to their higher surface area to particle volume and lower sedimentation rates. In this paper, we report our both theoretical and experimental investigation of the motion of magnetic particles in a magnetic field gradient with particle sizes from 425 nm down to 50 nm. In the experimental measurements, we monitor the absorbance change of the sample volume as the particle concentration varies over time. We also implement a Brownian dynamics algorithm to investigate the influence of particle interactions during the separation and compare it to the experimental results for validation. The simulation agrees well with the measurements for particle sizes around 425 nm. Some discrepancies remain for smaller particle sizes, which may indicate that additional factors also influence the separation for the smaller size range. We observe that the separation process includes the formation of...

Towards an electrowetting-based digital microfluidic platform for magnetic immunoassays

We demonstrate ElectroWetting-On-Dielectric (EWOD) transport and SQUID gradiometer detection of magnetic nanoparticles (MNPs) suspended in a 2 microl de-ionized water droplet. This proof-of-concept methodology constitutes the first development step towards a highly sensitive magnetic immunoassay platform with SQUID readout and droplet-based sample handling. Magnetic AC-susceptibility measurements were performed on MNPs with a hydrodynamic diameter of 100 nm using a high-Tc dc Superconducting Quantum Interference Device (SQUID) gradiometer as detector. We observed that the signal amplitude per unit volume is 2.5 times higher for a 2 microl sample droplet compared to a 30 microl sample volume.

Conductivity-Dependent Strain Response of Carbon Nanotube Treated Bacterial Nanocellulose

This paper reports the strain sensitivity of flexible, electrically conductive, and nanostructured cellulose which was prepared by modification of bacterial cellulose with double-walled carbon nanotubes (DWCNTs) and multiwalled carbon nanotubes (MWCNTs). The electrical conductivity depends on the modifying agent and its dispersion process. The conductivity of the samples obtained from bacterial cellulose (BNC) pellicles modified with DWCNT was in the range from 0.034 S·cm−1 to 0.39 S·cm−1, and for BNC pellicles modified with MWCNTs it was from 0.12 S·cm−1 to 1.6 S·cm−1. The strain-induced electromechanical response, resistance versus strain, was monitored during the application of tensile force in order to study the sensitivity of the modified nanocellulose. A maximum gauge factor of 252 was found from the highest conductive sample treated by MWCNT. It has been observed that the sensitivity of the sample depends on the conductivity of the modified cellulose.

InGaAs/InAlAs/AlAs Heterostructure Barrier Varactors on Silicon Substrate

We present the results of a study on epitaxial transfer of InP-based heterostructure barrier varactor (HBV) materials onto a silicon substrate employing the low-temperature plasma-activated bonding technique. The test diodes fabricated on the bonded samples exhibit symmetric electrical characteristics, over the temperature range of 25°C-165°C, and show no degradation compared to previously reported InP-based diodes. Moreover, the onset temperature for debonding, the effective barrier height extracted from the measured data, and the maximum voltage of the HBVs for a current density of 100 A/cm2 were extracted to be 260°C, 0.56 eV, and 10.5 V, respectively.

Cobalt (II) chloride promoted formation of honeycomb patterned cellulose acetate films

CoCl(2) containing honeycomb patterned films were prepared from cellulose acetate (CA)/CoCl(2)/acetone solutions by the breath figure method in a wide range of humidities. Size and pore regularity depend on the CA/CoCl(2) molar ratio and humidity. When replacing CoCl(2) with Co(NO(3))(2) or CoBr(2), no formation of ordered porosity in the cellulose acetate films is observed. According to data from scanning electron microscopy (SEM), Energy Dispersive X-ray Microanalysis (EDX), X-ray Diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy, the key role in the formation of honeycomb structures can be attributed to the physical and chemical properties of CoCl(2) - hygroscopicity, low interaction with CA, and extraction from CA/CoCl(2)/acetone solution by water droplets condensed on the surface of the CA/CoCl(2) solution. Obtained films are prospective for using in catalysis, hydrogen fuel cells, and optical sensing materials.

Combining Scanning Probe Microscopy and Transmission Electron Microscopy

This chapter is a review of an in situ method where a scanning probe microscope (SPM) has been combined with a transmission electron microscope (TEM). By inserting a miniaturized SPM inside a TEM, a large set of open problems can be addressed and, perhaps more importantly, one may start to think about experiments in a new kind of laboratory, an in situ TEM probing laboratory, where the TEM is transformed from a microscope for still images to a real-time local probing tool. In this method, called TEMSPM, the TEM is used for imaging and analysis of a sample and SPM tip, while the SPM is used for probing of electrical and mechanical properties or for local manipulation of the sample. This chapter covers both instrumental and applicational aspects of TEMSPM.

MICRO PINBALL GAME DEMONSTRATING AN EASY MEMS TRANSFER PROCESS USING ROOM TEMPERATURE PLASMA BONDING

An easy wafer level transfer process for fabrication of electrostatically actuated structures such as bulk micromachined motors or cantilevers is described. The actual structures were fabricated by dry etching of a donor wafer, transferred to a handling wafer using room temperature oxygen plasma assisted bonding and then revealed through etchback of the donor wafer. Notching during the dry etch was avoided since there is no need for a buried oxide etch stop layer. Etch depth differences after the dry etch were eliminated in the etchback step. The process was used to fabricate MEMS demonstrators in the form of micro pinball games and microelectromechanical wobble motors. This process is a low cost alternative to using SOI wafers and it also circumvents some of the problems of deep dry etching that arise when using buried etch stop layers as in the case of SOI wafers. Another advantage of using SOI wafers is that double-sided micromachining becomes less complicated.

Novel Method for Controlled Wetting of Materials in the Environmental Scanning Electron Microscope

Environmental scanning electron microscopy has been extensively used for studying the wetting properties of different materials. For some types of investigation, however, the traditional ways of conducting in situ dynamic wetting experiments do not offer sufficient control over the wetting process. Here, we present a novel method for controlled wetting of materials in the environmental scanning electron microscope (ESEM). It offers improved control of the point of interaction between the water and the specimen and renders it more accessible for imaging. It also enables the study of water transport through a material by direct imaging. The method is based on the use of a piezo-driven nanomanipulator to bring a specimen in contact with a water reservoir in the ESEM chamber. The water reservoir is established by local condensation on a Peltier-cooled surface. A fixture was designed to make the experimental setup compatible with the standard Peltier cooling stage of the microscope. The developed technique was successfully applied to individual cellulose fibers, and the absorption and transport of water by individual cellulose fibers were imaged.