Modification of HF-treated silicon (100) surfaces by scanning tunneling microscopy in air under imaging conditions

The modification of HF-etched silicon (100) surface with a scanning tunneling microscope(STM) operated in air is studied for the first time in samples subjected to the standard HF etching without the follow-up rinsing in H2O. The modifications are produced in air under normal STM imaging conditions (V t =−1.4 V and I t =2 nA). The simultaneous acquisition of topographical, current image tunneling spectroscopy and local barrier-height images clearly shows that the nature of the modification is not only topographical but also chemical. The features produced with a resolution better than 25 nm are attributed to a tip-induced oxidation enhanced by the presence of fluorine on the surface

VHF band-pass filter based on a single CMOS-MEMS doubleended tuning fork resonator

AbstractThis paper presents a single Double-Ended Tuning Fork (DETF) MEMS resonator-based band-pass filter fabricated on a commercial standard CMOS technology. The accurate design of this resonator demonstrates the ability to perform filtering without the need of coupling multiple resonators. The main characteristic is to define the out-of-phase mode resonance frequency of the DETF smaller than the in-phase mode frequency. The electrical characterization shows that this stand-alone band-pass filter presents a 44.4MHz central frequency with a 0.6% bandwidth in air

Monolithic mass sensor fabricated using a conventional technology with attogram resolution in air conditions

Premi a l'excel·lència investigadora. Àmbit de les Ciències Tecnològiques. 2008Monolithic mass sensors for ultrasensitive mass detection in air conditions have been fabricated using a conventional 0.35 μm complementary metal-oxide-semiconductor (CMOS) process. The mass sensors are based on electrostatically excited submicrometer scale cantilevers integrated with CMOS electronics. The devices have been calibrated obtaining an experimental sensitivity of 6×10−11 g/cm2 Hz equivalent to 0.9 ag/Hz for locally deposited mass. Results from time-resolved mass measurements are also presented. An evaluation of the mass resolution have been performed obtaining a value of 2.4×10−17 g in air conditions, resulting in an improvement of these devices from previous works in terms of sensitivity, resolution, and fabrication process complexity

Measuring electrical current during scanning probe oxidation

Electrical current is measured during scanning probe oxidation by performing force versus distance curves under the application of a positive sample voltage. It is shown how the time dependence of the current provides information about the kinetics of oxide growth under conditions in which the tip-surface distance is known unequivocally during current acquisition. Currentmeasurements at finite tip-sample distance, in particular, unveil how the geometry of the meniscus influences its electrical conduction properties as well as the role of space charge at very small tip-sample distances

Nanometer-scale oxidation of Si(100) surfaces by tapping mode atomic force microscopy

The nanometer¿scale oxidation of Si(100) surfaces in air is performed with an atomic force microscope working in tapping mode. Applying a positive voltage to the sample with respect to the tip, two kinds of modifications are induced on the sample: grown silicon oxide mounds less than 5 nm high and mounds higher than 10 nm (which are assumed to be gold depositions). The threshold voltage necessary to produce the modification is studied as a function of the average tip¿to¿sample distance

Integrated tunneling sensor for nanoelectromechanical systems

Transducers based on quantum mechanical tunneling provide an extremely sensitive sensor principle, especially for nanoelectromechanical systems. For proper operation a gap between the electrodes of below 1nm is essential, requiring the use of structures with a mobile electrode. At such small distances, attractive van der Waals and capillary forces become sizable, possibly resulting in snap-in of the electrodes. The authors present a comprehensive analysis and evaluation of the interplay between the involved forces and identify requirements for the design of tunnelingsensors. Based on this analysis, a tunnelingsensor is fabricated by Si micromachiningtechnology and its proper operation is demonstrated

Modeling the high-energy emission in GRB 110721A and implications on the early multiwavelength and polarimetric observations

GRB 110721A was detected by the Gamma-ray Burst Monitor and the Large Area Telescope (LAT) onboard the Fermi satellite and the Gamma-ray Burst Polarimeter onboard the IKAROS solar mission. Previous analysis done of this burst showed: i) a linear polarization signal with position angle stable ($\phi_p= 160^\circ\pm11$) and high degree of $\Pi=84^{+16}_{-28}$, ii) an extreme peak energy of a record-breaking at 15$\pm$2 MeV, and iii) a subdominant prompt thermal component observed right after the onset of this burst. In this paper, the LAT data around the reported position of GRB 110721A are analysed with the most recent software and then, the LAT light curve above 100 MeV was obtained. The LAT light curve is modelled in terms of adiabatic early-afterglow external shocks when the outflow propagates into a stellar wind. Additionally, we discuss the possible origins and also study the implications of the early-afterglow external shocks on the extreme peak energy observed at 15$\pm$2 MeV, the polarization observations and the subdominant prompt thermal component.Comment: 9 pages and one figure. Accepted for publication in Ap