4,275 research outputs found
Capillary origami of micro-machined micro-objects: Bi-layer conductive hinges
Recently, we demonstrated controllable 3D self-folding by means of capillary
forces of silicon-nitride micro-objects made of rigid plates connected to each
other by flexible hinges [1]. In this paper, we introduce platinum electrodes
running from the substrate to the plates over these bendable hinges. The
fabrication yield is as high as (77 +/- 2) % for hinges with a length less than
75 {\mu}m. The yield reduces to (18 +/- 2) % when the length increases above
100 {\mu}m. Most of the failures in conductivity are due to degradation of the
platinum/chromium layer stack during the final plasma cleaning step. The
bi-layer hinges survive the capillary folding process, even for extremely small
bending radii of 5 {\mu}m, nor does the bending have any impact on the
conductivity. Stress in the different layers deforms the hinges, which does not
affect the conductivity. Once assembled, the conductive hinges can withstand a
current density of (1.6 +/- 0.4) A/cm . This introduction of
conductive electrodes to elastocapillary self-folded silicon-based
micro-objects extends the range of their possible applications by allowing an
electronic functionality of the folded parts.Comment: Currently on a peer review process. 13 page
Elastocapillary folding using stop-programmable hinges fabricated by 3D micro-machining
We show elasto-capillary folding of silicon nitride objects with accurate
folding angles between flaps of 70.60.1{\deg} and demonstrate the
feasibility of such accurate micro-assembly with a final folding angle of
90{\deg}. The folding angle is defined by stop-programmable hinges that are
fabricated starting from silicon molds employing accurate three-dimensional
corner lithography. This nano-patterning method exploits the conformal
deposition and the subsequent timed isotropic etching of a thin film in a 3D
shaped silicon template. The technique leaves a residue of the thin film in
sharp concave corners which can be used as an inversion mask in subsequent
steps. Hinges designed to stop the folding at 70.6{\deg} were fabricated
batchwise by machining the V-grooves obtained by KOH etching in (110) silicon
wafers; 90{\deg} stop-programmable hinges were obtained starting from silicon
molds obtained by dry etching on (100) wafers. The presented technique is
applicable to any folding angle and opens a new route towards creating
structures with increased complexity, which will ultimately lead to a novel
method for device fabrication.Comment: Submitted to a peer reviewed journa
Nonequilibrium Electron Interactions in Metal Films
Ultrafast relaxation dynamics of an athermal electron distribution is
investigated in silver films using a femtosecond pump-probe technique with 18
fs pulses in off-resonant conditions. The results yield evidence for an
increase with time of the electron-gas energy loss rate to the lattice and of
the free electron damping during the early stages of the electron-gas
thermalization. These effects are attributed to transient alterations of the
electron average scattering processes due to the athermal nature of the
electron gas, in agreement with numerical simulations
Consumer credit in comparative perspective
We review the literature in sociology and related fields on the fast global growth of consumer credit and debt and the possible explanations for this expansion. We describe the ways people interact with the strongly segmented consumer credit system around the world—more specifically, the way they access credit and the way they are held accountable for their debt. We then report on research on two areas in which consumer credit is consequential: its effects on social relations and on physical and mental health. Throughout the article, we point out national variations and discuss explanations for these differences. We conclude with a brief discussion of the future tasks and challenges of comparative research on consumer credit.Accepted manuscrip
3D-Fractal engineering based on oxide-only corner lithography
This paper reports a new highly simplified machining process for three dimensional (3D)-fractal nanofabrication based on oxide-only corner lithography. It consists of a repeated sequence of wet etching (silicon), thermal oxidation and wet etching (silicon oxide). The previously reported 3D-fractal fabrication process needed additional low pressure chemical vapor deposition (LPCVD) steps of silicon nitride, as well as local oxidation of silicon (LOCOS). Employing this new procedure, a three generation folded silicon oxide fractal sheet with approx. a 10 µm footprint has been fabricated
DE Canum Venaticorum : a bright, eclipsing red dwarf–white dwarf binary
Context. Close white dwarf–red dwarf binaries must have gone through a common-envelope phase during their evolution. DE CVn is a detached white dwarf–red dwarf binary with a relatively short (∼8.7 h) orbital period. Its brightness and the presence of eclipses makes this system ideal for a more detailed study.
Aims. From a study of photometric and spectroscopic observations of DE CVn we derive the system parameters that we discuss in the framework of common-envelope evolution.
Methods. Photometric observations of the eclipses are used to determine an accurate ephemeris. From a model fit to an average lowresolution spectrum of DE CVn, we constrain the temperature of the white dwarf and the spectral type of the red dwarf. The eclipse light curve is analysed and combined with the radial velocity curve of the red dwarf determined from time-resolved spectroscopy to derive constraints on the inclination and the masses of the components in the system.
Results. The derived ephemeris is HJDmin = 2 452 784.5533(1) + 0.3641394(2) × E. The red dwarf in DE CVn has a spectral type of M3V and the white dwarf has an effective temperature of 8 000 K. The inclination of the system is 86+3◦ −2 and the mass and radius of the red dwarf are 0.41 ± 0.06 M and 0.37+0.06 −0.007 R, respectively, and the mass and radius of the white dwarf are 0.51+0.06
−0.02 M and 0.0136+0.0008 −0.0002 R, respectively.
Conclusions. We found that the white dwarf has a hydrogen-rich atmosphere (DA-type). Given that DE CVn has experienced a common-envelope phase, we can reconstruct its evolution and we find that the progenitor of the white dwarf was a relatively lowmass star (M ≤ 1.6 M). The current age of this system is 3.3−7.3 × 109 years, while it will take longer than the Hubble time for DE CVn to evolve into a semi-detached system
Young people, crime and school exclusion: a case of some surprises
During the 1990s the number of young people being permanently excluded from schools in England and Wales increased dramatically from 2,910 (1990/91) to a peak of 12,700 (1996/97). Coinciding with this rise was a resurgence of the debate centring on lawless and delinquent youth. With the publication of Young People and Crime (Graham and Bowling 1995) and Misspent Youth (Audit Commission 1996) the 'common sense assumption' that exclusion from school inexorably promoted crime received wide support, with the school excludee portrayed as another latter day 'folk devil'. This article explores the link between school exclusion and juvenile crime, and offers some key findings from a research study undertaken with 56 young people who had experience of being excluded from school. Self-report interview questions reveal that whilst 40 of the young people had offended, 90% (36) reported that the onset of their offending commenced prior to their first exclusion. Moreover, 50 (89.2% of the total number of young people in the sample), stated that they were no more likely to offend subsequent to being excluded and 31 (55.4%) stated that they were less likely to offend during their exclusion period. Often, this was because on being excluded, they were 'grounded' by their parents
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