2,763 research outputs found
Nanometer-scale patterning and individual current-controlled lithography using multiple scanning probes
Cataloged from PDF version of article.Scanning probe lithography(SPL) is capable of sub-30-nm-patterning resolution and nanometer-scale alignment registration, suggesting it might provide a solution to the semiconductor industry’s lithography challenges. However, SPL throughput is significantly lower than conventional lithography techniques. Low throughput most limits the widespread use of SPL for high resolution patterning applications. This article addresses the speed constraints for reliable patterning of organic resists. Electrons field emitted from a sharp probe tip are used to expose the resist. Finite tip-sample capacitance limits the bandwidth of current-controlled lithography in which the tip-sample voltage bias is varied to maintain a fixed emission current during exposure. We have introduced a capacitance compensation scheme to ensure continuous resist exposure of SAL601 polymerresist at scan speeds up to 1 mm/s. We also demonstrate parallel resist exposure with two tips, where the emission current from each tip is individually controlled. Simultaneous patterning with multiple tips may make SPL a viable technology for high resolution lithography.
© 1999 American Institute of Physic
Surface micromachined capacitive ultrasonic transducers
Cataloged from PDF version of article.The current state of a novel technology, surface
microfabricated ultrasonic transducers, is reported.
Experiments demonstrating both air and water transmission
are presented. Air-coupled longitudinal wave transmission
through aluminum is demonstrated, implying a 110 dB
dynamic range for transducers at 2.3 MHz in air. Water
transmission experiments from 1 to 20 MHz are performed,
with a measured 60 dB SNR at 3 MHz. A theoretical model
is proposed that agrees well with observed transducer behavior.
Most significantly, the model is used to demonstrate
that microfabricated ultrasonic transducers constitute an
attractive alternative to piezoelectric transducers in many
applications
Conditional linearizability criteria for a system of third-order ordinary differential equations
We provide linearizability criteria for a class of systems of third-order
ordinary differential equations (ODEs) that is cubically semi-linear in the
first derivative, by differentiating a system of second-order quadratically
semi-linear ODEs and using the original system to replace the second
derivative. The procedure developed splits into two cases, those where the
coefficients are constant and those where they are variables. Both cases are
discussed and examples given
Understanding suicide attempts among gay men from their self-perceived causes
Gay men are at higher risk of suicidality. This paper describes the causes of suicide attempts as perceived by the men themselves and analyzes their impact on severity and recidivism. Mental health surveys conducted among gay men in Geneva, Switzerland, from two probability-based time-space samples in 2007 and 2011, were merged to yield a combined sample N = 762. Suicide ideation, plans, and attempts were assessed, and respondents who had ever attempted suicide answered open questions about perceived causes which were coded and categorized for analysis within the framework of cultural epidemiology. In all, 16.7% of the respondents reported a suicide attempt in their lifetime (59.5% of them with multiple attempts). At their latest attempt, over two thirds asserted intent to die, and half required medical assistance. There was a wide variety of perceived causes, with most individuals reporting multiple causes and many of the most common causes cited at both the first and most recent subsequent attempts. Social/inter-personal problems constitute the most prominent category. Problems with love/relationship and accepting one's homosexuality figure consistently among the top three causes. Whereas the former tend to be associated with weaker intent to die, the latter are associated with the strongest intent to die and reported at multiple attempts. Problems with family are among the most common perceived causes at first attempt but not at the most recent subsequent attempt. Nevertheless, they tend to be related to the strongest intent to die and the greatest medical severity of all the perceived causes. Ten percent of men attempting suicide cited depression as a cause. Although it tended to be associated with weaker intent to die, depression was most likely to be reported at multiple attempts. Respondent-driven assessment yielded both common and idiosyncratic causes of suicide and their distinct effects. Some of these perceived causes are not prominent in the curren literature, yet they have important implications for understanding risk and preventing suicide among gay men
Mesoscopic Phase Coherence in a Quantum Spin Fluid
Mesoscopic quantum phase coherence is important because it improves the
prospects for handling quantum degrees of freedom in technology. Here we show
that the development of such coherence can be monitored using magnetic neutron
scattering from a one-dimensional spin chain Y2BaNiO5, a quantum spin fluid
where no classical, static magnetic order is present. In the cleanest samples,
the quantum coherence length is 20 nm, almost an order of magnitude larger than
the classical antiferromagnetic correlation length of 3 nm. We also demonstrate
that the coherence length can be modified by static and thermally activated
defects in a quantitatively predictable manner
High-Field Electrical Transport in Single-Wall Carbon Nanotubes
Using low-resistance electrical contacts, we have measured the intrinsic
high-field transport properties of metallic single-wall carbon nanotubes.
Individual nanotubes appear to be able to carry currents with a density
exceeding 10^9 A/cm^2. As the bias voltage is increased, the conductance drops
dramatically due to scattering of electrons. We show that the current-voltage
characteristics can be explained by considering optical or zone-boundary phonon
emission as the dominant scattering mechanism at high field.Comment: 4 pages, 3 eps figure
Current carrying capacity of carbon nanotubes
The current carrying capacity of ballistic electrons in carbon nanotubes that
are coupled to ideal contacts is analyzed. At small applied voltages, where
electrons are injected only into crossing subbands, the differential
conductance is . At applied voltages larger than
( is the energy level spacing of first non crossing subbands),
electrons are injected into non crossing subbands. The contribution of these
electrons to current is determined by the competing processes of Bragg
reflection and Zener type inter subband tunneling. In small diameter nanotubes,
Bragg reflection dominates, and the maximum differential conductance is
comparable to . Inter subband Zener tunneling can be non negligible as
the nanotube diameter increases because is inversely
proportional to the diameter. As a result, with increasing nanotube diameter,
the differential conductance becomes larger than , though not
comparable to the large number of subbands into which electrons are injected
from the contacts. These results may be relevant to recent experiments in large
diameter multi-wall nanotubes that observed conductances larger than .Comment: 12 pages, 4 figure
Disorder, pseudospins, and backscattering in carbon nanotubes
We address the effects of disorder on the conducting properties of metal and
semiconducting carbon nanotubes. Experimentally, the mean free path is found to
be much larger in metallic tubes than in doped semiconducting tubes. We show
that this result can be understood theoretically if the disorder potential is
long-ranged. The effects of a pseudospin index that describes the internal
sublattice structure of the states lead to a suppression of scattering in
metallic tubes, but not in semiconducting tubes. This conclusion is supported
by tight-binding calculations.Comment: four page
Integration of through-wafer interconnects with a two-dimensional cantilever array
Cataloged from PDF version of article.High-density through-wafer interconnects are incorporated in a two-dimensional (2D) micromachined cantilever array. The design addresses alignment and density issues associated with 2D arrays. Each cantilever has piezoresistive deflection sensors and high-aspect ratio silicon tips. The fabrication process and array operation are described. The integration of cantilevers, tips, and interconnects enables operation of a high-density 2D scanning probe array over large areas. (C) 2000 Elsevier Science S.A. All rights reserved
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