34 research outputs found
Enhancing ordering dynamics in solvent-annealed block-copolymer films by lithographic hard masks supports
We studied solvent-driven ordering dynamics of block copolymer films
supported by a densely cross-linked polymer network designed as organic hard
mask (HM) for lithographic fabrications. The ordering of microphase separated
domains at low degrees of swelling corresponding to intermediate/strong
segregation regimes was found to proceed significantly faster in films on a HM
layer as compared to similar block copolymer films on silicon wafers. The
ten-fold enhancement of the chain mobility was evident in the dynamics of
morphological phase transitions and of related process of terrace-formation on
a macroscale, as well as in the degree of long-range lateral order of
nanostructures. The effect is independent of the chemical structure and on the
volume composition (cylinder-/ lamella-forming) of the block copolymers.
In-situ ellipsometric measurements of the swelling behavior revealed a
cumulative increase in 1-3 vol. % in solvent up-take by HM-block copolymer
bilayer films, so that we suggest other than dilution effect reasons for the
observed significant enhancement of the chain mobility in concentrated block
copolymer solutions. Another beneficial effect of the HM-support is the
suppression of the film dewetting which holds true even for low molecular
weight homopolymer polystyrene films at high degrees of swelling. Apart from
immediate technological impact in block copolymer-assisted nanolithography, our
findings convey novel insight into effects of molecular architecture on
polymer-solvent interactions.Comment: This document is the unedited Author's version of a Submitted Work
that was subsequently accepted for publication in Macromolecules, copyright
\c{opyright} American Chemical Society after peer review. To access the final
edited and published work see http://pubs.acs.org/doi/abs/10.1021/ma500561
Sub 20 nm Silicon Patterning and Metal Lift-Off Using Thermal Scanning Probe Lithography
The most direct definition of a patterning process' resolution is the
smallest half-pitch feature it is capable of transferring onto the substrate.
Here we demonstrate that thermal Scanning Probe Lithography (t-SPL) is capable
of fabricating dense line patterns in silicon and metal lift-off features at
sub 20 nm feature size. The dense silicon lines were written at a half pitch of
18.3 nm to a depth of 5 nm into a 9 nm polyphthalaldehyde thermal imaging layer
by t-SPL. For processing we used a three-layer stack comprising an evaporated
SiO2 hardmask which is just 2-3 nm thick. The hardmask is used to amplify the
pattern into a 50 nm thick polymeric transfer layer. The transfer layer
subsequently serves as an etch mask for transfer into silicon to a nominal
depth of 60 nm. The line edge roughness (3 sigma) was evaluated to be less than
3 nm both in the transfer layer and in silicon. We also demonstrate that a
similar three-layer stack can be used for metal lift-off of high resolution
patterns. A device application is demonstrated by fabricating 50 nm half pitch
dense nickel contacts to an InAs nanowire.Comment: 7 pages, 5 figures, to be published in JVST
Gate Electrodes Enable Tunable Nanofluidic Particle Traps
The ability to control the location of nanoscale objects in liquids is
essential for fundamental and applied research from nanofluidics to molecular
biology. To overcome their random Brownian motion, the electrostatic fluidic
trap creates local minima in potential energy by shaping electrostatic
interactions with a tailored wall topography. However, this strategy is
inherently static -- once fabricated the potential wells cannot be modulated.
Here, we propose and experimentally demonstrate that such a trap can be
controlled through a buried gate electrode.We measure changes in the average
escape times of nanoparticles from the traps to quantify the induced
modulations of 0.7k_\rm{B}T in potential energy and 50 mV in surface
potential. Finally, we summarize the mechanism in a parameter-free predictive
model, including surface chemistry and electrostatic fringing, that reproduces
the experimental results. Our findings open a route towards real-time
controllable nanoparticle traps
Evolution of reproductive development in the volvocine algae
The evolution of multicellularity, the separation of germline cells from sterile somatic cells, and the generation of a male–female dichotomy are certainly among the greatest innovations of eukaryotes. Remarkably, phylogenetic analysis suggests that the shift from simple to complex, differentiated multicellularity was not a unique progression in the evolution of life, but in fact a quite frequent event. The spheroidal green alga Volvox and its close relatives, the volvocine algae, span the full range of organizational complexity, from unicellular and colonial genera to multicellular genera with a full germ–soma division of labor and male–female dichotomy; thus, these algae are ideal model organisms for addressing fundamental issues related to the transition to multicellularity and for discovering universal rules that characterize this transition. Of all living species, Volvox carteri represents the simplest version of an immortal germline producing specialized somatic cells. This cellular specialization involved the emergence of mortality and the production of the first dead ancestors in the evolution of this lineage. Volvocine algae therefore exemplify the evolution of cellular cooperation from cellular autonomy. They also serve as a prime example of the evolution of complex traits by a few successive, small steps. Thus, we learn from volvocine algae that the evolutionary transition to complex, multicellular life is probably much easier to achieve than is commonly believed
The nanofluidic confinement apparatus: studying confinement-dependent nanoparticle behavior and diffusion
The behavior of nanoparticles under nanofluidic confinement depends strongly on their distance to the confining walls; however, a measurement in which the gap distance is varied is challenging. Here, we present a versatile setup for investigating the behavior of nanoparticles as a function of the gap distance, which is controlled to the nanometer. The setup is designed as an open system that operates with a small amount of dispersion of ≈20 μL, permits the use of coated and patterned samples and allows high-numerical-aperture microscopy access. Using the tool, we measure the vertical position (termed height) and the lateral diffusion of 60 nm, charged, Au nanospheres as a function of confinement between a glass surface and a polymer surface. Interferometric scattering detection provides an effective particle illumination time of less than 30 μs, which results in lateral and vertical position detection accuracy ≈10 nm for diffusing particles. We found the height of the particles to be consistently above that of the gap center, corresponding to a higher charge on the polymer substrate. In terms of diffusion, we found a strong monotonic decay of the diffusion constant with decreasing gap distance. This result cannot be explained by hydrodynamic effects, including the asymmetric vertical position of the particles in the gap. Instead we attribute it to an electroviscous effect. For strong confinement of less than 120 nm gap distance, we detect the onset of subdiffusion, which can be correlated to the motion of the particles along high-gap-distance paths