Bottom-up alternative lithographic masks from directed self-assembly systems have been extending the limits of critical
dimensions in a cost-effective manner although great challenges in controlling defectivity remain open. Particularly,
defectivity and dimensional metrology are two main challenges in lithography due to the increasing miniaturisation of
circuits. To gain insights about the percentage of alignment, defectivity and order quantification, directed self-assembly
block copolymer fingerprints were investigated via an image analysis methodology. Here we present the analysis of
hexagonal phase of polystyrene-b-polydimethylsiloxane (PS-b-PDMS) forming linear patterns in topological substrates.
From our methodology, we have performed dimensional metrology estimating pitch size and error, and the linewidth of
the lines was estimated. In parallel, the methodology allowed us identification and quantification of typical defects
observable in self-assembly, such as turning points, disclination or branching points, break or lone points and end points.
The methodology presented here yields high volume statistical data useful for advancing dimensional metrology and
defect analysis of self- and directed assembly systems.
The line patterns obtained by the self-assembly of the block copolymer (BCP) polystyrene-b-polyethylene oxide (PS-b-PEO)
was investigated. The hexagonal PS-b-PEO 42k-11.5k in a thin film was solvent annealed in a chlorophorm saturated
atmosphere for three different annealing times. The microphase segregation of this BCP returned 18nm cylinders of PEO
through the PS matrix, with an approximately 40 n periodicity, as expected. Under chlorophorm vapours, the PEO cylinders
oriented perpendicular to the silicon substrate while increasing the annealing time. These cylinders formed linear patterns
with different alignment. To achieve insights about the percentage of alignment, defect type pareto and density, and order
quantification to compare the three annealing recipes, the samples were analysed with innovative image analysis software
specifically developed in our laboratory to identify elements and defects of line arrays from block copolymer self-assembly.
From this technique, it was extracted dimensional metrology estimating pitch size and placement error, and the line-width of
the lines was estimated. Secondly, the methodology allows identification and quantification of typical defects observable in
BCP systems, such as turning points, disclination or branching points, break or lone points and end points. The defect density
and the quantification of the alignment were estimated using our technique. The methodology presented here represents a
step forward in dimensional metrology and defect analysis of BCP DSA systems and can be readily used to analyze other
lithographic or non-lithographic patterns.
Different linear patterns obtained from the directed self-assembly of the block copolymer (BCP) polystyrene-b-polyethylene oxide (PS-b-PEO) were analysed and compared. The hexagonal phase PS-b-PEO in a thin film exhibits linear pattern morphology, by conventional solvent annealing in an atmosphere saturated in chloroform. The surface energy of the silicon substrates was varied using surface functionalization of a self-assembly monolayer (SAM) and a polymer brush, chosen to investigate the influence of the surface energy on the self-assembly of the BCP. The linear patterns formed were analyzed with innovative image analysis software specifically developed in our laboratory to identify elements and defects of line arrays from block copolymer self-assembly. The technique starts by performing dimensional metrology to calculate the pitch size and estimate the linewidth of the lines. Secondly, the methodology allows identification and quantification of typical defects observable in BCP systems, such as turning points, disclination or branching points, break or lone points and end points. The defect density and the quantification of the alignment were estimated using our technique. The methodology presented here represents a step forward in dimensional metrology and defect analysis of BCP DSA systems and can be readily used to analyze other lithographic or non-lithographic patterns.
In this paper we numerically demonstrate that an optical memory can be based on a two-mode laser diode with
optical feedback and injection in the short external cavity regime. For modelling this system we use a two-mode
extension of the Lang-Kobayashi rate equations with gain saturation and optical injection. The parameters
chosen are consistent with the simultaneous oscillation of the two modes in the free running laser, which is
possible for frequency spacings greater than approximately 500 GHz at optical frequencies around 200 THz. For
certain values of the system parameters, we have found a hysteresis loop between single-mode equilibrium states
for increasing and decreasing feedback strength. Our simulations show that injected optical pulses can switch the
system between single mode equilibrium states when the feedback parameters are fixed in this bistable region,
demonstrating the function of the optical memory. This system has attractive features such as the absence of a
holding beam and the symmetry between the two states of the memory element. These properties along with
the external cavity length of 1 cm make the system an interesting candidate for optical integration.
We have generalized the concept of nonlinear periodic structures to dielectric systems that show
arbitrary spatial and temporal variations of the refractive index. Nonlinear pulse propagation
through these spatiotemporal photonic crystals can be described, for shallow nonstationary
gratings, by coupled mode equations which are a generalization of the traditional equations
used for stationary Bragg gratings. Novel gap soliton solutions are found analytically. They
represent a generalization of the gap solitons in static photonic crystals and resonance solitons
found in dynamic gratings.
We study the role of noise during the growth process of opal-based photonic crystals, and demonstrate
that noise significantly improves their structural properties. We observe a stochastic resonance-like
behaviour, where the ordering of the resulting structure improves up to a certain optimal noise level
and then deteriorates for larger noise volumes. This demonstrates that noise can have a nontrivial
effect when applied during a non-equilibrium pattern forming process.
Charge accumulation in the quantum-well of a double-barrier resonant-tunneling diode (DBRT) may result in bistability that provides a basis for formation of lateral current-density patterns. A typical pattern expected to appear is a current density front. Such fronts correspond to switching transitions and generally cannot be stabilized by a conventional external circuit. In this paper we discuss formation and stabilization of stationary current density patterns in bistable DBRT. We demonstrate that the intrinsic dynamics of the DBRT can lead to the onset of regular or chaotic spatio-temporal oscillations if an attempt to stabilize unstable current density patterns by means of a simple control loop is undertaken.
We consider a semiconductor superlattice biased into the regime of negative differential conductivity and driven by an additional GHz ac voltage, and find frequency-locked or quasiperiodic propagating field domains. With increasing driving frequency, the complex impedance exhibits strong variations of its amplitude and phase. An anomalous phase shift appears as a result of phase synchronization of the traveling domains.
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