Douglas Adamson - Academia.edu (original) (raw)
Papers by Douglas Adamson
We present a novel technique which allows the investigation of thin film diblock copolymer microp... more We present a novel technique which allows the investigation of thin film diblock copolymer microphase morphology on a variety of substrates and at different film depths. Using a high resolution, low voltage Scanning Electron Microscope (SEM), we examined the topology and underlying morphology of styrene-butadiene diblock copolymer films. In order to enhance the contrast between the styrene and butadiene regions, we stained the butadiene with osmium tetraoxide. The internal morphology of the diblock copolymer film was exposed by using a non-selective fluorine-based reactive ion etching (RIE) technique. By controlling the depth of the RIE, we can effectively peel off one monolayer at a time. By alternating between RIE and SEM, we can examine the diblock copolymer film morphology at different depths. We also investigated the relationship between island formation and internal polymer microstructure. This work was supported by the NSF under DMR 9400362.
Instrumental aliasing, a usually undesired consequence of limited sampling resolution, can be put... more Instrumental aliasing, a usually undesired consequence of limited sampling resolution, can be put to good use in some circumstances in order to extend imaging capabilities. Normally, the resolution of an AFM picture is limited by the maximum number of pixels that can be acquired per scan line (512 in the case of the Digital Instruments Nanoscope IIIa controller used). A new AFM technique is reported through which the aliasing patterns obtained from large-area scans of hexagonal microdomains are analyzed and mapped onto the orientation of the underlying crystal grains. The experimental system used is a diblock copolymer film consisting of a monolayer of spherical microdomains. The AFM sampling is done close to the Nyquist frequency and the patterns obtained are analyzed by local Fourier transforms. The orientation and spacing of the lines in the aliasing pattern can be uniquely mapped onto the orientation of the hexagonal lattice, and thus we are able to o orientational maps for significantly larger areas than by the traditional technique of directly imaging (DI) each individual microdomain. We successfully applied the technique to measuring grain sizes in microdomain crystals where the correlation length exceeds by far the size of th picture that can be obtained by the DI technique.
Aps Meeting Abstracts, 2005
We have studied the phase diagram of a two dimensional smectic system, a monolayer film of di-blo... more We have studied the phase diagram of a two dimensional smectic system, a monolayer film of di-block copolymer cylinders. Previous work was done on sphere-forming diblock polymer films. In this work we anneal PS-PEP 5-13 cylinder-forming diblock copolymer using a temperature gradient system, to investigate the orientational order-disorder (melting) transition. We find that on the high temperature side correlation lengths are very small, revealing complete lack of orientational order. This corresponds to annealing far above the order-disorder (or melting) transition. The disordered state in this case is a thermodynamic equilibrium state, continued annealing of the sample will not produce more ordering in this region of the sample. The order-disorder transition, ODT, occurred at 163 oC, higher than the bulk ODT of the same polymer (TODT =144 ^oC). We present data on the temperature dependence of the correlation functions and the densities of topological defects. By lowing the temperature of the high T end of the gradient, we can also sweep the temperature gradient to study the effects of zone refining.
Block copolymer thin films present an ideal environment in which to study the microdomain orienta... more Block copolymer thin films present an ideal environment in which to study the microdomain orientation. By using a novel depth profiling technique which combines a CF4 based reactive ion etcher and a low voltage, high resolution scanning electron microscope, we have successfully depth profiled block copolymer films by subsequent etching and imaging to study the local orientation of microdomains. In depth profiling films composed of three layers of microdomain cylinders with this technique, we have observed both the propagation and evolution of disclinations through microdomain layers. We have also studied the range of influence of an aligning surface on the cylindrical microdomain orientation director. Alternatively, by modifying the top and bottom surfaces of a lamellar block copolymer film with a random copolymer of similar composition as the block copolymer, we can minimize the preferential wetting of the polymer surface by either block. We present data which show that these tailored surfaces induce microdomain lamellae to orient perpendicular to the substrate over several microdomain spacings.
Aps March Meeting Abstracts, Mar 1, 1998
Thin films of block copolymer microdomains are becoming increasingly useful for the <A HREF=http:... more Thin films of block copolymer microdomains are becoming increasingly useful for the <A HREF=http://www.Princeton.edu/ ckh/research.html>fabrication of nanostructures, for microphase separation produces a lengthscale (10 nanometers) that is difficult to access with conventional lithographic techniques. To use such thin films in a controlled manner, we investigated the dominant factors that influence the long-range order of the resulting microdomain pattern on a silicon substrate. We use a novel imaging and analysis technique that involves first etching the polymer film to expose microdomains for imaging by a scanning electron microscope, and secondly determining the microdomain persistence length from the exponential decay of the orientational autocorrelation function (azimuthally averaged). We demonstrate that the copolymer diffusion in thin films is reduced by an attractive substrate, but this can be mitigated by attaching a buffer layer of PS brushes to the substrate's oxide layer. In addition, we use this technique to study the kinetics of the ordering as a function of time and temperature, showing that the long-range order grows exponentially with annealing temperature.
The coarsening of two-dimensional hexatic patterns was studied via cell dynamics simulations as a... more The coarsening of two-dimensional hexatic patterns was studied via cell dynamics simulations as a model for grain growth in thin films of sphere-forming block copolymers. In the late stage of coarsening, the orientational correlation length follows a power law in time, with an exponent which depends on the noise level chosen in the simulations. The kinetic exponent increases from 0 .0 to 0.45 as the noise increases, suggesting an analogy between noise and temperature. Finally, at a noise level beyond a critical value there is a sudden transition to a completely disordered pattern, which we suggest is analogous to a melting transition. The correlation length extracted from the vector fields of the dislocations displays a similar behavior, suggesting that dislocations play the key role in pattern formation. Movies of defect motion from such simulations reveal that the primary annihilation events involve dislocations rather than disclinations. At intermediate noise levels the simulations adequately describe experimental results for sphere-forming diblock copolymer thin films.
Aps Meeting Abstracts, Feb 27, 2002
Thin films forming monolayers of diblock copolymer microdomains provide a readily-accessible syst... more Thin films forming monolayers of diblock copolymer microdomains provide a readily-accessible system for studying two dimensional melting for both spherical and cylindrical microdomain patterns. By annealing a thin film sample under a constant temperature gradient and rapidly quenching it below the glass transition temperature we are able to produce a sample which consists of the equilibrium microdomain pattern below and above the order-disorder transition (ODT), or melting temperature. By real space analysis of atomic force micrographs we are able to determine the behavior of the orientational correlation functions as a function of temperature. Orientational correlation of microdomains is seen to abruptly disappear at the melting transition along with an increase in topological defect density. The experimental techniques developed can also be used to study directional solidification in two dimensional diblock copolymer systems.
Macromolecules, 1995
Dynamics of Structure Formation in Crystallizable Block Copolymers ... Department of Chemical Eng... more Dynamics of Structure Formation in Crystallizable Block Copolymers ... Department of Chemical Engineering, Princeton University, Princeton, New Jersey 08544 Douglas H. Adamson and Lewis J. Fetters Emon Research and Engineering Company, Annandale, New Jersey 08801
Morphological studies of self assembled polymeric structures with length scales of interest below... more Morphological studies of self assembled polymeric structures with length scales of interest below 100 nm have typically been conducted either by scattering-based techniques or electron and scanning probe microscopes. These techniques, however, do not provide easy access to truly 3D-structural information. In contrast, Far-field optical methods retain the advantage of simultaneously providing local, dynamic, and in situ three-dimensional (3D) structural information. The diffraction limited resolution of its standard variants, however, restricts the minimum feature size that can be examined. We exploit molecular transitions of the fluorophores to circumvent the diffraction barrier and demonstrate the power of emerging far-field fluorescence microscopy with nanoscale resolution for the study of self-assembly. We simultaneously improve both the lateral (x,y) and the axial (z) resolution of stimulated emission depletion (STED) microscopy. The increased 3D resolution is used to unambiguously map the morphology of self assembled polymeric nanostructures in a facile manner.
We prepared films with a range of thicknesses (50-300 nm) of a styrene-butadiene diblock copolyme... more We prepared films with a range of thicknesses (50-300 nm) of a styrene-butadiene diblock copolymer, synthesized to produce a cylindrical morphology. Solutions of different polymer concentrations in toluene were spun onto carbon-coated glass slides. The films were then placed onto a Transmission Electron Microscope (TEM) grid by water lift-off, annealed, stained with osmium tetraoxide, and examined with a TEM. Over a wide range of film thicknesses, the cylinders lie parallel to the substrate. We present preliminary results that show a cylinder orientation perpendicular to the substrate at a thickness of many microdomain spacings. We speculate that the alignment mechanism is different from that found in a previous study of Kraton D1102(M. A. van Dijk and R. van den Berg, Macromolecules 28), 6773 (1995) which shows a perpendicular orientation with spin-coated films, but for a film thickness between one and two microdomain spacings. This work was supported by the NSF under DMR 9400362.
Aps March Meeting Abstracts, Mar 1, 1997
We present successful patternings of an anti-dot hexagonal array and fingerprint-like lines over ... more We present successful patternings of an anti-dot hexagonal array and fingerprint-like lines over micron size areas with feature sizes and periods of ~10 nm and ~30 nm, respectively. The technique uses self-assembled ordered structures of polystyrene-polybutadiene (PS-PB) diblock copolymers as nanolithography templates. Diblock copolymers, consisting of two different polymer chains, microphase separate in ordered structures due to incompatibility between the two chains and connectivity constraints. The size and period of these microstructures are ~10 nm and governed by the chain dimensions. Two types of PS-PB diblock copolymer films are used each to produce a monolayer of hexagonally ordered spherical patterns or fingerprint-like lines. The microphase separated patterns in the spin-coated copolymer films are then directly used to subsquently pattern underlying silicon nitride. The pattern-transfer is achieved by a reactive ion etching technique.
We present movies of pattern coarsening of block copolymer microdomains in thin films. The system... more We present movies of pattern coarsening of block copolymer microdomains in thin films. The system consists of a single layer of polystyrene spheres or cylinders in a poly(ethylene-alt-propylene) matrix. The modulus difference of the two blocks provides contrast for time-lapse tapping mode atomic force microscopy. For cylindrical microdomains, the orientational correlation function xi has been shown to grow with time
Spherical microdomains in a thin film of a polystyrene-poly(ethylene-alt-propylene) diblock copol... more Spherical microdomains in a thin film of a polystyrene-poly(ethylene-alt-propylene) diblock copolymer are found to align locally with step edges on a cleaved mica substrate. In principle, it may be possible to use a sparse array of similar straight-line features to fabricate dense, individually addressable nanostructures with 30 nm periodicity over an arbitrarily large area. We use time lapse atomic force
Diblock copolymers can be used as templates for nanolithography, but some applications would requ... more Diblock copolymers can be used as templates for nanolithography, but some applications would require at least local alignment and registration of copolymer microdomains with other features on a particular device. We present here the results of a systematic study of the alignment of spherical microdomains with step edges on a substrate as a function of both step edge height and
We present a novel technique which allows the investigation of thin film diblock copolymer microp... more We present a novel technique which allows the investigation of thin film diblock copolymer microphase morphology on a variety of substrates and at different film depths. Using a high resolution, low voltage Scanning Electron Microscope (SEM), we examined the topology and underlying morphology of styrene-butadiene diblock copolymer films. In order to enhance the contrast between the styrene and butadiene regions, we stained the butadiene with osmium tetraoxide. The internal morphology of the diblock copolymer film was exposed by using a non-selective fluorine-based reactive ion etching (RIE) technique. By controlling the depth of the RIE, we can effectively peel off one monolayer at a time. By alternating between RIE and SEM, we can examine the diblock copolymer film morphology at different depths. We also investigated the relationship between island formation and internal polymer microstructure. This work was supported by the NSF under DMR 9400362.
Instrumental aliasing, a usually undesired consequence of limited sampling resolution, can be put... more Instrumental aliasing, a usually undesired consequence of limited sampling resolution, can be put to good use in some circumstances in order to extend imaging capabilities. Normally, the resolution of an AFM picture is limited by the maximum number of pixels that can be acquired per scan line (512 in the case of the Digital Instruments Nanoscope IIIa controller used). A new AFM technique is reported through which the aliasing patterns obtained from large-area scans of hexagonal microdomains are analyzed and mapped onto the orientation of the underlying crystal grains. The experimental system used is a diblock copolymer film consisting of a monolayer of spherical microdomains. The AFM sampling is done close to the Nyquist frequency and the patterns obtained are analyzed by local Fourier transforms. The orientation and spacing of the lines in the aliasing pattern can be uniquely mapped onto the orientation of the hexagonal lattice, and thus we are able to o orientational maps for significantly larger areas than by the traditional technique of directly imaging (DI) each individual microdomain. We successfully applied the technique to measuring grain sizes in microdomain crystals where the correlation length exceeds by far the size of th picture that can be obtained by the DI technique.
Aps Meeting Abstracts, 2005
We have studied the phase diagram of a two dimensional smectic system, a monolayer film of di-blo... more We have studied the phase diagram of a two dimensional smectic system, a monolayer film of di-block copolymer cylinders. Previous work was done on sphere-forming diblock polymer films. In this work we anneal PS-PEP 5-13 cylinder-forming diblock copolymer using a temperature gradient system, to investigate the orientational order-disorder (melting) transition. We find that on the high temperature side correlation lengths are very small, revealing complete lack of orientational order. This corresponds to annealing far above the order-disorder (or melting) transition. The disordered state in this case is a thermodynamic equilibrium state, continued annealing of the sample will not produce more ordering in this region of the sample. The order-disorder transition, ODT, occurred at 163 oC, higher than the bulk ODT of the same polymer (TODT =144 ^oC). We present data on the temperature dependence of the correlation functions and the densities of topological defects. By lowing the temperature of the high T end of the gradient, we can also sweep the temperature gradient to study the effects of zone refining.
Block copolymer thin films present an ideal environment in which to study the microdomain orienta... more Block copolymer thin films present an ideal environment in which to study the microdomain orientation. By using a novel depth profiling technique which combines a CF4 based reactive ion etcher and a low voltage, high resolution scanning electron microscope, we have successfully depth profiled block copolymer films by subsequent etching and imaging to study the local orientation of microdomains. In depth profiling films composed of three layers of microdomain cylinders with this technique, we have observed both the propagation and evolution of disclinations through microdomain layers. We have also studied the range of influence of an aligning surface on the cylindrical microdomain orientation director. Alternatively, by modifying the top and bottom surfaces of a lamellar block copolymer film with a random copolymer of similar composition as the block copolymer, we can minimize the preferential wetting of the polymer surface by either block. We present data which show that these tailored surfaces induce microdomain lamellae to orient perpendicular to the substrate over several microdomain spacings.
Aps March Meeting Abstracts, Mar 1, 1998
Thin films of block copolymer microdomains are becoming increasingly useful for the <A HREF=http:... more Thin films of block copolymer microdomains are becoming increasingly useful for the <A HREF=http://www.Princeton.edu/ ckh/research.html>fabrication of nanostructures, for microphase separation produces a lengthscale (10 nanometers) that is difficult to access with conventional lithographic techniques. To use such thin films in a controlled manner, we investigated the dominant factors that influence the long-range order of the resulting microdomain pattern on a silicon substrate. We use a novel imaging and analysis technique that involves first etching the polymer film to expose microdomains for imaging by a scanning electron microscope, and secondly determining the microdomain persistence length from the exponential decay of the orientational autocorrelation function (azimuthally averaged). We demonstrate that the copolymer diffusion in thin films is reduced by an attractive substrate, but this can be mitigated by attaching a buffer layer of PS brushes to the substrate's oxide layer. In addition, we use this technique to study the kinetics of the ordering as a function of time and temperature, showing that the long-range order grows exponentially with annealing temperature.
The coarsening of two-dimensional hexatic patterns was studied via cell dynamics simulations as a... more The coarsening of two-dimensional hexatic patterns was studied via cell dynamics simulations as a model for grain growth in thin films of sphere-forming block copolymers. In the late stage of coarsening, the orientational correlation length follows a power law in time, with an exponent which depends on the noise level chosen in the simulations. The kinetic exponent increases from 0 .0 to 0.45 as the noise increases, suggesting an analogy between noise and temperature. Finally, at a noise level beyond a critical value there is a sudden transition to a completely disordered pattern, which we suggest is analogous to a melting transition. The correlation length extracted from the vector fields of the dislocations displays a similar behavior, suggesting that dislocations play the key role in pattern formation. Movies of defect motion from such simulations reveal that the primary annihilation events involve dislocations rather than disclinations. At intermediate noise levels the simulations adequately describe experimental results for sphere-forming diblock copolymer thin films.
Aps Meeting Abstracts, Feb 27, 2002
Thin films forming monolayers of diblock copolymer microdomains provide a readily-accessible syst... more Thin films forming monolayers of diblock copolymer microdomains provide a readily-accessible system for studying two dimensional melting for both spherical and cylindrical microdomain patterns. By annealing a thin film sample under a constant temperature gradient and rapidly quenching it below the glass transition temperature we are able to produce a sample which consists of the equilibrium microdomain pattern below and above the order-disorder transition (ODT), or melting temperature. By real space analysis of atomic force micrographs we are able to determine the behavior of the orientational correlation functions as a function of temperature. Orientational correlation of microdomains is seen to abruptly disappear at the melting transition along with an increase in topological defect density. The experimental techniques developed can also be used to study directional solidification in two dimensional diblock copolymer systems.
Macromolecules, 1995
Dynamics of Structure Formation in Crystallizable Block Copolymers ... Department of Chemical Eng... more Dynamics of Structure Formation in Crystallizable Block Copolymers ... Department of Chemical Engineering, Princeton University, Princeton, New Jersey 08544 Douglas H. Adamson and Lewis J. Fetters Emon Research and Engineering Company, Annandale, New Jersey 08801
Morphological studies of self assembled polymeric structures with length scales of interest below... more Morphological studies of self assembled polymeric structures with length scales of interest below 100 nm have typically been conducted either by scattering-based techniques or electron and scanning probe microscopes. These techniques, however, do not provide easy access to truly 3D-structural information. In contrast, Far-field optical methods retain the advantage of simultaneously providing local, dynamic, and in situ three-dimensional (3D) structural information. The diffraction limited resolution of its standard variants, however, restricts the minimum feature size that can be examined. We exploit molecular transitions of the fluorophores to circumvent the diffraction barrier and demonstrate the power of emerging far-field fluorescence microscopy with nanoscale resolution for the study of self-assembly. We simultaneously improve both the lateral (x,y) and the axial (z) resolution of stimulated emission depletion (STED) microscopy. The increased 3D resolution is used to unambiguously map the morphology of self assembled polymeric nanostructures in a facile manner.
We prepared films with a range of thicknesses (50-300 nm) of a styrene-butadiene diblock copolyme... more We prepared films with a range of thicknesses (50-300 nm) of a styrene-butadiene diblock copolymer, synthesized to produce a cylindrical morphology. Solutions of different polymer concentrations in toluene were spun onto carbon-coated glass slides. The films were then placed onto a Transmission Electron Microscope (TEM) grid by water lift-off, annealed, stained with osmium tetraoxide, and examined with a TEM. Over a wide range of film thicknesses, the cylinders lie parallel to the substrate. We present preliminary results that show a cylinder orientation perpendicular to the substrate at a thickness of many microdomain spacings. We speculate that the alignment mechanism is different from that found in a previous study of Kraton D1102(M. A. van Dijk and R. van den Berg, Macromolecules 28), 6773 (1995) which shows a perpendicular orientation with spin-coated films, but for a film thickness between one and two microdomain spacings. This work was supported by the NSF under DMR 9400362.
Aps March Meeting Abstracts, Mar 1, 1997
We present successful patternings of an anti-dot hexagonal array and fingerprint-like lines over ... more We present successful patternings of an anti-dot hexagonal array and fingerprint-like lines over micron size areas with feature sizes and periods of ~10 nm and ~30 nm, respectively. The technique uses self-assembled ordered structures of polystyrene-polybutadiene (PS-PB) diblock copolymers as nanolithography templates. Diblock copolymers, consisting of two different polymer chains, microphase separate in ordered structures due to incompatibility between the two chains and connectivity constraints. The size and period of these microstructures are ~10 nm and governed by the chain dimensions. Two types of PS-PB diblock copolymer films are used each to produce a monolayer of hexagonally ordered spherical patterns or fingerprint-like lines. The microphase separated patterns in the spin-coated copolymer films are then directly used to subsquently pattern underlying silicon nitride. The pattern-transfer is achieved by a reactive ion etching technique.
We present movies of pattern coarsening of block copolymer microdomains in thin films. The system... more We present movies of pattern coarsening of block copolymer microdomains in thin films. The system consists of a single layer of polystyrene spheres or cylinders in a poly(ethylene-alt-propylene) matrix. The modulus difference of the two blocks provides contrast for time-lapse tapping mode atomic force microscopy. For cylindrical microdomains, the orientational correlation function xi has been shown to grow with time
Spherical microdomains in a thin film of a polystyrene-poly(ethylene-alt-propylene) diblock copol... more Spherical microdomains in a thin film of a polystyrene-poly(ethylene-alt-propylene) diblock copolymer are found to align locally with step edges on a cleaved mica substrate. In principle, it may be possible to use a sparse array of similar straight-line features to fabricate dense, individually addressable nanostructures with 30 nm periodicity over an arbitrarily large area. We use time lapse atomic force
Diblock copolymers can be used as templates for nanolithography, but some applications would requ... more Diblock copolymers can be used as templates for nanolithography, but some applications would require at least local alignment and registration of copolymer microdomains with other features on a particular device. We present here the results of a systematic study of the alignment of spherical microdomains with step edges on a substrate as a function of both step edge height and