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Full-Text Articles in Engineering
Block-Copolymer Ordering With A Spatiotemporally Heterogeneous Mobility, Alamgir Karim
Block-Copolymer Ordering With A Spatiotemporally Heterogeneous Mobility, Alamgir Karim
Alamgir Karim
Motivated by recent zone annealing measurements on stripe-forming block-copolymer films [B. C. Berry, Nano Lett. 7, 2789 (2007)], we study block-copolymer ordering with a spatiotemporally heterogeneous mobility. Specifically, we implement a time- and space-dependent mobility field in the relaxation of a diblock copolymer self-consistent field theory. The model includes a gradient in the local mobility and intrinsic nanoscale mobility variations characteristic of glass phenomenology. The simulations demonstrate that a spatiotemporally heterogeneous mobility can have a significant influence on microdomain ordering in block-copolymer systems, and that nanoscale dynamic heterogeneities associated with glass formation can impact the structure of the ordered block-copolymer …
The Direct Patterning Of Nanoporous Interlayer Dielectric Insulator Films By Nanoimprint Lithography, Alamgir Karim
The Direct Patterning Of Nanoporous Interlayer Dielectric Insulator Films By Nanoimprint Lithography, Alamgir Karim
Alamgir Karim
The Direct Patterning of Nanoporous Interlayer Dielectric Insulator Films by Nanoimprint Lithography Official contribution of the National Institute of Standards and Technology; not subject to copyright in the United States. The error bars presented throughout this manuscript indicate the relative standard uncertainty of the measurement. Certain commercial materials and equipment are identified in this paper in order to specify adequately the experimental procedure. In no case does such identification imply recommendation by the National Institute of Standards and Technology nor does it imply that the material or equipment identified is necessarily the best available for this purpose.
Self-Assembly Of Polymer-Coated Ferromagnetic Nanoparticles Into Mesoscopic Polymer Chains, Alamgir Karim
Self-Assembly Of Polymer-Coated Ferromagnetic Nanoparticles Into Mesoscopic Polymer Chains, Alamgir Karim
Alamgir Karim
The self-assembly of dispersed polymer-coated ferromagnetic nanoparticles into micron-sized one-dimensional mesostructures at a liquid–liquid interface was reported. When polystyrene-coated Co nanoparticles (19 nm) are driven to an oil/water interface under zero-field conditions, long (≈ 5 μm) chain-like assemblies spontaneously form because of dipolar associations between the ferromagnetic nanoparticles. Direct imaging of the magnetic assembly process was achieved using a recently developed platform consisting of a biphasic oil/water system in which the oil phase was flash-cured within 1 s upon ultraviolet light exposure. The nanoparticle assemblies embedded in the crosslinked phase were then imaged using atomic force microscopy. The effects of …
Surface Morphology Diagram For Cylinder-Forming Block Copolymer Thin Films, Alamgir Karim
Surface Morphology Diagram For Cylinder-Forming Block Copolymer Thin Films, Alamgir Karim
Alamgir Karim
We investigate the effect of annealing temperature (T) and film thickness (hf) on the surface morphology of flow coated films of a cylinder forming block copolymer, poly (styrene-block-methyl methacrylate) (PS-b-PMMA). A transition from a perpendicular to a parallel cylinder orientation with respect to the substrate is observed upon increasing hf when the substrate interaction is highly selective for one of the blocks (PMMA) and the polymer-air interface has a nearly neutral interaction with both blocks. Surface morphology transitions with increasing hf are observed in these model `frustrated-interaction' films: (a) first, a transition occurs from cylinders oriented parallel to the substrate …
Langmuir Adsorption Study Of The Interaction Of Cdse/Zns Quantum Dots With Model Substrates: Influence Of Substrate Surface Chemistry And Ph, Alamgir Karim
Alamgir Karim
We investigate the utility of Langmuir adsorption measurements for characterizing nanoparticle-substrate interactions. Spherical CdSe/ZnS core-shell nanoparticles were chosen as representative particles because of their widespread use in biological labeling measurements and their relatively monodisperse dimensions. In particular, the quantum dots were functionalized with 11-mercaptoundecanoic acid, and we utilized an amine-terminated self-assembled monolayer (SAM) as a model substrate. SAMs with different end-groups (-CH(3) and -COOH) were also considered to contrast with the adsorption behavior on the amine-terminated SAM substrates. We followed the kinetics of nanoparticle adsorption on the aminosilane layer by quartz crystal microgravimetry (QCM) over a range of particle concentrations …
Characterization Of Non-Equilibrium Nanoparticle Adsorption On A Model Biological Substrate, Alamgir Karim
Characterization Of Non-Equilibrium Nanoparticle Adsorption On A Model Biological Substrate, Alamgir Karim
Alamgir Karim
The kinetics of nanoparticle (NP) adsorption on a model biological interface (collagen) is measured in microfluidic channels using surface plasmon resonance (SPR) imaging over a range of CdSe/ZnS quantum dot concentrations to investigate the underlying binding process. Spherical CdSe/ZnS core-shell NP, derivatized with 3-mercaptopropionic acid (3-MPA), were considered to be model NPs because of their widespread use in biological applications and their relatively monodisperse size. The kinetic adsorption data suggests that the binding between the NP and the collagen substrate is irreversible at room temperature (pH approximately 7.4), and this type of adsorption process was further characterized in the context …
Self-Sealing Of Nanoporous Low Dielectric Constant Patterns Fabricated By Nanoimprint Lithography, Alamgir Karim
Self-Sealing Of Nanoporous Low Dielectric Constant Patterns Fabricated By Nanoimprint Lithography, Alamgir Karim
Alamgir Karim
No abstract provided.
Target Patterns Induced By Fixed Nanoparticles In Block Copolymer Films, Alamgir Karim
Target Patterns Induced By Fixed Nanoparticles In Block Copolymer Films, Alamgir Karim
Alamgir Karim
It is well-known that thin films of cylinder-forming block copolymers (BCP) can exhibit a transition from a perpendicular to a parallel cylinder orientation with respect to the supporting solid substrate upon varying film thickness. We show that wave-like oscillations between these morphologies can be induced through the introduction of nanoparticles (NP) into flow-coated and annealed BCP films where the particles span the film thickness and are fixed by irreversible adsorption to the supporting substrate. We hypothesize that these novel "target" patterns arise from residual stresses that build up in the film while undergoing thermal treatment and film formation, and we …
Crystallization Of Poly(Ethylene Oxide) Patterned By Nanoimprint Lithography, Alamgir Karim
Crystallization Of Poly(Ethylene Oxide) Patterned By Nanoimprint Lithography, Alamgir Karim
Alamgir Karim
The crystallization behavior of poly(ethylene oxide) (PEO) films patterned by nanoimprint lithography is studied. The imprinted PEO film consists of parallel lines, approximately 240 nm wide and 320 nm tall, on a 400 nm pitch with a residual layer of approximately 10 nm. A spherulitic superstructure, typically observed for bulk PEO samples, is observed by optical microscopy. This result indicates that the crystal lamellae communicate through the continuous thin residual layer into discrete patterned regions that span hundreds of micrometers. In the discrete imprinted lines, the lamellae generally have a flat-on orientation with respect to the substrate. When the radial …
Effect Of Fluorosurfactant On Capillary Instabilities In Nanoimprinted Polymer Patterns, Alamgir Karim
Effect Of Fluorosurfactant On Capillary Instabilities In Nanoimprinted Polymer Patterns, Alamgir Karim
Alamgir Karim
Surface forces play a paramount role in most aspects of Nanoimprint Lithography. In particular, subjecting nanoimprinted patterns to moderate heating allows surface tension to smooth out undesirable roughness and defects in the patterns, but this “thermal reflow” treatment can induce structural decay or even collapse of the patterns by capillary instability if this process is not carefully controlled. Adhesion between the mold and polymer film can also cause the imprinted structure to tear or fracture. Fluorinated surfactants (FS) are attractive for reducing mold adhesion, yet the effects of these additives on nanostructure stability during thermal reflow are not well understood. …
Competition Between Crystallization And Dewetting Fronts In Thin Polymer Films, Alamgir Karim
Competition Between Crystallization And Dewetting Fronts In Thin Polymer Films, Alamgir Karim
Alamgir Karim
We investigate the competition between dewetting and crystallization fronts in thin polymer films where the velocities of these fronts are modulated by varying the temperature from a low temperature regime, where crystallization dominates, to a high temperature regime, where dewetting is more rapid and dominates the film structure. Specifically, thin films of poly(caprolactone) (PCL) on n-octyldimethylchlorosilane (ODS)-treated substrates are investigated as a model system exhibiting this general phenomenon. Structure formation at low temperatures is dominated by polycrystalline spherulitic structures that nucleate at random positions within the plane of the film, but at intermediate temperatures, where the crystallization and dewetting are …
Environment-Controlled Spin Coating To Rapidly Orient Microdomains In Thin Block Copolymer Films, Alamgir Karim
Environment-Controlled Spin Coating To Rapidly Orient Microdomains In Thin Block Copolymer Films, Alamgir Karim
Alamgir Karim
We demonstrate a simple and fast methodology to control the orientation of cylindrical microdomains in thin block copolymer films using environment-controlled spin coating. During spinning, the preferential affinity of vapor atmosphere successfully directs the cylinders to be aligned from parallel to perpendicular with respect to the film surface and also improve the degree of lateral order. A combinatorial gradient technique was used to prove that the interfacial energy at the air/film interface is more important for solvent-induced orientation.
Effect Of Temperature On The Morphology And Kinetics Of Surface Pattern Formation In Thin Block Copolymer Films, Alamgir Karim
Effect Of Temperature On The Morphology And Kinetics Of Surface Pattern Formation In Thin Block Copolymer Films, Alamgir Karim
Alamgir Karim
Hole formation and growth on the top layer of thin symmetric diblock copolymer films, forming an ordered lamellar structure parallel to the solid substrate (silicon wafer) within these films, is investigated as a function of time (t), temperature (T), and film thickness (l), using a high-throughput experimental technique. The kinetics of this surface pattern formation process is interpreted in terms of a first-order reaction model with a time-dependent rate constant determined uniquely by the short-time diffusive growth kinetics characteristic of this type of ordering process. On the basis of this model, we conclude that the average hole size, lambda(h), approaches …
Orientational Order In Block Copolymer Films Zone Annealed Below The Order-Disorder Transition Temperature, Alamgir Karim
Orientational Order In Block Copolymer Films Zone Annealed Below The Order-Disorder Transition Temperature, Alamgir Karim
Alamgir Karim
We report measurements of rapid ordering and preferential alignment in block copolymer films zone annealed below the order-disorder transition temperature. The orientational correlation lengths measured after approximately 5 h above the glass-transition temperature ( approximately 2 microm) were an order of magnitude greater than that obtained under equivalent static annealing. The ability to rapidly process polymers with inaccessible order-disorder transition temperatures suggests zone annealing as a route toward more robust nanomanufacturing methods based on block copolymer self-assembly.
Polymer Viscoelasticity And Residual Stress Effects On Nanoimprint Lithography, Alamgir Karim
Polymer Viscoelasticity And Residual Stress Effects On Nanoimprint Lithography, Alamgir Karim
Alamgir Karim
The decay kinetics of polystyrene (PS) gratings are monitored by tracking the intensity of the first-order laser diffraction peak as a function of annealing time. For low-molecular-mass PS (24 kg mol–1, blue circles), an exponential response suggests that the pattern decay is a surface-tension- driven viscous flow. In high-molecular-mass PS (1007 kg mol–1, green circles) a complicated response includes a rapid elastic recovery, a power-law creep, and a viscouslike flow
Quantum Mazes: Luminescent Labyrinthine Semiconductor Nanocrystals Having A Narrow Emission Spectrum, Alamgir Karim
Quantum Mazes: Luminescent Labyrinthine Semiconductor Nanocrystals Having A Narrow Emission Spectrum, Alamgir Karim
Alamgir Karim
We exploit the polytypism of group II-VI semiconductors and the long-range dipolar interactions typical of CdSe nanoparticle formation to modulate the geometrical structure and the optical emission properties of novel branched CdSe nanocrystals through shape-dependent quantum confinement effects. X-ray diffraction confirms that these materials incorporate crystalline domains of cubic zinc-blende and hexagonal wurtzite within a polycrystalline growth form whose geometry can be controlled by varying thermodynamic conditions. In particular, labyrinthine-shaped nanoparticles of tunable dimensions are reproducibly synthesized based on a heterogeneous reaction between cadmium acetate in a solution in hexadecylamine and trioctylphosphine with Se as a solid precursor at a …
Interaction Of Gold Nanoparticles With Common Human Blood Proteins, Alamgir Karim
Interaction Of Gold Nanoparticles With Common Human Blood Proteins, Alamgir Karim
Alamgir Karim
In order to better understand the physical basis of the biological activity of nanoparticles (NPs) in nanomedicine applications and under conditions of environmental exposure, we performed an array of photophysical measurements to quantify the interaction of model gold NPs having a wide range of NP diameters with common blood proteins. In particular, absorbance, fluorescence quenching, circular dichroism, dynamic light scattering, and electron microscopy measurements were performed on surface-functionalized water-soluble gold NPs having a diameter range from 5 to 100 nm in the presence of common human blood proteins: albumin, fibrinogen, gamma-globulin, histone, and insulin. We find that the gold NPs …
Nanoscale Thermal-Mechanical Probe Determination Of 'Softening Transitions' In Thin Polymer Films, Alamgir Karim
Nanoscale Thermal-Mechanical Probe Determination Of 'Softening Transitions' In Thin Polymer Films, Alamgir Karim
Alamgir Karim
We report a quantitative study of the softening behavior of glassy polystyrene (PS) films at length scales on the order of 100 nm using nano-thermomechanometry (nano-TM), an emerging scanning probe technique in which a highly doped silicon atomic force microscopy (AFM) tip is resistively heated on the surface of a polymer film. The apparent 'softening temperature' T(s) of the film is found to depend on the logarithm of the square root of the thermal ramping rate R. This relation allows us to estimate a quasi-equilibrium (or zero rate) softening transition temperature T(s0) by extrapolation. We observe marked shifts of T(s0) …
Thermally Reversible Surface Morphology Transition In Thin Diblock Copolymer Films, Alamgir Karim
Thermally Reversible Surface Morphology Transition In Thin Diblock Copolymer Films, Alamgir Karim
Alamgir Karim
Many phase transitions exhibit ordering transitions at the boundary of the material that are distinct from its interior where intermolecular interactions can be significantly different. The present work considers the existence of a surface thermodynamic order-order transition between two distinct morphologies in thin block copolymer (BCP) films that are of interest in nanomanufacturing applications. Specifically, we find a thermally reversible interfacial transition between sphere-like structures and cylinders in flow-coated films of poly(styrene-block-methyl methacrylate) (PS-b-PMMA), where the BCP forms a cylinder microphase in the bulk. We present direct evidence from atomic force microscopy (AFM) of ion-etched films and grazing-incidence small-angle X-ray …
Nanoimprint Lithography And The Role Of Viscoelasticity In The Generation Of Residual Stress In Model Polystyrene Patterns, Alamgir Karim
Nanoimprint Lithography And The Role Of Viscoelasticity In The Generation Of Residual Stress In Model Polystyrene Patterns, Alamgir Karim
Alamgir Karim
Understanding polymer deformation during the nanoimprinting process is key to achieving robust polymer nanostructures. Information regarding this process can be extracted from monitoring the decay of the imprinted polymer patterns during thermal annealing. In the present work, the effect of both the molar mass and the imprinting temperature on the pattern decay behavior during thermal annealing is investigated. Previously, it was found that the decay rate is fastest for a highly entangled polymer due to the elastic recovery caused by the residual stress created during the imprinting process. The present paper demonstrates that this residual stress level can be modified …
Disordered Nanoparticle Interfaces For Directed Self-Assembly, Alamgir Karim
Disordered Nanoparticle Interfaces For Directed Self-Assembly, Alamgir Karim
Alamgir Karim
Self-assembly is a promising route for controlling the nanoscale structure and material properties of coatings, yet it remains difficult to control the microstructure of these systems. In particular, self-assembling materials typically have complex and delicate energy landscapes, which are sensitive to defects, making it difficult to control morphology or orientation. We present a simple and robust strategy for modulating the film-substrate interaction, which can bias the self-assembly energy landscape and thus enforce a desired microstructure. The technique uses nanoparticles with tunable surface energy to generate a rough interface with controlled properties. The intentionally disordered interface is tolerant to variation in …
Imaging Magnetic Flux Lines With Iron Oxide Nanoparticles Using A Fossilized Liquid Assembly, Alamgir Karim
Imaging Magnetic Flux Lines With Iron Oxide Nanoparticles Using A Fossilized Liquid Assembly, Alamgir Karim
Alamgir Karim
Directed self-assembly of nanomaterials via external fields is an attractive processing tool for industry as it is inherently inexpensive and flexible. Direct observations of this process are however challenging due to the nano and meso length scales involved. The self-assembly of magnetic nanoparticles in particular has gained much recent interest for applications ranging from biomedical imaging and targeted cancer therapy to ferrofluid mechanical damping devices, that rely on the state of aggregation and alignment of the nanoparticles. We utilize an oil–water platform to directly observe directed self-assembly of magnetic nanoparticles that are field ordered into two-dimensional mesostructures through the fossilized …