Gyula J. Vancso

Formation of a Cobalt Magnetic Dot Array via Block Copolymer Lithography

Single-domain cobalt dot arrayswith high magnetic particle density, patterned over large areas (e.g., 10 cm diameter wafers) are fabricated by self-assembled block copolymer lithography, using a polystyrene-poly(ferrocenyldimethylsilane) copolymer as a template. By varying the copolymer type and etching conditions the magnetic properties can be tuned. The Figure shows a typical array of Co dots with tungsten caps obtained via this procedure.

Transparent Nanocomposites with Ultrathin, Electrospun Nylon-4,6 Fiber Reinforcement

Transparent sheets of epoxy resin reinforced with nylon-4,6 nanofibers are described. The 30-200 nm diameter fibers, obtained by electrospinning from formic acid solutions, are reported to provide significant improvement in strength and stiffness to the epoxy film. The Figure is a scanning electron microscopy image of the electrospun nanofibers.

Fabrication of nanostructures with long-range order using block copolymer lithography

Block copolymer lithography makes use of the self-assembling properties of block copolymers to pattern nanoscale features over large areas. Although the resulting patterns have good short-range order, the lack of long-range order limits their utility in some applications. This work presents a lithographically assisted self-assembly method that allows ordered arrays of nanostructures to be formed by spin casting a block copolymer over surfaces patterned with shallow grooves. The ordered block copolymer domain patterns are then transferred into an underlying silica film using a single etching step to create a well-ordered hierarchical structure consisting of arrays of silica pillars with 20 nm feature sizes and aspect ratios greater than 3.

Nanostructured thin films of organic-organometallic block copolymers: one-step lithography with poly(ferrocenylsilanes) by reactive ion etching

The deposition of thin films of inorganic nanoclusters as a route to one-step lithography has been achieved using block copolymers with inherent inorganic (Fe and Si) components. Nanodomains of the organometallic part are resistant to removal during the subsequent O2 etch, which results in well-ordered and separate domains of iron and silicon oxides, as can be seen in the Figure.

Si-containing block copolymers for self-assembled nanolithography

Block copolymers can self-assemble to generate patterns with nanoscale periodicity, which may be useful in lithographic applications. Block copolymers in which one block is organic and the other contains Si are appealing for self-assembled lithography because of the high etch contrast between the blocks, the high etch resistance of the Si-containing block, and the high Flory–Huggins interaction parameter, which is expected to minimize line edge roughness. The locations and long range order of the microdomains can be controlled using shallow topographical features. Pattern generation from poly(styrene)-poly(ferrocenyldimethylsilane) and poly(styrene)-poly(dimethylsiloxane) block copolymers, and the subsequent pattern transfer into metal, oxide, and polymer films, is described

Real-time crystallization study of poly(e-caprolactone) by hot-stage atomic force microscopy

The morphological development and lamellar growth kinetics of poly(e-caprolactone) (PCL) were investigated in real-time by hot-stage atomic force microscopy (AFM). The morphology of PCL crystals grown in the melt was studied to obtain insight into the mechanism, which controls the lateral shape of the lamellae in this polymer. Melt-grown PCL crystals showed a truncated lozenge lateral shape, with curved or chair-like three-dimensional morphology. Similar lamellar morphologies were observed in larger crystal aggregates, i.e. hedrites, grown at lower crystallization temperatures in the melt. The individual lamellae in these crystal aggregates also showed an elongated truncated lozenge shape. The AFM examination of the hedritic morphologies revealed the dynamics of the dominant/subsidiary crystallization process. The use of a hot-stage allowed us to perform real-time observation of growth faces in different crystallographic directions. The results support previous evidence, which suggested that the elongated lamellar habit is related to growth rate anisotropy. Morphological observations suggest a mechanism including {110} growth faces. In addition, visualization of the lamellar morphology indicates that the PCL crystals are obtained under regime II crystallization conditions.

Crystal melting and its kinetics on poly(ethylene oxide) by in situ atomic force microscopy

The process of melting in poly(ethylene oxide) (PEO) is followed in real-time at elevated temperatures by atomic force microscopy (AFM) using a simple hot stage apparatus. AFM imaging of the morphology above the onset of melting revealed the dynamics of a complex melting process. The observed melting behavior of PEO is associated with the existence of separate dominant and subsidiary morphological entities. The morphological observations revealed that the melting process is not explained by a mechanism of crystal reorganization (melting–recrystallization–remelting or crystal thickening. The kinetic data shows that the crystal dimensions decrease proportional to time indicating a nucleation controlled melting process. The crystals melt instantaneously on heating and reveal a spread in the rates of melting of the radial {120} faces. This variation in rate of retrogression of the crystals is assumed to be related to a lamellar thickness distribution of the melt grown crystals.

Morphology of Polyurethanes Revisited by Complementary AFM and TEM

Cast, segmented polyetherurethanes with 30 and 50% hard-segment content (HSC), respectively, were studied by transmission electron microscopy (TEM) and atomic force microscopy (AFM). Multi-phase segregation was observed in both samples on two levels (micro and nano) of structural organization. Spherulites with a prominent radial structure, built of branched fibrils and globules, were captured on the micrometer level. The use of AFM enabled us to investigate the nanostructure in the polyurethanes studied here. In the sample with low (30%) HSC, nano-scale phase separation was observed by AFM in areas outside the crystalline aggregates. The morphology in these domains exhibited short, rodlike hard domains embedded in the matrix of the soft segments. The other sample (50% HSC) contained four identifiable morphological features. These included spherulites, globules, bundles of lamellae, and nanophase-separated, rodlike hard domains, embedded in the soft-segment matrix. The globules did not have any internal structure visible by AFM down to the nanometer scale. We speculate that the globules form as a result of macro-phase segregation, due to incompatibility of the reactants, during synthesis and may thus be identified as pockets of free hard segments. The AFM phase imaging has been very useful to observe the bundles of lamellae and the nanoscale phase-separated structures, which were not captured by TEM, due to large differences in AFM phase signal contrast between the hard and the soft domains. †On leave from Technical University of Gdańsk.

Microparticle Adhesion Studies by Atomic Force Microscopy

Atomic force microscopy (AFM) is one of the most flexible and simple techniques for probing surface interactions. This article reviews AFM studies on particle adhesion. Special attention is paid to the characterization of roughness and its effect on adhesion. This is of importance when comparing the measured adhesion forces to theoretical values, as the contact area is included in the contact mechanics theories. Even though adhesion models for time-independent adhesion are reasonably well developed, it remains difficult to connect the measured values to model predictions, especially because of the unknown value of the true contact area. The true area of contact depends on both the roughness of the probe as well as of the substrate. Our studies on the interactions between smooth silica particles, or rougher toner particles, and silicon substrates as a function of the surface roughness of the latter has shown the utility of AFM for measuring both roughness and particle adhesion.

Real-time imaging of melting and crystallization in poly(ethylene oxide) by atomic force microscopy

The processes of melting and crystallization of poly(ethylene oxide) are followed in real time at elevated temperature by atomic force microscopy using a simple hot stage apparatus. Hedritic development at a temperature of 57°C is monitored, including the process of lamellar splaying to yield a spherical morphology. Crystal growth kinetics are measured by monitoring the growth of individual lamellae and found to agree with those obtained by conventional optical microscopy.