Variable-temperature Atomic Force Microscopy Research Articles

Shear viscosity of a near-critical binary system analyzed with variable-temperature atomic force microscopy

Variation in shear viscous drag in a near-critical binary mixture was measured between a hydrophilic probe sphere and a hydrophilic substrate down to a distance range comparable to or smaller than the correlation length ξ using a magnetic excitation method of atomic force microscopy at temperatures T=Tc−∆T with ∆T varying from 0.1 to 0.7 K. As the temperature approached the Tc, the increase in the drag coefficient toward the zero distance was observed to be less pronounced in the distance range below ca. 100 nm. The data was discussed as arising from suppression in a concentration gradient in the intersurface region due to the overlap of the affected layers on similar surfaces.

In Situ AFM Imaging of Microstructural Changes Associated with The Spin Transition in [Fe(Htrz)₂(Trz)](Bf₄) Nanoparticles.

Topographic images of [Fe(Htrz)2(trz)](BF4) nanoparticles were acquired across the first-order spin transition using variable-temperature atomic force microscopy (AFM) in amplitude modulation mode. These studies revealed a complex morphology of the particles consisting of aggregates of small nanocrystals, which expand, separate and re-aggregate due to the mechanical stress during the spin-state switching events. Both reversible (prompt or slow recovery) and irreversible effects (fatigue) on the particle morphology were evidenced and correlated with the spin crossover properties.

Hydrodynamic Transformation of a Freestanding Polymer Nanosheet Induced by a Thermoresponsive Surface

Freestanding quasi-two-dimensional ultrathin films (e.g., 41 nm thick polymer nanosheets) were produced, on which stimuli-responsive 47 nm thick polymer brushes were constructed by atom transfer radical polymerization (ATRP) of poly(N-isopropylacrylamide). The resulting surfaces of the multilayered polysaccharide ultrathin films were evaluated by ellipsometry, IR imaging, in situ variable-temperature atomic force microscopy (AFM), and contact angle measurements. The morphological transformation of the freestanding polymer nanosheet bearing thermoresponsive polymer brushes was observed macroscopically through reversible structural color changes at the air-water interface. The dynamic shape change of the nanosheet was also monitored with the addition of a surfactant such as sodium n-dodecylsulfate to reduce the hydrophobicity of the surface. It was then demonstrated that the highly flexible freestanding polymer nanosheet is capable of acting as a unique platform for inducing stimuli-responsive behavior in nanomaterials.

Role of Columnar Mesophase in the Morphological Evolution of Polymer Single Crystals upon Heating: A Combined Atomic Force Microscopy and Electron Diffraction Study

The crystal-to-hexagonal columnar mesophase transition in solution-grown single crystals of poly(di-n-propyl siloxane), PDPS, was studied in situ with selected-area electron diffraction and variable-temperature atomic force microscopy. It was observed that, upon the transition, the hexagonal columnar mesophase displays two mutually orthogonal orientations of the lattice. The 2a* and 2b* reciprocal lattice vectors of the α-phase crystal coincide with the a* vectors of each of the two differently oriented mesophase lattices. The in situ atomic force microscopy study of the evolution of a single PDPS crystal upon heating shows that crystal thickening can occur via a short-term dwelling in the mesophase. The high chain mobility in the mesophase can account for the exceptional range of accessible crystal thicknesses of PDPS, which is much larger than that observed for polyethylene single crystals.

Deposition of copper into thin ice buffer layers on MgO(1 0 0) produces uniform and sinter-resistant nanoparticles

Noncontact variable temperature atomic force microscopy has been employed to study the deposition of copper onto thin layers of ice formed on a MgO(1 0 0) surface. Deposition of submonolayer coverages of copper onto an ice modified oxide surface at 100 K, followed by annealing to 300 K, produces uniform nanometer-sized copper particles on the MgO surface. Copper particles resulting from a 0.5 monolayer deposition possess an average diameter of 7 nm and an average height of 0.3 nm. Further studies reveal that this buffer-layer-assisted deposition process produces a coverage-dependent density of particles with a narrow size distribution and a resistance to sintering for temperatures up to 750 K.

Substrate-facilitated assembly of elastin-like peptides: studies by variable-temperature in situ atomic force microscopy.

Extended duration in situ variable-temperature atomic force microscopy performed on a series of coacervating hydrophobic peptides based on human elastin revealed a novel multistage surface assembly process. Formation of epitaxially arranged peptide rods was preceded by rapid expansion of a two-dimensional film on the nucleating substrate, a process facilitated by specific hydrophobic peptide-substrate and intrapeptide interactions.

In situ variable temperature atomic force microscopy measurements of copper growth on MgO( [formula omitted

The nucleation properties and thermal stability of the copper on MgO(1 0 0) have been investigated with variable temperature atomic force microscopy. Using non-contact imaging techniques, the nucleation and diffusion of submonolayer coverages of copper on MgO(1 0 0) have been visualized over the temperature range of 300–750 K. For deposition at 300 K, islands one to two layers in thickness form across the terraces of the MgO surface. Upon annealing, the average diameter of the copper islands increases slowly between 300 and 550 K. At higher temperatures, a dramatic increase in island diameter and height occurs. Time dependent images of the Cu/MgO system at temperatures above 550 K reveal a complex evolution of the island structures involving growth, decay, coalescence, and diffusion of the islands.

Temperature dependence of polarization and charge dynamics on the BaTiO3(100) surface by scanning probe microscopy

Variable-temperature atomic force microscopy, piezoresponse force microscopy (PFM), and scanning surface potential microscopy were combined to determine the temperature response of polarization and screening charge on BaTiO3(100) surfaces. The ferroelectric-domain induced surface corrugations and piezoelectric response decrease with temperature and disappear at the Curie temperature. The temperature dependence of the PFM contrast is explained within the framework of the Ginzburg–Devonshire theory with the effect of a dielectric tip-surface gap taken into account. The temperature dependence of the surface potential contrast is ascribed to the interplay between the release of the screening charges with temperature and their slow relaxation. The results indicate that surface potential polarity is reversed relative to that expected from polarization orientation on BaTiO3 in ambient.

Nanometer-Scale Characterization of Ferroelectric Polymer Thin Films by Variable-Temperature Atomic Force Microscopy

The morphological changes of ferroelectric polymer thin films during the annealing process were directly imaged by variable-temperature atomic force microscopy (AFM). The growing process of the crystallites underlying the surface amorphous layer was observed as well as the morphological changes using intermittent-contact AFM. We found that fine structures appeared in the rod like grains at a temperature corresponding to the Curie point of the bulk copolymer in the cooling process. In addition, local piezoelectric response was mapped in order to investigate the relationship between the structural change and the ferroelectric phase transition. The local polarization prepared at room temperature disappeared after the film was heated above 120°C, which agreed with both the Curie temperature and the temperature of the observed structural change.

Effect of phase transition on the surface potential of the BaTiO3 (100) surface by variable temperature scanning surface potential microscopy

Variable temperature atomic force microscopy and scanning surface potential microscopy are used to characterize the ferroelectric BaTiO3 (100) surface. The influence of domain structure on surface topography and surface potential distribution is discussed. Domain induced surface corrugations were found to disappear above the Curie temperature confirming the local phase transition. Associated variations of surface potential are quantified. Relaxation of surface potential after the transition to paraelectric state on heating and during the transition to the ferroelectric state on cooling was observed. Differences in kinetics of the topographic structure and surface potential variations are used to distinguish polarization compensation mechanisms.

Nucleation and growth of supported clusters at defect sites: Pd/MgO(001)

Nucleation and growth of Pd on cleaved MgO(001) surfaces were studied by variable-temperature atomic force microscopy in the temperature range 200-800 K. Constant island densities (similar to 3x10(12)cm(-2)) were observed over a wide temperature range, indicating nucleation kinetics governed by point defects with a high trapping energy. These results are compared to a rate equation model that describes the principal atomistic nucleation and growth processes, including nucleation at attractive point defects. Energies for defect trapping, adsorption, surface diffusion, and pair binding are deduced, and compared with recent nb initio calculations.

Nucleation and growth of supported metal clusters at defect sites on oxide and halide (0 0 1) surfaces

Nucleation and growth at defect sites is discussed in terms of rate equation models, which can be applied to metals deposited on oxide and halide surfaces. Strong trapping and rapid adatom diffusion is characterized by an extensive plateau, where the island density stays constant over a wide range of deposition parameters. Energies for defect trapping, adsorption, surface diffusion and pair binding are deduced for Pd deposited on Ar-cleaved MgO(0 0 1), which has recently been studied in situ by variable temperature atomic force microscopy (AFM). Calculations of these energies for Pd and Ag metals on both NaCl and MgO(0 0 1) surfaces are presented, and compared with earlier data for Ag, Au and Pd on NaCl.

Nucleation and Growth of Supported Metal Clusters at Defect Sites on Mgo and NaCl (001) Surfaces: The Cases of Pd and Ag

ABSTRACTNucleation and growth of metal clusters at defect sites is discussed in terms of rate equation models, which are applied to the cases of Pd and Ag on MgO(001) and NaCl(001) surfaces. Pd/MgO has been studied experimentally by variable temperature atomic force microscopy (AFM). The island density of Pd on Ar-cleaved surfaces was determined in-situ by AFM for a wide range of deposition temperature and flux, and stays constant over a remarkably wide range of parameters; for a particular flux, this plateau extends from 200 K ≤ T ≤ 600 K, but at higher temperatures the density decreases. The range of energies for defect trapping, adsorption, surface diffusion and pair binding are deduced, and compared with earlier data for Ag on NaCl, and with recent calculations for these metals on both NaCl and MgO