Imaging domains in BaTiO3 single crystal nanostructures: comparing information from transmission electron microscopy and piezo-force microscopy

This article compares and contrasts information
obtained, using transmission electron microscopy (TEM)
and piezo-force microscopy (PFM), on domain configurations
adopted in single crystal lamellae of BaTiO3, that had
been cut directly from bulk using a focused ion beam
microscope with top and bottom surfaces parallel to
{100}pseudocubic. Both forms of imaging reveal domain
walls parallel to {110}pseudocubic, consistent with sets of 90
domains with dipoles oriented parallel to the two
\001[pseudocubic directions in the plane of the lamellae.
However, the domain width was observed to be dramatically
larger using PFM than it was using TEM. This suggests
significant differences in the surface energy densities
that drive the domain formation in the first place, that could
relate to differences in the boundary conditions in the two
modes of imaging (TEM samples are imaged under high
vacuum, whereas PFM imaging was performed in air).
Attempts were made to map local dipole orientations
directly, using a form of ‘vector’ PFM. However, information
inferred was largely inconsistent with the known
crystallography of the samples, raising concern about the
levels of care needed for accurate interpretation of PFM
images.

The potential of electron beam radiation for simultaneous surface modification and bioresorption control of PLLA

Bioresorbable polymers have been widely investigated as materials exhibiting significant potential for successful application in the fields of tissue engineering and drug delivery. Further to the ability to control degradation, surface engineering of polymers has been highlighted as a key method central to their development. Previous work has demonstrated the ability of electron beam (e-beam) technology to control the degradation profiles and bioresorption of a number of commercially relevant bioresorbable polymers (poly-l-lactic acid (PLLA), Llactide/DL-lactide co-polymer (PLDL) and poly(lactic-co-glycolic acid (PLGA)). This work investigates the further potential of ebeam technology to impart added biofunctionality through the manipulation of polymer (PLLA) surface properties. PLLA samples were subjected to e-beam treatments in air, with varying beam energies and doses. Surface characterization was then performed using contact angle analysis, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and atomic force microscopy. Results demonstrated a significant increase in surface wettability post e-beam treatment. In correlation with this, XPS data showed the introduction of oxygen-containing functional groups to the surface of PLLA. Raman spectroscopy indicated chain scission in the near surface region of PLLA (as predicted). However, e-beam effects on surface properties were not shown to be dependent on beam energy or dose. E-beam irradiation did not seem to affect the surface roughness of PLLA as a direct consequence of the treatment.

Resolution theory, and static and frequency-dependent cross-talk in piezoresponse force microscopy

Probing the functionality of materials locally by means of scanning probe microscopy (SPM) requires a reliable framework for identifying the target signal and separating it from the effects of surface morphology and instrument non-idealities, e.g. instrumental and topographical cross-talk. Here we develop a linear resolution theory framework in order to describe the cross-talk effects, and apply it for elucidation of frequency-dependent cross-talk mechanisms in piezoresponse force microscopy. The use of a band excitation method allows electromechanical/electrical and mechanical/topographic signals to be unambiguously separated. The applicability of a functional fit approach and multivariate statistical analysis methods for identification of data in band excitation SPM is explored.

Mapping piezoelectric nonlinearity in the Rayleigh regime using band excitation piezoresponse force microscopy

Band excitation piezoresponse force microscopy enables local investigation of the nonlinear piezoelectric behavior of ferroelectric thin films. However, the presence of additional nonlinearity associated with the dynamic resonant response of the tip-surface junction can complicate the study of a material's nonlinearity. Here, the relative importance of the two nonlinearity sources was examined as a function of the excitation function. It was found that in order to minimize the effects of nonlinear tip-surface interactions but achieve good signal to noise level, an optimal excitation function must be used. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3593138]

Real-space mapping of dynamic phenomena during hysteresis loop measurements: Dynamic switching spectroscopy piezoresponse force microscopy

Dynamic switching spectroscopy piezoresponse force microscopy is developed to separate thermodynamic and kinetic effects in local bias-induced phase transitions. The approaches for visualization and analysis of five-dimensional data are discussed. The spatial and voltage variability of relaxation behavior of the a-c domain lead zirconate-titanate surface suggest the interpretation in terms of surface charge dynamics. This approach is applicable to local studies of dynamic behavior in any system with reversible bias-induced phase transitions ranging from ferroelectrics and multiferroics to ionic systems such as batteries, fuel cells, and electroresistive materials. (C) 2011 American Institute of Physics. [doi:10.1063/1.3590919]

Probing charge screening dynamics and electrochemical processes at the solid–liquid interface with electrochemical force microscopy

The presence of mobile ions complicates the implementation of voltage-modulated scanning probe microscopy techniques such as Kelvin probe force microscopy (KPFM). Overcoming this technical hurdle, however, provides a unique opportunity to probe ion dynamics and electrochemical processes in liquid environments and the possibility to unravel the underlying mechanisms behind important processes at the solid–liquid interface, including adsorption, electron transfer and electrocatalysis. Here we describe the development and implementation of electrochemical force microscopy (EcFM) to probe local bias- and time-resolved ion dynamics and electrochemical processes at the solid–liquid interface. Using EcFM, we demonstrate contact potential difference measurements, consistent with the principles of open-loop KPFM operation. We also demonstrate that EcFM can be used to investigate charge screening mechanisms and electrochemical reactions in the probe–sample junction. We further establish EcFM as a force-based imaging mode, allowing visualization of the spatial variability of sample-dependent local electrochemical properties.

Piezoresponse force microscopy of ferroelectric thin films: Frequency dependence of phase imaging

The objective of this work is an evaluation of quantitative measurements of piezoresponse force microscopy for nanoscale characterization of ferroelectric films. To this end, we investigate how the piezoresponse phase difference Delta Phi between c domains depends on the frequency omega of the applied ac field much lower than the cantilever first resonance frequency. The main specimen under study was a 102 nm thick film of Pb(Zr(0.2)Ti(0.8))O(3). For the sake of comparison, a 100 nm thick PbTiO(3) film was also used. From our measurements, we conclude a frequency dependent behavior Delta Phi similar to omega(-1), which can only be partially explained by the presence of adsorbates on the surface. (C) 2008 American Institute of Physics.

Self-assembly using dendritic building blocks - towards controllable nanomaterials

Dendritic molecules have well defined, three-dimensional branched architectures, and constitute a unique nanoscale toolkit. This review focuses on examples in which individual dendritic molecules are assembled into more complex arrays via non-covalent interactions. In particular, it illustrates how the structural information programmed into the dendritic architecture controls the assembly process, and as a consequence, the properties of the supramolecular structures which are generated. Furthermore, the review emphasises how the use of non-covalent (supramolecular) interactions, provides the assembly process with reversibility, and hence a high degree of control. The review also illustrates how self-assembly offers an ideal approach for amplifying the branching of small, synthetically accessible, relatively inexpensive dendritic systems (e.g. dendrons), into highly branched complex nanoscale assemblies.

The review begins by considering the assembly of dendritic molecules to generate discrete, well-defined supramolecular assemblies. The variety of possible assembled structures is illustrated, and the ability of an assembled structure to encapsulate a templating unit is described. The ability of both organic and inorganic building blocks to direct the assembly process is discussed. The review then describes larger discrete assemblies of dendritic molecules, which do not exist as a single well-defined species, but instead exist as statistical distributions. For example, assembly around nanoparticles, the assembly of amphiphilic dendrons and the assembly of dendritic systems in the presence of DNA will all be discussed. Finally, the review examines dendritic molecules, which assemble or order themselves into extended arrays. Such systems extend beyond the nanoscale into the microscale or even the macroscale domain, exhibiting a wide range of different architectures. The ability of these assemblies to act as gel-phase or liquid crystalline materials will be considered.

Taken as a whole, this review emphasises the control and tunability that underpins the assembly of nanomaterials using dendritic building blocks, and furthermore highlights the potential future applications of these assemblies at the interfaces between chemistry, biology and materials science. 

Contrasting damage characteristics in direct incidence and surface plasmon mediated single-shot laser ablation of aluminium films

Thin, oxidised Al films grown an one face of fused silica prisms are exposed. tinder ambient conditions, to single shots from an excimer laser operating at wavelength 248 nm. Preliminary characterisation of the films using attenuated total reflection yields optical and thickness data for the Al and Al oxide layers; this step facilitates the subsequent, accurate tuning of the excimer laser pulse to the: surface plasmon resonance at the Al/(oxide)/air interface and the calculation of the fluence actually absorbed by the thin film system. Ablation damage is characterised using scanning electron, and atomic force microscopy. When the laser pulse is incident, through the prism on the sample at less than critical angle, the damage features are molten in nature with small islands of sub-micrometer dimension much in evidence, a mechanism of film melt-through and subsegment blow-off due to the build up of vapour pressure at the substrate/film interface is appropriate. By contrast, when the optical input is surface plasmon mediated, predominately mechanical damage results with the film fragmenting into large flakes of dimensions on the order of 10 mu m. It is suggested that the ability of surface plasmons to transport energy leads to enhanced, preferential absorption of energy at defect sites causing stress throughout the film which exceeds the ultimate tensile stress for the film: this in turn leads to film break-up before melting can onset. (C) 1998 Elsevier Science B.V.

Microelectronic manufacturing of a microsensor based on polyaniline for ammonia gas sensing

The fabrication and operation of an ammonia chemoresistor is described. The sensor responds to changes in the resistance (impedance) of a thin layer of conductive polymer is due to changes in ammonia concentration. The polyaniline film was deposited by electroless plating (dipping) method on interdigitated array made by photolithographic technique. The PANI film was characterized by UV/VIS and IR Spectroscopy and respectively, Atomic Force Microscopy. Impedance Spectroscopy was used for sensor characterization

The potential of electron beam irradiation for simultaneous surface modification and bioresorption control of PLLA for medical device applications

Bioresorbable polymers have been widely investigated as materials exhibiting significant potential for successful application in the medical fields of bone fixation devices and drug delivery. Further to the ability to control degradation, surface engineering of polymers has been highlighted as a key method central to their development. Previous work has demonstrated the ability of electron beam (e-beam) technology to control the degradation profiles and bioresorption of a number of commercially relevant bioresorbable polymers (poly-l-lactic acid (PLLA), L-lactide/ DL-lactide co-polymer (PLDL) and poly(lactic-co-glycolic acid) (PLGA). This work investigates the further potential of e-beam technology to impart added biofunctionality through the manipulation of polymer (PLLA) surface properties. A Dynamatron Continuous DC e-beam unit (Synergy Health, UK), with beam energies of 0.5, 0.75, and 1.5 MeV, was used for the irradiation of PLLA samples with delivered surface doses of 150 or 500 kGy at each energy level. The chosen conditions reflect the need to achieve a specific surface modification for the control of surface degradation as demonstrated in previous work. Surface characterization was then performed using contact angle analysis, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and atomic force microscopy.
Results demonstrated a significant increase in surface wettability post e-beam treatment. In correlation with this, XPS data showed the introduction of oxygen-containing functional groups to the surface of PLLA. Raman spectroscopy indicated chain scission in the near surface region of PLLA. E-beam irradiation did not seem to affect the surface roughness of PLLA as a direct consequence of the treatment. In conclusion electron beam surface modification has been found to modify both the surface-to-bulk bioresorption profile and the surface hydrophilicity. Both could provide benefits in relation to the performance of implantable medical devices.