Dynamic atomic force microscopy methods

Ferroelectrics and multiferroics have recently emerged as perspective materials for information technology and data storage applications. The combination of extremely narrow domain wall width and the capability to manipulate polarization by electric field opens the pathway toward ultrahigh (>10 TBit inch−2) storage densities and small (sub-10 nm) feature sizes. The coupling between polarization and chemical and transport properties enables applications in ferroelectric lithography and electroresistive devices. The progress in these applications, as well as fundamental studies of polarization dynamics and the role of defects and disorder on domain nucleation and wall motion, requires the capability to probe these effects on the nanometer scale. In this review, we summarize the recent progress in applications of piezoresponse force microscopy (PFM) for imaging, manipulation and spectroscopy of ferroelectric switching processes. We briefly introduce the principles and relevant instrumental aspects of PFM, with special emphasis on resolution and information limits. The local imaging studies of domain dynamics, including local switching and relaxation accessed through imaging experiments and spectroscopic studies of polarization switching, are discussed in detail. Finally, we review the recent progress on understanding and exploiting photochemical processes on ferroelectric surfaces, the role of surface adsorbates, and imaging and switching in liquids. Beyond classical applications, probing local bias-induced transition dynamics by PFM opens the pathway to studies of the influence of a single defect on electrochemical and solid state processes, thus providing model systems for batteries, fuel cells and supercapacitor applications.

https://iopscience.iop.org/article/10.1088/0034-4885/73/5/056502/pdf

Local polarization dynamics in ferroelectric materials

This review article aims to provide an updated and comprehensive description on the development of atomic force microscopy (AFM) nanolithography for structuring and fabrication at the nanometer scale. The many AFM nanolithographic techniques are classified into two general groups of force-assisted and bias-assisted nanolithography on the basis of their mechanistic and operational principles. Force-assisted AFM nanolithography includes mechanical indentation and plowing, thermomechanical writing, manipulation and dip-pen nanolithography. Bias-assisted AFM nanolithography encompasses probe anodic oxidation, field evaporation, electrochemical deposition and modification, electrical cutting and nicking, electrostatic deformation and electrohydrodynamic nanofluidic motion, nanoexplosion and shock wave generation, and charge deposition and manipulation. The experimental procedures, pattern formation mechanisms, characteristics, and functionality of nanostructures and nanodevices fabricated by AFM nanolithography are reviewed. The capabilities of AFM nanolithography in patterning a large family of materials ranging from single atoms and molecules to large biological networks are presented. Emphasis is given to AFM nanolithographic techniques such as dip-pen nanolithography, probe anodic oxidation, etc. due to the rapid progress and wide applications of these techniques.

Nanoscale materials patterning and engineering by atomic force microscopy nanolithography

The application of ferroelectric materials for nonvolatile memory and ferroelectric data storage necessitates quantitative studies of local switching characteristics and their relationship to material microstructure and defects. Switching spectroscopy piezoresponse force microscopy (SS-PFM) is developed as a quantitative tool for real-space imaging of imprint, coercive bias, remanent and saturation responses, and domain nucleation voltage on the nanoscale. Examples of SS-PFM implementation, data analysis, and data visualization are presented for epitaxial lead zirconate titanate (PZT) thin films and polycrystalline PZT ceramics. Several common artifacts related to the measurement method, environmental factors, and instrument settings are analyzed.

Quantitative mapping of switching behavior in piezoresponse force microscopy

Nanometer-size water bridges have been used to confine the oxidation of silicon surfaces with a noncontact atomic force microscope. The formation of a water bridge between two surfaces separated by a gap of a few nanometers is driven by the application of an electrical field. Once a liquid bridge is formed, its length and neck diameter can be modified by changing the tip-sample separation. The liquid bridge provides the ionic species and the spatial confinement to pattern Si(100) surfaces in noncontact force microscopy. The method is applied to write arrays of several thousands dots with a periodicity of 40 nm and an average width of 10 nm.

/pdf/patterning-of-silicon-surfaces-with-noncontact-atomic-force-pbwll6viz2.pdf

Patterning of silicon surfaces with noncontact atomic force microscopy: Field-induced formation of nanometer-size water bridges

The growth rate and electrical character of nanostructures produced by scanned probe oxidation are investigated by integrating an in situ electrical force characterization technique, scanning Maxwell-stress microscopy, into the fabrication process. Simultaneous topographical, capacitance, and surface potential data are obtained for oxide features patterned on n- and p-type silicon and titanium thin-film substrates. The electric field established by an applied voltage pulse between the probe tip and substrate depends upon reactant and product ion concentrations associated with the water meniscus at the tip-substrate junction and within the growing oxide film. Space-charge effects are consistent with the rapid decline of high initial growth rates, account for observed doping and voltage-pulse dependencies, and provide a basis for understanding local density variations within oxide features. An obvious method for avoiding the buildup of space charge is to employ voltage modulation and other dynamic pulse-sha...

Role of space charge in scanned probe oxidation

n‐Cycloparaphenylene ([n]CPP) is a non‐planar π‐conjugated molecule with a macrocyclic, hoop‐like molecular structure that allows for control of the electronic structure unlike planar molecules. Thus, [n]CPP has the potential as a novel functional material in organic electronics. In this study, the unique electronic structure of [6]CPP is revealed, which originates from its macrocyclic molecular structure by comparison with p‐sexiphenyl, a linear molecule also consisting of six phenylenes. The morphology of the vapor‐deposited [6]CPP polycrystalline film is found to be highly dependent on the evaporation rate and the type of substrate. It is also found that a [6]CPP molecular layer is formed at the interface between the film and gold substrate, which has a much smaller energy gap than that of the bulk [6]CPP. This anomalous molecular layer is composed of [6]CPP molecules with a smaller dihedral angle than that in the bulk because of the interaction with a gold substrate. When [6]CPP is used as a semiconducting layer in electronic devices, this layer can play a role in improving the charge injection efficiency from the electrode to the [6]CPP film.

T. Inoue

Papers

Role of space charge in scanned probe oxidation

Anomalous Interfacial Electronic Structure of Solid Films of Non‐Planar π‐Conjugated Molecule 6‐Cycloparaphenylene