1,423 research outputs found
Nanoscale Electric Phenomena at Oxide Surfaces and Interfaces by Scanning Probe Microscopy
Scanning Probe Microscopy is used to study and quantify the nanoscale
electric phenomena in the two classes of oxide systems, namely transport at
electroactive grain boundaries and surface behavior of ferroelectric materials.
Scanning Impedance Microscopy is developed to study the capacitance and local
C-V characteristic of the interfaces combining the spatial resolution of
traditional SPMs with the precision of conventional electrical measurements.
SPM of SrTiO3 grain boundaries in conjunction with variable temperature
impedance spectroscopy and I-V measurements allowed to find and theoretically
justify the effect of field suppression of dielectric constant in the vicinity
of the electroactive interfaces in strontium titanate. Similar approaches were
used to study ferroelectric properties and ac and dc transport behavior in a
number of polycrystalline oxides.
In the second part, the effects of local charge density on the chemistry and
physics of ferroelectric surfaces are studied. The kinetics and thermodynamics
parameters of adsorption are assessed by variable temperature SPM.
Piezoresponse force microscopy is used to engineer domain patterns on
ferroelectric surfaces. Localized photochemical activity of ferroelectric
surfaces is explored as a new tool for metallic nanostructures fabrication.Comment: Ph.D. Thesis, September 2002, 304 pages, 108 figures, 2.4 MB PDF
file, Higher quality version available at sergei2.kalininweb.co
Carbon nanotubes as a tip calibration standard for electrostatic scanning probe microscopies
Scanning Surface Potential Microscopy (SSPM) is one of the most widely used
techniques for the characterization of electrical properties at small
dimensions. Applicability of SSPM and related electrostatic scanning probe
microscopies for imaging of potential distributions in active micro- and
nanoelectronic devices requires quantitative knowledge of tip surface contrast
transfer. Here we demonstrate the utility of carbon-nanotube-based circuits to
characterize geometric properties of the tip in the electrostatic scanning
probe microscopies (SPM). Based on experimental observations, an analytical
form for the differential tip-surface capacitance is obtained.Comment: 14 pages, 4 figure
Tip-gating Effect in Scanning Impedance Microscopy of Nanoelectronic Devices
Electronic transport in semiconducting single-wall carbon nanotubes is
studied by combined scanning gate microscopy and scanning impedance microscopy
(SIM). Depending on the probe potential, SIM can be performed in both invasive
and non-invasive mode. High-resolution imaging of the defects is achieved when
the probe acts as a local gate and simultaneously an electrostatic probe of
local potential. A class of weak defects becomes observable even if they are
located in the vicinity of strong defects. The imaging mechanism of tip-gating
scanning impedance microscopy is discussed.Comment: 11 pages, 3 figures, to be published in Appl. Phys. Let
Scanning Impedance Microscopy: From Impedance Spectra to Impedance Images
Impedance spectroscopy has long been recognized as one of the major techniques for the characterization of ac transport in materials. The primary limitation of this technique is the lack of spatial resolution that precludes the equivalent circuit elements from being unambiguously associated with individual microstructural features. Here we present a scanning probe microscopy technique for quantitative imaging of ac and dc transport properties of electrically inhomogeneous materials. This technique, referred to as Scanning Impedance Microscopy (SIM), maps the phase and amplitude of local potential with respect to an electric field applied across the sample. Amplitude and phase behavior of individual defects can be correlated with their transport properties. The frequency dependence of the voltage phase shift across an interface yields capacitance and resistance. SIM of single interfaces is demonstrated on a model metal-semiconductor junction. The local interface capacitance and resistance obtained from SIM measurements agrees quantitatively with macroscopic impedance spectroscopy. Superposition of a dc sample bias during SIM probes the C-V characteristics of the interface. When combined with Scanning Surface Potential Microscopy (SSPM), which can be used to determine interface I-V characteristic, local transport properties are completely determined. SIM and SSPM of polycrystalline materials are demonstrated on BiFeO3 and p-doped silicon. An excellent agreement between the properties of a single interface determined by SIM and traditional impedance spectra is demonstrated. Finally, the applicability of this technique for imaging transport behavior in nanoelectronic devices is illustrated with carbon nanotube circuit
Physics and Chemistry from Parsimonious Representations: Image Analysis via Invariant Variational Autoencoders
Electron, optical, and scanning probe microscopy methods are generating ever
increasing volume of image data containing information on atomic and mesoscale
structures and functionalities. This necessitates the development of the
machine learning methods for discovery of physical and chemical phenomena from
the data, such as manifestations of symmetry breaking in electron and scanning
tunneling microscopy images, variability of the nanoparticles. Variational
autoencoders (VAEs) are emerging as a powerful paradigm for the unsupervised
data analysis, allowing to disentangle the factors of variability and discover
optimal parsimonious representation. Here, we summarize recent developments in
VAEs, covering the basic principles and intuition behind the VAEs. The
invariant VAEs are introduced as an approach to accommodate scale and
translation invariances present in imaging data and separate known factors of
variations from the ones to be discovered. We further describe the
opportunities enabled by the control over VAE architecture, including
conditional, semi-supervised, and joint VAEs. Several case studies of VAE
applications for toy models and experimental data sets in Scanning Transmission
Electron Microscopy are discussed, emphasizing the deep connection between VAE
and basic physical principles. All the codes used here are available at
https://github.com/saimani5/VAE-tutorials and this article can be used as an
application guide when applying these to own data sets.Comment: 55 pages, 16 figure
Contrast mechanism maps for piezoresponse force microscopy
Piezoresponse force microscopy (PFM) is one of the most established techniques for the observation and local modification of ferroelectric domain structures on the submicron level. Both electrostatic and electromechanical interactions contribute at the tip-surface junction in a complex manner, which has resulted in multiple controversies in the interpretation of PFM. Here we analyze the influence of experimental conditions such as tip radius of curvature, indentation force, and cantilever stiffness on PFM image contrast. These results are used to construct contrast mechanism maps, which correlate the imaging conditions with the dominant contrast mechanisms. Conditions under which materials properties can be determined quantitatively are elucidated
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