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Rodriguez, Brian J.
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Rodriguez, Brian J.
Official Name
Rodriguez, Brian J.
Research Output
Now showing 1 - 10 of 105
- PublicationNanoscale characterization of β-phase HxLi1−xNbO3 layers by piezoresponse force microscopy(American Institute of Physics, 2014)
; ; ; We investigate a non-destructive approach for the characterization of proton exchanged layers in LiNbO3 with sub-micrometric resolution by means of piezoresponse force microscopy (PFM). Through systematic analyses, we identify a clear correlation between optical measurements on the extraordinary refractive index and PFM measurements on the piezoelectric d 33 coefficient. Furthermore, we quantify the reduction of the latter induced by proton exchange as 83 ± 2% and 68 ± 3% of the LiNbO3 value, for undoped and 5 mol. % MgO-doped substrates, respectively.309Scopus© Citations 7 - PublicationOpen loop Kelvin probe force microscopy with single and multi-frequency excitation(Institute of Physics, 2013-11-29)
; ; ; ; Conventional Kelvin probe force microscopy (KPFM) relies on closed loop (CL) bias feedback for the determination of surface potential (SP). However, SP measured by CL-KPFM has been shown to be strongly influenced by the choice of measurement parameters due to non-electrostatic contributions to the input signal of the bias feedback loop. This often leads to systematic errors of several hundred mV and can also result in topographical crosstalk. Here, open loop (OL)-KPFM modes are investigated as a means of obtaining a quantitative, crosstalk free measurement of the SP of graphene grown on Cu foil, and are directly contrasted with CL-KPFM. OL-KPFM operation is demonstrated in both single and multi-frequency excitation regimes, yielding quantitative SP measurements. The SP difference between single and multilayer graphene structures using OL-KPFM was found to be 63 ± 11 mV, consistent with values previously reported by CL-KPFM. Furthermore, the same relative potential difference between Al2O3-coated graphene and Al2O3-coated Cu was observed using both CL and OL techniques. We observed an offset of 55 mV between absolute SP values obtained by OL and CL techniques, which is attributed to the influence of non-electrostatic contributions to the input of the bias feedback used in CL-KPFM.541Scopus© Citations 56 - PublicationControlling polarization dynamics in a liquid environment: from localized to macroscopic switching in ferroelectricsThe effect of disorder on polarization switching in ferroelectric materials is studied using piezoresponse force microscopy in a liquid environment. The spatial extent of the electric field created by a biased tip is controlled by the choice of medium, resulting in a transition from localized switching dictated by tip radius, to uniform switching across the film. In the localized regime, the formation of fractal domains has been observed with dimensionality controlled by the length scale of the frozen disorder. In the nonlocal regime, preferential nucleation at defect sites and the presence of long-range correlations has been observed.
323Scopus© Citations 47 - PublicationAtomic and Close-to-Atomic Scale Manufacturing: A Review on Atomic Layer Removal Methods Using Atomic Force MicroscopyManufacturing at the atomic scale is the next generation of the industrial revolution. Atomic and close-to-atomic scale manufacturing (ACSM) helps to achieve this. Atomic force microscopy (AFM) is a promising method for this purpose since an instrument to machine at this small scale has not yet been developed. As the need for increasing the number of electronic components inside an integrated circuit chip is emerging in the present-day scenario, methods should be adopted to reduce the size of connections inside the chip. This can be achieved using molecules. However, connecting molecules with the electrodes and then to the external world is challenging. Foundations must be laid to make this possible for the future. Atomic layer removal, down to one atom, can be employed for this purpose. Presently, theoretical works are being performed extensively to study the interactions happening at the molecule–electrode junction, and how electronic transport is affected by the functionality and robustness of the system. These theoretical studies can be verified experimentally only if nano electrodes are fabricated. Silicon is widely used in the semiconductor industry to fabricate electronic components. Likewise, carbon-based materials such as highly oriented pyrolytic graphite, gold, and silicon carbide find applications in the electronic device manufacturing sector. Hence, ACSM of these materials should be developed intensively. This paper presents a review on the state-of-the-art research performed on material removal at the atomic scale by electrochemical and mechanical methods of the mentioned materials using AFM and provides a roadmap to achieve effective mass production of these devices.
116Scopus© Citations 32 - PublicationMapping bias-induced phase stability and random fields in relaxor ferroelectrics(AIP Publishing, 2009-09)
; ; ; ; The spatial variability of polarization reversal behavior in the relaxor 0.9Pb(Mg1/3Nb2/3O3)-0.1PbTiO(3) crystal, is revealed on the similar to 100 nm scale using switching spectroscopy piezoresponse force microscopy. Quenched fields conjugate to polarization are found, which show mesoscopic (similar to 100-200 nm) spatial fluctuations around near-zero bias values. The mapping of the stability gap of the bias-induced phase and conjugate random fields is demonstrated. The origin of the observed nanoscale domains and the field-induced part of the polarization are discussed.330Scopus© Citations 26 - PublicationSpatial distribution of relaxation behavior on the surface of a ferroelectric relaxor in the ergodic phaseSpatial homogeneity of polarization relaxation behavior on the surface of 0.9Pb(Mg1/3Nb2/3)O-3-0.1PbTiO(3) crystals in the ergodic relaxor phase is studied using three-dimensional time-resolved spectroscopic piezoresponse force microscopy. The number of statistically independent components in the spectroscopic image is determined using principal component analysis. In the studied measurement time interval, the spectra generally exhibit logarithmic behavior with spatially varying slope and offset, and the statistical distribution of these parameters are studied. The data illustrate the presence of mesoscopic heterogeneity in the dynamics of the relaxation behavior that can be interpreted as spatial variation in local Vogel-Fulcher temperatures.
357Scopus© Citations 32 - PublicationSelf-Assembly of Amyloid-Beta and Its Piezoelectric Properties(Scientific Research Publishing, 2021-01)
; ; ; ; Investigating amyloid nanofibril self-assembly, with an emphasis on the electromechanical property of amyloid peptides, namely, piezoelectricity, may have several important implications: 1) the self-assembly process can hinder the biological stability and give rise to the formation of amyloid structures associated with neurodegenerative diseases; 2) investigations in this field may lead to an improved understanding of high-performance, functional biological nanomaterials, 3) new technologies could be established based on peptide self-assembly and the resultant functional properties, e.g., in the creation of a piezoelectric device formed with vertical diphenylalanine peptide tubes as a piezoelectric biosensor, and 4) new knowledge can be generated about neurodegenerative disorders, potentially yielding new therapies. Therefore, in this review, we will present the current investigations associated with self-assembly of amyloid-beta, the mechanisms that generate new structures, as well as theoretical calculations exploring the functionality of the structures under physiological pressure and electric field.180 - PublicationMicro-Raman study of electronic properties of inversion domains in GaN-based lateral polarity heterostructuresThe electronic properties of inversion domains in a GaN-based lateral polarity heterostructure were investigated using micro-Raman spectroscopy. The piezoelectric polarization of each domain was calculated from strain determined via Raman scattering. The free carrier concentration and electron mobility were deduced from the longitudinal optical phonon-plasmon coupled mode. The electron concentration in the N-face domain was slightly higher than that in the Ga-face domain. It appears that during growth, a larger number of donor impurities may have been incorporated into the N-face domain than into the Ga-face domain.
401Scopus© Citations 34 - PublicationDual harmonic Kelvin probe force microscopy for surface potential measurements of ferroelectrics(IEEE, 2012-07)
; ; ; ; ; ; In this work, we implemented dual harmonic Kelvin probe force microscopy (DH-KPFM) for surface potential mapping of ferroelectric thin films, namely bismuth ferrite (BFO) and strontium barium niobate (SBN). We applied DH and conventional KPFM to charge-patterned BFO and found agreement between recorded relative surface potential values between domains, demonstrating that DH-KPFM can be used for quantitative mapping of relative surface potentials. We used piezoresponse force microscopy (PFM) to determine whether polarization switching had occurred. From the PFM data, we found that BFO was poled successfully, and that the measured surface potential was consistent with the sign of the bound polarization charge. For SBN, a thin surface layer was evident in the topography after the application of DC bias, suggesting an electrochemical reaction had taken place between the tip and the sample. We used DH-KPFM to simultaneously map the surface potential and changes in the dielectric properties resulting from this surface layer. The results presented herein demonstrate that DH-KPFM can be used for electric characterization of voltagesensitive materials, and we anticipate that DH-KFPM will become a useful tool for non-intrusive electrical characterization of materials.558Scopus© Citations 14 - PublicationNanoelectromechanics of polarization switching in piezoresponse force microscopy(American Institute of Physics, 2005-04)
; ; ; Nanoscale polarization switching in ferroelectric materials by piezoresponse force microscopy in weak and strong indentation limits is analyzed using exact solutions for coupled electroelastic fields under the tip. Tip-induced domain switching is mapped on the Landau theory of phase transitions, with domain size as an order parameter. For a point charge interacting with a ferroelectric surface, switching by both first and the second order processes is possible, depending on the charge-surface separation. For a realistic tip, the domain nucleation process is first order in charge magnitude and polarization switching occurs only above a certain critical tip bias. In pure ferroelectric or ferroelastic switching, the late stages of the switching process can be described using a point charge model and arbitrarily large domains can be created. However, description of domain nucleation and the early stages of growth process when the domain size is comparable with the tip curvature radius (weak indentation) or the contact radius (strong indentation) requires the exact field structure. For higher order ferroic switching (e.g., ferroelectroelastic), the domain size is limited by the tip-sample contact area, thus allowing precise control of domain size. (C) 2005 American Institute of Physics.237Scopus© Citations 59