Peter Maksymovych

Publications of Peter Maksymovych

• Tunable metallic conductance in ferroelectric nanodomains.

  Authors: Peter Maksymovych, Anna N Morozovska, Pu Yu, Eugene A Eliseev, Ying-Hao Chu, Ramamoorthy Ramesh, Arthur P Baddorf, Sergei V Kalinin

  Nano letters. 12/2011; 12(1):209-13.

  Metallic conductance in charged ferroelectric domain walls was predicted more than 40 years ago as the first example of an electronically active homointerface in a nonconductive material. DespiteMetallic conductance in charged ferroelectric domain walls was predicted more than 40 years ago as the first example of an electronically active homointerface in a nonconductive material. Despite decades of research on oxide interfaces and ferroic systems, the metal-insulator transition induced solely by polarization charges without any additional chemical modification has consistently eluded the experimental realm. Here we show that a localized insulator-metal transition can be repeatedly induced within an insulating ferroelectric lead-zirconate titanate, merely by switching its polarization at the nanoscale. This surprising effect is traced to tilted boundaries of ferroelectric nanodomains, that act as localized homointerfaces within the perovskite lattice, with inherently tunable carrier density. Metallic conductance is unique to nanodomains, while the conductivity of extended domain walls and domain surfaces is thermally activated. Foreseeing future applications, we demonstrate that a continuum of nonvolatile metallic states across decades of conductance can be encoded in the size of ferroelectric nanodomains using electric field.

• Domain wall conduction in multiaxial ferroelectrics

  Authors: Eugene A. Eliseev, Anna N. Morozovska, George S. Svechnikov, Peter Maksymovych, Sergei V Kalinin

  08/2011;

  The conductance of domain wall structures consisting of either stripes or cylindrical domains in multi-axial ferroelectric-semiconductors is analyzed. The effects of the domain size, wall tilt andThe conductance of domain wall structures consisting of either stripes or cylindrical domains in multi-axial ferroelectric-semiconductors is analyzed. The effects of the domain size, wall tilt and curvature, on charge accumulation, are analyzed using the Landau-Ginsburg Devonshire (LGD) theory for polarization combined with Poisson equation for charge distributions. Both the classical ferroelectric parameters including expansion coefficients in 2-4-6 Landau potential and gradient terms, as well as flexoelectric coupling, inhomogeneous elastic strains and electrostriction are included in the present analysis. Spatial distributions of the ionized donors, free electrons and holes were found self-consistently using the effective mass approximation for the respective densities of states. The proximity and size effect of the electron and donor accumulation/depletion by thin stripe domains and cylindrical nanodomains are revealed. In contrast to thick domain stripes and thicker cylindrical domains, in which the carrier accumulation (and so the static conductivity) sharply increases at the domain walls only, small nanodomains of radius less then 5-10 correlation length appeared conducting across entire cross-section. Implications of such conductive nanosized channels may be promising for nanoelectronics.

• Scaling and disorder analysis of local I-V curves from ferroelectric thin films of lead zirconate titanate.

  Authors: Peter Maksymovych, Minghu Pan, Pu Yu, Ramamoorthy Ramesh, Arthur P Baddorf, Sergei V Kalinin

  Nanotechnology. 06/2011; 22(25):254031.

  Differential analysis of current-voltage characteristics, obtained on the surface of epitaxial films of ferroelectric lead zirconate titanate (Pb(Zr(0.2)Ti(0.8))O(3)) using scanning probe microscopy,Differential analysis of current-voltage characteristics, obtained on the surface of epitaxial films of ferroelectric lead zirconate titanate (Pb(Zr(0.2)Ti(0.8))O(3)) using scanning probe microscopy, was combined with spatially resolved mapping of variations in local conductance to differentiate between candidate mechanisms of local electronic transport and the origin of disorder. Within the assumed approximations, electron transport was inferred to be determined by two mechanisms depending on the magnitude of applied bias, with the low-bias range dominated by the trap-assisted Fowler-Nordheim tunneling through the interface and the high-bias range limited by the hopping conduction through the bulk. Phenomenological analysis of the I-V curves has further revealed that the transition between the low- and high-bias regimes is manifested both in the strength of variations within the I-V curves sampled across the surface, as well as the spatial distribution of conductance. Spatial variations were concluded to originate primarily from the heterogeneity of the interfacial electronic barrier height with an additional small contribution from random changes in the tip-contact geometry.

• Dynamic conductivity of ferroelectric domain walls in BiFeO₃.

  Authors: Peter Maksymovych, Jan Seidel, Ying Hao Chu, Pingping Wu, Arthur P Baddorf, Long-Qing Chen, Sergei V Kalinin, Ramamoorthy Ramesh

  Nano letters. 05/2011; 11(5):1906-12.

  Topological walls separating domains of continuous polarization, magnetization, and strain in ferroic materials hold promise of novel electronic properties, that are intrinsically localized on theTopological walls separating domains of continuous polarization, magnetization, and strain in ferroic materials hold promise of novel electronic properties, that are intrinsically localized on the nanoscale and that can be patterned on demand without change of material volume or elemental composition. We have revealed that ferroelectric domain walls in multiferroic BiFeO(3) are inherently dynamic electronic conductors, closely mimicking memristive behavior and contrary to the usual assumption of rigid conductivity. Applied electric field can cause a localized transition between insulating and conducting domain walls, tune domain wall conductance by over an order of magnitude, and create a quasicontinuous spectrum of metastable conductance states. Our measurements identified that subtle and microscopically reversible distortion of the polarization structure at the domain wall is at the origin of the dynamic conductivity. The latter is therefore likely to be a universal property of topological defects in ferroelectric semiconductors.

• Gold adatom as a key structural component in self-assembled monolayers of organosulfur molecules on Au(111)

  Authors: Peter Maksymovych, Oleksandr Voznyy, Daniel B. Dougherty, Dan C. Sorescu, John T. Yates Jr.

  Progress in Surface Science. 05/2010; 85:206-240.

  Chemisorption of organosulfur molecules, such as alkanethiols, arenethiols and disulfide compounds on gold surfaces and their subsequent self-organization is the archetypal process for molecularChemisorption of organosulfur molecules, such as alkanethiols, arenethiols and disulfide compounds on gold surfaces and their subsequent self-organization is the archetypal process for molecular self-assembly on surfaces. Owing to their ease of preparation and high versatility, alkanethiol self-assembled monolayers (SAMs) have been widely studied for potential applications including surface functionalization, molecular motors, molecular electronics, and immobilization of biological molecules. Despite fundamental advances, the dissociative chemistry of the sulfur headgroup on gold leading to the formation of the sulfur–gold anchor bond has remained controversial. This review summarizes the recent progress in the understanding of the geometrical and electronic structure of the anchor bond. Particular attention is drawn to the involvement of gold adatoms at all stages of alkanethiol self-assembly, including the dissociation of the disulfide (S–S) and hydrogen-sulfide (S–H) bonds and subsequent forma

• Defect-mediated polarization switching in ferroelectrics and related materials: from mesoscopic mechanisms to atomistic control.

  Authors: Sergei V Kalinin, Brian J Rodriguez, Albina Y Borisevich, Arthur P Baddorf, Nina Balke, Hye Jung Chang, Long-Qing Chen, Samrat Choudhury, Stephen Jesse, Peter Maksymovych, Maxim P Nikiforov, Stephen J Pennycook

  Advanced materials (Deerfield Beach, Fla.). 01/2010; 22(3):314-22.

  The plethora of lattice and electronic behaviors in ferroelectric and multiferroic materials and heterostructures opens vistas into novel physical phenomena including magnetoelectric coupling andThe plethora of lattice and electronic behaviors in ferroelectric and multiferroic materials and heterostructures opens vistas into novel physical phenomena including magnetoelectric coupling and ferroelectric tunneling. The development of new classes of electronic, energy-storage, and information-technology devices depends critically on understanding and controlling field-induced polarization switching. Polarization reversal is controlled by defects that determine activation energy, critical switching bias, and the selection between thermodynamically equivalent polarization states in multiaxial ferroelectrics. Understanding and controlling defect functionality in ferroelectric materials is as critical to the future of oxide electronics and solid-state electrochemistry as defects in semiconductors are for semiconductor electronics. Here, recent advances in understanding the defect-mediated switching mechanisms, enabled by recent advances in electron and scanning probe microscopy, are discussed. The synergy between local probes and structural methods offers a pathway to decipher deterministic polarization switching mechanisms on the level of a single atomically defined defect.

• The role of gold adatoms and stereochemistry in self-assembly of methylthiolate on Au(111).

  Authors: Oleksandr Voznyy, Jan J Dubowski, J T Yates, Peter Maksymovych

  Journal of the American Chemical Society. 10/2009; 131(36):12989-93.

  On the basis of high resolution STM images and DFT modeling, we have resolved low- and high-coverage structures of methylthiolate (CH(3)S) self-assembled on the Au(111) surface. The key new findingOn the basis of high resolution STM images and DFT modeling, we have resolved low- and high-coverage structures of methylthiolate (CH(3)S) self-assembled on the Au(111) surface. The key new finding is that the building block of all these structures has the same stoichiometry of two thiolate species joined by a gold adatom. The self-arrangement of the methylthiolate-adatom complexes on the surface depends critically on their stereochemical properties. Variations of the latter can produce local ordering of adatom complexes with either (3 x 4) or (3 x 4 square root(3)) periodicity. A possible structural connection between the (3 x 4 square root(3)) structure and commonly observed (square root(3) x square root(3))R30 degrees phase in methylthiolate self-assembled monolayers is developed by taking into account the reduction in the long-range order and stereochemical isomerization at high coverage. We also suggest how the observed self-arrangements of methylthiolate may be related to the c(4 x 2) phase of its longer homologues.

• Polarization control of electron tunneling into ferroelectric surfaces.

  Authors: Peter Maksymovych, Stephen Jesse, Pu Yu, Ramamoorthy Ramesh, Arthur P Baddorf, Sergei V Kalinin

  Science (New York, N.Y.). 07/2009; 324(5933):1421-5.

  We demonstrate a highly reproducible control of local electron transport through a ferroelectric oxide via its spontaneous polarization. Electrons are injected from the tip of an atomic forceWe demonstrate a highly reproducible control of local electron transport through a ferroelectric oxide via its spontaneous polarization. Electrons are injected from the tip of an atomic force microscope into a thin film of lead-zirconate titanate, Pb(Zr0.2Ti0.8)O3, in the regime of electron tunneling assisted by a high electric field (Fowler-Nordheim tunneling). The tunneling current exhibits a pronounced hysteresis with abrupt switching events that coincide, within experimental resolution, with the local switching of ferroelectric polarization. The large spontaneous polarization of the PZT film results in up to 500-fold amplification of the tunneling current upon ferroelectric switching. The magnitude of the effect is subject to electrostatic control via ferroelectric switching, suggesting possible applications in ultrahigh-density data storage and spintronics.

• Intrinsic nucleation mechanism and disorder effects in polarization switching on ferroelectric surfaces.

  Authors: Peter Maksymovych, Stephen Jesse, Mark Huijben, Ramamoorthy Ramesh, Anna Morozovska, Samrat Choudhury, Long-Qing Chen, Arthur P Baddorf, Sergei V Kalinin

  Physical review letters. 02/2009; 102(1):017601.

  The temperature dependence of ferroelectric domain nucleation in epitaxial films of BiFeO3 is studied using variable temperature ultrahigh vacuum piezoresponse force spectroscopy in the 50 to 300 KThe temperature dependence of ferroelectric domain nucleation in epitaxial films of BiFeO3 is studied using variable temperature ultrahigh vacuum piezoresponse force spectroscopy in the 50 to 300 K temperature range. The nucleation bias corresponding to the onset of local ferroelectric switching in the volume of an electrostatic field confined by the metal tip was found to change less than 20% across the entire temperature range. A combination of the analytical and phase-field analysis proves that the weak temperature dependence of nucleation bias is a hallmark of an intrinsic nucleation mechanism with minimal contribution of thermal fluctuations. The effect of disorder on the observed distribution of the nucleation bias between vacuum and ambient environments is compared.

• Collective reactivity of molecular chains self-assembled on a surface.

  Authors: Peter Maksymovych, Dan C Sorescu, Kenneth D Jordan, John T Yates

  Science (New York, N.Y.). 01/2009; 322(5908):1664-7.

  Self-assembly of molecules on surfaces is a route toward not only creating structures, but also engineering chemical reactivity afforded by the intermolecular interactions. DimethyldisulfideSelf-assembly of molecules on surfaces is a route toward not only creating structures, but also engineering chemical reactivity afforded by the intermolecular interactions. Dimethyldisulfide (CH3SSCH3) molecules self-assemble into linear chains on single-crystal gold surfaces. Injecting low-energy electrons into individual molecules in the self-assembled structures with the tip of a scanning tunneling microscope led to a propagating chemical reaction along the molecular chain as sulfur-sulfur bonds were broken and then reformed to produce new CH3SSCH3 molecules. Theoretical and experimental evidence supports a mechanism involving electron attachment followed by dissociation of a CH3SSCH3 molecule and initiation of a chain reaction by one or both of the resulting CH3S intermediates.

• Thermodynamics of nanodomain formation and breakdown in Scanning Probe Microscopy: Landau-Ginzburg-Devonshire approach

  Authors: Anna N. Morozovska, Eugene A. Eliseev, Sergei V. Svechnikov, Peter Maksymovych, Sergei V Kalinin

  12/2008;

  Thermodynamics of tip-induced nanodomain formation in scanning probe microscopy of ferroelectric films and crystals is studied using the Landau-Ginzburg-Devonshire phenomenological approach. TheThermodynamics of tip-induced nanodomain formation in scanning probe microscopy of ferroelectric films and crystals is studied using the Landau-Ginzburg-Devonshire phenomenological approach. The local redistribution of polarization induced by the biased probe apex is analyzed including the effects of polarization gradients, field dependence of dielectric properties, intrinsic domain wall width, and film thickness. The polarization distribution inside subcritical nucleus of the domain preceding the nucleation event is very smooth and localized below the probe, and the electrostatic field distribution is dominated by the tip. In contrast, polarization distribution inside the stable domain is rectangular-like, and the associated electrostatic fields clearly illustrate the presence of tip-induced and depolarization field components. The calculated coercive biases of domain formation are in a good agreement with available experimental results for typical ferroelectric materials. The microscopic origin of the observed domain tip elongation in the region where the probe electric field is much smaller than the intrinsic coercive field is the positive depolarization field in front of the moving counter domain wall. For infinitely thin domain walls local domain breakdown through the sample depth appears. The results obtained here are complementary to the Landauer-Molotskii energetic approach.

• Au adatoms in self-assembly of benzenethiol on the Au(111) surface.

  Authors: Peter Maksymovych, John T Yates

  Journal of the American Chemical Society. 07/2008; 130(24):7518-9.

• Nonlocal dissociative chemistry of adsorbed molecules induced by localized electron injection into metal surfaces.

  Authors: Peter Maksymovych, Daniel B Dougherty, X-Y Zhu, John T Yates

  Physical review letters. 08/2007; 99(1):016101.

  We present a novel approach to surface chemistry studies using scanning tunneling microscopy (STM), where dissociation of molecules adsorbed on metal surfaces is induced nonlocally in a 10-100 nmWe present a novel approach to surface chemistry studies using scanning tunneling microscopy (STM), where dissociation of molecules adsorbed on metal surfaces is induced nonlocally in a 10-100 nm radius around the STM tip by hot electrons that originate from the STM tip and transport on the surface. Nonlocal molecular excitation eliminates the influence of the STM tip on the outcome of the electron-induced chemical reaction. The spatial attenuation of the nonlocal reaction is used as a direct measure of hot-electron transport on the surface.

• Gold-adatom-mediated bonding in self-assembled short-chain alkanethiolate species on the Au(111) surface.

  Authors: Peter Maksymovych, Dan C Sorescu, John T Yates

  Physical review letters. 11/2006; 97(14):146103.

  Microscopic evidence for Au-adatom-induced self-assembly of alkanethiolate species on the Au(111) surface is presented. Based on STM measurements and density-functional theory calculations, a newMicroscopic evidence for Au-adatom-induced self-assembly of alkanethiolate species on the Au(111) surface is presented. Based on STM measurements and density-functional theory calculations, a new model for the low-coverage self-assembled monolayer of alkanethiolate on the Au(111) surface is developed, which involves the adsorbate complexes incorporating Au adatoms. It is also concluded that the Au(111) herringbone reconstruction is lifted by the alkanethiolate self-assembly because the reconstructed surface layer provides reactive Au adatoms that drive self-assembly.

• Methanethiolate adsorption site on Au(111): a combined STM/DFT study at the single-molecule level.

  Authors: Peter Maksymovych, Dan C Sorescu, John T Yates

  The journal of physical chemistry. B. 11/2006; 110(42):21161-7.

  The chemisorptive bonding of methanethiolate (CH(3)S) on the Au(111) surface has been investigated at a single-molecule level using low-temperature scanning tunneling microscopy (LT-STM) and densityThe chemisorptive bonding of methanethiolate (CH(3)S) on the Au(111) surface has been investigated at a single-molecule level using low-temperature scanning tunneling microscopy (LT-STM) and density functional theory (DFT). The CH(3)S species were produced by STM-tip-induced dissociation of methanethiol (CH(3)SH) or dimethyl disulfide (CH(3)SSCH(3)) at 5 K. The adsorption site of an isolated CH(3)S species was assigned by comparing the experimental and calculated STM images. We conclude that the S-headgroup of chemisorbed CH(3)S adsorbs on the 2-fold coordinated bridge site between two Au atoms, consistent with theoretical predictions for CH(3)S on the nondefective Au(111) surface. Our assignment is also supported by the freezing of the tip-induced rotational dynamics of a single CH(3)SH molecule upon conversion to CH(3)S via deprotonation.

• Propagation of conformation in the surface-aligned dissociation of single CH3SSCH3 molecules on Au(111).

  Authors: Peter Maksymovych, John T Yates

  Journal of the American Chemical Society. 09/2006; 128(33):10642-3.

  Single CH3SSCH3 molecules adsorb on the Au(111) surface in a trans-conformation. Subsequent electron-induced dissociation of CH3SSCH3 cleaves the S-S bond and produces a pair of CH3S fragments. TheSingle CH3SSCH3 molecules adsorb on the Au(111) surface in a trans-conformation. Subsequent electron-induced dissociation of CH3SSCH3 cleaves the S-S bond and produces a pair of CH3S fragments. The dissociation process was found to preserve the conformation of the parent molecule with a high probability of 75% and imprint it in the relative position and orientation of the product CH3S species on the surface. The high probability of the conformation-retaining scenario is likely due to surface alignment of the S-S bond-breaking reaction coordinate.

• Surface bonding and dynamical behavior of the CH3SH molecule on Au(111).

  Authors: Peter Maksymovych, Dan C Sorescu, Dan Dougherty, John T Yates

  The journal of physical chemistry. B. 01/2006; 109(47):22463-8.

  The chemisorption of the undissociated CH3SH molecule on the Au(111) surface has been studied at 5 K using scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. TheThe chemisorption of the undissociated CH3SH molecule on the Au(111) surface has been studied at 5 K using scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. The molecule was found to adsorb on atop Au sites on the defect-free surface. CH3SH undergoes hindered rotation about the Au-S bond on the defect-free surface which is seen in STM as a time-averaged 6-fold pattern. The pattern suggests that the potential minima directions occur for the rotating molecule at the six hollow sites surrounding the atop adsorption site. The barrier for rotation, obtained by DFT calculations, is approximately 0.1 kcal.mol(-1). At low coverages, preferential adsorption occurs at defect sites in the surface, namely, the herringbone "elbows" and random atomic step sites. Molecules adsorbed on these sites do not exhibit rotational freedom.

• Gold adatom as a key structural component in self-assembled monolayers of organosulfur molecules on Au(111)

  Authors: Peter Maksymovych, Oleksandr Voznyy, Daniel B. Dougherty, Dan C. Sorescu, John T. Yates

  Progress in Surface Science.

  Chemisorption of organosulfur molecules, such as alkanethiols, arenethiols and disulfide compounds on gold surfaces and their subsequent self-organization is the archetypal process for molecularChemisorption of organosulfur molecules, such as alkanethiols, arenethiols and disulfide compounds on gold surfaces and their subsequent self-organization is the archetypal process for molecular self-assembly on surfaces. Owing to their ease of preparation and high versatility, alkanethiol self-assembled monolayers (SAMs) have been widely studied for potential applications including surface functionalization, molecular motors, molecular electronics, and immobilization of biological molecules. Despite fundamental advances, the dissociative chemistry of the sulfur headgroup on gold leading to the formation of the sulfur–gold anchor bond has remained controversial. This review summarizes the recent progress in the understanding of the geometrical and electronic structure of the anchor bond. Particular attention is drawn to the involvement of gold adatoms at all stages of alkanethiol self-assembly, including the dissociation of the disulfide (S–S) and hydrogen-sulfide (S–H) bonds and subsequent formation of the self-assembled structure. Gold adatom chemistry is proposed here to be a unifying theme that explains various aspects of the alkanethiol self-assembly and reconciles experimental evidence provided by scanning probe microscopy and spectroscopic methods of surface science. While several features of alkanethiol self-assembly have yet to be revisited in light of the new adatom-based models, the successes of alkanethiol SAMs suggest that adatom-mediated surface chemistry may be a viable future approach for the construction of self-assembled monolayers involving molecules which do not contain sulfur.