chunjuan zhang - Academia.edu (original) (raw)

Papers by chunjuan zhang

Nature Nanotechnology, 2007

As dimensions of a metallic conductor is reduced, spin-dependent conductance quantization in unit... more As dimensions of a metallic conductor is reduced, spin-dependent conductance quantization in units of e^2/hleads to unusual magnetoresistive phenomena. One of them is ballistic anisotropic magnetoresistance (BAMR), a quantized change in the ballistic conductance according to the direction of magnetization. Here we present a first observation of BAMR in Co electrodeposited nanocontacts by in-situ investigation of their spin-dependent transport properties. We compare the results from electrochemically synthesized and break junction contacts. By measuring the conductance as a function of the applied magnetic field direction at saturation, we find the step-wise variation of the ballistic conductance, signature of the BAMR effect. Our results show that BAMR can be positive and negative, and have symmetric and asymmetric angular dependence. This behavior is explained using a simple tight-binding model in terms of the effect of the spin-orbit interaction on the electronic band structure of nanocontacts.

Chemical Physics Letters, 2003

Ovchenkov, Y.A.; Geisler, H.; Burst, J.M.; Thornburg, S.N.; Ventrice , C.A. Jr.; Zhang, Chunjuan ... more Ovchenkov, Y.A.; Geisler, H.; Burst, J.M.; Thornburg, S.N.; Ventrice , C.A. Jr.; Zhang, Chunjuan ; Redepenning, Jody; Losovyj, Y.; Rosa, Luis; Dowben, Peter A.; and Doudin, B., "The electronic structure of metal/alkane thiol self-assembled monolayers/metal junctions for magnetoelectronics applications" (2003). Jody Redepenning Publications. Paper 2.

Nature Nanotechnology, 2007

When the dimensions of a metallic conductor are reduced so that they become comparable to the de ... more When the dimensions of a metallic conductor are reduced so that they become comparable to the de Broglie wavelengths of the conduction electrons, the absence of scattering results in ballistic electron transport 1 and the conductance becomes quantized 2, 3, 4 . In ferromagnetic metals, the spin angular momentum of the electrons results in spin-dependent conductance quantization 5, 6, 7 and various unusual magnetoresistive phenomena . Theorists have predicted a related phenomenon known as ballistic anisotropic magnetoresistance (BAMR) 13 . Here we report the fi rst experimental evidence for BAMR by observing a stepwise variation in the ballistic conductance of cobalt nanocontacts as the direction of an applied magnetic fi eld is varied. Our results show that BAMR can be positive and negative, and exhibits symmetric and asymmetric angular dependences, consistent with theoretical predictions.

Nature Materials, 2010

Photoelectron spectroscopic measurements have the potential to provide detailed mechanistic insig... more Photoelectron spectroscopic measurements have the potential to provide detailed mechanistic insight by resolving chemical states, electrochemically active regions and local potentials or potential losses in operating solid oxide electrochemical cells (SOCs), such as fuel cells. However, high-vacuum requirements have limited X-ray photoelectron spectroscopy (XPS) analysis of electrochemical cells to ex situ investigations. Using a combination of ambient-pressure XPS and CeO2-x/YSZ/Pt single-chamber cells, we carry out in situ spectroscopy to probe oxidation states of all exposed surfaces in operational SOCs at 750°C in 1mbar reactant gases H2 and H2O. Kinetic energy shifts of core-level photoelectron spectra provide a direct measure of the local surface potentials and a basis for calculating local overpotentials across exposed interfaces. The mixed ionic/electronic conducting CeO2-x electrodes undergo Ce3+/Ce4+ oxidation-reduction changes with applied bias. The simultaneous measurements of local surface Ce oxidation states and electric potentials reveal the active ceria regions during H2 electro-oxidation and H2O electrolysis. The active regions extend ~150μm from the current collectors and are not limited by the three-phase-boundary interfaces associated with other SOC materials. The persistence of the Ce3+/Ce4+ shifts in the ~150μm active region suggests that the surface reaction kinetics and lateral electron transport on the thin ceria electrodes are co-limiting processes.

Physical Chemistry Chemical Physics, 2010

Interfacial systems chemistry: out of the vacuum-through the liquid-into the cell Phys. Chem. Che... more Interfacial systems chemistry: out of the vacuum-through the liquid-into the cell Phys. Chem. Chem. Phys.

Nature Nanotechnology, 2007

As dimensions of a metallic conductor is reduced, spin-dependent conductance quantization in unit... more As dimensions of a metallic conductor is reduced, spin-dependent conductance quantization in units of e^2/hleads to unusual magnetoresistive phenomena. One of them is ballistic anisotropic magnetoresistance (BAMR), a quantized change in the ballistic conductance according to the direction of magnetization. Here we present a first observation of BAMR in Co electrodeposited nanocontacts by in-situ investigation of their spin-dependent transport properties. We compare the results from electrochemically synthesized and break junction contacts. By measuring the conductance as a function of the applied magnetic field direction at saturation, we find the step-wise variation of the ballistic conductance, signature of the BAMR effect. Our results show that BAMR can be positive and negative, and have symmetric and asymmetric angular dependence. This behavior is explained using a simple tight-binding model in terms of the effect of the spin-orbit interaction on the electronic band structure of nanocontacts.

Chemical Physics Letters, 2003

Ovchenkov, Y.A.; Geisler, H.; Burst, J.M.; Thornburg, S.N.; Ventrice , C.A. Jr.; Zhang, Chunjuan ... more Ovchenkov, Y.A.; Geisler, H.; Burst, J.M.; Thornburg, S.N.; Ventrice , C.A. Jr.; Zhang, Chunjuan ; Redepenning, Jody; Losovyj, Y.; Rosa, Luis; Dowben, Peter A.; and Doudin, B., "The electronic structure of metal/alkane thiol self-assembled monolayers/metal junctions for magnetoelectronics applications" (2003). Jody Redepenning Publications. Paper 2.

Nature Nanotechnology, 2007

When the dimensions of a metallic conductor are reduced so that they become comparable to the de ... more When the dimensions of a metallic conductor are reduced so that they become comparable to the de Broglie wavelengths of the conduction electrons, the absence of scattering results in ballistic electron transport 1 and the conductance becomes quantized 2, 3, 4 . In ferromagnetic metals, the spin angular momentum of the electrons results in spin-dependent conductance quantization 5, 6, 7 and various unusual magnetoresistive phenomena . Theorists have predicted a related phenomenon known as ballistic anisotropic magnetoresistance (BAMR) 13 . Here we report the fi rst experimental evidence for BAMR by observing a stepwise variation in the ballistic conductance of cobalt nanocontacts as the direction of an applied magnetic fi eld is varied. Our results show that BAMR can be positive and negative, and exhibits symmetric and asymmetric angular dependences, consistent with theoretical predictions.

Nature Materials, 2010

Photoelectron spectroscopic measurements have the potential to provide detailed mechanistic insig... more Photoelectron spectroscopic measurements have the potential to provide detailed mechanistic insight by resolving chemical states, electrochemically active regions and local potentials or potential losses in operating solid oxide electrochemical cells (SOCs), such as fuel cells. However, high-vacuum requirements have limited X-ray photoelectron spectroscopy (XPS) analysis of electrochemical cells to ex situ investigations. Using a combination of ambient-pressure XPS and CeO2-x/YSZ/Pt single-chamber cells, we carry out in situ spectroscopy to probe oxidation states of all exposed surfaces in operational SOCs at 750°C in 1mbar reactant gases H2 and H2O. Kinetic energy shifts of core-level photoelectron spectra provide a direct measure of the local surface potentials and a basis for calculating local overpotentials across exposed interfaces. The mixed ionic/electronic conducting CeO2-x electrodes undergo Ce3+/Ce4+ oxidation-reduction changes with applied bias. The simultaneous measurements of local surface Ce oxidation states and electric potentials reveal the active ceria regions during H2 electro-oxidation and H2O electrolysis. The active regions extend ~150μm from the current collectors and are not limited by the three-phase-boundary interfaces associated with other SOC materials. The persistence of the Ce3+/Ce4+ shifts in the ~150μm active region suggests that the surface reaction kinetics and lateral electron transport on the thin ceria electrodes are co-limiting processes.

Physical Chemistry Chemical Physics, 2010

Interfacial systems chemistry: out of the vacuum-through the liquid-into the cell Phys. Chem. Che... more Interfacial systems chemistry: out of the vacuum-through the liquid-into the cell Phys. Chem. Chem. Phys.