H. Ito

Circularly polarized near-field optical mapping of spin-resolved quantum Hall chiral edge states.

We have successfully developed a circularly polarized near-field scanning optical microscope (NSOM) that enables us to irradiate circularly polarized light with spatial resolution below the diffraction limit. As a demonstration, we perform real-space mapping of the quantum Hall chiral edge states near the edge of a Hall-bar structure by injecting spin polarized electrons optically at low temperature. The obtained real-space mappings show that spin-polarized electrons are injected optically to the two-dimensional electron layer. Our general method to locally inject spins using a circularly polarized NSOM should be broadly applicable to characterize a variety of nanomaterials and nanostructures.

Dissociative Adsorption of Nitric Oxide on Si(111)-(7×7) Surface

The dissociative adsorption of nitric oxide (NO) on a Si(111)-(7×7) surface between 330 and 600 K was investigated using X-ray photoelectron spectroscopy (XPS). The uptake curves of both the N and O atoms as functions of NO exposure revealed a prominent temperature dependence for the dissociative adsorption of NO on a Si(111)-(7×7) surface. The decrease in the rates of the dissociative adsorption of NO with an increase in surface temperature (Ts) suggests that a precursor exists. Additionally, the number ratio of N atoms to O atoms on the surface (N/O ratio) changed from 1.0 (Ts = 330 K) to 1.2 (Ts = 600 K). This increase in N/O ratio with an increase in Ts suggests that an additional reaction path becomes available at higher Ts.

Real-space Mapping of Spin-resolved Quantum Hall Chiral Edge States by Near-field Scanning Optical Microscopy

The quantum Hall edge states are formed in the vicinity of the edge of a sample that hosts two-dimensional electron system (2DES) in a perpendicular magnetic field at low temperature. The bulk 2DES states rise up due to the confinement potential near the edge and intersect with the Fermi-level, forming current carrying compressible states. The compressible states are separated by insulating incompressible states. The distribution of the compressible/ incompressible states has been investigated by various scanning probe microscopy, however, there have been few reports on real-space mapping of spin-resolved quantum Hall edge states. Here we report on the first observation of spin-resolved chiral quantum Hall edge states by a low-temperature near-field scanning optical microscope.

Imaging of quantum Hall edge states under quasiresonant excitation by a near-field scanning optical microscope

A high resolution mapping of quantum Hall edge states has been performed by locally creating electrons with small excess energies with a near-field scanning optical microscope in a dilution refrigerator. We have observed fine structures parallel to the edge in photovoltage signals, which appear only at low temperature. The observed fine structures near sample edges have been seen to shift inward with increase in magnetic field in accordance with Chklovskii Shklovskii, and Glazman model.

Real‐space mapping of compressible and incompressible strips by a near‐field scanning optical microscope

Compressible and incompressible strips formed near the boundary of a two‐dimensional electron system were mapped out by near‐field scanning optical microscope at 230 mK. Dilution‐refrigerator based near‐field scanning optical microscope enables us to investigate spatial properties of the electrons in semiconductor nanostructures with a subwavelength spatial resolution. We obtain real‐space mapping of photovoltage in the vicinity of the edge of Hall‐bar, which reflects the local chemical potential determined by the distribution of the compressible and incompressible strips.

MAPPING OF QUANTUM-HALL EDGE CHANNELS BY A DILUTION-REFRIGERATOR BASED NEAR-FIELD SCANNING OPTICAL MICROSCOPE

A real-space mapping of photovoltage near the edge of the Hall-bar of a GaAs/AlGaAs single heterojunction has been obtained using a dilution-refrigerator-based near-field scanning optical microscope in magnetic fields. The optical probe-sample surface distance dependence of photovoltage is investigated. We obtain photovoltage profile in the vicinity of the edge, which reflects the local chemical potential of the two-dimensional electron gas determined by the distribution of the compressible and incompressible strips.

Fabrication of Highly Ordered Arrays of Nanoparticles by Mechanical Process

We have developed a new method of fabricating nanoparticles utilizing a mechanical rubbing process. Highly ordered arrays of Au nanoparticles with a diameter of 60 nm have been fabricated on a porous anodic alumina template. Pressure measurements during the mechanical rubbing process confirmed that these nanoparticles were formed only by a mechanical separation process. Our method can be applied to fabricate nanocapsules and has a wide range of applicability to materials that have never been controlled in the nanoscale.