Optical and magneto-optic Kerr effects of MnBi, Ni2MnGa, and Gd5Si2Ge2

The magneto-optic Kerr angle spectrum of a single crystal of MnBi was measured at room temperature and also calculated with the TB-LMTO methods including the spin-orbit interaction. Previously measured Kerr spectra with thin films had two negative peaks, except for one film grown in ultra high vacuum. The later had a first peak and a shoulder at the second peak position, indicating the second originated from oxygen in the other films. Comparing first-principles calculations and previous thin-film results with our single crystal data indicated that the second peak originated from the combination of a weak intrinsic MnBi peak and oxygen in the sample. The complex dielectric constants and magneto-optic Kerr spectra of electro-polished (100), (110), and (111) planes Ni2MnGa were measured. Also optical and magneto-optical spectra were calculated with the TB-LMTO methods including the spin-orbit interaction. Measured Kerr and optical spectra with three surfaces at room temperature had the same peak positions, but different amplitudes. The difference between (100) and (110) surfaces are probably due to the polishing process, not intrinsic bulk properties. Angle-dependent reflectance difference spectroscopy of (100), (010), and (001) planes Gd5Si2Ge2, and (100) plane Tb5Si2.2Ge1.8, which are optically anisotropic materials, were measured with the Kerr spectrometer by rotating the samples. The replacing the rare earth Gd to Tb atoms and 10% changing Ge to Si atoms did not change the spectra much. The complex dielectric constants of (100) and (001) planes Gd5Si2Ge2 were measured by the spectroscopic ellipsometer. Two reflectance differences, measured by the Kerr spectrometer at near normal incidence and converted from the dielectric constants measured by ellipsometer at oblique incidence, agreed well

Fabrication of submicron metallic grids with interference and phase-mask holography

Complex, submicron Cu metallic mesh nanostructures are made by electrochemical deposition using polymer templates made from photoresist. The polymer templates are fabricated with photoresist using two-beam interference holography and phase mask holography with three diffracted beams. Freestanding metallic mesh structures are made in two separate electrodepositions with perpendicular photoresist grating templates. Cu mesh square nanostructures having large (52.6%) open areas are also made by single electrodeposition with a photoresist template made with a phase mask. These structures have potential as electrodes in photonic devices

Cryogenic Magneto-Terahertz Scanning Near-field Optical Microscope (cm-SNOM)

We have developed a versatile near-field microscopy platform that can operate at high magnetic fields and below liquid-helium temperatures. We use this platform to demonstrate an extreme terahertz (THz) nanoscope operation and to obtain the first cryogenic magneto-THz time-domain nano-spectroscopy/imaging at temperatures as low as 1.8 K and magnetic fields of up to 5 T simultaneously. Our cryogenic magneto-THz scanning near-field optical microscopy, or cm-SNOM, instrument comprises three main equipment: i) a 5 T split pair magnetic cryostat with a custom made insert for mounting SNOM inside; ii) an atomic force microscope (AFM) unit that accepts ultrafast THz excitation and iii) a MHz repetition rate, femtosecond laser amplifier for high-field THz pulse generation and sensitive detection. We apply the cm-SNOM to obtain proof of principle measurements of superconducting and topological materials. The new capabilities demonstrated break grounds for studying quantum materials that requires extreme environment of cryogenic operation and applied magnetic fields simultaneously in nanometer space, femtosecond time, and terahertz energy scales

Angle-resolved photoemission study of the rare-earth intermetallic compounds: RNi2Ge2(R=Eu,Gd)

Experimental energy bands mapped from normal-emission photoelectron spectra of EuNi2Ge2 and GdNi2Ge2(001)surfaces show four photoemission features that disperse in both materials in good agreement with band calculations. Segments of the Fermi surfaces mapped by angle-resolved photoemission spectroscopy in the ΓXPZ plane of the Brillouin zones for both EuNi2Ge2 and GdNi2Ge2 are in good agreement with band calculations. This Fermi surface segment changes when one electron is added to EuNi2Ge2, corresponding to GdNi2Ge2, based on the rigid-band approximation

Photonic crystal: energy-related applications

We review recent work on photonic-crystal fabrication using soft-lithography techniques. We consider applications of the resulting structures in energy-related areas such as lighting and solar-energy harvesting. In general, our aim is to introduce the reader to the concepts of photonic crystals, describe their history, development, and fabrication techniques and discuss a selection of energy-related applications

High aspect ratio nanoscale metallic structures as transparent electrodes

A novel technique based on the two polymer micro-transfer molding (2-P μTM) for fabricating one dimensional (1D) high aspect ratio nanoscale metallic structures is presented and experimental characterization is described. Glancing angle metal deposition and physical argon ion milling (etching) techniques were also employed in processing. The resulting metallic structures have high transmission (~80%) in the visible spectrum and have superior electrical conductivity (resistance from 2.4 -7.3 Ω) compared to standard indium-tin oxide (ITO) glass. Thus, the high aspect ratio metallic structures are a promising alternative with potentially superior performances to ITO glass as transparent electrodes for organic solar cells

Soft lithography microlens fabrication and array for enhanced light extraction from organic light emitting diodes (OLEDs)

Provided are microlens arrays for use on the substrate of OLEDs to extract more light that is trapped in waveguided modes inside the devices and methods of manufacturing same. Light extraction with microlens arrays is not limited to the light emitting area, but is also efficient in extracting light from the whole microlens patterned area where waveguiding occurs. Large microlens array, compared to the size of the light emitting area, extract more light and result in over 100% enhancement. Such a microlens array is not limited to (O)LEDs of specific emission, configuration, pixel size, or pixel shape. It is suitable for all colors, including white, for microcavity OLEDs, and OLEDs fabricated directly on the (modified) microlens array

Soft holographic interference lithography microlens for enhanced organic light emitting diode light extraction

Very uniform 2 μm-pitch square microlens arrays (μLAs), embossed on the blank glass side of an indium-tin-oxide (ITO)-coated 1.1 mm-thick glass, are used to enhance light extraction from organic light-emitting diodes (OLEDs) by ~100%, significantly higher than enhancements reported previously. The array design and size relative to the OLED pixel size appear to be responsible for this enhancement. The arrays are fabricated by very economical soft lithography imprinting of a polydimethylsiloxane (PDMS) mold (itself obtained from a Ni master stamp that is generated from holographic interference lithography of a photoresist) on a UV-curable polyurethane drop placed on the glass. Green and blue OLEDs are then fabricated on the ITO to complete the device. When the μLA is ~15 × 15 mm2, i.e., much larger than the ~3 × 3 mm2 OLED pixel, the electroluminescence (EL) in the forward direction is enhanced by ~100%. Similarly, a 19 × 25 mm2μLA enhances the EL extracted from a 3 × 3 array of 2 × 2 mm2 OLED pixels by 96%. Simulations that include the effects of absorption in the organic and ITO layers are in accordance with the experimental results and indicate that a thinner 0.7 mm thick glass would yield a ~140% enhancement