Spectrally Tunable Ultrafast Long Wave Infrared Detection at Room Temperature.

Room-temperature longwave infrared (LWIR) detectors are preferred over cryogenically cooled solutions due to the cost effectiveness and ease of operation. The performance of present uncooled LWIR detectors such as microbolometers, is limited by reduced sensitivity, slow response time, and the lack of dynamic spectral tunability. Here, we present a graphene-based efficient room-temperature LWIR detector with high detectivity and fast response time utilizing its tunable optical and electronic characteristics.

Dirac plasmon-assisted asymmetric hot carrier generation for room-temperature infrared detection.

Due to the low photon energy, detection of infrared photons is challenging at room temperature. Thermoelectric effect offers an alternative mechanism bypassing material bandgap restriction. In this article, we demonstrate an asymmetric plasmon-induced hot-carrier Seebeck photodetection scheme at room temperature that exhibits a remarkable responsivity of 2900 VW, detectivity of 1.

Multi-spectral frequency selective mid-infrared microbolometers.

Frequency selective detection of low energy photons is a scientific challenge using natural materials. A hypothetical surface which functions like a light funnel with very low thermal mass in order to enhance photon collection and suppress background thermal noise is the ideal solution to address both low temperature and frequency selective detection limitations of present detection systems. Here, we present a cavity-coupled quasi-three dimensional plasmonic crystal which induces impedance matching to the free space giving rise to extraordinary transmission through the sub-wavelength aperture array like a "light funnel" in coupling low energy incident photons resulting in frequency selective perfect (~100%) absorption of the incident radiation and zero back reflection.

Wide Angle Dynamically Tunable Enhanced Infrared Absorption on Large-Area Nanopatterned Graphene.

Enhancing light-matter interaction by exciting Dirac plasmons on nanopatterned monolayer graphene is an efficient route to achieve high infrared absorption. Here, we designed and fabricated hexagonal planar arrays of nanoholes and nanodisks with and without optical cavity to excite Dirac plasmons on patterned graphene and investigate the role of plasmon lifetime, extinction cross-section, incident light polarization, angle of incident light, and pattern dimensions on the light-absorption spectra. By incorporating a high-k AlO layer as the gate dielectric for dynamic electrostatic tuning of the Fermi level, we demonstrate peak absorptions of 60% and 90% for the nanohole and nanodisk patterns, respectively, in the atmospheric transparent 8-12 μm infrared imaging band with high spectral tunability.

Epitaxial magnetite nanorods with enhanced room temperature magnetic anisotropy.

Nanostructured magnetic materials with well-defined magnetic anisotropy are very promising as building blocks in spintronic devices that operate at room temperature. Here we demonstrate the epitaxial growth of highly oriented FeO nanorods on a SrTiO substrate by hydrothermal synthesis without the use of a seed layer. The epitaxial nanorods showed biaxial magnetic anisotropy with an order of magnitude difference between the anisotropy field values of the easy and hard axes.

Exchange Bias Effects in Iron Oxide-Based Nanoparticle Systems.

The exploration of exchange bias (EB) on the nanoscale provides a novel approach to improving the anisotropic properties of magnetic nanoparticles for prospective applications in nanospintronics and nanomedicine. However, the physical origin of EB is not fully understood. Recent advances in chemical synthesis provide a unique opportunity to explore EB in a variety of iron oxide-based nanostructures ranging from core/shell to hollow and hybrid composite nanoparticles.

Exchange bias effect in Au-Fe3O4 nanocomposites.

We report exchange bias (EB) effect in the Au-Fe3O4 composite nanoparticle system, where one or more Fe3O4 nanoparticles are attached to an Au seed particle forming 'dimer' and 'cluster' morphologies, with the clusters showing much stronger EB in comparison with the dimers. The EB effect develops due to the presence of stress at the Au-Fe3O4 interface which leads to the generation of highly disordered, anisotropic surface spins in the Fe3O4 particle. The EB effect is lost with the removal of the interfacial stress.

Inverse magnetocaloric and exchange bias effects in single crystalline La0.5Sr0.5MnO3 nanowires.

We report the first observation of inverse magnetocaloric effect (IMCE) in hydrothermally synthesized single crystalline La0.5Sr0.5MnO3 nanowires.

Magnetic entropy change in core/shell and hollow nanoparticles.

The development of positive magnetic entropy change in the case of ferromagnetic (FM) nanostructures is a rare occurrence. We observe positive magnetic entropy change in core/shell (Fe/γ-Fe2O3) and hollow (γ-Fe2O3) nanoparticles and its origin is attributed to a disordered state in the nanoparticles due to the random distribution of anisotropy axes which inhibits any long range FM ordering. The effect of the energy barrier distribution on the magnetic entropy change and its impact on the universal behavior based on rescaled entropy change curves for core/shell and hollow nanostructures is discussed.

Mechanism and controlled growth of shape and size variant core/shell FeO/Fe3O4 nanoparticles.

We report a novel synthesis approach for the growth of core/shell FeO/Fe3O4 nanoparticles with controlled shape and size. FeO particles were partially oxidized to form core/shell FeO/Fe3O4 structures, as evidenced from transmission electron microscopy, X-ray diffraction, and magnetometry analysis. We find that the molar ratios and concentrations of surfactants are the key parameters in controlling the particle size.

Evidence of a canted magnetic state in self-doped LaMnO(3+δ) (δ = 0.04): a magnetocaloric study.

We report a detailed investigation of the magnetocaloric properties of self-doped polycrystalline LaMnO(3+δ) with δ = 0.04. Due to the self-doping effect, the system exhibits a magnetic transition from a paramagnetic to ferromagnetic-like canted magnetic state (CMS) at ~120 K, which is associated with an appreciably large magnetocaloric effect (MCE).

Carbon nanostraws: nanotubes filled with superparamagnetic nanoparticles.

A two-step magnetically assisted capillary action method is demonstrated as a facile technique to produce hollow carbon nanotubes filled with uniformly dispersed Fe3O4 nanoparticles (NPs). Template-assisted chemical vapor deposition (CVD) grown CNTs with average diameter 200-300 nm and length 5-6 microm were effectively used as 'nanostraws' to suck in chemically synthesized Fe3O4 nanoparticles (mean size approximately 6 nm) in a ferrofluid suspension. Temperature and magnetic field-dependent DC magnetization measurements indicate that these functionalized nanotubes are superparamagnetic at room temperature with enhanced interparticle interactions due to the close packing of the nanoparticles within the tubes.