Broadband tunability is a central theme in contemporary nanophotonics and metamaterials research. Combining metamaterials with phase change media offers a promising approach to achieve such ...tunability, which requires a comprehensive investigation of the electromagnetic responses of novel materials at subwavelength scales. In this work, we demonstrate an innovative way to tailor band-selective electromagnetic responses at the surface of a heavy fermion compound, samarium sulfide (SmS). By utilizing the intrinsic, pressure sensitive, and multi-band electron responses of SmS, we create a proof-of-principle heavy fermion metamaterial, which is fabricated and characterized using scanning near-field microscopes with <50 nm spatial resolution. The optical responses at the infrared and visible frequency ranges can be selectively and separately tuned via modifying the occupation of the 4f and 5d band electrons. The unique pressure, doping, and temperature tunability demonstrated represents a paradigm shift for nanoscale metamaterial and metasurface design.
Terahertz Nanoimaging of Graphene Zhang, Jiawei; Chen, Xinzhong; Mills, Scott ...
ACS photonics,
07/2018, Volume:
5, Issue:
7
Journal Article
Accessing the nonradiative near-field electromagnetic interactions with high in-plane momentum (q) is the key to achieve super resolution imaging far beyond the diffraction limit. At far-infrared and ...terahertz (THz) wavelengths (e.g., 300 μm = 1 terahertz = 4 meV), the study of high q response and nanoscale near-field imaging is still a nascent research field. In this work, we report on THz nanoimaging of exfoliated single and multilayer graphene flakes by using a state-of-the-art scattering-type near-field optical microscope (s-SNOM). We experimentally demonstrated that the single layer graphene is close to a perfect near-field reflector at ambient environment, comparable to that of the noble metal films at the same frequency range. Further modeling and analysis considering the nonlocal graphene conductivity indicate that the high near-field reflectivity of graphene is a rather universal behavior: graphene operates as a perfect high-q reflector at room temperature. Our work uncovers the unique high-q THz response of graphene, which is essential for future applications of graphene in nano-optics or tip-enhanced technologies.
The Mott insulatorCa2RuO4is the subject of much recent attention following reports of emergent nonequilibrium steady states driven by applied electric fields or currents. In this paper, we carry out ...infrared nano-imaging and optical-microscopy measurements on bulk single crystalCa2RuO4under conditions of steady current flow to obtain insight into the current-driven insulator-to-metal transition. We observe macroscopic growth of the current-induced metallic phase, with nucleation regions for metal and insulator phases determined by the polarity of the current flow. A remarkable metal-insulator-metal microstripe pattern is observed at the phase front separating metal and insulator phases. The microstripes have orientations tied uniquely to the crystallographic axes, implying a strong coupling of the electronic transition to lattice degrees of freedom. Theoretical modeling further illustrates the importance of the current density and confirms a submicron-thick surface metallic layer at the phase front of the bulk metallic phase. Our work confirms that the electrically induced metallic phase is nonfilamentary and is not driven by Joule heating, revealing remarkable new characteristics of electrically induced insulator-metal transitions occurring in functional correlated oxides.
In this letter, we report optical pump terahertz (THz) near-field probe (n-OPTP) and optical pump THz near-field emission (n-OPTE) experiments of graphene/InAs heterostructures. Near-field imaging ...contrasts between graphene and InAs using these newly developed techniques as well as spectrally integrated THz nano-imaging (THz s-SNOM) are systematically studied. We demonstrate that in the near-field regime (λ/6000), a single layer of graphene is transparent to near-IR (800 nm) optical excitation and completely "screens" the photo-induced far-infrared (THz) dynamics in its substrate (InAs). Our work reveals unique frequency-selective ultrafast dynamics probed at the near field. It also provides strong evidence that n-OPTE nanoscopy yields contrast that distinguishes single-layer graphene from its substrate.
The Mott insulator Ca2RuO4 is the subject of much recent attention following reports of emergent nonequilibrium steady states driven by applied electric fields or currents. In this paper, we carry ...out infrared nano-imaging and optical-microscopy measurements on bulk single crystal Ca2RuO4 under conditions of steady current flow to obtain insight into the current-driven insulator-tometal transition. We observe macroscopic growth of the current-induced metallic phase, with nucleation regions for metal and insulator phases determined by the polarity of the current flow. A remarkable metal-insulator-metal microstripe pattern is observed at the phase front separating metal and insulator phases. The microstripes have orientations tied uniquely to the crystallographic axes, implying a strong coupling of the electronic transition to lattice degrees of freedom. Theoretical modeling further illustrates the importance of the current density and confirms a submicron-thick surface metallic layer at the phase front of the bulk metallic phase. Our work confirms that the electrically induced metallic phase is nonfilamentary and is not driven by Joule heating, revealing remarkable new characteristics of electrically induced insulator-metal transitions occurring in functional correlated oxides.
The Mott insulator Ca_{2}RuO_{4} is the subject of much recent attention following reports of emergent nonequilibrium steady states driven by applied electric fields or currents. In this paper, we ...carry out infrared nano-imaging and optical-microscopy measurements on bulk single crystal Ca_{2}RuO_{4} under conditions of steady current flow to obtain insight into the current-driven insulator-to-metal transition. We observe macroscopic growth of the current-induced metallic phase, with nucleation regions for metal and insulator phases determined by the polarity of the current flow. A remarkable metal-insulator-metal microstripe pattern is observed at the phase front separating metal and insulator phases. The microstripes have orientations tied uniquely to the crystallographic axes, implying a strong coupling of the electronic transition to lattice degrees of freedom. Theoretical modeling further illustrates the importance of the current density and confirms a submicron-thick surface metallic layer at the phase front of the bulk metallic phase. Our work confirms that the electrically induced metallic phase is nonfilamentary and is not driven by Joule heating, revealing remarkable new characteristics of electrically induced insulator-metal transitions occurring in functional correlated oxides.
Curved X‐ray detectors have the potential to revolutionize diverse sectors due to benefits such as reduced image distortion and vignetting compared to their planar counterparts. While the use of ...inorganic semiconductors for curved detectors are restricted by their brittle nature, organic–inorganic hybrid semiconductors which incorporated bismuth oxide nanoparticles in an organic bulk heterojunction consisting of poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) and 6,6‐phenyl C71 butyric acid methyl ester (PC70BM) are considered to be more promising in this regard. However, the influence of the P3HT molecular weight on the mechanical stability of curved, thick X‐ray detectors remains less well understood. Herein, high P3HT molecular weights (>40 kDa) are identified to allow increased intermolecular bonding and chain entanglements, resulting in X‐ray detectors that can be curved to a radius as low as 1.3 mm with low deviation in X‐ray response under 100 repeated bending cycles while maintaining an industry‐standard dark current of <1 pA mm−2 and a sensitivity of ≈ 0.17 μC Gy−1 cm−2. This study identifies a crucial missing link in the development of curved detectors, namely the importance of the molecular weight of the polymer semiconductors used.
Solution processable organic–inorganic hybrid semiconductors for flexible curved X‐ray detector components have the potential to revolutionize diverse sectors in terms of its cost and performance. This work introduces a strategy for realizing the optimum balance for detector performance at low operating voltages with mechanical flexibility by tuning the organic semiconductor molecular weight for such curved hybrid detectors.
In this paper, we present a high performance planar 20nm CMOS bulk technology for low power mobile (LPM) computing applications featuring an advanced high-k metal gate (HKMG) process, strain ...engineering, 64nm metal pitch & ULK dielectrics. Compared with 28nm low power technology, it offers 0.55X density scaling and enables significant frequency improvement at lower standby power. Device drive current up to 2X 28nm at equivalent leakage is achieved through co-optimization of HKMG process and strain engineering. A fully functional, high-density (0.081um 2 bit-cell) SRAM is reported with a corresponding Static Noise Margin (SNM) of 160mV at 0.9V. An advanced patterning and metallization scheme based on ULK dielectrics enables high density wiring with competitive R-C.
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