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Dingbo Chen, Junbo Yang, Jingjing Zhang, Jie Huang, Zhaojian Zhang
A novel metamaterial structure consisting of multiple graphene/dielectric layers and metallic substrate is proposed to achieve the broadband absorption response at terahertz (THz) frequencies. Utilizing the phase modulation effect generated by graphene ribbons, the bright-dark field is formed to suppress the reflection based on interference theory in a wide period. By irregularly stacking four graphene ribbons of varying widths on four dielectric layers with unequal thickness in a period, we merge successive absorption peaks into a broadband absorption spectrum successfully...
November 20, 2017: Scientific Reports
Cherif Belacel, Yanko Todorov, Stefano Barbieri, Djamal Gacemi, Ivan Favero, Carlo Sirtori
Most of the common technologies for detecting terahertz photons (>1 THz) at room temperature rely on slow thermal devices. The realization of fast and sensitive detectors in this frequency range is indeed a notoriously difficult task. Here we propose a novel device consisting of a subwavelength terahertz meta-atom resonator, which integrates a nanomechanical element and allows energy exchange between the mechanical motion and the electromagnetic degrees of freedom. An incident terahertz wave thus produces a nanomechanical signal that can be read out optically with high precision...
November 17, 2017: Nature Communications
Long Ju, Lei Wang, Ting Cao, Takashi Taniguchi, Kenji Watanabe, Steven G Louie, Farhan Rana, Jiwoong Park, James Hone, Feng Wang, Paul L McEuen
Excitons, the bound states of an electron and a hole in a solid material, play a key role in the optical properties of insulators and semiconductors. Here, we report the observation of excitons in bilayer graphene (BLG) using photocurrent spectroscopy of high-quality BLG encapsulated in hexagonal boron nitride. We observed two prominent excitonic resonances with narrow line widths that are tunable from the mid-infrared to the terahertz range. These excitons obey optical selection rules distinct from those in conventional semiconductors and feature an electron pseudospin winding number of 2...
November 17, 2017: Science
Kieran Hand, Edwin Yates
Conditions on exoplanets include elevated temperatures and pressures. The response of carbon-based biological macromolecules to such conditions is then relevant to the viability of life. The capacity of proteins and ribozymes to catalyse reactions or bind receptors, and nucleic acids to convey information, depends on them sampling different conformational states. These are determined by macromolecular vibrational states, or phonon modes, accessible using terahertz (THz: 10(12)Hz) absorption spectroscopy. THz spectra of biological macromolecules exhibit broad absorption at approximately 6 THz (equating to approx...
November 2017: Journal of the Royal Society, Interface
Mostafa Shalaby, Carlo Vicario, Christoph P Hauri
Charge-coupled devices (CCDs) are a well-established imaging technology in the visible and x-ray frequency ranges. However, the small quantum photon energies of terahertz radiation have hindered the use of this mature semiconductor technological platform in this frequency range, leaving terahertz imaging totally dependent on low-resolution bolometer technologies. Recently, it has been shown that silicon CCDs can detect terahertz photons at a high field, but the detection sensitivity is limited. Here we show that silicon, complementary metal-oxide-semiconductor (CMOS) technology offers enhanced detection sensitivity of almost two orders of magnitude, compared to CCDs...
November 15, 2017: Optics Letters
Tiina Lipiäinen, Sara J Fraser-Miller, Keith C Gordon, Clare J Strachan
This study considers the potential of low-frequency (terahertz) Raman spectroscopy in the quantitative analysis of ternary mixtures of solid-state forms. Direct comparison between low-frequency and mid-frequency spectral regions for quantitative analysis of crystal form mixtures, without confounding sampling and instrumental variations, is reported for the first time. Piroxicam was used as a model drug, and the low-frequency spectra of piroxicam forms β, α2 and monohydrate are presented for the first time...
November 11, 2017: Journal of Pharmaceutical and Biomedical Analysis
Patricia Abellan, Patrick Z El-Khoury, Quentin M Ramasse
Heterogeneous assemblies of molecules (Rhodamine B) adsorbed onto a nano-corrugated metallic surface (a percolated Au network) are investigated using electron energy loss spectroscopy in the scanning transmission electron microscope (STEM-EELS). Our first measurements target the native metallic substrate, which consists of a commercial Au thin film atop an ultrathin carbon membrane. The Au film displays a percolated morphology with nanostructures of estimated thickness ≤10 nm approximately. We observe a rich plasmonic response from the metallic substrate; one which varies nanometrically and spans the VIS-terahertz region...
November 9, 2017: Microscopy
Ali Farmani, Mahdi Yavarian, Abbas Alighanbari, Mehdi Miri, Mohammad H Sheikhi
A tunable graphene plasmonic Y-branch switch at THz wavelengths is proposed. The effects of magnetic and electric biasing are studied to harness the transmission of the transverse electric and magnetic guided mode resonances. In the structure, hexagonal boron nitride is utilized as a substrate for graphene. The application of hexagonal boron nitride, with the advantages of high mobility and ultralow ohmic loss, introduces a promising alternative substrate for graphene. Analytical and numerical results show that, by slight variation of the doping level in graphene through magnetic and electric biasing, the characteristics of the propagation of the guided mode resonances can be manipulated...
November 10, 2017: Applied Optics
Le Chang, Yue Li, Yongmin Liu
Efficiently manipulating the polarization states of electromagnetic waves is of great importance for communication, imaging, and sensing. In this paper, we aim to control the circular polarization states, e.g., left-hand, or right-hand, for the bidirectional radiated waves utilizing a pair of back-to-back quarter-wave plates, which are integrated within an ultrathin cavity. As an example, a bidirectional circularly polarized wave with the same helicity in forward and backward is generated based on numerical analyses, and proved by experiments in microwave region...
November 10, 2017: Scientific Reports
Xiang Yang, Ke Yang, Xiang Zhao, Zhongquan Lin, Zhiyong Liu, Sha Luo, Yang Zhang, Yunxia Wang, Weiling Fu
The demand for rapid and sensitive bacterial detection is continuously increasing due to the significant requirements of various applications. In this study, a terahertz (THz) biosensor based on rolling circle amplification (RCA) was developed for the isothermal detection of bacterial DNA. The synthetic bacterium-specific sequence of 16S rDNA hybridized with a padlock probe (PLP) that contains a sequence fully complementary to the target sequence at the 5' and 3' ends. The linear PLP was circularized by ligation to form a circular PLP upon recognition of the target sequence; then the capture probe (CP) immobilized on magnetic beads (MBs) acted as a primer to initialize RCA...
November 9, 2017: Analyst
Junliang Dong, Alexandre Locquet, Marcello Melis, D S Citrin
The process by which art paintings are produced typically involves the successive applications of preparatory and paint layers to a canvas or other support; however, there is an absence of nondestructive modalities to provide a global mapping of the stratigraphy, information that is crucial for evaluation of its authenticity and attribution, for insights into historical or artist-specific techniques, as well as for conservation. We demonstrate sparsity-based terahertz reflectometry can be applied to extract a detailed 3D mapping of the layer structure of the 17th century easel painting Madonna in Preghiera by the workshop of Giovanni Battista Salvi da Sassoferrato, in which the structure of the canvas support, the ground, imprimatura, underpainting, pictorial, and varnish layers are identified quantitatively...
November 8, 2017: Scientific Reports
Yinyin Qian, Qing Yang
Indium antimonide (InSb) enables diverse applications in electronics and optoelectronics. However, to date, there has not been a report on the synthesis of InSb nanowires (NWs) via a solution-phase strategy. Here, we demonstrate for the first time the preparation of high-quality InSb NWs with twinning superlattices from a mild solution-phase synthetic environment from the reaction of commercial triphenylantimony with tris(2,4-pentanedionato)-indium(III). This reaction occurs at low temperatures from 165 to 195 °C (optimized at ∼180 °C), which is the lowest temperature reported for the growth of InSb NWs to date...
November 14, 2017: Nano Letters
Lukasz A Sterczewski, Kacper Nowak, Boguslaw Szlachetko, Michal P Grzelczak, Berenika Szczesniak-Siega, Stanislawa Plinska, Wieslaw Malinka, Edward F Plinski
In this paper we discuss the link between the domain of physical parameters - molecular descriptors of a drug, and terahertz (THz) spectra. We measured the derivatives of the well-known anti-inflammatory drug Piroxicam using THz spectroscopy and employed Principal Component Analysis to build similarity maps in the molecular descriptor and spectral domains. We observed, that the spatial neighborhood on the molecular descriptors map is highly correlated with the spectral neighbourhood within a group of structurally-similar molecules...
November 6, 2017: Scientific Reports
Ashish Chanana, Yaxin Zhai, Sangita Baniya, Chuang Zhang, Z Valy Vardeny, Ajay Nahata
Controlling and modulating terahertz signals is of fundamental importance to allow systems level applications. We demonstrate an innovative approach for controlling the propagation properties of terahertz (THz) radiation, through use of both the excitation optical wavelength (colour) and intensity. We accomplish this using two-dimensional (2D) layered hybrid trihalide perovskites that are deposited onto silicon substrates. The absorption properties of these materials in the visible range can be tuned by changing the number of inorganic atomic layers in between the organic cation layers...
November 6, 2017: Nature Communications
Yoshitake Toda, Shintaro Ishiyama, Eduard Khutoryan, Toshitaka Idehara, Satoru Matsuishi, Peter V Sushko, Hideo Hosono
A simple and robust approach to visualization of continuous wave terahertz (CW-THz) light would open up opportunities to couple physical phenomena that occur at fundamentally different energy scales. Here we demonstrate how nanoscale cages of Ca12Al14O33 crystal enable conversion CW-THz radiation to visible light. These crystallographic cages are partially occupied with weakly bonded oxygen ions and give rise to a narrow conduction band that can be populated with localized, yet mobile electrons. CW-THz light excites a nearly stand-alone rattling motion of the encaged oxygen species, which promotes electron transfer from them to the neighboring vacant cages...
November 3, 2017: ACS Nano
Giacomo Baldi, Paola Benassi, Aldo Fontana, Andrea Giugni, Giulio Monaco, Michele Nardone, Flavio Rossi
We report a compared analysis of inelastic X ray scattering (IXS) and of low frequency Raman data of glassy 3-methylpentane. The IXS spectra have been analysed allowing for the existence of two distinct excitations at each scattering wavevector obtaining a consistent interpretation of the spectra. In particular, this procedure allows us to interpret the linewidth of the modes in terms of a simple model which relates them to the width of the first sharp diffraction peak in the static structure factor. In this model, the width of the modes arises from the blurring of the dispersion curves which increases approaching the boundary of the first pseudo-Brillouin zone...
October 28, 2017: Journal of Chemical Physics
Michael T Ruggiero, Marcin Krynski, Eric Ofosu Kissi, Juraj Sibik, Daniel Markl, Nicholas Y Tan, Denis Arslanov, Wim van der Zande, Britta Redlich, Timothy M Korter, Holger Grohganz, Korbinian Löbmann, Thomas Rades, Stephen R Elliott, J Axel Zeitler
The fundamental origins surrounding the dynamics of disordered solids near their characteristic glass transitions continue to be fiercely debated, even though a vast number of materials can form amorphous solids, including small-molecule organic, inorganic, covalent, metallic, and even large biological systems. The glass-transition temperature, Tg, can be readily detected by a diverse set of techniques, but given that these measurement modalities probe vastly different processes, there has been significant debate regarding the question of why Tg can be detected across all of them...
November 2, 2017: Physical Chemistry Chemical Physics: PCCP
Zhiyuan Fan, Zhaoxin Geng, Xiaoqin Lv, Yue Su, Yuping Yang, Jian Liu, Hongda Chen
The terahertz (THz) modulator, which will be applied in next-generation wireless communication, is a key device in a THz communication system. Current THz modulators based on traditional semiconductors and metamaterials have limited modulation depth or modulation range. Therefore, a THz modulator based on annealed tungsten disulfide (WS2, p-type) and high-resistivity silicon (n-type) is demonstrated. Pumped by a laser, the modulator presents a laser power-dependent modulation effect. Ranging from 0.25 to 2 THz, the modulation depth reaches 99% when the pumping laser is 2...
November 1, 2017: Scientific Reports
Thomas Siday, Michele Natrella, Jiang Wu, Huiyun Liu, Oleg Mitrofanov
We propose and characterize a scattering probe for terahertz (THz) near-field microscopy, fabricated from indium, where the scattering efficiency is enhanced by the dipolar resonance supported by the indium probe. The scattering properties of the probe were evaluated experimentally using THz time-domain spectroscopy (TDS), and numerically using the finite-difference time-domain (FDTD) method in order to identify resonant enhancement. Numerical measurements show that the indium probes exhibit enhanced scattering across the THz frequency range due to dipolar resonance, with a fractional bandwidth of 0...
October 30, 2017: Optics Express
Yannan Jiang, Lei Wang, Jiao Wang, Charles Nwakanma Akwuruoha, Weiping Cao
The polarization conversion of electromagnetic (EM) waves, especially linear-to-circular (LTC) polarization conversion, is of great significance in practical applications. In this study, we propose an ultra-wideband high-efficiency reflective LTC polarization converter based on a metasurface in the terahertz regime. It consists of periodic unit cells, each cell of which is formed by a double split resonant square ring, dielectric layer, and fully reflective gold mirror. In the frequency range of 0.60 - 1.41 THz, the magnitudes of the reflection coefficients reach approximately 0...
October 30, 2017: Optics Express
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