Thursday, May 25, 2017

Abstract-Visualization of a nonlinear conducting path in an organic molecular ferroelectric by using emission of terahertz radiation

M. Sotome, N. Kida, Y. Kinoshita, H. Yamakawa, T. Miyamoto, H. Mori, and H. Okamoto

A nonlinear electric transport and switching to a negative resistance state is one of typical electric-field-induced phenomena in correlated electron materials, while their mechanisms are generally difficult to solve. In the present study, we apply the terahertz-radiation imaging method to an organic ferroelectric, α-(BEDT-TTF)2I3 [BEDT-TTF: bis(ethylenedithio)tetrathiafulvalene] and investigate the nature of its negative resistance phenomenon. When the negative resistance state is produced, the ferroelectric order is melted in an elongated region with the width of ∼100 μm and that region grows along the direction inclined by about 40° from the b axis with the increase of nonlinear current. A comparison of the terahertz radiation intensity with the current magnitude revealed that the melted region forms a conducting path. We interpreted the diagonal growth of the conduction path by taking into account the anisotropy of the intermolecular transfer integrals.

Abstract-Interconnect and packaging technologies for terahertz communication systems

Goutam Chattopadhyay, Theodore Reck,  Cecile Jung-Kubiak,   Maria Alonso-delPino, 
Choonsup Lee

Using newly developed silicon micromachining technology that enables low-loss and highly integrated packaging solutions, we are developing vertically stacked transmitters and receivers at terahertz frequencies that can be used for communication and other terahertz systems. Although there are multiple ways to address the problem of interconnect and packaging solutions at these frequencies, such as system-on-package (SOP), multi-chip modules (MCM), substrate integrated waveguide (SIW), liquid crystal polymer (LCP) based multilayer technologies, and others, we show that deep reactive ion etching (DRIE) based silicon micromachining with vertical integration allows the most effective solutions at terahertz frequencies.

Abstract-Fabry-Pérot interferometer for sensing polar liquids at terahertz frequencies

David Jahn1Amin Soltani1Jan C. Balzer1Withawat Withayachumnankul2, and Martin Koch

We propose and validate a sensor for polar liquids that operates in conjunction with terahertz time-domain spectroscopy. The sensor is constructed from an optically thick silicon wafer and a ground plane, separated by a gap into which the liquid is injected. This arrangement represents a Fabry-Pérot interferometer that causes a sharp minimum in the reflection spectrum. Compared to resonance-based sensors, this sensor design can maintain its sharp spectral response when loaded with highly absorbing polar liquids. This overcomes an issue of damped resonance caused by material losses in resonance-based sensors. We report a reflection minimum shift of 8 GHz per percent ethanol in water. The sensor can be readily integrated with a microfluidic channel for real-time fluid monitoring.

Wednesday, May 24, 2017

Three-dimensional graphene: Experiment at BESSY II shows that optical properties are tuneable

SEM-images of 3-D graphene with different pore size (a,b,c, scale = 1μm). Optical properties (d,e,f) change with pore size. Credit: Nature Communications: 10.1038/ncomms14885

An international research team has for the first time investigated the optical properties of three-dimensional nanoporous graphene at the IRIS infrared beamline of the BESSY II electron storage ring. The experiments show that the plasmonic excitations (oscillations of the charge density) in this new material can be precisely controlled by the pore size and by introducing atomic impurities. This could facilitate the manufacture of highly sensitive chemical sensors.

Carbon is a very versatile element. It not only forms diamonds, graphite, and coal, but can also take a planar form as a hexagonal matrix - . This material, consisting of only a single atomic layer, possesses many extreme properties. It is highly conductive, optically transparent, and is mechanically flexible as well as able to withstand loads. André Geim and Konstantin Novoselov received the 2010 Nobel Prize in Physics for the discovery of this exotic form of carbon. And just recently, a Japanese team has been successful in stacking two-dimensional graphene layers in a three-dimensional architecture with nanometre-sized pores.
Tuneable plasmons
A research team operated by a group at Sapienza University in Rome has now for the first time made a detailed investigation of the  of 3D graphene at BESSY II. The team was able to ascertain from the data how  oscillations, known as plasmons, propagate in three-dimensional graphene. In doing so, they determined that these plasmons follow the same physical laws as 2D graphene. However, the frequency of the plasmons in 3D graphene can be very precisely controlled, either by introducing atomic impurities (doping), by the size of the nanopores, or by attaching specific molecules in certain ways to the graphene. In this way, the novel material might also lend itself to manufacturing specific chemical sensors, as the authors write in Nature Communications. In addition, the new material is interesting as an electrode material for employment in solar cells.
Advantages provided by the IRIS beamline
The researchers used the IRIS beamline at the BESSY II synchrotron source in Berlin to their advantage for their investigations. Broad-band infrared is available there, which especially facilitates spectroscopic analysis of novel  using terahertz radiation. "A special operating mode of the BESSY II storage ring called low-alpha allowed us to measure the optical conductivity of three-dimensional graphene with a particularly high signal-to-noise ratio. This is hardly possible with standard methods, especially in the terahertz region. However, it is exactly this region that is important for observing critical physical properties", says Dr. Ulrich Schade, head of the group at the infrared beamline.
More information: Fausto D'Apuzzo et al, Terahertz and mid-infrared plasmons in three-dimensional nanoporous graphene, Nature Communications (2017). DOI: 10.1038/ncomms14885 

Abstract-Mars Micro-Satellite for Terahertz Remote Sensing

Richard Larsson, Yasko Kasai, Takeshi Kuroda, Hiroyuki Maezawa, Takeshi Manabe, Toshiyuki Nishibori, Shinichi Nakasuka, Akifumi Wachi, Hideo Sagawa,

We present an idea for an instrument aimed to measure Martian oxygen isotopologue ratios in several species (including O2, CO, H2O, and others) by flying a terahertz sensor to Mars on a micro-satellite mission that will orbit the planet for a short while before landing the instrument on the surface. The presentation will discuss the scientific targets, the instrumental details, and the expected outcome of the measurements. As is generally known, Martian atmospheric chemistry is governed by the photolytic destruction of carbon dioxide, forming free oxygen and carbon monoxide. A complicated chemical chain then resupply the atmosphere with carbon dioxide and leaves behind a mixture of some of the trace gases involved in the chain. Our interest here is that the oxygen isotopologue ratios, in its various forms, is a result of the entire resupply chain. We are presently (January and onward) performing tests of the design of the instrument, so more details will be available in time for the presentation.