Terahertz Conductivity of Twisted Bilayer Graphene

Physical Review Letters 110, 067401 (2013)  Received 9 April 2012; published 7 February 2013
doi:10.1103/PhysRevLett.110.067401

Authors: Xingquan Zou1, Jingzhi Shang¹, Jianing Leaw¹, Zhiqiang Luo¹, Liyan Luo¹, Chan La-o-vorakiat¹, Liang Cheng¹, S. A. Cheong¹, Haibin Su², Jian-Xin Zhu³, Yanpeng Liu⁴, Kian Ping Loh⁴, A. H. Castro Neto⁵, Ting Yu¹, and Elbert E. M. Chia¹

1. Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 637371 Singapore
2. Division of Materials Science, School of Materials Science and Engineering, Nanyang Technological University, 639798 Singapore
3. Theoretical Division and Center for Integrated Nanotechnologies, +Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
4. Department of Chemistry, +National University of Singapore , 3 Science Drive 3, 117543 Singapore
5. Graphene Research Centre and Physics Department, National University of Singapore, 6 Science Drive 2, 117546 Singapore

More details at: http://prl.aps.org/abstract/PRL/v110/i6/e067401

Abstract

Using terahertz time-domain spectroscopy, the real part of optical conductivity [σ1(ω)] of twisted bilayer graphene was obtained at different temperatures (10–300 K) in the frequency range 0.3–3 THz. On top of a Drude-like response, we see a strong peak in σ1(ω) at ∼2.7  THz. We analyze the overall Drude-like response using a disorder-dependent (unitary scattering) model, then attribute the peak at 2.7 THz to an enhanced density of states at that energy, which is caused by the presence of a van Hove singularity arising from a commensurate twisting of the two graphene layers.
© 2013 +American Physical Society

... The transmission THz spectra of the BLG were measured using a conventional THz-TDS system (TeraView TPS Spectra 3000)... THz TDS has proven to be a very useful noncontact technique to study material properties such as dielectric response, complex conductivity and refractive index in the far-infrared range without the need for Kramers-Kronig analysis ...

Realization of Variable Three-Dimensional Terahertz Metamaterial Tubes for Passive Resonance Tunability

1. Chen Zaichun^1,2, 
2. Mohsen Rahmani^1,3,
3. Gong Yandong², 
4. Chong Tow Chong^1,4,
5. Hong Minghui^1,*

1. 1. ¹
      Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117576
   2. ²
      Institute for Infocomm Research, 1 Fusionopolis Way, #21-01 Connexis, Singapore 138632
   3. ³
      Data Storage Institute, ASTAR, DSI Building, 5 Engineering Drive 1, Singapore 117608
   4. ⁴
      Singapore University of Technology and Design, 287 Ghim Moh Road #04-00, Singapore 279623
   Email: Hong Minghui (elehmh@nus.edu.sg)
   ^*Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117576.
   
   
   Abstract
    
   
   
A three-dimensional metamaterial tube is fabricated by rolling up 2D metamaterials on flexible PEN substrate. This novel 3D design of metamaterials can be used to effectively tune the resonance frequency by varying its diameter. Meanwhile, it can also be applied in material identification with a solid-core metamaterials tube.

... Characterization: The characterization is carried out by terahertz time- domain spectroscopy
(THz-TDS, Teraview TPS3000) in transmission mode. The axis of the 3D metamaterials tube
is kept parallel to the propagation direction of the incident terahertz wave, as illustrated ...

for full paper see Adv. Mater.. doi: 10.1002/adma.201104575

See how TeraView can help your metamaterial research visit http://www.teraview.com/products/terahertz-pulsed-spectra-3000/index.html

The ideal tool for researching metamaterials

If you are working on metamaterials, you will be interested in knowing that a growing number of researchers around the world are using the Spectra 3000 as a tool for investigating metamaterials. Here you can find a brief description of the benefits of TeraView's spectrometer to investigate metamaterials, but if you would like to know more visit our website on:
http://www.teraview.com/terahertz/applications/material-characterization/metamaterials.html

Spectra 3000 as a tool to investigate metamaterials

Instrument performance is our one of key design criteria, our terahertz spectral range, power, dynamic range and signal to noise ratio are world leading. Using our patented detector and emitter system we have designed a platform that can accommodate multiple modules to allow full flexibility and ease of use. No alignment is needed and the system is completely laser safe.  As terahertz light is invisible to the naked eye and the exposure to the generation laser is not safe, alignment of bench top systems can be difficult and time consuming, this is eliminated with the Spectra 3000. With powerful, flexible, bespoke software and field proven design, time can be directly spent on measurements and research rather than equipment set-up. It is typical from delivering a Spectra 3000 the customer is taking readings on their samples within minutes. In many cases, purchasing a Spectra 3000 is less expensive than assembling your own bench-top system, can allow more flexibility and prices are less than you might expect for the level of performance and range of applications.

The main benefits include:

• Truly expandable with the addition of modules and fibre probes now or later
• Terahertz transmission and reflectance measurements on solids, liquids, suspensions, slurries and films
• Spectral Range – 0.06 THz to 4 THz (2 cm^-1 - 120 cm^-1) best in class with maximum power levels across the whole range
• Accommodates standard IR sampling accessories
• Solid-state emitter and detector for ambient temperature operation
• Bespoke optics casting with  aligned optics for consistent maximum performance
• Fully integrated spectroscopy and imaging software with file export functions
• Easy to use modules for a variety of experiments:  
• Transmission
• Transmission XY mapping
• Reflection imaging
• Attenuated total Reflection (ATR)
• Remote fibre probes heads
• Cryostat for transmission and reflection
• Cooled and heated transmission cells
• Large area and portable scanning gantries
• Angular goniometer systems
• Specular reflection
• Medical scanning probes
• Standoff detection modules 

If you would like more information, research papers or full specification of the instrument, please reply to this mail and I will send you an information pack. 

Institutes are already getting good results with the Spectra 3000 researching into metamaterials and split ring resonators using the Spectra 3000. Details can be found here.

http://www.teraview.com/terahertz/applications/material-characterization/metamaterials.html

If you have any questions do not hesitate to get in touch.

http://www.teraview.com/info/contact-us.php

Maskless multiple-beam laser lithography for large-area nanostructure/microstructure fabrication

Min Tang, Zai Chun Chen, Zhi Qiang Huang, Yoo Sang Choo, andMing Hui Hong

Applied Optics, Vol. 50, Issue 35, pp. 6536-6542 (2011)
http://dx.doi.org/10.1364/AO.50.006536

Abstract

This paper reports a maskless multiple-beam laser lithography technique for large-area nanostructure/microstructure fabrication. This lithography technique can flexibly generate arbitrary nanostructures/microstructures over a large area at a high speed. The feature size of the nanostructures/microstructures can be controlled by exposure time and moving speed of the nanostage. Functional predesigned patterns, including split-ring resonator metamaterials for terahertz waves, can be obtained. More complicated structures can be made by single- and double-exposure schemes to make hybrid nanostructures/microstructures and tune surface plasmonic resonance properties. Meanwhile, microstructures with large height to lateral dimension ratios (2.5D microstructures) fabricated on silicon substrates can be used as mold tools for soft lithography. This technology shows its unique capacity to create various nanostructures/microstructures for extensive applications.

Measurements were performed using TeraView's TPS Spectra 3000 

... The line width of the SRR structure is ∼6μm, and the SRR dimension is 40μm. The trans-
mission spectra of the terahertz metamaterials are characterized by a terahertz time-domain
spectro- scope (TeraView, TPS3000) with a normal incident ...

Citation
Min Tang, Zai Chun Chen, Zhi Qiang Huang, Yoo Sang Choo, and Ming Hui Hong, "Maskless multiple-beam laser lithography for large-area nanostructure/microstructure fabrication," Appl. Opt. 50, 6536-6542 (2011)
http://www.opticsinfobase.org/abstract.cfm?URI=ao-50-35-6536

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