Advances in terahertz research - recent papers and publications

Technology Update: 

TeraView continues to support and promote fundamental and applied research within the terahertz field.

Each year the breadth and depth of interest in the area increases and TeraView is happy to help highlight these.

Below is a small selection of work from our customers and partners highlighting advances across a diverse range of application areas. These include work on; graphene, composite materials, explosives  and art conservation.

Chinese Academy of Sciences, Xi’an, China

Terahertz Spectral Investigation of Anhydrous and Monohydrated Glucose Using Terahertz Spectroscopy and Solid-State Theory

Woosuk University, Chonbuk, Republic of Korea

Influence of terahertz waves on the penetration in thick FRP composite materials

Chung-Ang University, Anseong, Republic of Korea

Foreign-body detection in dry food using continuous sub-terahertz wave imaging

University of Cambridge, Cambridge, United Kingdom

Low-Bias THz Amplitude Modulator Based on Split-Ring Resonators and Graphene

University College London, London, United Kingdom

Systematic study of terahertz time-domain spectra of historically informed black inks

Military University of Technology, Warsaw, Poland

Identification of concealed materials, including explosives, by terahertz reflection spectroscopy

To keep up to date with the latest articles and publications from TeraView, as well as gain access to an archive of all our publications, visit our website or our blog at:

Website: http://www.teraview.com/news/terahertz-publications/index.html

Graphene-based optical modulator realized in metamaterial split-ring resonators operating in the THz frequency range

Riccardo Degl'Innocenti ; David S. Jessop ; Yash D. Shah ; Juraj Sibik ; Axel Zeitler ; Piran R. Kidambi ; Stephan Hoffman ; Harvey E. Beere ; David A. Ritchie


Abstract

The integration of quantum cascade lasers with devices capable of efficiently manipulating terahertz light, represents a fundamental step for many different applications. Split-ring resonators, sub-wavelength metamaterial elements exhibiting broad resonances that are easily tuned lithographically, represent the ideal route to achieve such optical control of the incident light. We have realized a design based on the interplay between metallic split rings and the electronic properties of a graphene monolayer integrated into a single device. By acting on the doping level of graphene, an active modulation of the optical intensity was achieved in the frequency range between 2.2 THz and 3.1 THz, with a maximum modulation depth of 18%.

This study was performed using TeraView's TPS Spectra 3000 system. (TeraView, Cambridge, UK)

Full Article: http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=1846017

Low-Bias THz Amplitude Modulator Based on Split-Ring Resonators and Graphene

Riccardo Degl'Innocenti , Davide Stephan Jessop , Yash Diptesh Shah , Juraj Sibik , J Axel Zeitler , Piran Ravichandran Kidambi , Stephan Hofmann , Harvey E Beere , and David Ritchie


Abstract

Split-ring resonators represent the ideal route to achieve optical control of the incident light at THz frequencies. These sub-wavelength metamaterial elements exhibit broad resonances that can be easily tuned lithographically. We realized a design based on the interplay between the resonances of metallic split-rings and the electronic properties of a monolayer graphene integrated in a single device. By varying the major carrier concentration of graphene, an active modulation of the optical intensity was achieved in the frequency range between 2.2 THz and 3.1 THz, achieving a maximum modulation depth of 18\%, with a bias as low as 0.5 V.

This study was performed using TeraView's TPI Imaga 2000 system. (TeraView, Cambridge, UK)

Full Article: http://pubs.acs.org/doi/abs/10.1021/nn406136c

The Society for Applied Spectroscopy (SAS) UK Regional Section will hold its 3rd Annual Technical Meeting: “Graphene Spectroscopy”

The Society for Applied Spectroscopy (SAS) UK Regional Section will host its 3^rd Annual Technical Meeting Graphene Spectroscopy on Tuesday 29^th October 2013. This one day meeting will be held at Trinity Hall in Cambridge and will focus on recent advances in the characterization of graphene and two dimensional crystals by spectroscopic methods.

Graphene, thanks to its unique structural and electronic properties, has been called the “miracle material” of the 21st Century. Its isolation in 2004 has sparked a considerable scientific activity that has now established a broad international community with interest ranging from fundamental studies to applications in different fields e.g. composite materials, (opto)electronics, energy, etc. Graphene is just the first of a new class of two dimensional (2d) materials, derived from layered bulk crystals.

Studying and understanding the structure of graphene and 2d crystals is therefore of utmost importance for materials optimization and devices integration. This timely meeting strives to bring together international stakeholders in the field, to give perspectives on the current status of graphene spectroscopy. 

The speakers will be:

Prof. Ping-Heng Tan, Chinese Academy of Sciences, Beijing, P.R. China, “Application of ultra-low frequency Raman spectroscopy in two-dimensional layered materials.”

Prof. Andrea C. Ferrari, Cambridge Graphene Centre, UK, ““Raman Spectroscopy in Graphene: State of the Art” 

Dr. Cinzia Casiraghi, University of Manchester, UK. "Raman spectroscopy of defective graphene: Effect of the excitation energy, type, amount of defects and applied gate voltage."

Dr. Duhee Yoon Cambridge Graphene Centre, UK, “Raman spectroscopy for characterization of strained 
graphene.”

Prof. Günter G. Hoffmann, Eindhoven University of Technology, The Netherlands, “Tip-enhanced Raman Spectroscopy (TERS) and Mapping (TERM) of graphene and related materials”.

Prof. Giulio Cerullo, Politecnico di Milano, Italy. "Ultrafast electron-electron scattering in graphene.”

Prof. Euan Hendry, University of Exeter, UK. "Ultrafast optical measurements of graphene."

Dr. Michael Johnston, University of Oxford, UK. “Terahertz spectroscopy of graphene.”

Dr. Rahul Raveendran-Nair, University of Manchester, UK, “Characterisation of graphene and its chemical derivatives by different spectroscopic techniques.”

[The scientific program for the meeting has been co-organised by Francesco Bonaccorso (CNR-IPCF (Italy) and CGC, Cambridge University) and John Chalmers (SAS UK Regional Section.]

For registration details for this meeting or for more information, please email:

John Chalmers at: vibspecconsult@aol.com or visit: https://sites.google.com/site/sasukregion

Terahertz, optical, and Raman signatures of monolayer graphene behavior in thermally reduced graphene oxide films

Journal of Applied Physics / Volume 113 / Issue 18 / ARTICLES / Structural, Mechanical, Thermodynamic, and Optical Properties of Condensed Matter

Authors: Juhwan Lim¹, Kyujin Choi², J. R. Rani¹, Jin-Seon Kim^3,4, Changgu Lee^3,4, Jae Hoon Kim², and Seong Chan Jun¹
1 Department of Mechanical Engineering, Yonsei University, Seoul 120-749, Republic of Korea 
2 Department of Physics and Institute of Physics and Applied Physics, Yonsei University, Seoul 120-749, Republic of Korea 
3 School of Mechanical Engineering, Sungkyunkwan University, 2066, Seobu-ro, Jangan-gu, Suwon, Gyeonggi, Republic of Korea 
4 Center for Integrated Nanostructure Physics (CINAP), Institute for Basic Science (IBS), Sungkyunkwan University, Republic of Korea 

Abstract

We report on our joint spectroscopic study of the thermal reduction process of quasi-monolayer graphene oxide films grown on fused silica substrates by spin-coating. We estimate that about 65% of our film area consists of monolayer platelets of reduced graphene oxide, based on our quantitative analysis of the local atomic force microscopy topography. With thermal annealing under suitable conditions, clear signatures of monolayer graphene behavior were identified in the resonant excitonic absorption at 4.55 eV, the overall decrease in the visible-range transmission, the re-emergence of the Raman 2D band, the red-shift of the Raman G band toward the monolayer position, and the decrease in the optical sheet resistance in the terahertz range.

... The VUV, terahertz, and Raman measurements on our GO thin films, rGO thin films, and monolayer graphene grown by CVD were carried out with a grating spectrophotometer (Cary 5G), a terahertz time-domain spectrometer (TPS Spectra 3000, TeraView), and a WITEC ALPHA300M Raman ...

Terahertz and optical study of monolayer graphene processed by plasma oxidation

Appl. Phys. Lett. 102, 131901 (2013); http://dx.doi.org/10.1063/1.4795526
(Received 7 February 2013; accepted 26 February 2013; published online 1 April 2013)

Authors: Kyujin Choi¹, Juhwan Lim², J. R. Rani², Hyong Seo Yoon², Juyeong Oh², Taeyoon Hong¹, Taewoo Ha¹, Byung Cheol Park¹, Kyung Ik Sim¹, Seong Chan Jun², and Jae Hoon Kim^1
1 Department of Physics and Institute of Physics and Applied Physics, +Yonsei University, Seoul 120-749, Republic of Korea 
² Department of Mechanical Engineering, +Yonsei University, Seoul 120-749, Republic of Korea 

Abstract

We report on our terahertz and optical study of monolayer graphene grown by chemical vapor deposition and processed by plasma oxidation. The plasma oxidation induces oxygen-related defects, and the resulting disorder increases the sheet resistance of graphene as measured via terahertz spectroscopy. The excitonic absorption peak weakens considerably and blue shifts upon plasma oxidation, resulting in higher transmittance in both the visible and ultraviolet regions. Our oxygen plasma-treated graphene also exhibits a free-carrier doping effect as confirmed by the blue shift of the Raman G band.

... Raman spectroscopy was performed with WITEC ALPHA300M Raman System (excitation at 532 nm, 2.33 eV). The VUV spectrophotometry was carried out with a Cary 5G spectrophotometer and THz-TDS with TeraView TPS Spectra 3000 ... 

More details at: http://apl.aip.org/resource/1/applab/v102/i13/p131901_s1?isAuthorized=no

More about terahertz equipment: http://www.teraview.com/products/index.html

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 ...