Construction of terahertz spectrometers and their use in characterization of conductivities and modulation behaviors of graphene layers /

Kaya, Emine
Aim of this thesis was to construct two new terahertz spectrometers, THz Time Domain Spectroscopy (THz-TDS) and Time Resolved THz Spectroscopy (TRTS) for characterization of the static and dynamic properties of novel materials. After successful construction and signal optimization, system characterizations of both systems were completed with well-known samples. Possible use of ionic liquid doped graphene devices on PVC and PE substrates were characterized by THz-TDS. Devices operated at low voltages and provided nearly 100 % modulation between 0.2 THz and 1.5 THz at ca. 3.5 V. High modulation depth over such a broad spectrum and simple device structure make these modulators promising candidates in THz and related technologies. THz sheet conductivities of large-area CVD grown graphene samples were extracted with THz-TDS measurements. Comparison of results with literature showed that THz-TDS is a noncontact and reliable technique that allows characterization of frequency dependent sheet conductivity of graphene. Carrier relaxation dynamics of graphene samples were investigated with TRTS. A decrease in photo induced conductivity is observed with single layer graphene sample with 800 nm excitation due to its highly doped nature. Thickness dependent THz dynamics of multi layer graphene samples with 800 nm showed that samples had similar initial responses which can be explained as hot carrier cooling via carrier-carrier scattering and carrier-phonon scattering. Existence of interlayer charge transfers were suggested with observation of slower decay times of thicker samples due to slower recombinations. 400 nm pump studies of samples resulted in comparably shorter decay times due to initial hot carrier cooling and fast recombination rates of charges stemming from existence of easier interlayer transfer of charges.


Experimental investigation of nanofluids using terahertz time domain spectroscopy (THz TDS)
Koral, Can; Okutucu Özyurt, Hanife Tuba; Altan, Hakan; Department of Micro and Nanotechnology (2012)
In this study, suspensions of metallic nanoparticles in base fluids, nanofluids, are investigated by using terahertz time domain spectroscopy (THz-TDS). Nanofluids are used as the working fluid in a variety of applications especially for the purpose of heat transfer enhancement. Polar fluids are being used as the base in nanofluids for their tendency to stop aggregation and sedimentation. Polar fluids highly absorb THz signal. In order to select the best possible host, various polar liquids have been invest...
Observation of Gate-Tunable Coherent Perfect Absorption of Terahertz Radiation in Graphene
Kakenov, Nurbek; Balci, Osman; Takan, Taylan; ÖZKAN, VEDAT ALİ; Altan, Hakan; KOCABAŞ, COŞKUN (2016-09-01)
We report experimental observation of electrically tunable coherent perfect absorption (CPA) of terahertz (THz) radiation in graphene. We develop a reflection-type tunable THz cavity formed by a large-area graphene layer, a metallic reflective electrode, and an electrolytic medium in between. Ionic gating in the THz cavity allows us to tune the Fermi energy of graphene up to 1 eV and to achieve a critical coupling condition at 2.8 THz with absorption of 99%. With the enhanced THz absorption, we were able to...
Photoluminescence properties of Si nanocrystals embedded in SiO2 matrix
Seyhan, Ayşe; Turan, Raşit; Department of Physics (2010)
This thesis examines the luminescence properties of nanoscale silicon (Si) by using spectroscopic techniques. Since the development of new optical devices requires understanding light emission mechanism optical spectroscopy has become more important tool in the analysis of these structures. In this thesis, Si nanocrystals embedded in SiO2 matrix will be studied. Photoluminescence (PL) and Time-resolved photoluminescence spectroscopy (TRPL) have been used to detect the light emission in UV-Vis-NIR range. Exp...
Material characterization with terahertz time-domain spectroscopy
Köseoğlu, Devrim; Bilikmen, Kadri Sinan; Department of Physics (2010)
Terahertz time-domain spectroscopy systems were developed and used for the anaylsis and characterization of various materials. By using ultra-fast Ti:Sapphire and Er-doped fiber lasers, terahertz time-domain spectrometers of different configurations were constructed and tested. To increase the accuracy and sensitivity of the measurements, the systems were optimized for spectroscopic analysis. MBE grown nominally undoped epitaxial GaAs samples were used for the spectroscopic measurements. These samples were ...
Structural, electronic, and magnetic properties of smmcon (m + n _ 3) microclusters: density functional theory calculations
Kara, Nazan; Erkoç, Şakir; Oymak, Hüseyin; Department of Physics (2013)
Performing density functional theory calculations with many possible exchange correlational energy functionals, the most stable structures, symmetries, electronic, and magnetic properties of SmMCoN (M + N 3) microclusters have been studied in a systematic and statistical manner. Starting from the atoms of cobalt and samarium, dimers and trimers have been investigated in their ground states. The optimum geometries, binding energies, vibrational properties, possible dissociation channels, local magnetic mom...
Citation Formats
E. Kaya, “Construction of terahertz spectrometers and their use in characterization of conductivities and modulation behaviors of graphene layers /,” Ph.D. - Doctoral Program, Middle East Technical University, 2017.