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.


Gelgeç, Melis; Altan, Hakan; Department of Physics (2022-8-25)
In this thesis, a Terahertz Attenuated Total Reflection Time Domain Spectroscopy (THz ATR-TDS) system was constructed to measure biological media. The constructed system driven by a Yb:doped mode-locked fiber laser had a limited bandwidth of about 0.3 THz. This bandwidth limited the analysis of various samples in the frequency domain. To overcome this limitation a method was developed so that the samples can be analyzed in the time-domain. Oral soft tissue samples collected were used in order to demonstrate...
Fabrication and characterization of photocrosslinked phase change materials by using conventional and terahertz spectroscopy techniques
Aytan, Emre; Aytekin, Yusuf Samet; Esentürk, Okan; KAHRAMAN, MEMET VEZİR (2019-12-01)
A series of novel photocrosslinked shape-stabilized phase change materials (PCMs) based on tetradecanol and lauric acid have been prepared by UV technique for the purpose of thermal energy storage applications. Both lauric acid and tetradecanol were reacted with glycidyl methacrylate to form acrylated structures for covalently integrate into polyurethane (PU) based UV matrix to prevent leakage problem. The heating process phase change enthalpy is measured between 9 and 77 J/g, and the freezing process phase...
Probing Charge Transfer and Hot Carrier Dynamics in Organic Solar Cells with Terahertz Spectroscopy
CUNNINGHAM, Paul D.; LANE, Paul A.; MELINGER, Joseph S.; Esentürk, Okan; HEILWEIL, Edwin J. (2016-04-19)
Time-resolved terahertz spectroscopy (TRTS) was used to explore charge generation, transfer, and the role of hot carriers in organic solar cell materials. Two model molecular photovoltaic systems were investigated: with zinc phthalocyanine (ZnPc) or alpha-sexathiophene (alpha-6T) as the electron donors and buckminsterfullerene (C-60) as the electron acceptor. TRTS provides charge carrier conductivity dynamics comprised of changes in both population and mobility. By using time-resolved optical spectroscopy i...
Terahertz study of 1,3,5-trinitro-s-triazine by time-domain and Fourier transform infrared spectroscopy
Huang, F; Schulkin, B; Altan, Hakan; Federici, JF; Gary, D; Barat, R; Zimdars, D; Chen, M; Tanner, DB (2004-12-06)
This letter describes the use of THz time-domain spectroscopy (TDS) applied in transmission to the secondary explosive 1,3,5 trinitro-s-triazine. Samples were also subjected to Fourier transform infrared spectroscopy over the same range for comparison. A detailed spectroscopy study is presented. General agreement between results from both methods confirms the absorption features found. A comparison study with computer molecular simulations shows that THz-TDS is sensitive to collective modes or vibrational m...
Terahertz Transmission Through Patterened Vanadium Oxide Thin Films on Dielectric Substrates
AKKAYA, MAHİNUR; Demirhan, Y.; Yuce, H.; Aygun, G.; Ozyuzer, L.; SABAH, CUMALİ; Altan, Hakan (SCITEPRESS, AV D MANUELL, 27A 2 ESQ, SETUBAL, 2910-595, PORTUGAL; 2017-03-01)
Patterned and unpatterned films of vanadium oxide grown on dielectric substrates such as fused silica and sapphire were grown and analysed by varying the temperature using terahertz time domain spectroscopy. After investigating the critical transition temperature near 340K, a well-known cross-shaped pattern was studied to observe any resonances upon transmission. Due to the poor conductivity of the films the frequency selective nature of the structure was not observed, however an etalon effect could be seen...
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.