Prof. Papagelis group shares its activities at the Laboratory of Optical Spectroscopy hosted at the School of Physics, Department of Solid State Physics, Aristotle University of Thessaloniki, and the Laboratory of Optical spectroscopy and Molecular Materials (OSMML) at the Institute of Chemical Engineering Sciences of the Foundation of Research and Technology-Hellas. Both laboratories are of high specifications and excellent capability. Also, the group has access to state-of-the-art equipment available at AUTh and FORTH/ICE-HT.
Dilor-XY: triple grating spectrometer suitable for various spectroscopic investigations down to 5 cm-1 (THz regime) with various excitation wavelengths in the extended visible range (350-900 nm). The three gratings of 1800 lines/mm can be used either in a subtractive or an additive mode. The detection takes place with a liquid-nitrogen-cooled CCD (EG&G 1433-C) detector.
RAMALOG 5: equipped with a Peltier-cooled photomultiplier tube with GaAs photocathode and a triple-monochromator that covers the wavelength range 12000 – 28000 cm-1 (850-350nm), fully automated and PC controlled.
Renishaw inVia: Single-pass spectrograph with extremely high efficiency (30% throughput) with two gratings of 2400 and 1200 grooves/mm and a Peltier cooled UV CCD array detector (576×384 pixels). Motorized translation sample stage for Raman mapping (point-by-point mapping, line focus mapping). Available wavelengths 325 nm, 514.5 nm, 632.8 nm, 785 nm).
Two Ar+ Lasers of Spectra-Physics 2W, and one Kr Laser of Lexel 1.5 W, serve as standard excitation sources.
Cryostat accompanied by a diffusion pump of Cryogenic that works down to 20 K
Gas membrane-driven diamond anvil cells
Three electrode electrochemical cells for in-situ Raman/PL measurements
Micro-tensiometers for the application of mechanical deformation (uniaxial, biaxial)
A mode-locked Ti: sapphire laser with an 86 MHz repetition rate is utilized. The pump and probe beams are cross-polarized and focused to a spot of 7.5 μm diameter; the incident pump fluence varies from 0.37 to 1.93 mJ/cm2 and the probe beam fluence is 0.18 mJ/cm2. A fast photodiode and 400 MHz oscilloscope are used to display the temporal structure of output radiation. Raman backscattered light is detected by a thermoelectrically cooled, CCD camera at the output of an imaging spectrograph. Exclusion of depolarized Raman scattering created by the pump beam is achieved by the “two-tint” pump-probe method based on optical filters and the broad bandwidth of the Ti: sapphire laser oscillator; the laser oscillator is tuned to a bandwidth of 10 nm and a central wavelength of 816 nm. To slice the broad bandwidth of the laser oscillator, we place a long-wave pass optical filter with a cutoff of 790 nm in the path of the pump and a narrow band-pass filter with a transmission band of 785±1.5 nm in the path of the probe.
Growth of TMDCs by Atmospheric Pressure Chemical Vapor Deposition (APCVD)
A two-zone high-temperature tube furnace is used to synthesize large are WS2 and MoS2 crystals or their heterostructures and alloys. The growth takes place in atmospheric pressure inert nitrogen atmosphere and is completed in one step. The growth substrate, usually a Si/SiO2 wafer, is spin-coated with an aqueous solution of Mo and/or W sodium salts. The hydrophilic nature of SiO2 promotes homogeneous distribution of the metal precursors on the substrate resulting in homogeneous nucleation density during TMDC crystal growth. By varying the concentration of the precursor solution, it is possible to directly control the substrate coverage yielding either isolated single-layer MoS2 or WS2 triangles or continuous MoS2 films with single- and few-layered domains. Moreover, by mixing the Mo and W precursor solutions we can achieve in the one-step, the growth of lateral and vertical heterostructures.
Mechanical exfoliation of 2D crystals and production of large size flakes.
Application of transfer methods to deposit high-quality, wrinkle-free 2D sheets onto target substrates.
The laboratory has all the necessary equipment to handle the CVD fabricated samples 2D materials.
The group employing a set of experimental techniques available to our group at AUTh and FORTH/ICE-HT to in-depth characterization the fabricated materials such as Raman, PL, Reflectance and absorption spectroscopies, Optical microscopy, AFM using various modules, SEM/TEM, XPS/AES/UPS/EELS, XRD, FTIR, UV-Vis-NIR, Hg-porosimetry, particle size analyzer, DSC/μ-DSC, and DMA.
Integration of a spectroscope into an optical microscope for in-situ acquisition of reflectance and absorption spectra of 2D materials. The spectrograph includes various optical elements and two rotating diffraction gratings of 300 and 1200 lines / mm. The spectral range of the spectroscope is 400 – 1000 nm and the lateral resolution of the system is ~ 1μm.
