DEPARTMENT OF SOLID STATE PHYSICS

DEPARTMENT RESEARCH ACTIVITY

By using spectroscopic techniques (Raman, IR, absorption, Photoluminescence) and the synergy of theoretical calculations (phenomenological models, first-principles calculations, group theory) the optical properties of a wide range of materials (semiconductors, fullerenes, carbon nanotubes, garnets, low-dimensional materials etc.) are studied. These techniques and theoretical methods are utilized for materials characterization (identification of polytypes and phases, crystallinity, presence of mechanical stress/strain, chemical functionalization, electronic doping etc.) as well as for the study of fundamental physical phenomena (electron-phonon interaction, Kohn anomalies, immediate neighboring interactions etc.).

Moreover, the influence of external perturbations (temperature, uniaxial or biaxial mechanical deformation, hydrostatic pressure, electrochemical doping etc.) modifies drastically the optical properties of a material providing, thus, information on the physical phenomena themselves and allows the investigation of structural stability and the study of pressure induced structural or electronic phase transitions of materials.

  • Indicative activities:
    1. Study of optical properties under normal conditions, high pressure and as a function of temperature of materials such as semiconductors (ΙΙΙ-V, II-VI), fullerenes and related compounds, chemically modified carbon nanotubes and scheelite compounds (ABO4, Α = Ca, Sr, Ba and B = W, Mo).
    2. Study of the optical properties of two-dimensional materials such as graphene (single or multilayers), BN, transition metal dichalcogenides (MoS2, WS2, Mo1-xWxS2, MoSe2) as a function of their interaction with various substrates, physical or chemical electronic doping, mechanical deformation and hydrostatic pressure.
    3. Study of III-V nitrides (AlN, Gan, InN and their alloys) using Raman spectroscopy: effect of ion implantation and doping as well as of the stresses induced during the epitaxial growth.
    4. Lattice dynamics of the rare earth aluminum and gallium garnets in a crystal form and as solid solutions (RE3Al5O12 and RE3Ga5O12, RE=rare earth).
  • Equipment:
    1. Raman and photoluminescence set-up consisted of a triple monochromator (DILOR ΧΥ) with gratings of 1800 lines/mm and a CCD (EG&G 1433-C) liquid-nitrogen-cooled detector.
    2. Raman spectrometer 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 (8500-3500Å), fully automated and PC controlled.
    3. Two Ar+ Lasers of Spectra Physics 2W.
    4. One Kr Laser of Lexel 1.5 W.
    5. One cryostat accompanied by a diffusion pump of Cryogenic that works down to 20 K.
    6. Gas membrane driven diamond anvil cells, micro-tensiometers for the application of mechanical deformation (uniaxial, biaxial).

 

RESEARCHERS

Use of FTIR - UV/VIS in combination with thermal analysis methods to solve problems of technological materials

Α) High technology materials:
Narrow gap semiconductors, laminate compounds, γ and X-ray sensing materials, Sensors materials, Thermoelectric materials, Phase sensitive materials, Biodegradable polymers, Silicides, Phase sensitive materials, Optical data storage materials.
Β) Biomaterials:
Synthesis and Characterization of bioactive glass ceramics. Fabrication of composite materials with bioactive materials, Study of bioactivity in vitro, Cell-material interaction.
Γ) Cultural heritage materials:
Study and preservation of paintings and ceramics of cultural heritage.
Δ) Geological samples, (minerals, gemstones):
Mineral characterization, Classification of natural or artificial precious gemstones,Zeolithes, Oxides, Glass oxides, Glass waste materials.

The activities are held in collaboration with other institutes under the framework of national and international funding schemes.

RESEARCHERS

AC electrical measurements is an extension (in frequency domain) of the DC electrical measurements. AC electrical measurements may map the charges' transport (current) with common electrical elements (CEE) that we know from textbooks for DC/AC electrical circuits, i.e. we map the local charges' transport with CEE models. So, the parameters affecting current can be understood better, offering tools for material's optimization. For example, a piezoelectric quartz-crystal oscillator (PZT) has a simple direct model map between materials' or mechanical parameters of mass (m), spring constant (k) and energy losses (γ) with electrical equivalent model parameters of a coil (L), a capacitance (C) and a resistor(R) connected in series. This map is: m->L, k->1/C, γ->R. Thus, we may form a PZT-material's optimization process changing one (only) parameter in a well known RLC-model.

RESEARCHERS

Quantum dots and nanowires are widely studied due to their potential electrical and/or optical properties.
Their successfull and reproducible fabrication still remains a challenge for the scientists
The scientific activity of our group involves: Atomistic modelling, determination of atom equilibrium positions with simulation methods, electronic state and optical property evaluation.

RESEARCHERS

•Research Activities:

- Cognitive studies in Physics.
- Development of teaching activities (traditional and advanced technology).
- Development of integrated learning environments.



• Equipment:
1. Closed-loop TV circuit with capability of mixing sound and video in digital format (DVD), 4 SONY cameras, ZOOM 6x, video mixing console, U'matic video 3/4 250 lines.
2. Portable color video recorder JV-VHS 250 lines and video camera JVC KY-610, f = 1.4, ZOOM 10x.
3. Stereo color TV set (46").
4. Portable sound mixers (4 & 6 channels), directional and ambient microphones.
5. Devices for demonstration experiments in the fields of Mechanics, Electricity, Magnetism and Fluids.
6. Projectors for still and moving images.
7. A collection of videotapes VHS and DVD with experiments in Physics and a collection videotaped past student presentations.
8. Setups for on line measurements (MBL) and projection of educational activities.

RESEARCHERS

The electrical characterisation process aims to determine the electrical properties of materials and conductive systems as part of the general transport properties of solids. .
The group is specialised in the parametric study of the electrical behaviour of materials and its interpretation when exposed to controlled steady electric and magnetic fields. The parameters include temperature (10 – 300 K), magnetic field (1.4 T), the composition and structure of the materials, as well as the geometry and topography of the samples under test and their electrical contacts.
The characterisation process is based on the online measurement of the electrical conductivity, the Hall Effect and the magnetoresistance of materials, according to the Van der Pauw and Wascher methodologies. .
The group has extensive experience in the characterisation of semiconductors, metals and semi-metals, as well as in the exploration of suitable theoretical models in order to further investigate and expand the methodologies of measurement of inhomogeneous and anisotropic materials. .

RESEARCHERS

Research Activities:
•Thin Film Transistors of poly-nano-crystalline Si
•Nanoscale multigate MOSFETs •Nanomaterials, Quantum Dots in GaAs and Si
•Low Frequency Noise Characterization of Semiconductor Devices
•Hot Carriers Effects in CMOS Devices
•Theoretical Simulation of MOS Devices with the Silvaco Simulation Tool
•Compact drain current and low frequency Noise models in TFTs and nanoscale multigate MOSFETs

RESEARCHERS

The research activities of this group, (Lab for Thin Films- Nanosystems & Nanometrology- LTFN) involve:

  1. Development of Flexible and Printed Electronic Devices for Energy, Lighting, Medicine, etc Applications.
  2. Growth and study of nanomaterials and thin films on 2D and 3D substrates in high and ultra high vacuum environment with the use of Physical Vapor Deposition- PVD.
  3. Surface engineering of inorganic and organic materials with the use of ion bonds and plasma.
  4. Study of optical and electronic, structural and nanomechanical properties of thin films and bulk materials with state of the art techniques (such as Spectroscopic Ellipsometry, X ray diffraction and reflection, Atomic Force Microscopy and Nanoidentation).
  5. Development of in-situ and real-time optical monitoring methods of atomic processes and interactions that take place during films growth or surface modification and activation.

The scope of the above mentioned activities is the development of the research in basic level (understanding the growth mechanisms of the thin films and nanostructures, correlation of the structure of thin films and nanostructures with the optical- electronic- mechanical properties, computational methods and techniques) and also application level.
The applications include new advanced materials for microelectronics, flexible electronic devices, photovoltaics, barrier in gas nanocoatings for flexible packaging, hydrogen sensors and biosensors, coatings for medical implants and biocompatible materials etc.

RESEARCHERS

A battery is an electrical source device offering charge, current and power for a load. High charge is offered using all volume (3D) of active materials. High current is offered by considerable mixed electronic-ionic conductivity of active materials (anode and cathode) as well as by high-ionic / low-electronic conductivity of the electrolyte during all working duty cycles of charge/discharge. So, a vast number of theoretical candidate materials for batteries, under the above constrains, is limited into an extemelly small number of materials for commercial batteries. The near future of batteries, though, is mainly the Li-ion Batteries, fulfilling better the consumers' demands for portable devices.

Activities:
A. Preparation of cathodic, anodic and electrolytic materials either in powders or in thin films
B. Investigation of the structural properties of these materials
C. Investigation of their electrical properties
D. Formation of Li-ion batteries and microbatteries
E.Investigation of the batteries by measuring the charging-discharging, the charge capacity and the stability of their properties with the number of cycles of charging-discharging.

RESEARCHERS

The group is involved in projects studying the phases, the microstructures and the morphology of magnetic materials focusing on correlations of structure and magnetism not only in bulk materials but in magnetic nanostructures as well. The various activities may be summarized as follows:

Α). Growth - Fabrication of magnetic materials of technological interest.
Β). Characterization and study of microstructure till the atomic level.
C). Temperature-dependent magnetic characterization.
D). Thermal, mechanical and magnetic treatments for improving the magnetic study.
E). Theoretical study and simulation of magnetic features.

•Equipment:
- UHV chamber with 3 sources for e-beam evaporation of thin and multilayered films.
- Monocrystal fabrication with Czochralski – Bridgeman method.
- Inductive furnace for metal casting and alloy formation.
- Vibrating Sample Magnetometer - VSM for thin films (77-300K, 0-1.2T, 0–2T).
- Moessbauer spectrometer 57Fe (77 – 300 K)

RESEARCHERS

The Electron Microscopy Laboratory (EML) of Physics Department was established in 1963. The Lab is located at the west wing of the Science School and belongs to the Solid State Physics Section of the Physics Department. Today, the Lab comprises seven research staff members and two staff for technical support. The Lab hosts PhD and MSc Students, as well as Marie Curie Research fellows. The mission of EML is to provide to its members access to materials characterization equipment, training, and consultation, as well as to perform a range of services for end-users in the area of electron microscopy. In general, the laboratory’s activity comprises the integrated structural characterization and study of solid materials (metals, ceramics, polymers, glasses), as well as complex materials and composite crystals of advanced materials such as semiconductor thin films, nanostructures and heterostructures, natural or engineering materials in powder form and coatings. Μore specifically, the current research activity includes:
•Study and structural characterization of various materials (metals, semiconductors, ceramics, polymers, composites and advanced materials) by various transmission electron microscopy (TEM) techniques.
• Study of the nanostructure and structural defects of bulk materials, thin films and nanomaterials by High Resolution Transmission Electron Microscopy (HRTEM).
• Localized crystallographic and topological characterization of phases, interfaces, symmetries, orientation relationships, polarity, and line, planar or other extended structural defects.
• High accuracy nanoscale determination of internal strain fields.
• Structural and chemical characterization of homophase and heterophase interfaces down to the atomic scale.
• Integrated structural characterization of nano-heterostructures such as quantum wells, quantum dots, and nanowires.
• Study of nano-scale interaction mechanisms between defects, interfaces, internal fields and the kinetics of growth.
• Growth and characterization of engineering materials fabricated by advanced methods mechanosynthesis and thermal treatment.
• Study of phase transitions and vitrification of amorphous glassy materials.
• Research of transformation of phases and the crystallization of amorphous alloys by in situ thermal treatment.
• Development of integrated models of structures, interfaces and defects through the simulation of CTEM and HRTEM observations by computational methods such as Molecular Dynamics, ab initio DFT, and Monte-Carlo.
• Development of methods and software form quantitative HRTEM (qHRTEM) analysis (e.g. peak finding methods).
• Electron microscopy simulations of diffraction patterns, CTEM and HRTEM images. Software development for the processing and analysis of TEM images and diffraction patterns.
• Study of surface morphologies and properties by atomic force microscopy (AFM).
Through collaborations with international acknowledged electron microscopy centres:
- Two-dimensional nano-scale chemical mapping
- Chemical imaging of atomic structures.
- Nano-scale quantitative determination of chemical concentration.
- Nano-scale chemical profile determination across interfaces.
- Analysis of chemical bonding.
Instrumentation
The EM Laboratory possesses the necessary instrumentation for the precise HRTEM and CTEM characterisation of solid matter, as well as state-of-the-art instruments for TEM sample preparation, such as:
• High Resolution Transmission Electron Microscope JEOL 2011 (200KV), with a point resolution of 0.194 nm (purchased 2001). The microscope is equipped with:
i. KeenView G2 TEM CCD camera system (Olympus Soft Imaging Solutions)
ii. SPININGSTAR P020 device, for the precession and tilting of the electron beam (Nanomegas) accompanied with the necessary software.
• High Resolution Transmission Electron Microscope JEOL 2000FX (200KV), with a point resolution of 0.28 nm (purchased 1992).
• Conventional Transmission Electron Microscope JEOL 1010 (100KV) with a resolution 0.5nm, with heating, cooling and tensile stress facilities (purchased 1978).
• Atomic Force Microscope (AFM) Explorer 2000 Truemetrix Topometrix, with two scanners of (100X100) μm, (2.5X2.5) μm, and a liquid scanner of (2.5X2.5) μm. Resolution in the nanometre scale. Working at Contact mode, Tapping mode, Lateral Force mode.
• Argon ion-milling machines: Edwards (model IBMA2), MTA-MFKI and TECHNOORG LINDA with a liquid nitrogen facility.
• Precision ion polishing system, PIPS Gatan (model 691).
• Diamond lapping and polishing machine for use with the tripod polisher, South Bay Technology (model 910).
• Precise semi-automated grinding/polishing equipment, Allied MultiPrep.
• Precision dimpling instrument, South Bay Technology (model 515).
• Electropolishing devices Tenupol-2, Tenupol-3 (Struers).
• Dark room facility.
• Software for HRTEM image processing and simulations.

RESEARCHERS

1. "Speckle phenomena": Relating to the properties (statistically) of light (partial coherence and coherence) and the statistics of surfaces where the light is reflected or refracted. Our research is concerned with "Speckle" interferometry issues and optical image processing with carriers the "grains" of "Speckle".
2. Optical Image Processing: This is based on a general view of the scalar theory of diffraction of light in classical optics, which is called Furrier Optics. Our operations are mainly concerned with the research of methods of observing phase objects (e.g. transparent materials with variable refractive index).
3. Photorefractive Crystals: In these crystals phase gratings may be recorded. These phase gratings are carriers of record, storage and optical image processing. In specific sections of these crystals gratings are recorded versus the orientation of vector grating and versus the high voltage that is applied at their ends. With incidence in the grating of a proper light beam, the recorded information is reproduced via diffraction. We study the diffraction efficiency of gratings and the polarization properties of the diffracted beam, in terms of the polarization state of the incident beam, and other properties of phase gratings.
4.Physical Properties of Crystals: Here we are dealing with crystals which are: electro-optic, (Pockel effect), photo-elastic (via the inverse piezoelectric effect), optical-active, shows linear electro-gyration effect, etc. Using specified optical experimental arrangements we measure: The dispersion (depending on the wavelength) in the visible region of the electromagnetic spectrum: a) The refractive indices of crystals, b) The optical activity, c) The electro-optical coefficients and d) The electro-gyration coefficients.
Laboratory Infrastructure
1. Optical and mechanical systems controlled by PC
2. Optical components and systems
3. Sources of Light and Lasers
4. Electronic Systems (oscilloscopes, power supplies, etc.)
5. Monochromators, spectrometers
6. Full range of microscopes
7. Diffractometers, interferometers and other optical instruments

RESEARCHERS

Study of the nanostructure (nearest neighbor distances, coordination numbers and bond angles) as well as optical properties (density of unoccupied states) in the soft and hard x-ray spectral region using x-ray absorption spectroscopies EXAFS & NEXAFS.

Elemental mapping using the x-ray fluorescence spectroscopy (XRF mapping) and micro XAFS. The samples under study are:
i) compounds of Si (mainly SiNx)
ii) group III nitrides (GaN, AlN, InN and their alloys)
iii) glasses and glass ceramics containing solid wastes (information on the sample preparation can be found in the web page of WFENV-NET http://web.auth.gr/wfenv-net
iv) biological samples for the determination of the trace element concentration

Moreover, inelastic X-ray (and alternatively neutron) scattering for the study of dispersion curves and the density of states of crystalline solids can be conducted.

The measurements are conducted at Synchrotron Radiation facilities:
BESSY http://www.hasylab.de,
HASYLAB http://www.bessy.de,
ELETTRA http://www.elettra.trieste.it,
ESRF http://www.esrf.fr.

RESEARCHERS

Activities:

  • Dynamics and Kinetics of disordered solid state systems and fractals.
  • Dynamics of neural networks and signal transfer.
  • Estimation of electronic and optical properties of conventional and novel semiconductor material with technological applicability.
  • Interface study (symmetry, energy and structure features) in polycrystalline materials with lattice model.
  • Study of crystallite triplets in polycrystalline materials.
  • Estimation of electronic and dynamic properties in crystals, amorphous materials, superlattices.
  • Properties and Critical phenomena in ionic crystals.
  • Lattice dynamics of crystalline solids (3D and 2D) using phenomenological models and first-principles calculations. Application of group theory for the interpretation of Raman and Infrared spectra.
  • Difussion modelling, random walk, complex systems, low-dimensional systems, fractals, trapping events. - Statistical Physics Methodology.

Equipment:

PC Lab with parallel processing. Consists of 32 PCs (Intel Core 2 Duo, 64 processors), Total RAM 128 Gb, Storage Space 6.7 Tb, Operating System Scientific Linux.

RESEARCHERS

The research activities of the Thermal Analysis lab are:
•Thermal characterization of materials in the temperature range –150 till 1750 oC. The studied materials cover a large are such as: semiconductors, magnetic materials, rocks, polymers, ceramics, biomaterials etc.

•Kinetic study of amorphous materials
•Kinetic study of phase transformation and decomposition
And specifically with:
•Thermal characterization of polymers - biocompatible polymers - nanocomposite polymers. Kinetic study of the crystallization of these materials. Study of thermal stability and kinetics of thermal degradation.
•Study of metal’s oxidation, coatings oxidation in high temperatures. Kinetic study of oxidation.
The equipments of the Thermal Analysis lab are:
1.Differential Scanning Calorimeter (DSC), SETARAM-DSC 141, which covers the temperature area –150 till 550 oC
2.Thermogravimetry (TGA), SETARAM SetSys 16/18 TG-DTA, which covers the temperature area 20 till 1750 oC

RESEARCHERS

The Computational Physics group specializes in the study of “Complex Systems”, or “Complexity”, a new area in Physics that sees several Physical Problems as a structure of a Network, where the nodes represent the atoms and molecules and the connections between the nodes represent the existing bonds. A major characteristic is that such problems are studied with the use of large scale computer simulations. In condensed matter Physics, there are many dynamic phenomena offering a wide spectrum of technological applications, primarily in Material Science. Such an example is diffusion. When the materials that we study is not pure but have a variety of impurities, inhomogeneities, breaks, etc. then the laws of diffusion become more complex. The study of materials with Fractal structure is a very good example of this. Additionally, we observe that the simulation techniques that we use can also be extended to other physical systems, which may be completely different from the above. Such examples are the diffusion of medicines in conditions in vivo, the creation and study of neural networks and other networks in the form of Internet, even the dynamics in social networks. This leads to problems of distribution of information to complex structures, such as the development of human language and other interesting problems.

RESEARCHERS

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