Keynote 1
Dr. Udo Schwingenschlogl, King Abdullah University Of Science And Technology(KAUST)
Speech Title:
First-principles predictions of substrate effects on silicene
Abstract:
Silicene is the Si analogue of graphene with the same honeycomb structure and linear dispersions of the π and π* bands at the K point of the Brillouin zone. It realizes a buckled structure, due to sp2-sp3 hybridization, and is compatible with current Si-based nano-electronics. Silicene yet has not been achieved by mechanical exfoliation, but can be deposited on metallic substrates such as Ag(111), Ir(111), and ZrB2(0001). Regrettably, strong interaction to these substrates destroys the Dirac physics. For this reason, semiconducting substrates have been explored in the literature, including Si(111) and SiC(0001). However, surface passivation is inevitable for these and similar substrates due to dangling bonds. Layered materials such as MgBr2(0001), MoX2, and GaX2 (X = S, Se, and Te), on the other hand, simplify the preparation procedure (as passivation is not required), while preserving silicene's characteristic electronic states. Effects of different substrates on silicene will be compared and evaluated with respect to technological requirements.
Keynote 2
Prof. Pierre Ruterana, Centre de Recherche sur les Matériaux, les Ions et la Photonique
Speech Title:
The structural properties of strained heterostructures in hexagonal symmetry semiconducting materials at atomic level
Abstract:
The hexagonal semiconductors crystallize in the wurtzite structure; they include the nitride (Al,Ga,In)N family and ZnO, and they have undergone extensive investigation for the last 20 years. These materials exhibit physical properties which are subject to highly strategic applications; for instance, the nitride semiconductors constitute the unique family whose alloys direct band gaps allow to cover the largest wavelength span for emission and detection. Moreover, they are ceramics and polar especially along the main growth axis [0001]; this leads to spontaneous piezoelectricity which is now intensively applied to the fabrication of high power, high frequency transistors. For ZnO, its large exciton energy means that it should be at the origin of highest performance emitters in the blue range. Still, the active devices are made of heterostructures which involve various alloy compositions and, it is still a challenge to grow optimal quality devices even on free standing substrates, as for instance, the elemental compounds exhibit large lattice, as well as, thermal mismatch, moreover they grow at largely different temperatures. Therefore, it is important to investigate the extended defects in these heterostructures and at their interface, and to determine their formation mechanisms with the objective of contributing to the optimization of the layers structural quality and performances for the fabricated devices. In our work, using high resolution electron microscopy, atomistic modeling and image simulations, we have identified the atomic structure of a type threading dislocations. In the nitride layers, they typically exhibit three different cores which are found inside the high quality layers as well as in grain boundaries. In ZnO, it was possible to point out, for the first time, inside grain boundaries, depending on the tilt angles, the [10-10] dislocation which has only been suggested to exist in the wurtzite system through a theoretical report. In these materials, it was shown that stacking faults not only occur in the basal planes, but also inside the prismatic {11-20} planes with two displacement vectors. Due to the polarity of the wurtzite structure, other typical defects are inversion domains, such defects habit planes are usually {10-10}. They form in order to relieve residual strain at surface steps and their formation inside the basal plane has been shown to be connected to a precipitation of impurities such as Mg from heavy p-doping of the nitride layers. Very recently, we showed that such a (0001) polarity inversion can be driven to take place upon growth of ZnO/GaN heterostructure and within only one monolayer.
Keynote 3
Dr. Jiangwei Liu, National Institute for Materials Science (NIMS)
Speech Title:
Abstract:
It is well-known that wide bandgap semiconductors such as GaN, SiC, and diamond are suitable to replace silicon partly for fabrication of high-power and high-frequency electronic devices because of their large band-gap energies, high carrier mobility, and high breakdown field. According to figure of merit, diamond-based electronic devices have the largest power-frequency product, the highest thermal limitation, and the lowest power-loss at high-frequency. Thus, diamond semiconductor devices are expected to be of very importance for the future practice applications.
Recently, diamond-based metal-oxide-semiconductor (MOS) capacitors and MOS field-effect transistors (MOSFETs) have developed greatly. They were fabricated on p-type boron-doped oxygenated diamond (O-diamond) and hydrogenated diamond (H-diamond) channel layers.1,2 Although thermal stability of the O-diamond is believed better than that of the H-diamond, trap charge density at insulator/O-diamond interfaces and leakage current density of the O-diamond based MOS capacitors are very high. It is still difficult to fabricate high-performance O-diamond based MOSFETs. On the other hand, many successful diamond MOSFETs were fabricated on the H-diamond channel layers. The H-diamond epitaxial layer has a high surface conductivity. The holes are accumulated on the surface with the sheet hole density of 1012∼1013 cm-2. Notably, it was reported that the exposure of the H-diamond in NO2 gas could increase the sheet hole density of H-diamond significantly to be as high as 1 × 1014 cm-2.3 Therefore, it is promising to fabricate high performance H-diamond based electronic devices.
In this talk, the fabrication of H-diamond-based electronic devices such as MOS capacitors, MOSFETs, and MOSFET logic circuits will be demonstrated and discussed.4-11
Keynote 4
Prof. Malgorzata Sopicka-Lizer, Silesian University of Technology
Speech Title:
Eu/Ce:oxynitride phosphors: advantages and drawbacks
Abstract:
Some ceramic compounds can be used as a solid matrix for accommodation of rare earth elements playing the role of the optical activators. The optical properties of these compounds are extremely related to their electronic band structure and can be tailored by changing the chemical composition and processing methods. Oxynitride compounds with ionic-covalent bonds show interesting physical and chemical properties due to their substantial structural diversity and possibility of solid solution formation with various nitrogen to oxygen ratio. However, synthesis of those compounds requires very high temperature and careful control of ambient atmosphere. This paper presents the optical properties of three main groups of RE:oxynitrides as prepared in Silesian University of Technology. The solid state method has been chosen for synthesis of the chosen phosphors. The efforts in the presented studies were oriented for the launching of nitrogen-silicon into Ce:Al5Y3O12 garnet, for controlling an oxygen amount in SrSi2N2O2:Eu2+ and for tailoring the range of solid solution in Ca, Eu-α-sialon powdered phosphors. As a result of the performed research, the green, yellow and orange phosphor powders with the excellent emission intensity and the high quantum yield after excitation under the blue light have been obtained and are presented.
Keynote 5
Dr. Hajime Hirao, City University of Hong Kong
Speech Title:
Computationally Looking into Complex Metal-Organic Frameworks and Nanomaterials
Abstract:
The physical principles used in computational chemistry underlie all branches of chemistry; as such, computational chemistry has unlimited potential to contribute to the advancement of fundamental chemistry in every different subdiscipline as well as to finding solutions to critical challenges that humankind faces today, such as healthcare and energy/environmental issues. With this in mind, our computational exploration of chemistry applies quantum chemistry, multiscale QM/MM and QM/QM approaches, and many other advanced computational chemistry techniques to a broad range of complex molecular systems such as metalloenzymes, transition-metal catalysts, drugs/drug targets, metal-organic frameworks (MOFs), and nanomaterials. In particular, using computational approaches and often with experimental collaborators, we seek to derive information about chemical reaction mechanisms and bonding patterns of these complex molecules. We are also developing efficient computational methods and algorithms, in the hope that our new computational methods will expand the capability of computational chemistry and thereby enable one to simulate the behavior of complex molecular systems with higher reliability and predictability in the future.
