Seminars
NanoLab seminar (weekly): Wednesday 12:00, room 658.
NanoLab Seminar: Tuesday: 11:00
9. June 2009.room 661, Faculty of Physics
Dr Vojislav Krstic (Trinity College, Dablin, Irska)
Impact of Phosphorous-Doping on Electrical and transport in Single-Walled Carbon Nanotubes
| Doping of single-walled carbon nanotubes is a powerful technological tool to tune their electronic properties and thus has a wide impact on many fields of nanotechnology. We report on the doping of single-walled carbon nanotubes by incorporation of phosphorous atoms into the nanotube honey-comb lattice by the arc-discharge method. The proof and the impact of phosphorous doping on the helicity and electronic properties of the single-walled carbon nanotubes is investigated by charge-transport, nuclear magnetic resonance and electron microscopy studies and underpinned by density-functional structural modelling. The phosphorous-doped nanotubes show a significant variation in tube morphology compared to their undoped counterparts going along with a non-Luttinger liquid like behaviour of the zero-bias conductance with additional irregular step-like features. A decrease and an inversion of the nuclear-magnetic-resonance relaxation times are observed suggesting and enhanced spin-cattering. This observation can be linked to the step-like features through a one-dimensional spin-chain model. |
Quanta symetria geometria: Wednesday: 13:00
13. May 2009.room 661, Faculty of Physics
Dr Edib Dobardzic (Fizicki fakultet Univerziteta u Beogradu)
Fononi u BC3 sloju i nanotubama
| We have found force constants providing excellent agreement to the experimental phonon dispersions along Γ-M direction. Using them we discuss vibrational properties of BC3 layer and nanotubes. Particularly, we analyze Raman and infrared activity singling out the relevant modes by symmetry. The diameter/chiral angle dependence of the active modes is derived, and its application to the sample characterization is emphasized. |
Quanta symetria geometria: Wednesday: 13:00
25. March 2009.room 661, Faculty of Physics
Prof. dr Milan Damnjanovic (Fizicki Fakultet, Univerzitet u Beogradu)
Simetrija kvazijednodimenzionalnih kristala i nanotuba
| Koriscenjem simetrije izvrsena je klasifikacija sistema periodicnih duz jednog pravca. Koristeci ove rezultate, bice objasnjene neke njihove zajednicke fizicke osobine. Posebno ce biti razmotrene nanotube i njihova simetrija, pri cemu ce ugljenicne nanotube biti najvaznijii primer. |
Quanta symetria geometria: Wednesday: 13:00
28. January 2009.room 661, Faculty of Physics
dr Bozidar Nikolic (Faculty of Physics)
Rezonantno Ramanovo rasejanje na jednoslojnim ugljenicnim nanotubama
| Intenziteti Ramanovog rasejanja za totalno simetricne mode za jednoslojne ugljenicne nanotube su racunati uz koriscenje potpune simetrije sistema. Zbog intenzivne apsorpcije svetlosti jednoslojnih tuba Ramanovo rasejanje je uglavnom rezonantno. Dobijeni rezonantni intenziteti pokazuju vrlo jaku zavisnost od parametara tube sto moze da posluzi za karakterizaciju tuba. Uz pomoc dobijenih rezultata moze se jednostavno objasniti iscezavanje rezonance na drugom optickom prelazu kod metalnih tuba. |
Quanta symetria geometria: Wednesday: 13:00
24. December 2008.room 661, Faculty of Physics
Prof. Dr Miodrag Mateljevic (Matematicki fakultet, Univerzitet u Beogradu)
Lorencove transformacije
| Razmatra se precizno izvodjenje Lorencovih transformacija na osnovu matematicke tacke gledista. Na primer, u izvodjenju Lorencovih transformacija, Landau i Lifsic koriste rotaciju za ugao f. Pokazuje se da je f kompleksan broj! Pomocu kompleksne analize moze
se objasniti ova "rotacija"! Predlazemo jos dva nacina da se opisu pseudo-euklidske izometrije kretanja u prostoru Minkovskog): pomocu hiperbolicke rotacije ili svodjenjem na euklidska kretanja. Razmatraju se izometrije i kvazi-izometrije u odnosu na euklidsku, pseudoeuklidsku i hiperbolicku geometriju. Ocekujemo da razmena misljenja sa kolegama sa Fizike da impuls ovim razmatranjima. movie Part I movie Part II |
Quanta symetria geometria: Wednesday: 13:00
18. June 2008.room 661, Faculty of Physics
Marcel Mohr (Institute of solid state physics, TU Berlin, Germany)
First-principles calculations of CdSe nanowires
| We present first-principles calculations on the structural, electronic and vibrational properties of small diameter CdSenanowires depending on size and surface termination.The evolution of phonon frequencies with decreasing diameter is analyzed.We find strongly size-dependent and nearly constant modes.We find a low-frequency, diameter-dependent radial breathing mode (RBM) in CdSe nanowires. A comparison with Raman data is given. |
Quanta symetria geometria: Wednesday: 13:00
26. September 2007.room 661, Faculty of Physics
Nenad Vukmirovic (Institute of Microwaves and Photonics School of Electronic and Electrical Engineering, University of Leeds)
Unutarzonske optoelektronske naprave na bazi kvantnih tačaka
| U poslednje dve decenije, unutarzonski prelazi u poluprovodničkim nostrukuturama se primenjuju za izvore i detektore elektromagnetskih talasa u srednje i daleko-infracrvenoj oblasti spektra. NajviÅ¡e uspeha je postignuto sa unutarzonskim optoelektronskim napravama na bazi kvantnih jama, kao Å¡to su kvantno kaskadni laseri i infracrveni detektori. Zbog dužeg vremena života nosilaca u kvantnim tačkama, očekuje se da bi optoelektronske naprave na bazi unutarzonskih prelaza u kvantnim tačkama trebalo da imaju znanto bolje karakteristike. Da bi se ova mogućnost u potpunosti iskoristila, neophodno je razviti odgovarajuće teorijske modele za elektronske, optičke i transportne osobine aktivne oblasti ovih naprava, Å¡to ce biti glavna tema ovog predavanja. Najpre će biti prikazano kako se simetrija oblika kvantne tačke može iskoristiti da se efikasno izračunaju energijski nivoi u okviru kp metode. Semiklasicni model unutarzonske dinamike nosilaca ce zatim biti predstavljen, kao i njegova primena na dizajn optički pumpanog lasera na bazi unutarzonskih prelaza u kvantnim tačkama. Zatim će biti prikazana teorija elektronskog transporta u fotodetektorima na bazi kvantnih tačaka, koja polazi od energijskih nivoa i talasnih funkcija dobijenih reÅ¡avanjem kp Hamiltonijana, a kao izlaz daje merljive karakteristike naprava, kao Å¡to su struja mraka i odziv. Konacno će biti opisan elektronski transport kroz nizove elektronski spregnutih kvantnih tačaka, gde koherentni i polaronski efekti postaju važni, zbog čega je neophodan tretman u okviru formalizma neravnotežnih Grinovih funkcija. Moguća primena tih struktura za kvantno kaskadne lasere na bazi kvantnih tačaka ce biti diskutovana. |
Quanta symetria geometria: Friday: 16:00
29. June 2007.Faculty of Physics, room 661
Doc. Danica Krstevska (Prirodnomatematicki fakultet, Institut za fizika, Skopje)
ELECTRONIC PROCESSES IN LOW-DIMENSIONAL ORGANIC CONDUCTORS
| General characteristics of the low-dimensional organic conductors with quasi-one and quasi-two dimensional electron energy spectrum will be presented. The origin of some of the phenomena which occur in these conductors and make them different from the ordinary metals will be explained. |
Quanta symetria geometria: Wednesday: 13:00
30. May 2007.room 661, Faculty of Physics
Jelena Radovanović (Elektrotehnički fakultet, Beograd)
GL SPEKTRI U NAPONU PROBOJA TANKIH OKSIDNIH SLOJEVA
| Abstract: Na seminaru ce biti predstavljeni i objasnjeni galvanoluminescentni spektri dobijeni pri naponu proboja barijernih oksidnih filmova dobijenih anodizacijom aluminijuma u elektrolitima organskog i neorganskog porekla. Analizirace se morfologija povrsina dobijenih oksidnih slojeva na osnovu skenirajuce elektronske mikroskopije. |
Quanta symetria geometria: Wednesday: 13:00
14. March 2007.room 661, Faculty of Physics
Vladan Stevanović (Institute of Theoretical Physics, Ecole Polytechnique Federale de Lausanne Switzerland)
Efekat adsorpcije ugljenika na strukturnu stabilnost Ir4 klastera
| Abstract: Struktura i elektronske osobine Ir4 klastera u gasnoj fazi i adsorbovanih na MgO(100) proučavane su koristeći teoriju funkcionala gustine (DFT). Teorijski opis sistema interagujućih elektrona u spoljašnjem polju, baziran na DFT, etablirao se kao standardni pristup u fizici kondenzovanog stanja materije. Čak i u situacijama u kojima DFT ne daje korektan opis, razvijene su teorije koje koriste DFT za svoju osnovu. Dotaći će se neki od najvažnijih problema DFT-a, i opisati načini za njihovo prevazilaženje. Takođe će se izložiti originalni rezultati o osobinama Ir4 klastera dobijeni na osnovu standardnog DFT i diskutovati mogućnost njihove eksperimentalne verifikacije. |
Quanta symetria geometria: Monday: 13:00
20. November 2006.room 661, Faculty of Physics
Prof. Pierre Tronc (ESPCI, Paris)
SYMMETRY OF WURTZITE NANOSTRUCTURES WITH THE C AXIS IN THE LAYER PLANE
| Abstract: In wurtzite-based quantum wells and superlattices with the c axis parallel to the layer plane, the plane is parallel to either a symmetry plane of the wurtzite lattice (Type I structures) or a glide plane containing the c axis (Type II structures). In both cases, the symmetry of the structure depends on the parity of the number of monolayers within the slabs. Only Type II structures with odd monolayer numbers can present a built-in electric field. The field can arise from both the piezoelectric effect and the difference in spontaneous polarizability between the well and barrier materials. Quite different selection rules, depending on the structure symmetry, govern electron optical transitions and exciton radiative recombination as well as infrared absorption. On the contrary, Raman scattering obey rules that cannot easily help in distinguishing among the structures. The effect of applied magnetic and electric fields is presented. A simple test is proposed to distinguish the structures with the σv point symmetry and those with the C2v one. |
Quanta symetria geometria: Monday: 11:00
22. May 2006.Faculty of Physics, room 654
Mr. Becko Kasalica (Faculty of Physics, Belgrade)
Galvanoluminescentni i fotoluminescentni efekti na anodnim, oksidnim slojevima Al
| Abstract: Na seminaru ce biti predstavljeni i objasnjeni galvanoluminescentni spektri dobijeni pri naponu proboja barijernih oksidnih filmova dobijenih anodizacijom aluminijuma u elektrolitima organskog i neorganskog porekla. Analizirace se morfologija povrsina dobijenih oksidnih slojeva na osnovu skenirajuce elektronske mikroskopije. |
Quanta symetria geometria: Friday: 14:00
19. May 2006.Faculty of Physics, room 658
Prof. M. Drazic (Faculty of Mathematics, Belgrade)
O numerickom trazenju globalnog ekstremuma
Quanta symetria geometria: Wednesday: 13:00
12. April 2006.Faculty of Physics, room 661
Prof. Fedor Herbut (SANU)
Kvantno brisanje u dvo-fotonskoj interferenciji, nelokalnost i identicnost cestica
| Abstract: Objasniće se interferencija, potiskivanje interferencije i brisanje potiskivanja na dvo-fotonskom interferometru. Ukazaće se na nelokalnost u ponašanju dva fotona i na paradoksalnost takvog ponašanja (sa klasične tačke gledišta). Identičnost fotona uporediće se sa identičnošću nukleona u atomskom jezgru. |
Quanta symetria geometria: Tuesday: 13:00
11. April 2006.Faculty of Physics, room 661
Dr Janina Maultzsch (Technical University, Berlin)
Excitons in Carbon Nanotubes
| Abstract: The optical spectra of carbon nanotubes have been interpreted in terms of single-particle transitions until recently. In this talk I will show that the optical excitations are due to excitons, i.e. electron-hole pairs bound by Coulomb interaction. By two-photon luminescence excitation spectroscopy, we address exciton states with different symmetry and determine the binding energy to be around 400 meV. |
Quanta symetria geometria: Friday: 11:00
6. May 2005.Faculty of Physics, room 661
Prof. Maja Remskar (Jozef Stefan Institute Ljubljana)
Synthesis, electron microscopy and applications of inorganic nanotubes
| Abstract: The MoS2 and WS2 nanotubes synthesized by chemical transport reaction are the longest known inorganic nanotubes grown up to several millimetre lengths, with diameters from several micrometers to less than ten nanometers. The conditions of synthesis will be explained. The nanotubes grown at nearly equilibrium conditions are almost defect free. They have been successfully alloyed with metals, which suppresses the tube chirality and changes electrical properties. Microtubes usually grow as single tubes, the nanotubes combine in ropes. The self-assembly tendency is the most obvious in the sub-nanometer MoS2-xIy nanotubes, synthesized using C60 as a growth promoter. Due to the metallic behavior, these smallest known inorganic nanotubes are promising molecular wires. Foreseen applications: high porous catalytic and ultra light anticorrosive materials, non-toxic strengthening fibers, cantilevers in AFM or STM tips, sources of coherent electrons in field emission devices. |
Quanta symetria geometria: Wednesday: 13:00
4. May 2005.Faculty of Physics, room 661
Dr. Andrej Detela (Jozef Stefan Institute Ljubljana)
Quantum basis for self-organization in living organisms
| Absrtact: In recent years we have been facing exciting challenges that are emerging in the interdisciplinary area at the frontiers of physics, biology, and cognitive sciences. What is the origin of the wonderful self-organization inside living organisms? Is the origin possibly embodied in quantum phenomena? Is our established quantum picture a satisfactory description? Introductory ideas can be explained by means of an easy-to-imagine model with photons, an the complex dynamic systems by modern non-linear theory. Key topics: informational processes in biological structures, quantum coherence, electromagnetic aspects of self-organization in living organisms, magnetic knots and informational webs, complex systems. |
Quanta symetria geometria: Wednesday: 13:00
30. March 2005.Faculty of Physics, room 661
Prof. Pierre Tronc (ESPCI, Paris)
Symmetry properties of zinc-oxide nanorods and nanotubes
| Abstract: The point and space symmetries of ZnO nanorods and nanotubes are described by C6v point group and R70 (p63mc,L63mc) rod/line group. While C6v is the little group along Brillouin zone, the site-symmetry may be C3v, C3, or C1. Hence, the direct optical transitions in these nanostructures obey the same selection rules as those at Γ point of bulk, whereas the rules for transitions involving bound states are different. Heterostructures and effects of magnetic or/and an electric field(s) on the symmetry properties of the nanostructures are considered. |
Quanta symetria geometria: Wednesday: 13:00
23. March 2005.Faculty of Physics, room 661
Prof. Vitomir Milanovic (Electrotechnical Faculty - Belgrade)
Family of isospectral supersymmetric potentials
| Apstract: Dvostrukom faktorizacijom Hamiltonijana jednodimenzione Sredingerove jednacine moguce je generisati familiju potencijala, izospektralnih u odnosu na unapred zadati potencijal. Izvedene su analiticke relacije za izospektralni potencijal i odgovarajuce talasne funkcije. Izlozena metoda efikasno se primenjuje kod optimizacije elektricnih i optickih parametara poluprovodnickih nanostruktura. |
Quanta symetria geometria: Sunday: 11:00
13. March 2005.Faculty of Physics, room 661
Prof. Fedor Herbut (SANU)
Dvesta godina paradigmaticne difrakcije kroz dva otvora
| Abstract: Prikazane su fotonske i česticne realizacije Young-ovog eksperimenta difrakcije svetlosti kroz dva otvora kroz dva veka. Ukazano je na vezu Schröedinger-ove mačke i paradoksa Einstein-a, Podolskog i Rosen-a sa Young-ovim eksperimentom. (Predavanje održano u okviru ciklusa "Trijumf fizike XX veka" na Institutu za Fiziku, 23.3.2005.) |
Quanta symetria geometria: Monday: 13:00
15. March 2004.Faculty of Physics, room 661
Prof. Pierre Tronc (ESPCI, Paris)
Symmetry of electron states and optical selection rules in GaN/AlN quantum dots