90 research outputs found
Impact of surface topography and laser pulse duration for laser ablation of solar cell front side passivating SiNx layers
No full textLocal contact openings in SiNx layers that passivate the front side of solar cells offer an attractive alternative to the current standard "fire-through" screen printing process for front grid fabrication. Additionally, this technology can be used for enabling a selective emitter. In the present paper, we investigate laser ablation of SiNx layers on planar and textured silicon surfaces for various laser wavelengths and pulse durations in the nanosecond (ns) to femtosecond (fs) range. We characterize the dark J-V characteristics of diodes with laser contact openings in the SiNx layer passivating the emitter. Our results show that on alkaline textured surfaces the ablation by a ns laser produces less damage than by an ultrashort pulse laser. The dark currents of alkaline textured diodes treated with picosecond (ps) or fs lasers are one order of magnitude higher than those of ns laser treated diodes. High ideality factors furthermore indicate crystal damage in the similar to 500 nm deep space charge region of the diodes. Scanning electron microscope and transmission electron microscope images of textured samples, confirm the presence of extensive and deep crystal damage after ps laser ablation, which are not observed in laser treated samples with planar surfaces. Correspondingly, for planar surfaces we find for both, ns and for ps laser ablated regions, emitter saturation current densities J(0e, abl) of similar to 2 pA/cm(2). The recombination in textured samples in contrast differs vastly for ns and ps laser ablation. The ns laser results in an only slightly increased value of 3.7 pA/cm(2) while the ps laser treated sample was not evaluable due to severe crystal damage leading to effective lifetimes of <5 mu s. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3493204
Micro-machining of PMN-PT Crystals with Ultrashort Laser Pulses
No full textLead–magnesium niobate lead titanate (PMN-PT) has been proven as an excellent material for sensing and actuating applications. The fabrication of advanced ultra-small PMN-PT-based devices relies on the availability of sophisticated procedures for the micro-machining of PMN-PT thin films or bulk substrates. Approaches reported up to date include chemical etching, excimer laser ablation, and ion milling. To ensure an excellent device performance, a key mandatory feature for a micro-machining process is to preserve as far as possible the crystalline quality of the substrates; in other words, the fabrication method must induce a low density of cracks and other kind of defects. In this work, we demonstrate a relatively fast procedure for the fabrication of high-quality PMN-PT micro-machined actuators employing green femtosecond laser pulses. The fabricated devices feature the absence of extended cracks and well-defined edges with relatively low roughness, which is advantageous for the further integration of nanomaterials onto the piezoelectric actuators
Univerzální Turingův stroj
No full textNázev práce: Univerzální Turingův stroj Autor: Viktor Bahýľ Katedra: Katedra Algebry Vedoucí bakalářské práce: prof. RNDr. Jan Krajíček, DrSc., Katedra algebry Abstrakt: Práce se zaměřuje na problematiku výpočetních úloh a jejich řešení. Na jejich řešení lze využít model Turingova stroje, který je plnou náplní této práce. Pro samotné řešení problémů je důležitá obecnost daného mechanismu, která je v teorií Turingova strojů zastoupena v podobě jejich univerzálnosti, která spojuje pojmy simulace a reprezentace. Hlavním výsledkem a úkolem práce je formulovat univerzální Turingův stroj a následně o něm tuto univerzálnost dokázat. V úvodních částech práce se nacházejí teoretické definice potřebné pro práci s těmito metodami řešení výpočetních úloh. Jako klíčové se ukáží již zmíněné pojmy simulace Turingových strojů a jejich reprezentace. Na oba pojmy je kladen samostatný důraz a snaha o co nejlepší vysvětlení těchto pojmů. V práci se pracuje s vlastní formou reprezentace, která je podrobně popsána a s nadefinovaným Turingovým strojem, jehož definice je také podrobně popsána, spolu s kompletním důkazem o univerzálnosti tohoto stroje. Klíčová slova: Turing, stroj, univerzálnost, reprezentaceTitle: Universal Turing machine Author: Viktor Bahýľ Department: Department of Algebra Supervisor: RNDr. Jan Krajíček, DrSc., Department of Algebra Abstract: This thesis is focused on the processes of solving computational problems. The Turing machine is an example of a model which we can use to solve these problems and these machines are the main objective of this Bachelor thesis. The generality of the model is important; it allows us to simulate any conceivable algorithm. In the theory of Turing machines, the generality is demonstrated by the construction of a universal Turing machine. This is the task of this Thesis: to define a universal Turing machine and to prove its universality. Key definitions, linked with the Turing machines, are recalled at the beginning of the Thesis. The simulation and representation of Turing machines will prove to be the key concepts. We make an extra effort to explain these fundamental notions. The thesis has its own form of representation and defined Turing machine with detailed descriptions for them, together with complete proof of the universality of the mentioned Turing machine. Keywords: Turing, machine, universality, representationDepartment of AlgebraKatedra algebryFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult
Wavelength-tunable sources of entangled photons interfaced with atomic vapours
No full textThe prospect of using the quantum nature of light for secure communication keeps spurring the search and investigation of suitable sources of entangled photons. A single semiconductor quantum dot is one of the most attractive, as it can generate indistinguishable entangled photons deterministically and is compatible with current photonic-integration technologies. However, the lack of control over the energy of the entangled photons is hampering the exploitation of dissimilar quantum dots in protocols requiring the teleportation of quantum entanglement over remote locations. Here we introduce quantum dot-based sources of polarization-entangled photons whose energy can be tuned via three-directional strain engineering without degrading the degree of entanglement of the photon pairs. As a test-bench for quantum communication, we interface quantum dots with clouds of atomic vapours, and we demonstrate slow-entangled photons from a single quantum emitter. These results pave the way towards the implementation of hybrid quantum networks where entanglement is distributed among distant parties using optoelectronic devices
Strain-controlled quantum dot fine structure for entangled photon generation at 1550 nm
No full textEntangled photon generation at 1550 nm in the telecom C-band is of critical importance as it enables the realization of quantum communication protocols over long distance using deployed telecommunication infrastructure. InAs epitaxial quantum dots have recently enabled on-demand generation of entangled photons in this wavelength range. However, time-dependent state evolution, caused by the fine-structure splitting, currently limits the fidelity to a specific entangled state. Here, we show fine-structure suppression for InAs quantum dots using micromachined piezoelectric actuators and demonstrate generation of highly entangled photons at 1550 nm. At the lowest fine-structure setting, we obtain a maximum fidelity of 90.0 ± 2.7% (concurrence of 87.5 ± 3.1%). The concurrence remains high also for moderate (weak) temporal filtering, with values close to 80% (50%), corresponding to 30% (80%) of collected photons, respectively. The presented fine-structure control opens the way for exploiting entangled photons from quantum dots in fiber-based quantum communication protocols
Reversible control of in-plane elastic stress tensor in nanomembranes
No full textA new class of strain actuators is presented, which allows the three components of the in‐plane stress tensor in a nanomembrane to be independently controlled. The functionality of the actuators is demonstrated using a semiconductor nanomembrane, whose light emission acts as a local and sensitive strain gauge
Stroj času jako kulečník
No full textNázev práce: Stroj času jako kulečník Autor: Jindřich Dolanský Katedra: Ústav teoretické fyziky Školitel: doc. RNDr. Jiří Langer, CSc. Školitelova e-mailová adresa: [email protected] Abstrakt: V této práci zkoumáme jednoduchý interagující systém dokonale pružné částice v nerelativistickém časoprostoru s netriviální kauzální strukturou uskutečněnou červí dírou s časovým posunem. Požadujeme platnost standardních lokálních fyzikálních zákonů a hledáme globálně konzistentní řešení, t.j., předpokládáme, že platí princip self-konzistence. Jestliže by existovala netriviální množina počátečních hodnot, která by porušovala tento princip, systém by byl logicky nekonzistentní. Ukážeme, že zk- oumaný systém není nekonzistentní v tomto smyslu, t.j., že pro všechny počáteční podmínky existují globálně konzistentní řešení. Dokonce i pro potenciálně paradoxní podmínky, které by mohly vyústit v nekonzistentní situace, lze nalézt konzistentní řešení. V tomto případě jsou nesrážkové paradoxní trajektorie nahrazeny speciálními konzis- tentními srážkovými trajektoriemi. Demonstrujeme, že pro širokou množinu počátečních dat existuje více než jedno globálně konzistentní řešení. Vývoj...Title: Billiard time machine Author: Jindřich Dolanský Department: Institute of Theoretical Physics Supervisor: doc. RNDr. Jiří Langer, CSc. Supervisor's e-mail address: [email protected] Abstract: In this work we investigate a simple interacting system of an elastic particle in the non-relativistic spacetime with a nontrivial causal structure realized by a worm- hole with a time shift. We require that standard local physical laws hold, and search for their globally consistent solutions, i.e, we assume the validity of the principle of self-consistency. If there were nontrivial set of initial conditions which would violate this principle, the system would be logically inconsistent. We show that the investigated system is not inconsistent in this sense, i.e., that all standard initial conditions have a globally consistent evolution. Even for the so called dangerous initial conditions which threaten to result into the paradoxical situation a consistent solution exists. In this case, the paradoxical collision-free trajectory is superseded by a special consistent self-colliding trajectory. Moreover, we demonstrate that more than one globally consistent evolution exists for a wide class of initial conditions. Thus, the evolution of the described system is not unique due to the nontrivial causal structure...Ústav teoretické fyzikyInstitute of Theoretical PhysicsMatematicko-fyzikální fakultaFaculty of Mathematics and Physic
A Proposal for a Contribution to the Oeuvre of Mihael Stroj
No full textDosad nepoznatu sliku »Portret Caroline Mazzalors-Hassmann«, nedavno doniranu Pomorskom muzeju Crne Gore u Kotoru, datirali smo oko godine 1840., a ukupnost dojma i pomna raščlamba, unatoč elementima koji mogu upućivati i na druge autore, navode nas na prijedlog atribucije ovog djela slovenskom slikaru Mihaelu Stroju. Ovaj tako jedinstven rad koji zrači ljepotom i začudnošću, smatramo da je naslikan upravo prepoznatljivom elegantnom manirom ovog autora.The paper analyses the “Portrait of Carolina Mazzalors-Hassmann”, recently donated to the Maritime Museum of Montenegro in Kotor from the estate of the noble Boka family of Smecchia. On the basis of comparison with autograph works from museum and private collections, the author attributes the portrait to the Slovenian painter Mihael Stroj (Ljubno, 1803 – Ljubljana, 1871), motivated by the unique modelling of the face, the grace of the figure and the position of the portrayed lady’s stylized hands, carefully and skilfully painted drapery, but also the balance between the figure and other figural elements – the romantic landscape in the distance, and especially the painter’s idiomatic treatment of skin which results in characteristically rendered smoothness of porcelain-like surface. All these elements of incontestable quality, despite evident decorative features, encourage the attribution of this unknown but complete work which emanates beauty and wondrousness to precisely this author and his characteristic elegant manner.
On the basis of similar hairstyles and clothes and by comparison with other portraits and surveys of contemporary fashion and biographical details of the portrayed person, the author attempts to determine the year in which the painting was created, concluding that it was executed around 1840. It could have been painted during the life of Mrs Mazzalors-Hassmann, but also after her premature death, after a portrait miniature by Andrea de Castro preserved by the heirs, which displays an identical facial expression and pose of the portrayed lady.
The relocation of the “Portrait of Carolina Mazzalors-Hassmann” from the salon of its previous owners to the permanent collection of the museum in Kotor has prompted an interest among both the public and art professionals, and the proposed attribution to Mihael Stroj is believed to earn the portrait a special place within the oeuvre of this prominent painter of the Viennese circle of the Biedermeier period
Laser material processing in the ablation-cooled regime: Ablation efficiency and quality using single fs-, bursts of fs-, and single ns-pulses (Conference Presentation)
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