Nanovezetékeken alapuló áramkörök gyártása és kvantum effektusainak elektron transzport vizsgálata = Fabrication and Electron Transport Study of Nanowire based Quantum Devices

Az anyagtudomány fejlődésének köszönhetően számos nanoméretű objektum létrehozására nyílik mód napjainkban, ilyenek például a félvezető nanopálcák (NW). Kis méretük miatt ezek a NW-k nagyon ígéretesek kvantum elektronikai célokra. Kvantum elektronika a modern szilárdtestfizika dinamikusan fejlődő területe, melynek fő célja elektromos áramkörök kvantum mechanikai szabadsági fokainak kontrollálása és kiolvasása, mint amilyen egy mesterséges atomba (QD) zárt elektron spinje. Jelen projektben nanoméretű áramkörök készítésére és kvantum effektusainak alacsony hőmérsékleti vizsgálatára alkalmas infrastruktúrát építettünk ki. Vizsgáltuk InAs NW-kból és szupravezető (S) ill. ferromágneses (F) elektródák kombinációjából készített áramköröket. InAs NW-ban kialakított dupla kvantum dotot szupravezetőhöz csatolva megmutattuk, hogy Cooper- párokat lehet térben szeparálni, ami megnyitja az utat mobil elektronokból álló Einstein Podolsky Rosen párok keltésére és összefonódottságuk tanulmányozására. Másrészről, ha F vezetéket kapcsolunk InAs NW-ban kialakított QD-hoz, akkor a ferromágnesség lokális kicserélődési téret kelt a mesterséges atomon. Megmutattuk, hogy ez a tér erősen függ a QD töltés állapotától. Sőt a tér még előjelet is válthat ugyanazon töltés állapotban, lehetővé téve az alap állapot spinjének megfordítását kapu feszültség segítségével. Megmutattuk, hogy egy ilyen F-QD rendszer hatékony spin áram erősítőként tud funkcionálni. | Recent development in material science allowed the synthesis of various nanoscale objects, like semiconductor nanowires (NW). Due to their small size, these NWs are very attractive for quantum electronic purpose. Quantum electronics is a dynamically progressing field of modern solid state physics, where the central goal is to manipulate and read out quantum mechanical degrees of freedom of circuits, like the spin of an electron trapped into a quantum dot (QD). In the present project the fabrication and transport characterization infrastructure have been established, which allows the production of nanocircuits and exploring their quantum effects in cryogenic measurements. We have investigated various InAs NW based electric circuits, where superconducting (S) and ferromagnetic (F) leads were attached to the wire. Coupling S lead to NW based double QD system, we have demonstrated, that Cooper pairs can be separated, which opens the way for Einstein Podolsky Rosen pair generation and entanglement analysis of mobile electrons. On the other hand attaching F lead to a QD, ferromagnetism penetrates into the dot inducing a local exchange field. We have shown that this exchange field strongly depends on the charge state of the QD. Furthermore it can even change sign for the same state, which allows the spin reversal of the ground state of the QD by gate voltage. We have shown that such an F- quantum dot system act as an efficient spin current amplifier

Kvantitatív Makyoh-topográfia = Quantitative Makyoh topography

A korszerű félvezető-technológiában alapvető fontosságú a szeletek felületi morfológiájának, az ideális síkjellegtől való eltérésének a minősítése. A korszerű nagy átmérőjű szeletek megjelenésével a síkjelleg problémája és így a megfelelő minősítési eljárás szükségessége fokozottabban jelentkezik. A jelen pályázat témája egy, a Távol-Keletről származó ősi, "mágikus" tulajdonságú tükör elvén alapuló optikai vizsgálati módszer, a Makyoh-topográfia alkalmassá tétele igényes metrológiai célokra. A kutatás során új koncepciójú, nagy méretű minták vizsgálatára alkalmas mérési összeállításokat valósítottunk meg. Tanulmányoztuk a felületi domborzat visszanyerésére szolgáló eljárások érzékenységét és pontosságát, valamint a leképezés alapvető tulajdonságait. A kidolgozott mérési eljárást számos félvezető-technológiai és egyéb kutatásban alkalmaztuk. Lépéseket tettünk a mérési eljárás gazdasági hasznosítása érdekében. | The assessment of the surface morphology and flatness of the wafers is a key issue in modern semiconductor technology. The need for a proper flatness characterisation method became even more important with the advent of today's large-diameter wafers. The aim of the present project is to make Makyoh topography, an optical characterisation tool based on an ancient 'magic' mirror of Far-East origin suitable for advanced metrological purposes. During our research, we have constructed novel measurement set-ups suitable for the study of large-diameter samples. We have studied the sensivity and accuracy of the numerical methods for the reconstruction of the surface topography and investigated the basic characteristics of the imaging mechanism. The developed methods have been applied in semicondutor technolgy research as well as in other areas. We have taken steps forward the industrial exploitation

Effect of Different Anions Upon the WO3 Morphology and Structure

In this study the effects of various anions (SO42-, ClO4- and PO43-) were investigated on the hydrothermal treatment of WO3 from Na2WO4 and HCl at 180 and 200 degrees C. The products were analyzed by XRD and SEM. With the usage of SO42- the obtained product was hexagonal (h-) WO3 in the form of nanorods at both temperatures. Applying ClO4- resulted in a mixture of WO3 center dot 0.33H(2)O and small amount of m-WO3 at 180 degrees C and pure WO3 center dot 0.33H(2)O at 200 degrees C. The morphology was consisted of cuboid shapes arranged into spherical structures at 180 degrees C and longitudinal ones at 200 degrees C. By the application of PO43- no product formed at either temperature. Using the combination of SO42-, and ClO4- the product was h-WO3 at both 180 and 200 degrees C with rod-like crystals; thus, the effect of ClO4- was overdominated by the SO42- ions. Utilization of PO43- together with SO42-, and/or ClO4- resulted again in no product, meaning that adding PO43- to the reaction mixture completely blocks the hydrothermal formation of solid products by forming water soluble phosphotungstic acids

Piezo-force and Vibration Analysis of ZnO Nanowire Arrays for Sensor Application

To estimate the potential of ZnO nanostructures for force sensing applications, arrays of single nanowires and arrays of nanowire bundles have been fabricated by wet chemical growth method. The piezoelectrical and electrical properties of the single nanowires have been investigated by atomic force microscopy based techniques. The piezoelectric constant d33 = 15 pm/V has been determined from vibration analyses. The electrical response in the range up to 400 fA upon applying force between 40 nN and 1 μN has been recorded. The nanowire bundles were studied by electro-mechanical macro probing technique within the force range 1 - 10 mN, where a reproducible response in pA range has been measured

Resolving lateral and vertical structures by ellipsometry using wavelength range scan

For most thin film structures, by changing the wavelength range to fit ellipsometric spectra, the values of the fitted parameters also change to a certain extent. The reason is that compared with the ellipsometric sensitivity many thin films are vertically non-uniform. In absorbing films with significant dispersion in the used wavelength range, the penetration depth of probing light can show large variations depending on the wavelength. Consequently, the value of a fitted parameter for a certain wavelength range is a weighted sum of structural information over different depth ranges corresponding to the different wavelengths. By changing the wavelength range, the range of penetration depths can be adjusted, and the fitted values can be plotted as a function of the probed depth range calculated directly from the determined or tabulated extinction coefficients. We demonstrate the results on deposited polycrystalline thin films. The advantage of this approach over the parameterization of structural properties as a function of depth is that the wavelength scan approach requires no parameterized depth distribution model for the vertical dependence of a layer property. The difference of the wavelength scan method and the vertical parameterization method is similar to the difference between the point-by-point and the parameterized dielectric function methods over the used wavelength range. The lateral structures strongly influence the ellipsometric response, as well. One of the most remarkable effects is when the lateral feature sizes approach the wavelength of the probing light. In this case the effective medium method is not valid any more, since scattering and depolarization occurs. By scanning the wavelength range, the limit wavelength of the onset of scattering can be found, and used for the determination of the corresponding critical lateral period length

Hydrothermal Synthesis and Gas Sensing of Monoclinic MoO3 Nanosheets

Effects of different reaction parameters in the hydrothermal synthesis of molybdenum oxides (MoO3) were investigated and monoclinic (β-) MoO3 was prepared hydrothermally for the first time. Various temperatures (90/210 °C, and as a novelty 240 °C) and durations (3/6 h) were used. At 240 °C, cetyltrimethylammonium bromide (CTAB) and CrCl3 additives were also tested. Both the reaction temperatures and durations played a significant role in the formation of the products. At 90 °C, h-MoO3 was obtained, while at 240 °C the orthorhombic (α-) MoO3 formed with hexagonal rod-like and nanofibrous morphology, respectively. The phase transformation between these two phases was observed at 210 °C. At this temperature, the 3 h reaction time resulted in the mixture of h- and α-MoO3, but 6 h led to pure α-MoO3. With CTAB the product was bare o-MoO3, however, when CrCl3 was applied, pure metastable m-MoO3 formed with the well-crystallized nanosheet morphology. The gas sensing of the MoO3 polymorphs was tested to H2, which was the first such gas sensing study in the case of m-WO3. Monoclinic MoO3 was found to be more sensitive in H2 sensing than o-MoO3. This initial gas sensing study indicates that m-MoO3 has promising gas sensing properties and this MoO3 polymorph is promising to be studied in detail in the future

Effect of pH in the hydrothermal preparation of monoclinic tungsten oxide

This paper presents the preparation of monoclinic WO3 by a one-step hydrothermal method. The effect of very acidic pH (0.1) and the significance of various additives (CH3COOH, NaClO4, Na2SO4) were investigated. To clarify the role of pH on the obtained crystal structure and morphology, every synthesis using pH 1 were repeated, and the effect of temperature, using 180 and 200 °C, was also studied. All samples prepared at pH 0.1 were pure, well crystallized monoclinic WO3 independently from the temperature, the presence and the quality of the additives. At 180 and 200 °C, applying CH3COOH and NaClO4 resulted nanosheets similar in size. With Na2SO4 additive at 180 °C sheets, at 200 °C sheets and also rods formed indicating that SO4 2− was a capping agent only at 200 °C. For comparison, at pH 1 at both temperatures the crystalline phases and the morphologies varied depending on the type of the additive. © 2019 The Author