Fókuszált ionsugaras és elektronsugaras nano-megmunkálás fizikai-kémiai alapjainak vizsgálata különös tekintettel a potenciális nanoelektronikai alkalmazásokra = Investigation of physical and chemical basics of focused electron and ion beam nano-machining with special emphasis on possible applications in nanoelectronics

Jelen OTKA pályázat tette lehetővé, hogy unikális LEO 1540XB keresztsugaras rendszerünk installációs és betanulási periódusa után kutatva „vegyük birtokba” a pásztázó nanosugaras vizsgálati és megmunkálási technikákat (litográfia / kisenergiás SEM és mikroanalízis / mikroszkópia és nanoméretekben folytatott marás és mintázatok kialakítása FIB segítségével / valamint ion vagy elektronsugaras anyagleválasztás nanoméretekben gázok injektálásával (GIS). Elsőnek a napelemtechnológiában használt Mo és ZnO FIB porlasztási sajátosságait és effektiv hozamát vizsgáltuk. A Mo erős anizotrópiájával szemben a ZnO homogén porlódást mutatott. Következő lépésként a FIB segítségével pórusos Si multirétegben fotonikus kristály szerkezeteket alakítottunk ki, majd W nanovezeték leválasztását tanulmányoztuk FIB- és SEM technikával. Az ionokkal leválasztott W réteg egyenletes leválási sebességet mutatott, míg az elektronsugár energiája és beesési szöge erősen hatott az így leválasztott réteg morfológiájára, bizonyítva a szekunder elektron emisszió hatását. In-situ és ex-situ ellenállásméréseket folytattunk, szobahőmérsékleten és hőkezelés közben. Az ionokkal leválasztott réteg ohmos jellegű volt, és hőkezelés után irreverzibilis ellenállás változást mutatott, ami W kristályosodásra utal. Az elektronsugárral leválasztott rétegen nemlineáris I-V karakterisztikát mértünk. A fenti kutatások tapasztalatai számos további kutatást segítettek, melyekről a „hasznosítás” pontban lesz szó. | The focused beam methods of shaping (lithography, milling, deposition), observation, and characterization of nanoscale objects had to be established in the MTA-MFA. After the installation and the basic training period of the new FEG-SEM/FIB cross beam instrument - being unique in Hungary – a combination of systematic training and research had to be carried out. As an example, basic FIB cutting and shaping properties and parameters of materials used in solar cell research (Mo and ZnO) were investigated. In the case of Mo layers strong sputtering anisotropy could be observed, while the ZnO showed uniform sputtering. As a next step FIB feature milling of photonic crystal structures followed. Optimization of FIB and SEM deposition of W nanowires had been carried out. The FIB deposited nanowires showed constant sputtering rate, while thickness of W layers deposited with e-beam of different energy and angle of incidence showed strong influence of secondary electrons. In-situ and ex-situ electrical resistivity measurement of the nanowires had been carried out at RT and elevated temperatures. The FIB deposited layers showed ohmic character,and a irreversible change of resistivity after heat treatment,- due to crystallization of W. The SEM deposited layers showed quasi-linear and nonlinear I-V characteristics. The methodology based on the results of the research contributed to several other research, mentioned in the section „usability”

Highly Homogeneous 2D/3D Heterojunction Diodes by Pulsed Laser Deposition of MoS2 on Ion Implantation Doped 4H-SiC

In this paper, 2D/3D heterojunction diodes have been fabricated by pulsed laser deposition (PLD) of MoS2 on 4H-SiC(0001) surfaces with different doping levels, i.e., n(-) epitaxial doping (approximate to 10(16) cm(-3)) and n(+) ion implantation doping (>10(19) cm(-3)). After assessing the excellent thickness uniformity (approximate to 3L-MoS2) and conformal coverage of the PLD-grown films by Raman mapping and transmission electron microscopy, the current injection across the heterojunctions is investigated by temperature-dependent current-voltage characterization of the diodes and by nanoscale current mapping with conductive atomic force microscopy. A wide tunability of the transport properties is shown by the SiC surface doping, with highly rectifying behavior for the MoS2/n(-) SiC junction and a strongly enhanced current injection for MoS2/n(+) SiC one. Thermionic emission is found the dominant mechanism ruling forward current in MoS2/n(-) SiC diodes, with an effective barrier phi(B) = (1.04 +/- 0.09) eV. Instead, the significantly lower effective barrier phi(B) = (0.31 +/- 0.01) eV and a temperature-dependent ideality factor for MoS2/n(+) SiC junctions is explained by thermionic-field-emission through the thin depletion region of n(+) doped SiC. The scalability of PLD MoS2 deposition and the electronic transport tunability by implantation doping of SiC represents key steps for industrial development of MoS2/SiC devices

A Graphene Surface Force Balance

We report a method for transferring graphene, grown by chemical vapor deposition, which produces ultraflat graphene surfaces (root-mean-square roughness of 0.19 nm) free from polymer residues over macroscopic areas (>1 cm2). The critical step in preparing such surfaces involves the use of an intermediate mica template, which itself is atomically smooth. We demonstrate the compatibility of these model surfaces with the surface force balance, opening up the possibility of measuring normal and lateral forces, including friction and adhesion, between two graphene sheets either in contact or across a liquid medium. The conductivity of the graphene surfaces allows forces to be measured while controlling the surface potential. This new apparatus, the graphene surface force balance, is expected to be of importance to the future understanding of graphene in applications from lubrication to electrochemical energy storage systems

Effects of temperature and ammonia flow rate on the chemical vapour deposition growth of nitrogen-doped graphene

We doped graphene in situ during synthesis from methane and ammonia on copper in a low-pressure chemical vapour deposition system, and investigated the effect of the synthesis temperature and ammonia concentration on the growth. Raman and X-ray photoelectron spectroscopy was used to investigate the quality and nitrogen content of the graphene and demonstrated that decreasing the synthesis temperature and increasing the ammonia flow rate results in an increase in the concentration of nitrogen dopants up to ca. 2.1% overall. However, concurrent scanning electron microscopy studies demonstrate that decreasing both the growth temperature from 1000 to 900 1C and increasing the N/C precursor ratio from 1/50 to 1/10 significantly decreased the growth rate by a factor of six overall. Using scanning tunnelling microscopy we show that the nitrogen was incorporated mainly in substitutional configuration, while current imaging tunnelling spectroscopy showed that the effect of the nitrogen on the density of states was visible only over a few atom distances

Controlling pyridinic, pyrrolic, graphitic, and molecular nitrogen in multi-wall carbon nanotubes using precursors with different N/C ratios in aerosol assisted chemical vapor deposition

Nitrogen-containing multi-wall carbon nanotubes (N-MWCNTs) were synthesized using aerosol assisted chemical vapor deposition (CVD) techniques in conjunction with benzylamine:ferrocene or acetonitrile: ferrocene mixtures. Different amounts of toluene were added to these mixtures in order to change the N/C ratio of the feedstock. X-ray photoelectron and near-edge X-ray absorption fine structure spectroscopy detected pyridinic, pyrrolic, graphitic, and molecular nitrogen forms in the N-MWCNT samples. Analysis of the spectral data indicated that whilst the nature of the nitrogen-containing precursor has little effect on the concentrations of the different forms of nitrogen in N-MWCNTs, the N/C ratio in the feedstock appeared to be the determining factor. When the N/C ratio was lower than ca. 0.01, all four forms existed in equal concentrations, for N/C ratios above 0.01, graphitic and molecular nitrogen were dominant. Furthermore, higher concentrations of pyridinic nitrogen in the outer shells and N2 molecules in the core of the as-produced N-MWCNTs suggest that the precursors were decomposed into individual atoms, which interacted with the catalyst surface to form CN and NH species or in fact diffused through the bulk of the catalyst particles. These findings are important for a better understanding of possible growth mechanisms for heteroatom-containing carbon nanotubes (CNTs) and therefore paving the way for controlling the spatial distribution of foreign elements in the CNTs using CVD processes

Szén nanocső jellegű nanoszerkezetek előállítása, módosítása és jellemzése fizikai, kémiai és szimulációs módszerekre alapozva = Production, modification and characterization by physical, chemical and computer simulation of carbon nanotube type nanostructures

Kimutattuk, hogy a nem-hatszöges (n-H) gyűrűket is tartalmazó szén nanoszerkezetek (Y-elágazás, hengerspirálok, stb.) növekedését az n-H gyűrűk beépülésének mikéntje határozza meg, új modellt javasoltunk hengerspirálok szerkezetére. Elsőként készítettünk Si3N4/szén nanocső kompozitokat és megmutattuk, hogy megfelelő szinterelési paraméterek alkalmazásával megőrizhetők az elektromosan vezetővé tett mátrix jó tulajdonságai. Új nanocső növesztési módszereket dolgoztunk ki. Elsőként bizonyítottuk, hogy az ionos besugárzás nyomán a szén nanocsöveken, valóban a szimulációknak megfelelő topográfiai alakzatok jelennek meg. Elméleti modellt adtunk a hibák környezetében azt STM felvételeken megfigyelhető szuperstruktúrák eredetére. Megmutattuk, hogy a funkcionalizálás módjától függően a funkciós csoportok szigetszerűen, vagy folytonoshelyezkednek el. A funkciós csoportok megváltoztatják a nanocsövek válaszjelét a környezetben jelenlévő gázokra/gőzökre. Sikeresen fejlesztettünk elméleti módszereket a gyengén kölcsönható nagy atomszámú rendszerek leírására és elsőkként vizsgáltuk sok szén nanocsöből felépülő kötegekben a csövek egymással való kölcsönhatását. Első elvekre illetve sűrűségfunkcionál módszerre alapozva vizsgáltuk a duplafalú szén nanocsövek, illetve a nanocsőben elhelyezkedő szénláncok tulajdonságait. A sajátfejlesztésű hullámcsomagdinamikai módszerünkkel elsőkként vizsgáltuk az elektronhullámok terjedését szén nanocső Y elágazásokban. | We showed that the growth of carbon nanostructures containing non-hexagonal (n-H) rings (Y-branches, coils etc.) is determined by the incorporation of the n-H rings, we proposed a new model for the structure of regularly coiled carbon nanotubes. We prepared the first Si3N4/carbon nanotube composites and we showed the under proper sintering conditions the composite can be made conductive while keeping the remarkable properties of the matrix. We developed new growth methods for carbon nanotubes. We showed for the first time that ion irradiation of carbon nanotubes indeed creates the features predicted by simulations. We proposed a theoretical description of the superstructures observed in STM in the vicinity of the defects. Depending on the way in which the functionalization is done, the functional groups appear on the nanotubes in an island-like or a continuous fashion. Their presence influences the response of the carbon nanotubes to the gases/vapors present in the atmosphere. We developed successfully theoretical tools for the description of weakly interacting large system and investigated for the first time the interaction of tubes in carbon nanotube bundles containing many tubes. Based on first principle and density functional calculations we investigated the double wall carbon nanotubes and linear carbon chains located inside a SWCNT. Using our own wave packet dynamical software we investigated the propagation of electronic waves in carbon nanotube Y junctions

Aerosol-assisted chemical vapour deposition synthesis of multi-wall carbon nanotubes: III. Towards upscaling

We report the optimisation of the experimental variables for the synthesis of large-area (90 cm2), mm-thick carpets of vertically aligned multi-wall carbon nanotubes (MWCNTs) using the aerosol-assisted chemical vapour deposition technique. The effect of the reactor size, temperature, time and the flow rate of the carrier gas on the catalytic conversion rate of the precursor, composition of the atmosphere of the reactor and various properties of MWCNTs such as the mass, length, outer diameter, defect density, oxidation resistance and residual catalyst concentration was investigated. By increasing the volume of the reactor from around 0.2 to 8.5 L, the mass of synthesised MWCNTs and the efficiency of the precursor were increased fivefold (up to 14 g/h.) and twice (up to 88%), respectively. Freestanding and on-substrate carpets of MWCNTs could withstand normal handling without falling apart, making them suitable for characterisations and applications from nano to macro scales. The synthesis recipe also improved the production rate of nitrogen-containing MWCNTs by an order of magnitude