Márton Major

High mobility indium zinc oxide thin film field-effect transistors by semiconductor layer engineering.

Indium zinc oxide thin-film transistors are fabricated via a precursor in solution route on silicon substrates with silicon dioxide gate dielectric. It is found that the extracted mobility rises, peaks, and then decreases with increasing precursor concentration instead of rising and saturating. Investigation with scanning probe techniques reveals full thickness variations within the film which are assumed to adversely affect charge transport. Additional layers are coated, and the extracted mobility is observed to increase up to 19.7 cm(2) V(-1) s(-1). The reasons for this are examined in detail by direct imaging with scanning tunneling microscopy and extracting electron density profiles from X-ray reflection measurements. It is found that the optimal concentration for single layer films is suboptimal when coating multiple layers and in fact using many layers of very low concentrations of precursor in the solution, leading to a dense, defect and void free film, affording the highest mobilities. A consistent qualitative model of layer formation is developed explaining how the morphology of the film develops as the concentration of precursor in the initial solution is varied.

Influence of tetragonal platelets on the dielectric permittivity of0.964Na1/2Bi1/2TiO3−0.036BaTiO3

We study the temperature-dependent evolution of the octahedral tilt order in a lead-free relaxor ferroelectric and its impact on the ferroelectric properties. Using diffuse neutron scattering on a

Origin of superstructures in (double) perovskite thin films

0.964{\mathrm{Na}}_{1/2}{\mathrm{Bi}}_{1/2}{\mathrm{TiO}}_{3}\text{\ensuremath{-}}0.036{\mathrm{BaTiO}}_{3}

(001) and (111) Single-Oriented Highly Epitaxial CeO2 Thin Films on r-Cut Sapphire Substrates

single crystal, we suggest a model for the temperature-dependent nanostructure of this perovskite that features chemically pinned tetragonal platelets embedded in the rhombohedral matrix, often separated by a cubic intermediate phase. Our results show a clear correlation between the squared thickness of the tetragonal platelets and the dielectric permittivity. This is interpreted as a sign for increased polarizability of the strained and distorted lattice at the center of the tetragonal platelets.

Relaxation of dynamically disordered tetragonal platelets in the relaxor ferroelectric 0.964Na1/2Bi1/2TiO3-0.036BaTiO3

We have investigated the origin of superstructure peaks as observed by X-ray diffraction of multiferroic Bi(Fe0.5Cr0.5)O3 thin films grown by pulsed laser deposition on single crystal SrTiO3 substrates. The photon energy dependence of the contrast between the atomic scattering factors of Fe and Cr is used to rule out a chemically ordered double perovskite Bi2FeCrO6 (BFCO). Structural calculations suggest that the experimentally observed superstructure occurs due to unequal cation displacements along the pseudo-cubic [111] direction that mimic the unit cell of the chemically ordered compound. This result helps to clarify discrepancies in the correlations of structural and magnetic order reported for Bi2FeCrO6. The observation of a superstructure in itself is not a sufficient proof of chemical order in double perovskites.

Disordered structures in lead-free piezoelectrics

We have studied the growth of CeO2 thin films by molecular beam epitaxy on r-cut sapphire substrates. The oxidation state of the substrate surface controls the growth direction of CeO2. Oxygen pre-annealed substrates favor (001) growth, while oxygen vacancies lead to a mixed (001) and (111) orientation. Combining pre- and post-annealing, it is possible to achieve single- oriented CeO2 in both growth directions. Furthermore, post-annealing results in a dramatic increase of crystallinity with a rocking curve width of the (002) reflection as small as 0.004°. We provide a consistent growth model involving oxygen vacancies at the substrate to thin film interface.

Preparation for Cavity Material Studies at the Vertical High-Temperature UHV-Furnace of the S-DALINAC

The local dynamics of the lead-free relaxor

Upgrade of a UHV Furnace for 1700 C Heat Treatment and Processing of Niobium Samples

0.964{\mathrm{Na}}_{1/2}{\mathrm{Bi}}_{1/2}{\mathrm{TiO}}_{3}\ensuremath{-}0.036{\mathrm{BaTiO}}_{3}

Temperature‐Dependent Deformation and Dislocation Density in SrTiO3 (001) Single Crystals

(NBT-3.6BT) have been investigated by a combination of quasielastic neutron-scattering (QENS) and ab initio molecular dynamics simulations. In a previous paper, we were able to show that the tetragonal platelets in the microstructure are crucial for understanding the dielectric properties of NBT-3.6BT [Pforr et al., Phys. Rev. B 94, 014105 (2016)]. To investigate their dynamics, ab initio molecular dynamics simulations were carried out using

Epitaxial growth and control of the sodium content in NaxCoO2 thin films

{\mathrm{Na}}_{1/2}{\mathrm{Bi}}_{1/2}{\mathrm{TiO}}_{3}