S. Kipp

Stability of transparent zinc tin oxide transistors under bias stress

Shifts in the threshold voltage (ΔVth) of transparent zinc tin oxide (ZTO) transistors under gate bias stress are studied. The effect of composition and processing temperature on the device stability has been investigated. Based on the research, highly stable transistors with ΔVth as small as 30mV after 1000min of operation have been fabricated with a composition of [Zn]:[Sn]=36:64. As current drivers in active matrix displays their stability renders ZTO thin film transistors (TFTs) a very attractive alternative to TFTs based on established technologies.

Problems in temperature control performing in situ investigations with the scanning force microscope

Abstract Up to now, various publications dealing with in situ scanning force microscopy without any temperature control have been published. In this paper it is demonstrated that the temperature increase in the sample chamber due to the use of a diode laser in the detection unit cannot be neglected. The effect was quantified as 3–4 K per hour in the non-thermostatted SFM cell and by the recirculation of thermostatted liquid limited to 0.6 k.

Methods and apparatus for in situ investigations with the scanning force microscope

Abstract Various methods of carrying out time resolved in situ monitoring of crystallization processes with the scanning force microscope (SFM) were tested and improved. First investigations, taking place in static liquids, were performed in a simple cup sample holder and in the liquid cell supplied by the manufacturers of the SFM. Continuous flow conditions were realized with a new recirculating flow system, which in addition allows temperature control. The different apparative approaches were tested with lab-grown crystals of L-ascorbic acid and lithium fluoride, as well as freshly cleaved fragments of the naturally occurring mineral calcite.

Characterization of quantum structures by atomic-force microscopy

Abstract After a short discussion of errors incurred during atomic-force microscopy (AFM), we suggest methods for calibration. We describe specifically designed standards fabricated by metal organic vapor-phase epitaxy (MOVPE) which are utilized as a basis to calibrate the AFM microscope against a mechanical surface profiler and a scanning electron microscope (SEM). An important prerequisite is a well controlled technique to prepare the surface of the sample for AFM. This is demonstrated for the case of InGaAs/InP.

Crystallization of potassium nitrate (KNO3) in aqueous solution I. Growth kinetics of the pure system

Abstract The face specific crystal growth rates of potassium nitrate (KNO 3 ) in aqueous solution have been determined without the presence of additives. The results lead to the conclusion that each face exhibits its own crystal growth rate. The influence of the solutions flow rate and flow angle is given. The apparatus to observe two crystals and several crystallographic faces under identical conditions is described and the effect of growth rate dispersion is discussed.

Cooling crystallization experiments observed by in situ scanning force microscopy

The change in surface morphology of potassium nitrate and potassium alum has been studied in situ by means of scanning force microscopy. The supersaturation and undersaturation were varied in a cooling crystallizer under flow conditions. To keep the crystal growth rate of potassium nitrate low, the specific additive DOW FAX 3B2 had been used in different concentrations. The crystal growth rate of both systems could be determined and the growth and dissolution surface morphologies of potassium alum exhibited structures similar to those of microscopic measurements.

Reactive Processes of Nickel Oxide on Oxidic Substrates as Observed by Scanning Force Microscopy

High-temperature diffusion/reaction processes of nickel oxide (NiO) have been studied on oxidic surfaces. Nickel was sputtered on silicon dioxide (SiO2, quartz) and on yttrium stabilized zircon dioxide (YSZ). The metallic films with layer-thicknesses of 200 - 800 nm possessing well-defined steps and shapes, subsequently were annealed in air. On quartz, the thermal anneal at 500°C led to the formation of nickel olivine. Thermal anneal on YSZ at 500°C led to the formation of NiO. Further treatment at 1200°C caused the development of a sigmoid profile at the former step of the NiO film. The evolution of the topological changes with annealing time is not completely understood, but surface diffusion of NiO must play an essential role.

Topological aspects of iron corrosion in alkaline solution by means of scanning force microscopy (SFM)

Abstract The formation and growth of microcrystalline corrosion centers on polished iron surfaces are studied in the initial stages by scanning force microscopy (SFM). The corrosion process is controlled by cyclic voltammetry in 1M aqueous NaOH. The results concerning electrochemical aspects correspond to the literature. The in situ technique allows the observation of the crystal growth processes during corrosion. The formation of a surface layer overgrowing the initial structures caused by mechanical pretreatment has been found. Additionally defined polyhedral crystals were obtained with increasing number of cylic voltammograms.

Crystallization of potassium nitrate (KNO3) in aqueous solution Part II. Kinetical studies under the influence of additives

Abstract The face specific crystal growth rates of potassium nitrate (KNO 3 ) in aqueous solution have been determined under the influence of various additives. The additives were preselected by a very simple method and the concentration of the additives was in the range from 0.5–8000 ppm, corresponding to the mass of soluted potassium nitrate. The changes in the crystal habit and in the surface topographies were observed and could be explained by the differences in the adsorption energies on the various faces of potassium nitrate.

Heterogeneous dielectric mixtures in the terahertz frequency range: Theory and experiment

We present a new physical model for describing heterogeneous dielectric mixtures in the terahertz frequency range, which overcomes drawbacks of established models. The theory is confirmed by highly accurate data on polymeric compounds.