J.G. Na

Few-Layer Black Phosphorus Field-Effect Transistors with Reduced Current Fluctuation

We investigated the reduction of current fluctuations in few-layer black phosphorus (BP) field-effect transistors resulting from Al2O3 passivation. In order to verify the effect of Al2O3 passivation on device characteristics, measurements and analyses were conducted on thermally annealed devices before and after the passivation. More specifically, static and low-frequency noise analyses were used in monitoring the charge transport characteristics in the devices. The carrier number fluctuation (CNF) model, which is related to the charge trapping/detrapping process near the interface between the channel and gate dielectric, was employed to describe the current fluctuation phenomena. Noise reduction due to the Al2O3 passivation was expressed in terms of the reduced interface trap density values D(it) and N(it), extracted from the subthreshold slope (SS) and the CNF model, respectively. The deviations between the interface trap density values extracted using the SS value and CNF model are elucidated in terms of the role of the Schottky barrier between the few-layer BP and metal contact. Furthermore, the preservation of the Al2O3-passivated few-layer BP flakes in ambient air for two months was confirmed by identical Raman spectra.

Correlation between interfacial segregation and surface-energy-induced selective grain growth in 3% silicon-iron alloy

Abstract Effects of final reduction and interfacial segregation of sulfur on surface-energy-induced selective grain growth have been investigated in 3% silicon–iron alloy strips with various bulk content of sulfur. Interfacial segregation kinetics of sulfur varies with annealing atmosphere: a convex profile under vacuum or hydrogen and a gradual increase under argon. This is because the segregated sulfur evaporates or gasifies to hydrogen sulfide during final vacuum or hydrogen annealing, resulting in a sulfur-depleted zone just below the strip surface. The surface-energy-induced selective growth of a grain at time t is determined by the concentration of segregated sulfur. The selective growth rate depends on the combined effect of the segregated sulfur and the final reduction that determines the average grain size. For obtaining (110)[001] Goss texture, the final reduction should, therefore, be controlled, depending on the bulk content of sulfur which influences directly the segregation kinetics of sulfur and thus the texture development.

Effect of surface segregation of sulfur on recrystallization kinetics in 3% Si–Fe alloy strip

Effects of bulk content of sulfur on sulfur segregation and surface energy induced recrystallization kinetics have been investigated in two alloys containing 6 and 30 ppm sulfur. During final annealing under a high vacuum, the convex profile in sulfur concentration, which is attributed to sulfur segregation and evaporation, corresponded to the trough in magnetic induction, irrespective of bulk sulfur content. During annealing, surface energy induced secondary and tertiary recrystallization were in turn observed. While the grain boundary pinning effect of segregated sulfur was very weak in the alloy containing 6 ppm sulfur, the grain boundaries in the other alloy were strongly pinned by the segregated sulfur. Under the relatively higher sulfur atmosphere appearing in the alloy containing 30 ppm sulfur, the growth rate of {100} grain was absolutely governed by the Zener term related to the segregation concentration of sulfur. Through such a recrystallization process, a complete {110}〈001〉 Goss texture was f...

High coercivity and small grains of (Fe/sub 57/Pt/sub 43/)/sub 100-x/Cu/sub x/ ternary thin films

(Fe/sub 57/Pt/sub 43/)/sub 100-x/Cu/sub x/ ternary films with x=0-4 at.% were prepared on Corning 7059 glass by dc magnetron sputtering in order to investigate the effect of Cu addition on the transformation rate of FePt alloy films. Structural and chemical analysis revealed that Cu was very effective in promoting the transformation to the L1/sub 0/ ordered phase and in suppressing grain growth of the L1/sub 0/ ordered phase when films were annealed at 400/spl deg/C-700/spl deg/C in vacuum. During the annealing, Cu atoms diffused onto the film surface, probably yielding many defects that remained inside the film. This Cu diffusion may be the reason for the rapid transformation.

Magnetic induction and surface segregation in thin-gauged 3% Si steel

A correlation between magnetic induction and surface phenomena has been investigated in a 3% Si steel 0.1 mm thick. During final annealing at several temperatures, the saturation level in magnetic induction increased with increasing final annealing temperature, and reached 1.93 T after final annealing at 1300 °C for 4.9 ks. This is attributed to the formation of complete (110)[001] Goss texture. During final annealing, the magnetic induction of the thin-gauged 3% Si strip was inversely proportional to the sulfur concentration on the surface. The surface segregation of sulfur occurred after a critical time the silicon concentration on the surface dropped to the level obtained from the α-iron matrix containing 3% Si. The drop in silicon level on the thin-gauged strip surface is due to the volatile silicon monoxide, which arises from the reaction between the silicon dioxide and the silicon segregated, or between the silicon segregated and the oxygen from the high vacuum condition.

Tertiary recrystallization and magnetic induction under various annealing atmospheres in thin-gauged 3% Si–Fe strip

Surface-energy-induced secondary or tertiary recrystallization by grains with a specific surface plane can be freely governed in thin-gauged 3% Si–Fe strips by controlling the bulk content of sulfur and annealing atmosphere. During a vacuum or hydrogen annealing process, a convex profile in segregated-sulfur concentration is formed due to evaporation or desorption of segregated sulfur as a hydrogen sulfide, corresponding to a trough in magnetic induction. High magnetic induction is obtained after the annealing treatments. Final annealing under an argon atmosphere caused a saturation in segregated-sulfur concentration with annealing time. Under this extremely high segregated sulfur, grains of high index crystal plane including {111} continued to grow, resulting in low magnetic induction.

Nucleation and development of Goss texture and magnetic induction in thin-gauged 3% Si–Fe alloy

Nucleation and development of Goss texture have been investigated in high-purity 3% silicon–iron alloy strips. During final annealing, under a high vacuum, Goss texture can form independently from cold-rolled matrix at the early stage of primary recrystallization, regardless of any pre-existing Goss texture near the strip surface. The formation mechanism of the new Goss texture probably follows the oriented nucleation theory, which is due to segregated sulfur present on the strips in a final annealing time. Goss texture in the primary recrystallization develops into the final Goss texture or not, depending on cold rolling conditions.

Initial recrystallization texture and magnetic induction in single-oriented electrical steel

Initial recrystallization texture is influenced by the bulk content of sulfur and by the final reduction. At a given bulk content of sulfur, a lower final reduction is favorable for obtaining the initial {011} Goss texture. Under a fixed final reduction, a lower bulk content of sulfur is good for this purpose. As the intensity of initial Goss texture increases, it is easier to obtain magnetic induction (B/sub 10/). This is because the probability, that the initial Goss grains survive within the time range of highly segregated sulfur and have a chance for surface-energy-induced selective growth, becomes higher under the later segregated-sulfur-free condition.

Effects of segregated sulfur on recrystallization texture and magnetic induction in thin-gauged 3% silicon steel

During final annealing at 1200/spl deg/C under a high vacuum, changes in recrystallization texture with final annealing time were observed in thin-gauged 3% Si-Fe alloys. In the alloy containing 30 ppm bulk sulfur, the recrystallization texture varied from the {111} to the {001} and finally to the {110} Goss texture, resulting in higher magnetic induction than 1.90 T. The trough in magnetic induction, which corresponds to the relatively high surface-segregated sulfur range, is due to the magnetically detrimental effect of those textures, i.e. the {111} and the {001} . In the alloy containing 6 ppm bulk sulfur, the correlation between magnetic induction and surface-segregated sulfur was the same as that in the other alloy. These results clearly indicate that the surface energy induced recrystallization in the thin-gauged 3% Si-Fe alloys is strongly affected by the segregation and the evaporation of sulfur.

Effects of flow rate of hydrogen on selective growth kinetics and magnetic induction in thin-gauged 3% Si-Fe strip

During final annealing, microalloyed sulfur in thin-gauged silicon steel segregates to the strip surface and on grain boundaries and thus affects the texture development. With increasing flow rate of hydrogen, the profile of magnetic induction was shifted to a shorter annealing time, and the time range of lower magnetic induction was drastically shortened. This is ascribed to the faster depletion of surface-segregated sulfur that accelerates surface-energy-induced selective growth of (110)[001] Goss grains. After final annealing for 14.4 ks, the strips showed a high magnetic induction of about 1.9 T. By controlling the surface segregation behavior of sulfur, it is possible to achieve the surface-energy-induced selective growth of grains favorable for magnetic induction in thin-gauged silicon steel.