Surface freezing in liquid Ga–Bi alloys: optical second harmonic and plasma generation study

Abstract

The phenomenon of surface freezing has been studied by second harmonic and plasma generation measurements in the entire composition range of liquid Ga-Bi alloys. Surface freezing was observed for the first time for all alloys with compositions between the eutectic (x Bi ¼ 0.0022, T eut ¼ 29.48 C) and monotectic point (x Bi ¼ 0.085, T mono ¼ 222 C). On cooling of such alloys a Bi-rich solid-like film forms on top of the bulk liquid phase at temperatures well above the liquidus line. On melting of these films a clear hysteresis behaviour is found, characterizing this type of transition as a first order phase transition. The maximum difference of 20 K between the liquidus temperature and the melting temperature of the surface freezing films was observed for the eutectic alloy. The line of surface freezing temperatures merges with the liquidus approaching the monotectic point. An estimate of the thickness of the Bi-rich surface freezing films from the interfacial free energies yields a value of the order of 10 nm. The correlation of the surface freezing and wetting transition occurring in the Ga-Bi system as well as the thermodynamics of surface freezing are qualitatively discussed.

Oscillatory wetting instability induced by liquid–liquid decomposition in a Ga–Pb alloy

“…16,17 Here we list only the information which is relevant to the results of this study. To generate the SHG and PG signals at the alloy-vapor interface, a Q-switched Nd-YAG laser ͑ϭ1064 nm͒ with a pulse duration of 4 ns, an irradiance of about 1 W/m 2 , a beam diameter of about 2 mm and a repetition rate of 5 Hz is used as a light source at an angle of incidence of about 70 degrees.…”

Surface solidification in liquid Ga‐Tl alloys

“…At this temperature an abrupt change in ∆ from 124° to 115° and in Ψ from 40.5° to 38.25° degree is observed within 45 seconds! The solidification temperature was reproducible in several runs within ±1.5 K. This jump was identified for Ga-Bi, Ga-Pb and Ga-Tl with the formation of a smooth solid surface film [6,9]. The quality of the surface and the reflection alignment is only marginally altered as can be seen by the small change in S 0 .…”

“…This transition was detected by different spectroscopic methods (second harmonic generation, SHG, [6], surface light scattering [7], x-ray photoelectron spectroscopy, XPS, [8], ellipsometry [9]) and was also found in a model calculation of surface phase transitions in Ga-Bi alloys [10]. Ellipsometric investigations showed that this surface solidification phenomenon is robust with respect to significant temperature gradients across the sample and to a variation of the cooling rate.…”

“…The characteristic kinetics of the film formation leads to the conclusion that at least two separate processes have to be considered: there is at first the fast preceding front that leads to the crystalline film (see e. g. [6,9]). The thin liquid like layer of Tl can be regarded as a precursor for the complete wetting transition as well as for the solidification process.…”

Phase behavior of binary mixtures composed of ethylene carbonate and various organic solvents

“…The monotectic reactions are widely known in the binary mixture of various kinds of metals, such as Zn/Pb, Zn/Bi, Cu/Pb, Na/Ca [15], and K/KCl [16,17] systems, or in the binary mixture of semiconductive materials, such as Si/Tl, Si/Pb, Si/Bi [17][18][19][20], Ga/Pb [21], Ga/Tl [20,[22][23][24], and Ga/Bi [25] systems. Today there are several papers concerning the binary mixture of organic compounds having a monotectic point; for examples, succinonitrile/water [26,27], succinonitrile/benzene [27], succinonitrile/hexamethylbenzene [7], aniline/water [15], and propylene carbonate/water [7] systems are reported as the samples for the binary mixture having a monotectic point.…”