In this paper the concept of pseudospinodal decomposition introduced by Ni and Khachaturyan [1] as a symmetry-lifting continuous phase separation, which can produce coherent nanoscale morphologies ranging from nanowires to nanolaminates, is reviewed. The term spinodal arises from the continuous change in the compositions of emerging cubic and tetragonal phases resulting in quasi-periodic microstructures stemming from the attendant transformation strain and surface energy anisotropies. It is argued here that important features of the pseudospinodal mechanism can be understood in terms of conventional classical and non-classical nucleation and that the behaviour is more general than the cubic → tetragonal transformation context articulated by its authors. Also, the possible relevance of the pseudospinodal mechanism to studies of decomposition of hypostoichiometric Fe-Pd alloys will be presented.

Laboratory experiments demonstrate that olivine irradiated with keV ions and exposed to water exhibits up to a 60% reduction from the original near‐surface concentration of magnesium, as measured by X‐ray photoelectron spectroscopy. The depth of this depletion layer is measured to be ∼15 nm. Irradiations were performed with 4 keV ions at fluences from 10 14 –10 19 ions cm –2 and water immersion times ranging from 3 s to more than 100 h in neutral (pH = 6.8), high‐purity water. The depletion of Mg depends strongly on ion fluence but weakly on immersion time after 3 min, when it saturates. Remarkably, ion irradiation enhances the rate of surface depletion of Mg from olivine by a factor of 26,000. This effect must be considered when assessing the surface composition of samples exposed to simulated space weathering in the laboratory and during the handling and analysis of irradiated extraterrestrial specimens acquired via sample return missions.

Recent laboratory experiments investigating the effect of ion irradiation on planetary minerals, show that changes in the surface composition differ depending on whether the analysis is done in situ, without removing the sample from vacuum, or ex situ. We find that olivine samples, irradiated with keV ions, show preferential loss of magnesium when exposed to water or the atmosphere. Irradiations were performed with 4 keV Ar ions to fluences between 10 and 10 ions/cm. Soak times in high purity water (pH = 7) ranged from minutes to days, and exhibit the same degree of Mg depletion independent of soak time. The concentration of magnesium on the surface of irradiated natural olivine decreases by as much as 60% upon contact with water, as measured with x-ray photoelectron spectroscopy. This finding is important for laboratory simulations of regolith processes and for establishing procedures for the handling of irradiated samples, especially those returned to Earth from space.

X-Ray photoelectron spectroscopy (XPS) provides surface sensitive chemical analysis of materials in vacuum, enabling the determination of atomic concentrations and chemical bonding within the first 50 nanometers of the sample surface. We will present progress on the design of an imaging XPS system with anticipated lateral resolution of 50 microns and 0.5 eV energy resolution. Sample illumination is accomplished using aluminum K- alpha X-rays. Scattered electron energy analysis is performed with the Physical Electronics 10-360 Spherical Energy Analyzer. The Sensor Sciences Cross Delay Line MCP detector provides position sensitive detection of scattered electrons. The case is also made for a low-power XPS instrument for in situ chemical analysis of extraterrestrial geologies.