The objectives of No Net Loss and Net Gain have emerged as key principles in conservation policy. Both give rise to mechanisms by which certain unavoidable biodiversity losses associated with development are quantified, and compensated with comparable gains (e.g. habitat restoration). The former seeks a neutral outcome for biodiversity after losses and gains are accounted for, and the latter seeks an improved outcome. Policy-makers often assume that the transition from one to the other is straightforward and essentially a question of the amount of compensation provided. Consequently, companies increasingly favour Net Gain type commitments, and financial institutions make lending conditional on either objective, depending on the habitat involved. We contend, however, that achieving Net Gain is fundamentally different to achieving No Net Loss, and moving from one to the other is less trivial than is widely realized. Our contention is based on four arguments: (1) the two principles represent different underlying conservation philosophies; (2) ecological uncertainties make it difficult to know where the threshold between No Net Loss and Net Gain lies; (3) different frames of reference are more or less appropriate in evaluating the ecological outcomes, depending on the principle chosen; and (4) stakeholder expectations differ considerably under the two principles. In exploring these arguments we hope to support policy-makers in choosing the more appropriate of the two objectives. We suggest that financial institutions should provide greater clarity regarding the explicit requirements for each principle. We conclude by highlighting questions of relevance to this topic that would benefit from focused research.

Thin films of cobalt have been deposited by photo-assisted metal-organic chemical vapour deposition. Samples of thickness less than 60 nm, grown at 110 °C, exhibit inverse hysteresis when an external magnetic field is applied in a particular direction normal to the plane of the film. These films are a mixture of crystalline and, possibly, amorphous phases with a grain size of about 130 nm and a significant oxygen content throughout. The potential roles of the various physical characteristics, as well as that of the photolytic deposition process itself, in the origin of the inverse hysteresis are discussed, as is a possible self-limiting growth mechanism.

Thin films of titania have been grown by photo-assisted MOCVD which are amorphous and relatively strain free, with high refractive index, low optical loss and structural features all less than 100 nm in size. The stoichiometry is very close to TiO2 and the impurity content is negligible except for a small amount of calcium, thought to have been leached from the glass substrate. The optimum deposition conditions were found to involve a deposition temperature of around 200 °C, a cell pressure of 5.6 torr and the introduction of nitrous oxide, decomposed by UV irradiation to give oxygen free radicals which acted as an oxidant.