In a recent paper, Zhang et al. (2008b) described the results from an infrared (IR) spectroscopic study that addressed structural changes in a synthetic zircon (ZrSiO4) sample that resulted from the irradiation with heavy (i.e., 280 keV Pb+) ions. Infrared analyses of the same zircon sample have been also described by Zhang et al. (2008a). I see major problems with some of the interpretations presented in these two papers. Problems arise from the failure to consider the significant discrepancy between the sample volumes that were irradiated and analyzed, respectively. To illustrate the following discussion, a largely simplified sketch of the irradiated sample is shown in Figure 1⇓. On the one hand, the Pb+-implanted sample described by Zhang et al. (2008b) has certainly experienced surficial damage, due to displacive collision events, in a surficial volume zone extending only ~0.1 μm into the sample. On the other hand, the sampling depth of infrared reflectance measurements of transparent samples with a Bruker grazing angle objective is in the micrometer-range or even larger (n.b., this depends on several factors such as the irradiation angle, optical properties of the solid to be analyzed, and especially the wavelength of the infrared light; J. Sawatzki and G. Zachmann, Bruker GmbH, personal communication; see also Brunner et al. 1997). This makes conventional IR reflectance analysis extremely difficult, or even impossible, if thin films or layers with thicknesses well below the micrometer-range, located on top of a transparent host material, are to be analyzed. The IR analysis of such samples requires the application of special preparation and/or analysis techniques (see for instance Otto and Korte 1988; Amekura et al. 2004), which have not been implemented by Zhang et al. (2008b). This discrepancy in length scales suggests that in their IR …