The application of Makyoh (magic-mirror) topography for the study of deformations in dielectric membrane structures

The flatness of membranes for micromachining applications is extremely important. Any deformation is a sign of internal stress that makes the structure susceptible to mechanical damage therefore unsuitable for any practical application. In microwave applications, surface protrusions act as harmful radiating elements. There is therefore a demand for the characterisation of the flatness and surface morphology of such structures. Usual methods are scanning electron microscopy, surface stylus profilometry, atomic force microscopy and various optical methods. One of the potential optical methods is the so-called Makyoh (or magic-mirror) topography, which has proved to be a powerful topographic method for the characterisation of the morphology of mirror-.like surfaces, such as semiconductor wafers and layer structures. In Makyoh topography, the local irregularities of the sample surface act as concave or convex mirrors therefore a collimated light beam impinging on the surface produces an image on a screen that, in a certain extent, reflects the sample morphology. Makyoh topography is advantageous for the studies of membrane structures for the following reasons: (i) Makyoh is contactless, which is important for the delicate structures, (ii) It gives instantaneous results, (iii) The set-up is simple and inexpensive, (iv) The resulting ‘raw’ image is visually informative. However, the quantitative interpretation of Makyoh images is not straightforward. This work firs describes a comprehensive geometrical optical model of the Makyoh image formation mechanism with an aim to provide a basis both for the in-depth quantitative analysis as well as for the quick, qualitative or semi-quantitative visual interpretation of the images. Methods for the measurement of overall curvature and the reconstruction of the surface profile from the observed images are described. One-dimensional simulations of the images of a hillock (or depression) and a periodic (sinusoidal) surface are presented as well. Then, the construction of our Makyoh-topography set-up is detailed. Then, the study of the deformations of dielectric membranes and structures is reported. It is shown that Makyoh is suitable to detect and quantify the deformations of the whole wafer, the individual membranes as well as the substrate areas adjacent to the membranes. For small membranes and strongly patterned structures, the imaging is limited by diffraction effects. However, qualitative study is possible. The results are interpreted qualitatively within the framework of continuum mechanic

Optimising DTwP-containing vaccine infant immunisation schedules (OptImms) — a protocol for two parallel, open-label, randomised controlled trials

Abstract Background Universal immunisation is the cornerstone of preventive medicine for children, The World Health Organisation (WHO) recommends diphtheria-tetanus-pertussis (DTP) vaccine administered at 6, 10 and 14 weeks of age as part of routine immunisation. However, globally, more than 17 unique DTP-containing vaccine schedules are in use. New vaccines for other diseases continue to be introduced into the infant immunisation schedule, resulting in an increasingly crowded schedule. The OptImms trial will assess whether antibody titres against pertussis and other antigens in childhood can be maintained whilst adjusting the current Expanded Programme on Immunisation (EPI) schedule to provide space for the introduction of new vaccines. Methods The OptImms studies are two randomised, five-arm, non-inferiority clinical trials in Nepal and Uganda. Infants aged 6 weeks will be randomised to one of five primary vaccination schedules based on age at first DTwP-vaccination (6 versus 8 weeks of age), number of doses in the DTwP priming series (two versus three), and spacing of priming series vaccinations (4 versus 8 weeks). Additionally, participants will be randomised to receive their DTwP booster at 9 or 12 months of age. A further sub-study will compare the co-administration of typhoid vaccine with other routine vaccines at one year of age. The primary outcome is anti-pertussis toxin IgG antibodies measured at the time of the booster dose. Secondary outcomes include antibodies against other vaccine antigens in the primary schedule and their safety. Discussion These data will provide key data to inform policy decisions on streamlining vaccination schedules in childhood. Trial registrations ISRCTN12240140 (Nepa1, 7th January 2021) and ISRCTN6036654 (Uganda, 17th February 2021)