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Atmospheric pressure chemical vapor deposition (APCVD) of ZnO from diethyl zinc (DEZn) and t-butanol was performed using an industrial reactor design. Deposition profiles were recorded to gain insight in the position dependent variations in layer thickness in such a reactor. We observed that for a deposition temperature below 400°C most of the deposition took place close to the exit of the gasses, while for increasing temperatures the deposition shifts towards the gas inlet. This trend can be explained by the reaction mechanism through an intermediate alkoxide species from DEZn and t-butanol, which in turn leads to ZnO deposition through a surface reaction. The deposition profile is dependent on the local alkoxide concentration. With increasing temperature, the formation rate increases. This translates in an earlier formation, i.e. in a shift upstream towards gas inlet because this alkoxide formation takes place during the transport through the reactor. Chemical vapor deposition (CVD) is a highly complex system with many interacting physical and chemical processes. Modeling was used to gain insight on the local variations of the concentration of reactive species inside a reactor and was shown to predict the deposition profiles. Moreover, the impact of changes in reactor design on the deposition is discussed.

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We present a preliminary report on the intra-operative use of a head-mounted microscope ("Varioscope" Leica HM500) in spinal neurosurgery. The Varioscope is a dynamic microscope mounted on a head-set. It weights 297 g and measures 73 x 120 x 63 mm (length x width x height). It offers an infinitely variable range of magnification from 3.6x to 7.2x. The working distance ranges from 300 to 600 mm. The field of view varies between 30-144 mm, depending on the selected enlargement factor and the working distance. In addition to the zoom function, the device offers a focus function (automatic or on demand). The optical elements for focus and zoom are located in two separate tubes which are mounted on a middle section containing the mechanical components as well as the receiver unit for the focussing elements. The lenses are adjusted by means of motor-driven push/pull cables. The autofocus works well in larger operative fields and a working distance between 30 and 60 cm. Nevertheless, when used in today's "keyhole" approaches, the autofocus is not helpful when operating in deep structures. Based on the satisfactory results achieved in our series, we can recommend the Varioscope, especially when no stationary microscope is available. The portable device can be packed in a suitcase and can travel with the consultant microsurgeon to different hospitals and distant units. The built-in video camera is ideal for patients, staff, assistant surgeons, and student education with real-time video monitoring of procedures from the microsurgeon's perspective. For daily microsurgery, we felt more comfortable with fixed, stationary operating microscopes.

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