Francesco Marinello

Critical factors in SEM 3D stereo microscopy

This work addresses dimensional measurements performed with the scanning electron microscope (SEM) using 3D reconstruction of surface topography through stereo-photogrammetry. The paper presents both theoretical and experimental investigations, on the effects of instrumental variables and measurement parameters on reconstruction accuracy. Investigations were performed on a novel sample, specifically developed and implemented for the tests. The description is based on the model function introduced by Piazzesi and adapted for eucentrically tilted stereopairs. Two main classes of influencing factors are recognized: the first one is related to the measurement operation and the instrument set-up; the second concerns the quality of scanned images and represents the major criticality in the application of SEMs for 3D characterizations.

Atomic force microscopy analysis shows surface structure changes in carvacrol-treated bacterial cells

Carvacrol is a major component in some essential oils such as oregano and thyme and its inhibitory effect on the growth of various microorganisms is well documented. However, the active mechanism of carvacrol, as well as that of other essential oil components, has not yet been fully established and has generally not been well investigated. In this study, the antimicrobial activity of carvacrol against some Gram-positive and Gram-negative food-related bacterial strains was preliminarily verified and the effect of carvacrol on their cell envelope was further investigated by atomic force microscopy analysis. The atomic force microscopy images of the cells treated with carvacrol 3.3 mM for 1 h were analyzed by an appropriate software in order to visualize the effect of the treatment and to determine the values of cell surface roughness and some biometric parameters (cell length and width). The results showed that all microorganisms tested were sensitive to carvacrol both in solid and liquid media. Furthermore, images of cells of all strains treated with carvacrol exhibited appreciable modifications, indicating a change in cell surface structure. Finally, both length and diameter of the microorganisms decreased after contact with carvacrol.

Testing of x-ray microtomography systems using a traceable geometrical standard

X-ray computed microtomography is an interesting imaging technique for many applications, and is also very promising in the field of coordinate metrology at the micro scale. The main advantage with respect to traditional tactile-probing or optical coordinate measurement systems is that x-ray tomography can acquire dimensional and geometrical data for both inner and outer surfaces, without accessibility restrictions. However, there are no accepted test procedures available so far and measurement uncertainty is unknown in many cases, due to complex and numerous error sources. The paper presents the first results of a test procedure implemented for determining the errors of indication for length measurements of x-ray microtomography systems, using a new reference standard featuring a regular array of inner and outer cylindrical shapes. The developed test method allows the determination of specific characteristics of x-ray microtomography systems and can be used for the correction of systematic errors.

Application of the Kinect sensor for dynamic soil surface characterization

Agricultural soil roughness is pertinent to important agricultural phenomena, such as evaporation, infiltration or compression. Monitoring roughness variations would make possible the improvement of tillage operations. In the present work, implementation of the Microsoft Kinect™ RGB-depth camera for dynamic characterization of soil micro-relief is proposed and discussed. The metrological performance and the effect of the operating conditions on three-dimensional reconstruction was analyzed considering both laboratory tests on calibrated reference surfaces and field tests on different agricultural soil surfaces. Data set analysis was made on the basis of surface roughness parameters, as defined by ISO 25178 (2012) series: average roughness, root mean square roughness, skewness and kurtosis. Correlation between different tillage conditions and roughness parameters describing soil morphology was finally discussed.

Fast technique for AFM vertical drift compensation

The paper presents implementation and validation of a method for accurate imaging of three-dimensional surface topographies, developed for AFM metrology but in principle applicable to the whole family of scanning probe microscopes. The method provides correction of the vertical drift, and can be applied to any AFM scanner system, without need for modification of the instrument hardware. Surface correction is performed based on two topographies taken with mutually orthogonal scanning directions. Reconstruction is rapidly achieved through the use of an automatic routine developed for the purpose. The proposed method has been tested by using an optical and a silicon flat and a high precision cylindrical artefact. Examples of successful reconstructions on different samples are also reported within the paper.

Development and analysis of a software tool for stitching three-dimensional surface topography data sets

This paper presents development and application of a new software solution for stitching surface three-dimensional topography data where best matching positions are detected through maximization of a cross-correlation function. Differently from other stitching software tools developed in the past, the one here presented is based not on colour gradients but on matching of physical coordinates. The developed routine fully compensates positioning errors occurring when the measuring instrument is displaced relative to the surface. Qualitative as well as quantitative analyses were carried out in order to verify the applicability of the stitching process. Both synthetic and real scanned surfaces were used for testing. It was demonstrated that misalignments after software compensation are negligible: sub-pixel level inaccuracies, with absolute deviations <0.2%, were in fact verified when stitching two images. The method was developed specifically for atomic force microscopy, but can be effectively applied to any 3D topography measuring instrument.

Increase of maximum detectable slope with optical profilers, through controlled tilting and image processing

Optical methods are of choice in a huge number of applications. In particular, those instruments based on vertical scanning methods provide extremely fast, non-contact characterization of surface topography. However some limitations are present. Among them, maximum detectable slope is limited (generally <30°). Local loss of signal, resulting from this limited detection, originates data files containing void pixels, which eventually provide poor surface characterization. This work presents an original approach to overcome instrumental limitation on the maximum detectable slope. The method presented here is based on a software tool that processes images taken with controlled tilt, and returns a high-quality 3D profile of the sample being investigated. Experimental evidence is given with reference to the case of a Vickers indentation on steel.

Coordinate metrology using scanning probe microscopes

New positioning, probing and measuring strategies in coordinate metrology are needed for the accomplishment of true three-dimensional characterization of microstructures, with uncertainties in the nanometre range. In the present work, the implementation of scanning probe microscopes (SPMs) as systems for coordinate metrology is discussed. A new non-raster measurement approach is proposed, where the probe is moved to sense points along free paths on the sample surface, with no loss of accuracy with respect to traditional raster scanning and scan time reduction. Furthermore, new probes featuring long tips with innovative geometries suitable for coordinate metrology through SPMs are examined and reported.

Acoustic scanning probe microscopy

From the contents: Overview of acoustic techniques.- Contact dynamics modelling.- Cantilever dynamics: theoretical modeling.- Finite elements modelling.- AFAM calibration.- Enhanced sensitivity.- UAFM.- Holography calibration.- UFM.- Friction/lateral techniques.- Harmonix.- Scanning microdeformation microscopy (SMM).- Tip wear.- Comparison with other techniques.- Applications polymer.- Thin films.

Characterisation and analysis of microchannels and submicrometre surface roughness of injection moulded microfluidic systems using optical metrology

Abstract Precision injection moulding of miniaturised products with microfeatures, such as channels for microfluidic applications, poses the greatest challenges in terms of tooling technology and process optimisation. The injection moulding process window of polypropylene was validated using a metrological approach for the production of a microfluidic substrate. The dimensional accuracy of microchannels that are 48 μm wide and 110 μm deep and the quality surface topography replication (surface roughness from 30 to 360 nm) were investigated using non-contact measuring instruments, such as an optical coordinate measuring machine and a white light interferometer respectively. The effect of the dimensional scale range on the micro-/nanofeature replication was evaluated, and it was found to be the dominant parameter if compared with the effect of the other process related parameters investigated (melt and mould temperatures and injection speed).