We have recently implemented a trimodal tapping mode atomic force microscopy (AFM) imaging scheme for ambient air with which it is possible to simultaneously acquire topographical, phase and frequency shift contrast images. In implementing this method we have identified conditions, such as very low fundamental amplitude setpoints and very low oscillation amplitudes for the higher eigenmodes, for which the stability of the imaging process can be compromised. In this work we use numerical simulations to gain insight into the changes in the frequency response of the higher eigenmodes in bimodal and trimodal operation for different levels of sample stiffness, tip–sample dissipative forces, oscillation amplitudes for each of the eigenmodes and cantilever rest positions above the surface. Although we do not attempt to convey a complete dynamics picture of the system, the results provide general guidelines for the selection of conditions that lead to stable imaging as well as insight into the observed phase and frequency shift contrast, highlighting a few potential imaging artifacts. Our simulation results are in general agreement with our experimental observations.

We compare the ability of higher cantilever eigenmodes to map conservative and dissipative tip-sample interactions in bimodal atomic force microscopy under three different control schemes, namely, open-loop (OL), constant-excitation phase-locked-loop (CE-PLL), and constant-amplitude phase-locked-loop (CA-PLL). We perform a direct comparison of these schemes by applying analytical expressions of the virial and dissipated power to imaging and spectroscopy experiments conducted on a two-component polymer sample in air. We find that OL and CE-PLL provide similar information, while CA-PLL explores a broader range of interactions, especially for softer samples, due to its constant sensitivity to tip-sample forces.

We present computational simulation and experimental results of ambient air atomic force microscopy (AFM) characterization with simultaneous excitation and control of three eigenmodes of a rectangular microcantilever beam. Trimodal characterization combining amplitude and frequency modulation is an enhancement of the capabilities of the AFM technique, which could allow the rapid acquisition of topographical, phase, and frequency shift contrast with a single surface scan at normal scan rates. The results suggest that, in general, the phase and frequency shift contrast are affected similarly but in opposite directions by the tip-sample interactions, although deviations from this trend are often observed in the experiments, such that all available sources of contrast could provide complementary information on surface properties.

Sustainability in project operations such as financial, social and environmental sustainability is one of the most prominent issues of the present times to address. The increased focus on sustainable business operations has changed the viewpoint of researchers and corporate community towards the project management. Today sustainability in business operations along with sustainability of natural and environmental resources are of paramount significance which has further caused a huge impact on conception, planning, scheduling and execution of the project management activities. In this paper, a literature review between 1987 and 2018 on different issues affecting the sustainability in project management is carried out. The present study also identifies and discusses the future possibilities to apply computational procedures in order to estimate and optimize the sustainability issues in the management of projects, for example the computational evolutionary algorithms can be applied to formulate the multi-objective decisionmaking problem after considering critical factors of sustainability in the projects and then yielding optimized solutions for the formulated problem to achieve sustainability in the projects. A new integrated framework with the inclusion of feedback function for assessment of each decision and actions taken towards the sustainability of the projects is also identified and presented.

One common application of atomic force microscopy (AFM) is the acquisition of tip–sample interaction force curves. However, this can be a slow process when the user is interested in studying non-uniform samples, because existing contact- and dynamic-mode methods require that the measurement be performed at one fixed surface point at a time. This paper proposes an AFM method based on dual frequency modulation using two cantilevers in series, which could be used to measure the tip–sample interaction force curves and topography of the entire sample with a single surface scan, in a time that is comparable to the time needed to collect a topographic image with current AFM imaging modes. Numerical simulation results are provided along with recommended parameters to characterize tip–sample interactions resembling those of conventional silicon tips and carbon nanotube tips tapping on silicon surfaces.