Atomic force microscope adhesion measurements and atomistic molecular dynamics simulations at different humidities

Due to their operation principle atomic force microscopes (AFMs) are sensitive to all factors affecting the detected force between the probe and the sample. Relative humidity is an important and often neglected-both in experiments and simulations-factor in the interaction force between AFM probe and sample in air. This paper describes the humidity control system designed and built for the interferometrically traceable metrology AFM (IT-MAFM) at VTT MIKES. The humidity control is based on circulating the air of the AFM enclosure via dryer and humidifier paths with adjustable flow and mixing ratio of dry and humid air. The design humidity range of the system is 20-60 % rh. Force-distance adhesion studies at humidity levels between 25 % rh and 53 % rh are presented and compared to an atomistic molecular dynamics (MD) simulation. The uncertainty level of the thermal noise method implementation used for force constant calibration of the AFM cantilevers is 10 %, being the dominant component of the interaction force measurement uncertainty. Comparing the simulation and the experiment, the primary uncertainties are related to the nominally 7 nm radius and shape of measurement probe apex, possible wear and contamination, and the atomistic simulation technique details. The interaction forces are of the same order of magnitude in simulation and measurement (5 nN). An elongation of a few nanometres of the water meniscus between probe tip and sample, before its rupture, is seen in simulation upon retraction of the tip in higher humidity. This behaviour is also supported by the presented experimental measurement data but the data is insufficient to conclusively verify the quantitative meniscus elongation.Peer reviewe

Towards improved humidity measurements at high temperatures and transient conditions

Humidity is a key parameter in controlling drying processes and ambient conditions in many industrial manufacturing, storage and test applications. Air humidity is routinely measured at temperatures above 100 °C and at conditions that are often challenging due to temporal and local variations. Calibrations of humidity sensors do not provide appropriate representativeness of measurement conditions because they are limited to temperatures below 100 °C and static conditions. A European metrology research project HIT (“Metrology for Humidity at High Temperatures and Transient conditions”) is developing improved humidity measurement and calibration techniques to temperatures up to 180 °C and non-static conditions. This paper summaries developments of the project: calibration and test facilities for industrial hygrometers, studies on humidity control in specific microbial transient processes and a new measurement approach for water activity measurements

A new challenge for meteorological measurements: The meteoMet project-Metrology for meteorology

Climate change and its consequences require immediate actions in order to safeguard the environment and economy in Europe and in the rest of world. Aiming to enhance data reliability and reduce uncertainties in climate observations, a joint research project called MeteoMet-Metrology for Meteorology started in October 2011 coordinated by the Italian Istituto Nazionale di Ricerca Metrologica (INRiM). The project is focused on the traceability of measurements involved in climate change: surface and upper air measurements of temperature, pressure, humidity, wind speed and direction, solar irradiance and reciprocal influences between measurands. This project will provide the first definition at the European level of validated climate parameters with associated uncertainty budgets and novel criteria for interpretation of historical data series. The big challenge is the propagation of a metrological measurement perspective to meteorological observations. When such an approach will be adopted the requirement of reliable data and robust datasets over wide scales and long terms could be better met. © 2013 AIP Publishing LLC