26 research outputs found
A phantom force induced by the tunneling current, characterized on Si(111)
Simultaneous measurements of tunneling currents and atomic forces on surfaces
and adsorbates provide new insights into the electronic and structural
properties of matter on the atomic scale. We report on experimental
observations and calculations of a strong impact the tunneling current can have
on the measured force, which arises when the resistivity of the sample cannot
be neglected. We present a study on Si(111)-7\times7 with various doping
levels, but this effect is expected to occur on other low-conductance samples
like adsorbed molecules, and is likely to strongly affect Kelvin probe
measurements on the atomic scale.Comment: 4 pages, 4 figures, submitte
Scanning probe microscope simulator for the assessment of noise in scanning probe microscopy controllers
We present an electronic circuit that allows to calibrate and troubleshoot scanning probe microscopy (SPM) controllers with respect to their noise performance. The control signal in an SPM is typically highly nonlinearâthe tunneling current in scanning tunneling microscopy (STM) varies exponentially with distance. The exponential current-versus-voltage characteristics of diodes allow to model the current dependence in STM. Additional inputs allow to simulate the effects of external perturbations and the reactions of the control electronics. We characterized the noise performance of the feedback controller using the apparent topography roughness of recorded images. For a comparison of different STM controllers, an optimal gain parameter was determined by exploring settling times through a rectangular perturbation signal. We used the circuit to directly compare the performance of two types of SPM controllers used in our laboratory
Note: In situ cleavage of crystallographic oriented tips for scanning probe microscopy
We report an in situ method of preparing tips for scanning probe microscopy (SPM). Oriented single-crystal nickel oxide (NiO) rods were diced, using a wafer saw, to prepare artificial breaking points. Two geometries, a single rod and a two-sided cut rod were fabricated. The cleavable tips were mounted to a force sensor based on a quartz tuning fork and cleaved using the coarse approach of the SPM. Atomically resolved force microscopy images of NiO (001) were taken with these NiO tips
Scanning probe microscope simulator for the assessment of noise in scanning probe microscopy controllers
Detection and identification of canker and blight on orange trees using a handâheld Raman spectrometer
Evaluation of the Physico-mechanical Properties and Electrostatic Charging Behavior of Different Capsule Types for Inhalation Under Distinct Environmental Conditions
Capsule-based dry powder inhaler (DPI) products can be influenced by a multitude of interacting factors, including electrostatic charging. Tribo-charging is a process of charge transfer impacted by various factors, i.e., material surface characteristics, mechanical properties, processing parameters and environmental conditions. Consequently, this work aimed to assess how the charging behavior of capsules intended for inhalation might be influenced by environmental conditions. Capsules having different chemical compositions (gelatin and hydroxypropyl methylcellulose (HPMC)) and distinct inherent characteristics from manufacturing (thermally and cold-gelled) were exposed to various environmental conditions (11%, 22% and 51% RH). Their resulting properties were characterized and tribo-charging behavior was measured against stainless steel and PVC. It was observed that all capsule materials tended to charge to a higher extent when in contact with PVC. The tribo-charging of the thermally gelled HPMC capsules (VcapsÂź Plus) was more similar to the gelatin capsules (Quali-Gâą-I) than to their HPMC cold-gelled counterparts (Quali-VÂź-I). The sorption of water by the capsules at different relative humidities notably impacted their properties and tribo-charging behavior. Different interactions between the tested materials and water molecules were identified and are proposed to be the driver of distinct charging behaviors. Finally, we showed that depending on the capsule types, distinct environmental conditions are necessary to mitigate charging and assure optimal behavior of the capsules