Low-cost spectrum analyzer for trouble shooting noise sources in scanning probe microscopy

Abstract

Scanning probe microscopes are notoriously sensitive to many types of external and internal interference including electrical, mechanical and acoustic noise. Sometimes noise can even be misinterpreted as real features in the images. Therefore, quantification of the frequency and magnitude of any noise is key to discovering the source and eliminating it from the system. While commercial spectrum analyzers are perfect for this task, they are rather expensive and not always available. We present a simple, cost effective solution in the form of an audio output from the instrument coupled to a smart phone spectrum analyzer application. Specifically, the scanning probe signal, e.g. the tunneling current of a scanning tunneling microscope is fed to the spectrum analyzer which Fourier transforms the time domain acoustic signal into the frequency domain. When the scanning probe is in contact with the sample, but not scanning, the output is a spectrum containing both the amplitude and frequency of any periodic noise affecting the microscope itself, enabling troubleshooting to begin.

Ethanol on Graphite: Ordered Structures and Delicate Balance of Interfacial and Intermolecular Forces

“…It is known that structures at interfaces where different materials and/or molecules meet have fundamental impacts on materials properties and behavior, interfacial phenomena, and even device performance in practical applications. − For small molecules, especially those capable of forming hydrogen bonds such as water, methanol, ethanol, and so on, knowledge of their interfacial structures has particular importance due to their broad existence as common solvents and in fuel cells, catalysis, macromolecular systems, and interstellar matter. − Given the relatively large strength and directional nature among intermolecular forces, hydrogen bonds play an important role in the organization of assembly structures, which may be in competition or sometimes cooperation with substrate–molecule interactions. Hence, to reveal interfacial structural details as a result of a delicate balance of all forces involved, it is crucial to use structure-probing techniques with suitable surface sensitivity, for example, scanning probe microscopy, , reflection–absorption infrared spectroscopy, − and reflection diffraction methods. − In recent years, reflection high-energy electron diffraction (RHEED) has been used to elucidate unanticipated ordered assemblies and unusual phase-transformation behavior of small molecules physisorbed or chemisorbed on different surfaces. − The technique’s strengths of a (sub)­nanometer thick penetration depth at grazing incidence angles and resulting surface sensitivity make noncontacting RHEED highly suitable for temperature- and thickness-dependent studies of interfacial structures and phase transitions of molecular systems, beside its typical use during thin-film fabrications in materials science.…”