In situ characterization of nanoscale contaminations adsorbed in air using atomic force microscopy

Abstract

Under ambient conditions, surfaces are rapidly modified and contaminated by absorbance of molecules and a variety of nanoparticles that drastically change their chemical and physical properties. The atomic force microscope tip–sample system can be considered a model system for investigating a variety of nanoscale phenomena. In the present work we use atomic force microscopy to directly image nanoscale contamination on surfaces, and to characterize this contamination by using multidimensional spectroscopy techniques. By acquisition of spectroscopy data as a function of tip–sample voltage and tip–sample distance, we are able to determine the contact potential, the Hamaker constant and the effective thickness of the dielectric layer within the tip–sample system. All these properties depend strongly on the contamination within the tip–sample system. We propose to access the state of contamination of real surfaces under ambient conditions using advanced atomic force microscopy techniques.

Removal of Surface Oxygen Vacancies Increases Conductance Through TiO2 Thin Films for Perovskite Solar Cells

“…39 Such hydrocarbon adsorbates change surface properties and the local conductance. 40 To examine this effect, we performed consecutive cSFM control measurements on a freshly prepared and UV–ozone-treated sample over a period of 12 h. We found a decrease of the median current by 50% after 3 h (Figure 4). After 12 h, the median current value had dropped to 12% of the initial value.…”

Charge Calibration Standard for Atomic Force Microscope Tips in Liquids

“…This is more likely to occur at the AFM tip since this surface is being dynamically scanned through the fluid and is in contact with the surface many times. In fact, it has been shown previously that the AFM tip shape does change at the nanometer level likely due to surface adsorbates. − In the current experiment, this could result in adventitious hydrocarbon adsorption, which would add an uncharged layer to the tip, effectively increasing the tip–sample separation over what was assumed in our model. In addition, counter-charged solution ions or surface impurities could attach themselves to the tip, thus lowering its net surface charge.…”

“…Unless all future experiments were to be done only on mica, using such a surface for the calibration standard requires doing two experiments serially in time: one to calibrate the tip and a second to collect data over the unknown sample. AFM tips change their shape while scanning, − making it desirable to collect calibration data simultaneously with the scan including the unknown samples. Second, while the crystal structure of mica is well-known, there are intercalated cations (often potassium) that are mobile and just beneath the surface.…”

Hydration Dynamics and the Future of Small-Amplitude AFM Imaging in Air

“…Perhaps counter-intuitively to the newcomer, the field has rapidly advanced in two extremes—in liquid [ 11 , 12 , 13 , 14 ] and UHV environments [ 15 ]—while several complex phenomena have hindered the imaging and quantification of phenomena in air [ 16 ] with similar resolutions, controls, or throughputs [ 3 ]. There has been research in air in terms of capillary interactions [ 17 ], spontaneous capillary condensation [ 16 ], and the way the air environment affects surfaces [ 18 ], molecules on it, and modes of imaging [ 3 , 19 , 20 , 21 ]. In terms of force measurements in air, most have focused on capillary interactions [ 22 ] arising from the formation and rupture of a capillary neck as a function of the relative humidity (RH), either experimentally [ 16 ] or theoretically [ 23 ].…”

“…It is worth noting, in the context of the topic under consideration, that even current research tends to focus on [ 26 ] the distinction between dry conditions and high-humidity conditions, i.e., extremes, and might obviate the aging process of the surface [ 27 ]. In short, while extremes, i.e., dry conditions and high relative humidity (RH) conditions, are sometimes considered by the community, in 2018, some [ 18 ] emphasized that the dynamic processes occurring on the surfaces due to nanoscale contamination are still largely neglected. This is even the case when the state of the surface is known to affect properties such as conductance [ 28 ], and research on surface contaminants and the quantification of interfacial properties in air is ongoing [ 29 ].…”