A comparative investigation of thickness measurements of ultra-thin water films by scanning probe techniques

Abstract

The reliable operation of micro- and nanomechanical devices necessitates a precise knowledge of the water film thickness present on the surfaces of these devices with accuracy in the nanometer range. In this work, the thickness of an ultra-thin water film was measured by distance tunneling spectroscopy and distance dynamic force spectroscopy during desorption in an ultra-high vacuum system, from about 2.5 nm up to complete desorption at 10-8 mbar. The tunneling current and the amplitude of vibration and the normal force were detected as a function of the probe-sample distance. In these experiments, a direct comparison of both methods was possible. It was determined that dynamic force spectroscopy provides the most accurate values. The previously reported tunneling spectroscopy, which requires the application of significantly high voltages generally leads to values that are 25 times higher than values determined by dynamic force spectroscopy

Superhydrophobic properties of ultrathin rf-sputtered Teflon films coated etched aluminum surfaces

“…1(b) shows the contact angle data of water on ultrathin rf-sputtered Teflon thin film coated etched aluminum substrates. According to the literatures, the term "ultrathin" films mean that the thickness of the films is less than 5 nm [17], [18], [19], [20] and [21].…”

Q‐factor study of nanomechanical system “metal tip – carbon nanowhisker” at low and ambient pressure

“…It is well known that for removing adsorbed water, solid surface has to be heated with temperatures higher than 100 8C [21]. That is why resonance frequency and Q-factor of CNW at RLP regime do not return to the initial LP values.…”

Dielectric sensing by charging energy modulation in a nano-granular metal

“…A quantitative comparison of our calculations with the experimental data is not readily possible since, to the best of our knowledge, the relation between the adsorbate layer thickness and the relative humidity level is not known. What can be stated from independent research using scanning probe [19] and dynamic force spectroscopy [20] is the following: (1) The water adsorbate layer thickness changes from one monolayer (0.25 nm) to 5 nm as the humidity level grows from about 0 (low vacuum conditions) to more than 90 % under ambient temperature conditions. (2) The actual layer thickness for a given humidity level may show transient behavior, in particular, a crossover from droplet formation (about 5 nm height) to closed layers (about 2 nm thickness) over several hours.…”

“…We comment on this simplifying assumption in the discussion section. With regard to the relevant thickness range we use results from scanning probe microscopy (SPM) and dynamic force spetroscopy (DFS) experiments on the coverage of different surfaces with water films under different conditions of relative humidity [19,20]. From these experiments we identify the suitable thickness range for d A to be from 0.25 nm, corresponding to one monolayer of water, to 5 nm, as is observed at room temperature for relative humidity levels up to 90 %.…”

“…From these experiments we identify the suitable thickness range for d A to be from 0.25 nm, corresponding to one monolayer of water, to 5 nm, as is observed at room temperature for relative humidity levels up to 90 %. Since the thickness of the water film depends on the substrate material, we took values which were found for graphite [20]. This should be representative for the Pt(C) FEBID structures employed here, if we assume that the surface termination layer of the nano-granular metal is amorphous carbon.…”