Intermittent contact hydration scanning probe microscopy

Abstract

Hydration scanning probe microscopy is a technique similar to scanning tunneling microscopy, in which the probe current, sustained by the slight surface conduction of a thin hydration layer covering an insulating support surface, is essentially electrochemical in nature instead of electronic tunneling. Such a technique allows the imaging of a great variety of samples, including insulators, provided that they are hydrophilic, as well as the study of molecular samples of biological interest (such as DNA) fixed on a suitable supporting surface. The main problem to obtain stable and reproducible images comes from the very critical determination of the operating conditions under which the probe-hydration layer interaction does not lead to the formation of a relatively large water meniscus. It has been suggested that this issue can be removed by adding a high frequency oscillation to the probe movement, as in tapping atomic force microscopy. Meniscus formation and breakup have been investigated in order to determine the best values for the amplitude and the frequency of the oscillation. Results obtained in this mode are discussed in comparison with the usual continuous contact mode.

Electron-paramagnetic resonance detection with software time locking

“…This open source package, operating in a Linux environment, has been originally developed for real time control of the feedback of a scanning microscope. [20][21][22] The second channel of the ADC is used to directly sample the f m signal. Acquired data are stored to disk for off-line processing.…”

Use of scanning probe microscopy to study the evolution of nanometer sized liquid structures

“…This phenomenon, described both in AFM (Ref. 22) and in HSPM, 23,24 is usually a severe hindrance in measurements; probe oscillation has often been used both for AFM (Ref. 25) and HSPM (Ref.…”

The mechanism of light emission from a scanning tunnelling microscope operating in air

“…The key difference for STM in air is that a thin water layer (<1 nm) [48] is present on the STM tip and sample surface under typical laboratory conditions. This may lead to a water bridge between the tip and sample [44,[48][49][50][51]. In such a configuration, the current between the biased tip and sample may have two sources: the expected tunnel current [52][53][54][55][56], and an ionic or Faradaic current of electrochemical nature [44,49,51,[57][58][59].…”

“…This may lead to a water bridge between the tip and sample [44,[48][49][50][51]. In such a configuration, the current between the biased tip and sample may have two sources: the expected tunnel current [52][53][54][55][56], and an ionic or Faradaic current of electrochemical nature [44,49,51,[57][58][59]. This latter current is expected to exist in particular at relatively high applied voltages, for example above 1.23 V, the standard theoretical electrochemical potential for water electrolysis [60].…”

“…In order that the light emitted from an STM tunnel junction be in the visible, the applied voltage between the tip and sample must lie in the ∼1.5-3 V range (i.e., in the energy range of visible photons). At such high surface voltages, the electrochemical component of the STM current may be significant, resulting in unstable imaging [44,48,49,51].…”