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Superhydrophobic surfaces with ultra-low contact angle hysteresis fi nd a wide range of applications in the fi elds of selfcleaning, anti-icing, anti-fogging, or microfl uidics. [ 1,2 ] Here, the feasibility of a novel type of superhydrophobic surface for guided droplet transport, which is a key issue for microfl uidic systems, is demonstrated. Among such applications, open-surface digital microfl uidics (OSDM) offers specifi c advantages in terms of remote controllability and programmability of droplet transport. [ 3,4 ] One of the major concerns while manipulating aqueous droplets at solid surfaces is the large contact angle hysteresis which arises due to chemical or physical heterogeneities of the surface. [ 5 ] Moreover, it is usually desirable to locally tune the surface properties in a well-controlled and reversible manner. Although several examples have been reported demonstrating the fabrication of chemically or physically modifi ed superhydrophobic surfaces, [ 6,7 ] tunability and fast control over the surface properties remains a challenge. Among the different materials used for the fabrication of superhydrophobic surfaces, carbon nanotubes (CNTs) are interesting because of their chemically well-defi ned nature and response in wettability to different stimuli (using plasma [ 8 ] or UV light). [ 9,10 ] Vertically aligned CNT structures gain additional signifi cance since transport properties of corresponding surfaces are strongly anisotropic, [ 11 ] which facilitates localized changes in temperature or electric fi eld. Several studies have been made in the past to tune the hydrophobic nature of aligned carbon nanotubes to produce superhydrophobic surfaces. In general, two methods have been developed to increase the hydrophobicity of CNT surfaces a) coating with a low surface energy material [ 12,13 ] and b) micropatterning of the CNT surface structure [ 14 ] so as to increase their surface roughness. Desirable characteristics of CNTs like, for example, thermal conductivity are compromised on coating with a foreign material. CNTs thus act as mere template structure for providing the desired nanoscale roughness. Micropatterning, on the other hand, is able to induce controlled surface roughness but relies on complex and expensive masking/lithography techniques involving multiple process steps. Superhydrophobic materials, including CNTs, exhibit two types of wetting behavior at high contact angles: a) very low contact angle hysteresis (like on lotus leaves) where the water droplet easily rolls off [ 10,15,16 ] or b) very high hysteresis (like on rose petals) where the water droplets pins to the surface. [ 17,18 ] While most of the surface modifi cation processes result in either one of these states, it is highly desirable to achieve a reversible switching between these two states on the same material. A reversible and localized switching between states with different contact angles and different levels of contact angle hysteresis has an enormous potential, for instance, for microfl uidic applications. By cre...

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Combined atomic force-scanning electrochemical microscopy (AFM-SECM) has been explored for monitoring copper ions generated by dissolution of copper samples while recording induced changes in topography. Released Cu 2+ ions were detected via reduction to metallic copper at the AFM tip-integrated electrode followed by subsequent re-dissolution in bulk solution by anodic stripping voltammetry. Copper crystals electrodeposited on gold substrates were used as model systems to demonstrate the laterally resolved analysis of topographical changes and the simultaneous measurement of localized cation release, which was anodically activated upon exposure to acidified chloride-containing solution. Finally, the potential of AFM-SECM for monitoring spatially resolved corrosion processes with sub-micrometer resolution was illustrated using a pure copper sample.

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Atomic force microscopy can be readily combined with complementary instrumental techniques ranging from optical to mass-sensitive methods. This Feature highlights recent advances on hyphenated AFM technology, which enables localized studies and mapping of complementary information at surfaces and interfaces.

No abstract

The anodic dissolution of pure copper surfaces in acidic chloride solution has been monitored insitu using combined atomic force -scanning electrochemical microscopy (AFM-SECM). Here, the initial studies performed on model copper-modified substrates have been extended to the investigation of bulk copper samples used in industrial settings. The local release of Cu 2+ ions was monitored through electrochemical reduction and deposition of the metal ions on the conductive frame of the AFM-SECM probe. Simultaneous monitoring of the topographical changes due to the corrosion process allowed the distinction and correlation of local passivation and pitting phenomena. The extent of the attack was estimated by anodic stripping of the copper metal deposited at the probe.