electrochemical AFM

The technique consists in an AFM apparatus integrated with a three electrode electrochemical cell.

File:Cellaechem.png[[File:Liquido.png|thumb|Electrochemical AFM section.
(a) Cantilever and tip

(b) electrochemical cell

(c) Liquid (electrolyte)

(d) sample

(e) Sample holder. The electrochemical connections are usually placed under the sample holder.|alt=|350x350px]] The sample works as working electrode (WE) and must be conductive. The AFM probe is a "passive" element, as it is unbiased and it monitors the surface changes as a function of time, when a potential is applied to the sample. Several electrochemical experiments can be performed on the sample, such as cyclic voltammetry, pulse voltammetry etc. During the potential sweeping, the current flows through the sample and the morphology is monitored.{{cite journal |last1=Reggente |first1=Melania |last2=Passeri |first2=Daniele |last3=Rossi |first3=Marco |last4=Tamburri |first4=Emanuela |last5=Terranova |first5=Maria Letizia |title=Electrochemical atomic force microscopy: In situ monitoring of electrochemical processes |volume=1873 |pages=020009 |date=2017 |doi=10.1063/1.4997138 |ref=Romani |publisher=Author(s)|series=AIP Conference Proceedings |doi-access=free |hdl=2108/248223 |hdl-access=free }}

The electrochemical cell is made of a plastic material resistant to various chemical solvents (e.g. sulfuric acid, perchloric acid etc.), with a good mechanical resistance and low fabrication costs.{{cite book |last1=DuPont Fluoroproducts |title=Teflon Ptfe Fluoropolymer Resin: Properties Handbook |date=1996 |publisher=Paperback}} In order to satisfy these requirements, various materials can be employed, such as polytetrafluoroethylene (PTFE) or teflon. Platinum and AgCl wires are widely employed as reference electrode and platinum wires as counter electrode.

Since the measurement is performed in a liquid environment, some precautions must be taken. The chosen electrolyte must be transparent, in order to allow the laser beam to reach the sample and be deflected. For the right electrolyte opacity, depending on the solute concentration, very diluted solutions should be selected. The choice of a suitable electrolyte for the measurement must be taken considering also possible corrosion effects on the AFM scanner, which can be affected by strong acid solutions. The same problem affects the AFM cantilever. It is preferable to select an AFM tip with a specific coating resistant to acids, for example gold. The liquid environment adds one more constraint related to the choice of the tip material, as the laser sum registered on the photodiode must be scarcely affected. The change in the refractive index of the solution with respect to air leads to a change in the position of the laser spot, necessitating a repositioning of the photodiode.

EC-AFM has various applications, where monitoring the electrode surface during electrochemical reactions leads to interesting results.

Among the applications, the studies on battery and electrode corrosion in acid environment are widely spread.

Concerning batteries, studies on lead–acid battery pointed out the change in the morphology during the reduction/oxidation cycles in a CV, when an acid electrolyted is used.{{cite journal |last1=Yamaguchi |first1=Yoshiaki |last2=Shiota |first2=Masashi |last3=Nakayama |first3=Yasuhide |last4=Hirai |first4=Nobumitsu |last5=Hara |first5=Shigeta |title=Combined in situ EC-AFM and CV measurement study on lead electrode for lead–acid batteries |journal=Journal of Power Sources |date=February 2001 |volume=93 |issue=1–2 |pages=104–111 |doi=10.1016/S0378-7753(00)00554-1}}{{cite journal |last1=Shiota |first1=Masashi |last2=Yamaguchi |first2=Yoshiaki |last3=Nakayama |first3=Yasuhide |last4=Hirai |first4=Nobumitsu |last5=Hara |first5=Shigeta |title=In situ EC-AFM observation of antimony effect for lead dioxide electrode |journal=Journal of Power Sources |date=January 2003 |volume=113 |issue=2 |pages=277–280 |doi=10.1016/S0378-7753(02)00523-2}}

Different corrosion effects are widely considered for the applications of EC-AFM. Different phenomena are studies, from pitting corrosion of steel,{{cite journal |last1=Reynaud-Laporte |first1=Isabelle |last2=Vayer |first2=Marylène |last3=Kauffmann |first3=Jean-Pierre |last4=Erre |first4=René |title=An Electrochemical-AFM Study of the Initiation of the Pitting Corrosion of a Martensitic Stainless Steel |journal=Microscopy Microanalysis Microstructures |date=1997 |volume=8 |issue=3 |pages=175–185 |doi=10.1051/mmm:1997117|doi-access=free }} to crystal dissolution.{{cite journal |last1=Macpherson |first1=Julie V. |last2=Unwin |first2=Patrick R. |last3=Hillier |first3=Andrew C. |last4=Bard |first4=Allen J. |title=In-Situ Imaging of Ionic Crystal Dissolution Using an Integrated Electrochemical/AFM Probe |journal=Journal of the American Chemical Society |date=January 1996 |volume=118 |issue=27 |pages=6445–6452 |doi=10.1021/ja960842r |language=en |issn=0002-7863}}

Highly oriented pyrolytic graphite (HOPG) is widely employed as an electrode for EC-AFM. In fact, various surface phenomena are studied, from the application to lithium batteries{{cite journal |last1=Domi |first1=Y. |last2=Ochida |first2=M. |last3=Tsubouchi |first3=S. |last4=Nakagawa |first4=H. |last5=Yamanaka |first5=T. |last6=Doi |first6=T. |last7=Abe |first7=T. |last8=Ogumi |first8=Z. |title=Electrochemical AFM Observation of the HOPG Edge Plane in Ethylene Carbonate-Based Electrolytes Containing Film-Forming Additives |journal=Journal of the Electrochemical Society |date=20 July 2012 |volume=159 |issue=8 |pages=A1292–A1297 |doi=10.1149/2.059208jes}} to anion intercalation leading to blister formation on the electrode surface.{{cite journal |last1=Bussetti |first1=Gianlorenzo |last2=Yivlialin |first2=Rossella |last3=Alliata |first3=Dario |last4=Li Bassi |first4=Andrea |last5=Castiglioni |first5=Chiara |last6=Tommasini |first6=Matteo |last7=Casari |first7=Carlo Spartaco |last8=Passoni |first8=Matteo |last9=Biagioni |first9=Paolo |last10=Ciccacci |first10=Franco |last11=Duò |first11=Lamberto |title=Disclosing the Early Stages of Electrochemical Anion Intercalation in Graphite by a Combined Atomic Force Microscopy/Scanning Tunneling Microscopy Approach |journal=The Journal of Physical Chemistry C |date=10 March 2016 |volume=120 |issue=11 |pages=6088–6093 |doi=10.1021/acs.jpcc.6b00407|hdl=11311/981354 |hdl-access=free }}

A rather interesting application is the EC-AFM Dip pen nanolithography.{{cite journal |last1=Li |first1=Yan |last2=Maynor |first2=Benjamin W. |last3=Liu |first3=Jie |title=Electrochemical AFM "Dip-Pen" Nanolithography |journal=Journal of the American Chemical Society |date=March 2001 |volume=123 |issue=9 |pages=2105–2106 |doi=10.1021/ja005654m|pmid=11456853 }} Recently, SPM based lithography gained attention due to its simplicity and precise control the structure and location. A new development of this technique is the dip pen nanolithography (DPN), which uses the AFM technique to deliver organic molecules on different substrates, as gold. Using EC-AFM allows to fabricate metal and semiconductor nanostructures on the WE, gaining high thermal stability and a higher chemical diversity.

Finally, it is possible to perform and study the electrodeposition of different materials on electrodes, from metals (i.e. copper{{cite journal |last1=Koinuma |first1=M. |last2=Uosaki |first2=K. |title=An electrochemical AFM study on electrodeposition of copper on p-GaAs(100) surface in HCl solution |journal=Electrochimica Acta |date=July 1995 |volume=40 |issue=10 |pages=1345–1351 |doi=10.1016/0013-4686(95)00070-U}}) to polymers, such as polyaniline (PANI).{{cite journal |last1=Singh |first1=Pankaj R. |last2=Mahajan |first2=Sumeet |last3=Rajwade |first3=Shantanu |last4=Contractor |first4=A.Q. |title=EC-AFM investigation of reversible volume changes with electrode potential in polyaniline |journal=Journal of Electroanalytical Chemistry |date=January 2009 |volume=625 |issue=1 |pages=16–26 |doi=10.1016/j.jelechem.2008.10.005|url=http://dspace.library.iitb.ac.in/xmlui/handle/10054/1687 |url-access=subscription }}{{cite journal |last1=Reggente |first1=Melania |last2=Passeri |first2=Daniele |last3=Rossi |first3=Marco |last4=Tamburri |first4=Emanuela |last5=Terranova |first5=Maria Letizia |title=Electrochemical atomic force microscopy: In situ monitoring of electrochemical processes |volume=1873 |pages=020009 |date=2017 |doi=10.1063/1.4997138 |ref=Romani |publisher=Author(s)|series=AIP Conference Proceedings |doi-access=free |hdl=2108/248223 |hdl-access=free }}

Category:Scanning probe microscopy