文档介绍：Ultramicroelectrodes
Electroanalytical Chemistry
Lecture #7
11/11/2017
1
UME’s
Geometries
Disk
Recessed disk . Henry; I. Fritsch Anal. Chem. 1999, 71, 550-6.
Band
Cylinder
Materials
Carbon fiber
UME’s - Advantages
Reduced capacitance
Low iR drop
UME’s - Disadvantages
Noise
Electrochemical Fouling
Analyte
Method of electrode prep’n (epoxy)
Stray capacitance
Impurities
Maintenance
Cost
Fragile construction
UME’s - Applications
Determine [analyte]
Study reactions
at low temperatures = frozen glasses
in solvents of moderate to high permittivity w/o electrolyte
in solvents of high resistance
in solid state
in gas phase
UME’s - Applications (cont’d)
Biological systems
Single anelles
Fast ics
Development of analytical tools for electrode/solution interface
SECM (Bard)
EQCM
SERS (Van Duyne)
Scanning Electrochemical Microscopy (SECM)
Diffusion is hemispherical
iss = 4 n F Co* Do a where a = diam. of UME
Acquire I vs. tip position (x,y)
Plot of d vs. tip position
piezoelectric positioning
Bipotentiostat
Sample
C
W
R
Ref.: Bard et al. Science 1991, 254, 68-74.
d
SECM (cont’d)
W - 100 nm (diam.)
Determines resolution
2 nm best at present
Sample
Conducting
Insulator
Mineral
Biological
Semiconductor
Sample
C
W
R
Common Modes of Operation
Feedback
Positive or negative
Collection
flux of species generated/consumed probed
SECM- Positive Feedback
If sample conductive, we get positive feedback i > iss
Conductive Sample
C
W
R
R
O