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Solution-deposited ZnO FET (a) as-deposited and (b) after the attachment of the stearic acid layer. The chemical structure of stearic acid is shown in (b). (c) Drain current as a function of gate voltage for an as-deposited ZnO FET (solid curve) and for the same device after surface treatment with stearic acid (dashed curve). Output characteristics of the ZnO FETs (d) before and (e) after surface treatment with stearic acid. The gate voltage increases in steps of 20 V from −60 V (off) to +60 V (on).
Drain current as a function of gate voltage for a ZnO FET after etching in dilute solutions of HCl in THF. The as-deposited ZnO device (diamonds) has the highest current. The source-drain current decreases after immersion in pure THF for 2 h (circles) and continues to decrease after 10 min immersion in solutions of HCl in THF with concentrations of 10−6 M (triangles) and 10−4 M (dashed line). The channel is completely removed after 10 min. in a solution of 10−2 M HCl in THF (solid line).
(a) Transfer curves of a single ZnO FET device measured after alternating surface treatments of stearic acid and UV-ozone showing the reversibility of the carboxylic acid electronic effect. The numbered boxes indicate the sequence of the surface treatments. (b) The zero gate bias drain current as a function of drain voltage after alternating treatments with stearic acid (solid curves, left axis) and UV-ozone exposure (dashed curves, right axis). The scale for the left y-axis (μA) is a factor of 103 larger than the right axis (nA).
pKa, molecular dipole moment, dielectric constant εr, and hydrogen ion concentration under common carboxylic acid attachment conditions for acetic acid solutions in solvents used for ZnO surface functionalization. The pKa and dielectric constants are from Ref. 23 for acetonitrile and THF, and from Ref. 25 for other solvents. The pKa are taken from Ref. 26 for DMSO and DMF and from Ref. 24 for other solvents. The dipole moments are from Ref. 24 .
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