Table 2.
Quantitative XPS analysis of pure NTA and NTA/OEG monolayers: elemental compositions for different take-off angles.a,b
| monolayer | take-off angle | time in NTA thiol | time in OEG thiol | atomic percentage (std dev) | |||
|---|---|---|---|---|---|---|---|
| C 1s | O 1s | N 1s | S 2p | ||||
| NTA a | 0° | 24hr | -- | 68.7 (0.7) | 25.5 (1.6) | 4.5 (0.7) | 1.3 (0.8) |
| 55° | 68.9 (1.0) | 25.0 (0.2) | 4.9 (0.7) | 1.2 (0.5) | |||
| 75° | 73.0 (1.4) | 22.0 (0.9) | 4.7 (0.7) | 0.3 (0.3) | |||
|
| |||||||
| NTA b | 0° | 5min | -- | 76.5 (3.5) | 19.9 (3.2) | 2.5 (0.8) | 1.1 (0.5) |
| 55° | 75.5 (3.1) | 21.1 (2.7) | 2.7 (0.7) | 0.7 (0.3) | |||
| 75° | 75.5 (3.1) | 20.7 (3.6) | 3.2 (0.1) | 0.6 (0.5) | |||
|
| |||||||
| OEG 1 | 0° | 5min | 0.5hr | 75.0 (1.7) | 23.0 (2.0) | 0.5 (0.3) | 1.5 (0.3) |
| 55° | 72.6 (1.3) | 24.0 (0.8) | 2.1 (0.4) | 1.3 (0.3) | |||
| 75° | 73.7 (1.9) | 23.1 (1.1) | 2.2 (0.3) | 1.0 (0.5) | |||
|
| |||||||
| OEG 2 | 0° | 5min | 24hr | 75.1 (1.3) | 22.1 (1.0) | 1.2 (0.3) | 1.6 (0.3) |
| 55° | 72.6 (2.0) | 24.2 (1.9) | 1.9 (0.7) | 1.3 (0.5) | |||
| 75° | 73.9 (0.3) | 22.2 (0.7) | 2.6 (0.5) | 1.3 (0.2) | |||
|
| |||||||
| Pure OEG | 0° | 0 | 24hr | 77.6 (1.4) | 20.2 (1.4) | nd | 2.1 (0.1) |
| 55° | 75.7 (1.2) | 22.5 (1.0) | nd | 1.8 (0.3) | |||
| 75° | 75.7 (0.4) | 22.8 (0.4) | nd | 1.6 (0.1) | |||
a
All the data were taken at 0°, 55° and 75° take-off angles in the electrostatic mode. The take-off angle is defined as the angle between the sample surface normal and the axis of the XPS analyzer lens
b
The gold substrate Au 4f signal was excluded to better show the elemental composition of the organic overlayers. The remaining signals from the organic SAM were re-normalized to 100%.
c
nd: not detected