Cl₂-NDI
A molecular semiconductor linking crystal steps, site-selective surface doping and measured transistor current.
A molecular semiconductor linking crystal steps, site-selective surface doping and measured transistor current.
- Material form
- β-phase single crystal
- Function
- Electron transport
- Application
- Organic field-effect transistor
Structure
The studied compound is N,N′-bis(heptafluorobutyl)-2,6-dichloro-naphthalene tetracarboxylic diimide. Its β-phase crystals have a brick-wall molecular arrangement in the (001) plane.
Properties and function
- n-type transport
- Electrons carry current through the transistor channel.
- Surface step edges
- Positive step-edge potentials can trap electrons, affecting mobility and threshold voltage.
- Direction-dependent transport
- In the reported crystals, crossing steps is more strongly affected than travelling parallel to them.
Device and processing
Grow the crystal
Physical vapour transport produces single crystals with differing thickness and step density.
Form the channel
A crystal bridges contacts in a vacuum-gap field-effect transistor.
Compare structure and transport
AFM and surface-potential mapping are compared with electrical measurements.
Surface chemistry and charge transport
Same representative Cl₂-NDI single-crystal transistor before and after N-silane exposure: 47 µm thick, 29 steps per 10 µm, drain voltage 10 V, 300 K (workbook metadata). A 100 µL liquid dose supplied the vapour for 1 h; it is not the incorporated dopant volume.
| Sweep | Original current / nA | Doped current / nA | After / before current |
|---|---|---|---|
| forward | 17.2275 | 1002.44 | 58.1884 |
| reverse | 17.0775 | 993.447 | 58.1729 |
These are drain-current ratios at fixed gate bias, not mobility gains. The 204 original measured rows retain both sweep directions and gate leakage; no interpolation or curve fitting is used. The supplementary characterisation provides same-study controls, not proof that every measurement used this selected transistor.
AFM: Where does the dopant accumulate?
Observation: Ridges develop preferentially at crystal steps at the selected dose. Inference: Surface topography supports site-selective accumulation. Limit: Height alone does not identify charge transfer or chemical composition. Source: Supplementary Figs. 3 and 16.
XPS + diffraction: Surface treatment or bulk restructuring?
Observation: The Si signal disappears with sputtering; diffraction peaks remain similar. Inference: Together these observations support a surface-localised modification. Limit: They do not prove that every bulk site is unchanged. Source: Supplementary Figs. 14–15.
Kelvin probe: Does the local electrical potential change?
Observation: Step-potential profiles change after doping and persist across several scan settings. Inference: The authors associate the profiles with local charge redistribution. Limit: Tip geometry broadens the signal; contrast is not a direct trap-count image. Source: Supplementary Figs. 16–30.
Optical spectroscopy: Electron transfer or covalent substitution?
Observation: Treated-film absorption resembles electrochemically reduced Cl₂-NDI; the solution reaction differs. Inference: The solid-state data support reduction; amines can also substitute chlorine in solution. Limit: A familiar nucleophile does not imply the same reaction in every phase. Source: Supplementary Fig. 4.
He et al., Nature Materials 20, 1532–1538 (2021); Author dataset version 3, CC BY 4.0; Reproducible data and analysis.
Evidence and limits
The 2018 study connects step-edge potentials with electron trapping. The 2021 follow-up adds source-backed transfer sweeps before and after N-silane treatment, supported by complementary surface and spectroscopic measurements.
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