High Sensitivity and Ultra‐Broad‐Range NH3 Sensor Arrays by Precise Control of Step Defects on The Surface of Cl2‐Ndi Single Crystals

Abstract Vapor sensors with both high sensitivity and broad detection range are technically challenging yet highly desirable for widespread chemical sensing applications in diverse environments. Generally, an increased surface‐to‐volume ratio can effectively enhance the sensitivity to low concentrations, but often with the trade‐off of a constrained sensing range. Here, an approach is demonstrated for NH3 sensor arrays with an unprecedentedly broad sensing range by introducing controllable steps on the surface of an n‐type single crystal. Step edges, serving as adsorption sites with electron‐deficient properties, are well‐defined, discrete, and electronically active. NH3 molecules selectively adsorb at the step edges and nearly eliminate known trap‐like character, which is demonstrated by surface potential imaging. Consequently, the strategy can significantly boost the sensitivity of two‐terminal NH3 resistance sensors on thin crystals with a few steps while simultaneously enhancing the tolerance on thick crystals with dense steps. Incorporation of these crystals into parallel sensor arrays results in ppb–to–% level detection range and a convenient linear relation between sheet conductance and semi‐log NH3 concentration, allowing for the precise localization of vapor leakage. In general, the results suggest new opportunities for defect engineering of organic semiconductor crystal surfaces for purposeful vapor or chemical sensing.

formance at NH3 concentrations of ˂ 5ppb.The calculation of LOD for parallel sensors is also based on the same method.
Response time and recovery time: The response time is the time needed for the current change to reach 90% after the NH3 supply is turned on, and the recovery time is the time for the current to decrease from 90% to initialization after the NH3 is turned off. [2] Cl2-NDI single crystal sensors for NH3 sensing    in VT, which is ascribed to the presence of shallow traps with positive potential of +55±5 mV (~2 kBT/e) at step edges and a small number of deep traps at the intersection of crystal steps, respectively.With exposure to 500 ppm NH3, although a significant increase in σs was demonstrated in thick crystals, it was still unable to reach the "idea" performance based on thin single crystals with negligible step edge traps.It is attributed to the charge transport primarily occurring at the interface between the crystal and SiO2 dielectric layer, but the adsorption of NH3 at and shows performance gains with increasing NH3 concentration.It eliminates a gate voltage of several tens of volts required to sustain the device in an "on state" to compensate for charge depletion caused by structural defects and gas exposure (see Table S2).This result enables the utilization of two terminal resistance sensors, simplifying the device structure while simultaneously ensuring that both the charge transport layer and the reactive sites of analytes are situated on the upper surface of the crystal.The maximum adsorption energy and lowest total energy are observed in Configurations 3 and 4, suggesting that the adsorption of NH3 at the lateral side of the NDI core is the most favorable.

Figure S1 .
Figure S1.The comparison for Cl2-NDI single crystal FETs with Au and Ag electrodes.a)

Figure
Figure S2.a) Step density on the surface of Cl2-NDI single crystal versus crystal thicknesses.

Figure
Figure S3.a) Schematic diagram of the sensor testing system.b) Transfer characteristic curves

Figure S4 .
Figure S4.(a) ID-VG transfer characteristics for Cl2-NDI single crystal FETs before and after

Figure S5 .
Figure S5.The comparison of output characteristic curves of sensors before and after exposure

Figure
Figure S6.a) Cross-shaped two-terminal device geometry of Cl2-NDI single crystal sensor.

Figure S7 .
Figure S7.Schematic models of NH3 adsorbed at various positions on Cl2-NDI molecules (a)

Figure S8 .
Figure S8.Sensing performance for three Cl2-NDI single crystals with varying thicknesses

Figure S9 .
Figure S9.Cycle sensing experiments of Cl2-NDI single crystals with different thicknesses.a)

Figure S11 .
Figure S11.The stability of a parallel sensor array over three weeks.a,b) The sensing perfor-

Figure S12 .
Figure S12.The long-term stability test for the parallel sensor array stored in air for eight

Figure S13 .
Figure S13.The selectivity of a Cl2-NDI sensor for various types of orangic amines at the

Figure S15 .
Figure S15.X-ray diffraction for a Cl2-NDI crystal before and after exposure to NH3.The

Figure S16 .
Figure S16.XPS profiling spectra for a 1.5 μm-thick Cl2-NDI crystal before and after exposure

Figure S17 .
Figure S17.KPFM surface potential images of Cl2-NDI single crystal flat surface terrace with

Figure S18 .
Figure S18.The surface potential of a Cl2-NDI single crystal by exposed to varied concentra-

Figure S19 .
Figure S19.AFM topography images of Cl2-NDI single crystal under varying concentrations

Figure
Figure S21.a-e) AFM topography of Cl2-NDI single crystal by alternating exposure to

Figure
Figure S22.a-e) Corresponding KPFM surface potential images for Figure S21.f) The varia-

Table S1 .
The comparison of the total energy (Etotal), adsorption energy (Ead), the shortest distance between NH3 and Cl2-NDI molecules, and the Bader charge transfer value (ΔQb) for the six configurations in FigureS7.