Supporting Information

A strategy for ultrasensitive and selective detection of methylamine using p-type

Cr2O3: Morphological design of sensing materials, control of charge carrier

concentrations, and configurational tuning of Au catalysts

Tae-Hyung Kima, Ji-Wook Yoona, Yun Chan Kanga,

Faissal Abdel-Hadyb, Abdulaziz A. Wazzanb, and Jong-Heun Leea,b,*

aDepartment of Materials Science and Engineering,

Korea University, Seoul 02841, Republic of Korea

bDepartment of Chemical and Materials Engineering, King Abdulaziz University, Jeddah 21589,

Saudi Arabia

* Author to whom correspondence should be addressed.

Email: jongheun@korea.ac.kr ; Fax: +82-2-928-3584 ; Tel: +82-2-3290-3282

Figure. S1 SEM and TEM images of (a-c) Cr2O3-H and (d-f) Cr2O3-YS spheres

1

Figure. S2 Mechanism of the formation of the multi-shelled Cr2O3 yolk-shell spheres

Figure. S3 TEM images of 1S-Au-Cr2O3-YS spheres

2

Figure. S4 TEM images of 2S-Au-Cr2O3-YS spheres

3

Figure. S5 XPS spectra of 1S-Au-Cr2O3-YS and 2S-Au-Cr2O3-YS spheres: (a) full range

spectra and (b) Au 4f5/2 and 4f7/2 peaks

4

Figure. S6 90% response time (tres) upon exposure to 5 ppm TMA and 90% recovery time

(trecov) upon exposure to air at 225 oC. (a) Cr2O3-H, (b) Cr2O3-YS, (c) 1S-Au-Cr2O3-

YS, and (d) 2S-Au-Cr2O3-YS sensors

Figure. S7 Dynamic sensing transients to 5 ppm TMA at 225 oC: (a) Cr2O3-H, (b) Cr2O3-YS,

(c) 1S-Au-Cr2O3-YS, and (d) 2S-Au-Cr2O3-YS sensors

5