Electronic Supplementary Information For
Surface oxygen vacancy defect engineering of p-CuAlO2 via Ar&H2 plasma
treatment for enhancing VOCs sensing performances
   Bin Tong, a b Gang Meng, * a c Zanhong Deng, a c Mati Horprathum, d Annop
   Klamchuen e and Xiaodong Fang * a c
    aAnhui Provincial Key Laboratory of Photonic Devices and Materials, Anhui Institute of         Optics and Fine
    Mechanics, Chinese Academy of Sciences, Hefei, 230031, China
    bUniversity of Science and Technology of China, Hefei 230026, China
   cKey Lab of Photovoltaic and Energy Conservation Materials, Chinese Academy of Sciences, Hefei
   230031, China
  d Opto-Electrochemical Sensing Research Team, National Electronic and Computer Technology Center,
 PathumThani 12120, Thailand
 eNational Nanotechnology Center, National Science and Technology Development Agency, Pathum
Thani 12120, Thailand
 

Experimental Section
       1.1 Synthesis of CuAlO2 particles
First of all, 0.04 mol Cu(CH3COO)2·H2O (Alfa Aesar, 99.9%) was dissolved in 160 mL absolute alcohol with
vigorous stirring, and then 16 mL HNO3 (Sinopharm Chemical Reagent, 99.7%), 0.2 mol C6H8O7·H2O
(Sinopharm Chemical Reagent, 99.8%) and 0.04 mol Al[OCH(CH3)CH2CH3]3 (Alfa Aesar, 97%) were added into
the above solution in sequence. After stirring for 6 hours, 16 mL HNO3 was added to the solution drop by drop to
obtain a well-mixed precursor solution. The precursor solution was dried at 100 °C overnight. In order to remove
the organics, the condensed solution was heated to 300 °C for 6 hours. After that, the dried powders were milled
for 24 h using a planetary ball miller and then annealed at 1100 °C for 10 h under air atmosphere. Subsequently,
the powders were reground and heated to 950 °C under flowing N2 atmosphere for 6 hours to form delafossite
CuAlO2 particles. To ensure the pure phase of delafossite CuAlO2, trace (excess) CuxO was washed with 1 M
diluted hydrochloric acid, 11 deionized water and absolute alcohol in sequence several times, and the final products
were dried in an oven at 80 °C for 24 h.
 1.2 Fabrication of CuAlO2 sensors
        The CuAlO2 slurry was prepared by dispersing the powders in appropriate isopropyl alcohol. CuAlO2 sensors
were prepared by brushing the above paste onto a thin alumina substrate with micro-interdigital Pt electrodes.
CuAlO2 films on slide glass substrates were fabricated simultaneously for characterization. After naturally drying,
the CuAlO2 sensors and films were heated at 350 °C under flowing air atmosphere for 3 hours. Afterwards, the
samples were treated by Ar&H2 plasma in KT-S2DQX (150 W, 13.56 MHz, （郑州九游网址j9设备有限公司）)plasma etching system
at 10 sccm 4% H2 in Ar and the pressure of ~ 99.8 Pa for 30 min, 60 min and 90 min, herein are referred to as
pristine, PT-30, PT-60 and PT-90.
1.3 Characterization and gas sensing test
       CuAlO2 samples were characterized by X-ray diffraction (XRD, Rigaku Smartlab), scanning electron
microscope (SEM, VEGA3 TESCAN), field emission high resolution transmission electron microscope
(HRTEM, Talos F200X), X-ray photoelectron spectroscopy (XPS, Thermo Scientific Esca Lab 250Xi
spectrometer ), photoluminescence (PL, JY Fluorolog-3-Tou) and Electron spin resonance (ESR, JEOL, JES
FA200 ESR spectrometer ). Mott-Schottky measurements were carried out on an electrochemical work-station
(Zahner Company, Germany) in 1M NaOH solution (pH=12.5) with frequency of 5000 Hz. Platinum sheet,
Ag/AgCl electrode and pristine/ PT-30 CuAlO2 samples were used as counter electrode, reference electrode and
work electrode, respectively. Gas sensing tests were examined in SD101 (Hua Chuang Rui Ke Technology Co.,
Ltd.) sensing system. The response was defined as ΔR/Ra, ΔR = Rg − Ra, where Ra and Rg are sensor resistance in
2flowing drying air and synthetic VOCs, respectively. During gas sensing test, the total flow rate of the dry air and
VOCs gas were adjusted to be 1000 sccm by mass flow controllers (MFCs)

Fig. S1. Cross-sectional SEM image of typical CuAlO2 sensors. The inset shows a low-magnification image.
The sensing layer is comprised of loosely packed CuAlO2 particles, with a thickness of ~ 15 μm.

Fig. S2. XRD patterns of pristine and Ar&H2 plasma treated CuAlO2 sensors. Ar&H2 plasma treatment didn’t
cause any detectable impurity phase. All the samples show a 3R (dominent) and 2H mixed CuAlO2 phase.

Fig. S3. SEM images of pristine (a) and Ar&H2 plasma treated PT-30 (b), PT-60 (c) and PT-90 (d) CuAlO2
sensors. Except for 90 minitues treated sample (PT-90) with appearance of small nanodots, no obrvious change
of surface morphology was obervered via Ar&H2 plasma treatment

Fig. S4. I-V curves of pristine and Ar&H2 plasma treated CAO sensors, measured under ambient environment
at room temperature. All the sensors exhibit linear (Ohmic) contact behavior.

Fig. S5. Mott-Schottky plot of pristine and PT-30 CuAlO2 sensors. Negative slope of 1/C2 versus V infers p
type conductivity. 2, 3

Fig. S6. XPS O 1s spectra of pristine, PT-30 and PT-60 CuAlO2, and the fitting results of three compositions.

Fig. S7. Stability test of pristine and PT-30 CuAlO2 sensors toward 100 ppm ethanol at 300 °C.

Fig. S8. ESR signals of pristine and Ar&H2 plasma treated CAO samples. Ar&H2 plasma treatment results in
a significant increase of unpaired electron resonance. The asymetric ESR profiles of PT-30, PT-60 and PT-90
CuAlO2 may arise from weakend surfce crystalllinity induced by ion bombardment.4
 
 中国科学技术大学   论文CC - 2019 - SI - Surface oxygen vacancy defect engineering of p-CuAlO2 via Ar&H2 plasma treatment

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