Structural, optical and gas sensing properties of vertically well-aligned ZnO nanowires grown on graphene/Si substrate by thermal evaporation method

Journal Article · Sun Jul 15 04:00:00 EDT 2018 · Materials Characterization

DOI:https://doi.org/10.1016/J.MATCHAR.2018.04.047· OSTI ID:22805046

Van Thu, Le ^[1]; Ha, La Thi Thai ^[2]; Thanh, Vu Minh ^[3]; Lam, Tran Dai ^[4]

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1. Technical Equipment and Allocation Administration, Ministry of Public Security, 47 Pham Van Dong, Cau Giay, Ha Noi (Viet Nam)
2. Faculty of Materials Technology, Ho Chi Minh city University of Technology, VNU-HCM, 268 Ly Thuong Kiet street, Ward 14, District 10, Ho Chi Minh City (Viet Nam)
3. Institute of Chemistry and Materials, 17 Hoang Sam, Cau Giay, Ha Noi (Viet Nam)
4. Graduate University of Science and Technology, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Hanoi (Viet Nam)

Highlights: • Vertically well-aligned ZnO NW arrays with high aspect ratio and extremely large-surface-volume ratio were synthesized on graphene/Si substrate without the aid of metal catalyst by a simple thermal evaporation. • The gas sensor based on the vertical ZnO NW arrays-graphene structure exhibited high sensitivity and rapid response/recovery characteristics to NO{sub 2} gas at 200oC, and could be used to detect NO{sub 2} gas at very low levels (2, 6, 10 ppm). • The excellent sensing performance is mainly because of the large specific surface area and the presence of oxygen-vacancies at the surface of ZnO NWs, together with the creation of p-n heterojunctions between n-type ZnO NW and p-type graphene. • The common defects and optical properties of the ZnO NW arrays-graphene structure were studied in detail. • The possible growth mechanism of vertically well-aligned ZnO NWs on graphene and the gas-sensing mechanism of sensors were proposed. - Abstract: We report catalyst-free vertical growth of high-density ZnO nanowire (NW) arrays on Si substrate with a graphene buffer layer by thermal evaporation method. Structural, surface morphology, chemical composition and optical properties of ZnO NWs were studied by Field emission scanning electron microscopy (FE-SEM), High-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL) and Raman spectroscopy. The results indicate that the grown ZnO NWs are single-crystalline and exhibit the hexagonal wurtzite crystal structure with a preferred orientation along the [0001] direction; all of the ZnO NWs vertically grow on the graphene/Si substrate. The majority of the as-grown NWs have diameters in the range of 250–300 nm and length up to several tens of micrometers, whereas a small portion of NWs have a diameter of approximately of 9–12 nm. Room temperature PL spectrum of the ZnO NWs exhibits a sharp and strong ultraviolet emission at 380 nm and a weak visible emission at around 516 nm. The role of graphene buffer layer in the vertical-aligned ZnO NW arrays growth and its improved optical properties is demonstrated. Importantly, the gas sensor based on these ZnO NWs exhibits high sensitivity and rapid response/recovery characteristics to NO{sub 2} gas at 200 °C, and can detect NO{sub 2} concentration as low as 2, 6 and 10 ppm. The excellent sensing performance is mainly due to the combination of the large specific surface area and the presence of oxygen-vacancies at the surface of ZnO NWs, together with the creation of p-n heterojunctions between n-type ZnO NW and p-type graphene. Such a ZnO NW/graphene structure is very promising for various applications, such as photonic, optoelectronic and sensor devices. In addition, the possible growth mechanism and the NO{sub 2} sensing gas mechanism of the ZnO NWs-graphene structure have been discussed.

• OSTI ID: 22805046
• Journal Information: Materials Characterization, Journal Name: Materials Characterization Vol. 141; ISSN 1044-5803; ISSN MACHEX
• Country of Publication: United States
• Language: English

Related Subjects

77 NANOSCIENCE AND NANOTECHNOLOGY
CATALYSTS
FIELD EMISSION
FOURIER TRANSFORM SPECTROMETERS
GRAPHENE
INFRARED SPECTRA
LAYERS
NANOWIRES
NITROGEN DIOXIDE
OPTICAL PROPERTIES
P-N JUNCTIONS
PHOTOLUMINESCENCE
RAMAN SPECTROSCOPY
SCANNING ELECTRON MICROSCOPY
SILICON
SUBSTRATES
TRANSMISSION ELECTRON MICROSCOPY
ULTRAVIOLET RADIATION
X-RAY DIFFRACTION
X-RAY PHOTOELECTRON SPECTROSCOPY
ZINC OXIDES