Detection of hydrogen gas in industry, biomedical systems and combustion systems is important for safety reasons. Silver doping in zinc oxide and zinc doping in copper oxide were investigated to obtain improved hydrogen sensing performances for sensors. Samples were grown by chemical method and studied by X-ray diffraction, SEM and sensorial techniques. For selectivity study samples were exposed to hydrogen, methane and ethanol gases. Were found growth and annealing regimes which allow us fabrication of faster and more selective gas sensors based on Zn1-xAgxOy nanostructured films and nanocrystallite Cu1-xZnxOy films with respect to 100 ppm H2

Ababii, N.

Cretu, V.

Lupan, O.

Postica, V.

Sontea, V.

Electronic Sumy State University Institutional Repository

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  NANOMATERIALS: APPLICATIONS AND PROPERTIES Vol. 3 No 1, 01NTF14(3pp) (2014)   2304-1862/2014/3(1)01NTF14(3) 01NTF14-1  2014 Sumy State University Hydrogen Gas Response of Zn1 – xAgxOy and Cu1 – xZnxOy Nanostructured Films   V. Cretu, V. Postica, N. Ababii, V. Sontea, O. Lupan  Technical University of Moldova, 168 Stefan cel Mare Blvd, MD-2004, Chisinau, Republic of Moldova  (Received 01 July 2014; published online 29 August 2014)  Detection of hydrogen gas in industry, biomedical systems and combustion systems is important for safety reasons. Silver doping in zinc oxide and zinc doping in copper oxide were investigated to obtain improved hydrogen sensing performances for sensors. Samples were grown by chemical method and studied by X-ray diffraction, SEM and sensorial techniques. For selectivity study samples were exposed to hydrogen, methane and ethanol gases. Were found growth and annealing regimes which allow us fabrica-tion of faster and more selective gas sensors based on Zn1 – xAgxOy nanostructured films and nanocrystallite Cu1 – xZnxOy films with respect to 100 ppm H2.  Keywords: Cu1 – xZnxOy, Zn1 – xAgxOy, Chemical synthesis, Nanostructures, hydrogen, oxide, film, RTA.   PACS numbers: 81.05.DZ, 81.07.Bc   1. INTRODUCTION  Metal oxide nanoscale materials have been attract-ing much attention due to their unique size- and mor-phology-dependent physical and chemical properties [1]. It is also promising in the development of gas sensors applications and it should be expected that metal oxide nanostructures exhibit better performance than the bulk based devices [1-2]. The monitoring of H2 and other flammable gases in industry, biomedical systems, and combustion systems is becoming important factor by increasing the requirements for sustainable and renewable energy sources. Among various types of sensors for detection such gases, chemoresistive gas sensors have been intensively investigated because of their simple usability and low cost [1-2]. Zinc oxide (ZnO) is a well known n-type wide band gap semiconductor (3.37 eV at 300 K for bulk material). It has been studied extensively as the main material for many modern applications, especially for sensors applications. In this regard, various synthesis methods have been explored to fabricate different nanostruc-tures like nanowires by hydrothermal method for sen-sor applications [2,3], by electrodeposition for light emitting devices by europium doping [4], etc. Cupric oxide (CuO) is a typical p-type semiconduc-tor with a band gap of 1.2–1.9 eV and a monoclinic crystal structure [5-9]. Additionally, compared with other metal oxide nanostructures, such as TiO2, ZnO, and SnO2, copper oxide nanostructures have more interesting magnetic and superhydrophobic properties [5]. In recent years, the „mesoporous‟ metal oxides, containing pores [1,6], have attracted interest for the application in gas sensors because of their high sur-face-to-volume ratio that can lead to improve sensitiv-ity by the increased adsorption/reaction sites. Various works have reported about the gas-sensing properties of copper oxide, especially on quasi1D structures, like nanowires growth by surface oxidation of a Cu foil for biosensor application [7], by in situ thermal oxidation in air on Cu2O [8], by low temperature solid-phase process [9], etc. Also were studied sensing characteris-tics to H2 and C2H5OH of CuO mesoporous films pre-pared via a precursor-based ink solution route [1].  Compared to n-type semiconducting oxide based gas sensors, p-type oxide semiconductor gas sensors exhibit not only shortcomings but also promising potentials for practical applications [10]. In this work, were studied gas response and selectivity of Zn1-xAgxOy and Cu1-xZnxOy nanostructured films to different gases, namely hydrogen, methane and ethanol.  2. EXPERIMENTAL  2.1 Growth of Zn1-xAgxOy and Cu1-xZnxOy nanostructured films synthesized by chemi-cal solution approach  Glass substrates were used for growth of both types of metal oxides. The cleaning process were reported in our previous work [11]. For growth Zn1-xAgxOy nanostructured films were used the aqueous zinc complex solution approach. It comprises a mixture of zinc sulfate (Zn(SO4) ∙ 7H2O), silver nitrate (AgNO3) and sodium hydroxide (NaOH) mixed until complete dissolution. The concentration of the complex solution was diluted to obtain 0.05 – 0.15 M zinc concentration for deposition by adding respective quantities of deionized (DI) water. For growth Cu1-xZnxOy nanocrystalline films were used the aqueous copper complex solution of copper sulfate (CuSO4 ∙ 5H2O) and sodium thiosulfate (Na2S2O3). Finally nanostructured films were exposed to different dura-tions of rapid thermal annealing at various tempera-tures for 60 s.  2.2 Characterization  The samples of Zn1-xAgxOy and Cu1-xZnxOy nanostructured films were analyzed by X-ray diffrac-tion (XRD) using a Rigaky “DB/MAX” powder diffrac-tometer with a nickel-filtered CuKα radiation source (λ = 1.54178 Å) and a scanning rate of 0.05 °/s in the 2θ range from 30 to 90 °. The compositional analysis was carried out using energy-dispersive X-ray spectroscopy (EDX), in combination with SEM. The different charac-terization techniques confirmed that the nanostruc-tured films are crystalline material.   V. CRETU, V. POSTICA, N. ABABII, V. SONTEA, O. LUPAN PROC. NAP 3, 01NTF14 (2014)   01NTF14-2 3. RESULTS AND DISCUSSIONS  In this work were investigated gas response and se-lectivity to H2 of Zn1-xAgxOy nanostructured films (with thickness of 2.6 µm) treated by rapid thermal annealing (RTA) in air and nanocrystallite Cu1-xZnxOy films treat-ed by rapid thermal annealing (RTA) in furnace (with thickness of 0.95 µm). Also were investigated response (τr) time and recovery (τf) time of both type of elaborated sensors at 300 ºC operating temperature (OPT).  3.1 Chemical and Morphological Characteriza-tion  According to EDX studies the Ag content in nanostructured Zn1-xAgxOy films was found to be at 1.3wt%Ag, while for Cu1-xZnxOy samples about 3wt%Zn. The typical SEM image of 1.3 wt%Ag nanostructured Zn1-xAgxOy films RTA treated at 500 ºC is represented in Figure 1a.      Fig. 1 – SEM images of: (a) Zn1-xAgxOy nanostructured film RTA treated in air at 500 ºC with 2.6 µm thickness; and (b) Cu1-xZnxOy nanocrystallite film treated RTA in furnace at 450 ºC with 0.95 µm thickness.  It can be seen that the Zn1-xAgxOy films are composed of nanocrystallites with different diameter size (250-500 nm), while 3wt%Zn nanocrystallite Cu1-xZnxOy films have a different structure (Fig. 1b).  3.2 Structural analysis  Fig. 2a shows the XRD pattern of as-grown and RTA treated (500 ºC for 60 s) 1.3wt%Ag nanostructured    Zn1-xAgxO films recorded in the range of 30-90º with scanning step of 0.02º. All diffraction peaks can be at-tributed to crystalline ZnO with the hexagonal wurtzite structure (space group: P63mc (186); a = 0.3249 nm, c = 0.5206 nm). The data are in agreement with the Joint Committee on Powder Diffraction Standards (JCPDS) card for ZnO (JCPDS 036-1451). In Figure 2 (a) the strongest detected (hkl) peaks are at 2θ values which correspond to the following lattice planes: (100), (002), (101), (102), (110), (103), (112), (004) and (104), respectively. From the Fig. 2a was observed that diffraction peaks at the intensity of the (100), (002) and (101) were shifted by 0.1º for RTA treated sample to a lower 2θ angle value as compared with those of as-grown sample. Such lattice deformation might be result of Ag atoms incorporation in lattice of ZnO, which have greater ion radius (r(Ag1+) = 0.126 nm) than that of Zn2+ (r(Zn2+) = 0.074 nm).      Fig. 2 – XRD patterns of: (a) the as-grown and  RTA treated in air at 500 ºC Zn1-xAgxOy nanostructured film; (b) as-grown and RTA in furnace at 450 ºC nanocrystallite Cu1-xZnxOy film.  Fig. 2b shows the XRD pattern of as-grown and RTA treated in furnace (450 ºC for 60 s) 3wt%Zn nanostruc-tured Cu1-xZnxOy films recorded in the range of 23-100º with scanning step of 0.02º. All diffraction peaks for as-grown nanocrystallite films can be attributed to cuprite (Cu2O) phase with cubic structure (space group: Pn-3m; a = 4.2685 Å). Rapid thermal annealing in air at 450 °C with fast temperature ramp rate resulted in formation of coexist-ing cuprite and tenorite (CuO) phases of the deposition with monoclinic structure (space group: C2h6-C2/c; a=4.6837 Å, b=3.4226 Å, c=5.1288 Å, β=99.54 Å).   3.3 Gas sensing studies  In order to test the gas response and selectivity to H2 gas of Zn1-xAgxOy and Cu1-xZnxOy nanostructured films, the response to ethanol and CH4 have also been investigated. The gas response of the sensors is given by the resistance change of the sensor in dry air and the resistance in the test gas as reported before [2].   There was observed no response to 100 ppm C2H5OH and CH4 for of Zn1-xAgxOy and Cu1-xZnxOy samples at OPT 300 ºC. In Fig. 3a is demonstrated gas  HYDROGEN GAS RESPONSE OF … PROC. NAP 3, 01NTF14 (2014)   01NTF14-3 response to 100 ppm H2 versus time for nanostructured Zn1-xAgxOy film RTA treated in air at 500 ºC and nanocrystallite Cu1-xZnxOy film treated RTA in furnace at 450 ºC. Resistance of Zn1-xAgxOy sample under H2 gas exposition was decrease, so it can reach a maximum of 100% according to formula above, and demonstrate 85 % gas response, while resistance of Cu1-xZnxOy sample was increase and demonstrate 382 % gas response.     Fig. 3 – Gas response to 100 ppm H2 of the: (a) nanostructured Zn1-xAgxO film RTA treated in air at 500 ºC with 2.6 µm thickness and nanocrystallite Cu1-xZnxO film treated RTA in furnace at 450 ºC with 0.95 µm thickness versus time to 100 ppm H2 at OPT 300 ºC; (b) nanocrystallite Cu1-xZnxO film and (c) nanostructured Zn1-xAgxO film versus temperature of treatment type, RTA in air for Zn1-xAgxO samples after different regimes of RTA in furnace for samples, at operating temperature of 300 °C. Also were investigated response τr and recovery τf time (τ = |τ(90%) - τ(10%)|). From Fig. 3a it can be observed that τr for Zn1-xAgxOy (τr = 2.8 s) sample is smaller than for Cu1-xZnxOy (τr  = 7.8 s) sample, while τf for Cu1-xZnxOy (τf  = 6.1 s) sample is smaller than τr for the same sample and smaller than τf  for Zn1-xAgxOy (τf = 11 s) sample. In Fig. 3b is presented dependence of gas response to H2 for Cu1-xZnxOy samples at different temperatures of RTA treatment in furnace, and can be observed that optimal temperature of treatment is 450 °C, while for Zn1-xAgxOy samples (Fig. 3c) the optimal temperature of RTA treatment in air is 500 °C.  4. CONCLUSIONS  In summary, Zn1-xAgxOy nanostructured films and nanocrystallite Cu1-xZnxOy films with high crystallinity were grown on glass substrate using a chemical deposi-tion method. SEM, EDX, and X-ray diffraction have been used to characterize the morphology, chemical composition and structure of the samples. XRD meas-urements indicate that synthesized Zn1-xAgxO samples are in the hexagonal phase and from XRD pattern were observed deformation in lattice by incorporation of Ag atoms, that have a higher ionic radii. XRD measure-ments of Cu1-xZnxO samples indicate that nanocrystal-line films are synthesized in cuprite (Cu2O) phase with cubic structure, but RTA treatment in furnace results in formation of monoclinic structure of tenorite (CuO) phase in addition to cuprite phase. From 2.6 µm thick-ness 1.3wt%Ag Zn1-xAgxO nanostructured films were fabricated faster sensors with 85 % gas response to 100 ppm H2 and from 0.95 µm thickness 3wt% Zn nano-crystallite Cu1-xZnxO films were fabricated rapid sen-sors with 382 % gas response to 100 ppm H2 at operat-ing temperature of 300 °C.  AKNOWLEDGEMENTS  The authors gratefully acknowledge collaboration with Prof. Chow from UCF, USA and financial support of the STCU and ASM through Grant 09_STCU_A/5833.   REFERENCES  1. Y.H. Choi, D.H. Kim, S.H. Hong, K.S. Hong, Sensor. Actu-at. B 178, 395 (2013). 2. L. Chow, O. Lupan, G. Chai, H. Khallaf, L.O. Ono, B. Roldan Cuenya, I.M. Tiginyanu, V.V. Ursaki, V. Sontea, A. Schulte, Sensor. Actuat. A 189, 399 (2013). 3. O. Lupan, L. Chow, L.K. Ono, B. Roldan Cuenya, G. Chai, H. Khallaf, S. Park, A. Schulte, J. Phys. Chem. C 114, 12401 (2010). 4. O. Lupan, T. Papourte, B. Viana, P. Acshehoug, M. Ah-madi, B. Roldan Cuenya, Y. Rudzevich, Y. Lin, L. Chow, Appl. Surf. Sci. 282, 782 (2013). 5. Q. Zhang, K. Zhang, D. Xu, G. Yang, H. Huang, F. Nie, C. Liu, S. Yang, Prog. Mater. Sci. 60, 208 (2014). 6. V. Cretu, N. Ababii, V. Postica, V. Sontea, V. Trofim, S. Railean, I. Pocaznoi, O. Lupan, II-Th Regional Workshop Health Technology Management 1, 72 (2014). 7. O. Akhavan, E. Ghaderi, J. Mater. Chem. 21, 12935 (2011). 8. A. Li, H. Song, J. Zhou, X. Chen, S. Liu, CrystEngComm 15, 8559 (2013). 9. W. Wang, Y. Zhuang, L. Li, Mater. Lett. 62, 1724 (2008). 10. H.J. Kim, J.H. Lee, Sensor. Actuat. 192, 607 (2014). 11. V. Postica, N. Ababii, V. Cretu, Conferinta Stiintifica a Colaboratorilor, Doctoranzilor si Studentilor UTM, 234 (2013). 12. L. Debbichi, M.C. Marco de Lucas, J.F. Pierson, P. Kruger, J. Phys. Chem. C 116, 10232 (2012).   

Hydrogen Gas Response of Zn1 – xAgxOy and Cu1 – xZnxOy Nanostructured Films

SocioEconomic Challenges Journal (Sumy State University)

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE  
NANOMATERIALS: APPLICATIONS AND PROPERTIES 
Vol. 3 No 1, 01NTF14(3pp) (2014) 
 
 
2304-1862/2014/3(1)01NTF14(3) 01NTF14-1  2014 Sumy State University 
Hydrogen Gas Response of Zn1 – xAgxOy and Cu1 – xZnxOy Nanostructured Films  
 
V. Cretu, V. Postica, N. Ababii, V. Sontea, O. Lupan 
 
Technical University of Moldova, 168 Stefan cel Mare Blvd, MD-2004, Chisinau, Republic of Moldova 
 
(Received 01 July 2014; published online 29 August 2014) 
 
Detection of hydrogen gas in industry, biomedical systems and combustion systems is important for 
safety reasons. Silver doping in zinc oxide and zinc doping in copper oxide were investigated to obtain 
improved hydrogen sensing performances for sensors. Samples were grown by chemical method and 
studied by X-ray diffraction, SEM and sensorial techniques. For selectivity study samples were exposed to 
hydrogen, methane and ethanol gases. Were found growth and annealing regimes which allow us fabrica-
tion of faster and more selective gas sensors based on Zn1 – xAgxOy nanostructured films and nanocrystallite 
Cu1 – xZnxOy films with respect to 100 ppm H2. 
 
Keywords: Cu1 – xZnxOy, Zn1 – xAgxOy, Chemical synthesis, Nanostructures, hydrogen, oxide, film, RTA. 
 
 PACS numbers: 81.05.DZ, 81.07.Bc 
 
 
1. INTRODUCTION 
 
Metal oxide nanoscale materials have been attract-
ing much attention due to their unique size- and mor-
phology-dependent physical and chemical properties 
[1]. It is also promising in the development of gas sensors 
applications and it should be expected that metal oxide 
nanostructures exhibit better performance than the 
bulk based devices [1-2]. The monitoring of H2 and 
other flammable gases in industry, biomedical systems, 
and combustion systems is becoming important factor 
by increasing the requirements for sustainable and 
renewable energy sources. Among various types of 
sensors for detection such gases, chemoresistive gas 
sensors have been intensively investigated because of 
their simple usability and low cost [1-2]. 
Zinc oxide (ZnO) is a well known n-type wide band 
gap semiconductor (3.37 eV at 300 K for bulk material). 
It has been studied extensively as the main material 
for many modern applications, especially for sensors 
applications. In this regard, various synthesis methods 
have been explored to fabricate different nanostruc-
tures like nanowires by hydrothermal method for sen-
sor applications [2,3], by electrodeposition for light 
emitting devices by europium doping [4], etc. 
Cupric oxide (CuO) is a typical p-type semiconduc-
tor with a band gap of 1.2–1.9 eV and a monoclinic 
crystal structure [5-9]. Additionally, compared with 
other metal oxide nanostructures, such as TiO2, ZnO, 
and SnO2, copper oxide nanostructures have more 
interesting magnetic and superhydrophobic properties 
[5]. In recent years, the „mesoporous‟ metal oxides, 
containing pores [1,6], have attracted interest for the 
application in gas sensors because of their high sur-
face-to-volume ratio that can lead to improve sensitiv-
ity by the increased adsorption/reaction sites. Various 
works have reported about the gas-sensing properties 
of copper oxide, especially on quasi1D structures, like 
nanowires growth by surface oxidation of a Cu foil for 
biosensor application [7], by in situ thermal oxidation 
in air on Cu2O [8], by low temperature solid-phase 
process [9], etc. Also were studied sensing characteris-
tics to H2 and C2H5OH of CuO mesoporous films pre-
pared via a precursor-based ink solution route [1].  
Compared to n-type semiconducting oxide based gas 
sensors, p-type oxide semiconductor gas sensors exhibit 
not only shortcomings but also promising potentials for 
practical applications [10]. In this work, were studied 
gas response and selectivity of Zn1-xAgxOy and Cu1-
xZnxOy nanostructured films to different gases, namely 
hydrogen, methane and ethanol. 
 
2. EXPERIMENTAL 
 
2.1 Growth of Zn1-xAgxOy and Cu1-xZnxOy 
nanostructured films synthesized by chemi-
cal solution approach 
 
Glass substrates were used for growth of both 
types of metal oxides. The cleaning process were 
reported in our previous work [11]. For growth Zn1-
xAgxOy nanostructured films were used the aqueous 
zinc complex solution approach. It comprises a 
mixture of zinc sulfate (Zn(SO4) ∙ 7H2O), silver nitrate 
(AgNO3) and sodium hydroxide (NaOH) mixed until 
complete dissolution. The concentration of the 
complex solution was diluted to obtain 0.05 – 0.15 M 
zinc concentration for deposition by adding respective 
quantities of deionized (DI) water. For growth Cu1-
xZnxOy nanocrystalline films were used the aqueous 
copper complex solution of copper sulfate (CuSO4 ∙ 
5H2O) and sodium thiosulfate (Na2S2O3). Finally 
nanostructured films were exposed to different dura-
tions of rapid thermal annealing at various tempera-
tures for 60 s. 
 
2.2 Characterization 
 
The samples of Zn1-xAgxOy and Cu1-xZnxOy 
nanostructured films were analyzed by X-ray diffrac-
tion (XRD) using a Rigaky “DB/MAX” powder diffrac-
tometer with a nickel-filtered CuKα radiation source (λ 
= 1.54178 Å) and a scanning rate of 0.05 °/s in the 2θ 
range from 30 to 90 °. The compositional analysis was 
carried out using energy-dispersive X-ray spectroscopy 
(EDX), in combination with SEM. The different charac-
terization techniques confirmed that the nanostruc-
tured films are crystalline material. 
 
 V. CRETU, V. POSTICA, N. ABABII, V. SONTEA, O. LUPAN PROC. NAP 3, 01NTF14 (2014) 
 
 
01NTF14-2 
3. RESULTS AND DISCUSSIONS 
 
In this work were investigated gas response and se-
lectivity to H2 of Zn1-xAgxOy nanostructured films (with 
thickness of 2.6 µm) treated by rapid thermal annealing 
(RTA) in air and nanocrystallite Cu1-xZnxOy films treat-
ed by rapid thermal annealing (RTA) in furnace (with 
thickness of 0.95 µm). Also were investigated response 
(τr) time and recovery (τf) time of both type of elaborated 
sensors at 300 ºC operating temperature (OPT). 
 
3.1 Chemical and Morphological Characteriza-
tion 
 
According to EDX studies the Ag content in 
nanostructured Zn1-xAgxOy films was found to be at 
1.3wt%Ag, while for Cu1-xZnxOy samples about 
3wt%Zn. The typical SEM image of 1.3 wt%Ag 
nanostructured Zn1-xAgxOy films RTA treated at 500 ºC 
is represented in Figure 1a.  
 
 
 
 
Fig. 1 – SEM images of: (a) Zn1-xAgxOy nanostructured film 
RTA treated in air at 500 ºC with 2.6 µm thickness; and (b) 
Cu1-xZnxOy nanocrystallite film treated RTA in furnace at 450 
ºC with 0.95 µm thickness. 
 
It can be seen that the Zn1-xAgxOy films are composed 
of nanocrystallites with different diameter size (250-
500 nm), while 3wt%Zn nanocrystallite Cu1-xZnxOy 
films have a different structure (Fig. 1b). 
 
3.2 Structural analysis 
 
Fig. 2a shows the XRD pattern of as-grown and RTA 
treated (500 ºC for 60 s) 1.3wt%Ag nanostructured    
Zn1-xAgxO films recorded in the range of 30-90º with 
scanning step of 0.02º. All diffraction peaks can be at-
tributed to crystalline ZnO with the hexagonal wurtzite 
structure (space group: P63mc (186); a = 0.3249 nm, c = 
0.5206 nm). The data are in agreement with the Joint 
Committee on Powder Diffraction Standards (JCPDS) 
card for ZnO (JCPDS 036-1451). 
In Figure 2 (a) the strongest detected (hkl) peaks are 
at 2θ values which correspond to the following lattice 
planes: (100), (002), (101), (102), (110), (103), (112), (004) 
and (104), respectively. From the Fig. 2a was observed 
that diffraction peaks at the intensity of the (100), (002) 
and (101) were shifted by 0.1º for RTA treated sample to 
a lower 2θ angle value as compared with those of as-
grown sample. Such lattice deformation might be result 
of Ag atoms incorporation in lattice of ZnO, which have 
greater ion radius (r(Ag1+) = 0.126 nm) than that of Zn2+ 
(r(Zn2+) = 0.074 nm).   
 
 
 
Fig. 2 – XRD patterns of: (a) the as-grown and  RTA treated 
in air at 500 ºC Zn1-xAgxOy nanostructured film; (b) as-grown 
and RTA in furnace at 450 ºC nanocrystallite Cu1-xZnxOy film. 
 
Fig. 2b shows the XRD pattern of as-grown and RTA 
treated in furnace (450 ºC for 60 s) 3wt%Zn nanostruc-
tured Cu1-xZnxOy films recorded in the range of 23-100º 
with scanning step of 0.02º. 
All diffraction peaks for as-grown nanocrystallite 
films can be attributed to cuprite (Cu2O) phase with 
cubic structure (space group: Pn-3m; a = 4.2685 Å). 
Rapid thermal annealing in air at 450 °C with fast 
temperature ramp rate resulted in formation of coexist-
ing cuprite and tenorite (CuO) phases of the deposition 
with monoclinic structure (space group: C2h6-C2/c; 
a=4.6837 Å, b=3.4226 Å, c=5.1288 Å, β=99.54 Å).  
 
3.3 Gas sensing studies 
 
In order to test the gas response and selectivity to 
H2 gas of Zn1-xAgxOy and Cu1-xZnxOy nanostructured 
films, the response to ethanol and CH4 have also been 
investigated. The gas response of the sensors is given 
by the resistance change of the sensor in dry air and 
the resistance in the test gas as reported before [2].   
There was observed no response to 100 ppm 
C2H5OH and CH4 for of Zn1-xAgxOy and Cu1-xZnxOy 
samples at OPT 300 ºC. In Fig. 3a is demonstrated gas 
 HYDROGEN GAS RESPONSE OF … PROC. NAP 3, 01NTF14 (2014) 
 
 
01NTF14-3 
response to 100 ppm H2 versus time for nanostructured 
Zn1-xAgxOy film RTA treated in air at 500 ºC and 
nanocrystallite Cu1-xZnxOy film treated RTA in furnace 
at 450 ºC. Resistance of Zn1-xAgxOy sample under H2 
gas exposition was decrease, so it can reach a 
maximum of 100% according to formula above, and 
demonstrate 85 % gas response, while resistance of 
Cu1-xZnxOy sample was increase and demonstrate 382 
% gas response.  
 
 
 
Fig. 3 – Gas response to 100 ppm H2 of the: (a) 
nanostructured Zn1-xAgxO film RTA treated in air at 500 ºC 
with 2.6 µm thickness and nanocrystallite Cu1-xZnxO film 
treated RTA in furnace at 450 ºC with 0.95 µm thickness 
versus time to 100 ppm H2 at OPT 300 ºC; (b) nanocrystallite 
Cu1-xZnxO film and (c) nanostructured Zn1-xAgxO film versus 
temperature of treatment type, RTA in air for Zn1-xAgxO 
samples after different regimes of RTA in furnace for samples, 
at operating temperature of 300 °C. 
Also were investigated response τr and recovery τf 
time (τ = |τ(90%) - τ(10%)|). From Fig. 3a it can be 
observed that τr for Zn1-xAgxOy (τr = 2.8 s) sample is 
smaller than for Cu1-xZnxOy (τr  = 7.8 s) sample, while 
τf for Cu1-xZnxOy (τf  = 6.1 s) sample is smaller than τr 
for the same sample and smaller than τf  for Zn1-
xAgxOy (τf = 11 s) sample. In Fig. 3b is presented 
dependence of gas response to H2 for Cu1-xZnxOy 
samples at different temperatures of RTA treatment 
in furnace, and can be observed that optimal 
temperature of treatment is 450 °C, while for Zn1-
xAgxOy samples (Fig. 3c) the optimal temperature of 
RTA treatment in air is 500 °C. 
 
4. CONCLUSIONS 
 
In summary, Zn1-xAgxOy nanostructured films and 
nanocrystallite Cu1-xZnxOy films with high crystallinity 
were grown on glass substrate using a chemical deposi-
tion method. SEM, EDX, and X-ray diffraction have 
been used to characterize the morphology, chemical 
composition and structure of the samples. XRD meas-
urements indicate that synthesized Zn1-xAgxO samples 
are in the hexagonal phase and from XRD pattern were 
observed deformation in lattice by incorporation of Ag 
atoms, that have a higher ionic radii. XRD measure-
ments of Cu1-xZnxO samples indicate that nanocrystal-
line films are synthesized in cuprite (Cu2O) phase with 
cubic structure, but RTA treatment in furnace results 
in formation of monoclinic structure of tenorite (CuO) 
phase in addition to cuprite phase. From 2.6 µm thick-
ness 1.3wt%Ag Zn1-xAgxO nanostructured films were 
fabricated faster sensors with 85 % gas response to 100 
ppm H2 and from 0.95 µm thickness 3wt% Zn nano-
crystallite Cu1-xZnxO films were fabricated rapid sen-
sors with 382 % gas response to 100 ppm H2 at operat-
ing temperature of 300 °C. 
 
AKNOWLEDGEMENTS 
 
The authors gratefully acknowledge collaboration 
with Prof. Chow from UCF, USA and financial support 
of the STCU and ASM through Grant 
09_STCU_A/5833. 
 
 
REFERENCES 
 
1. Y.H. Choi, D.H. Kim, S.H. Hong, K.S. Hong, Sensor. Actu-
at. B 178, 395 (2013). 
2. L. Chow, O. Lupan, G. Chai, H. Khallaf, L.O. Ono, 
B. Roldan Cuenya, I.M. Tiginyanu, V.V. Ursaki, V. Sontea, 
A. Schulte, Sensor. Actuat. A 189, 399 (2013). 
3. O. Lupan, L. Chow, L.K. Ono, B. Roldan Cuenya, G. Chai, 
H. Khallaf, S. Park, A. Schulte, J. Phys. Chem. C 114, 
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Hydrogen Gas Response of Zn1 – xAgxOy and Cu1 – xZnxOy Nanostructured Films

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