hydrogen sensor application of pd doped anodic tio 2 film
Post on 23-Jan-2016
61 Views
Preview:
DESCRIPTION
TRANSCRIPT
Hydrogen sensor application of Pd doped anodic TiO2 film
23. Aug. 2013
Jongyun Moon, Hannu-Pekka Hedman, Risto Punkkinen
Department of Information Technology
Workshop onWorkshop onAtomic-Scale Challenges in Advanced MaterialsAtomic-Scale Challenges in Advanced Materials
Defects in MaterialsDefects in MaterialsASCAM VIASCAM VI
23年 4月 21日
2
IntroductionIntroduction
Hydrogen sensor based on semiconductor
Semiconducting oxides that can be used for hydrogen detection SnO2, ZnO, TiO2, FeO, Fe2O3, NiO, Ga2O3, In2O3, MoO3 and WO3
Hydrogen is detected by the change of the electrical properties when the metal oxide are exposed to target gases.
Advantages:
High sensitivity, feasibility of miniaturization, low production cost Shortcoming:
low selectivity toward carbon monoxide, methane, alcohols, humidity etc. Decoration with catalytic materials can achieve improvements in selectivity
and sensitivity
23年 4月 21日
3
Hydrogen sensor using TiO2 thin film via anodization
23年 4月 21日
4
TiO2 has a large electric band gap of 3.0 eV.
Crystallized TiO2 nanostructures prepared by anodization has shown a remarkable hydrogen sensing performance (TiO2 nanotube arrays:to 1000 ppm H2 a resistance variation of 107).
O.K. Varghese, Mater. Res. Soc. Symp. Proc. 835 (2005)O.K. Varghese, Mater. Res. Soc. Symp. Proc. 835 (2005)
Low production cost due to an easy synthesis method Shortcoming:
Ti foil which underlines TiOTi foil which underlines TiO22 film, limit the usage of the material in various applications. film, limit the usage of the material in various applications.
i) metal electrode atop the oxide layer may diffuse into the Ti metal layer and cause i) metal electrode atop the oxide layer may diffuse into the Ti metal layer and cause an electrical short circuitan electrical short circuit
Ii) vulnerable to mechanical shock or vibrations.Ii) vulnerable to mechanical shock or vibrations.
Figure 1. Schematic of a gas sensor using TiOFigure 1. Schematic of a gas sensor using TiO22 nanotube arrays on Ti metal sheet nanotube arrays on Ti metal sheet
Research objective
Synthesis of TiO2 thin film on foreign substrate with metal electrodes
by using anodization → Reliable sensor structure.
Decoration of the sensor material with catalyric material (ex. Pd)
Improvement of gas sensor performance
→ Sensitivity, response/recovery time and selectivity to other gases
23年 4月 21日
5
Materials and MethodsMaterials and Methods
23年 4月 21日
6
Anodization of Ti on SiO2/Si wafer
Substrate: SiO2 (1 µm)/Si ( 2 cm × 2.5 cm)
Anode : Ti film (500 nm) by DC sputtering in argon (Ar) at a pressure of 0.02 mbar at
150°C
Cathode : Platinum sheet (99.98%)
Electric potential : 30 - 60 V
(Voltage ramping rage: 0.5 V/s)
Electrolyte : NH4F 0.25wt % in Ethylene Glycol
Anodization bath temperature : 5 °C
23年 4月 21日
7
Figure 2. An image of the anodization experiment instrumentFigure 2. An image of the anodization experiment instrument
Schematic of the sensor preparation
23年 4月 21日
8
Pt
Al
Au/Al metal electrode deposition by DC sputtering Heat treatment at 300 °C for 10 min
Ti film (500 nm) deposition by DC sputtering at 150°C
Anodization
Formation of Porous TiO2 film Pd thin film depostion
Heat treatment for crystallization at 500°C
Analysis
Material characteristics
i) Observation of current behavior during the andization
ii) FESEM (Field Emission Scanning Electron Microscope) analysis
iii) EDS (Energy-dispersive X-ray spectroscopy)
Gas sensor measurement
i) Sensor Temperature control: Heater plate (15 mm × 15 mm × 10 mm, Ultramic 600, Watlow)
ii) Measurement chamber: 56 l glass test chamber with continuous air circulation
iii) Desired volume of hydrogen was inserted to chamber.
* Concentration was verified by a commercial sensor (SX-917, Sensorex, Finland)
23年 4月 21日
9
23年 4月 21日
10
ResultsResults
Current plot during anodization
23年 4月 21日
11
Voltage increaseVoltage increase0-60V0-60V
Voltage: 60VVoltage: 60V
FESEM (Field Emission Scanning Electron Microscope)
23年 4月 21日
12
Thickness : ≈ 20nmThickness : ≈ 20nm
Diameter : ≈ 15-20 nmDiameter : ≈ 15-20 nm
FESEM image of TiOFESEM image of TiO22 layer prepared by anodization using 30V layer prepared by anodization using 30V
EDS (Energy-dispersive X-ray spectroscopy)
23年 4月 21日
13
Element Weight% Atomic%O K 29.56 69.16Ti K 29.38 22.96Pt M 41.06 7.88Totals 100.00
Element Weight% Atomic%O K 42.28 63.16Si K 22.82 19.42Ti K 34.90 17.42Totals 100.00
TiOTiO 22 area area
Metal Metal electrode electrode
areaarea
Gas sensor measurement
23年 4月 21日
14
Low concentration of H2 : 1 – 50 ppm
180°C180°C
160°C160°C
140°C140°C
Sensor response
23年 4月 21日
15
Y (Trend line equation) = 1.3219xY (Trend line equation) = 1.3219x0.89140.8914
R² (correlation coefficient) = 0.9652
Operating temperature: 160Operating temperature: 160°C°C
Conclusion
Porous TiO2 film with Pd thin film was synthesized on SiO2/Si
substrate with metal electrodes without loss of Ti/TiO2 layer
Its morphology modification is feasible by the control of the
anodization experimental parameters, such as the voltage.
The formation of TiO2 nanostructure can be interpreted by
monitoring the anodic current variation
The sensor exhibited a three order magnitude drop in resistance on
exposing to 10,000 ppm hydrogen gas at 160°C
23年 4月 21日
16
Future work
Since the study is still ongoing, more material characteristics are
required.
Selectivity measurement to various gases
Modification of the nanostructure to improve sensor’s performance
Material decoration using various doping methods
Miniaturization for the mass production
Integration of the sensor into a practical electric device
23年 4月 21日
17
23年 4月 21日
18
Thank you for your attentionThank you for your attention
top related