REFRACTORY METAL OXIDES: FABRICATION OF NANOSTRUCTURES, PROPERTIES AND APPLICATIONS S.K. Lazarouk, D.A. Sasinovich BELARUSIAN STATE UNIVERSITY OF INFORMATICS AND RADIOELECTRONICS Outline: -- experimental setup, -- structural properties of refractory metal oxides, -- electro-optical properties of refractory metal oxides, -- possible applications.
Fabrication of refractory metal (Ti, W, Nb) oxide nanostructure Al/W Si magnetron deposition of Al/W nanocomposite film anodic oxide of Al/W nanocomposite film Si anodization of Al/W nanocomposite film porous WO 3 Schematical view of magnetron Al/W (Al/Ti, Al/Nb) co-sputtering process selective Al O etching 2 3 Si
Equipment for electrochemical anodization on semiconductor wafers
AFM studying of Al, Nb and Al/Nb magnetron sputtered films AFM images of Al, Nb and Al/Nb magnetron sputtered films
SEM studying of Al/Ti nanocomposite films SEM image (planar view) of Al/Ti cosputtering nanocomposite film SEM image (cross-section view) of Al/Ti co-sputtering nanocomposite film
SEM studying of Al/W nanocomposite films SEM image (planar view) of Al/W cosputtering nanocomposite film SEM image (cross-section view) of Al/W co-sputtering nanocomposite film
SEM studying of Al-refractory metal nanocomposite films after Al etching SEM image of Al/Ti nanocomposite films after Al etching SEM image of Al/Nb nanocomposite films after Al etching
SEM studying of Al/W nanocomposite films after Al etching SEM image (planar view) of Al/W nanocomposite films after Al etching SEM image (cross-section view) of Al/W nanocomposite films after Al etching
TEM studying of Al/W nanocomposite films after Al etching 50 nm TEM image (planar view) of Al/W nanocomposite films after Al etching TEM image (cross-section view) of Al/W nanocomposite films after Al etching
Auger analysis of Al/Nb nanocomposite films A. C. % 100 90 80 70 60 50 40 30 20 10 Al Nb O Si 0 0 10 20 30 40 Sputter time, min A. C. % 100 90 80 70 60 50 40 30 20 10 Al Nb O Si 0 0 5 10 15 20 Sputter time, min Auger profiles of Al/Nb nanocomposite films after magnetron deposition Auger profiles of Al/Nb nanocomposite films after Al etching
SEM and TEM studying of Al/Ti nanocomposite films after porous anodization process after anodization C D Cross-section view after selective alumina etching SEM images of planar view Planar view TEM images
SEM and TEM studying of Al/W films after porous anodization process 100 nm SEM image of cross-section view of Al/W films after porous anodization process TEM image of cross-section view of Al/W films after porous anodization process
Auger analysis of Al/Ti nanocomposite films Atomic concetration, % 100 90 80 70 60 50 40 30 20 Al Ti O Si Atomic concetration, % 100 90 80 70 60 50 40 30 20 Al Ti O Si Atomic concentration, % 100 90 80 70 60 50 40 30 20 Al Ti O Si 10 10 10 0 0 2 4 6 8 10 12 14 16 Sputter time, min 0 0 2 4 6 8 10 12 14 16 18 20 22 Sputter time, min 0 0 2 4 6 8 10 Sputter time, min Al/Ti nanocomposite film after magnetron sputtering process Al/Ti nanocomposite film after porous anodization process Al/Ti nanocomposite film after selective alumina etching
Parameters of porous oxides formed from Al/Ti composites Porosity, % 90 80 70 60 50 40 Porosity, % Surface area, m 2 /cm 3 450 400 350 300 250 200 150 100 50 Specific surface area, m 2 /cm 3 LC with vertical orientation 30 10 15 20 25 30 35 40 45 50 55 Concentration, at.% 0
Electro-optical properties of nanostructure titania Photovoltage, mkv 0,4 0,2 porous ТiO 2 with p = 40 % porous ТiO 2 with p = 60 % tubular TiO 2 Current density, mkа/сm 2 100 80 60 40 20 dark curve porous TiO 2 with p= 40% tubular TiO 2 porous TiO 2 with p=60% 0,0 2,5 3,0 3,5 4,0 Photon energy, ev 0-0,6-0,4-0,2 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 Voltage, V Photovoltage spectra of nanostructure titania films Current voltage characteristics of nanostructure titania films in an electrochemical cell with UV light (100mW/cm 2 )
Electro-optical properties of refractory metal oxides 0,4 Nb 2 O 5 WO 3 Photovoltage, mkv 0,2 0,0 2,5 3,0 3,5 4,0 Photon energy, ev Photovoltage spectra of refractory metal oxides
Applications of refractory metal oxides Electrochromic devices based on nanoporous titania 60 50 Diffuse reflectance, % 40 30 20 10 0 bleached (initial) state bleached state after colored state colored state at -1,5 V colored state after 1 hour storage without bias 500 600 700 Wavelength, nm Electrochromic cell in the bleached state Electrochromic cell in the colored state Diffuse reflectance spectra of reflective electrochromic cell in colored and bleached states at different biases
Applications of refractory metal oxides Photoelectrolysis cell for hydrogen generation Photoelectrolysis cell Pt cathode Porous WO 3 anode Hydrogen generation Aqueous solution Oxygen generation
Applications of refractory metal oxides Photovoltaic cell based on porous tungsten oxide 12 10 - dark - WO 3 /W - WO 3 /Si j, ma/cm 2 8 6 4 2 0 0,0 0,5 1,0 1,5 2,0 U, V TEM image of porous tungsten oxide on silicon Variation of current density vs. measured potential for WO 3 electrodes. The samples were measured under AM-1 illumination
Conclusion We have developed the technological approach for fabrication of porous refractory metal oxides with nanoscale and subnanoscale pores. Its advantage is anodization of the aluminum + refractory metal composite film in a fluorine-free electrolyte, providing formation of nanoporous refractory metal oxide films as thick as 5 µm with the specific surface up to 460 m 2 /cm 3. Porous oxides of refractory metals have interest due to their prospects for applications in water photolysis, solar cells, electrochromic displays and other electro-optical devices.