Subject Number : S-15-JI-0015
Support Type : Technical consultation
Proposal Title (English) : Characterization of Al doped TMW
Username (English) :A. Akrajas Ali Umar1) underline applicant’s name)
Affiliation (English) :1) Universiti Kebangsaan Malaysia

1. Summary
Thin film sample of doped metal oxide namely Aluminium doped TiO2 was synthesized using wet chemical deposition has been submitted for technical consultation in JAIST (approximately 20 hours for 8 samples). Al doped TiO2 nanoparticles with five different concentrations of Al sources were prepared here in Universiti Kebangsaan Malaysia (UKM) and were submitted to be characterized for X-ray Photoelectron Spectroscopy (XPS model Shimadzu Kratos Axis Ultra DLD). From the XPS characterization, it is shown that the presence of Al element only can be detected at Al precursor (A l(NO3)2.9H2O) concentration used at or more than 0.1M. Elemental analysis obtained from XPS characterization shows that the presence of Al doping increased with the increasing of Al dopant precursor.

2. Experimental
(Describe main facilities you used and your experimental method.)
The preparation of Al-doped TiO2 was performed using our previously reported method with slight modification done in OPEL Lab, Institute of Microengineering and Nanoelectronics, Universiti Kebangsaan Malaysia, Malaysia. By using liquid phase deposition method, 0.1 M Al (NO3)2.9H2O was added into an aqueous solution of Ti precursor (0.5 M (NH4)2TiF6) followed by 0.5 M Hexamethyltetramine. Briefly, in typical process, a clean ITO substrate (sheet resistance of 9-22 Ω per square) was immersed into the growth solution. Prior to a growth process, the solution was ultrasonicated for 2 minutes for a better mixing the solution. The mixed growth solution was kept undisturbed for 5h in a water bath at a temperature of 90 oC. In order to obtain Al-TNW with different Al3+ content, during the Al-TNW growth, five different concentrations of Al (NO3)2.9H2O was used, namely 0.05, 0.1, 0.15, 0.2 and 0.3 M respectively. Then samples were then taken out from the solution and rinsed with copious amount of pure water. To obtained anatase phase of TiO2, the samples prepared were then.
. Field Emission Scanning Electron Microscope (FESEM) characterization was carried out in Centre for Research and Management (CRIM), UKM to observe the morphology of the Al doped TiO2 prepared. XPS analysis was carried out in JAIST using the Bruker XPS apparatus XSAM-HS from KRATOS, UK equipped with monoenergetic X-ray Mg Ka (1253.6 eV) or Al Ka (1486.6 eV) irradiation and an Omni Focus III input lens to the analyser. Atomic concentration for the elements exists in Al doped TiO2 nanoparticles can be obtained by elemental analysis using XPS technique.

3. Results and Discussion
As reported in our work previously, typical microwall TiO2 (TMW) produced using liquid phase deposition method can be observed. Figure 1 shows a typical structure of Al doped TMW with growth solution containing 0.1 M where vertical-oriented and branched-nanowalls like structure was observed. At higher magnification, as can be observed in Figure 1 (B) and (C), these microwalls actually appear to be constructed by well-aligned small-nanocuboids as has been reported in our recent work. Due to the nature of these aligned nanocuboids, there also appears to be the presence of voids, making these microwalls formed highly porous. Thus, it is expected higher performance for potential application utilizing Al doped TMW such as catalytic and solar cells can be achieved due to the abundant and large surface area provided.
The mechanism for the Al doped TMW formation is predicted to follow typical oriented attachment process. However, due to the addition of Al elements in the growth reaction, the microwalls appears to be slightly different in shape compared to our previous reported results were at the edge of the TMW, a thin sheet-like structure can be observe with the length of 200 nm.

Figure 1: FESEM micrograph for Al doped TMW
Figure 2(A) shows the wide scan XPS analysis without carbon correction indicating the presence of Ti, O, and Al elements for most of the studied samples. Meanwhile, Figure 2(B) shows the fitted spectrum for Ti 2p with the presence of its two typical peaks namely Ti4+2p3/2 and Ti4+2p1/2. Both of these peaks observed at binding energy of 456 eV and 461.8 eV belongs in its designated oxidation state group region of Ti4+2p3/2 and Ti4+2p1/2.

Figure 2: Widescan spectra (A) and Ti2p BE (B) for Al doped TMW prepared at various Al (NO3)2.9H2O concentration.
It can be observed that both of these peaks however shift slight towards lower binding energy indicates the TMW formed is indeed are high in oxygen vacancy. It is due to the fact that this peculiar behavior was contributed by the presence of Al element in the samples.
The atomic concentration of three different elements namely, Ti, O and Al exists in Al doped TMW prepared at five different Al precursor concentrations (Al (NO3)2.9H2O) were determined using XPS analysis as shown in Table. As can be observed in Table 1, the presence of Al was undetected for low Al precursor concentration of 0.05 M and only can be detected when the number of precursor concentration used was doubled (0.1 M). It is expected as it is due to the nature of Ostwald ripening process, that Al element are at its lowest concentration ever and the TMW was mainly dominated by the Ti and O element. With the increase of the amount of Al precursor used for higher Al doping study, the Al element detected was higher while Ti element concentration decreased.

Table 1. Atomic concentration and binding energy (BE) position for Al doped TMW prepared at various Al (NO3)2.9H2O concentration.
Al (NO3)2.9H2O
Concentration (M) Atomic Concentration (%) BE
O 1s Ti 2p Al 2p Al 2p
0.05 75.13 24.87 0 84.7
0.1 68.13 29.9 1.97 70.2
0.15 66.41 29.8 0.15 70.8
0.2 66.43 28.53 0.2 71.2
0.3 67.32 15.62 0.3 71.4

The oxygen element shows a slight decreased when the Al concentration varies from 0.05 to 0.15. However, the oxygen concentration increased when Al concentration used was more than 0.2. It is suspected that at high concentration of Al (NO3)2.9H2O used in the growth solution, a phase change might occur. It can be seen from the slight shift of the BE position for Al 2p indicates that the formation of Al2O3 in the synthesis process replacing the growth of TMW. From these study, it can be conclude that Al doped TMW was successfully prepared. Further studies on the formation Al doped TMW and its application will be reported in upcoming research reports.

4. Others
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5. Publication/Presentation
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6. Patent
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