Block Copolymer Templated Fabrication of TiO2 Nanodot Films Using

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C: Physical Processes in Nanomaterials and Nanostructures

Block Co-Polymer Templated Fabrication of TiO2 Nanodot Films using Pulsed Laser Deposition Krishna Pandey, Kartik C. Ghosh, Uttam Manna, and Mahua Biswas J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b01605 • Publication Date (Web): 26 Jun 2018 Downloaded from http://pubs.acs.org on June 27, 2018

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The Journal of Physical Chemistry

Block Co-Polymer Templated Fabrication of TiO2 Nanodot Films using Pulsed Laser Deposition Krishna Pandey1, Kartik Ghosh1, Uttam Manna2, Mahua Biswas1,3,* 1

Department of Physics, Astronomy and Materials Science, Missouri State University, Springfield,

MO, USA 2

Department of Physics, Illinois State University, Normal, IL, USA

3

Department of Physics & Astronomy, Millikin University, Decatur, IL, USA

*

To whom correspondence should be addressed, [email protected]

ACS Paragon Plus Environment

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ABSTRACT: Block copolymer (BCP) templated inorganic material nanopatterning, often termed as BCP lithography has received significant attention in recent years due to its selfassembly property offering direct synthesis of nanostructures with different morphologies. In this paper, we report an approach combining BCP template and pulsed laser deposition (PLD) to synthesize TiO2 nanodots of sub-50 nm dimension. Our results show that the BCP templated TiO2 nanodots maintained the exact form of the top of PS cylindrical template in the growth process as seen from top view of scanning electron microscopy (SEM) images. X-ray photoelectron spectroscopy (XPS) confirms the presence of Ti and O, and X-ray diffraction (XRD) results show existence of both anatase and rutile TiO2 crystalline phase in the nanodot films. The photoluminescence(PL) spectrum for the fabricated TiO2 is dominated by a broad peak extending from visible to near infrared (NIR) that appears due to overlap of the characteristic peaks for TiO2 anatase (visible) and rutile phase (NIR). The formation of crystalline TiO2 nanodots can be explained by crystallization by particle attachment phenomena around the BCP cylindrical domains during annealing. Fabrication of nanostructured titania or any other materials in combination with PLD and BCP as template has not been explored so far with the exception of lead titanate (PbTiO3) nanostructures; hence our demonstrated approach could be extended to fabricate other inorganic nanostructures integrated with BCP lithography for optoelectronics, sensing, and catalysis applications.


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I. INTRODUCTION Low dimensional nanostructures have gained significant attention in recent years because of their unique optical, electrical, magnetic and chemical properties in advanced technological field.1 The properties of these structures usually depend on their shape, size, arrangements and overall material quality. There exists several bottom up nanofabrication approaches, such as various vapor deposition methods (e.g. atomic layer deposition (ALD), pulsed laser deposition (PLD) & chemical vapor deposition (CVD)), and chemical solution process to perform direct synthesis of nanostructures at the atomic or molecular level.2-5 Although nanostructures grown using these methods show good structural, electrical and optical properties, in practice, these methods are not yet self-sufficient enough to produce reproducible, well-ordered and large area patterns for devices. In particular, PLD is a well-known method for inorganic thin film6-7 or nanostructured thin film8-11 growth and usually needs some templates12-13 or other mean14 for aligned and ordered micro and nano structures fabrication. In nanofabrication research the use of self-assembled block copolymers (BCPs) has advanced remarkably well in a short-period of time to produce well-ordered and wide area patterns for direct synthesis of polymeric nanostructures or as mask and templates for inorganic nanostructures synthesis with dimension as low as sub-10 nm.15-17 BCPs can self-assemble into a range of morphologies like lamellar, cylindrical and spherical that make them suitable candidates for two and three dimensional lithographic processes as template;17-19 where subsequent deposition of inorganic materials in these nanostructured BCP films can lead to formation of inorganic nanostructures with the same morphology as that of the BCP template. By varying parameters like molecular ratio and volume fraction of BCP during synthesis, and with the help of other lithography tools the shape and size of nano-patterns can be tuned.16, 20


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In inorganic semiconductor research, titanium dioxide (TiO2) is considered as a highly promising semiconductor material for various applications because of its large band gap, high refractive index, high dielectric constant, and high surface-activity,21 which could be developed into applications such as photo catalysis, water splitting, solar cells, super capacitors and lithiumion batteries.22-24 In this regard, control over TiO2 nanostructure fabrication can lead to desired as well as improved optical and electrical properties.23, 25-26 Hence, highly ordered, and superior quality TiO2 materials are important criteria for the future optoelectronics and energy industry to thrive. In this article, we report an approach to fabricate aligned TiO2 nanodots of sub-50 nm dimension using BCP cylindrical nanostructures as template in spite of PLD being a thin film deposition technique. In this approach, the PLD at room temperature and in vacuum has been used as inorganic deposition method to fabricate the TiO2 nanodots. The PLD technique is wellknown for deposition of high quality TiO2 films (both amorphous and crystalline) with excellent adhesive strength6-7, 27; usually highly crystalline TiO2 films can be deposited using high temperature PLD deposition method.27 However, since combining self-assembled BCP template in inorganic nanostructure fabrication requires a low temperature (approximately 100 oC or less) inorganic deposition process to avoid polymer degradation, in this this work, we have used room temperature PLD method to deposit TiO2. We show that the fabricated TiO2 nanostructures replicate the shape of the PS cylinders as seen from top view scanning electron microscopy (SEM) and atomic force microscopy (AFM) images; even though a thin film deposition on entire substrate is expected from PLD. The nandots were further characterized by x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD) and photoluminescence (PL) spectroscopy to perform elemental and structural analysis.


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Other low temperature inorganic oxide deposition methods (such as ALD, sol gel, etc.) have been previously used in conjunction with BCP template to fabricate different TiO2 nanostructures28-29. PLD grown micro and nanostructures using polymers, such as polystyrene microsphere as template has been demonstrated in few works as well 12-13 30. However, to our knowledge, fabrication of nanostructured titanium or any other materials in combination with PLD and BCP as template has not be explored so far with the exception of lead titanate (PbTiO3) nanostructures30. Hence, our developed method of BCP templated PLD grown TiO2 nanodots will open up new avenues of fabrication of other PLD deposited inorganic materials in conjunction with BCP lithography.

II. EXPERIMENTAL METHODS The schematic diagram for the whole procedure to fabricate TiO2 nanodots using BCP lithography and PLD method is shown in Figure 1. The details are as follows. BCP nanostructures fabrication: Si wafers with thin layer of native oxide were used as substrates in this work. The substrates were cleaned to remove any organic residue on the native oxide layer using hydrogen peroxide (H2O2), ammonium hydroxide (NH4OH) and DI water (H2O) at 65 oC for 2.5 hrs. In this work, to achieve perpendicular orientation of the BCP domains, a brush layer was deposited on the cleaned Si substrate. The orientation of BCP nanostructures is determined by the surface energy of the substrate.31 Polystyrene-randomPolymethylmethacrylate (PS-r-PMMA) with total molecular weight 156000 and 55 mole% PS was used as brush layer; the grafted brush layer helps to achieve perpendicular orientation of the BCP domains. The brush layer was deposited on silicon substrate from 1 wt% toluene solution using a spin coater (Laurell Technology) with 2000 rpm speed for 40s. The layer was annealed at


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240 oC on a hot plate inside a nitrogen atmosphere glove box for 40 minutes to graft the random polymer on the substrate surface. The layer was then toluene rinsed to remove the unreacted polymer from the substrate resulting ~5 nm thickness brush layer. The BCP used in this study was Polystyrene-block-Polymethylmethacrylate (PS-b-PMMA) of molecular weight (Mn) 52000 kg/mole (PS) and 142000 kg/mole (PMMA). The BCP layer was deposited on the brush layer grafted substrate from 1 wt% toluene solution using a spin coater with 2500 rpm speed for 40s, resulting a film thickness of ~40nm. The samples, were then annealed in a furnace situated inside the glove box at 180 oC for 24 hrs to facilitate microphase separation of PS and PMMA domains; which formed PS cylinders in PMMA matrix for this polymer with the above mentioned experimental conditions. All the chemicals were purchased from Sigma Aldrich and the polymers were purchased from Polymer Source Inc. TiO2 Nanostructures deposition: For depositing ordered TiO2 nanostructures, first PMMA domain was etched selectively from the BCP nanostructured film. It is known that PMMA preferably etched compared to PS polymer during oxygen (O2) plasma etching.32 In this work, controlled O2 plasma etching with power 50 W and 400 mTorr pressure for 5 Sec was used to etch the PMMA domain selectively using a March plasma etcher. A commercial TiO2 target (Kurt J. Lesker) was used for the PLD deposition. At 2×10-5 mbar PLD chamber pressure a beam of nanosecond pulse laser using a 248 nm UV excimer laser was focused onto the target; the laser beam used in this work, with 1.2 J/cm2 energy density and 1mm diameter spot size was fallen on the TiO2 target and the evaporated plasma plume deposited on the surface of the PMMA etched BCP nanostructures sample placed at room temperature. The TiO2 target was fixed with an electric motor inside the PLD chamber to avoid the deposition of material only at particular spot on substrate. The distance between samples to target was 4.5 cm.


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The number of laser pulse shots used in this work were 6000, 9000 and 12000 with thickness measured on a bare Si substrate by profilometry (Dectak) were 34 nm, 58 nm and 78 nm, respectively. The PLD deposition conditions are summarized in Table 1. Following the deposition, the samples were annealed into a tube furnace (MTI corporation MTI 11000X) at 500 o

C for 7hrs in air; to remove any remaining polymers and to transform the amorphous TiO2 into

crystal. This high temperature annealing step also promotes the formation of TiO2 nanodots around the PS cylinders from the thin layer of TiO2. Characterizations: Field Emission Scanning Electron Microscope (FESEM-Quanta 200) was used to do the imaging of BCP and TiO2 nanostructures samples. The elemental analysis of the TiO2 nanostructure samples were done by XPS using Physical Electronics (PHI) VersaProbe station, and XPS spectra was analyzed by Multipak Data Reduction Software. Surface morphology of the nanodot films were investigated using an AFM (Bruker-Dimension Icon). The AFM was performed using 8 nm TESP Si tip in tapping mode. The AFM data were processed using Bruker NanoScope Analysis Suite 1.30 software. XRD measurements were done using a Bruker D8 Discover instrument operating at 40 kV and 40 mA. The XRD instrument with a characteristic X-ray source of Cu tube (Cu Kα, λ= 1.5406 Å) was used. The PL measurements were done with a Horiba Labram HR Raman-PL system using 325 nm He-Cd laser. III. RESULTS AND DISCUSSION The schematic diagram in Figure1 highlights the key procedure steps within dotted areas: (i) BCP nanostructures fabrication steps, (ii) BCP template formation, (iii) PLD deposition and annealing to obtain the TiO2 nanodot structures. The details of the procedure have been described in the Experimental Method. As mentioned earlier, the PS-b-PMMA deposited on the brush layer


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was annealed in an inert atmosphere to facilitate microphase separation of PS and PMMA domains; which forms a periodic arrangement of vertical PS cylindrical nanostructures in PMMA matrix. Figure 2 shows SEM images at different stages of fabrication. Figure 2 (a) shows the SEM image of the as grown microphase separated PS-b-PMMA without any further treatment for imaging. This microphase separated PS-b-PMMA samples were etched in a controlled manner by O2 plasma to remove PMMA selectively. Although it is expected that PMMA preferentially etches to PS, but there might be some residual PMMA and some of the PS polymer may get etched in the process due to the proximity of the etching rate for these two polymers. Figure 2 (b) shows the SEM image of the same sample shown in Figure 2 (a) after PMMA etching. The average cylinder diameter and the domain size (center to center cylinder distance) are ~ 43 nm and ~ 70 nm, respectively. The PMMA etched sample was used as the template for PLD deposition of TiO2 nanostructures at room temperature. Note that it is difficult to achieve well-ordered vertical PS cylinders due to narrow perpendicular window of PS forming cylinders compared to PMMA forming cylinders33, and higher molecular weight of the polymers (52K kg/mole (PS) and 142K kg/mole (PMMA)) used in our experiment34; hence the horizontal cylindrical defects are observed in our sample. The PLD deposition conditions are summarized in Table 1. The substrate was held at room temperature to avoid any degradation of polymer template; which leads to formation of amorphous TiO2 thin layer. The amorphous TiO2 deposited sample was then annealed at 500 oC for 7 hours in air to achieve dotted crystalline TiO2 as well as to etch the polymers in the same step. Figure 2 (c) shows the SEM image of the same sample used in Figures 2 (a) & (b) after PLD deposition and temperature annealing. Number of pulse shots used was 6000 for the sample shown here in Figure 2. The SEM images of samples fabricated using 6000 shots (another


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sample), 9000 shots and 12000 shots are shown in Figures S1 (a)-(c), respectively in the Supplementary Information (SI). The corresponding TiO2 thin film thickness deposited on bare Si for 6000, 9000 and 12000 shots were 34 nm, 58 nm and 78 nm, respectively (measured using Dectak profilometer). Figures S1 (a)-(c) show that number of deposition shots did not affect the morphology of the nanodot formation significantly0020up to 78 nm equivalent film thickness.

Figure 1. Schematic diagram of the TiO2 nanodots fabrication procedure using BCP template assisted PLD deposition method. The dotted boxes show the procedure steps: (i) BCP nanostructures fabrication steps, (ii) BCP template formation, (iii) PLD deposition and annealing to obtain the TiO2 nanodot structures. Figures 3 (a) and (d) show the SEM and AFM images of the TiO2 nanodots sample, respectively. The SEM image has been used to calculate the nanodot size and domain; the average diameter and domain size were determined to be ~38 nm and ~75 nm, respectively with Figures 3 (b) and (c) showing the corresponding histograms. From the low magnification image shown in Figure 3 (a) it is observed that, the nanodots are formed uniformly throughout the


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sample following almost same diameter and domain size of the PS template and it was reproducible for all the samples grown in this study. Figure 3 (d) shows the AFM topographical image of the same sample, and Figure 3 (e) is the 3D projection of image Figure 3 (d). The average height of the nanodots are ~10 nm, calculated from depth histogram of the topographical image (Figure 3 (d)) using Bruker NanoScope Analysis Suite 1.30 (plot not shown). Table 1. Pulsed Laser Deposition (PLD) method parameters used in this work PLD Deposition Parameters

Values

Chamber Pressure

2 ´ 10-5 mbar

Growth Temperature

22 oC

Laser Energy Density

1.2 J/cm2

Spot Size

1 mm dia

Sample-target distance Pulse shots used Laser Wavelength

45 mm 6000, 9000 &12000 248 nm

Figure 2: SEM images at different stage of fabrication of TiO2 Nanodots. (a) as-grown PS-bPMMA nanostructures after phase separation, (b) PS cylinders after selective PMMA etching from the casted BCP nanostructured film shown in (a), and (c) TiO2 only nanodots after PLD deposition and high temperature (500 oC) annealing.


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(a)

Counts

12

(b)

8 4 0 25

30

35

40

45

TiO2 nanodot diameter (nm)

50

15 12

Counts

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1 µm

6 3 0

100 nm

(d)

(c)

9

60

70

80

90

TiO2 nanodot domain (nm)

100

(e)

500 nm

Figure 3: (a) Low magnification SEM image of TiO2 nanodot sample after annealing. (b) and (c) are the histograms of the diameter and domain distance of the nanodots calculated from the SEM image shown in (a). (d) is the AFM topographical image of the same sample and (e) is the 3D projection of (d).

Figure 4: Elemental analysis of TiO2 nanodots using XPS spectrum. (a) XPS survey AlKα photoelectron spectrum. (b) High resolution XPS spectrum of Ti 2P peaks of TiO2; at 458.63 eV for Ti 2P3/2 and at 464.43 eV for Ti 2P1/2 spin orbital splitting photoelectrons35-37 (c) High resolution XPS spectrum of O 1s peaks; 529.8 eV and 531.8 eV peaks correspond to bulk oxide and hydroxyl (OH) species, respectively.38-39


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To confirm the deposition of TiO2, the elemental analysis was performed using XPS on the TiO2 nanodot film sample as shown in Figure 4. The survey spectrum (Figure 4 (a)) shows two intense peaks of Ti 2P and O 1S along with C 1S peak and Si 2P due to the presence of TiO2 nanodots, contaminated and probable residual C, and native SiO2 thin layer on Si substrate, respectively. The high resolution spectra of the Ti 2P peaks and O1S peaks are shown in Figure 4 (b) & (c). The Ti 2P1/2 and Ti 2P3/2 spin-orbital splitting photoelectrons are located at binding energies of 464.43 and 458.63 eV (Figure 4(b)), respectively, which are in good agreement with the peaks seen for TiO2 nanostructures.35-36, 38-41 The O 1S high resolution spectrum shows two distinct peaks at 529.8 and 531.8 eV binding energy, respectively (Figure 4(c)); these peaks named as O2- and OH, respectively are assigned due to bulk oxide and OH species as shown by others as well.35, 37, 39, 42 The peak positions and difference in eV between Ti 2P and O 1S is in good agreement with the literature of TiO2 XPS data. The O2- peak is due to both bulk oxygen from the TiO2 nanodots and the ultrathin SiO2 layer on the substrate, whereas the OH peak can be observed from any moisture contamination. The binding energy for the bulk O from SiO2 is at ~533 eV43-44 almost overlapping with the bulk O from TiO2. The Si 2P peak at 102.5 eV is due to the Si bonded to O.43-44 The C 1S peak at ~285 eV is usually seen in XPS survey spectrum due to adventitious carbon contamination of few nm thickness on the sample surface.45 In our sample the C 1S peak centered at ~284.8 eV is primarily due to the carbon contamination, considering all the polymers were expected to be etched out by 500oC 7hrs annealing. There might be some residual C related species even after the etching which is difficult to distinguish given the overlap of the binding energies of residual and contaminated C in the spectrum. XRD of the TiO2 nanodot sample was performed to investigate the structural properties of the material. As mentioned before, due to room temperature PLD deposition the as deposited


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TiO2 was amorphous in nature. However, after annealing at 500 oC for 7hrs the resultant TiO2 nanodots were expected to become crystalline. Figure 5 shows the XRD intensity- 2q plot for the TiO2 nanodot sample. The measurements were done using CuKα1 ( 1.5406Å) radiation on x-ray diffractometer. The intensity of TiO2 peaks were very low in comparison to the peak coming from Si substrate. To eliminate the Si peak, the sample was tilted 7.8o using c-rotation. The Bragg’s diffraction peaks observed at 27.44o, 44.97o, 54.77o and 56.77o correspond to TiO2 rutile phase with hkl plane of (110), (210), (211) and (220), respectively.46-48 The peak at Bragg’s angle 38.67o corresponds to TiO2 anatase (112) hkl plane.46 It is noted from the XRD data that, the rutile phase of TiO2 was observed dominantly at relatively low annealing temperature of 500 o

C compared to the usual high temperature required for stable rutile phase formation49. This can

be attributed to oxygen deficiency during PLD deposition, which was performed at room temperature under vacuum. Our observation is in agreement with previously obtained rutile phase for PLD grown TiO2 this film at relatively low annealing temperature.50 This rutile TiO2 nanodot formation at relatively low annealing temperature is expected to be attractive for optical applications.51-52 Finally, PL spectroscopy was performed to study the optical properties of the TiO2 nanodot films. The sample used for this study was the same sample shown in Figures 2 (c) and 5. As seen from Figure 6, the PL spectrum of the TiO2 sample is dominated by a broad peak extending from visible to near infrared (NIR) region (~1.5-2.6 eV), which can be explained by the presence of the characteristic peaks of TiO2 anatase phase in the visible region and TiO2 rutile phase in the NIR region, as reported extensively.47, 53-63 The broad PL spectrum of anatase TiO2 in the visible region is attributed to combination of different reasons such as self-trapped excitons, oxygen vacancies and defect sites, impurities or reduced metal ions, etc.55-60 The PL


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spectrum of rutile phase is somewhat difficult to interpret; however there are several reports attributing the NIR region broad peak to interstitial Ti3+ ions, trapped holes and free holes etc. in the rutile phase.47, 60-63 The lack of oxygen during PLD growth in the chamber can be identified as one of the reason in the exhibition of the broad peak seen in Figure 6 due to the formation of oxygen vacancies and Ti interstitials. In addition, this PL spectrum also confirms that the fabricated nanostructures are mixture of two TiO2 crystalline phases; which is in agreement with the XRD data.

Figure 5: XRD intensity- 2q plot of the TiO2 nanodot sample after annealing at 500 oC for 7 hrs. The nanodots exhibit mostly TiO2 rutile phase peaks and one TiO2 anatase phase peak.


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1000

800

Intensity (Arb. Unit)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


600

400

200

0 1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Photon Energy (eV)

Figure 6: Room temperature PL spectrum of TiO2 nanodot sample showing a broad peak in the visible and NIR region (~1.5-2.6 eV) of the spectrum. From the morphology evolution, and average diameter and domain size values of the TiO2 nanodots it is noted that, TiO2 nanodots took the form of the PS cylinder domain template even though one would expect the TiO2 to form porous (pore in the place of PS cylinder) film on the substrate. The TiO2 nanodot formation in our experiments can be explained as follows. The deposition of TiO2 plume produces uniform amorphous TiO2 nanoparticle film on the substrate. Subsequent annealing of the nanoparticle film produces crystallized TiO2 nanodots taking the exact form of the top of PS cylinders as found in our experiments. This growth mechanism of TiO2 crystal around the PS cylinder domain can be justified by crystallization by particle attachment (CPA) which is a phenomenon of crystal formation from particle building blocks.64-65 In case of TiO2 nanodot formation in this work we predict that, after few nanometers thickness of TiO2 nanoparticle deposition on the entire substrate (both PS and void PMMA part), the deposition amount of TiO2 particles increase on the PS cylinder part compared to the void PMMA domain due to the shadowing effect of adjacent cylinders13. During annealing the comparatively larger amount of TiO2 particles on PS cylinders act as template for the integration


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and crystallization of remaining TiO2 particles. However, the initial nucleation mechanism that starts the preferential crystallization is difficult to predict; the orientation may happen through crystallization first and recrystallization of particles around existing large crystallites66 or due to the Ostwald ripening mechanism where the nanoparticles assemble rapidly at elevated temperature.67-68 IV. CONCLUSIONS To conclude, we demonstrated fabrication of sub-50 nm TiO2 nanodots using BCP cylindrical template by deposition of TiO2 using room temperature PLD. We show that, even though PLD is a thin film deposition technique after crystallization the TiO2 nanostructures take exact shape of the BCP template. The XPS elemental analysis shows the presence of Ti and O element from the TiO2 nanodots. The presence of mixed TiO2 anatase and rutile crystalline phases was confirmed from the XRD 2q scan. In addition, PL spectrum showed a broad peak in the visible and NIR spectral region, which is usually observed for TiO2 anatase and rutile phases, respectively. Our results show that the TiO2 nanodots maintain the size and shape of the top of BCP cylinders after deposition and annealing, in other word maintaining the diameter and domain of the cylindrical template. The growth mechanism can be explained by the crystallization by particle attachment (CPA) of the nanodots from PLD deposited film on and around the BCP cylindrical domains during annealing. Apart from demonstrating the method of PLD grown TiO2 nanodot fabrication replicating BCP template, we also demonstrate the formation of stable TiO2 rutile phase at relatively low temperature, which will be very attractive for optical applications.51-52 The BCP templated PLD grown TiO2 nanodots fabrication procedure established here is expected to open up a new avenue for various inorganic nanostructures deposition method using BCP lithography.


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Supporting Information. Supporting information showing SEM images of TiO2 Nanodots fabricated using different PLD pulse shot numbers.

ACKNOWLEDGMENT The authors acknowledge the funding support from Missouri State University in the form of start-up funding. The authors would like to thank Rishi Patel of the Jordan Valley Innovation Center at MSU for performing the AFM imaging and measurements and Dr. Mourad Benamara of the Arkansas Nano & Bio Materials Characterization Facility, Fayetteville, Arkansas for performing the XPS measurement on our samples.


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TOC GRAPHICS


22

Page 23 of 29


Step (i) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Substrate

Spin Coating Brush layer deposition

Step (iii) Oxide nanostructur es

Spin BCP deposition Coating

Annealing

Step (ii)

Oxide deposition

Annealing ACS Paragon Plus Environment

BCP Self-assembly

PLD

Selective Etching of one domain

(a) 1 2 3 4 5 6 7 8 9 10 11 12 13 14

As grown PS-b-PMMA Nanostructures

500 nm

(b)

The Journal of Physical Chemistry PMMA


etched

500 nm

(c)

Page 24 of 29 TiO2 only nanostructures after polymer etching

500 nm

Page 25 of 29

The Journal 16of Physical Chemistry

(a) 1

Counts

(b)

8 4 0 25

30

35

40

45

TiO2 nanodot diameter (nm)

50

15 12

Counts

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39

12

1 µm

(c)

9 6 3 0

100 nm

60

70

80

90

TiO2 nanodot domain (nm)

(d)

100

(e)

500 nm



Page 26 of 29

4

4

1.2x10

800

600

O1S Peaks

400

Binding Energy (eV)

4

3

8.0x10

3

6.0x10

Si 2p

4.0x10

200

0

3

8.0x10

3

6.0x10

OH

3

3

4.0x10

0.0

2.0x10

2.0x10

0.0 1000

1.2x10

2-

O

(c)

1.0x10

3

C 1s

3

8.0x10

1200

4

Counts

4

1.6x10

Ti 2P Peaks

4

4

2.4x10

(b)

1.4x10

1.0x10

Counts

4

3.2x10

Ti 2p3

Survey Scan

Ti 2p1

O 1S

(a)

Ti 2p3

4

4.0x10

Ti 2P1

Counts

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

4

1.4x10

3

470

ACS465 Paragon 460 Plus Environment 455 450

Binding Energy (eV)

445

545

540

535

530

525

Binding Energy (eV)

520

Page 27 of 29


1200 (110)

TiO2 Anatase Phase TiO2 Rutile Phase

(210)

800

(211)

600

(220)

(112)

1000


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

400 200 0 20

30ACS Paragon 40 Plus Environment 50

2q (Degree)

60

70


Page 28 of 29

1000


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Room Temperature PL of TiO2 nanostructures

800

600

400

200

0 1.0

1.5

2.0

2.5

3.0


3.5

Photon Energy (eV)

4.0

4.5

PMMA etched PS

Page 29 of 29The Journal of Physical Chemistry cylinders PLD

Annealing

1 2 3 4 5 6 7 8

ACS Paragon Plus Environment TiO2 Nanodots

500 nm

Block Copolymer Templated Fabrication of TiO2 Nanodot Films Using

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