Browsing by Subject "Titanium dioxide"

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Open Access
97 percent light absorption in an ultrabroadband frequency range utilizing an ultrathin metal layer: randomly oriented, densely packed dielectric nanowires as an excellent light trapping scaffold
(Royal Society of Chemistry, 2017) Ghobadi, A.; Dereshgi, S. A.; Hajian, H.; Birant, G.; Butun, B.; Bek, A.; Özbay, Ekmel
In this paper, we propose a facile and large scale compatible design to obtain perfect ultrabroadband light absorption using metal-dielectric core-shell nanowires. The design consists of atomic layer deposited (ALD) Pt metal uniformly wrapped around hydrothermally grown titanium dioxide (TiO2) nanowires. It is found that the randomly oriented dense TiO2 nanowires can impose excellent light trapping properties where the existence of an ultrathin Pt layer (with a thickness of 10 nm) can absorb the light in an ultrabroadband frequency range with an amount near unity. Throughout this study, we first investigate the formation of resonant modes in the metallic nanowires. Our findings prove that a nanowire structure can support multiple longitudinal localized surface plasmons (LSPs) along its axis together with transverse resonance modes. Our investigations showed that the spectral position of these resonance peaks can be tuned with the length, radius, and orientation of the nanowire. Therefore, TiO2 random nanowires can contain all of these features simultaneously in which the superposition of responses for these different geometries leads to a flat perfect light absorption. The obtained results demonstrate that taking unique advantages of the ALD method, together with excellent light trapping of chemically synthesized nanowires, a perfect, bifacial, wide angle, and large scale compatible absorber can be made where an excellent performance is achieved while using less materials.
Open Access
An all-dielectric metasurface coupled with two-dimensional semiconductors for thermally tunable ultra-narrowband light absorption
(Springer, 2020) Buhara, Ebru; Ghobadi, Amir; Özbay, Ekmel
Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have attracted tremendous attention over the past decades. Due to their unique features such as high mobility and direct bandgap, they are suitable candidate for the optoelectronic devices. However, due to their ultrathin thickness, their optical absorption is quite weak, and therefore, a trapping scheme for strong light- matter interaction is essential to overcome this deficiency. To accomplish strong light absorption, loss-less dielectric-based metasurfaces with ideally no parasitic absorption are excellent choices. Herein, we report an ultra-narrowband thermally tunable all-dielectric metasurface coupled absorber with TMD monolayer. In this proposed structure, high absorption with ultra-narrow full-width-at-half-maximum (FWHM) is achieved. Different design configurations are studied to find the most suitable structure. In the optimized design, an absorptance as high as 0.85 with a FWHM of 3.1 nm is achieved. This structure also shows thermal sensitivity of 0.0096 nm/°C, without the use of any phase change material component. This architecture can be used as a 2D and highly efficient tunable single-color photodetector. The proposed dielectric metasurface can be adopted for other types of 2D and ultrathin semiconductor-based optoelectronics.
Open Access
Amyloid-like peptide nanofiber templated titania nanostructures as dye sensitized solar cell anodic materials
(Royal Society of Chemistry, 2013) Acar, H.; Garifullin, R.; Aygun, L. E.; Okyay, Ali Kemal; Güler, Mustafa O.
One-dimensional titania nanostructures can serve as a support for light absorbing molecules and result in an improvement in the short circuit current (Jsc) and open circuit voltage (Voc) as a nanostructured and high-surface-area material in dye-sensitized solar cells. Here, self-assembled amyloid-like peptide nanofibers were exploited as an organic template for the growth of one-dimensional titania nanostructures. Nanostructured titania layers were utilized as anodic materials in dye sensitized solar cells (DSSCs). The photovoltaic performance of the DSSC devices was assessed and an enhancement in the overall cell performance compared to unstructured titania was observed.
Open Access
Anatase TiO2 nanowires functionalized by organic sensitizers for solar cells: a screened Coulomb hybrid density functional study
(American Institute of Physics Inc., 2015) Ünal, H.; Gunceler, D.; Gülseren, O.; Ellialtıoğlu, S.; Mete, E.
The adsorption of two different organic molecules cyanidin glucoside (C21O11H20) and TA-St-CA on anatase (101) and (001) nanowires has been investigated using the standard and the range separated hybrid density functional theory calculations. The electronic structures and optical spectra of resulting dye-nanowire combined systems show distinct features for these types of photochromophores. The lowest unoccupied molecular orbital of the natural dye cyanidin glucoside is located below the conduction band of the semiconductor while, in the case of TA-St-CA, it resonates with the states inside the conduction band. The wide-bandgap anatase nanowires can be functionalized for solar cells through electron-hole generation and subsequent charge injection by these dye sensitizers. The intermolecular charge transfer character of Donor-π-Acceptor type dye TA-St-CA is substantially modified by its adsorption on TiO2 surfaces. Cyanidin glucoside exhibits relatively stronger anchoring on the nanowires through its hydroxyl groups. The atomic structures of dye-nanowire systems re-optimized with the inclusion of nonlinear solvation effects showed that the binding strengths of both dyes remain moderate even in ionic solutions.
Open Access
A baseball-bat-like CdTe/TiO2 nanorods-based heterojunction core–shell solar cell
(Elsevier, 2013) Karaagac, H.; Parlak, M.; Aygun, L. E.; Ghaffari, M.; Bıyıklı, Necmi; Okyay, Ali Kemal
Rutile TiO2 nanorods on fluorine-doped thin oxide glass substrates via the hydrothermal technique were synthesized and decorated with a sputtered CdTe layer to fabricate a core-shell type n-TiO2/p-CdTe solar cell. Absorbance spectrum verified the absorption contribution of both TiO2 and CdTe to the absorption process. The solar cell parameters, such as open circuit voltage, short circuit current density, fill factor and power conversion efficiency were found to be 0.34 V, 1.27 mA cm-2, 28% and 0.12%, respectively. .
Open Access
CdTe quantum dot-functionalized P25 titania composite with enhanced photocatalytic NO2 storage selectivity under UV and vis irradiation
(American Chemical Society, 2019) Balcı-Leinen, Merve; Dede, Didem; Khan, Münir Ullah; Çağlayan, Mustafa; Koçak, Yusuf; Demir, Hilmi Volkan; Özensoy, Emrah
Composite systems of P25 (titania) functionalized with thioglycolic acid (TGA)-capped CdTe colloidal quantum dots (QDs) were synthesized, structurally characterized, and photocatalytically tested in the photocatalytic NOx oxidation and storage during NO(g) + O2(g) reaction. Pure P25 yielded moderate-to-high NO conversion (31% in UV-A and 40% in visible (vis)) but exhibited extremely poor selectivity toward NOx storage in solid state (25% in UV-A and 35% in vis). Therefore, P25 could efficiently photooxidize NO(g) + O2(g) into NO2; however, it failed to store photogenerated NO2 and released toxic NO2(g) to the atmosphere. CdTe QD-functionalized P25 revealed a major boost in photocatalytic performance with respect to pure P25, where NO conversion reached 42% under UV-A and 43% under vis illumination, while the respective selectivity climbed up to 92 and 97%, rendering the CdTe/P25 composite system an efficient broad-band photocatalyst, which can harvest both UV-A and vis light efficiently and display a strong NOx abatement effect. Control experiments suggested that photocatalytic active sites responsible for the NO(g) + O2(g) photooxidation and formation of NO2 reside mostly on titania, while the main functions of the TGA capping agent and the CdTe QDs are associated with the photocatalytic conversion of the generated NO2 to the adsorbed NOx species, significantly boosting the selectivity toward solid-state NOx storage. Reuse experiments showed that photocatalytic performance of the CdTe/P25 system can be preserved to a reasonable extent with only a moderate decrease in the photocatalytic performance. Although some decrease in the photocatalytic activity was observed after aging, CdTe/P25 could still outperform P25 benchmark photocatalyst. Increasing CdTe QDs loading from the currently optimized minuscule concentrations could be a useful strategy to increase further the catalytic lifetime/stability of the CdTe/P25 system with only a minor penalty in catalytic activity.
Open Access
Comparative study of optically activated nanocomposites with photocatalytic TiO2 and ZnO nanoparticles for massive environmental decontamination
(S P I E - International Society for Optical Engineering, 2007) Tek, S.; Mutlugun, E.; Soganci, I. M.; Perkgoz, N. K.; Yucel, D.; Celiker, G.; Demir, Hilmi Volkan
Nanocomposites that incorporate TiO2 and ZnO nanoparticles separately in three-dimensional solgel matrices through full chemical integration are prepared to perform highly efficient photocatalytic activities for applications of environmental decontamination. Spectral responses of photocatalytic TiO2 and ZnO nanoparticles exposed to UV activation for self-cleaning process were obtained as also their optical relative spectral efficiency curves from 270 to 370 nm in the UV regime. Our investigations of the optimal conditions to increase their spectral photocatalytic efficiencies resulted in remarkably high levels of optical recovery and efficiency.
Open Access
Core-crown quantum nanoplatelets with favorable type-II heterojunctions boost charge separation and photocatalytic NO oxidation on TiO2
(Wiley, 2020-09) Ebrahimi, Elnaz; İrfan, Muhammad; Shabani, Farzan; Koçak, Yusuf; Karakurt, Bartu; Erdem, E.; Demir, Hilmi Volkan; Özensoy, Emrah
Functionalization of TiO2 (P25) with oleic acid‐capped CdSe(core)/CdSeTe(crown) quantum‐well nanoplatelets (NPL) yielded remarkable activity and selectivity toward nitrate formation in photocatalytic NOx oxidation and storage (PHONOS) under both ultraviolet (UV‐A) and visible (VIS) light irradiation. In the NPL/P25 photocatalytic system, photocatalytic active sites responsible for the NO(g) photo‐oxidation and NO2 formation reside mostly on titania, while the main function of the NPL is associated with the photocatalytic conversion of the generated NO2 into the adsorbed NO3− species, significantly boosting selectivity toward NOx storage. Photocatalytic improvement in NOx oxidation and storage upon NPL functionalization of titania can also be associated with enhanced electron‐hole separation due to a favorable Type‐II heterojunction formation and photo‐induced electron transfer from the CdSeTe crown to the CdSe core of the quantum well system, where the trapped electrons in the CdSe core can later be transferred to titania. Re‐usability of NPL/P25 system was also demonstrated upon prolonged use of the photocatalyst, where NPL/P25 catalyst surpassed P25 benchmark in all tests.
Open Access
Core-crown quantum-well nanoplatelet functionalized TIO2 for photocatalytic NOx abatement
(2020-07) Ebrahimi, Elnaz
Oleic acid capped core/crown CdSe/CdSeTe quantum-well nanoplatelets (NPL) were used in the surface functionalization of TiO2. Structural characterization of the synthesized photocatalytic architecture was carried out to shed light on its surface chemistry, electronic, and crystallographic structure. NPL/TiO2 composites were tested in NO photo-oxidation under ultraviolet-A (UVA) and visible (VIS) light, showing a remarkable activity in NOx abatement and high selectivity for nitrate storage as compared to standard benchmark TiO2 photocatalyst (i.e. P25). Improved photocatalytic behavior can be attributed to the decrease in the bandgap and enhanced photogenerated electron-hole pair separation as a result of the incorporation of CdSe/CdSeTe NPL onto TiO2. Stability of composites was also investigated in durability tests. Even though some decrease in photocatalytic activity and selectivity of NPL/TiO2 composites was observed, performance of the NPL/TiO2 composites was found to be significantly better than pure TiO2.
Open Access
Core/shell-structured, covalently bonded TiO2/poly(3,4-ethylenedioxythiophene) dispersions and their electrorheological response: The effect of anisotropy
(Royal Society of Chemistry, 2015) Erol, O.; Unal, H. I.
As a new electrorheological (ER) material, core/shell nanorods composed of a titania core and conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) shell were prepared via covalent bonding to achieve a thin polymer shell and make the interfacial interactions between the two components more impressive. The successful coating of PEDOT on the nanorod-TiO2 particles was confirmed by TEM analysis. The antisedimentation stability of the core/shell nanorod-TiO2/PEDOT particles was determined to be 100%. The ER properties of the materials were studied under controlled shear, oscillatory shear and creep tests. The dielectric spectra of the dispersions were obtained to further understand their ER responses and fitted with the Cole-Cole equation. The ER behavior of the dispersions was also observed using an optical microscope. The flow curves of these ER fluids were determined under various electric field strengths and their flow characteristics examined via a rheological equation using the Cho-Choi-Jhon (CCJ) model. In addition, the results were also compared with nanoparticle-TiO2/PEDOT. It was concluded that the conducting thin polymer shell and elongated structure of the hybrid material introduced a synergistic effect on the electric field induced polarizability and colloidal stability against sedimentation, which resulted in stronger ER activity, storage modulus and higher recovery after stress loadings when compared to nanoparticle-TiO2/PEDOT. © The Royal Society of Chemistry.
Open Access
Development of photoanodes for performance enhanced dye sensitized solar cells
(2015-08) Ulusoy, Türkan Gamze
With a raising demand for clean and renewable energy sources in recent decades, dye sensitized solar cell (DSSC), as an efficient and low-cost solar cell technology, have attracted considerable attention and several efforts have been directed for the optimization of all components of DSSCs including photoanode, sensitizer dye, hole transport layer and counter electrode. The objective of this thesis is to provide a better understanding on the function of photoanode in overall performance of DSSC device by highlighting problems and limitations and offering proper solutions to tackle these deficiencies. Based on this understanding, this thesis reports, fabrication, characterization and analysis of designed three different cells to boost device photovoltaic performance which includes: 1) angstrom thick ZnO-sheathed TiO2 nanowires as photoanodes, 2) multifunctional omnidirectional antireflective coating, 3) peptide nanofiber network templated ALD-grown TiO2 nanostructures as photoanodes in DSSC. Since photoanode-dye interface engineering is of utmost importance, the first of our proposals in this thesis relies on a systematic approach to understand the impact of atomic layer deposited (ALD) angstrom-thick ZnO sheath on hydrothermally grown TiO2 nanowires (NWs) core utilized as photoanodes in DSSC. The results show that this ultrathin layer will contribute at device efficiency enhancement almost three times via reducing recombination rate of injected electrons, enhancement in collection efficiency of electrons via reducing density of surface trap states without hampering injection efficiency and increased dye uptake on TiO2 nanowires’ surface which in turn leads to increased light absorption. On the other work, we also utilized multifunctional organically modified silica (ORMOSIL) as antireflection coating layer on DSSC to improve conversion efficiency of the device via reduction in the light reflection. ORMOSIL coated DSSC surfaces show a low-reflective omnidirectional response in a wide range of wavelengths (400-800 nm). At normal incidence (𝜃=0°), the short circuit current density (JSC) is improved to an amount of 23% as a result of ORMOSIL coating. In addition, JSC meets even higher amounts of enhancement where 84% increase is recorded at 𝜃=30°. Moreover, this coating exhibits superhydrophobicity representing a contact angle of 155º. Finally, we proposed and implemented, self-assembled peptide amphiphiles nanofiber 3D networks in order to obtain TiO2 nanotube structures as a template in DSSC. These self-assembled peptide amphiphiles are resistant to high temperature and more durable than other kinds of peptide amphiphiles. The advantage of this 3D fiber composed template is its high surface area and interconnected solid support providing an effective template for formation of TiO2 network using ALD. On the other hand, since ALD offers uniform and conformal coating of high aspect ratio features, it ensures an ideal thin film coating method on high surface area nano-template materials such as the peptide nanofiber templates proposed in this study.
Open Access
Digitally alloyed ZnO and TiO2 thin film thermistors by atomic layer deposition for uncooled microbolometer applications
(AVS Science and Technology Society, 2017) Tilkioğlu, Bilge T.; Bolat, Sami; Tanrıkulu, Mahmud Yusuf; Okyay, Ali Kemal
The authors demonstrate the digital alloying of ZnO and TiO2 via atomic layer deposition method to be utilized as the active material of uncooled microbolometers. Depositions are carried out at 200 °C. Crystallinity of the material is shown to be degraded with the increase of the Ti content in the grown film. A maximum temperature coefficient of resistance (TCR) of −5.96%/K is obtained with the films containing 12.2 at. % Ti, and the obtained TCR value is shown to be temperature insensitive in the 15-22 °C, thereby allowing a wide range of operation temperatures for the low cost microbolometers. © 2017 American Vacuum Society.
Open Access
Direct evidence for the instability and deactivation of mixed-oxide systems: influence of surface segregation and subsurface diffusion
(2011) Emmez, E.; Vovk, E. I.; Bukhtiyarov V. I.; Ozensoy, E.
In the current contribution, we provide a direct demonstration of the thermally induced surface structural transformations of an alkaline-earth oxide/transition metal oxide interface that is detrimental to the essential catalytic functionality of such mixed-oxide systems toward particular reactants. The BaOx/TiO2/Pt(111) surface was chosen as a model interfacial system where the enrichment of the surface elemental composition with Ti atoms and the facile diffusion of Ba atoms into the underlying TiO2 matrix within 523 873 K leads to the formation of perovskite type surface species (BaTiO3/Ba2TiO4/BaxTiyOz). At elevated temperatures (T > 973 K), excessive surface segregation of Ti atoms results in an exclusively TiO2/TiOx-terminated surface which is almost free of Ba species. Although the freshly prepared BaOx/TiO2/Pt(111) surface can strongly adsorb ubiquitous catalytic adsorbates such as NO2 and CO2, a thermally deactivated surface at T > 973 K practically loses all of its NO2/CO2 adsorption capacity due to the deficiency of surface BaOx domains.
Open Access
Enhanced photoresponse of conformal TiO2/Ag nanorod array-based Schottky photodiodes fabricated via successive glancing angle and atomic layer deposition
(AVS Science and Technology Society, 2015) Haider A.; Cansizoglu, H.; Cansizoglu, M. F.; Karabacak, T.; Okyay, Ali Kemal; Bıyıklı, Necmi
In this study, the authors demonstrate a proof of concept nanostructured photodiode fabrication method via successive glancing angle deposition (GLAD) and atomic layer deposition (ALD). The fabricated metal-semiconductor nanorod (NR) arrays offer enhanced photoresponse compared to conventional planar thin-film counterparts. Silver (Ag) metallic NR arrays were deposited on Ag-film/Si templates by utilizing GLAD. Subsequently, titanium dioxide (TiO2) was deposited conformally on Ag NRs via ALD. Scanning electron microscopy studies confirmed the successful formation of vertically aligned Ag NRs deposited via GLAD and conformal deposition of TiO2 on Ag NRs via ALD. Following the growth of TiO2 on Ag NRs, aluminum metallic top contacts were formed to complete the fabrication of NR-based Schottky photodiodes. Nanostructured devices exhibited a photo response enhancement factor of 1.49 × 102 under a reverse bias of 3 V. © 2014 American Vacuum Society.
Open Access
Facile Synthesis of Three-Dimensional Pt-TiO2Nano-networks: A Highly Active Catalyst for the Hydrolytic Dehydrogenation of Ammonia–Borane
(Wiley, 2016) Khalily, M. A.; Eren, H.; Akbayrak, S.; Susapto, H. H.; Bıyıklı, Necmi; Özkar, S.; Güler, Mustafa O.
Three‐dimensional (3D) porous metal and metal oxide nanostructures have received considerable interest because organization of inorganic materials into 3D nanomaterials holds extraordinary properties such as low density, high porosity, and high surface area. Supramolecular self‐assembled peptide nanostructures were exploited as an organic template for catalytic 3D Pt‐TiO2 nano‐network fabrication. A 3D peptide nanofiber aerogel was conformally coated with TiO2 by atomic layer deposition (ALD) with angstrom‐level thickness precision. The 3D peptide‐TiO2 nano‐network was further decorated with highly monodisperse Pt nanoparticles by using ozone‐assisted ALD. The 3D TiO2 nano‐network decorated with Pt nanoparticles shows superior catalytic activity in hydrolysis of ammonia–borane, generating three equivalents of H2.
Open Access
High-efficiency and low-loss gallium nitride dielectric metasurfaces for nanophotonics at visible wavelengths
(American Institute of Physics Inc., 2017) Emani, N. K.; Khaidarov, E.; Paniagua-Domínguez, R.; Fu, Y. H.; Valuckas, V.; Lu S.; Zhang X.; Tan S.T.; Demir, Hilmi Volkan; Kuznetsov, A. I.
The dielectric nanophotonics research community is currently exploring transparent material platforms (e.g., TiO2, Si3N4, and GaP) to realize compact high efficiency optical devices at visible wavelengths. Efficient visible-light operation is key to integrating atomic quantum systems for future quantum computing. Gallium nitride (GaN), a III-V semiconductor which is highly transparent at visible wavelengths, is a promising material choice for active, nonlinear, and quantum nanophotonic applications. Here, we present the design and experimental realization of high efficiency beam deflecting and polarization beam splitting metasurfaces consisting of GaN nanostructures etched on the GaN epitaxial substrate itself. We demonstrate a polarization insensitive beam deflecting metasurface with 64% and 90% absolute and relative efficiencies. Further, a polarization beam splitter with an extinction ratio of 8.6/1 (6.2/1) and a transmission of 73% (67%) for p-polarization (s-polarization) is implemented to demonstrate the broad functionality that can be realized on this platform. The metasurfaces in our work exhibit a broadband response in the blue wavelength range of 430-470 nm. This nanophotonic platform of GaN shows the way to off- and on-chip nonlinear and quantum photonic devices working efficiently at blue emission wavelengths common to many atomic quantum emitters such as Ca+ and Sr+ ions.
Open Access
Hybrid functional calculated optical and electronic structures of thin anatase TiO2 nanowires with organic dye adsorbates
(Elsevier, 2015) Ünal, H.; Gunceler, D.; Gülseren, O.; Ellialtioğlu, Ş.; Mete, E.
The electronic and optical properties of thin anatase TiO2 (1 0 1) and (0 0 1) nanowires have been investigated using the screened Coulomb hybrid density functional calculations. For the bare nanowires with sub-nanometer diameters, the calculated band gaps are larger relative to the bulk values due to size effects. The role of organic light harvesting sensitizers on the absorption characteristics of the anatase nanowires has been examined using the hybrid density functional method incorporating partial exact exchange with range separation. For the lowest lying excitations, directional charge redistribution of tetrahydroquinoline (C2-1) dye shows a remarkably different profile in comparison to a simple molecule which is chosen as the coumarin skeleton. The binding modes and the adsorption energies of C2-1 dye and coumarin core on the anatase nanowires have been studied including non-linear solvation effetcs. The calculated optical and electronic properties of the nanowires with these two different types of sensitizers have been interpreted in terms of their electron-hole generation, charge carrier injection and recombination characteristics.
Open Access
Hydrogenation of naphthalene and methylnaphthalene: modeling and spectroscopy
(Elsevier BV, 2002) Sayan, Ş.; Paul, J.
In situ infrared spectra of 1-methylnaphthalene (1-MeNapht)hydrogenation, over sulfided NiMo/Al2O3-TiO2 catalysts, were compared with theoretically derived properties of methylnaphthalene and its bicyclic products: MeDilin, MeTetralin, MeOctalin and MeDecalin, and with conversion data from literature. Comparisons were also made between the un-substituted and methyl-substituted two-rings, and between the 1- and 5-methyl isomers of 1,4-dihydronaphthalene (dilin) and 1,2,3,4-tetrahydronaphthalene (tetralin). IR spectra of MeNapht adsorption, on the sulfided catalyst, were matched with data for adsorption on the catalyst without sulfidation and the empty support. Surface bound MeNapht is observed below 250°C on all catalysts. MeNapht adsorption suppresses OH groups nondiscriminatory on the empty support and the metal loaded catalyst. We relate the results to previous data on the interaction between the supported metal sulfides and titanium modified aluminas. Calculated total energies, and experimentally derived heats of formation, pointed at decahydronaphthalene (decalin) as the dominant product of naphthalene hydrogenation, with tetralin as an abundant intermediate, and dilin and 1,2,3,4,5,6,7,8-octahydronaphthalene (octalin) as short lived transient stages. The spectroscopic modeling showed that the orbital fingerprints of the five bicyclic compounds were not distinctly different, nor more than marginally modified by methyl substitution or isomerization. The only significant difference came at the highest occupied orbital, where a high naphthalene density of states (DoS) overlapped with the valence bands of metal or metal sulfide catalysts. The vibrational bands for naphthalene, dilin, tetralin and octalin were well separated. Octalin and decalin, alone, have similar vibrational spectra. Upheaval of ring degeneracy for methyl-substituted two-ring structures broadened all infrared bands in a characteristic way.
Open Access
Multi-temperature zone droplet-based microreactor for increased temperature control in nanoparticle synthesis
(Wiley-VCH Verlag, 2014) Erdem, E. Y.; Cheng, J. C.; Doyle, F. M.; Pisano, A. P.
Microreactors are an emerging technology for the controlled synthesis of nanoparticles. The Multi-Temperature zone Microreactor (MTM) described in this work utilizes thermally isolated heated and cooled regions for the purpose of separating nucleation and growth processes as well as to provide a platform for a systematic study on the effect of reaction conditions on nanoparticle synthesis.
Open Access
Nanoscale selective area atomic layer deposition of TiO2 using e-beam patterned polymers
(Royal Society of Chemistry, 2016) Haider A.; Yilmaz, M.; Deminskyi, P.; Eren, H.; Bıyıklı, Necmi
Here, we report nano-patterning of TiO2via area selective atomic layer deposition (AS-ALD) using an e-beam patterned growth inhibition polymer. Poly(methylmethacrylate) (PMMA), polyvinylpyrrolidone (PVP), and octafluorocyclobutane (C4F8) were the polymeric materials studied where PMMA and PVP were deposited using spin coating and C4F8 was grown using inductively coupled plasma (ICP) polymerization. TiO2 was grown at 150 °C using tetrakis(dimethylamido) titanium (TDMAT) and H2O as titanium and oxygen precursors, respectively. Contact angle, scanning electron microscopy (SEM), spectroscopic ellipsometry, and X-ray photoelectron spectroscopy (XPS) measurements were performed to investigate the blocking/inhibition effectiveness of polymer layers for AS-ALD of TiO2. TiO2 was grown with different numbers of growth cycles (maximum = 1200 cycles) on PMMA, PVP, and C4F8 coated substrates, where PMMA revealed complete growth inhibition up to the maximum number of growth cycles. On the other hand, PVP was able to block TiO2 growth up to 300 growth cycles only, whereas C4F8 showed no TiO2-growth blocking capability. Finally, mm-, μm-, and nm-scale patterned selective deposition of TiO2 was demonstrated exploiting a PMMA masking layer that has been patterned using e-beam lithography. SEM, energy-dispersive X-ray spectroscopy (EDX) line scan, EDX elemental mapping, and XPS line scan measurements cumulatively confirmed the self-aligned deposition of TiO2 features. The results presented for the first time demonstrate the feasibility of achieving self-aligned TiO2 deposition via TDMAT/H2O precursor combination and e-beam patterned PMMA blocking layers with a complete inhibition for >50 nm-thick films.