Article pubs.acs.org/JPCC
Nano- and Submicrometer-Sized Spherical Particle Fabrication Using a Submicroscopic Droplet Formed Using Selective Laser Heating Yoshie Ishikawa,*,† Naoto Koshizaki,‡ Alexander Pyatenko,† Noriyuki Saitoh,§ Noriko Yoshizawa,∥ and Yoshiki Shimizu† †
Nanomaterials Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan ‡ Graduate School of Engineering, Hokkaido University, Kita13 Nishi8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan § Electron Miroscope Facility, TIA and ∥Research Institute of Energy Frontier, National Institute of Advanced Industrial Science and Technology (AIST), 16-1 Onogawa, Tsukuba, Ibaraki 305-8569, Japan S Supporting Information *
ABSTRACT: Detailed characterization of products by pulsed laser melting in liquid was performed for TiO2 particles obtained at different laser fluences. The size, crystal structure, and inner structure of obtained spherical particles depended on the irradiating laser fluence. Single crystalline submicrometer spherical TiO2 particles of 200 nm were obtained using nanosecond pulsed laser irradiation at 100 mJ cm−2 pulse−1 onto raw particles dispersed in ethanol using cross-sectional high-resolution transmission electron microscopy observation. At higher laser fluence (e.g., 225 mJ cm−2 pulse−1), large submicrometer spheres with strain and twin structures 500 nm in diameter and nanometer spheres of 70 nm were simultaneously observed. The formation of such bimodal size distribution of obtained particles was explained based on the phase transition fluence curves deduced by Mie theory and the optical absorption increase induced by the formation of nonstoichiometric TiO2 particles. Thus, with the appropriate laser fluence, this laser process can produce single crystalline submicrometer spherical particles and nanometer spheres via cooling of droplets formed by a selective laser heating by optical absorption.
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INTRODUCTION Nanoparticle fabrication in the liquid phase using a high-power pulsed laser has been widely studied in the past few decades because of its convenience and interesting particle formation mechanism known as pulsed laser ablation in liquid (PLAL).1−5 This technique is based on explosive ejection of atoms, molecules, ions, radicals, and clusters using high fluence laser light absorption of target material immersed in liquid.4,6 The obtained material is nanoparticles that are smaller than the target materials. In contrast, we found the formation of submicrometer spherical particles using relatively low fluence laser irradiation on raw particles dispersed in liquid. These irradiated particles were melted and fused, resulting in a submicrometer spherical particle formation via cooling.7−10 Our group’s first report on this process focused on submicrometer spherical B4C particle formation from B raw nanoparticles irradiated in organic solvent.7 Wang et al. later applied this technique to various materials (e.g., ZnO, TiO2, and CuO).8−10 In these reports, the spherical particle formation mechanism was solely discussed based on submicrometer-sized spherical particles collected by an overnight natural sedimentation. Tsuji also reported on the fabrication of size-controlled Au spheres using this technique.11,12 With this process, raw particles with adequate optical absorption can immediately be changed to droplets by © XXXX American Chemical Society
absorbing energy supplied by a single laser pulse, whereas the temperature of the dispersion medium hardly increases, due to optical transparency. The melt droplet formed using laser irradiation is quickly quenched by the surrounding dispersion medium without changing the spherical shape of the droplet. The droplet also merges with neighboring droplets during repetitive laser-pulse irradiation, resulting in larger spherical particle formation than that of the raw primary particle.8,13,14 We refer to this process as pulsed laser melting in liquid (PLML). In addition, Pyatenko physicochemically constructed a submicrometer spherical particle formation mechanism using a heating−melting−evaporation model by interaction of target material and laser beam based on Mie theory.15,16 This proposed mechanism agrees rather well with experiment results of the submicrometer sphere formation. Submicrometer materials have promising optical functions because their size is comparable to the visible-light wavelengths.17−22 A self-assembled array of submicrometer spherical particles has been studied for facile fabrication of a device with submicrometer ordered structure.21−24 Commercially available spherical particles with narrow size distribution (e.g., Received: November 1, 2015 Revised: December 21, 2015
A
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using a centrifuge (at 15 000g for 60 min) to observe the fine structure using a field emission scanning electron microscope (SEM; Hitachi S4800). More than 200 spherical particles in SEM images were measured for particle size distribution analysis. The obtained particles were also embedded in epoxy resin and then thinned by mechanical polishing and ion milling to observe a particle inside using a high-resolution transmission electron microscope (HRTEM; FEI Tecnai Osiris) operated at 200 kV. In a cross-sectional observation, selected area electron diffraction (SAED) analysis and dark-field observation were carried out in parallel with an ordinary bright-field observation to evaluate the crystallinity of the inside, particularly single crystalline or not.
polystyrene and silica glass) typically used in these studies are usually amorphous.22,24,25 Ordered-structure devices constructed using crystalline spheres are expected to have useful intrinsic functions derived from the constituent crystalline material. Many reports focus on TiO2 inverse opal structures made from polystyrene spheres as a mold due to the high refractive index and semiconductor properties of TiO2.26 Selfassembled structures using TiO2 spheres with a narrow size distribution are also attractive.27 In both cases, postannealing is necessary for TiO2 crystallization, resulting in a thermally deformed submicrometer-ordered structure composed of a nanoporous matrix with nano-TiO2 crystals.27 Spherical particles with ideal optical properties (i.e., single-crystal spherical particles) are preferable, especially for optical devices.27 There are two essentials for crystalline submicrometer spherical particle formation in PLML: (1) spontaneously determined spherical shape of a droplet by surface tension at the interface between the droplet and suspension medium and (2) crystallization of the spherical droplet in suspension medium from undercooling. Thus, we can obtain a highly pure product with a spherical shape without mold material. Obtained spherical particles have a uniformly dense inner structure, which is evidently different from that of porous particles prepared by chemical reaction (e.g., sol−gel process)27−29 followed by post heat treatment for crystallization. Fujiwara and Nakamura constructed a novel random lasing device using highly dense crystalline submicrometer spherical particles fabricated using PLML.30−32 In this study, we comprehensively discussed details of the PLML spherical particle formation mechanism based on newly and strictly obtained experimental results for TiO2, which is a prospective material for optical devices due to its high refractive index (2.5) and wide application.33−35 Submicrometer spherical TiO2 particle fabrication using PLML has been reported in ref 8, which only focuses on submicrometer particles collected by overnight natural sedimentation. In this study, however, we newly found considerable simultaneous nanometer spherical particle formation along with submicrometer sphere formation by rigorously collected particles by a centrifugation. Furthermore, we characterize fluence-dependent products, focusing on the inner crystalline structures of particles by direct crosssectional HRTEM observation and an X-ray powder diffraction analysis. We also correlate spherical single-crystal TiO2 particle formation with the fluence condition and particle size.
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RESULTS AND DISCUSSION SEM images of raw TiO2 particles and particles obtained using laser irradiation at 133 mJ cm−2 pulse−1 are presented in Figures 1(a) and (b). Aggregates of primary 20 nm diameter
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Figure 1. SEM images of TiO2 particles. (a) Raw particles. (b) Particles obtained by irradiation at 133 mJ cm−2 pulse−1.
EXPERIMENTAL SECTION In this study, a TiO2 suspension was irradiated with an unfocused laser beam. Reagent-grade anatase TiO2 powder (Sigma-Aldrich Co., LLC) was dispersed in ethanol (99.5%, Wako Pure Chemical Industries, Ltd.). Next, 6 mL of the suspension in a glass vessel with a TiO2 concentration of 0.04 mg/mL was irradiated at various fluences using the third harmonic (355 nm) of a Nd:YAG laser (Spectra Physics Lab150−30) operated at 30 Hz with a pulse width of 7 ns for 10 min. The suspension was agitated using a magnetic stirrer during laser irradiation. The irradiated suspension was dropped onto a Si substrate and dried in air for X-ray powder diffraction analysis (XRD; Rigaku Ultima with Cu Kα radiation) of obtained particles. Particles were rinsed with 0.1 M HCl aqueous solution after laser irradiation to dissolve the byproduct titanium hydrate, followed by repetitive washing of particles with deionized water
particles with a variety of shapes were observed in raw TiO2 particles. The temperature of the particles instantaneously increases with laser irradiation, due to laser energy absorption by photoexcitation and subsequent energy transfer from electrons to phonons during nanosecond pulse duration. Particles irradiated with the appropriate fluence are melted and fused, resulting in submicrometer spherical particle formation via cooling (Figure 1(b)). Details of submicrometer sphere formation were reported and discussed in our previous papers.7,8,13 Uniform contrast within these particles observed by TEM suggested homogeneous internal structure. XRD patterns obtained using laser irradiation at various fluences are depicted in Figure 2. Raw anatase TiO2 particles were changed to high-temperature stable rutile structure by laser irradiation. Both anatase and rutile structures formed at B
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of submicrometer spherical particles, but a few nonspherical large particles are also observed. TEM observation (not shown here) indicated that most particles fixed on a microgrid by drying suspension were not porous but had a uniform structure, and few hollow particles reported for those obtained by laser irradiation in acetone were observed.8 Because raw TiO2 nanoparticles dispersed in acetone were strongly agglomerated, the acetone will permeate an interspace between TiO2 nanoparticles and compress the air remaining in the agglomerates. The compressed air was maintained in the agglomerates even during melting and solidification, resulting in hollow sphere formation.8 In contrast, TiO2 nanoparticles in ethanol agglomerate by weaker interaction than those in acetone more significantly allowing interspace permeation of ethanol without incorporating the air because of a good dispersibility in ethanol due to the larger polarity of the ethanol molecule than that of acetone. The laser irradiation onto agglomerated particles in ethanol brought solid sphere formation. Figure 3(b) depicts a TEM image of a cross section obtained by slicing a typical spherical particle. The selected area electron diffraction pattern (SAED) (Figure 3(b), top right) indicates the [110] zone axis of rutile structure. In a dark-field image derived from the (−110) reflection of the rutile structure (Figure 3(b), bottom right), the sphere image illuminates through the entire sphere, suggesting that the spherical particle consists of a single crystal. In a previous report, we speculated that the as-prepared spherical particle obtained by PLML was a single crystal, based on the coincidence of crystalline direction at several surface points in the TEM image. However, we have directly confirmed a single crystal by cross-sectional observation of particles. Spherical single-crystal particles similar to the particle depicted in Figure 3(b) were frequently observed.
Figure 2. XRD patterns of particles obtained by laser irradiation at various laser fluences.
100 mJ cm−2 pulse−1 irradiation. Anatase peaks were not observed with irradiation at 133 mJ cm−2 pulse−1 and higher fluences, and only rutile peaks were observed. A small broad peak at 28.3° indicated by a pink band was identified as Ti8O15 for particles formed by a 175 mJ cm−2 pulse−1.36 This broad peak became prominent and shifted to a higher angle with increasing laser fluence, indicating the formation of lower oxidation state components (Ti7O13 and Ti6O11). Peaks at 41.3° and 54.4° shifted to a lower angle with increased laser fluence, and a broad peak at 56.0° marked by a pink band appeared above 175 mJ cm−2 pulse−1. These changes are also due to lower oxidation state components.36 Irradiation at Relatively Low Laser Fluence. A typical SEM image of particles irradiated at 100 mJ cm−2 pulse−1 is presented in Figure 3(a). The obtained particles consist mostly
Figure 3. Particles obtained by laser irradiation at 100 mJ cm−2 pulse−1. (a) SEM image. (b) Cross-sectional TEM image of a typically obtained spherical particle. Top-right inset is the selected area diffraction pattern; bottom-right inset is a dark-field image of the sphere by rutile (−110) reflection. (c) TEM image of a cross section of a distorted particle. (d) TEM image of a cross section of polycrystalline particles containing anatase grain, circled with a dashed line, and the selected area electron diffraction pattern. C
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The Journal of Physical Chemistry C A TEM image of a cross section of a distorted large particle is presented in Figure 3(c). This large particle has a partially smooth rutile surface, and inside nanoparticles are identified as anatase TiO2 using SAED analysis. Such distorted particles were still observed even after a longer irradiation time (30 min), indicating that distorted particle formation is not due to an insufficient number of laser pulse irradiations (Figure S1). In contrast, these distorted particles were less frequently observed with increasing laser fluence. The laser fluence at 100 mJ cm−2 pulse−1 was insufficient to melt the inside of these large aggregates completely. Only the surface of the aggregate melted, resulting in a smooth surface and internal nonmelted raw anatase particles. Some submicrometer spherical particles consisted of polycrystalline structures that contained anatase grains (denoted by a dashed circle in Figure 3(d)) identified by a SAED pattern, which were larger than raw anatase particles. The large anatase grain indicates anatase crystal growth by sintering caused by laser heating, rather than by melting with relatively low laser fluence irradiation. The sintered anatase grain is consistent with the XRD anatase peak narrowing at 100 mJ cm−2 pulse−1, compared with raw anatase particles (Figure 2). Irradiation at Relatively High Laser Fluence. The obtained spherical particle size depends on irradiation fluence. Figure 4 presents an SEM image of particles obtained by laser
Figure 4. SEM images of TiO2 particles obtained by irradiation at 300 mJ cm−2 pulse−1.
Figure 5. Spherical particle size distributions obtained at (a) 66 mJ cm−2 pulse−1, (b) 110 mJ cm−2 pulse−1, and (c) 200 mJ cm−2 pulse−1.
irradiation at 300 mJ cm−2 pulse−1. From the difference between Figures 1(b) and 4, the size of the obtained submicrometer spherical particles increased with increasing laser fluence, whereas nanometer spherical particles were also observed at higher fluence. Figure 5 plots size distributions of spherical particles obtained at various laser fluences between 66 and 200 mJ cm−2 pulse−1. With increased laser fluence, the peak size for submicrometer spheres became larger, and the frequency of the nanosized particles increased. Thus, the size distribution widened and became bimodal at higher laser fluence. No 200 nm particles were observed in particles irradiated at 200 mJ cm−2 pulse−1 (Figure 5(c)). Figure S2 also plots a size distribution of spherical particles irradiated at 300 mJ cm−2 pulse−1 obtained from Figure 4. Further increase in fluence brought that the frequency of nanometer spherical particles was dominant, although the mass of the submicrometer spherical particles was still larger than that of the nanometer spherical particles. Further widened absence of particles from 120 to 300 nm in size was observed at 300 mJ cm−2 pulse−1, indicating the bimodal size distribution became prominent with laser fluence increase.
Given the absorbed laser energy by a particle is spent to increase particle temperature, laser fluence for the start of particle melting, complete particle melting, and particle evaporation start are defined in the following equations. Jσabs(d) = mp
∫T
Tm
cps(T )dT = mp(HTm − H0)
0
∫T
Jσabs(d) = mp⌊
Tm
(1)
cps(T )dT + ΔHm ⌋
0
= mp[(HTm − H0) + ΔHm]
∫T
Jσabs(d) = mp⌊
Tm
cps(T )dT + ΔHm +
0
(2)
∫T
Tb
cpl (T )dT ⌋
m
= mp[(HTm − H0) + ΔHm + (HTb − HTm)] (3) −2
−1
Here, J (J cm pulse ) is the laser fluence for such phase transition; σabs(d) (cm2) is the particle absorption cross section; D
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The Journal of Physical Chemistry C mp (g) is the particle mass; csp and clp (J g−1 K−1) are the particle heat capacities in solid and liquid states; T0 (K) is the initial temperature of the particle; Tm (K) is the melting temperature; Tb (K) is the boiling temperature; and ΔHm (J g−1) is the enthalpy of melting. According to Mie theory, particle-absorption efficiency Qλabs(d) depends on wavelength and particle size and is defined in eq 4. Characteristics of Qλabs(d) dependency on particle size can be calculated from Mie theory at a specific wavelength.15,16 λ Q abs (d ) =
λ 4σabs (d )
πd 2
(4)
mp is then transformed to eq 5 using particle density ρp (g cm−3).
mp = ρp
πd 3 6
(5)
Terms in the brackets consists of only enthalpy in eqs 1, 2, and 3 are translated to ΔH̃ . Laser fluence for phase transition is calculated in eq 6. J=
mpΔH̃ λ (d ) σabs
=
2 d ρp ΔH̃ λ 3 Q abs(d)
(6)
Thus, laser fluence for phase transition depends on particle size. Absorption efficiency Qλabs(d) and laser fluences for phase transition as functions of TiO2 particle size at a wavelength of 355 nm for melting start, melting completion, and evaporation start are depicted in Figures 6(a) and (b). Expected phases are also indicated between these curves as S for solid, L for liquid, and G for gas. All fluence curves for phase transition have minimal fluence at 200 nm particle diameter (Figure 6(b)). Mild increases of fluence curves for these phase transitions over 300 nm with a particle diameter increase are almost linear functions of d according to eq 6, due to nearly constant particleabsorption efficiency Qλabs(d) (Figure 6(a)) in this particle size region. In contrast, the drastic increase of these phase transition curves under 100 nm particle size with a particle diameter decrease is attributed to a radical decrease in Qλabs(d) with a particle diameter decrease in the same particle size region. The crossbars in Figure 6(b) denote particle size ranges experimentally obtained at various fluences, where frequency exceeded 10% of the main peaks in the size distribution curves in Figure 5. The region between the melting start curve and the evaporation start curve corresponds to spherical particle formation by melting, as previously reported for other materials.7−11,13,14 However, spherical particle formation practically occurred at fluences below the calculated value for melting start. This gap was possibly caused by TiO2 optical property change by laser irradiation from that of raw particles due to a laser-induced defect formation. TiO2 particles tended to become bluish with laser irradiation even for one or two seconds, indicating oxygen vacancy generation in TiO2. Absorbance of the TiO2 suspension at 355 nm wavelength changed from 0.86 to 1.5 with laser irradiation at 100 mJ cm−2 pulse−1 for 3 min. Thus, the absorbance increase by laser irradiation of TiO2 contributed to lowering the laser fluence required for particle melting. Figure 6(c) depicts phasetransition curves considering the experiment absorbance change obtained by laser irradiation. The black crossbars indicating the size distribution of particles obtained by laser irradiation at 110 and 200 mJ cm−2 pulse−1 are located almost
Figure 6. (a) Absorption efficiency Qλabs(d), (b) laser fluence J for phase transition as a function of TiO2 particle size at 355 nm wavelength obtained by Mie calculation, and (c) laser fluence J for phase transition considering experiment absorbance change of TiO2 by laser irradiation. Particle size ranges obtained experimentally at various fluences, those counted over 10% of size distribution frequency peaks in Figure 5, are also depicted in (b) and (c) as black crossbars. The purple crossbar in (c) indicates a particle size range over 10% of size distribution frequency peaks in Figure 7(b).
between phase transition curves, indicating melting start and evaporation start. In contrast, submicrometer particles were obtained by irradiation at 66 mJ cm−2 pulse−1, whereas the crossbar was located slightly under the curve indicating melting start. This particle growth will be due to particle sintering, as depicted in Figure 3(d). Submicrometer sphere size increased with particle fusion with neighboring particles in suspension induced by repetitive pulsed laser irradiation; however, particle size stopped increasing at a certain size due to an increase in required heat quantity for complete melting of a particle in proportion to the cube of d. Thus, the obtained submicrometer spherical particle size increased with increasing laser fluence. Similar size increases of submicrometer spheres were previously reported for various materials.8,9,13 According to Figure 6(c), 100−500 nm particles can be completely melted by laser irradiation at a fluence of 0.1 J cm−2 pulse−1. In contrast, at fluences above 0.2 J cm−2 pulse−1, the curve for evaporation start appears at an intermediate particle size range of 200 nm. Particles with 200 nm diameter irradiated at this fluence start partial evaporation. This phenomenon E
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Figure 7. (a) SEM image and (b) size distribution of nanometer spheres obtained at 270 mJ cm−2 pulse−1 after submicrometer sphere elimination using centrifugation.
corresponds to the experiment result of bimodal size distribution of spherical particles with the selective absence of particles 200 nm in diameter obtained by irradiation at 200 mJ cm−2 pulse−1 (Figure 5(c)) and 300 mJ cm−2 pulse−1 (Figure S2). Ti species generated after partial evaporation were corrected as titanium hydrate with nonspherical shapeless structure after drying of suspension medium. The quantity of formed titanium hydrate increased with laser fluence increase.37 This result is consistent with the increased size region of the particle evaporated selectively by increasing laser fluence (Figure 6(c)). Figures 7(a) and (b) present an SEM image and particle size distribution collected around 100 nm spherical particles obtained at 270 mJ cm−2 pulse−1 after removing submicrometer spheres using centrifugation. Particle size range, which exceeded 10% of the frequency peak in the size distribution, is also presented in Figure 6(c) as a purple crossbar. This crossbar is located almost between the melting start and the evaporation start curves, which is consistent with the above spherical particle formation. The relatively narrow size distribution was due to the precipitous gradient of the evaporation start curve in the nanometer-size region. Bimodality enhancement in the obtained particle size distribution by increasing laser fluence was also observed for ZnO and Fe3O4. The inner structure of particles obtained by laser irradiation at 225 mJ cm−2 pulse−1 is observed in the cross-sectional TEM. Figure 8(a) presents a cross-sectional TEM dark-field image of a submicrometer particle produced by (−2−20) reflection from rutile [−111] incidence and a SAED pattern in the [−111] zone axis of this particle (Figure 8(a), right). This particle is confirmed to be a single crystal according to SAED; however, many crystal strains, emerged as fringe contrast, were observed inside the particle (Figure 8 (a), left). A particle with twin structures was also observed (Figure 8(b)). The crystal strain and twin formation in rutile crystal are often reported for rutile with high oxygen vacancy concentrations and nucleation of reduced phases obtained by high-pressure processing and under a reducing atmosphere.38,39 Such crystal strains and twin formation enable reduction of system energy via formation of shear planes and lattice strain during particle crystallization.38,39 These observations are consistent with XRD patterns indicating the formation of nonstoichiometric TiO2 for particles obtained by high laser fluence irradiation. In contrast, the polycrystalline (Figure 8(c)) or amorphous phase was observed in nanosized particles similar to the particles depicted in Figure 7 because of a high degree of undercooling due to the small amount of heat
Figure 8. TEM images of cross section of particles obtained by laser irradiation at 225 mJ cm−2 pulse−1. (a) Dark-field image of particle with strain derived from the (−2 −2 0) reflection and SAED patterns. (b) Particle with twin crystal structure and a SAED pattern. (c) Nanometer polycrystalline particle.
in the small particle and the high ratio of surface area to particle volume. The peak broadening of XRD patterns with increasing laser fluence is due to crystal strain and amorphous phase formation. Thus, relatively high laser fluence irradiation is not F
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Irradiation of Boron in Liquid Medium. Appl. Phys. Lett. 2007, 91, 161110. (8) Wang, H. Q.; Miyauchi, M.; Ishikawa, Y.; Pyatenko, A.; Koshizaki, N.; Li, Y.; Li, L.; Li, X. Y.; Bando, Y.; Golberg, D. Single-Crystalline Rutile TiO2 Hollow Spheres: Room-Temperature Synthesis, Tailored Visible-Light-Extinction, and Effective Scattering Layer for Quantum Dot-Sensitized Solar Cells. J. Am. Chem. Soc. 2011, 133, 19102−19109. (9) Wang, H. Q.; Koshizaki, N.; Li, L.; Jia, L. C.; Kawaguchi, K.; Li, X. Y.; Pyatenko, A.; Swiatkowska-Warkocka, Z.; Bando, Y.; Golberg, D. Size-Tailored ZnO Submicrometer Spheres: Bottom-up Construction, Size-Related Optical Extinction, and Selective Aniline Trapping. Adv. Mater. 2011, 23, 1865−1870. (10) Wang, H. Q.; Kawaguchi, K.; Pyatenko, A.; Li, X. Y.; Swiatkowska-Warkocka, Z.; Katou, Y.; Koshizaki, N. General Bottom-up Construction of Spherical Particles by Pulsed Laser Irradiation of Colloidal Nanoparticles: A Case Study on CuO. Chem. - Eur. J. 2012, 18, 163−169. (11) Tsuji, T.; Yahata, T.; Yasutomo, M.; Igawa, K.; Tsuji, M.; Ishikawa, Y.; Koshizaki, N. Preparation and Investigation of the Formation Mechanism of Submicron-Sized Spherical Particles of Gold Using Laser Ablation and Laser Irradiation in Liquids. Phys. Chem. Chem. Phys. 2013, 15, 3099−3107. (12) Tsuji, T.; Higashi, Y.; Tsuji, M.; Ishikawa, Y.; Koshizaki, N. Preparation of Submicron-Sized Spherical Particles of Gold Using Laser-Induced Melting in Liquids and Low-Toxic Stabilizing Reagent. Appl. Surf. Sci. 2015, 348, 10−15. (13) Ishikawa, Y.; Feng, Q.; Koshizaki, N. Growth Fusion of Submicron Spherical Boron Carbide Particles by Repetitive Pulsed Laser Irradiation in Liquid Media. Appl. Phys. A: Mater. Sci. Process. 2010, 99, 797−803. (14) Ishikawa, Y.; Katou, Y.; Koshizaki, N.; Feng, Q. Raw Particle Aggregation Control for Fabricating Submicrometer-Sized Spherical Particles by Pulsed-Laser Melting in Liquid. Chem. Lett. 2013, 42, 530−531. (15) Pyatenko, A.; Wang, H. Q.; Koshizaki, N.; Tsuji, T. Mechanism of Pulse Laser Interaction with Colloidal Nanoparticles. Laser Photon. Rev. 2013, 7, 596−604. (16) Pyatenko, A.; Wang, H.; Koshizaki, N. Growth Mechanism of Monodisperse Spherical Particles under Nanosecond Pulsed Laser Irradiation. J. Phys. Chem. C 2014, 118, 4495−4500. (17) Yao, D. Y.; Zhang, J. C.; Liu, Y. H.; Zhuo, N.; Jia, Z. W.; Liu, F. Q.; Wang, Z. G. Small Divergence Substrate Emitting Quantum Cascade Laser by Subwavelength Metallic Grating. Opt. Express 2015, 23, 11462−11469. (18) Minovich, A. E.; Miroshnichenko, A. E.; Bykov, A. Y.; Murzina, T. V.; Neshev, D. N.; Kivshar, Y. S. Functional and Nonlinear Optical Metasurfaces. Laser Photon. Rev. 2015, 9, 195−213. (19) Leibovici, M. C. R.; Gaylord, T. K. Photonic-Crystal Waveguide Structure by Pattern-Integrated Interference Lithography. Opt. Lett. 2015, 40, 2806−2809. (20) Xue, X. Z.; Furlani, E. P. Analysis of the Dynamics of Magnetic Core-Shell Nanoparticles and Self-Assembly of Crystalline Superstructures in Gradient Fields. J. Phys. Chem. C 2015, 119, 5714−5726. (21) Lu, Y.; Yin, Y. D.; Gates, B.; Xia, Y. N. Growth of Large Crystals of Monodispersed Spherical Colloids in Fluidic Cells Fabricated Using Non-Photolithographic Methods. Langmuir 2001, 17, 6344−6350. (22) Xia, Y. N.; Gates, B.; Yin, Y. D.; Lu, Y. Monodispersed Colloidal Spheres: Old Materials with New Applications. Adv. Mater. 2000, 12, 693−713. (23) Kim, S.; Seo, Y. G.; Cho, Y.; Shin, J.; Gil, S. C.; Lee, W. Optimization of Emulsion Polymerization for Submicron-Sized Polymer Colloids Towards Tunable Synthetic Opals. Bull. Korean Chem. Soc. 2010, 31, 1891−1896. (24) Li, Y.; Sasaki, T.; Shimizu, Y.; Koshizaki, N. A Hierarchically Ordered TiO2 Hemispherical Particle Array with Hexagonal-NonClose-Packed Tops: Synthesis and Stable Superhydrophilicity without UV Irradiation. Small 2008, 4, 2286−2291. (25) Liu, K.-I.; Hsueh, Y.-C.; Su, C.-Y.; Perng, T.-P. Photoelectrochemical Application of Mesoporous TiO2/WO3 Nanohoney-
favorable for ideal single-crystal spherical TiO2 particle formation.
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CONCLUSIONS Cross-sectional TEM observation indicated that spherical particles obtained by laser irradiation at relatively low laser fluence using PLML were mostly single crystals. This PLML technique is valuable for fabricating submicrometer single crystalline spherical particles with advanced functions. Singlecrystal particles with strain and twin crystal particles formed by relatively high laser fluence irradiation. Thus, higher laser fluence was undesirable for highly crystallized submicrometer TiO2. Furthermore, both submicrometer spherical particles and nanometer spherical particles formed with PLML at higher fluences. The obtained broad particle size distribution from nanometer to submicrometer indicated an obvious bimodal distribution with the absence of 200 nm diameter particles. A curve of laser fluence for phase transition as a function of TiO2 particle size obtained by Mie calculation had a minimum value at 200 nm diameter. Therefore, 200 nm diameter particles were selectively evaporated by laser irradiation at higher laser fluences, resulting in size distribution without 200 nm diameter particles.
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ASSOCIATED CONTENT
* Supporting Information S
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcc.5b10691. Additional Figures S1 and S2 (PDF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected] Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was partially supported by JSPS KAKENHI 13328264, 14458401, and 14496996. REFERENCES
(1) Patil, P. P.; Phase, D. M.; Kulkarni, S. A.; Ghaisas, S. V.; Kulkarni, S. K.; Kanetkar, S. M.; Ogale, S. B.; Bhide, V. G. Pulsed-Laser Induced Reactive Quenching at a Liquid-Solid Interface - Aqueous Oxidation of Iron. Phys. Rev. Lett. 1987, 58, 238−241. (2) Neddersen, J.; Chumanov, G.; Cotton, T. M. Laser-Ablation of Metals - a New Method for Preparing Sers Active Colloids. Appl. Spectrosc. 1993, 47, 1959−1964. (3) Ershov, B. G.; Janata, E.; Henglein, A. Growth of Silver Particles in Aqueous-Solution - Long-Lived Magic Clusters and Ionic-Strength Effects. J. Phys. Chem. 1993, 97, 339−343. (4) Mafune, F.; Kohno, J.; Takeda, Y.; Kondow, T.; Sawabe, H. Formation and Size Control of Sliver Nanoparticles by Laser Ablation in Aqueous Solution. J. Phys. Chem. B 2000, 104, 9111−9117. (5) Liang, C. H.; Shimizu, Y.; Masuda, M.; Sasaki, T.; Koshizaki, N. Preparation of Layered Zinc Hydroxide/Surfactant Nanocomposite by Pulsed-Laser Ablation in a Liquid Medium. Chem. Mater. 2004, 16, 963−965. (6) Usui, H.; Sasaki, T.; Koshizaki, N. Optical Transmittance of Indium Tin Oxide Nanoparticles Prepared by Laser-Induced Fragmentation in Water. J. Phys. Chem. B 2006, 110, 12890−12895. (7) Ishikawa, Y.; Shimizu, Y.; Sasaki, T.; Koshizaki, N. Boron Carbide Spherical Particles Encapsulated in Graphite Prepared by Pulsed Laser G
DOI: 10.1021/acs.jpcc.5b10691 J. Phys. Chem. C XXXX, XXX, XXX−XXX
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The Journal of Physical Chemistry C comb Prepared by Sol-Gel Method. Int. J. Hydrogen Energy 2013, 38, 7750−7755. (26) Zhang, J.; Wang, M.; Ge, X.; Wu, M.; Wu, Q.; Yang, J.; Wang, M.; Jin, Z.; Liu, N. Facile Fabrication of Free-Standing ColloidalCrystal Films by Interfacial Self-Assembly. J. Colloid Interface Sci. 2011, 353, 16−21. (27) Jiang, X. C.; Herricks, T.; Xia, Y. N. Monodispersed Spherical Colloids of Titania: Synthesis, Characterization, and Crystallization. Adv. Mater. 2003, 15, 1205−1209. (28) Miao, Y.; Pan, G.; Huo, Y.; Li, H. Aerosol-Spraying Preparation of Bi2moo6: A Visible Photocatalyst in Hollow Microspheres with a Porous Outer Shell and Enhanced Activity. Dyes Pigm. 2013, 99, 382− 389. (29) Zhong, J.; Liang, S.; Zhao, J.; Wu, W. D.; Liu, W.; Wang, H.; Chen, X. D.; Cheng, Y.-B. Formation of Novel Mesoporous TiC Microspheres through a Sol-Gel and Carbothermal Reduction Process. J. Eur. Ceram. Soc. 2012, 32, 3407−3414. (30) Fujiwara, H.; Niyuki, R.; Ishikawa, Y.; Koshizaki, N.; Tsuji, T.; Sasaki, K. Low-Threshold and Quasi-Single-Mode Random Laser within a Submicrometer-Sized ZnO Spherical Particle Film. Appl. Phys. Lett. 2013, 102, 061110. (31) Nakamura, T.; Fujiwara, H.; Niyuki, R.; Sasaki, K.; Ishikawa, Y.; Koshizaki, N.; Tsuji, T.; Adachi, S. Origins of Lasing Emission in a Resonance-Controlled ZnO Random Laser. New J. Phys. 2014, 16, 093054. (32) Tsuji, T.; Higashi, Y.; Tsuji, M.; Fujiwara, H.; Ishikawa, Y.; Koshizaki, N. Fabrication of Spherical-Shaped Submicron Particles of ZnO Using Laser-Induced Melting of Submicron-Sized Source Materials. J. Laser Micro/Nanoeng. 2013, 8, 292−295. (33) Ohko, Y.; Tryk, D. A.; Hashimoto, K.; Fujishima, A. Autooxidation of Acetaldehyde Initiated by TiO2 Photocatalysis under Weak UV Illumination. J. Phys. Chem. B 1998, 102, 2699−2704. (34) Dominguez, C. T.; Lacroute, Y.; Chaumont, D.; Sacilotti, M.; de Araujo, C. B.; Gomes, A. S. L. Microchip Random Laser Based on a Disordered TiO2-Nanomembranes Arrangement. Opt. Express 2012, 20, 17380−17385. (35) Bi Tao, X.; Bao-Xue, Z.; Jing, B.; Qing, Q.Z.; Yan-Biao, L.; WeiMin, C.; Jun, C. Light Scattering of Nanocrystalline TiO2 Film Used in Dye-Sensitized Solar Cells. Chin. Phys. B 2008, 17, 3713−3719. (36) Szot, K.; Rogala, M.; Speier, W.; Klusek, Z.; Besmehn, A.; Waser, R. TiO2-a Prototypical Memristive Material. Nanotechnology 2011, 22, 254001. (37) Ishikawa, Y.; Koshizaki, N.; Alexander, P. Titanium Oxide Sphere Preparation by Pulsed Laser Melting in Liquid. Rev. Laser Eng. 2012, 40, 133−136. (38) Abazari, M.; Sim, J. S.; Viswanath, B.; Ramanathan, S. Fabrication and Physical Properties of Thin Tixoy Membranes from Single Crystal TiO2. J. Vac. Sci. Technol., A 2012, 30, 021601. (39) Gautam, S. K.; Singh, F.; Sulania, I.; Singh, R. G.; Kulriya, P. K.; Pippel, E. Micro-Raman Study on the Softening and Stiffening of Phonons in Rutile Titanium Dioxide Film: Competing Effects of Structural Defects, Crystallite Size, and Lattice Strain. J. Appl. Phys. 2014, 115, 143504.
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DOI: 10.1021/acs.jpcc.5b10691 J. Phys. Chem. C XXXX, XXX, XXX−XXX
