Shift To Higher Energy Research Articles

Mechanisms of the structural modification of Ti films by pulsed direct current and inductively coupled plasma-assisted pulsed direct current sputtering

Titanium (Ti) thin films have been deposited by direct current (dc), pulsed dc, and inductively coupled plasma (ICP)-assisted pulsed dc sputtering to investigate the effects of current pulsing and ICP assistance on film structure and properties. Ti thin films were deposited from a Ti target using Ar as a discharge gas. Ion energy was measured by energy-resolved mass spectrometry. The discharge plasma parameters were measured using a single probe with a time-resolved data acquisition system. The crystal structure was investigated by X-ray diffraction. Surface and cross-sectional morphologies were investigated by atomic force microscopy and scanning electron microscopy, respectively. The cross-sectional images demonstrated that the film structure changed from a coarse columnar structure with voids to a fine columnar structure. Changes in the roughness and crystallite sizes of the deposited Ti thin films indicated that the thin films were amorphized by the ICP-assisted sputtering, resulting in the smoothing of the film surface. Energy and mass analyses indicated that the energy fluxes to the substrate via Ar+ and Ti+ ions increased by more than four and two orders of magnitude, respectively, when ICP assistance was employed. This large difference in degree of enhancement generated by ICP assistance for Ar+ and Ti+ ions suggests different ionization efficiencies between gas-phase Ar and sputter-emitted energetic Ti, particularly in the ICP-assisted pulsed dc discharge. As a result of the increase in energy flux to the substrate, the mean energy transferred by both Ar+ and Ti+ ions per Ti metal particle (atom or ion) arriving at the substrate increased from approximately 40eV for dc sputtering to >104eV for ICP-assisted pulsed dc sputtering, and the mean energy transferred by Ti+ ions per Ti metal particle (atom or ion) arriving at the substrate increased from a few eV for dc sputtering to approximately 29–30eV for ICP-assisted pulsed dc sputtering. These increases in transferred energy reflect the formation of intense and broad high-energy peaks, as shown in the ion-energy spectra. It is shown that the formation of an additional high-energy peak to the single peak of the dc discharge results from the current pulsing, and that the further high-energy shift and splitting of the bimodal peaks result from the combination of the increase in plasma sheath potential to the grounded substrate and the increases in the electron density and electron temperature due to the subsequent ICP assistance to the pulsed dc discharge.

Emission transformation in CdSe/ZnS quantum dots conjugated to biomolecules

The variation of photoluminescence (PL) spectra in CdSe/ZnS quantum dots (QDs) at the conjugation to antibodies (ABs) has been investigated and discussed in this paper. Two types of CdSe/ZnS QDs with different CdSe core sizes (5.4 and 6.4nm) and emissions (605 and 655nm) were studied before and after the conjugation to anti-Interleukin-10 (IL-10) and anti-Pseudo rabies virus (PRV) ABs. The PL high energy shift and asymmetric shape of PL bands have been detected in bioconjugated QDs. Note that the bioconjugation impact on spectral characteristics of CdSe/ZnS QD emission has been not studied yet in details. The surface enhanced Raman scattering (SERS) effect is revealed in bioconjugated CdSe/ZnS QDs. The SERS effect testifies that the excitation light used at the Raman study generates the electric dipoles in AB molecules. At the same time, the permanent position of LO-phonon Raman lines in Raman spectra of nonconjugated and bioconjugated QDs confirms that QD materials do not change at the bioconjugation. It is shown as well that the compressive strains do not play any role in the PL high energy shift in bioconjugated QDs. PL spectra of pure anti IL-10 ABs, anti PRV ABs, a phosphate buffer saline (PBS) and PL spectrum dependences versus excitation light intensities have been investigated as well. Finally, the PL spectrum transformation in bioconjugated QDs is attributed to varying the quantum confinement effect in CdSe/ZnS QDs and the energy band profiles in QD cores. Both these effects are stimulated by the electromagnetic field of excited AB dipoles. The obtained results can be useful for sensitivity improving the QD bio-sensors.

Synthesis and study of superacid ZrO2–SiO2–Al2O3 mixed oxide

Strongly acidic ZrO2–SiO2–Al2O3 mixed oxide with different Zr:Si:Al ratios have been synthesized by sol–gel method. It was found that superacid (H0 = −14.52) sites are formed at 12 ≤ Zr4+ ≤ 39, 48 ≤ Si4+ ≤ 72, 3 ≤ Al3+ ≤ 31 at.%. According to the infrared spectra of adsorbed pyridine and acetonitrile-D3, acidic B- and strong L-sites are present on ZrO2–SiO2–Al2O3 surface. Observed high-energy shift of Zr 3d5/2 peak in the X-ray photoelectron spectrum and low-field shift of 29Si nuclear magnetic resonance signal of superacid Zr35Si53Al12 oxide indicate that the electron density transfers from zirconium to silicon atom. The generation of superacidity in ZrO2–SiO2–Al2O3 matrix could be explained by formation of coordinatively unsaturated Zr4+ ions which are strong L-sites. It was shown that superacid ZrO2–SiO2–Al2O3 efficiently catalyzes polymerization of tetrahydrofuran in the presence of acetic anhydride at 40℃ with 68% yield of polytetramethyleneoxide acetate.

Size-controlled nc-Si:H/a-SiC:H quantum dots superlattice and its application to hydrogenated amorphous silicon solar cells

Boron doped nc-Si:H/a-SiC:H quantum dot superlattice (QDSL) has a great potential to improve thin film silicon solar cells performance for high conductivity, wide band gap and anti-reflection effect. In this study p-type nc-Si:H/a-SiC:H QDSL has been fabricated by in situ grown method without subsequent annealing treatment. High resolution transmission electron microscopy and PL peak energy shift indicate that this method provides the possibility to precisely control the size of silicon quantum dots and the passivation at well/barrier interface. By optimizing structural characteristics and interface passivation, high perpendicular conductivity and strong anti-reflection effect was simultaneously obtained in QDSL films. An initial efficiency of 10.5% was achieved for n-i-p type hydrogenated amorphous silicon solar cell, which may guide further efforts arising the structure engineering of nc-Si:H/a-SiC:H QDSL for high efficient solar cells.

Bandgap engineering of the LuxY1−xPO4 mixed crystals

Bandgap modification of the LuxY1−xPO4 mixed crystals has been studied by thermostimulated luminescence (TSL) and ab-initio calculation methods. Doping of LuxY1−xPO4 with Ce3+ allowed to follow up the changes of electron traps depth, caused by the modification of the bottom of conduction band. The observed gradual shift of the most intensive TSL peaks to higher temperatures with increase of x value was connected with the high-energy shift of the conduction band bottom. According to the band structure calculations the bottom of the conduction band is formed by the 5d and 4d states of Lu and Y, respectively. Therefore, substitution of one cation by another is responsible for the observed variation of the electronic and optical properties. Doping with Eu3+ was used to study the modification of the hole traps and the top of the valence band in LuxY1−xPO4. The independence of the TSL peaks position on x value in LuxY1−xPO4:Eu3+ allows to conclude that the top of the valence band is negligibly affected by the cation substitution. According to the band structure calculations the top of the valence band is formed by the O 2p electronic states, which are not affected by the cation substitution. The resulting increase of the bandgap with x value is confirmed by the data of ab-initio calculations.

Laser-Induced Modification of Properties of CdZnTe Crystals

The photoconductivity (PC) spectra of CdZnTe (CZT) semiconductor solid solutions obtained from different manufacturers were investigated before and after irradiation with nanosecond laser pulses. Depending of energy density, irradiation of CZT crystals resulted in an increase in the photosensitivity, high-energy shift of the PC spectrum maximum and transformation of its profile. Laser processing with the certain energy densities improved homogeneity in the crystal surface area and provided equalization of structural characteristics in the surface region and bulk of the samples. Irradiation of CZT crystals pre-coated with an In electrode film caused rectification in the I-V characteristics because of the formation of a barrier structure. The application of the obtained In/CZT/Au diodes with low leakage current as X/γ-ray detectors is considered.

Electronic Raman scattering on out-of-plane disorderedBi2Sr2CaCu2O8+δ: How the pseudogap affects the superconducting Raman response

We report Raman scattering measurements on ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ single crystals with a different degree of out-of-plane disorder to examine the effect of ${T}_{c}$ change on the the electronic Raman response at the optimal doping level. The ${B}_{1g}$ peak energies for lower ${T}_{c}$ disordered samples are essentially independent of ${T}_{c}$. However, a further increase of ${T}_{c}$ by minimizing the degree of out-of-plane disorder leads to a high-energy shift of the ${B}_{1g}$ peak. Interestingly, abrupt change of the ${B}_{1g}$ peak energy occurs when the the superconducting gap energy exceeds the pseudogap energy, which results in the recovery of superconductivity-dominated Raman response in ${B}_{1g}$ symmetry. It suggests that these anomalous properties of the antinodal electrons are a consequence of the unconventional superconducting state of the cuprates where superconductivity coexists with the pseudogap in the ground state.

Light Emitting Properties of Si-Rich-Si3N4 Films Grown By PECVD Method

Bandgap engineering of Si-based materials through the control of the distribution of Si nanoclusters’ (Si-ncs) offered future applications of Si-based nanostructured materials in optoelectronics as low-cost, miniaturized, and CMOS-compatible, light-emitting and photovoltaic devices. In the past, most efforts were concentrated on the development of luminescent Si-ncs embedded in SiO2 host. However, its insulating nature remains a barrier for the production of future electrically pumped LEDs and efficient photovoltaic cells. This detrimental aspect can be coped with a medium of higher conductivity and lower band gap, for instance, Si nitride. Tunable room temperature visible light emission from Si-ncs embedded in Si nitride matrices has been recently demonstrated. Present work deals with the Si-rich Silicon nitride films were grown by PECVD technique on silicon substrates. The film stoichiometry was controlled via variation of NH3/SiH4 ratio from R=0.45 up to 1.0. Thermal treatment was performed at 1100°C for 30min in nitrogen flow to form Si-ncs. To control structural and light emitting properties of the films Raman scattering, X-ray diffraction (XRD), Transmission electron microscopy (TEM) and photoluminescence (PL) methods were used. The evolution of PL spectra with the temperature of measurements from 20 to 300 K was studied also aiming at the determination of the types of optical transitions. The PL spectra were found to be complex and the shape and magnitude of PL spectra depends on silicon nitride stoichiometry. The increase of gas ratio from R=0.63 to R=1 results in the shift of PL peak position from 1.6 eV up to 2.7 eV. Analysis of the temperature dependence of PL spectra revealed the presence of several PL components with the maxima at 2.9-3.0 eV, 2.5-2.7 eV, 1.9-2.2 eV and 1.8-1.9 eV. The peak position of the former three PL components unchanged with the decrease of temperature of the measurements. This allows describing all these components to the defects of silicon nitride host. At the same time, PL band peaked at 1.8-1.9 eV showed high-energy shift with sample cooling and can be ascribed to the exciton recombination inside Si-ncs. The presence of these latter was confirmed by Raman scattering spectra and TEM images. The nature of light emitting defects in silicon nitride, the mechanism of photoluminescence and the way for the optimization of light emitting properties are discussed.

Luminescent and scintillation properties of the Ce3+ doped Y3−xLuxAl5O12:Ce single crystalline films

The work is related to the investigation of scintillation and luminescent properties of single crystalline films (SCF) of solid solutions of Ce3+ doped Y3−xLuxAl5O12:Ce garnets with x value in the 0–3 range. We have shown a possibility of realization of high-energy shift of the Ce3+ ion emission spectrum in these garnets up to 22nm. We have also found that the light yield of the radioluminescence under α-particle excitation of LuAG:Ce SCF can exceed by 1.3 times the corresponding values for the YAG:Ce SCF counterpart. For investigation of the luminescent properties of Y3−xLuxAl5O12:Ce SCF at different x values the luminescent spectroscopy of these SCFs under excitation by synchrotron radiation in the VUV range was performed.

Reaction Dynamics of Magnesium Ions Insertion/Extraction of Olivine-Type FePO4

Magnesium battery is one of the candidates for the next generation battery system due to the high energy density and the environmentally friendly nature 1,2. Developing suitable cathode materials is a clue to the practical application. Divalent Mg2+ insertion/extraction reactions in host compounds is difficult, due to the stronger ionic interaction and harder charge redistribution of magnesium compared to lithium ions 3. Therefore suitable cathode materials are limited at this moment. In order to design the host materials for magnesium battery cathodes, it is important to understand the difference between the reaction dynamics of magnesium and that of lithium. Olivine-type lithium iron phosphate (LiFePO4) is a well-known cathode material in lithium ion batteries 4. By using delithiated FePO4, the electrochemical insertion/extraction of magnesium ions in FePO4 was reported by Le Paul et al. 5 Hence, FePO4 is suitable as a model compound to clarify the reaction dynamics of magnesium battery. In this study, we investigated the crystal structure change and the reaction dynamics during electrochemical magnesium insertion/extraction reactions of olivine-type FePO4.LiFePO4 was prepared by using a solid state reaction using Li2CO3, FeC2O4-2H2O and (NH4)2HPO4 as raw materials. After carbon-coated with acetylene black 10 wt% to LiFePO4, the mixture was pelletized and calcined. FePO4 was prepared by chemical oxidation of the obtained carbon coated LiFePO4 using nitronium tetrafluoroborate (NO2BF4) as an oxidizing agent. The particle size of the completed carbon coated FePO4 was about 65 nm determined by SEM observation. Electrochemical measurements were carried out using a three-electrode cell with an Ag+/Ag double junction reference electrode. The cathode material consists of 80 wt% FePO4, 15 wt% acetylene black and 5 wt% polytetrafluoroethylene. The counter electrode was a magnesium rod and the electrolyte was 0.5 M magnesium trifuluoromethanesulfonyl-imide (Mg(TFSI)2) in acetonitrile (AN). Galvanostatic discharge/charge measurements were conducted with C/30 rate at 55°C. X-ray absorption spectroscopy (XAS) measurements were carried out in a transmission mode at BL02B2 at SPring-8, Japan. Synchrotron X-ray diffraction (XRD) measurements were also carried out at BL01B1 and BL14B2 at SPring-8, Japan. Figure 1 shows discharge/charge profile of FePO4 in 0.5 M Mg(TFSI)2/AN. The obtained discharge capacity indicates 0.4 magnesium ions insertion into FePO4, comparable to 0.8 lithium ions insertion. In the charge process, the obtained capacity corresponds to the extraction of 0.3 magnesium ions. This result shows that magnesium insertion /extraction reaction of FePO4is irreversible and that the extraction is more difficult than the insertion process. In addition, discharge/charge curves are considerably dissimilar, suggesting that the reaction mechanism could be quite different between insertion and extraction processes. In order to characterize discharged and charged MgxFePO4, XAS and XRD measurements were performed. Fe K-edge XANES spectra shows lower and higher energy shifts with the discharge/charge reactions, respectively. This indicates the reduction and oxidation of Fe in FePO4 by magnesium insertion/extraction. XRD patterns show lower and higher peak shifts with the discharge/charge reactions, respectively. The peaks attributed to the two-phase reaction did not appear as shown in the charge/discharge reactions of LiFePO4. This result reveals that magnesium ions insertion/extraction reactions of FePO4proceeds via not a two-phase but a single-phase mechanism. Furthermore, we will present the reaction dynamics of magnesium ions insertion/extraction by using FePO4thin film as a model electrode. Acknowledgments This work was supported in part by Core Research for Evolutional Science and Technology (CREST) program of Japan Science and Technology Agency (JST) in Japan.

Mechanisms of large red-shift and intensity enhancement of absorption bands by π-bond breaking in a benzoporphyrin sensitizer for photodynamic therapy

A free-base monobenzoporphyrin photosensitizer called verteporfin for photodynamic therapy (PDT) has a benzopyrrole ring with a partial π-bond breaking. The π-bond breaking significantly red-shifts the absorption band (so-called Qy-band) to 688 nm and enhances the absorption intensity. In this paper, we theoretically study the mechanisms of the red-shift and intensity enhancement in verteporfin. Density functional analysis at the B3LYP-6-31G(d,p) level of theory reveals that the π-bond breaking increases the energies of the highest occupied molecular orbital (HOMO) and second lowest unoccupied molecular orbital (LUMO+1) by 0.28 and 0.11 eV, respectively, and decreases the energy of the lowest unoccupied molecular orbital (LUMO) by 0.08 eV, in contrast to the unmoving second lowest occupied molecular orbital (HOMO-1). In the consequence of the higher energy shift of the HOMO and lower energy shift of the LUMO, the HOMO–LUMO gap is significantly narrowed. Therefore, the absorption red-shift in verteporfin is attributed to the HOMO–LUMO gap narrowing. On the other hand, the molecular-orbital shifts split the four electronically excited states, (HOMO, LUMO), (HOMO, LUMO+1), (HOMO-1, LUMO), and (HOMO-1, LUMO+1). The splitting weakens the configuration interactions between the excited states, which enhances the transition probability of the Qy-band.

Local network structure of a-SiC:H and its correlation with dielectric function

The microscopic disordered structures of hydrogenated amorphous silicon carbide (a-Si1−xCx:H) layers with different carbon contents have been determined based on the correlations between the dielectric function in the ultraviolet/visible region and the local bonding states studied by high-sensitivity infrared attenuated total reflection spectroscopy. We find that the microscopic structure of the a-Si1−xCx:H layers fabricated by plasma-enhanced chemical vapor deposition shows a sharp structural transition at a boundary of x = 6.3 at. %. In the regime of x ≤ 6.3 at. %, (i) the amplitude of the a-SiC:H dielectric function reduces and (ii) the SiH2 content increases drastically with x, even though most of the C atoms are introduced into the tetrahedral sites without bonding with H. In the regime of x > 6.3 at. %, on the other hand, (i) the amplitude of the dielectric function reduces further and (ii) the concentration of the sp3 CHn (n = 2,3) groups increases. Moreover, we obtained the direct evidence that the sp2 C bonding state in the a-SiC matrix exists in the configuration of C = CH2 and the generation of the graphite-like C = CH2 unit suppresses the band gap widening significantly. At high C contents of x > 6.3 at. %, the a-SiC:H layers show quite porous structures due to the formation of microvoids terminated with the SiH2/CHn groups. By taking the SiH2/CHn microvoid generation in the network and the high-energy shift of the dielectric function by the local bonding states into account, the a-SiC:H dielectric function model has been established. From the analysis using this model, we have confirmed that the a-SiC:H optical properties in the ultraviolet/visible region are determined almost completely by the local network structures.

Theoretical study of the electronic excitations of free-base porphyrin–Ar2 van der Waals complexes

The intermolecular interaction of free-base porphine (FBP)-Ar2 and free-base tetraazaporphyrin (FBPz)-Ar2 van der Waals (vdW) complexes was calculated in the ground state and vertical excitations that correspond to the Q- and B-bands using the many-body wavefunction theory of the symmetry-adapted cluster-configuration interaction (SAC-CI) method and time-dependent density functional theory (TDDFT). For the 1(1)B3u state of FBP-Ar2 a blueshift (high-energy shift) of excitation energy was calculated using the SAC-CI method; such a blueshift was not obtained by TDDFT calculations. This calculated blueshift corresponds to the experimentally observed blueshift in the Qx-band of FBP for FBP-Arn complexes. For FBPz-Ar2, blueshifts of the Q-band were not obtained using SAC-CI and TDDFT. These behaviors of the energy shift of the Q-bands could not be explained by the point dipole-point dipole interaction model. Large redshifts (low-energy shift) were obtained for the B-band states (2(1)B3u and 2(1)B2u) of FBP and FBPz. The energy shift showed the inverse sixth-power dependence on the intermolecular distance. The point dipole-point dipole interaction model can describe the redshift of the B-band. For the excited states that exhibit large redshifts, the TDDFT can qualitatively describe the vdW interaction in the excited states by supermolecular calculations. The solvatochromic shifts for FBP and FBPz in an Ar matrix were examined by the linear-response polarizable continuum model and TDDFT. The magnitude of calculated solvatochromic redshifts is proportional to the square of the transition dipole moment.

Measurements of ion energy distributions in a dual-frequency capacitively coupled plasma for Ar/O2 discharges

Ion energy distributions (IEDs) of Ar+ and bombarding the grounded electrode are measured by an energy resolved quadrupole mass spectrometer in a dual-frequency capacitively coupled plasma (DF-CCP) operated in a gas mixture of Ar and O2 (90%/10%). The effects of external discharge parameters, such as the frequency and power of the low frequency (LF) source and the gas pressure, on the IEDs are investigated in detail. With the increase in the LF power, the high-energy peak shifts towards the high-energy region and the energy width ΔE between high- and low-energy peaks in the IEDs also increases. However, the increase in the LF frequency leads to the shift of the high-energy peak towards the low-energy region as well as a narrow energy width ΔE. The increase in the gas pressure results in the bimodal structure being unobvious because of intensive momentum transfer and charge exchange collisions between ions and background molecules. In addition, the distinctions between Ar+ and IEDs are also discussed. Finally, some experimental results are compared with numerical ones obtained from the particle-in-cell/Monte Carlo (PIC/MC) method and both results are in general agreement.

Arsenic Irradiation Induced Atomic Interdiffusion of In<sub>x</sub>Ga<sub>1-x</sub>As/InP Quantum Well Structures

The atomic intermixing of In x Ga 1-x As/InP quantum well structures induced by arsenic irradiation has been investigated using photoluminescence (PL) measurement. The ion doses used were varried from 5x10 11 As/cm 2 to 1x10 13 As/cm 2 . Also, the irradiation temperature were carried out from -200 o C to 300 o C. The samples were annealed under Argon flow in rapid thermal annealer (RTA) at 750 o C for 60 second. The photoluminescence result showed that there was increase in energy shift at lower doses. However, the energy shift was saturated at higher dose. At elevated temperature implantation showed that the energy shift did not change significantly for all the samples (LM, TS, CS). In additon to this, the higher energy shift was observed in the Compressive Strain (CS) samples, but the lower of the energy shift was experienced in the Tensile Strain (TS) samples. Received: 06 September 2012; Revised: 27 November 2012; Accepted: 03 December 2012

Investigation on the Optical Performance of Co and Al Co-Doping ZnO Films

ZnO is a novel kind of semiconductor material, which has hexagonal Wurtzite crystal structure, with a wide band-gap of 3.37eV at room temperature. It owns a large excitation binding energy of 60meV and excellent room temperature stability. ZnO has very useful properties of piezoelectricity, gas & pressure sensitivity etc. Therefore, application researches on low dimensional ZnO materials have become hot topics and significant values.In this paper, ZnO doped thin films were prepared by sol-gel method. Zn (CH3COO)2•2H2O was employed as the precursor, anhydrous alcohol was the solvent, monoethanolamine was the complexant, Co(CH3COO)2•4H2O was used as the source of the Co-dopant, Al(NO3)3•9H2O was used as the source of the Al-dopant in the experiment to yield the doped ZnO films. The sample preparation spin coating number is 6, the average grain size is in nanometer level, and the thermal treatment temperature is 450, 500, 550, 600°C, respectively. The effect of the doping proportion on the crystallization and energy band structure of the ZnO thin films were characterized by X-ray diffraction (XRD), the Infrared spectrum and the ultraviolet-visible transmission spectra (UV-Vis).The results show that the crystalline grain size of the ZnO doped films grown on glass substrates increases, since the thermal treatment temperature rise. In this paper, a best ZnO doped film was obtained at the temperature of 600°C. It preliminarily analyses that Co-doped ZnO films present a absorption peak in infrared area when the thermal treatment is at 550°C. Al or Co doped ZnO films can cause a redshift of ultraviolet absorption peaks. Energy gap is around 3.2eV when doped. The ultraviolet absorption peaks of Al-doped ZnO films will have a shift to high energy, since it has a better crystallinity.

Comparative electronic structures and UV–vis spectra of tribenzosubporphyrin, tribenzomonoazasubporphyrin, tribenzodiazasubporphyrin, and subphthalocyanine: Insight from DFT and TDDFT calculations

Electronic structures, geometries, and vertical excitation energies of chloroboron subphthalocyanine, tribenzodiazasubporphyrin, tribenzomonoazasubporphyrin, and tribenzosubporphyrin were calculated using density functional theory (DFT) and time-dependent (TD) DFT coupled with polarized continuum model (PCM) approach. Molecular geometries calculated at the BP86/6-311G(d) level reveal bowl-shape, trigonal prismatic conformations for all compounds with a variable bowl-depth that depends on the number of meso-nitrogen atoms in corresponding molecule. TDDFT-PCM calculations predict that the Q-band should undergo gradual high-energy shift, while the B-band should undergo low-energy shift upon stepwise substitution of the meso-nitrogen atoms in subphthalocyanine toward tribenzosubporphyrin. The TDDFT-PCM predicted trend was rationalized on the basis of electronic structures of target macrocycles. When comparison between theory and experiment is available, TDDFT-PCM calculations are in qualitative and quantitative agreement with experimental data.

Plasmon Resonance of Isolated Gold Hollow Nanoparticles and Nanoparticle Pairs: Insights from Electronic Structure Calculations

Because the feature sizes of noble metal nanoparticles (NPs) are smaller than a few of nanometers, simulations including quantum effects and atomistic details are inevitable. In this work, we report a detailed electronic structure study on the plasmon resonance of isolated gold hollow nanoparticles (NPs) and NP pairs. The long-range-corrected (LRC) density functional theory (DFT) has been employed. We find that the plasmon resonance of small-size gold NPs is very sensitive to NP sizes and interparticle distances. When the NP’s size changes from Au32 to Au17–, the high-energy absorption maximum blue shifts 50 nm and when the interparticle distance of Au17– NP pairs changes from 1.15 to 0.83 nm, the corresponding blue shift is ∼40 nm. The spectral line width becomes narrower as the NP size increases and the interparticle distance reduces. The insight of how the plasmon-resonance peaks of a NP pair are formed and how they are sensitive to the interparticle separation is revealed by the plots of transition de...

High-Energy Shift of Boson Peak and Its Broadening in Crystallization Regime: A Qualitative Aspect

Inelastic light scattering (i.e., Brillouin and Raman) can provide information about chemical bonding and coordination states, making it an efficient technique for studying amorphous matter in supercooled liquid (SCL) and melt regimes. Several studies have reported that, during crystallization (which occurs between these regimes), binary system glasses exhibit anomalous elastic behavior [i.e., simultaneous occurrence of increases in sound velocity (or elasticity), which is estimated by Brillouin spectra] and significant damping. Such behavior has also been reported in the low-energy vibration mode ( 1THz) of Raman scattering (known as the Boson peak, BP) during transition from SCL to crystals (SCL–crystal transition). Although the anomalies appear to be related to the crystallization phenomenon, in-depth analysis has not been conducted yet. Therefore, in this study, in order to obtain additional information concerning the anomaly in the crystallization regime, we prepared an appropriate sample for the in situ observation of the BP and examined the behavior of the BP under nonisothermal and isothermal heating conditions. For observing crystallization dynamics through inelastic light scattering, glass samples that show a strong tendency of homogeneous nucleation are preferable because the samples have a large interface, at which the SCL–crystal transition occurs. Since a BaSi2O5 glass possesses high nucleation ability and TiO2 is known to be an effective nucleation reagent in a silicate glass system, we prepared the glasses in which SiO2 was substituted by TiO2, i.e., BaTixSi2 xO5 (x 1⁄4 0{0:25), using a melt-quenching technique (melting condition: 1773K for 1 h). The as-quenched samples were annealed at each glass-transition temperature (Tg) [Fig. 1(b)] for 20 h to obtain nucleated samples. This was done because for glass with a homogeneous nucleation trend, the temperature at which the maximum nucleation rate is evident is close to Tg. 9) The samples were characterized by differential thermal analysis (DTA), transmission electron microscopy (TEM), and in situ inelastic light scattering observation. Detailed conditions for these analyses are described elsewhere. The spectra that were obtained in the low-energy region were reduced with respect to the Bose–Einstein factor and were fitted using the sum of the BP and the Gaussian function. This was done because the vibrational band, which results from the Ba–O bond, contributes to the spectra. The observed BP was analyzed using a log-normal function to evaluate the position of its maximum !BP and its full width at half maximum (FWHM). Figure 1 shows the results of thermal analysis in the studied samples. Here the samples with x 1⁄4 0:125 are representative of all the samples. In the as-quenched samples, their Tg increased with the value of x. The annealed samples at each Tg tended to show lower crystallization-peak temperatures (Tp) than the as-quenched samples [Figs. 1(a) and 1(b)]. In particular, the difference in Tp between the as-quenched and annealed samples (i.e., Tp) indicated the maximum value at x 1⁄4 0:125 (BaTi0:125Si1:875O5; Tp 1⁄4 73 K). This value was much larger than that of the base glass (BaSi2O5; Tp 1⁄4 40K). According to Marotta et al., oxide glass showing homogeneous nucleation and subjected to thermal treatment reveals a shift of Tp to a temperature that is lower than that of the nontreated glass because of the evolution of an excess of internal nuclei. These results suggest that the BaTi0:125Si1:875O5 glass possesses high nucleation ability. In addition, the annealed sample showed no structural development, and only the halo pattern was observed in the corresponding electron diffraction pattern [Fig. 1(c)]. We, therefore, selected the BaTi0:125Si1:875O5 glass as a test sample for the in situ observation. Figure 2 shows the result of the in situ measurements of the inelastic light scattering spectra of the test sample. We observed a BP around 1–4 THz, which is attributed to an excess of the vibrational density of states because of the nanometric heterogeneity/cohesive nanodomain. From the fitting, we estimated !BP to be 1:3THz at room temperature [Fig. 2(a)]. During heating (nonisothermal; 20K/min), the spectra showed no significant change up to 1273K. When the temperature was further increased, the BP revealed progressive broadening (or overdamping) in the isothermal stage (0–21min at 1273K; T=Tg 1:28). Eventually, a group of small peaks (closed circles) (as opposed to the BP) began to appear, indicating full crystallization of the test sample. In terms of the reduced temperature (T=Tg) dependence of !BP [Fig. 2(b)], !BP 0 0.1 0.2 970 980 99

Effects of La 3+ doping on the optical characteristics and color tunability of (Mg, Mn)(Y, Ce, La) 4Si 3O 13 phosphors

The doping effects of La 3+ ions on the photoluminescence properties and color tunability of (Mg, Mn)(Y, Ce, La) 4Si 3O 13 phosphors have been elaborated in this study. On increasing the La 3+ concentration in the host, tunability of excitation wavelength is achieved first, which in turn leads to the blue shift in the wavelength of Ce 3+ emission. The high-energy emission shift of Ce 3+ ions results from the change in the crystal field around Ce 3+ ions. With the incorporation of La 3+ ions, the chromaticity coordinates shift towards white-light region showing the tunable characteristics. Moreover, the correlated color temperature (CCT) change from warm white to cool white light region with different concentration of La 3+ ions. The variation of different excitation wavelength tunes the emission thus augmenting the probability of (Mg, Mn)(Y, Ce, La) 4Si 3O 13 phosphors for potential application in optical devices.