Theoretical study on photophysical property of cuprous bis-phenanthroline coordination complexes

The electronic structures and photophysical properties of phenathroline ligands coordinated to Cu(I), which are substituted in the 2,9-positions with methyl, phenyl, trifluoromethyl and tert-butyl groups, has been studied by density functional theory (DFT) and time-dependent DFT (TDDFT). To investigate the role played by counteranion in these complexes, the highest occupied orbital energies (HOMO), the lowest virtual orbital energies (LUMO), Δ_H–L (the energies difference between the HOMO and LUMO), the lowest excitation energies (E_S1), ionization potentials (IPs), electron affinities (EAs) and reorganization energies (λ) were computed. And through the study of the geometric relaxations, d-orbital splitting and spin-orbit couplings (SOC) at their optimized S₀ and T₁ geometries, non-radiative and radiative decay rate constants (k_nr and k_r) were determined, for comparing and analyzing the different size and push/pull substituents effect on the luminescence quantum yield. Considering these factors, the dtbpdmp complex with tert-butyl group in the 2,9-positions has faster k_r and singlet-triplet intersystem crossing (ISC) but slower k_nr, which leads to its higher photoluminescent quantum efficiency as compared to the methyl-, phenyl- and trifluoromethyl-based complexes.     

Li+附着CH3-nFnO2过氧自由基:络合物Li+-CH3-nFnO2(n=0～3)结构与性质的研究

采用了从头算分子轨道理论（MP2，非限性的二级微扰理论）和密度泛涵理论（B3LYP），分别在6-31G（d，p），6-311G（d，p），6-311＋G（d，p），6-311G（2d，p），和6-311＋G（2df,2p）基组上优化CH3-nFnO2-Li^＋（n=0～3）的几何结构，计算出了相关的NBO电荷分布和锂离子相对于自由基CH3-nFnO2的亲和能。并在同一水平上计算了自由基CH3-nFnO2和络合物CH3-nFnO2-Li^＋的相关伸缩振动频率。CH3-nFnO2在UB3LYP／6-311G（d，P）得到的振动频率与实验值符合得很好．根据相关的文献报道，我们运用从头算分子轨道理论和密度泛涵理论计算出的锂离子相对于CH3-nFnO2的亲和能都能够表明络合物CH3-nFnO2-Li^＋在气态下能以一种稳定的物种形态被离子附着质谱检测．     

Theoretical study on the neutral and ionic Cu(I) phosphorescent complexes with 2-(2′-quinolyl)benzimidazole and phosphine mixed ligand

The electronic structures and photophysical properties of a series of the neutral and ionic Cu(I) complexes with 2-(2′-quinolyl)benzimidazole and phosphine mixed ligand were investigated using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. To investigate the differences between the neutral and ionic complexes, the highest occupied molecular orbital (HOMO) energy, the lowest virtual molecular orbital (LUMO) energy, ΔE_H-L (the energy gap between HOMO and LUMO), the ionization potentials (IPs), electron affinities (EAs) and reorganization energies (λ) were computed. To explain the reason of the metal-to-ligand charge transfer (MLCT) hardly detection in the neutral complexes, the absorption and emission spectra were studied in detail. To evaluate the photoluminescence quantum yield (PLQY), the non-radiative and radiative decay rate constants (k_nr and k_r) were also presented. As a result, these calculations reveal that the structural distortion between the ground and excited states plays an important role in governing the PLQY. The charge transfer and the transport equilibrium property were markedly improved due to the lack of mobile counterions in the neutral form. Introducing the ether linkage together with the enhanced NˆN π-conjugation in 2b had obviously faster k_r but slower k_nr, which led to its higher PLQY relative to the introducing the ether linkage only or lacking of a proton and the counterions in complexes.     

(111)方向的InAs/GaSb超晶格材料电子结构的杂化泛函计算

采用电子密度泛函理论方法计算了一系列（111）方向的InAs/GaSb超晶格的电子结构和能带结构。将杂化泛函的计算结果与普通密度泛函方法的计算结果进行了比较。Heyd-Scuseria-Ernzerhof (HSE)杂化与对固体修正的Perdew-Burke-Ernzerhof (PBE)近似结合的杂化泛函显示了较传统PBE方法和若干其他杂化泛函更符合实验数据的结果。采用该方法研究了InAs/GaSb超晶格的带隙随超晶格周期厚度以及InAs/GaSb比例变化的规律。其结果与以往实验结果符合很好。这些结果表明HSE-PBEsol方法对于估计InAs/GaSb超晶格的电子性质适用。     

Spray deposited ZnO and Ga doped ZnO based DSSC with bromophenol blue dye as sensitizer: Efficiency analysis through DFT approach

Dye sensitized solar cells based on spray deposited ZnO and Ga doped ZnO (GZO) thin film were fabricated with Bromophenol Blue as the photo sensitizer. XRD results show the hexagonal wurtzite phase of ZnO and GZO thin films with c-axis growth orientation, and the diminished crystalline nature of GZO thin film as the effect of doping. FE-SEM results revealed the morphology induced internal light interaction capability of GZO thin film for better harvesting of photon energy. Photovoltaic studies showed that the DSSC fabricated with GZO thin film has obtained enhanced power conversion efficiency (1%) than the ZnO thin film based DSSC (0.2%), as a result of Ga doping. To investigate the obtained photovoltaic performance of the device, the electronic properties of Bromophenol Blue dye were theoretically analyzed with Density Functional Theory (DFT) study.     

有机半导体苝的DFT理论计算研究

采用密度泛函理论(DFT)方法对苝进行了B3LYP/6-31G水平上的分子结构优化、IR光谱、Raman光谱、THz光谱、UV-Vis光谱、分子前线轨道、分子电子密度、Mulliken电荷等理论计算。研究结果表明:理论计算结果与实验数据吻合得较好,对IR、THz、UV-Vis吸收光谱和Raman散射光谱中的特征峰进行了归属,发现苝的THz光谱有三个特征吸收峰,它们分别位于2.94、5.46和7.77 THz,其中5.46 THz的吸收是最强的,它是由以C4-C1-C11-C16为轴的苝分子面外对称弯曲振动产生的。苝在UV-Vis光波段有三个吸收峰,峰值波长分别位于420.79、328.14及303.80 nm,其中420.79nm的紫外吸收峰最强。前线轨道计算表明苝分子的HOMO与LUMO能量差值为3.077eV,它与用UV-Vis的理论计算能隙2.946eV仅有0.131eV(4.45%)的偏差。     

Structural and electronic properties of zirconia phases: A FP-LAPW investigations

The structural and electronic properties of ZrO₂ polymorphs were investigated using density functional theory (DFT). The Kohn–Sham equations were solved by applying the full-potential linearized augmented plane wave (FP-LAPW) method. We used the generalized gradient approximation (GGA) in the Perdew–Wang formalism to the exchange and correlation energy functional. The ground state properties such as lattice parameter, transition pressures, bulk modulus and its pressure derivative as well as the structural phase stability were calculated. The results were compared with previous calculations and experimental data when available. The FP-LAPW method correctly orders the zero temperature energies of all zirconia polymorphs. We have also studied the effect of distortion from the cubic to the tetragonal structure on the basis of charge density calculations. On the other hand, band structure and density of states (DOS), which allow us to discuss the features of orbital mixing, are also given. Our results suggest that the cotunnite structure should be better than the other zirconia phases as gate dielectric material.     

Density functional theory study of tin and titanium dioxides: Structural and mechanical properties in the tetragonal rutile phase

Structural and mechanical properties in rutile (tetragonal) phases of SnO₂ and TiO₂ are investigated by performing first-principle density functional theory (DFT) calculations. Generalized Gradient Approximation (GGA) potentials of electronic exchange and correlation part parameterized by Perdew–Burke–Ernzerhof (PBE) are used. Second order elastic stiffness constants, bulk modulus, first-derivative of bulk modulus, and pressure behavior of these mechanical properties are studied up to pressure of 10 GPa. Structural properties and elastic constants of SnO₂ and TiO₂ calculated in this study are compatible with experimental and other available theoretical studies. Electronic band gap energies of these semiconductors are also calculated. As expected, the calculated values by standard DFT calculations are underestimated in comparison to experimental values.     

Annealing and light effect on optical and electrical properties of ZnS thin films grown with the SILAR method

Zinc sulphide (ZnS) thin films were grown on glass substrates by the Successive Ionic Layer Adsorption and Reaction (SILAR) technique at room temperature and ambient pressure. Surface morphologies of grown films were characterized using scanning electron microscopy (SEM). The crystal structure and crystal size of the thin films were characterized by the X-ray diffraction (XRD) method and found that the films exhibit polycrystalline characterization. The optical absorption measurements were done as a function of the temperature at 10–320 K temperature range. Using absorption measurements, the band gap energies were calculated at 10 and 320 K, as 3.83 and 3.72 eV, respectively. The annealing temperature effect on optical band gap and the light effect on the electrical properties of ZnS thin films were investigated and it was found that the current increased with increasing light intensity. The annealed films were found have more resistance than the as-grown film.     

First-principles calculation of atomic configurations of carbon and tin near the surface of a silicon thin film used for solar cells

To achieve higher engineering efficiency in solar cells, group-IV compound semiconductors, such as silicon (Si) or germanium (Ge), in the form of thin films containing carbon (C) and/or tin (Sn) atoms, are gaining attention as alternatives to poly-silicon crystals. Atomic configurations of C and Sn atoms near the (001) surface of a Si thin film were analyzed by first-principles calculation based on density functional theory (DFT). The results of the analysis are threefold. First, C and Sn atoms are most stable at the first atomic layer of the Si thin film, and the surface does not affect the stability of C or Sn atoms deeper than the fifth layer. Second, C and Sn atoms deeper than the fifth layer do not affect the stability of newly arrived C and Sn atoms at the surface during film growth. The effects of the (001) surface and interacting C and/or Sn atoms on the thermal-equilibrium concentrations of C and Sn in each layer of the Si thin film were evaluated in consideration of the degeneracy of the atomic configurations. Third, in the case of mono-doping, formation energy of C (Sn) at the (001) surface increases with increasing concentration of surface C (Sn). In the case of co-doping at C/Sn concentration ratio of 1:1, the formation energies of C and Sn decrease with increasing surface concentrations of C and Sn. It is concluded from these results that co-doping enhances the incorporation of C and Sn atoms in the Si thin film.     

Optimising conditions for the growth of nanocrystalline ZnS thin films from acidic chemical baths

The growth of nanocrystalline zinc sulfide thin films onto glass substrates by chemical bath deposition has been optimized at acidic pH. Powder X-ray diffraction (p-XRD) confirms the deposition of sphalerite, the cubic phase of ZnS. The crystallite size calculated by Scherrer equation was found to be 4.0 nm. Scanning Electron Microscopy (SEM) show clusters of spherical nanoparticles uniformly distributed over the surface of the glass substrates. Energy Dispersive X-ray (EDX) analysis of the deposited thin films show the zinc to sulfur ratio close to 1:1. The observed band gap (3.78 eV) of the deposited thin films is higher than that reported for cubic phase of bulk ZnS (3.54 eV) as expected due to nano-size crystallites. Binding energies calculated by X-ray Photoelectron Spectroscopy (XPS) confirm the material as ZnS and the photoluminescence measurements show the blue shift in emission maximum.     

薄膜应力测量方法研究

总结了薄膜应力的一些测量方法。将经常使用的方法归纳为激光宏观变形分析法和X射线分析法。介绍了利用测量基片弯曲曲率的激光宏观变形分析法(包括激光干涉法和激光束偏转法)和品格变形的X射线衍射法等测量薄膜应力的理论依据及其测量原理,计算了各种测量方法的测量精度,X射线分析法的精度最高,其次是激光干涉法,而激光束偏转法的精度最低,分析了激光分析法和X射线分析法的优缺点。     

有机紫外半导体PMTC的制备及理论计算研究

进行了有机紫外半导体N-[5-甲基-1,3,4-噻二唑-2-取代]二硫代氨基甲酸钾(PMTC)的制备及FT-IR、Raman、UV-Vis及PL光谱实验表征。对实验测试FT-IR及Raman光谱的振动峰进行了归属,Raman光谱测试发现S-K在152 cm-1有v(S-K-S)伸缩振动。UV-Vis实验光谱表明PMTC在200～350nm波段有紫外吸收,PL实验光谱表明PMTC在340～400 nm波段有明显的紫外发光峰,峰值波长为373 nm,PL谱相对于吸收光谱有Stokes频移。采用密度泛函理论(DFT)方法对PMTC进行了B3LYP/6-31G水平上的分子结构优化、UV-Vis光谱、分子前线轨道、分子电子密度、Mulliken电荷等理论计算。理论研究结果表明:PMTC在UV-Vis波段有三个电子跃迁吸收。前线轨道计算表明PMTC的HOMO的电子主要分布在与K原子相连的两个S原子上,而LUMO轨道的电子主要集中在K原子上,PMTC吸收光子后,产生电子由HOMO至LUMO跃迁的实质是电子由配体(主要是配位S原子)向金属原子K的转移。     

Real-time carbon content control for PECVD ZrO/sub 2/ thin-film growth

We present a methodology for real-time control of thin-film carbon content in a plasma-enhanced metal-organic chemical vapor deposition process using combination of online gas phase measurements obtained through optical emission spectroscopy and off-line (ex situ) measurements of film composition obtained via X-ray photoelectron spectroscopy (XPS). Initially, an estimation model of carbon content of ZrO/sub 2/ thin films based on real-time optical emission spectroscopy data is presented. Then, a feedback control scheme, which employs the proposed estimation model and a proportional-integral controller, is developed to achieve carbon content control. Using this approach, a real-time control system is developed and implemented on an experimental electron cyclotron resonance high-density plasma-enhanced chemical vapor deposition system to demonstrate the effectiveness of real-time feedback control of carbon content. Experimental results of depositions and XPS analysis of deposited thin films under both open-loop and closed-loop operations are shown and compared. The advantages of operating the process under real-time feedback control in terms of robust operation and lower carbon content are demonstrated.     

薄膜电致发光器件中硫空位的散射作用

利用分波法计算了薄膜电致发光器件中硫空位对电子的散射速率,并将其与其它散射机制进行了比较。研究了散射速率与电子能量及温度的关系,并比较了硫空位俘获电子前后的散射速率。提出硫空位的存在是阻碍获得高亮度蓝色薄膜电致发光器件的关键。     

Toxic CO detection by B12N12 nanocluster

We have studied the adsorption of carbon monoxide (CO) on boron nitride nanocluster (B₁₂N₁₂) using density functional theory (DFT) through three different functionals. In contrary to the pristine boron nitride and carbon nanotubes, we found that CO adsorption can induce significant change in the cluster electronic properties, suggesting that B₁₂N₁₂ may be a potential sensor for CO detection. It was also found that the geometry parameters of the obtained structures are not sensitive to the used functional, while the energy values show strong dependency. The results indicated that the most stable configuration of the CO/cluster is a vertical orientation of the CO molecule on B₁₂N₁₂ cluster so that the C atom of CO is close to the B atom of the cluster with adsorption energy of 0.15–0.34 eV, based on the three functionals.     

Thickness‐Dependent Structural Evolutions and Growth Models in Relation to Carrier Transport Properties in Polycrystalline Pentacene Thin Films

Thickness‐dependent crystal structure, surface morphology, surface energy, and molecular structure and microstructure of a series of polycrystalline pentacene films with different film thickness ranging from several monolayers to the several hundred nanometers have been investigated using X‐ray diffraction (XRD), atomic force microscopy (AFM), contact angle meter, and Raman spectroscopy. XRD studies indicate that thin film polymorphs transformation behaviours are from the orthorhombic phase to the thin‐film phase and then to the triclinic bulk phase as measured by the increased tilt angle (θ_tilt) of the pentacene molecule from the c‐axis toward the a‐axis. We propose a growth model that rationalizes the θ_tilt increased along with increasing film thickness in terms of grain size and surface energy varying with film growth using AFM combined with contact angle measurements. The vibrational characterizations of pentacene molecules in different thickness films were investigated by Raman spectroscopy compared to density functional theory calculations of an isolated molecule. In combination with XRD and AFM the method enables us to distinguish the molecular microstructures in different thin film polymorphs. We proposed a methodology to probe the microscopic parameters determining the carrier transport properties based on Davydov splitting and the characteristics of aromatic C–C stretching modes in Raman spectra. When compared to the triclinic bulk phase at a high thickness, we suggest that the first few monolayer structures located at the dielectric surface could have inferior carrier transport properties due to weak intermolecular interactions, large molecular relaxation energy, and more grain boundaries.     

Low-voltage organic phototransistors based on naphthyl end-capped oligothiophene nanofibers

Organic crystalline semiconductors with highly ordered molecular packing could be vital components in novel low power consumption light sensors due to their unique light absorption and charge carrier transport properties. In this work, we show that nanofibers made from naphthyl end-capped bithiophenes can be used for low-voltage, high responsivity organic phototransistors (OPTs). Density functional theory (DFT) calculations have been carried out to estimate the device properties related to charge transport and photon absorption. In terms of the calculation of the reorganization energy upon charge transfer, we used an extended method to include inter-molecule interactions. Experimentally, the device performance of the 5,5-bis(naphthyl)-2,2′-bithiophene (NaT2) nanofiber OPTs has been compared with that of a thin film OPT with inferior molecular ordering. The better photoresponsivity of the nanofiber OPT compared with the thin film OPT under monochromatic illumination at various wavelengths suggests that the NaT2 nanofiber-based OPTs have great potential to be used as high performance nano-scale light detectors. Moreover, the absorption of the nanofiber-based OPTs is also polarization sensitive, which provides another advantage of nanofiber-based devices in terms of potential novel sensor design.     

Secondary-emission properties of the 2D-ordered linear chain carbon films

The secondary emission of thin films of the 2D-ordered linear-chain carbon (LCC) with a thickness of 100 nm are studied using transmission measurements at various energies of primary electrons. It is demonstrated that the coefficient of secondary emission of the LCC films substantially depends on the extraction field strength on the opposite side of the film and reaches a maximum value of 56 at a field strength of about 2 kV/cm.