丁胺包裹的CdSe量子点敏化的TiO2纳米晶薄膜电子转移机制

利用超快光谱技术系统研究了在丁胺包裹的CdSe量子点敏化的TiO₂纳米晶薄膜起始时刻界面间电子转移动力学。与之前的报道不同,该实验结果表明:CdSe量子点经过表面修饰后,两相电子注入机制--热电子和冷电子注入得以被证实,即:电子能分别从CdSe量子点导带中高的振动能级和导带底转移到TiO₂的导带。该机制详细描绘了电子在纳米界面间转移的图景。进一步研究发现:热电子注入的电子耦合强度(3.6±0.1 meV)比弛豫后的基态电子注入高两个数量级,基于Marcus理论,伴随着0.083 eV的重组能,冷电子注入的耦合强度值为~50 μeV。     

过渡金属Cu、Cr掺杂TiO2表面氧化性气体NO2光学气敏传感特性

采用密度泛函理论（DFT）体系广义梯度近似（GGA）第一性原理平面波超软赝势方法,分析锐钛矿型TiO₂（101）表面吸附NO₂分子光学气敏传感的微观机理.结果表明：Cu和Cr原子易于掺入TiO₂（101）表面,掺杂表面能稳定地吸附NO₂分子且吸附后光学性质发生显著变化.表面吸附NO₂分子后,Cu掺杂TiO₂（101）表面对分子的吸附能最大,吸附后结构更稳定,分子与表面的距离最短.通过分析差分电荷密度和电荷布居数发现,NO₂分子与基底表面间发生电荷转移,转移电子数目：Cu掺杂表面 > Cr掺杂表面 > 无掺杂表面.对比吸收光谱和反射光谱发现,在Cu掺杂表面吸附分子后,光学性质变化最明显,说明表面与吸附分子间氧化还原能力是决定光学气敏传感性能的核心因素.在过渡金属中,Cu与Cr都有4s价电子结构,其4s电子降低了材料表面氧空位的氧化性,增加了其还原性.对于氧化性气体,可以提升表面与分子的氧化还原作用,而Cu的4s电子更加活泼,从而光学气敏传感特性更加明显.因此,Cu掺杂的TiO₂对氧化性气体是一种较好的光学气敏传感材料.     

Interferometric two-photon photoemission correlation technique and femtosecond wet-electron dynamics at the TiO (110) surface

The femtosecond time-resolved two-photon photoemission (TR-2PP) and the ultra high vacuum (UHV) surface science techniques are integrated to investigate the elec- tronic structures and the interfacial electron transfer dynamics at the atomically ordered adsorbate overlayers on TiO₂ single- crystalline surfaces. Our research into the CH₃OH/TiO₂ system exhibits complex dynamics, providing abundant informa- tion with regard to electron transport and solvation processes in the interfacial solvent structures. These represent the fundamentally physical, photochemical, and photocatalytic reactions of protic chemicals covered with metal-oxides.     

Transmission of low-energy (< 10 eV) O ions through Au films on TiO2(110)

In an attempt to identify the fundamental processes that influence ion transport through metallic surface layers, we have studied the transmission of O⁺ ions through discontinuous Au films adsorbed on TiO₂(110). A low energy (< 10 eV) O⁺ ion beam is generated via electron stimulated desorption when an Au-dosed TiO₂(110) substrate is bombarded with a focused 250 eV electron beam. Low energy ion scattering data indicate that Au evaporated under ultrahigh vacuum conditions at 300 K forms three-dimensional clusters on TiO₂(110). As the Au coverage increases, the formation of Au clusters on TiO₂(110) blocks a fraction of the TiO₂ surface and the O⁺ yield is attenuated. However, for high coverages (≥30% Au covered substrate) the O⁺ signal decreases at a faster rate than the TiO₂ open area fraction. We attribute the attenuation of the O⁺ yield for high Au coverages mainly to blocking of O⁺ by Au clusters, to deflection of trajectories by the image force between ions and Au clusters, and to charge transfer between desorbing O⁺ and neighboring Au clusters.     

Ferroelectric Ba0.75Sr0.25TiO3 tunable charge transfer in perovskite devices

Interfacial charge recombination is a main issue causing the efficiency loss of the perovskite solar cells (PSCs). Here, ferroelectric Ba_0.75Sr_0.25TiO₃ (BST) is introduced as a polarization tunable layer to promote the interfacial charge transfer of the PSCs. The coexistence of ferroelectric polarization and charge carriers in BST is confirmed by density functional theory (DFT) calculations. Experimental characterization demonstrates the polarization reversal and the existence of domain in BST film. The BST film conductivity is tested as 2.98×10^-4 S/cm, which is comparable to the TiO₂ being used as the electron transporting layer (ETL) in PSCs. The calculations results prove that BST can be introduced into the PSCs and the interfacial charge transfer can be tuned by ferroelectric polarization. Thus, we fabricated the BST-based PSCs with a champion power conversion efficiency (PCE) of 19.05% after poling.     

5(6)羧基荧光素敏化TiO2纳米粒子的光致电子转移的荧光特性研究

通过水解TiCl₄制备了锐钛矿结构TiO₂纳米粒子, 并用时间分辨荧光光谱研究了5(6)CFL(5(6)-Carboxyfluorescein, 简称5(6)CFL)染料敏化TiO₂纳米粒子体系的光致电子转移动力学. 5(6)CFL染料敏化TiO₂纳米粒子能形成电荷转移复合物, 这归因于染料分子的激发电子态波函数Ψ(D^*)与电荷分离态波函数Ψ(D⁺ +e^-)之间的耦合作用. 当激发5(6)CFL染料敏化TiO₂纳米粒子体系时, 电子以两种不同方式注入TiO₂纳米粒子导带: 第一, 通过5(6)CFL染料分子的激发态注入; 第二, 从电荷转移复合物(5(6)CFL/TiO₂)直接注入. 时间分辨荧光光谱表明, 在水溶液中纯5(6)CFL染料的荧光以寿命为τ₁=41 ps (74.4%) 和τ₂=3.22 ns (25.6%) 的双e指数衰减, 而5(6)CFL染料敏化TiO₂纳米粒子体系的荧光分别以时间常数为τ₁=44 ps (90.4%), τ₂=478 ps (8.6%) 和τ₃=2.41 ns (1.0%) 的三e指数衰减. 本文的研究工作能够为染料敏化太阳能电池的光致电子转移机理提供有价值的参考.     

Influence of silver doping on the photocatalytic activity of titania films

By means of X-ray diffraction, BET nitrogen adsorption, UV-Vis-NIR transmission spectroscopy, transmission electron microscope, scanning electron microscope, X-ray photoelectron spectroscopy and photodegradation of methylene blue, effects of Ag doping on the microstructure and photocatalytic activity of TiO₂ films prepared by sol–gel method were studied. It is found that with a suitable amount (2–4 mol%), the Ag dopant increases the photocatalytic activity of TiO₂ films. The mechanism can be attributed to that (1) anatase grain sizes decrease with Ag doping and the specific surface areas of doped TiO₂ films increase, the charge transfer in TiO₂ films is promoted; (2) by enhancing the electron–hole pairs separation and inhibiting their recombination, the Ag dopant enhances the charge pair separation efficiency for doped TiO₂ films.     

Luminescence of charge transfer sensitizers anchored to metal oxide nanoparticles

The photoluminescence (PL) properties of inorganic charge transfer sensitizers anchored to nanometer sized metal oxide particles are presented. The charge transfer sensitizers are inorganic coordination compounds such as ruthenium tribipyridine, Ru(bpy)²⁺₃, which have long lived metal-to-ligand charge transfer (MLCT) excited states. The metal oxides are insulators or semiconductor materials in the form of powders, colloidal solutions, and porous nanocrystalline films. Time resolved PL decays from this and related sensitizers anchored to metal oxide surfaces are highly non-exponential. The MLCT excited states are quenched on semiconducting metal oxide particles by an apparent electron transfer mechanism. With some assumptions electron transfer rates from the MLCT excited states to the nanostructured surface are calculated. The PL properties of sensitizers bound to porous nanocrystalline TiO₂ films can be controlled electrochemically.     

酰胺化合物于金属修饰的TiO2粒子表面的光催化分解

用ESR方法研究了5种脂肪酰胺化合物在经金属银修饰后的二氧化钛微粒表面光诱导电子转移和有关光催化反应行为。结果发现经修饰过的与未修饰过的TiO₂粒子的光催化特性有极为明显的差别。当体系中无TiO₂存在时,只是甲酰胺有很微弱的反应,加合物(DMPO-CONH₂)·的信号被检出,而其它4种酰胺均无ESR信号。除碳中心自由基外,还有(DMPO-OH)·信号被检出,相同条件下,采用Ag-TiO₂时ESK信号明显增强,银用量为10%时比1%的更强。因此半导体TiO₂粒子表面进行银修饰后可显著提高光催化能力。     

(Cu,N)共掺杂TiO2/MoS2异质结的电子和光学性能:杂化泛函HSE06

在密度泛函理论的基础上,系统地研究了Cu/N（共）掺杂的TiO₂/MoS₂异质结体系的几何结构、电子结构和光学性质.计算发现,TiO₂/MoS₂异质结的带隙相比于纯的TiO₂（101）表面明显变小,Cu/N（共）掺杂TiO₂/MoS₂异质结体系的禁带宽度也明显地减小,这导致光子激发能量的降低和光吸收能力的提高.通过计算Cu/N（共）掺杂TiO₂/MoS₂的差分电荷密度,发现光生电子与空穴积累在掺杂后的TiO₂（101）表面和单层MoS₂之间,这表明掺杂杂质体系可以有效地抑制光生电子-空穴对的复合.此外,我们计算了在不同压力下TiO₂/MoS₂异质结的几何、电子和光学性质,发现适当增加压力可以有效提高异质结的光吸收性能.本文结果表明,Cu/N（共）掺杂TiO₂/MoS₂异质结和对TiO₂/MoS₂异质结加压都能有效地提高材料的光学性能.     

碳量子点负载TiO_2纳米棒阵列的光电化学性能

研究了碳量子点负载的Ti O2纳米棒阵列光阳极的光电化学过程和光催化行为。实验发现碳量子点的引入使Ti O2纳米棒阵列在可见光区域的吸收强度增强,对可见光的响应电流提高3倍,光照下的开路电位增加了2.5%,光生载流子的转移和传输能力得到相应提高。光阳极对亚甲基蓝的降解特性显示,碳量子点的引入使Ti O2纳米棒在可见光照射下的催化效率由25%提高到33%。利用电化学交流阻抗谱(EIS)、MottSchottky曲线讨论了光影响下的电荷运动过程,表明Ti O2纳米棒阵列负载碳量子点后的电荷转移电阻减小,电子寿命增加;碳量子点的负载使Ti O2纳米棒的平带电位负移,导带位置提高,电子的还原能力增强。     

基于电子顺磁共振的锌卟啉敏化TiO2光催化性机理的研究

为了研究锌卟啉/TiO₂复合光催化剂的光催化效率及电子转移问题, 本文采用溶胶凝胶法制备了锌卟啉/TiO₂的混合光催化材料, 并利用紫外可见光谱、电子顺磁共振谱对锌卟啉/TiO₂复合光催化剂进行了表征与分析. 采用溶胶凝胶法制备了锌卟啉-TiO₂的混合光催化材料, 通过比较纯P25型TiO₂和掺入质量比分别为0.2%, 0.5%, 0.9%锌卟啉敏化剂的锌卟啉/TiO₂混合光催化材料的紫外可见光谱图可知, 加入适量锌卟啉敏化剂可提高TiO₂对甲基橙溶液的降解效率, 过多的掺入锌卟啉敏化剂会导致TiO₂表面被敏化剂覆盖, 从而影响了其对光子的吸收, 降低TiO₂的光催化效率, 降低TiO₂的光降解率, 甚至低于纯TiO₂的光降解率. 应用电子顺磁共振技术对锌卟啉敏化TiO₂光催化剂的光催化机理进行了合理的解释, 当使用紫外可见光源对粉末样品进行辐照时, 锌卟啉受光辐照产生的激发态电子促进具有强氧化性的Ti³⁺和超氧根自由基的生成, 从而有效的促进了光生空穴-电子对的分离, 提高了TiO₂的光催化性能.     

CdS化学修饰TiO2纳米管阵列电极的传质特性分析

通过声电阳极氧化-化学沉积的方法制备CdS修饰的TiO₂纳米管阵列,并对其进行形貌表征及光电性能和传质特性的研究。结果表明;相对于未修饰的TiO₂纳米管列电极,CdS纳米粒子的化学修饰在增强电极对可见光吸收能力的同时,可减小电荷载流子的迁移阻力而有效提高光生电荷的分离和传递速率。在超声场中进行化学沉积,CdS纳米粒子可在TiO₂纳米管壁上均匀沉积,使得传质阻力进一步降低而获得相对最大的光电流和电荷载流子密度(9.29×10¹⁹cm^-3)。     

Adsorption of CO on Ni-promoted TiO2(110)

The valence-band structure and the vibrational modes of CO adsorbed on nickel-promoted TiO₂(110) surfaces as a function of CO exposure have been studied by means of ultraviolet photoelectron spectroscopy (UPS) and high-resolution electron energy-loss spectroscopy (HREELS). It is found that CO exists in molecular form at room temperature on the nickel-promoted TiO₂(110) surfaces and most likely binds to the Ni atoms or nickel-affected sites rather than to the substrate atoms. At saturation coverage, CO molecules adsorb simultaneously on the 2-fold bridge sites and terminal sites on the (111)-oriented Ni islands deposited upon TiO₂(110). The occupation of the edge sites of Ni islands gives rise to an anomalously low frequency of the C---O stretching vibration. This frequency, indicative of a weakened C---O bond, suggests existence of a precursor to the dissociated state.     

T4有机染料敏化薄膜的超快动力学特性

利用飞秒瞬态吸收光谱和基于飞秒荧光上转换技术的飞秒时间分辨荧光动力学对T4有机染料敏化的Al₂O₃薄膜和TiO₂薄膜中的激发态过程进行了研究。对这两种敏化薄膜中的荧光动力学进行了多指数拟合。所得到T4染料敏化TiO₂薄膜中的电子注入效率为93%。此外,通过静态非均匀电子耦合模型拟合,得到T4敏化TiO₂薄膜中的电子转移速率为1.17 ps^-1。     

基于Au/TiO_2/FTO结构忆阻器的开关特性与机理研究

采用简单的一步水热法在FTO导电玻璃上外延生长了锐钛矿TiO_2纳米线,制备了具有Au/TiO_2/FTO器件结构的锐钛矿TiO_2纳米线忆阻器,系统研究了器件的阻变开关特性和开关机理.结果表明,Au/TiO_2/FTO忆阻器具有非易失的双极性阻变开关特性.同时,在103s的时间内,器件在0.1 V的电阻开关比始终保持在20以上,表明器件具有良好的非易失性.此外,器件在低阻态时遵循欧姆导电特性,而在高阻态时则满足陷阱控制的空间电荷限制电流传导机制,同时提出了基于氧空位导电细丝形成与断开机制的阻变开关模型.研究结果表明Au/TiO_2/FTO忆阻器将是一种很有发展潜力的下一代非易失性存储器.     

TiO2/SnO2 electron transport double layers with ultrathin SnO2 for efficient planar perovskite solar cells

The electron transport layer (ETL) plays an important role on the performance and stability of perovskite solar cells (PSCs). Developing double ETL is a promising strategy to take the advantages of different ETL materials and avoid their drawbacks. Here, an ultrathin SnO₂ layer of ～ 5 nm deposited by atomic layer deposit (ALD) was used to construct a TiO₂/SnO₂ double ETL, improving the power conversion efficiency (PCE) from 18.02% to 21.13%. The ultrathin SnO₂ layer enhances the electrical conductivity of the double layer ETLs and improves band alignment at the ETL/perovskite interface, promoting charge extraction and transfer. The ultrathin SnO₂ layer also passivates the ETL/perovskite interface, suppressing nonradiative recombination. The double ETL achieves outstanding stability compared with PSCs with TiO₂ only ETL. The PSCs with double ETL retains 85% of its initial PCE after 900 hours illumination. Our work demonstrates the prospects of using ultrathin metal oxide to construct double ETL for high-performance PSCs.     

TiO_2薄膜的硼掺杂对TiO_2/p~+-Si异质结器件电致发光的增强

利用磁控溅射在重掺硼硅(p+-Si)衬底上分别沉积TiO2薄膜和掺硼的TiO2(Ti O2∶B)薄膜,并经过氧气氛下600℃热处理,由此形成相应的TiO2/p+-Si和TiO2∶B/p+-Si异质结。与Ti O2/p+-Si异质结器件相比,TiO2∶B/p+-Si异质结器件的电致发光有明显的增强。分析认为:TiO2∶B薄膜经过热处理后,B原子进入TiO2晶格的间隙位,引入了额外的氧空位,而氧空位是TiO2/p+-Si异质结器件电致发光的发光中心,所以上述由B掺杂引起的氧空位浓度的增加是TiO2∶B/p+-Si异质结器件电致发光增强的原因。     

Evidence for bicarbonate formation on vacuum annealed TiO2(110) resulting from a precursor-mediated interaction between CO2 and H2O

The reaction of CO₂ and H₂O to form bicarbonate (HCO⁻₃) was examined on the nearly perfect and vacuum annealed surfaces of TiO₂(110) with temperature programmed desorption (TPD), static secondary ion mass spectrometry (SSIMS) and high resolution electron energy loss spectrometry (HREELS). The vacuum annealed TiO₂(110) surface possesses oxygen vacancy sites that are manifested in electronic EELS by a loss feature at 0.75 V. These oxygen vacancy sites bind CO₂ only slightly more strongly (TPD peak at 166 K) than do the five-coordinated Ti⁴⁺ sites (TPD peak at 137 K) typical of the nearly perfect TiO₂(110) surface. Vibrational HREELS indicates that CO₂ is linearly bound at the latter sites with a ν_a(OCO) frequency similar to the gas phase value. In contrast, oxygen vacancies dissociate H₂O to bridging OH groups which recombine to liberate H₂O in TPD at 490 K. No evidence for a reaction between CO₂ and H₂O is detected on the nearly perfect surface. In sequentially dosed experiments on the vacuum annealed surface at 110 K, CO₂ adsorption is blocked by the presence of preadsorbed H₂O, adsorbed CO₂ is displaced by postdosed H₂O, and there is little or no evidence for bicarbonate formation in either case. However, when CO₂ and H₂O are simultaneously dosed, a new CO₂ TPD state is observed at 213 K, and the 166 K state associated with CO₂ at the vacancies is absent. SSIMS was used to tentatively assign the 213 K CO₂ TPD state to a bicarbonate species. The 213 K CO₂ TPD state is not formed if the vacancy sites are filled with OH groups prior to simultaneous CO₂+H₂O exposure. Sticking coefficient measurements suggest that CO₂ adsorption at 110 K is precursor-mediated, as is known to be the case for H₂O adsorption on TiO₂(110). A model explaining the circumstances under which the proposed bicarbonate species is formed involves the surface catalyzed conversion of a precursor-bound H₂O–CO₂ van der Waals complex to carbonic acid, which then reacts at unoccupied oxygen vacancies to generate bicarbonate, but falls apart to CO₂ and H₂O in the absence of these sites. This model is consistent with the conditions under which bicarbonate is formed on powdered TiO₂, and is similar to the mechanism by which water catalyzes carbonic acid formation in aqueous solution.     

不同组分厚度比的LaMnO3/SrTiO3异质界面电子结构和磁性的第一性原理研究

基于密度泛函理论的第一性原理计算, 研究了(LaMnO₃)_n/(SrTiO₃)_m(LMO/STO)异质界面的离子弛豫、电子结构和磁性质. 研究表明, 不同组分厚度比及界面类型时, 离子弛豫程度各不相同, 并且界面处的电子性质受此影响较大. 对于n型界面, 当LMO的厚度达到6个单胞层后, 电子会从LMO转移到STO, 转移的电子占据界面层Ti原子的3d电子轨道, 界面处出现二维电子气. 对于n型界面(LMO)_n/(STO)₂, 随着LMO厚度数n的增加, 由离子弛豫造成的结构畸变减小, 而界面处Ti原子周围电子的态密度和自旋极化却增大, 表明高厚度比的n型界面有利于产生高迁移率的二维电子气和自旋极化. 而对于p型(LMO)₂/(STO)₈界面, 在STO一侧基本没有结构畸变, 界面处无电子转移和自旋极化现象. 通过计算平均静电势发现n型和p型界面处的势差大小相差2 eV, 解释了p型界面不容易发生电荷转移的原因.