Site-Selective Excitation of Ti Ions in Rutile TiO via Anisotropic Intra-Atomic 3d → 3d Transition.

Site-selective excitation (SSE), which is usually realized by tuning the wavelength of absorbed light, is an ideal way to study bond-selective chemistry, analyze the crystal structure, investigate protein conformation, etc., eventually leading to active manipulation of desired processes. Herein, SSE has been explored in (110)-, (100)-, and (011)-faced rutile TiO, a prototypical material in both surface science and photocatalysis fields.

Unveiling the Intrinsic Photophysics in Quasi-Two-Dimensional Perovskites.

The two-dimensional (2D) perovskites have drawn intensive attention due to their unique stability and outstanding optoelectronic properties. However, the debate surrounding the spatial phase distribution and band alignment among different 2D phases in the quasi-2D perovskite has created complexities in understanding the carrier dynamics, hindering material and device development. In this study, we employed highly sensitive transient absorption spectroscopy to investigate the carrier dynamics of (BA)(MA)PbI quasi-2D Ruddlesden-Popper perovskite thin films, nominally prepared as = 4.

Noncollinear Optical Parametric Amplification of Broadband Infrared Sum Frequency Generation Vibrational Spectroscopy.

Sum-frequency generation (SFG) vibrational spectroscopy is an invaluable tool in surface science, known for its specificity to surfaces and interfaces. Despite its wide application, it is often hampered by weak signal detection. Here, we present an innovative enhancement technique of postsample amplification, using a picosecond noncollinear optical parametric amplifier (NOPA).

Vibronic coupling of Rhodamine 6G molecules studied by doubly resonant sum frequency generation spectroscopy with narrowband infrared and broadband visible.

Doubly resonant sum frequency generation (DR-SFG) serves as a potent characteristic technique for probing the electronic spectra and vibronic coupling of molecules on surfaces. In this study, we successfully developed a novel infrared (IR)-white light (WL) DR-SFG spectroscopy based on narrowband IR and tunable broadband WL. This novel method was employed to explore the excitation spectrum and vibronic couplings of sub-monolayer Rhodamine 6G molecules.

Regulating 3D Phase in Quasi-2D Perovskite Films for High-Performance and Stable Photodetectors.

The charge transport in quasi-2D perovskites limits their applications despite the superior stability and optoelectronic properties. Herein, a novel strategy is proposed to enhance the charge transport by regulating 3D perovskite phase in quasi-2D perovskite films. The carbohydrazide (CBH) as an additive is introduced into (PEA) MA Pb I precursors, which slows down the crystallization process and improves the phase ratio and crystal quality of the 3D phase.

Probing the Genuine Carrier Dynamics of Semiconducting Perovskites under Sunlight.

Understanding the nature of photogenerated carriers and their subsequent dynamics in semiconducting perovskites is important for the development of solar cell materials and devices. However, most ultrafast dynamic measurements on perovskite materials were conducted under high carrier densities, which likely obscures the genuine dynamics under low carrier densities in solar illumination conditions. In this study, we presented a detailed experimental study of the carrier density-dependent dynamics in hybrid lead iodide perovskites from femtosecond to microsecond using a highly sensitive transient absorption (TA) spectrometer.

Spatiotemporal imaging of charge transfer in photocatalyst particles.

The water-splitting reaction using photocatalyst particles is a promising route for solar fuel production. Photo-induced charge transfer from a photocatalyst to catalytic surface sites is key in ensuring photocatalytic efficiency; however, it is challenging to understand this process, which spans a wide spatiotemporal range from nanometres to micrometres and from femtoseconds to seconds. Although the steady-state charge distribution on single photocatalyst particles has been mapped by microscopic techniques, and the charge transfer dynamics in photocatalyst aggregations have been revealed by time-resolved spectroscopy, spatiotemporally evolving charge transfer processes in single photocatalyst particles cannot be tracked, and their exact mechanism is unknown.

Tandem fusion of albumin-binding domains promoted soluble expression and stability of recombinant trichosanthin in vitro and in vivo.

Trichosanthin (TCS), as a type 1 ribosome-inactivating protein, has a very high cytoplasmic activity in vitro and can quickly kill cancer cells. However, it is easily filtered and cleared by the kidney, which results in the short half-life and severely limits its application. In this study, we constructed several recombinant proteins by fusing the albumin binding domain mutant ABD035(abbreviated as ABD) to the N- or C-terminus of TCS to endow the recombinant TCS fusion protein with a longer half-life property binding with endogenous human serum albumin (HSA) via ABD to effectively exert its anti-tumor activity in vivo.

Valence Band of Rutile TiO(110) Investigated by Polarized-Light-Based Angle-Resolved Photoelectron Spectroscopy.

Band structure dictates optical and electronic properties of solids and eventually the efficiency of the semiconductor based solar conversion. Compared to numerous theoretical calculations, the experimentally measured band structure of rutile TiO, a prototypical photocatalytic material, is rare. In this work, the valence band structure of rutile TiO(110) is measured by angle-resolved photoelectron spectroscopy using polarized extreme ultraviolet light.

Chiral Hybrid Copper(I) Halides for High Efficiency Second Harmonic Generation with a Broadband Transparency Window.

Chiral hybrid organic-inorganic metal halides (HOMHs) with intrinsic noncentrosymmetry have shown great promise for applications in second-order nonlinear optics (NLO). However, established chiral HOMHs often suffer from their relatively small band gaps, which lead to negative impacts on transparent window and laser-induced damage thresholds (LDT). Here, we have synthesized two chiral HOMHs based on Cu halides, namely (R-/S-MBA)CuBr , which feature well-balanced NLO performances with a highly efficient SHG response, outstanding optical transparency, and high LDT.

Anisotropic d-d Transition in Rutile TiO.

The band gap state of TiO, which is dominated by Ti 3d character, is of great relevance to light absorption, electron trapping, charge recombination, and conduction band structure. Despite the importance, the explanation of the excitation from this state is controversial. To this end, the electronic structures of TiO(110) and TiO(011)-(2 × 1) have been systematically measured with two-photon photoemission spectroscopy.

Efficient generation of narrowband picosecond pulses from a femtosecond laser.

In some applications of broadband ultrafast spectroscopy, such as surface sum frequency generation vibrational spectroscopy, femtosecond stimulated Raman spectroscopy (SRS), and coherent anti-Stokes Raman spectroscopy, a narrowband picosecond pulse is required to obtain a high spectral resolution. Here, we present a method to generate narrowband picosecond second harmonic (SH) and fundamental frequency (FF) pulses with high-conversion efficiency from a Ti:sapphire femtosecond laser amplifier. The narrowband picosecond SH pulse was generated based on the group velocity mismatch between the SH and FF pulses in a nonlinear crystal of β-barium borate (BBO).

Ultrahigh sensitive transient absorption spectrometer.

Transient absorption (TA) spectroscopy is considered as a powerful technique that reflects the ultrafast dynamics of photogenerated carriers in photoelectric and photocatalysis materials. However, limited by its sensitivity, the photogenerated carrier density in TA measurements of solar energy materials is usually much higher than that in the real working condition. Here, we present a combination of kHz macro-pulse and MHz micro-pulse technique for an ultrahigh sensitive TA spectrometer, which improves the sensitivity to the 10 level of ΔOD.

Full diagnostics and optimization of time resolution for time- and angle-resolved photoemission spectroscopy.

Achieving a high time resolution is highly desirable for revealing the electron dynamics and light-induced phenomena in time- and angle-resolved photoemission spectroscopy (TrARPES). Here, we identify key factors for achieving the optimum time resolution, including laser bandwidth and optical component induced chirp. A full diagnostic scheme is constructed to characterize the pulse duration and chirp of the fundamental beam, second harmonic, and fourth harmonic, and prism pairs are used to compensate for the chirp.

Epitaxial Growth of Centimeter-Scale Single-Crystal MoS Monolayer on Au(111).

Two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) have emerged as attractive platforms in next-generation nanoelectronics and optoelectronics for reducing device sizes down to a 10 nm scale. To achieve this, the controlled synthesis of wafer-scale single-crystal TMDs with high crystallinity has been a continuous pursuit. However, previous efforts to epitaxially grow TMD films on insulating substrates (, mica and sapphire) failed to eliminate the evolution of antiparallel domains and twin boundaries, leading to the formation of polycrystalline films.

Single Molecule Photocatalysis on TiO Surfaces.

Heterogeneous photocatalysis has been widely applied in various fields, such as photovoltaic cell, solar water splitting, photocatalytic pollutant degradation, and so on. Therefore, the reaction mechanisms involved in these important photocatalytic processes, especially in TiO photocatalysis, have been extensively investigated by various surface science techniques in the past decade. In this review, we highlight the recent progress that provides fundamental insights into TiO photocatalysis through direct tracking the evolution of single molecule photochemistry on TiO single crystal surfaces using a combination of scanning tunneling microscopy (STM) and other surface science techniques.

Flexible high-resolution broadband sum-frequency generation vibrational spectroscopy for intrinsic spectral line widths.

The difficulty in achieving high spectral resolution and accurate line shape in sum-frequency generation vibrational spectroscopy (SFG-VS) has restricted its use in applications requiring precise detection and quantitative analysis. Recently, the development of high-resolution broadband sum-frequency generation vibrational spectroscopy (HR-BB-SFG-VS) with sub-wavenumber resolution generated by synchronizing two independent amplifier lasers have opened new opportunities for probing an intrinsic SFG response. Here, we present a new flexible approach to achieve HR-BB-SFG-VS.

Elementary Chemical Reactions in Surface Photocatalysis.

Photocatalytic hydrogen evolution and organic degradation on oxide materials have been extensively investigated in the last two decades. Great efforts have been dedicated to the study of photocatalytic reaction mechanisms of a variety of molecules on TiO surfaces by using surface science methods under ultra-high vacuum (UHV) conditions, providing fundamental understanding of surface chemical reactions in photocatalysis. In this review, we summarize the recent progress in the study of photocatalysis of several important species (water, methanol, and aldehydes) on different TiO surfaces.

A review of dynamical resonances in A + BC chemical reactions.

The concept of the transition state has played an important role in the field of chemical kinetics and reaction dynamics. Reactive resonances in the transition-state region can dramatically enhance the reaction probability; thus investigation of the reactive resonances has attracted great attention from chemical physicists for many decades. In this review, we mainly focus on the recent progress made in probing the elusive resonance phenomenon in the simple A  +  BC reaction and understanding its nature, especially in the benchmark F/Cl  +  H and their isotopic variants.

Compact ultrahigh vacuum/high-pressure system for broadband infrared sum frequency generation vibrational spectroscopy studies.

We have designed a compact ultrahigh vacuum/high-pressure system for in situ broadband infrared (IR) sum frequency generation vibrational spectroscopy (SFG-VS) studies. In this system, we have achieved a significant reduction in the distance between the sample and the optical window (<5 mm), which in turn considerably reduces the IR absorption from the gas phase under high pressure conditions. Moreover, with this new system, the IR transmission under high pressure conditions can be measured in situ for calibrating the SFG spectra.

Elementary photocatalytic chemistry on TiO2 surfaces.

Photocatalytic hydrogen production and pollutant degradation provided both great opportunities and challenges in the field of sustainable energy and environmental science. Over the past few decades, we have witnessed fast growing interest and efforts in developing new photocatalysts, improving catalytic efficiency and exploring the reaction mechanism at the atomic and molecular levels. Owing to its relatively high efficiency, nontoxicity, low cost and high stability, TiO2 becomes one of the most extensively investigated metal oxides in semiconductor photocatalysis.

Coverage Dependence of Methanol Dissociation on TiO(110).

Although the photochemistry of methanol on TiO(110) has been widely investigated as a prototypical model of the photocatalytic reaction of organic molecules, the most fundamental question of the adsorption state of methanol on TiO(110) is still unclear. We have investigated the adsorption of methanol on TiO(110) using sum frequency generation vibrational spectroscopy (SFG-VS) and density functional theory (DFT) calculations. The SFG results indicate the dissociation of methanol is highly dependent on the coverage.

Strong photon energy dependence of the photocatalytic dissociation rate of methanol on TiO2(110).

Photocatalytic dissociation of methanol (CH3OH) on a TiO2(110) surface has been studied by temperature programmed desorption (TPD) at 355 and 266 nm. Primary dissociation products, CH2O and H atoms, have been detected. The dependence of the reactant and product TPD signals on irradiation time has been measured, allowing the photocatalytic reaction rate of CH3OH at both wavelengths to be directly determined.