Unveiling localized electronic properties of ReS2 thin layers at nanoscale using Kelvin force probe microscopy combined with tip-enhanced Raman spectroscopy

Electronic properties of two-dimensional(2D) materials can be strongly modulated by localized strain. The typical spatial resolution of conventional Kelvin probe force microscopy(KPFM) is usually limited in a few hundreds of nanometers, and it is difficult to characterize localized electronic properties of 2D materials at nanoscales. Herein, tip-enhanced Raman spectroscopy(TERS) is proposed to combine with KPFM to break this restriction. TERS scan is conducted on ReS2bubbles deposited on a rough Au thin film to obtain strain distribution by using the Raman peak shift. The localized contact potential difference(CPD) is inversely calculated with a higher spatial resolution by using strain measured by TERS and CPD-strain working curve obtained using conventional KPFM and atomic force microscopy. This method enhances the spatial resolution of CPD measurements and can be potentially used to characterize localized electronic properties of 2D materials.

Fast Fabrication and Judgement of Tip-Enhanced Raman Spectroscopy-Active Tips

The quality of the scanning tip is crucial for tip-enhanced Raman spectroscopy(TERS)experiments towards large signal enhancement and high spatial resolution.In this work,we report a controllable fabrication method to prepare TERS-active tips by modifying the tip apex at the atomic scale,and propose two important criteria to in-situ judge the tip’s TERS activity for tip-enhanced Raman measurements.One criterion is based on the downshift of the first image potential state to monitor the coupling between the far-field incident laser and near-field plasmon;the other is based on the appearance of the low-wavenumber Raman peaks associated with an atomistic protrusion at the tip apex to judge the coupling efficiency of emissions from the near field to the far field.This work provides an effective method to quickly fabricate and judge TERS-active tips before real TERS experiments on target molecules and other materials,which is believed to be instrumental for the development of TERS and other tip-enhanced spectroscopic techniques.

Recent advances in tip-enhanced Raman spectroscopy probe designs

Tip-enhanced Raman spectroscopy(TERS)imaging is a super-resolution imaging technique that features the merits of both surface-enhanced Raman spectroscopy(SERS)and scanning probe microscopy(SPM),such as the high chemical sensitivity from the former and the nanoscale spatial resolution from the latter.These advantages make TERS an essential nanospectroscopic characterization technique for chemical analysis,materials science,bio-sensing,etc.TERS probes,the most critical factor determining the TERS imaging quality,are expected to provide a highly confined electromagnetic hotspot with a minimized scattering background for the generation of Raman signals with high spatial resolution.After two decades of development,numerous probe design concepts have been proposed and demonstrated.This review provides a comprehensive overview of the state-of-the-art TERS probe designs,from the working mechanism to the practical performance.We start with reviewing the recent development of TERS configurations and the corresponding working mechanisms,including the SPM platforms,optical excitation/collection techniques,and probe preparation methods.We then review the emerging novel TERS probe designs,including the remote-excitation probes,the waveguide-based nanofocusing probes,the metal-coated nanofocusing probes,the nanowire-assisted selective-coupling probes,and the tapered metal-insulator-metal probes.Our discussion focuses on a few critical aspects,including the surface-plasmon-polariton(SPP)hotspot excitation technique,conversion efficiency,working frequency,and controllability.In the end,we review the latest TERS applications and give a perspective on the future of TERS.

Probing On-Surface Chemistry at the Nanoscale Using Tip-Enhanced Raman Spectroscopy

Chemistry on solid surfaces is central to many research areas of practical interest,such as synthesis,catalysis,electrochemistry,photochemistry,and materials science.A comprehensive understanding of the nanoscale on-surface chemistry involved in these areas is important for establishing composition-structure-performance relationships.With the rapid development of tip-enhanced Raman spectroscopy(TERS),it has become possible to investigate physical and chemical processes on suitable surfaces at the nanoscale level and in real space.In this review,after a brief introduction of the background of onsurface chemistry and TERS,we systematically discuss the progress in the application of TERS in this field.Our focus is the applications of TERS to nanoscale coordination processes,decomposition reactions,polymerization processes,electrochemical reactions,catalytic chemistry,and functionalization chemistry on solid surfaces.We conclude by discussing the future challenges and development of TERS techniques and related applications in on-surface chemistry.

Surface bonding on silicon surfaces as probed by tip-enhanced Raman spectroscopy

Tip-enhanced Raman spectroscopy (TERS) has been used to obtain the Raman signal of surface species on silicon single crystal surfaces without the necessity for surface enhancement by addition of Ag nanoparticles. By illuminating the hydrogen terminated silicon surface covered with a droplet of 4-vinylpyridine with UV light, a 4-ethylpyridine modified silicon surface can be easily obtained. By bringing a scanning tunneling microscope (STM) Au tip with a nanoscale tip apex to a distance of ca. 1 nm from the modified silicon surface, enhanced Raman signals of the silicon phonon vibrations and the surface-bonded 4-ethylpyridine were obtained. The Raman enhancement factor was estimated to be close to 107. By comparing the surface enhanced Raman scattering (SERS) signal obtained after surface enhancement with Ag nanoparticles and the TERS signal of the surface, the advantage of TERS over SERS for characterizing the surface species on substrates becomes apparent: TERS readily affords vibrational information about the system without disturbing it by surface enhancement. In this sense, TERS can be considered a truly non-invasive tool which is ideal for characterizing the actual surface species on substrates.

In situ infrared, Raman and X-ray spectroscopy for the mechanistic understanding of hydrogen evolution reaction

Hydrogen production by water reduction reactions has received considerable attention because hydrogen is considered a clean-energy carrier,key for a sustainable energy future.Computational methods have been widely used to study the reaction mechanism of the hydrogen evolution reaction(HER),but the calculation results need to be supported by experimental results and direct evidence to confirm the mechanistic insights.In this review,we discuss the fundamental principles of the in situ spectroscopic strategy and a theoretical model for a mechanistic understanding of the HER.In addition,we investigate recent studies by in situ Fourier transform infrared(FTIR),Raman spectroscopy,and X-ray absorption spectroscopy(XAS) and cover new findings that occur at the catalyst-electrolyte interface during HER.These spectroscopic strategies provide practical ways to elucidate catalyst phase,reaction intermediate,catalyst-electrolyte interface,intermediate binding energy,metal valency state,and coordination environment during HER.

Investigation on Binding between Cations and Amides using UV Raman Spectroscopy

The interaction of proteins with salt ions plays an important role in life activities.We used butyramide as a model molecule to investigate the interaction of protein backbones with cations.The experiment was performed in an aqueous solution of metal chloride using UV Raman spectroscopy.It was found that well-hydrated metal cations(Ca^(2+),Mg^(2+))tend to bind to C=O in the amide bond,resulting in redistribution of the amide I band peaks.Specifically,the peak intensity ratio of 1655 cm^(-1)to 1610 cm^(-1)increases significantly with increasing concentrations.However,this phenomenon is not obviously observed in NaCl solution.Furthermore,we studied the effect of salt ions on the water structures.The addition of Ca^(2+)and Mg^(2+)is beneficial to the enhancement of the water signal at the 3400 cm^(-1)position,while the Na^(+)at the same concentration is not obvious.The results have shown that the interaction between cations and amides satisfies the following order:Ca^(2+)>Mg^(2+)>Na^(+),which conforms to the Hofmeister series.

Rapid and real-time analysis of multi-component dissolved gas in seawater by Raman spectroscopy combined with continuous gas-liquid separator

Rapid and sensitive detection of dissolved gases in seawater is quite essential for the investigation of the global carbon cycle.Large quantities of in situ optical detection techniques showed restricted measurement efficiency,owing to the single gas sensor without the identification ability of multiple gases.In this work,a novel gas-liquid Raman detection method of monitoring the multi-component dissolved gases was proposed based on a continuous gas-liquid separator under a large difference of partial pressure.The limit of detection(LOD)of the gas Raman spectrometer could arrive at about 14 ml·L^(-1)for N_(2)gas.Moreover,based on the continuous gas-liquid separation process,the detection time of the dissolved gases could be largely decreased to about 200 s compared with that of the traditional detection method(30 min).Effect of equilibrium time on gas-liquid separation process indicated that the extracted efficiency and decay time of these dissolved gases was CO_(2)>O_(2)>N_(2).In addition,the analysis of the relationship between equilibrium time and flow speed indicated that the decay time decreased with the increase of the flow speed.The validation and application of the developed system presented its great potential for studying the components and spatiotemporal distribution of dissolved gases in seawater.

Rapid analysis of Chinese steamed bread staling using Raman Spectroscopy

Staling is an important issue that Chinese steamed bread(CSB)may encounter during storage,which significantly affects their taste,flavor,and nutritional value.The monitoring technology for rapid aging is particularly important to effectively control the aging process of CSB,reduce quality deterioration,and promote the industrial production of CSB.Raman spectroscopy has been widely used in the study of food structure and properties due to its non-destructive and high-sensitivity characteristics,particularly demonstrating unique advantages in the analysis of starch structure.This study explored the possibility of analyzing the staling of CSB using Raman spectroscopy based on hardness and moisture content.Analysis of the correlation between the hardness of CSB and the full width at half maximum(FWHM)at 480 cm^(−1)during storage was conducted,and a significant positive correlation between them was found,with R^(2)above 0.8.Besides,nine characteristic peaks of CSB samples related to starch were selected for analysis.As the moisture content of CSB decreased,the peak intensities and areas of showed an upward trend during storage,with the best correlation coefficient above 0.8 revealed by linear regression analysis.Therefore,Raman spectra could be used as a potential method for the fast prediction of CSB staling.

Principle, system, and applications of tip-enhanced Raman spectroscopy

Raman spectroscopy is a powerful technique in chemical information characterization. However, this spectral method is sub- ject to two obstacles in nano-material detection. One is diffraction limited spatial resolution, and the other is its inherent small Raman cross section and weak signaling. To resolve these problems, a new approach has been developed, denoted as tip-enhanced Raman spectroscopy （TERS）. TERS is capable of high-resolution and high-sensitivity detection and demonstrat- ed to be a promising spectroscopic and micro-topographic method to characterize nano-materials and nanostructures. In this paper, the principle and experimental system of TERS are discussed. The latest application of TERS in molecule detection, bi- ological specimen identification, nanao-material characterization, and senti-conductor material determination with some spe- cific experimental examples are presented.

Scanning Raman Picoscopy: Angstrom-Resolved Tip-Enhanced Raman Spectromicroscopy

In this review,we present a brief overview on the recent advances in Angstr6m-resolved tip-enhanced Raman spectromicroscopy.We first introduce the theoretical understanding of the confinement of light at the atomistic scale,and explain how the Raman scattering from a single molecule happens under the“illumination”of such an atomically confined light.Then we describe the latest developments on Angstr6m-resolved tipenhanced Raman spectromicroscopy,particularly on a new methodology called“scanning Raman picoscopy”for visually cons true ting the chemical st ruc ture of a single molecule in real space.Finally,we give a perspective of this technique in various applications where iden ti fying the chemical st ruc tu res of mat erials at the chemical bond level is required.

基于Raman光谱的3,5-二氨基-1,2,4-三唑(DAT)合成反应在线监测与反应机理探究——推荐一个仪器分析综合实验

本实验介绍了一个仪器分析综合性实验——基于Raman光谱的3,5-二氨基-1,2,4-三唑(DAT)合成的在线监测与反应机理探究。该实验是一个科研转化的仪器分析综合实验,内容包括DAT的合成、基于Raman光谱的合成反应过程在线监测以及合成反应机理解析。在实验中,采用化学计量学方法对Raman光谱数据进行处理和分析,以更深入地理解合成反应的机理。通过本实验,可以巩固学生的化学专业知识,提高学生的综合实验操作技能,激发学生对科学研究的兴趣,培养学生的科研探究能力。

基于Raman的复方柳安咖注射液主要成分分析

本文应用拉曼光谱技术对复方柳安咖注射液的主要成分及含量进行了分析。首先测试分析了62个复方柳安咖注射液样品的拉曼光谱,结果表明62个注射液样品的拉曼光谱主要由水杨酸钠、安替比林和咖啡因的水溶液拉曼谱带组成;进一步利用密度泛函理论(DFT)计算了其主要成分的理论拉曼光谱和红外光谱,与实验测定的固体粉末光谱和溶液光谱进行比较分析,进而对复方柳安咖注射液拉曼光谱谱峰的振动模式进行了归属;最后利用水杨酸钠和安替比林浓度梯度溶液拉曼光谱特征峰的峰高和峰面积,分别建立定量分析模型,对62个复方柳安咖注射液样品中主要成分水杨酸钠和安替比林的含量进行预测,并与液相色谱法测试值进行了对比,结果显示预测值与液相色谱法测试值相近,得到了较好的主要成分含量预测结果。研究结果可为复方柳安咖注射液药剂的生产、药品质量的监控、药品光谱分析研究等方面提供参考。

A core-satellite self-assembled SERS aptasensor containing a“biological-silent region”Raman tag for the accurate and ultrasensitive detection of histamine

Herein,a novel interference-free surface-enhanced Raman spectroscopy(SERS)strategy based on magnetic nanoparticles(MNPs)and aptamer-driven assemblies was proposed for the ultrasensitive detection of histamine.A core-satellite SERS aptasensor was constructed by combining aptamer-decorated Fe_(3)O_(4)@Au MNPs(as the recognize probe for histamine)and complementary DNA-modified silver nanoparticles carrying 4-mercaptobenzonitrile(4-MBN)(Ag@4-MBN@Ag-c-DNA)as the SERS signal probe for the indirect detection of histamine.Under an applied magnetic field in the absence of histamine,the assembly gave an intense Raman signal at“Raman biological-silent”region due to 4-MBN.In the presence of histamine,the Ag@4-MBN@Ag-c-DNA SERS-tag was released from the Fe_(3)O_(4)@Au MNPs,thus decreasing the SERS signal.Under optimal conditions,an ultra-low limit of detection of 0.65×10^(-3)ng/mL and a linear range 10^(-2)-10^5 ng/mL on the SERS aptasensor were obtained.The histamine content in four food samples were analyzed using the SERS aptasensor,with the results consistent with those determined by high performance liquid chromatography.The present work highlights the merits of indirect strategies for the ultrasensitive and highly selective SERS detection of small biological molecules in complex matrices.

Recent advances in Raman spectroscopy for skin diagnosis

The skin is the largest organ in humans.It comprises about 16%of our body.Many diseases originate from the skin,including acne vulgaris,skin cancer,fungal skin disease,etc.As a common skin cancer in China,melanoma alone grows at year rate of nearly 4%.Therefore,it is crucial to develop an objective,reliable,accurate,non-invasive,and easy-to-use diagnostic method for skin diseases to support clinical decision-making.Raman spectroscopy is a highly specic imaging technique,which is sensitive,even to the single-cell level in skin diagnosis.Raman spectroscopy provides a pattern of signals with narrow bandwidths,making it a common and essential tool for researching individual characteristics of skin cells.Raman spectroscopy already has a number of clinical applications,including in thyroid,cervical and colorectal cancer.This review will introduce the advantages and recent developments in Raman spectroscopy,before focusing on the advances in skin diagnosis,including the advantages,methods,results,analysis,and notications.Finally,we discuss the current limitations and future progress of Raman spectroscopy in the context of skin diagnosis.

Quantification of radiation damage in natural and synthetic zircon by Raman spectroscopy:application to low-temperature thermochronology

Due to its ubiquitous occurrence in igneous,metamorphic,and sedimentary rocks and its wide application in geochronology and geochemistry,zircon has become the most widely used accessory mineral in the geological community.Nevertheless,the decay of U and Th causes radiation damage to the zircon structure,resulting in various degrees of metamictization,which can affect the accuracy of U–Pb dates and Hf and O isotope results.If the degree of zircon radiation damage can be quantified,the influence on geochemical analyses can be evaluated,and the results can be corrected more precisely.In this paper,synthetic and natural zircon crystals with different crystallization ages were selected for Raman spectroscopy analysis,cathodoluminescence imaging,and determination of the U and Th concentrations.The results show that Raman FWHM(full width at half bandmaximum)and Raman shift correlate with alpha dose(Da)ofzirconsfollowingtheseequations,FWHM=44.36(±2.32)×[1-exp(-2.74×Da)]-+1.7(±0.19),Raman Shift=-6.53×Da+1007.69.Analysis of synthetic zircon crystals shows that doped REEs(rare earth elements and P)can also lead to an increase in the FWHM.However,this effect can be ignored for natural zircon samples with REE contents at a normal level of hundreds to a few thousand ppm.The FWHM and Raman shift can be used as proxies to measure the degree of zircon radiation damage.Using the updated equations to calculate the latest age when zircon began to accumulate radiation damage,a more accurate and more meaningful“radiation damage age”can be obtained.

LiF-ZrF_(4)熔盐体系离子结构的Raman光谱

采用Raman光谱和量子化学计算相结合的方法,研究了803~1 086 K下,ZrF_(4)摩尔分数为10%~60%的LiF-ZrF_(4)熔盐体系的离子结构特征及变化规律.研究结果表明:熔体中含有ZrF_(5)^(-),ZrF_(6)^(2-),ZrF_(7)^(3-)和ZrF_(8)^(4-)四种络合阴离子团,其中以ZrF_(7)^(3-)和ZrF_(8)^(4-)为主,二者摩尔分数之和高达90%~94%,ZrF_(5)^(-)和ZrF_(6)^(2-)含量较少.在熔盐升温初始阶段,熔盐中发生ZrF_(7)^(3-)与ZrF_(6)^(2-)生成ZrF_(8)^(4-)和ZrF_(5)^(-)的反应(ZrF_(7)^(3-)+ZrF_(6)^(2-)→ZrF_(8)^(4-)+ZrF_(5)^(-));到达一定温度后,熔盐中发生ZrF_(8)^(4-)与ZrF_(6)^(2-)生成ZrF_(7)^(3-),ZrF_(5)^(-)和F-的反应(ZrF_(8)^(4-)+ZrF_(6)^(2-)→ZrF_(7)^(3-)+ZrF_(5)^(-)+2F-).随着ZrF_(4)质量分数增加,熔盐中ZrF_(5)^(-)含量增加,ZrF_(6)^(2-),ZrF_(7)^(3-)和ZrF_(8)^(4-)的含量减少.

Determination of esophageal squamous cell carcinoma and gastric adenocarcinoma on raw tissue using Raman spectroscopy

BACKGROUND Cancer detection is a global research focus,and novel,rapid,and label-free techniques are being developed for routine clinical practice.This has led to the development of new tools and techniques from the bench side to routine clinical practice.In this study,we present a method that uses Raman spectroscopy(RS)to detect cancer in unstained formalin-fixed,resected specimens of the esophagus and stomach.Our method can record a clear Raman-scattered light spectrum in these specimens,confirming that the Raman-scattered light spectrum changes because of the histological differences in the mucosal tissue.AIM To evaluate the use of Raman-scattered light spectrum for detecting endoscopically resected specimens of esophageal squamous cell carcinoma(SCC)and gastric adenocarcinoma(AC).METHODS We created a Raman device that is suitable for observing living tissues,and attempted to acquire Raman-scattered light spectra in endoscopically resected specimens of six esophageal tissues and 12 gastric tissues.We evaluated formalin-fixed tissues using this technique and captured shifts at multiple locations based on feasibility,ranging from six to 19 locations 200 microns apart in the vertical and horizontal directions.Furthermore,a correlation between the obtained Raman scattered light spectra and histopathological diagnosis was performed.RESULTS We successfully obtained Raman scattered light spectra from all six esophageal and 12 gastric specimens.After data capture,the tissue specimens were sent for histopathological analysis for further processing because RS is a label-free methodology that does not cause tissue destruction or alterations.Based on data analysis of molecular-level substrates,we established cut-off values for the diagnosis of esophageal SCC and gastric AC.By analyzing specific Raman shifts,we developed an algorithm to identify the range of esophageal SCC and gastric AC with an accuracy close to that of histopathological diagnoses.CONCLUSION Our technique provides qualitative information for real-time morphological diagnosis.However,further in vivo evaluations require an excitation light source with low human toxicity and large amounts of data for validation.

Reconstructing in vivo spatially offset Raman spectroscopy of human skin tissue using a GPU-accelerated Monte Carlo platform

As one type of spatially offset Raman spectroscopy(SORS), inverse SORS is particularly suited to in vivo biomedical measurements due to its ring-shaped illumination scheme. To explain inhomogeneous Raman scattering during in vivo inverse SORS measurements, the light–tissue interactions when excitation and regenerated Raman photons propagate in skin tissue were studied using Monte Carlo simulation. An eight-layered skin model was first built based on the latest transmission parameters. Then, an open-source platform, Monte Carlo e Xtreme(MCX), was adapted to study the distribution of 785 nm excitation photons inside the model with an inverse spatially shifted annular beam. The excitation photons were converted to emission photons by an inverse distribution method based on excitation flux with spatial offsets Δs of 1 mm, 2 mm, 3 mm and 5 mm. The intrinsic Raman spectra from separated skin layers were measured by continuous linear scanning to improve the simulation accuracy. The obtained results explain why the spectral detection depth gradually increases with increasing spatial offset, and address how the intrinsic Raman spectrum from deep skin layers is distorted by the reabsorption and scattering of the superficial tissue constituents. Meanwhile, it is demonstrated that the spectral contribution from subcutaneous fat will be improved when the offset increases to 5 mm, and the highest detection efficiency for dermal layer spectral detection could be achieved when Δs = 2 mm. Reasonably good matching between the calculated spectrum and the measured in vivo inverse SORS was achieved, thus demonstrating great utility of our modeling method and an approach to help understand the clinical measurements.

Accurate quantification of TiO_(2)(B)'s phase purity via Raman spectroscopy

Bronze phase titanium dioxide(TiO_(2)(B))could be a promising high-power anode for lithium ion battery.However,TiO_(2)(B)is a metastable material,so the as-synthesized samples are inevitably accompanied by the existence of anatase phases.It has been found that the TiO_(2)(B)'s purity is positively correlated with its electrochemical performance.Herein,we have established an accurate quantification of the TiO_(2)(B)/anatase ratio,by figuring out the function between the purity of TiO_(2)(B)phase in the high purity range and its Raman spectra features in combination of the calibration by the synchrotron radiation X-ray diffraction(XRD).Compared with the time-consuming electrochemical method,the rapid,sensitive and non-destructive features of Raman spectroscopy have made it a promising candidate for determining the purity of TiO_(2)(B).Further,the correlations developed in this work should be instructive in synthesizing pure TiO_(2)(B)and furthermore optimizing its electrochemical charge storage properties.