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The semiconductor industry is undergoing a transformative phase, marked by the relentless drive for miniaturization and a constant demand for higher performance and energy efficiency. However, the reduction of metal–oxide–semiconductor field-effect transistor sizes for advanced technology nodes below 10 nm presents several challenges. In response, strained silicon technology has emerged as a key player, exploiting strain induction in the silicon crystal lattice to improve device performance. At the same time, there has been a growing need for characterization techniques that allow in-line monitoring of sample conditions during semiconductor manufacturing, as an alternative to traditional methods such as transmission electron microscopy or high-resolution X-ray diffraction, which have several limitations in terms of measurement time and sample destructiveness. This paper explores the application of advanced spectroscopic characterization techniques, in particular µ-Raman spectroscopy and tip-enhanced Raman spectroscopy (TERS), to meet the evolving needs of the semiconductor industry for quality control and failure analysis, increasingly requiring faster and non-destructive characterization techniques. µ-Raman provides insight into strain values and distributions of strained layers with different thicknesses and germanium concentrations, but its lateral resolution is constrained by the Abbe diffraction limit. TERS, on the other hand, emerges as a powerful non-destructive technique capable of overcoming diffraction limits by exploiting the combination of an atomic force microscope with a Raman spectrometer. This breakthrough makes it possible to estimate the chemical composition and induced strain in the lattice by evaluating the Raman peak position shifts in strained and unstrained silicon layers, providing crucial insights for nanoscale strain control. In particular, this paper focuses on the TERS characterization of Si0.7Ge0.3 epitaxial layers grown on a silicon-on-insulator device, demonstrating the effectiveness of this technique and the high lateral resolution that can be achieved. [ABSTRACT FROM AUTHOR]

Extracellular vesicles (EVs) have shown great potential as biomarkers since they reflect the physio-pathological status of the producing cell. In the context of cytotoxicity, it has been found that exposing cells to toxicants leads to changes in protein expression and the cargo of the EVs they produce. Here, we studied large extracellular vesicles (lEVs) derived from human microvascular endothelial cells (HMEC-1) to detect the modifications induced by cell exposure to benzo[a]pyrene (B[a]P). We used a custom CaF2-based biochip which allowed hyphenated techniques of investigation: surface plasmon resonance imaging (SPRi) to monitor the adsorption of objects, atomic force microscopy (AFM) to characterise EVs' size and morphology, and Raman spectroscopy to detect molecular modifications. Results obtained on EVs by Raman microscopy and tip-enhanced Raman spectroscopy (TERS) showed significant differences induced by B[a]P in the high wavenumber region of Raman spectra (2800 to 3000 cm−1), corresponding mainly to lipid modifications. Two types of spectra were detected in the control sample. A support vector machine (SVM) model was trained on the pre-processed spectral data to differentiate between EVs from cells exposed or not to B[a]P at the spectrum level; this model could achieve a sensitivity of 88% and a specificity of 99.5%. Thus, this experimental setup facilitated the distinction between EVs originating from two cell culture conditions and enabled the discrimination of EV subsets within one cell culture condition. [ABSTRACT FROM AUTHOR]

Bacteriophages are emerging as a promising alternative in combating antibiotic-resistant bacteria amidst the escalating global antimicrobial resistance crisis. Recently, there has been a notable resurgence of interest in phages, prompting extensive research into their therapeutic potential. Beyond conventional microbiology and virology techniques, such as genomics and proteomics, novel phenotypic and chemical characterization methods are being explored. Among these, there is a growing interest in vibrational spectroscopy, especially in advanced modalities such as surface-enhanced Raman spectroscopy (SERS), tip-enhanced Raman spectroscopy (TERS), and atomic force microscopy-infrared spectroscopy (AFM-IR), which offer improved sensitivity and spatial resolution. This review explores the spectrum of uses of vibrational spectroscopy for bacteriophages, including its role in diagnostics, biosensing, phage detection, assistance in phage-based therapy, and advancing basic research. [ABSTRACT FROM AUTHOR]

An analytic model is used to calculate the Raman and fluorescence enhancement of a molecule in between two closely spaced gold nanospheres. Instead of using the conventional approach that only the dipolar plasmonic mode is considered, we calculate the electric field enhancement in the nanometre sized gap, by taking account of the higher order modes in one gold sphere, which couples to the dipolar mode of the other sphere. The experimental confirmation is performed by gap-dependent tip-enhanced Raman spectroscopy (TERS) measurements. The photoluminescence and Raman enhancement are both observed with different growing trends as the gap width decreases. Red-shift of the background spectra is observed and implies the increasing coupling between the nanospheres. This analytic model is shown to be able to interpret the enhancement mechanisms underlying gap-dependent TERS experimental results.

Microcantilever probes for tip-enhanced Raman spectroscopy (TERS) have a grainy metal coating that may exhibit multiple plasmon hotspots near the tip apex, which may compromise spatial resolution and introduce imaging artefacts. It is also possible that the optical hotspot may not occur at the mechanical apex, which introduces an offset between TERS and atomic force microscope maps. In this article, a gold nanocone TERS probe is designed and fabricated for 638 nm excitation. The imaging performance is compared to grainy probes by analysing high-resolution TERS cross-sections of single-walled carbon nanotubes. Compared to the tested conventional TERS probes, the nanocone probe exhibited a narrow spot diameter, comparable optical contrast, artefact-free images, and collocation of TERS and atomic force microscope topographic maps. The 1/e² spot diameter was 12.5 nm and 19 nm with 638 nm and 785 nm excitation, respectively. These results were acquired using a single gold nanocone probe to experimentally confirm feasibility. Future work will include automating the fabrication process and statistical analysis of many probes. [ABSTRACT FROM AUTHOR]

The interaction between a probing tip and an adsorbed molecule can significantly impact the molecular chemical structure and even induce its motion on the surface. In this study, the tip-induced bond weakening, tilting, and hopping processes of a single molecule were investigated by sub-nanometre resolved tip-enhanced Raman spectroscopy (TERS). We used single carbon monoxide (CO) molecules adsorbed on the Cu (100) surface as a model system for the investigation. The vibrational frequency of the C−O stretching mode is always redshifted as the tip approaches, revealing the weakening of the C−O bond owing to tip−molecule interactions. Further analyses of both the vibrational Stark effect and TERS imaging patterns suggest a delicate tilting phenomenon of the adsorbed CO molecule on Cu(100), which eventually leads to lateral hopping of the molecule. While a tilting orientation is found toward the hollow site along the [110] direction of the Cu(100) surface, the hopping event is more likely to proceed via the bridge site to the nearest Cu neighbour along the [100] or [010] direction. Our results provide deep insights into the microscopic mechanisms of tip−molecule interactions and tip-induced molecular motions on surfaces at the single-bond level.

DNA identification is possible by detecting its components through vibrational spectroscopy. Conventional Raman, Surface-enhanced Raman spectroscopy (SERS) and Tip-enhanced Raman spectroscopy (TERS) have shown a high capacity for the exploration of different molecules and materials (semi-conducting material, carbon nanotubes and biologicals molecules as DNA, proteins). Their applications extended to biological systems and brought significant information to this field. This review summarizes a high number of studies and research conducted with conventional Raman, SERS and TERS on every DNA component starting from the four different nucleic acids in their different forms (nucleosides, deoxyribonucleosides, deoxyribonucleotides) to their biological interaction to form one and double DNA strands. As SERS has an advantage on conventional Raman by exploiting the optical properties of metallic nanostructures to detect very small quantities of molecules, it also clarifies the DNA structure's orientation in addition to its composition. It also clarifies the influence of different parameters, such as the presence of a spacer or a mutation in the strand on the hybridization process. TERS was shown as a relevant tool to scan DNA chemically and to provide information on its sequence. [ABSTRACT FROM AUTHOR]

Tip-Enhanced Raman Spectroscopy (TERS) is an advanced analytical measurement technology combining Raman spectroscopy with Scanning Probe Microscopy, which can detect the molecular structure and chemical composition in micro-nano-scale. As an indispensable part, the micromotion system directly determines TERS spatial resolution. The existing multi-axis system is often composed of several single-axis nonlinear systems, which solves whole problems with a superposition idea of single-axis part. But the multi-axis crosstalk under an overall idea is not fully considered and will cause system uncooperative and even oscillational. Therefore, a multi-axis micromotion system in TERS and its correction method are proposed. The improved Duhem model, simple calculation without inversion, accurate matching and fast response, has been built for nonlinearity. And the feedforward decoupling method is designed for crosstalk, having a favorable multi-axis coordination, good error tracking and simplified controllers. Experimental results show that it can greatly correct the nonlinearity and crosstalk of multi-axis system simultaneously. • Multi-axis correction method under an overall idea for nonlinearity and crosstalk in TERS micromotion system. • Improved Duhem model for nonlinearity with simple calculation without inversion, accurate matching and fast response. • Feedforward decoupling method for crosstalk with favorable multi-axis coordination, good error tracking and simplified controllers. • Simulations and experiments verify the effectiveness of the multi-axis correction method. [ABSTRACT FROM AUTHOR]

Controlled manipulation of physical properties and creating complex surface features—nanosculpting—through particle irradiation is of immense interest in two-dimensional transition metal dichalcogenides (TMDs). In this work, we investigated the influence of SEM-generated low energy electron beam of 15 keV (electron flux 1.9 × 107e−s/nm2) on exfoliated monolayer MoS2 -gold interface for 15–600 s irradiation exposure. The mechanistic aspects including displacement damage, desorption, and dissociation via core hole Auger decay were proposed ,while morphology is evolved, and lattice defects (sulfur vacancies/nanoholes) are created affecting optical/electronic properties at nanoscale. We employed optical spectroscopy (PL and Raman), and electron and scanning probe microscopy, revealing spatial variations unique to topography, identifying defects, and quantifying surface work function (WF), respectively. Specifically, the monolayer surface structuration showed distinct inside–out concentric ring, starting at 120 s and irreversibly beyond ≥ 180 s prevailing Knotek–Feibelman mechanism, led by dissociation of ions following ionization (radiolysis), in contrast to primarily knock-on (atomic displacement) damage. We unraveled the importance of defect control of monolayer MoS2 leaving patches in the center (inner region) and edge constructs (outer region) due to metal ion movement, suggested by variation in WF ranging from 4.9 eV ± 0.006 eV (outer) to 5.2 ± 0.006 eV (inner) attributed to MoSxOy/MoO3-x chemical species. Tip-enhanced Raman spectroscopy (TERS) was instrumental in elucidating nanoscale inhomogeneities and molytrioxide-related defects besides nanovoids. Determining the impacts of these defects on properties is crucial while simultaneously sculpting desired structures, fabricating devices, doping in MoS2 , and for use in harsh conditions or a space radiation environment. [ABSTRACT FROM AUTHOR]

در این مقاله از روش تفاضل محدود در حوزه زمان برای تخمین شدت و توزیع میدان الکتریکی تقویت شده بصورت موضعی در طیف سنجی رامان تقویت شده با تیپ (TERS) در مجاورت تیپ مخروطی شکل به قطر نوک 10 نانومتر استفاده شده است. ضمن مقایسه میدان الکتریکی تقویت شده در دو پیکربندی با زیرلایه و بدون زیرلایه، تأثیر استفاده از مواد مختلف برای تیپ در مجاورت زیر لایه و همچنین اثر لایه‌نشانی نازک فلزهای مختلف بر روی تیپ در میزان تقویت میدان الکتریکی بررسی شده است. جنس تیپ در سیستم TERS از موادی نظیر طلا، نقره، آلومینیوم، مس و سیلیکون و همچنین حالت ترکیبی از این مواد بصورت لایه نشانی در نظر گرفته شده است. از نتایج شبیه‌سازی‌ بدست آمده می توان برای پیش‌بینی شدت و توزیع میدان الکتریکی تقویت شده موضعی در طراحی ساختار هندسی و فیزیکی مناسب برای پیاده سازی تجربی TERS استفاده کرد.

The comprehension of some diseases at the cellular and tissue scale is fundamental for the development of effective treatments for such conditions, and in this regard, Raman micro‐spectoscopy, atomic force microscopy (AFM), and tip‐enhanced Raman scattering (TERS) are techniques that have featured prominently in the characterization of biological materials like cells and tissues, since they allow the acquisition of detailed physical, chemical, biophysical, and physiological properties of the surface of these kind of samples such as elasticity, viscoelasticity, wettability, topography, molecular composition, and others. Due to this, this literature review has as its primary scope the presentation of some of the recent advances and new analysis methodologies using Raman, AFM, and TERS, pointing out what they can offer toward the investigation of the behavior of cells and biological tissues. Limits of usage, drawbacks, and future perspectives are presented and discussed. [ABSTRACT FROM AUTHOR]

N-heterocyclic carbenes (NHCs) have been established as powerful modifiers to functionalize metal surfaces for a wide variety of energy and nanoelectronic applications. To fundamentally understand and harness NHC modification, it is essential to identify suitable methods to interrogate NHC surface chemistry at the spatial limit. Here, we demonstrate tip-enhanced Raman spectroscopy (TERS) as a promising tool for chemically probing the surface properties of NHCs at the single-molecule scale. We show that with subnanometer resolution, TERS measurements are capable of not only unambiguously identifying the chemical structure of individual NHCs by their vibrational fingerprints but also definitively determining the binding mode of NHCs on metal surfaces. In particular, by investigating low-temperature NHC adsorption on Ag(111), our TERS studies provide insights into the temperature dependence of the adsorption properties of NHCs. This work suggests the potential of single-molecule vibrational spectroscopy for investigations of NHC surface modification at the most fundamental level.

Atmosphere aerosols have significant impact on human health and the environment. Aerosol particles have a number of characteristics that influence their health and environmental effects, including their size, shape, and chemical composition. A great deal of difficulty is associated with quantifying and identifying atmospheric aerosols because these parameters are highly variable on a spatial and temporal scale. An important component of understanding aerosol fate is Raman Spectroscopy (RS), which is capable of resolving chemical compositions of individual particles. This review presented strategic techniques, especially RS methods for characterizing atmospheric aerosols. The nature and properties of atmospheric aerosols and their influence on environment and human health were briefly described. Analytical methodologies that offer insight into the chemistry and multidimensional properties of aerosols were discussed. In addition, perspectives for practical applications of atmospheric aerosols using RS are featured.

This work demonstrates the enhancement in plasmonic sensing efficacy resulting from spatially-localized functionalization on nanostructured surfaces, whereby probe molecules are concentrated in areas of high field concentration. Comparison between SERS measurements on nanostructured surfaces (arrays of nanodisks 110 and 220 nm in diameter) with homogeneous and spatially-localized functionalization with thiophenol demonstrates that the Raman signal originates mainly from areas with high field concentration. TERS measurements with 10 nm spatial resolution confirm the field distribution profiles predicted by the numerical modeling. Though this enhancement in plasmonic sensing efficacy is demonstrated with SERS, results apply equally well to any type of optical/plasmonic sensing on functionalized surfaces with nanostructuring. [ABSTRACT FROM AUTHOR]

The genome packaging motor of bacteriophages and herpesviruses is built by two terminase subunits, known as large (TerL) and small (TerS), both essential for viral genome packaging. TerL structure, composition, and assembly to an empty capsid, as well as the mechanisms of ATP-dependent DNA packaging, have been studied in depth, shedding light on the chemo-mechanical coupling between ATP hydrolysis and DNA translocation. Instead, significantly less is known about the small terminase subunit, TerS, which is dispensable or even inhibitory in vitro, but essential in vivo. By taking advantage of the recent revolution in cryo-electron microscopy (cryo-EM) and building upon a wealth of crystallographic structures of phage TerSs, in this review, we take an inventory of known TerSs studied to date. Our analysis suggests that TerS evolved and diversified into a flexible molecular framework that can conserve biological function with minimal sequence and quaternary structure conservation to fit different packaging strategies and environmental conditions. [ABSTRACT FROM AUTHOR]

Optoelectronic properties of atomic thin van der Waals heterostructures (vdWHs) comprising transition metal dichalcogenides that harvest light energy are of paramount interest. In this work, the effects of underlying single- and bilayer graphene (Gr) layers on structural and physical properties of MoS2/Gr vertical heterostructures, i.e., (1-2L)MoS2/(1-2L)Gr, with additional interfaces including MoS2 folds/edges [MoS2(1L+1L))/Gr(1L)] and MoS2(1-2L)/Au, are investigated to unravel the excitonic properties. By employing correlative scanning probe microscopy combined with micro-spectroscopy, we observed multiple effects related to excitons (i.e., redshift of neutral excitons, ratio of charged excitons or trions to neutral exciton population, and long-tailed trions) and surface electronic properties (i.e., reduced work function suggesting electron transfer) in addition to significantly enhanced near-field Raman spectra, apparent n-p type current rectification behavior and increase in photogenerated carriers. All of these findings are attributed to interlayer electronic interactions while minimizing Fermi level pinning at the MoS2/Au interface, commonly observed in 2D semiconductor−3D metal junctions, which deepens our understanding of dissimilar 2D material junctions. Integrating MoS2 with an optimal number of graphene layers as a 'nanospacer' signifies substrate engineering that is versatile for key optoelectronic and photovoltaic applications. [ABSTRACT FROM AUTHOR]

To the best of our knowledge, it is for the first time thatTERS system in near-infrared (NIR) spectrum isreporting. The current study proposed a most favorableatomic force microscopy (AFM) tip based on anincorporated optimal grating structure close to the tipapex. The optimized M2 factor and the best spatialresolution are obtained as 5.9× 109 and 8.5 nmrespectively in the NIR range of radiation light. Theresults show that the optimized grating can effectivelyincrease the amount of intensity of electric field andimprove spatial resolution within the nanoslit between theAFM tip and substrate. The detection sensitivity ofmaterials can be done by our proposed AFM-TERSsystem. The difference between the maximumenhancement factors that are correlated to several undertest sample molecules show the selectivity potential ofthe proposed AFM-TERS system in material detectiontopic.

Two-dimensional transition metal dichalcogenides (2D-TMDs) are atomically thin semiconductors with a direct bandgap in monolayer thickness, providing ideal platforms for the development of exciton-based optoelectronic devices. Extensive studies on the spectral characteristics of exciton emission have been performed, but spatially resolved optical studies of 2D-TMDs are also critically important because of large variations in the spatial profiles of exciton emissions due to local defects and charge distributions that are intrinsically nonuniform. Because the spatial resolution of conventional optical microscopy and spectroscopy is fundamentally limited by diffraction, near-field optical imaging using apertured or metallic probes has been used to spectrally map the nanoscale profiles of exciton emissions and to study the effects of nanosize local defects and carrier distribution. While these unique approaches have been frequently used, revealing information on the exciton dynamics of 2D-TMDs that is not normally accessible by conventional far-field spectroscopy, a dedicated review of near-field imaging and spectroscopy studies on 2D-TMDs is not available. This review is intended to provide an overview of the current status of near-field optical research on 2D-TMDs and the future direction with regard to developing nanoscale optical imaging and spectroscopy to investigate the exciton characteristics of 2D-TMDs.

DNA identification is possible by detecting its components through vibrational spectroscopy. Conventional Raman, Surface-enhanced Raman spectroscopy (SERS) and Tip-enhanced Raman spectroscopy (TERS) have shown a high capacity for the exploration of different molecules and materials (semi-conducting material, carbon nanotubes and biologicals molecules as DNA, proteins). Their applications extended to biological systems and brought significant information to this field. This review summarizes a high number of studies and research conducted with conventional Raman, SERS and TERS on every DNA component starting from the four different nucleic acids in their different forms (nucleosides, deoxyribonucleosides, deoxyribonucleotides) to their biological interaction to form one and double DNA strands. As SERS has an advantage on conventional Raman by exploiting the optical properties of metallic nanostructures to detect very small quantities of molecules, it also clarifies the DNA structure’s orientation in addition to its composition. It also clarifies the influence of different parameters, such as the presence of a spacer or a mutation in the strand on the hybridization process. TERS was shown as a relevant tool to scan DNA chemically and to provide information on its sequence.

[Display omitted] • Probes made with DC-pulsed voltage provide better SNR compared to DC voltage ones. • Probes obtained with DC-pulsed voltage are more time-stable than with DC voltage. • Prepared plasmonic probes are efficient tool for the TER mapping of DPPE monolayer. Tip-enhanced Raman spectroscopy (TERS) is a label-free analytical technique that characterizes molecular systems, potentially even with a nanometric resolution. In principle, the metallic plasmonic probe is illuminated with a laser beam generating the localized surface plasmons, which induce a strong local electric field enhancement in close proximity to the probe. Such field enhancement improves the Raman scattering cross-section from the sample volume localized near the probe apex. TERS provides a high spatial resolution and a great sensitivity, however, it is rather rarely used due to technical limitations causing unstable enhancement and the relative lack of data reproducibility. Despite many scientific efforts for the fabrication of effective TER probes providing robust TER enhancement still requires further investigations. In this work, we explore new possibilities based on preparation of scanning tunnelling microscopy (STM) plasmonic probes, since by nature of the tunnelling effect, they potentially could offer a very high spatial resolution in STM guided TERS experiments. Here we compare two methods of STM-TERS probe preparation for effective spectra acquisition. Our results strongly indicate that an application of square pulse voltage upon the etching procedure significantly improves the quality of the TER data over those obtained with a constant voltage one. To demonstrate the efficiency of our probes we present the results of hyperspectral TER mapping of the 1,2-dipalmitoyl- sn -glycero-3-phosphoethanolamine (DPPE) monolayer deposited on an ultra-pure and atomically flat gold substrate. [ABSTRACT FROM AUTHOR]

This Article describes a method for the characterization of the imaging performance of tip-enhanced Raman spectroscopy probes. The proposed method identifies single-walled carbon nanotubes that are suitable as one-dimensional Raman scattering objects by using atomic force microscope maps and exciting the radial breathing mode using 785 nm illumination. High-resolution cross sections of the nanotubes are collected, and the point spread functions are calculated along with the optical contrast and spot diameter. The method is used to characterize several probes, which results in a set of imaging recommendations and a summary of limitations for each probe. Elemental analysis and boundary element simulations are used to explain the formation of multiple peaks in the point spread functions as a consequence of random grain formation on the probe surface. [ABSTRACT FROM AUTHOR]

This work presents an overview of the latest results and new data on the optical response from spherical CdSe nanocrystals (NCs) obtained using surface-enhanced Raman scattering (SERS) and tip-enhanced Raman scattering (TERS). SERS is based on the enhancement of the phonon response from nanoobjects such as molecules or inorganic nanostructures placed on metal nanostructured substrates with a localized surface plasmon resonance (LSPR). A drastic SERS enhancement for optical phonons in semiconductor nanostructures can be achieved by a proper choice of the plasmonic substrate, for which the LSPR energy coincides with the laser excitation energy. The resonant enhancement of the optical response makes it possible to detect mono- and submonolayer coatings of CdSe NCs. The combination of Raman scattering with atomic force microscopy (AFM) using a metallized probe represents the basis of TERS from semiconductor nanostructures and makes it possible to investigate their phonon properties with nanoscale spatial resolution. Gap-mode TERS provides further enhancement of Raman scattering by optical phonon modes of CdSe NCs with nanometer spatial resolution due to the highly localized electric field in the gap between the metal AFM tip and a plasmonic substrate and opens new pathways for the optical characterization of single semiconductor nanostructures and for revealing details of their phonon spectrum at the nanometer scale. [ABSTRACT FROM AUTHOR]

Illumination of noble metal nanostructures by electromagnetic radiation induces coherent oscillations of conductive electrons on their surfaces. These coherent oscillations of electrons, also known as localized surface plasmon resonances (LSPR), are the underlying physical cause of the electromagnetic enhancement of Raman scattering from analytes located in a close proximity to the metal surface. This physical phenomenon is broadly known as surface-enhanced Raman scattering (SERS). LSPR can decay via direct interband, phonon-assisted intraband, and geometry-assisted transitions forming hot carriers, highly energetic species that are responsible for a large variety of chemical transformations. This review critically discusses the most recent progress in mechanistic elucidation of hot carrier-driven chemistry and catalytic processes at the nanoscale. The review provides a brief description of tip-enhanced Raman spectroscopy (TERS), modern analytical technique that possesses single-molecule sensitivity and angstrom spatial resolution, showing the advantage of this technique for spatiotemporal characterization of plasmon-driven reactions. The review also discusses experimental and theoretical findings that reported novel plasmon-driven reactivity which can be used to catalyze redox, coupling, elimination and scissoring reactions. Lastly, the review discusses the impact of the most recently reported findings on both plasmonic catalysis and TERS imaging.

Near-field optical microscopy and spectroscopy provide high-resolution imaging below the diffraction limit, crucial in physics, chemistry, and biology for studying molecules, nanoparticles, and viruses. These techniques use a sharp metallic tip of an atomic force microscope (AFM) to enhance incoming and scattered light by excited near-fields at the tip apex, leading to high sensitivity and a spatial resolution of a few nanometers. However, this restricts the near-field orientation to out-of-plane polarization, limiting optical polarization choices. We introduce double tips that offer in-plane polarization for enhanced imaging and spectroscopy. These double tips provide superior enhancement over single tips, although with a slightly lower spatial resolution (∼30 nm). They enable advanced studies of nanotubes, graphene defects, and transition metal dichalcogenides, benefiting from polarization control. The double tips allow varied polarization in tip-enhanced Raman scattering and selective excitation of transverse-electric and -magnetic polaritons, expanding the range of nanoscale samples that can be studied.

Editor-in-Chief's Note: The Texas Water Journal accepted a request by Robert E. Mace, Executive Director and Chief Water Policy Officer at The Meadows Center for Water and the Environment, to share his thoughts on the article, Exploring Groundwater Recoverability in Texas: Maximum Economically Recoverable Storage,” published in the Texas Water Journal (2020) 11(1):152-171, by Justin C. Thompson, Charles W. Kreitler, and Michael H. Young. The opinion expressed in this commentary is the opinion of the individual author and not the opinion of the Texas Water Journal or the Texas Water Resources Institute.

Editor-in-Chief's Note: The Texas Water Journal accepted a request by authors, Justin C. Thompson, Charles W. Kreitler, and Michael H. Young, to reply to the commentary by Robert E. Mace on their article published in the Texas Water Journal (2021) 12(1):202-205, regarding “Exploring Groundwater Recoverability in Texas: Maximum Economically Recoverable Storage,” published in the Texas Water Journal (2020) 11(1):152-171, by Justin C. Thompson, Charles W. Kreitler, and Michael H. Young. The opinions expressed in this commentary are the opinions of the individual authors and not the opinion of the Texas Water Journal or the Texas Water Resources Institute.

Phthalocyanines are frequently used as probing molecules in the field of single-molecule surface-enhanced Raman spectroscopy (SERS) and tip-enhanced Raman spectroscopy (TERS). In this work, we systematically compare the SERS and TERS spectra from a thin cobalt phthalocyanine (CoPc) film that is deposited on a Au film. The contributions from electromagnetic (EM), resonance, and charge-transfer enhancements are discussed. Radially and azimuthally polarized vector beams are used to investigate the influences of molecular orientation and the localized surface plasmon resonance (SPR). Furthermore, two different excitation wavelengths (636 and 532 nm) are used to study the resonant excitation effect as well as the involvement of the charge-transfer processes between CoPc and the Au substrate. It is shown that the Raman peaks of CoPc are mostly enhanced by 636 nm excitation through a combination of resonant excitation, high EM enhancement, and chemical enhancement via charge transfer from the metal to the molecule. At 532 nm excitation, however, the SERS and TERS spectra are dominated by photoluminescence, which originates from a photo-induced charge-transfer process from the optically excited molecule to the metal. The contributions of the different enhancement mechanisms explain the optical contrasts seen in the TERS images of Au nanodisks covered by the CoPc film. The insight achieved in this work will help to understand the optical contrast in sub- or single-molecule TERS imaging and apply SERS or TERS in the field of photocatalysis.

This study aimed to develop and evaluate the psychometric properties of the Thai Elderly Resilience Scale (TERS). Its conceptual structure consists of three identified domains, I AM, I HAVE, and I CAN, within the 18 components that were initially used for developing the item pool. The first draft of the scale consisted of 50 items. A psychometric evaluation of content validity reliability and construct validity was conducted. The results yielded the current version of the TERS based on Exploratory Factor Analysis (EFA) consisting of 24 items categorized into 5 factors: 1) being able to join other people, 2) being confident in life 3) have social support 4) living with spiritual security and 5) being able to de-stress and manage problems. The scale had a high internal consistency (α=.94). A strong positive correlation between resilience and mental health scores were found (r=.84, p

In our proposed Atomic Force Microscopy combined with Tip-Enhanced Raman Spectroscopy (AFM-TERS) system, the intensity of the local electric field significantly increased by designing a grating structure on the tip of the system. Using Finite Difference Time Domain method, stimulation of surface plasmons and electron densities are done to determine the electric field around the tips of gold and silver cones. First, the geometric grating parameters are optimized to have the highest intensity of the electric field at the tip apex. Then, the distance of tip apex from the sample molecule and also the light source specifications are determined so that the highest field intensity is induced at the tip apex. To optimize the system operation the Particle Swarm Optimization algorithm is used at all stages. Among the parameters, the incident angle is the most effective one on increasing the electric field strength and quality factor of the spectral response of the enhancement factor. We also noticed that by applying an appropriate grating on the cone surface, the quality factor of the spectral response of our AFM-TERS system increases significantly. Finally, using two laser sources on both sides of the tip increases the amount of enhancement factor effectively. The optimized amounts of enhancement factors at the apex of the gold and silver tips are obtained as 3.11 × 109 and 3.79 × 109 respectively, where these values are much greater than those reported earlier. The results show a noticeable improvement in the performance of the proposed AFM-TERS system. [ABSTRACT FROM AUTHOR]

This article describes the scientific career of our dear friend Richard P. Van Duyne. Rick was the discoverer of surface‐enhanced Raman spectroscopy (SERS), and over the period from the mid‐1970s until his death in 2019, he served as both the intellectual leader of the field, and the technical genius who pushed the field forward through his numerous inventions and discoveries. Rick's work went through many phases, and even involved a significant period of inactivity that Rick was able to break out of, but especially after 2000, there was a period of incredible creativity that ultimately led to a detailed understanding of what the SERS enhancement factor is all about and also led to fabrication techniques for making optimum SERS substrates such that applications of SERS to a wide variety of real‐world problems in sensing became possible. In addition, Rick's SERS work spawned numerous related technologies, including index of refraction sensing based on localized surface plasmon resonance (LSPR) measurements, and the extension of SERS to its tip‐enhanced cousin TERS, to electrochemical versions of SERS and TERS, and to ultrafast nonlinear techniques. The practical applications he pursued included diagnostics for diseases such as cancer, hand‐held glucose sensing, and SERS studies related to art conservation. However, Rick's legacy will probably be best known through the numerous students, postdocs, and collaborators that passed through his lab and who are now active researchers in areas related to SERS at universities and industrial labs around the world. [ABSTRACT FROM AUTHOR]

Tip-enhanced Raman spectroscopy (TERS) under ultrahigh vacuum and cryogenic conditions enables exploration of the relations between the adsorption geometry, electronic state, and vibrational fingerprints of individual molecules. TERS capability of reflecting spin states in open-shell molecular configurations is yet unexplored. Here, we use the tip of a scanning probe microscope to lift a perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) molecule from a metal surface to bring it into an open-shell spin one-half anionic state. We reveal a correlation between the appearance of a Kondo resonance in differential conductance spectroscopy and concurrent characteristic changes captured by the TERS measurements. Through a detailed investigation of various adsorbed and tip-contacted PTCDA scenarios, we infer that the Raman scattering on suspended PTCDA is resonant with a higher excited state. Theoretical simulation of the vibrational spectra enables a precise assignment of the individual TERS peaks to high-symmetry A g modes, including the fingerprints of the observed spin state. These findings highlight the potential of TERS in capturing complex interactions between charge, spin, and photophysical properties in nanoscale molecular systems and suggest a pathway for designing single-molecule spin-optical devices.

The 2017 Texas state water plan projects total supply deficits of 4.8 and 8.9 million acre-feet under drought-of-record conditions by the year 2020 and 2070, respectively, driven by a growing population concurrent with declining available water supplies. Reductions in groundwater supply account for 95% of anticipated declines in total water supply. Meanwhile, restrictive groundwater management plans may be creating a regulation-induced shortage of groundwater in Texas, given the significant groundwater storage volumes that are unutilized under many management plans. However, these estimates do not account for many of the physical and none of the economic constraints to groundwater recoverability. We report an analysis of groundwater extraction feasibility and simulate maximum economically recoverable storage for conditions representative of the central section of the Carrizo-Wilcox Aquifer under economic constraints associated with agricultural uses. Two key limitations are applied to simulate recoverability: (1) the value of water pumped relative to pumping costs and (2) the capacity of the aquifer and well to meet demand. Our results indicate that these constraints may limit certain uses to as little as 1% of current groundwater availability estimates. We suggest that Texas groundwater managers, stakeholders, and policymakers assessing groundwater availability need an alternate approach for estimating recoverability. Citation: Thompson JC, Kreitler CW, Young MH. 2020. Exploring groundwater recoverability in Texas: maximum economically recoverable storage. Texas Water Journal. 11(1):152-171. Available from: https://doi.org/10.21423/twj.v11i1.7113.

Tip-enhanced Raman spectroscopy (TERS) has become a well-applied technique for nanospectroscopy, allowing for single molecule sensitivity with sub-nanometer spatial resolution. The demand for efficient, reproducible and cost-effective probes for TERS is increasing. Here we report on a new electrochemical etching protocol to fabricate TERS tips starting from 125 µm diameter gold wires in a reproducible way. The process is reliable (50% of the tips have radius of curvature

Fundamental understanding of chemistry and physical properties at the nanoscale enables the rational design of interface-based systems. Surface interactions underlie numerous technologies ranging from catalysis to organic thin films to biological systems. Since surface environments are especially prone to heterogeneity, it becomes crucial to characterize these systems with spatial resolution sufficient to localize individual active sites or defects. Spectroscopy presents as a powerful means to understand these interactions, but typical light-based techniques lack sufficient spatial resolution. This review describes the growing number of applications for the nanoscale spectroscopic technique, tip-enhanced Raman spectroscopy (TERS), with a focus on developments in areas that involve measurements in new environmental conditions, such as liquid, electrochemical, and ultrahigh vacuum. The expansion into unique environments enables the ability to spectroscopically define chemistry at the spatial limit. Through the confinement and enhancement of light at the apex of a plasmonic scanning probe microscopy tip, TERS is able to yield vibrational fingerprint information of molecules and materials with nanoscale resolution, providing insight into highly localized chemical effects. [ABSTRACT FROM AUTHOR]

Interactions between epitaxial graphene grown on Si- and C-faces were investigated using Raman imaging and tip-enhanced Raman scattering (TERS). In the TERS spectrum, which has a spatial resolution exceeding the diffraction limit, a D band was observed not from graphene surface, but from the edges of the epitaxial graphene ribbons without a buffer layer, which interacts with SiC on the Si-face. In contrast, for a graphene micro-island on the C-face, the D band disappeared even on the edges where the C atoms were arranged in armchair configurations. The disappearance of the edge chirality via combination between the C atoms and SiC on the C-face is responsible for this phenomenon. The TERS signals from the C-face were weaker than those from the Si-face without the buffer layer. On the Si-face with a buffer layer, the graphene TERS signal was hardly observed. TERS enhancement was suppressed by interactions on the edges or by the buffer layer between the SiC and graphene on the C- or Si-face, respectively. [ABSTRACT FROM AUTHOR]

We recorded the Raman spectrum of a single azobenzene thiol molecule upon picking it up from an atomically flat gold surface, using an electrochemically etched silver tip, in an ultrahigh vacuum cryogenic scanning tunneling microscope. While suppressed at the junction, the stationary spectrum appeared once the molecule was transferred to the tip, with line intensities that increased by a factor of ∼5 as the tip was retracted from 1 nm to 161 nm. The effect, and the enhanced tensorial Raman spectrum was reproduced using an explicit treatment of the electromagnetic fields to identify a cis-azobenzene thiol molecule, adsorbed on a nanometric asperity removed from the tip apex, lying in the plane normal to the tip z -axis, with enhanced incident and radiative local fields polarized in the same plane. Tips decorated with asperities break the rules and give unique insights on Raman driven by cavity modes of a plasmonic junction. [ABSTRACT FROM AUTHOR]

Both surface-enhanced Raman spectroscopy (SERS) and tip-enhanced Raman spectroscopy (TERS) are widely used for the investigation of nanoscale materials. One of the most critical aspects of both SERS and TERS is the control of both the plasmon and molecular resonance precisely. Here, we demonstrate single-molecule TERS under molecular resonance conditions using a scanning tunneling microscope. This was achieved by placing the molecule on a sodium chloride (NaCl) film in order to directly compare the absorption with Raman excitation spectra. Varying the NaCl film thickness changes the degree of screening effect from the metal surface, which leads to a variation of the molecular resonance phenomena. Although it is generally accepted that the target molecule should be directly attached to the metal surface in SERS, our observation using TERS suggests that this is not always optimal, especially under molecular resonance Raman conditions. Our work demonstrates the possibility of controlling molecular resonance by carefully modifying the local environment. This will be useful for future investigation of isolated single molecules or even two-dimensional molecular assemblies. [ABSTRACT FROM AUTHOR]

Tip-enhanced Raman spectroscopy (TERS) provides the sensitivity required to obtain the vibrational fingerprint of few molecules. While single molecule detection has been demonstrated in UHV experiments, the sensitivity of the technique in ambient, liquid and electrochemical conditions is still limited. In this work, we present a new strategy to increase the signal-to-noise in TERS by spatial light modulation. We iteratively optimize the phase of the excitation beam employing two different feedback mechanisms. In one optimization protocol, we monitor the spectral changes upon aberration correction and tight far-field focusing. In a second protocol, we use a phase-optimization strategy where TER spectra are directly used for feedback. Far-field tight focusing results in average signal enhancements of a factor of 3.5 in air and has no impact on TER signals obtained from solid/liquid interfaces. Using the TER spectrum as direct feedback, we obtain average signal enhancements between a factor of 2.6 in liquid and 4.3 in air. In individual cases, some bands increase by more than one order of magnitude in intensity upon spatial light modulation. Importantly, phase modulation in addition allowed the retrieval of bands that were initially not discernible from the noise. The proposed beam-modulation strategy can be easily implemented in existing TERS instruments and can help to push the detection limit of the technique in applications where the signal-to-noise level is low. [ABSTRACT FROM AUTHOR]

Tip-enhanced Raman spectroscopy (TERS) is a powerful tool for the characterization of surfaces and two-dimensional materials, delivering both topographical and chemical information with nanometer-scale spatial resolution. Atomic force microscopy (AFM)–TERS combines AFM with a Raman spectrometer and is a very versatile technique, capable of working in vacuum, air, and liquid, and on a variety of different samples. A metalized AFM tip is necessary in order to take advantage of the plasmonic enhancement. The most commonly used metal is Ag, thanks to its high plasmonic activity in the visible range. Unfortunately, though, the tip metallization process is still challenging and not fully reliable, yielding inconsistent enhancement factors even within the same batch of tips; as a consequence, many tips are usually prepared at once (for a single experiment), to ensure that at least one of them is sufficiently active. As the lifetime of an unprotected, Ag-coated plasmonic probe is only a few hours, the procedure is inefficient and results in a substantial waste of materials and money. In this work, we establish a cleaning routine to effectively re-use Ag-coated AFM–TERS probes, drastically reducing costs without compromising the quality of the experimental results. [ABSTRACT FROM AUTHOR]

The main limitation of the use of tip-enhanced Raman scattering (TERS) is due to the lack of reliable scanning probes. We present a simple procedure to manufacture TERS probes with highly reproducible characteristics that are reliable and provide sufficient enhancement. The procedure is based on the modification of conventional cantilevers of scanning probe microscopes by plasma etching, followed by the formation of a TERS enhancing region at the apex by deposition of colloidal nanoparticles by dielectrophoresis. [ABSTRACT FROM AUTHOR]