Mitigating Interfacial Capacity Fading in Vanadium Pentoxide by Sacrificial Vanadium Sulfide Encapsulation for Rechargeable Mg-Ion Batteries.

Rechargeable Mg-ion Batteries (RMB) containing a Mg metal anode offer the promise of higher specific volumetric capacity, energy density, safety, and economic viability than lithium-ion battery technology, but their realization is challenging. The limited availability of suitable inorganic cathodes compatible with electrolytes relevant to Mg metal anode restricts the development of RMBs. Despite the promising capability of some oxides to reversibly intercalate Mg+2 ions at high potential, its lack of stability in chloride-containing ethereal electrolytes, relevant to Mg metal anode hinders the realization of a full practical RMB. Here the successful in situ encapsulation of monodispersed spherical V2O5 (≈200 nm) is demonstrated by a thin layer of VS2 (≈12 nm) through a facile surface reduction route. The VS2 layer protects the surface of V2O5 particles in RMB electrolyte solution (MgCl2 + MgTFSI in DME). Both V2O5 and V2O5@VS2 particles demonstrate high initial discharge capacity. However, only the V2O5@VS2 material demonstrates superior rate performance, Coulombic efficiency (100%), and stability (138 mA h g-1 discharge capacity after 100 cycles), signifying the ability of the thin VS2 layer to protect the V2O5 cathode and facilitate the Mg+2 ion intercalation/deintercalation into V2O5.

High-energy all-solid-state lithium batteries enabled by Co-free LiNiO2 cathodes with robust outside-in structures.

A critical current challenge in the development of all-solid-state lithium batteries (ASSLBs) is reducing the cost of fabrication without compromising the performance. Here we report a sulfide ASSLB based on a high-energy, Co-free LiNiO2 cathode with a robust outside-in structure. This promising cathode is enabled by the high-pressure O2 synthesis and subsequent atomic layer deposition of a unique ultrathin LixAlyZnzOδ protective layer comprising a LixAlyZnzOδ surface coating region and an Al and Zn near-surface doping region. This high-quality artificial interphase enhances the structural stability and interfacial dynamics of the cathode as it mitigates the contact loss and continuous side reactions at the cathode/solid electrolyte interface. As a result, our ASSLBs exhibit a high areal capacity (4.65 mAh cm-2), a high specific cathode capacity (203 mAh g-1), superior cycling stability (92% capacity retention after 200 cycles) and a good rate capability (93 mAh g-1 at 2C). This work also offers mechanistic insights into how to break through the limitation of using expensive cathodes (for example, Co-based) and coatings (for example, Nb-, Ta-, La- or Zr-based) while still achieving a high-energy ASSLB performance.

Identification of Enantiomers Using Low-Frequency Raman Spectroscopy.

Distinguishing between d and l enantiomers is of important scientific interest, especially for the pharmaceutical industry. Enantiomeric differentiation in the solid form is repeatedly presented as a challenge in the research community. Raman spectroscopy is a nondestructive tool, widely used for the characterization of different materials by probing their vibrational modes. The low-frequency region of the Raman spectrum reveals lattice-level interactions and global fluctuations in the molecule. Lower frequencies correspond to vibrations arising from weaker bonds and long-range interactions and hence are very susceptible to polarization changes. This work presents low-frequency Raman (LFR) spectroscopy as a facile technique to identify enantiomers. The optical setup of conventional Raman spectroscopy is engineered such that the excitation and collection geometries use an asymmetrical focal cone. In addition, a half-wave retarder is added to the excitation path and a Glan-Taylor polarizer is added to the collection path, and these modifications allow us to select the polarization plane for both excitation and collection geometries. The asymmetry in the foci when using a polarized beam for excitation provides different intensities of the collected signal for each polarization plane. In a calibrated system, one can define the chirality of an analyte by comparing the intensity of the LFR signal along orthogonal sets of polarization planes. For nonchiral molecules, the spectral intensity is always higher in the co-polarized plane when compared to the orthogonally depolarized plane, as expected. This contrast in the intensity of Raman spectra serves as a distinct tool for identifying enantiomers.

CVD-Assisted Synthesis of 2D Layered MoSe2 on Mo Foil and Low Frequency Raman Scattering of Its Exfoliated Few-Layer Nanosheets on CaF2 Substrates.

Transition-metal dichalcogenides (TMDCs) are unique layered materials with exotic properties. So, examining their structures holds tremendous importance. 2H-MoSe2 (analogous to MoS2; Gr. 6 TMDC) is a crucial optoelectronic material studied extensively using Raman spectroscopy. In this regard, low-frequency Raman (LFR) spectroscopy can probe this material's structure as it reveals distinct vibration modes. Here, we focus on understanding the microstructural evolution of different 2H-MoSe2 morphologies and their layers using LFR scattering. We grew phase-pure 2H-MoSe2 (with variable microstructures) directly on a Mo foil using a two-furnace ambient-pressure chemical vapor deposition (CVD) system by carefully controlling the process parameters. We analyzed the layers of exfoliated flakes after ultrasonication and drop-cast 2H-MoSe2 of different layer thicknesses by choosing different concentrations of 2H-MoSe2 solutions. Further detailed analyses of the respective LFR regions confirm the presence of newly identified Raman signals for the 2H-MoSe2 nanosheets drop-cast on Raman-grade CaF2. Our results show that CaF2 is an appropriate Raman-enhancing substrate compared to Si/SiO2 as it presents new LFR modes of 2H-MoSe2. Therefore, CaF2 substrates are a promising medium to characterize in detail other TMDCs using LFR spectroscopy.

Improvement of the Electrochemical Performance of LiNi0.8Co0.1Mn0.1O2 via Atomic Layer Deposition of Lithium-Rich Zirconium Phosphate Coatings.

Owing to its high energy density, LiNi0.8Co0.1Mn0.1O2 (NMC811) is a cathode material of prime interest for electric vehicle battery manufacturers. However, NMC811 suffers from several irreversible parasitic reactions that lead to severe capacity fading and impedance buildup during prolonged cycling. Thin surface protection films coated on the cathode material mitigate degradative chemomechanical reactions at the electrode-electrolyte interphase, which helps to increase cycling stability. However, these coatings may impede the diffusion of lithium ions, and therefore, limit the performance of the cathode material at a high C-rate. Herein, we report on the synthesis of zirconium phosphate (ZrxPOy) and lithium-containing zirconium phosphate (LixZryPOz) coatings as artificial cathode-electrolyte interphases (ACEIs) on NMC811 using the atomic layer deposition technique. Upon prolonged cycling, the ZrxPOy- and LixZryPOz-coated NMC811 samples show 36.4 and 49.4% enhanced capacity retention, respectively, compared with the uncoated NMC811. Moreover, the addition of Li ions to the LixZryPOz coating enhances the rate performance and initial discharge capacity in comparison to the ZrxPOy-coated and uncoated samples. Using online electrochemical mass spectroscopy, we show that the coated ACEIs largely suppress the degradative parasitic side reactions observed with the uncoated NMC811 sample. Our study demonstrates that providing extra lithium to the ACEI layer improves the cycling stability of the NMC811 cathode material without sacrificing its rate capability performance.

Combining polarized low-frequency Raman with XRD to identify directional structural motifs in a pyrolysis precursor.

Long-range structures and dynamics are central to coordination chemistry, yet are hard to identify experimentally. By combining polarized low-frequency Raman spectroscopy with single crystal XRD to study barium nitrilotriacetate, a metal-organic coordination polymer and a useful pyrolysis precursor, we could assign Raman peaks experimentally to layer shear motions and perpendicular hydrogen bond vibrations. These directional long-range interactions further determined the preferred fracture directions during crystallization, establishing an important link between structural motifs in the precursor, and the porosity of the carbon it yields upon pyrolysis.

Higher Ultrasonic Frequency Liquid Phase Exfoliation Leads to Larger and Monolayer to Few-Layer Flakes of 2D Layered Materials.

Among the most reliable techniques for exfoliation of two-dimensional (2D) layered materials, sonication-assisted liquid-phase exfoliation (LPE) is considered as a cost-effective and straightforward method for preparing graphene and its 2D inorganic counterparts at reasonable sizes and acceptable levels of defects. Although there were rapid advances in this field, the effect and outcome of the sonication frequency are poorly understood and often ignored, resulting in a low exfoliation efficiency. Here, we demonstrate that simple mild bath sonication at a higher frequency and low power positively contributes to the thickness, size, and quality of the final exfoliated products. We show that monolayer graphene flakes can be directly exfoliated from graphite using ethanol as a solvent by increasing the frequency of the bath sonication from 37 to 80 kHz. The statistical analysis shows that ∼77% of the measured graphene flakes have a thickness below three layers with an average lateral size of 13 µm. We demonstrate that this approach works for digenite (Cu9S5) and silver sulfide (Ag2S), thus indicating that this exfoliation technique can be applied to other inorganic 2D materials to obtain high-quality few-layered flakes. This simple and effective method facilitates the formation of monolayer/few layers of graphene and transition metal chalcogenides for a wide range of applications.

Microcavity Enhanced Raman Spectroscopy of Fullerene C60 Bucky Balls.

Raman spectroscopy is a widely used characterization technique in material science. It is a non-destructive tool with relatively simple instrumentation, and provides intrinsic qualitative information of analytes by probing their vibrational modes. In many cases, Raman enhancement is essential for detecting low-intensity signals in high-noise environments, spectrally unresolved features, and hidden modes. Here we present optical and Raman spectroscopic characterization of fullerene C 60 in a gold microcavity. The fabrication of single-layered gold mirrors is facile, low cost and direct but was proven to give considerably significant enhancement. The findings of this work demonstrate the cavity resonance as a powerful tool in obtaining tunability over individual peak for selective enhancement in the tuned spectral range. The PL of the material within the cavity has demonstrated a red shift assumed to be caused by the low-energy transitions. These transitions are induced by virtual low-energy states generated by the cavity. We further observe that adopting this principle enables resolution of active Raman modes that until now were unobserved. Finally, we assigned the new experimentally observed modes to the corresponding motions calculated by DFT.

Chiral Purity of Crystals Using Low-Frequency Raman Spectroscopy.

The pharmaceutical industry is in need of new techniques to identify the chirality of solids due to regulatory and safety concerns regarding the biological activity of enantiomers. In this study, we present for the first time the application of low-frequency Raman spectroscopy as a new and sensitive method for analyzing the chiral purity of crystals. Using this method, we were able to identify small amounts, as low as 1 % w/w, of an enantiomer in racemic crystals. To demonstrate the capabilities of the method, we used a model system based on chiral crystals of enantiopure, racemic crystals and their mixtures in various ratios. We found that the low-frequency Raman spectra of racemic and enantiopure crystals are significantly different, reflecting the different hydrogen bond networks. Moreover, a comparison of the sensitivity of enantiomeric excess in chiral crystals to that of circular dichroism and X-ray diffraction measurements showed that low-frequency Raman attains high sensitivity comparable to chiral optical methods used for solutions. Overall, our proposed approach of using Raman spectroscopy for determining enantiomeric excess in crystals is simple, fast, and offers a high degree of chiral sensitivity.

Characterization of Crystal Chirality in Amino Acids Using Low-Frequency Raman Spectroscopy.

We present a new method for differentiating racemic crystals from enantiopure crystals. Recently, developments in optical filters have enabled the facile use of Raman spectroscopy to detect low-frequency vibrational (LFV) modes. Here, for the first time, we use Raman spectroscopy to characterize the LFV modes for crystalline organic materials composed of chiral molecules. The LF-Raman spectra of racemic and enantiopure crystals exhibit a significant variation, which we attribute to different hydrogen-bond networks in the chiral crystal structures. Across a representative set of amino acids, we observed that when comparing racemic versus enantiopure crystals, the available LFV modes and their relative scattering intensity are strong functions of side chain polarity. Thus, LF-Raman can be used as a method that is complementary to the currently used methods for characterizing crystal chirality due to simpler, faster, and more sensitive measurements, along with the small sample size required, which is limited by the laser-beam diameter in the focus.

Replacing a Century Old Technique - Modern Spectroscopy Can Supplant Gram Staining.

Rapid and accurate Gram differentiation is paramount as the first step of pathogen identification and antibiotics administration. However, the current method requires additional reagents, is time-consuming, and is operator dependent. Here we show the principle of tip enhanced Raman spectroscopy (TERS) can differentiate between Gram negative and positive species, by detecting the changes in tip-enhancement in the Raman scattering from the bacteria's lipid-bilayer membrane, which specifically enhances Gram negative bacteria.

Microcavity Laser Based on a Single Molecule Thick High Gain Layer.

The ability to confine excitons within monolayers has led to fundamental investigations of nonradiative energy transfer, super-radiance, strong light-matter coupling, high-efficiency light-emitting diodes, and recently lasers in lateral resonator architectures. Vertical cavity surface emitting lasers (VCSELs), in which lasing occurs perpendicular to the device plane, are critical for telecommunications and large-scale photonics integration, however strong optical self-absorption and low fluorescence quantum yields have thus far prevented coherent emission from a monolayer microcavity device. Here we show lasing from a monolayer VCSEL using a single molecule thick film of amphiphilic fluorescent dye, assembled via Langmuir-Blodgett deposition, as the gain layer. Threshold was observed when 5% of the molecules were excited (4.4 µJ/cm2). At this level of excitation, the optical gain in the monolayer exceeds 1056 cm-1. High localization of the excitons in the VCSEL gain layer can enhance their collective emission properties with Langmuir-Blodgett deposition presenting a paradigm for engineering the high gain layers on the molecular level.

Deposition and Characterization of Roughened Surfaces.

Phase separation occurs whenever a solvent leaves a solution of strongly incompatible polymers. This can happen in bulk and in films. Films can be tailored as substrates for multiple applications such as solar cells, surface catalysis, and antireflection coatings. In this study, polystyrene (PS) was dissolved with polyvinyl acetate (PVAc) in different ratios using chlorobenzene as the solvent. Thin films of different ratios of PS and PVAc were deposited on glass via spin coating. The deposited films were investigated for their morphology, strain, surface area, and Raman scattering. The incompatibility between the two polymers leads to the growth of roughened PVAc islands supported by the PS matrix. A down shift in the Raman PVAc signal was observed in the combined film as compared with a 100% PVAc film, which was attributed to the high strain of PVAc that grew as tips. As the PVAc concentration in the polymer blend increases, the porous regions in the film expand and the amount and height of PVAc tips increase as well, up to the point where the pores merge to create a uniform surface. The optimal ratio for the deposition of a uniformly roughened surface is 75% PVAc and 25% PS. For demonstrating a possible application, we applied the partially roughened surface as a substrate for surface-enhanced Raman scattering and demonstrated at least 500% increase in the signal intensity measured in roughened areas. This is explained by the rod effect from the PVAc tips.

Spectroscopic Method for Fast and Accurate Group A Streptococcus Bacteria Detection.

Rapid and accurate detection of pathogens is paramount to human health. Spectroscopic techniques have been shown to be viable methods for detecting various pathogens. Enhanced methods of Raman spectroscopy can discriminate unique bacterial signatures; however, many of these require precise conditions and do not have in vivo replicability. Common biological detection methods such as rapid antigen detection tests have high specificity but do not have high sensitivity. Here we developed a new method of bacteria detection that is both highly specific and highly sensitive by combining the specificity of antibody staining and the sensitivity of spectroscopic characterization. Bacteria samples, treated with a fluorescent antibody complex specific to Streptococcus pyogenes, were volumetrically normalized according to their Raman bacterial signal intensity and characterized for fluorescence, eliciting a positive result for samples containing Streptococcus pyogenes and a negative result for those without. The normalized fluorescence intensity of the Streptococcus pyogenes gave a signal that is up to 16.4 times higher than that of other bacteria samples for bacteria stained in solution and up to 12.7 times higher in solid state. This method can be very easily replicated for other bacteria species using suitable antibody-dye complexes. In addition, this method shows viability for in vivo detection as it requires minute amounts of bacteria, low laser excitation power, and short integration times in order to achieve high signal.

Utilizing pulsed laser deposition lateral inhomogeneity as a tool in combinatorial material science.

Pulsed laser deposition (PLD) is widely used in combinatorial material science, as it enables rapid fabrication of different composite materials. Nevertheless, this method was usually limited to small substrates, since PLD deposition on large substrate areas results in severe lateral inhomogeneity. A few technical solutions for this problem have been suggested, including the use of different designs of masks, which were meant to prevent inhomogeneity in the thickness, density, and oxidation state of a layer, while only the composition is allowed to be changed. In this study, a possible way to take advantage of the large scale deposition inhomogeneity is demonstrated, choosing an iron oxide PLD-deposited library with continuous compositional spread (CCS) as a model system. An Fe2O3-Nb2O5 library was fabricated using PLD, without any mask between the targets and the substrate. The library was measured using high-throughput scanners for electrical, structural, and optical properties. A decrease in electrical resistivity that is several orders of magnitude lower than pure α-Fe2O3 was achieved at ∼20% Nb-O (measured at 47 and 267 °C) but only at points that are distanced from the center of the PLD plasma plume. Using hierarchical clustering analysis, we show that the PLD inhomogeneity can be used as an additional degree of freedom, helping, in this case, to achieve iron oxide with much lower resistivity.

Quantum efficiency and bandgap analysis for combinatorial photovoltaics: sorting activity of Cu-O compounds in all-oxide device libraries.

All-oxide-based photovoltaics (PVs) encompass the potential for extremely low cost solar cells, provided they can obtain an order of magnitude improvement in their power conversion efficiencies. To achieve this goal, we perform a combinatorial materials study of metal oxide based light absorbers, charge transporters, junctions between them, and PV devices. Here we report the development of a combinatorial internal quantum efficiency (IQE) method. IQE measures the efficiency associated with the charge separation and collection processes, and thus is a proxy for PV activity of materials once placed into devices, discarding optical properties that cause uncontrolled light harvesting. The IQE is supported by high-throughput techniques for bandgap fitting, composition analysis, and thickness mapping, which are also crucial parameters for the combinatorial investigation cycle of photovoltaics. As a model system we use a library of 169 solar cells with a varying thickness of sprayed titanium dioxide (TiO2) as the window layer, and covarying thickness and composition of binary compounds of copper oxides (Cu-O) as the light absorber, fabricated by Pulsed Laser Deposition (PLD). The analysis on the combinatorial devices shows the correlation between compositions and bandgap, and their effect on PV activity within several device configurations. The analysis suggests that the presence of Cu4O3 plays a significant role in the PV activity of binary Cu-O compounds.

Synthesis and characterization of Bi2O3/HSA core-shell nanoparticles for X-ray imaging applications.

Bismuth oxide nanoparticles of 12.1 ± 3.0 nm diameter were prepared by thermal decomposition of bismuth acetate dissolved in ethylene glycol in the presence of an oxidizing agent. Functionalization and stabilization of the hydrophobic Bi(2)O(3) nanoparticles was accomplished by coating these core nanoparticles with human serum albumin (HSA), via a precipitation process. The formed Bi(2)O(3)/HSA core-shell nanoparticles were of 15.2 ± 3.5 nm diameter. Elemental analysis measurements indicated that the bismuth weight % of the Bi(2)O(3)/HSA core-shell nanoparticles is 72.9. The crystalline structure of these nanoparticles was examined by XRD. The radiopacity of these nanoparticles was demonstrated in vitro and in vivo by a CT scanner. In ovo and in vivo trials proved the safety of these Bi(2)O(3)/HSA core-shell nanoparticles. In the future, we plan to extend this study particularly for molecular imaging applications.

First multimodal embolization particles visible on x-ray/computed tomography and magnetic resonance imaging.

OBJECTIVES: Embolization therapy is gaining importance in the treatment of malignant lesions, and even more in benign lesions. Current embolization materials are not visible in imaging modalities. However, it is assumed that directly visible embolization material may provide several advantages over current embolization agents, ranging from particle shunt and reflux prevention to improved therapy control and follow-up assessment. X-ray- as well as magnetic resonance imaging (MRI)-visible embolization materials have been demonstrated in experiments. In this study, we present an embolization material with the property of being visible in more than one imaging modality, namely MRI and x-ray/computed tomography (CT). Characterization and testing of the substance in animal models was performed. MATERIALS AND METHODS: To reduce the chance of adverse reactions and to facilitate clinical approval, materials have been applied that are similar to those that are approved and being used on a routine basis in diagnostic imaging. Therefore, x-ray-visible Iodine was combined with MRI-visible Iron (Fe3O4) in a macroparticle (diameter, 40-200 µm). Its core, consisting of a copolymerized monomer MAOETIB (2-methacryloyloxyethyl [2,3,5-triiodobenzoate]), was coated with ultra-small paramagnetic iron oxide nanoparticles (150 nm). After in vitro testing, including signal to noise measurements in CT and MRI (n = 5), its ability to embolize tissue was tested in an established tumor embolization model in rabbits (n = 6). Digital subtraction angiography (DSA) (Integris, Philips), CT (Definition, Siemens Healthcare Section, Forchheim, Germany), and MRI (3 Tesla Magnetom Tim Trio MRI, Siemens Healthcare Section, Forchheim, Germany) were performed before, during, and after embolization. Imaging signal changes that could be attributed to embolization particles were assessed by visual inspection and rated on an ordinal scale by 3 radiologists, from 1 to 3. Histologic analysis of organs was performed. RESULTS: Particles provided a sufficient image contrast on DSA, CT (signal to noise [SNR], 13 ± 2.5), and MRI (SNR, 35 ± 1) in in vitro scans. Successful embolization of renal tissue was confirmed by catheter angiography, revealing at least partial perfusion stop in all kidneys. Signal changes that were attributed to particles residing within the kidney were found in all cases in all the 3 imaging modalities. Localization distribution of particles corresponded well in all imaging modalities. Dynamic imaging during embolization provided real-time monitoring of the inflow of embolization particles within DSA, CT, and MRI. Histologic visualization of the residing particles as well as associated thrombosis in renal arteries could be performed. Visual assessment of the likelihood of embolization particle presence received full rating scores (153/153) after embolization. CONCLUSIONS: Multimodal-visible embolization particles have been developed, characterized, and tested in vivo in an animal model. Their implementation in clinical radiology may provide optimization of embolization procedures with regard to prevention of particle misplacement and direct intraprocedural visualization, at the same time improving follow-up examinations by utilizing the complementary characteristics of CT and MRI. Radiation dose savings can also be considered. All these advantages could contribute to future refinements and improvements in embolization therapy. Additionally, new approaches in embolization research may open up.

Radiopaque iodinated copolymeric nanoparticles for X-ray imaging applications.

Recently we described iodinated homopolymeric radiopaque nanoparticles of 28.9+/-6.3 nm dry diameter synthesized by emulsion polymerization of 2-methacryloyloxyethyl(2,3,5-triiodobenzoate) (MAOETIB). The nanoparticle aqueous dispersion, however, was not stable and tended to agglomerate, particularly at weight concentration of dispersed nanoparticles above approximately 0.3%. The agglomeration rate increases as the concentration of nanoparticles in aqueous phase rises and prevents the potential in vivo use as contrast agent for medical X-ray imaging. Here we describe efforts to overcome this limitation by synthesis of iodinated copolymeric nanoparticles of 25.5+/-4.2 nm dry diameter, by emulsion copolymerization of the monomer, MAOETIB, with a low concentration of glycidyl methacrylate (GMA). The surface of resulting copolymeric nanoparticles is far more hydrophilic than that of polyMAOETIB (PMAOETIB) nanoparticles. Therefore, P(MAOETIB-GMA) nanoparticles are significantly more stable against agglomeration in aqueous continuous phase. After intravenous injection of P(MAOETIB-GMA) nanoparticles in rats and mice (including those with a liver cancer model) CT-imaging revealed a significant enhanced visibility of the blood pool for 30 min after injection. Later, lymph nodes, liver and spleen strongly enhanced due to nanoparticle uptake by the reticuloendothelial system. This favorably enabled the differentiation of cancerous from healthy liver tissue and suggests our particles for tumor imaging in liver and lymph nodes.