Optical Microspectroscopy Research Articles

A gate-free monolayer WSe2 pn diode

Interest in bringing p- and n-type monolayer semiconducting transition metal dichalcogenides (TMD) into contact to form rectifying pn diode has thrived since it is crucial to control the electrical properties in two-dimensional (2D) electronic and optoelectronic devices. Usually this involves vertically stacking different TMDs with pn heterojunction or, laterally manipulating carrier density by gate biasing. Here, by utilizing a locally reversed ferroelectric polarization, we laterally manipulate the carrier density and created a WSe2 pn homojunction on the supporting ferroelectric BiFeO3 substrate. This non-volatile WSe2 pn homojunction is demonstrated with optical and scanning probe methods and scanning photoelectron micro-spectroscopy. A homo-interface is a direct manifestation of our WSe2 pn diode, which can be quantitatively understood as a clear rectifying behavior. The non-volatile confinement of carriers and associated gate-free pn homojunction can be an addition to the 2D electron–photon toolbox and pave the way to develop laterally 2D electronics and photonics.

Photonic crystal micro-pixelation and additive color mixing in weevil scales

The origin of the brilliant near angle-independent coloration of the weevil Eupholus chevrolati was investigated by a combination of optical and electron microscopy tools, photonic band structure calculations, and color mixing analysis. Optical microscopy and scanning micro-spectroscopy revealed the presence of micrometer-sized red, yellow, green, and blue reflective pixels covering the entire exoskeleton of the weevil. Scanning electron microscopy in combination with focused ion beam milling showed that each micro-pixel consisted of a diamond-based photonic crystal structure and the different reflective colors were the result of different orientations of the photonic crystal. Color mixing analysis was used to study the collective behavior of the reflective micro-pixels. A pointillist, additive color-mixing scheme of the reflective photonic crystal micro-pixels was determined as the origin of the weevil’s bright and near angle-independent yellow-green coloration.

Material processed with 58,000‐year‐old grindstones from Sibudu (KwaZulu‐Natal, South Africa) identified by means of Raman microspectroscopy

AbstractDespite their high potential for understanding past human behaviours, the study of grindstones is limited in the literature compared with other forms of lithic tools. This paper reports the combination of optical microscopy and Raman microspectroscopy for understanding the uses of a selection of six grindstones from the post‐Howiesons Poort layers at Sibudu, South Africa, dating to 58,000 years ago. Five of the specimens exhibit numerous red haematite stains which imply red ochre processing. Nevertheless, each artefact seems to have been used for a specific task. For example, the smallest grindstone was used for a combination of tasks—ochre, bone, and organic matter processing. The distinction between use residues, sediment contamination, secondary mineral formation, modern contamination, and components included in the sandstone that the grindstones are made from is discussed.

Time-resolved optical absorption microspectroscopy of magnetic field sensitive flavin photochemistry.

The photochemical reactions of blue-light receptor proteins have received much attention due to their very important biological functions. In addition, there is also growing evidence that the one particular class of such proteins, the cryptochromes, may be associated with not only a biological photo-response but also a magneto-response, which may be responsible for the mechanism by which many animals can respond to the weak geomagnetic field. Therefore, there is an important scientific question over whether it is possible to directly observe such photochemical processes, and indeed the effects of weak magnetic fields thereon, taking place both in purified protein samples in vitro and in actual biochemical cells and tissues. For the former samples, the key lies in being able to make sensitive spectroscopic measurements on very small volumes of samples at potentially low protein concentrations, while the latter requires, in addition, spatially resolved measurements on length scales smaller than typical cellular components, i.e., sub-micron resolution. In this work, we discuss a two- and three-color confocal pump-probe microscopic approach to this question which satisfies these requirements and is thus useful for experimental measurements in both cases.

Effect of tribochemical treatments and silane reactivity on resin bonding to zirconia

ObjectiveThe aim of the study was to assess the roughness, structure and bond strength with zirconia of four grit-blasting treatments combined with three silane types, the reactivity of which was evaluated, as well. MethodsThe grit-blasted treatments performed on zirconia (Lava) were alumina (ALU), CoJet (COJ), SilJet (SLJ) and SilJet Plus (SJP, with silica-encapsulated silane). The other two silanes selected were the S-Bond (SB, prehydrolyzed) and Clearfil Ceramic Primer Plus (CP, prehydrolyzed with 10-MDP). The activity of the silanols in the silanes was evaluated by FTIR spectroscopy. Optical profilometry and Raman microspectroscopy were used for the assessment of roughness (Sa, Sz, Sdr parameters) and structure (monoclinic volume-Vm) of zirconia, before (REF) and after grit-blasting, and a shear bond strength (SBS) with a flowable resin composite, for the investigation of the bonding capacity of the treatments. ResultsOnly SB demonstrated reactive silanols. CP and the SJP silanes were mostly in a polymerized siloxane state. Roughness was increased after grit-blasting as follows: ALU>SLJ,SJP>COJ>REF (Sa,Sz) and ALU>SLJ,COJ,SJP>REF (Sdr). ALU demonstrated the highest Vm (7.52%) from all other treatments (4.16–4.81%) and the REF (0%). COJ and SLJ showed the highest SBS (14–15.94MPa) regardless of the silane type used. SJP showed no significant differences from SLJ-SB and COJ-SB. Weibull analysis showed a reliability (β) ranking of COJ, SJP, SLJ, ALU-CP>ALU-SB>REF and a characteristic life (η) ranking of COJ, SLJ, ≥SLJ-SB, SJP, ALU≥ALU-SB,REF-CP>REF-SB. SignificanceThe reactivity of the silanes used showed great variations to support a predictable effect in all treatments. CP with deactivated silanols demonstrated a) the most reliable and strongest treatment with a silica-rich powder (COJ), despite the lowest Sa,Sz substrate values and b) high strength with a low-silica powder (SLJ) with higher Sa,Sz substrate values. Therefore, it may be concluded that 10-MDP greatly contributes to the bonding mechanism of the silane containing primers.

Fabrication of spherical GeSbTe nanoparticles by laser printing technique

By using the laser printing technique, for the first time we fabricate spherical nanoparticles of germanium-antimony-telluride alloy possessing a high refractive index and amorphous-to-crystalline phase transition. The nanoparticles are examined by means of optical dark field micro-spectroscopy, which shows scatterers with different colours (with different optical resonances). The direct measurements of their diameters by using the transmission electron microscopy reveal that the nanoparticles’ colours are related to different sizes of the nanoparticles. While most of nanoparticles are homogeneous, our study shows that some fabricated particles have a core-shell structure.

An instrumental approach to combining confocal microspectroscopy and 3D scanning probe nanotomography

In the past decade correlative microscopy, which combines the potentials of different types of high-resolution microscopies with a variety of optical microspectroscopy techniques, has been attracting increasing attention in material science and biological research. One of outstanding solutions in this area is the combination of scanning probe microscopy (SPM), which provides data on not only the topography, but also the spatial distribution of a wide range of physical properties (elasticity, conductivity, etc.), with ultramicrotomy, allowing 3D multiparametric examination of materials. The combination of SPM and ultramicrotomy (scanning probe nanotomography) is very appropriate for characterization of soft multicompound nanostructurized materials, such as polymer matrices and microstructures doped with different types of nanoparticles (magnetic nanoparticles, quantum dots, nanotubes, etc.), and biological materials. A serious problem of this technique is a lack of chemical and optical characterization tools, which may be solved by using optical microspectroscopy.Here, we report the development of an instrumental approach to combining confocal microspectroscopy and 3D scanning probe nanotomography in a single apparatus. This approach retains all the advantages of SPM and upright optical microspectroscopy and allows 3D multiparametric characterization using both techniques. As the first test of the system developed, we have performed correlative characterization of the morphology and the magnetic and fluorescent properties of fluorescent magnetic microspheres doped with a fluorescent dye and magnetic nanoparticles. The results of this study can be used to obtain 3D volume images of a specimen for most high-resolution near-field scanning probe microscopies: SNOM, TERS, AFM–IR, etc. This approach will result in development of unique techniques combining the advantages of SPM (nanoscale morphology and a wide range of physical parameters) and high-resolution optical microspectroscopy (nanoscale chemical mapping and optical properties) and allowing simultaneous 3D measurements.

A Platform for Analysis of Nanoscale Liquids with an Array of Sensor Devices Based on Two-Dimensional Material.

Analysis of nanoscale liquids, including wetting and flow phenomena, is a scientific challenge with far reaching implications for industrial technologies. We report the conception, development, and application of an integrated platform for the experimental characterization of liquids at the nanometer scale. The platform combines the functionalities of a two-dimensional electronic array of sensor devices with in situ application of highly sensitive optical microspectroscopy and atomic force microscopy. We demonstrate the performance capabilities of the platform with an embodiment based on an array of optically transparent graphene sensors. The application of electronic and optical sensing in the platform allows for differentiating between liquids electronically, for determining a liquid's molecular fingerprint, and for monitoring surface wetting dynamics in real time. In order to explore the platform's sensitivity limits, we record topographies and optical spectra of individual, spatially isolated sessile oil emulsion droplets having volumes of less than ten attoliters. The results demonstrate that integrated measurement functionalities based on two-dimensional materials have the potential to push lab-on-chip based analysis from the microscale to the nanoscale.

Probing two dimensional (2D) semiconductors by employing nonliner optical microspectroscopy

Probing two dimensional (2D) semiconductors by employing nonliner optical microspectroscopy

Late Roman and Byzantine mosaic opaque “glass-ceramics” tesserae (5th-9th century)

Forty-two mosaic coloured/opaque “glass” tesserae from three sites (Milan, Italy; Durrës, Albania; Hierapolis, Turkey) situated in the Western and Eastern parts of the Roman/Byzantine Empire, dated between the 5th and the 9th centuries, were studied by optical microscopy, SEM-EDX and Raman microspectroscopy in order to investigate the nature of their pigments and opacifiers as well as the microstructure of glass ceramic materials. The Raman signatures of glass matrix and phases dispersed in the soda-lime glassy matrix showed the presence of six opacifiers/pigments. The use of soda ash glass in the tesserae from Durrës (post 8th c.) allows refining the mosaic debated chronology. The use of soda ash matrix glass together with the presence of calcium antimonates (Ca2Sb2O7 and CaSb2O6), pyrochlore solid solution/Naples’ yellow (PbSb2−x−ySnxMyO7−δ) and cuprite (Cu2O) or metallic copper (Cu0) in many samples show the technological continuity in a Roman tradition. However, the presence of cassiterite (SnO2) and quartz (SiO2) in one sample from the beginning of the 5th century, diverging from Roman technology, offers a chronological marker to identify newly (not re-used) produced tesserae.

Catalyst role of Nd3+ ions for the precipitation of silver nanoparticles in phosphate glass

The present work proposes that neodymium(III) performs as catalyst enhancing the precipitation of Ag nanoparticles (NPs) in silver-doped phosphate glass. In situ optical isothermal microspectroscopy was employed for evaluating the influence of the rare-earth dopant on the kinetics of Ag NP precipitation in real time in the solid-state host. A temperature-dependent first-order exponential increase with time of the peak optical density of the surface plasmon resonance of Ag NPs was observed in relation to concomitant particle nucleation and diffusion-driven growth. An Arrhenius-type plot was used for the activation energy estimation of the plasmonic Ag particles precipitation at 2.3 eV. This value is about 56% lower than the activation energy of 5.2 eV measured previously in our group [46] for the diffusion-based Ag NP growth in the glass without Nd3+ ions. Further characterizations were performed by differential scanning calorimetry, transmission electron microscopy, solid-state 31P nuclear magnetic resonance spectroscopy, and Raman scattering, in support of the in situ optical measurements. The distinctive results were discussed in the context of glass composition and structure.

Optical microspectroscopy study on enriched (11,10) SWCNTs encapsulating C60 fullerene molecules

The interaction between C60 fullerene molecules and single-chirality (11,10) single-walled carbon nanotubes (SWCNTs) is demonstrated by probing the optical transitions in (11,10) peapods by optical microspectroscopy. The results of the (11,10) SWCNTs and (11,10) peapods are compared to multi-chirality SWCNTs and peapods. The absence of the fine structure of the absorption bands in the case of (11,10) SWCNTs in comparison to multi-chirality SWCNTs demonstrates that the (11,10) SWCNTs provide a well-defined environment for studying the interaction between the encapsulated C60 molecules and the nanotubes. As compared to (11,10) SWCNTs, the absorption bands in (11,10) peapods show a large red shift and a reduction of the spectral weight. These findings suggest that the filling of the (11,10) SWCNTs with C60 molecules increases the internal dielectric constant and induces a charge transfer between the SWCNTs and the encapsulated C60 molecules. For testing the effect of the internal dielectric constant and charge transfer on the optical properties of the (11,10) SWCNTs, the (11,10) peapods were transformed to double-walled carbon nanotubes (DWCNTs) using the laser irradiation method. The transformation of the encapsulated fullerene molecules into inner wall reduces the environmental dielectric constant as well as the charge transfer from the outer tube.

Optics of an individual organic molecular mesowire waveguide: directional light emission and anomalous refractive index

We report on experimental investigations performed on an isolated organic mesowire waveguide resting on a glass substrate. The waveguide was made of diaminoanthraquinone (DAAQ) molecular aggregates. First, we show directional emission of light from distal ends of the DAAQ waveguide. For a given mesowire geometry, operating in passive or photoluminescence regimes, we quantified the emission angles by combining multi-wavelength Fourier-plane optical microscopy and photoluminescence micro-spectroscopy. We found light emission in the photoluminescence regime to be more directional in nature compared to the passive waveguiding regime, which was supported by three-dimensional finite-difference time-domain (FDTD) simulations. Second, we measured the anomalous behaviour of refractive index as a function of emission wavelength using the spectra of directionally emitted light. Third, by using spatial-filtered collection optics, we observed and quantified single-excitation dual-channel directional, active emission from DAAQ mesowire. The results discussed herein has implication not only in understanding some fundamental aspects of exciton-polariton mediated directional light emission, but also in applications such as organic optical antennas and photonic couplers.

Scanning near-field optical nanotomography: a new method of multiparametric 3D investigation of nanostructural materials

A new experimental approach to multiparametric three-dimensional (3D) investigation of a broad class of composite nanostructural materials is developed on the basis of scanning near-field optical nanotomography (SNONT). Using this method, it is possible to simultaneously study the optical properties, 3D morphology, and distribution of the mechanical and electrical properties of the same region of a sample. The proposed method combines features of the confocal and near-field optical microspectroscopy (fluorescence and Raman spectroscopy) with a lateral resolution of up to 50 nm and scanning-probe microscopy. The possibility of studying the volume distribution of optical, morphological, electrical, and mechanical characteristics of a material with nanoscale resolution is related to the probing of sequential layers at a step of up to 20 nm and a total Z-scan depth of up to 3 mm. In particular, the SNONT method has been used to study a liquid-crystalline polymer doped with fluorescent nanocrystals.

Resonant laser processing of nanoparticulate Au/TiO2 films on glass supports: Photothermal modification of a photocatalytic nanomaterial

Resonant laser processing at λ=532nm is used to modify thin Au/TiO2 nanoparticle films on soda lime glass plates. A microfocused continuous-wave laser is employed for local patterning at distinct laser powers. In conjunction with microscopic techniques this approach allows for reproducible high-throughput screening of laser-induced material modifications. Optical microscopy and microspectroscopy reveal laser darkening, i.e. a significantly increased optical absorbance. Scanning electron microscopy and X-ray photoelectron spectroscopy show laser-induced film growth and roughening along with the integration of SiO2 from the glass supports. Raman spectroscopy displays a phase transition from anatase to rutile. Au evaporation and/or integration only takes place at high laser powers. All these modifications provide promising perspectives in view of photocatalytic applications. Data from complementary laser experiments with unblended pure TiO2 coatings at λ=532nm and λ=355nm point to a photothermal process, in which the optical energy is selectively deposited in the Au nanoparticles and transformed into heat. As a result, thermally activated modifications take place. General prospects of laser processing in targeted modification of nanomaterials for photocatalysis are emphasized.

Label-free imaging and quantitative chemical analysis of Alzheimer's disease brain samples with multimodal multiphoton nonlinear optical microspectroscopy.

We developed multimodal multiphoton microspectroscopy using a small-diameter probe with gradient-index lenses and applied it to unstained Alzheimer's disease (AD) brain samples. Our system maintained the image quality and spatial resolution of images obtained using an objective lens of similar numerical aperture. Multicolor images of AD brain samples were obtained simultaneously by integrating two-photon excited fluorescence and second-harmonic generation on a coherent anti-Stokes Raman scattering (CARS) microendoscope platform. Measurements of two hippocampal regions, the cornus ammonis-1 and dentate gyrus, revealed more lipids, amyloid fibers, and collagen in the AD samples than in the normal samples. Normal and AD brains were clearly distinguished by a large spectral difference and quantitative analysis of the CH mode using CARS microendoscope spectroscopy. We expect this system to be an important diagnosis tool in AD research

Multimodal nonlinear Raman microspectroscopy with ultrashort chirped laser pulses

We demonstrate the physical principles of multimodal nonlinear optical microspectroscopy, integrating methods of coherent and stimulated Raman scattering of ultrashort chirped laser pulses in a single optical scheme. Nonlinear phase distortions of ultrashort laser pulses are accurately compensated within a broad spectral range in this scheme to enable a high-spectral-resolution laser microspectroscopy that can reliably resolve groups of fingerprint molecular vibrations with close frequencies, thus facilitating an analysis of complex multicomponent systems.

Experimental Verification of the Kinetic Theory of FRET Using Optical Microspectroscopy and Obligate Oligomers

Förster resonance energy transfer (FRET) is a nonradiative process for the transfer of energy from an optically excited donor molecule (D) to an acceptor molecule (A) in the ground state. The underlying theory predicting the dependence of the FRET efficiency on the sixth power of the distance between D and A has stood the test of time. In contrast, a comprehensive kinetic-based theory developed recently for FRET efficiencies among multiple donors and acceptors in multimeric arrays has waited for further testing. That theory has been tested in the work described in this article using linked fluorescent proteins located in the cytoplasm and at the plasma membrane of living cells. The cytoplasmic constructs were fused combinations of Cerulean as donor (D), Venus as acceptor (A), and a photoinsensitive molecule (Amber) as a nonfluorescent (N) place holder: namely, NDAN, NDNA, and ADNN duplexes, and the fully fluorescent quadruplex ADAA. The membrane-bound constructs were fused combinations of GFP2 as donor (D) and eYFP as acceptor (A): namely, two fluorescent duplexes (i.e., DA and AD) and a fluorescent triplex (ADA). According to the theory, the FRET efficiency of a multiplex such as ADAA or ADA can be predicted from that of analogs containing a single acceptor (e.g., NDAN, NDNA, and ADNN, or DA and AD, respectively). Relatively small but statistically significant differences were observed between the measured and predicted FRET efficiencies of the two multiplexes. While elucidation of the cause of this mismatch could be a worthy endeavor, the discrepancy does not appear to question the theoretical underpinnings of a large family of FRET-based methods for determining the stoichiometry and quaternary structure of complexes of macromolecules in living cells.

Growth Behavior of Monohydrocalcite (CaCO3·H2O) in Silica-Rich Alkaline Solution

Monohydrocalcite (CaCO3·H2O) has been crystallized in silica-rich alkaline water solution. The crystallization proceeds by a counterdiffusion method without the presence of any other additive except dissolved silica. The crystallization has been followed in situ by optical microscopy and Raman microspectroscopy, while the time evolution of the pH and the concentration of calcium and silica species in solution have also been followed either by in situ (pH) or ex-situ (calcium and silica) time-lapse analysis. The growth of monohydrocalcite particles occurs by different mechanisms that are related to the pH and the rate of pH change with time. The initial peanut-like crystal converts into an onion-like multilayered texture, which is built up by the alternation of loose layers and compact layers as a result of different levels of silica incorporation. A final silica-rich skin covers the hemisphere inhibiting the further growth of monohydrocalcite. When the silica skin fails to cover the whole surface of the hemisphere, a bulge of monohydrocalcite grows from the uncovered area until a new silica skin inhibits its growth except from a small uncovered area from which a new bulge forms. The iteration of this mechanism creates particles with caterpillar-like morphology. Our results show that silica plays a key role in the morphogenesis and texture of monohydrocalcite crystallization due to the coupled interaction between the reverse solubility of silica and carbonate versus pH.

Kinetics of copper nanoparticle precipitation in phosphate glass: an isothermal plasmonic approach.

The kinetics of copper nanoparticle (NP) precipitation in melt-quenched barium-phosphate glass has been studied by in situ isothermal optical micro-spectroscopy. A spectroscopically based approximation technique is proposed to obtain information about the activation energies of nucleation and growth in a narrow temperature range (530-570 °C). Pre-plasmonic and plasmonic NP precipitation stages are identified separated in time. The process as a whole is discussed employing classical nucleation/growth theory and the Kolmogorov-Johnson-Mehl-Avrami phase change model. Activation energies of 3.9(7) eV and 2.6(5) eV have been estimated for the pre-plasmonic and plasmonic spectroscopically assessed stages, respectively. High resolution transmission electron microscopy, differential scanning calorimetry, and Raman spectroscopy were used as complementary techniques for studying the nanoparticulate phase and glass host structure. An empirical linear dependence of the diffusion activation energy on the glass transition temperature with broad applicability is suggested.