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We present inelastic neutron scattering measurements of Y3Al5O12. The measured neutron-weighted phonon density-of-states and optical phonon frequencies are compared with the results from atomistic calculations within the Quasi-Harmonic Approximation (QHA) over a wide temperature range, using both first principles density functional theory calculations and also an extended empirical interatomic-potential shell model scheme. The phonon-related thermodynamic and elastic properties calculated within the QHA are in excellent agreement with the available experimental data.

(Sm1/3Ca2/3)2.75C60 is a member of the family of non-stoichiometric strongly-correlated rare-earth fullerides, (Sm1−xCax)2.75C60 (0 ≤ x ≤ 1), in which an orthorhombic 2 × 2 × 2 supercell of the face-centred cubic (fcc) unit cell of stoichiometric A3C60 (A = alkali metal) fullerides is stabilized by the long-range ordering of partially-occupied metal sites. At ambient temperature and pressure, it is a mixed valence compound with an average Sm valence of +2.33(2) implying a formal charge of −5.78 for the C60 anions. Here we study its electronic response to the application of pressure in the range 0–9 GPa. Synchrotron X-ray absorption measurements in the high-resolution partial fluorescence yield mode (PFY-XAS) at ambient temperature show the onset of an abrupt strongly hysteretic (width ∼2.5 GPa) first-order reversible phase transition at ∼4 GPa, accompanied by a drastic increase in the bulk Sm valence by ∼20% to +2.71(3). This is coincident with the huge lattice contraction and concomitant insulator-to-metal transition encountered before for Sm2.75C60 in the same pressure range and provides a possible explanation of the physical properties in terms of the strong coupling between the lattice and electronic degrees of freedom. The behaviour is reminiscent of the electronic and lattice response to pressure of highly correlated Kondo insulators like SmS and its ternary derivatives, Sm1−xRxS (R = Ca, Y, etc.). However, a distinguishing feature of the fulleride systems is that the C60 anionic sublattice can act as an electron reservoir due to the availability of a close-lying band derived by the t1g orbitals and can accept excess charge as the 4f-electron occupation number decreases. The observed electronic response as a function of pressure is thus opening new possibilities for accessing metallic fullerides at elevated pressures.

Surface enhanced Raman scattering (SERS) has emerged as a reliable and ultra-sensitive sensing technique used in analytical diagnostics, forensics, and biomedical applications. Although SERS may be sensitive enough todetect single molecules, such extreme performance is achieved with sophisticated and complex nanostructure designs that are hard to implement on an industrial scale. This work presents an understanding of the plasmonicand wetting phenomena taking place on Ag nanoparticles (supported on Si) produced by laser annealing and dewetting of sputtered ultra-thin layers enabling the fast (SERS templates with a hierarchical plasmonic structure. In particular, the produced SERS templates incorporate micron-scale accumulation spots of the Rhodamine 6 G test molecules, superimposed over nano-scale hot spots,where electric near field enhancement occurs due to plasmon resonances. This combination increases drastically the SERS signal, making it suitable for fast chemical diagnostics.

In the present work, we elucidate the interplay among energetic bombardment effects in magnetron sputtering and defect generation in two-dimensional (2D) materials. Using deposition of gold (Au) layers on single-layer graphene (SLG) as a model system, we study the effect of pressure-distance (pd) product during magnetron sputtering on the pristine SLG properties. Raman spectroscopy, complemented by X-ray photoelectron spectroscopy, shows that for pd = 8.2 Pa center dot cm, Au layer deposition causes defects in the SLG layer, which gradually diminish and eventually disappear with increasing pd to 82.5 Pa center dot cm. Stochastic and deterministic simulations of the sputtering process, the gas-phase transport, and the interaction of sputtered and plasma species with the substrate surface suggest that defects in SLG primarily emanate from ballistic damage caused by backscattered Ar atoms with energies above 100 eV. With increasing pd, and thereby gas-phase scattering, such high energy Ar species become thermalized and hence incapable of causing atomic displacements in the SLG layer. The overall results of our study suggest that control of backscattered Ar energy is a potential path toward enabling magnetron sputtering for fabrication of multifunctional metal contacts in devices founded upon 2D materials. Funding Agencies|Linkodping University ("LiU Career Contract) [Dnr-LiU-2015-01510]; Swedish research councilSwedish Research CouncilEuropean Commission [VR-2015-04630]; Aforsk foundation [AF 19-137]; Olle Engkvist foundation [SOEB 190-312]; Wenner-Gren foundations [UPD2018-0071, UPD2019-0007]

TiN and ZrN are emerging as important alternative plasmonic materials. In addition to their well-known assets, they can incorporate point defects that break the centrosymmetry of their cubic crystal structure, making them promising candidates as nonlinear optical materials, especially for second-harmonic generation (SHG). Their refractory character and chemical stability have been obstacles for the bottom-up fabrication of TiN and ZrN nanostructures so far. In this work, it is shown that highly directional dichroic nanostructures of TiN and ZrN may be indeed grown by self-assembly using glancing angle deposition on periodic rippled dielectric surfaces. The produced nitride nanostructures exhibit point defects and exceptional photothermal durability. These nanostructures exhibit strong SHG response when probed by a near-infrared laser. It is shown that SHG is strongly associated with the near-field enhancement due to localized surface plasmon resonance of the nanostructures. Given that such nanostructures can endure extremely high electric fields, they are expected to be able to emit massive SHG signals and be applied in laser technology as optical components such as polarizers and SHG emitters.

Starch systems containing indomethacin were prepared by the alkaline method and characterized in order to investigate the potential of this method to produce amylose molecular inclusion complexes as targeted and controlled drug delivery carriers. Three types of starches with different amylose/amylopectin composition were used to prepare the systems. Their structure was probed by X-ray diffraction (XRD) and Raman spectroscopy, whereas their morphology was investigated by Optical microscopy and Confocal laser scanning microscopy (CLSM). Raman spectroscopy revealed the presence of p-chlorobenzoic acid, the degradation product of the alkaline hydrolysis of indomethacin in the matrix of the starch systems. The results were confirmed by XRD measurements and the degree of crystallinity of the starch systems ranged from 35 to 90%. In vitro release testing of indomethacin from the starch systems in the simulated gastric and small intestine fluid showed very low concentrations of indomethacin. CLSM micrographs and optical microscopic examination revealed the presence mostly of the p-chlorobenzoic acid, in the matrix of the starch systems, rather than of indomethacin. The results, in general, indicated that the p-chlorobenzoic acid molecules were either included in the amylose helices or they have been entrapped between the helices of the complexed amylose whereas the few indomethacin molecules present in the starch matrix probably were also mechanically entrapped.

Copper(I) oxide (Cu2O) nanoparticles (NPs) of 30 nm with antifungal properties have been functionalized with 9 nm nickel ferrite (NiFe2O4) magnetic nanoparticles (MNPs) to construct hetero-nanocomposites (NCs) of a submicron hydrodynamic size for magnetomechanical stress induction in the yeast, Saccharomyces cerevisiae. A post-synthetic approach involving the assembly through hydrophobic interactions of the preformed NPs of non-uniform sizes, albeit coated with the same surfactant (oleylamine), is reported. Solvents of different polarity were implemented during the synthetic procedure resulting in NCs of similar composition consisting mainly of MNPs randomly decorated onto the bigger Cu2O NPs. The antifungal properties of the building NPs and the NCs were studied in terms of fungistatic and fungicidal activity, whereas the ionic leaching was found to be negligible, highlighting the nanosize effect. Although S. cerevisiae cells were found to be resistant to individual NiFe2O4 MNPs because of their small size, their sensitivity to NCs significantly increased upon short-time exposure to a rotating low-frequency magnetic field (10 min, 30 Hz, 35 G) and this arises from the collective properties. The magnetomechanical cell stress induction was accompanied by alteration of cellular membrane integrity and programmed cell death signaling.

The structural properties of InxGa1−xN epilayers, deposited on (0001) AlN templates by plasma-assisted molecular beam epitaxy, were studied by transmission electron microscopy and Raman spectroscopy, as a function of growth temperature. Single phase films with high indium content and well-ordered heteroepitaxial interfaces were attained at lower temperatures. Delayed plastic relaxation resulted in the structural stratification of high-temperature films due to the compositional pulling. Such films relaxed by a stacking fault mechanism, contrary to low temperature ones that exhibited relaxation by misfit dislocations. Despite the higher defect content of the former, their phonon mean free path was also higher, showing that alloying-induced fluctuations of the periodic potential constitute a more critical parameter. Cubic interfacial zones were suppressed at lower growth temperatures.This is part of a thematic issue on Nanoscale Materials Characterisation and Modeling by Advances Microscopy Methods -...

In the present study, for the first time we tailored organic chemistry traditional synthesis tools towards preparation of CexSm1-xO2 (x = 0.2, 0.5, 0.8, 1) fluorite-type mixed oxides which are used for CO abatement. In this study, microwave radiation has been used as stand-alone heating method (conventional microwave), in the presence of oxalic acid acting as complexing agent (OX), or it has been coupled with simultaneous air cooling (AC), reflux (RE) and on/off cycles of the magnetron power (C1 and C5) in the so called enhanced microwave synthesis (EMW) approach. The EMW methods were applied in the case of Ce0.5Sm0.5O2 composition and enlightened different aspects of the rational design of its morphology (flower-like, rod-shaped, random aggregates), as well as the engineering of its oxygen vacant sites. CO oxidation reaction, in the presence and absence of H2, was used as a model probe reaction towards the evaluation of the catalysts. Different characterization techniques, namely, XRD, BET, ICP-MS, Raman, SEM, FTIR, TEM, XPS, H2-TPR, and CO2-TPD, have been employed to understand the synthesis −structure-properties relationship of the catalysts. Interestingly, the EMW synthesis conditions affect the crystalline structure of the catalysts (XRD), and the crystal growth, giving rise to CexSm1-xO2 particles with a crystallite size in the range of 8–26 nm. A rational manipulation of the morphology of the CexSm1-xO2 was achieved under the different EMW synthesis conditions and reported herein for the first time in such a systematic way, where the Ce0.5Sm0.5O2 catalyst was crystallized in octahedral rods (RE), random aggregates (C1 and C5), and elongated flower-like shapes (AC). The co-presence of Ce3+ and Sm3+ in the metal oxides (XPS studies) facilitates the presence of oxygen vacant sites, as confirmed by the Raman spectra (550–590 cm‐1), the mobility of which, though, differs as has been proved by H2-TPR, following the order: Ce0.5Sm0.5 (RE) > Ce0.5Sm0.5 (AC) > Ce0.5Sm0.5 (C1). A tensile lattice strain in the 0.6–2.4% range of the cubic CexSm1-xO2 lattice was found to be strongly correlated with the CO oxidation performance. Two of the enhanced microwave methods, RE and AC, led to catalysts with improved catalytic performance, lowering the T50 by 130 °C (or 27%) and 30 °C (or 6%), respectively, compared to the Ce0.5Sm0.5O2 (OX). The superior performance is discussed in terms of oxygen vacancies, oxygen mobility, lattice strain and CO2-affinity of the surfaces involved. KP would like to acknowledge the financial support from Abu Dhabi Educational Council (ADEC B3111 ) and Khalifa University Internal Research Fund ( L1KUIRF-210103 ) for supporting this research. KP thanks Khalifa University Core Nanocharacterization Facilities and acknowledges KU and CNCF staff support. AFZ acknowledges the support of the grant number NPRP 6-351-1-072 from the Qatar National Research Fund (a member of Qatar Foundation). Work done by AFI was done at Cornell University CCMR and Brookhaven National Lab CFN, supported by US Department of Energy . This work made use of the Cornell Center for Materials Research Shared Facilities which are supported through the NSF MRSEC program (DMR-1719875). This research used resources of the Center for Functional Nanomaterials, which is a U.S. DOE Office of Science Facility, at Brookhaven National Laboratory under Contract No. DE-SC0012704. Scopus

In-K-edge x-ray absorption fine structure (EXAFS), x-ray photoelectron, and Raman spectroscopy results are combined for a comprehensive study of InxGa1−xN layers with energy gaps extending over nearly the whole visible spectrum. The In–N and In–(In,Ga) distances determined by EXAFS are used for the derivation of the In–N bond ionicity as well as for the phonon frequency dependence of the LO and B12 modes, assessed by Raman, and the N 1s, In 3d5/2, Ga 3s, and Ga 2p1/2 electron binding energies on those distances. Phonon confinement due to perturbation of the periodic potential caused by the alloying is also quantified.

There is a growing field of research on the physicochemical properties of bimetallic nanoparticles (BMNPs) and their potential use in different applications. Meanwhile, their antimicrobial activity is scarcely reported, although BMNPs can potentially achieve unique chemical transformations and synergetic effects can be presented. Towards this direction a reproducible simple hybrid polyol process under moderate temperature solvothermal conditions has been applied for the isolation of non-oxide contaminated bimetallic CuFe nanoparticles (NPs). 1,2-propylene glycol (PG), tetraethylene glycol (TEG) and polyethylene glycol (PEG 8000), that exhibit different physicochemical properties, have been utilized to regulate the size, structure, composition and the surface chemistry of NPs. The BMNPs were found to be of small crystalline size, 30–45 nm, and high hydrophilicity, different wt% percentage of organic coating and variable hydrodynamic size and surface charge. The antimicrobial activity of the BMNPs was evaluated against the bacterial strains B. subtilis , E. coli and fungus S. cerevisiae . The IC 50 values for CuFe NPs were found significantly lower compared with Cu NPs of the same size, revealing an enhancement in the antimicrobial activity when iron and copper coexist in the crystal structure. The reactive oxygen species (ROS) production was measured intracellularly and extracellularly by the nitroblue tetrazolium assay in the fungal cultures. No extracellular ROS were measured suggesting that both CuFe and Cu NPs enter the fungal cells during the incubation, also verified by optical imaging of the fungal cells in the presence of NPs. Higher ROS concentrations were generated intracellularly for CuFe NPs supporting different red/ox reaction mechanisms.

Raman spectroscopy is used to study the pressure response of crystalline fluorene up to 9 GPa. Pressures higher than 2.5 GPa cause a reversible rearrangement of the molecular stacking, changes in the electronic properties and structural stiffening, leading to a decrease of the pressure coefficients of the intermolecular peak frequencies. The coefficients are further reduced above 6 GPa where fluorene is fully transformed to its isostructural high-pressure phase, while the coexistence of the two phases is evident in the downstroke spectra. The phase transition has less profound effects on the intramolecular modes with the exception of the C–H vibrations.

The photopolymer formation in the fullerene layers of the C 60 complex with platinum dibenzyldithiocarbamate is reported for the first time. The photo-oligomer peaks appear in the Raman spectra near the A g (2) mode of the C 60 molecule upon sample illumination with various laser wavelengths. The photo-oligomers are unstable upon heating and revert back to the C 60 monomeric state. The activation energy of the thermal decomposition, obtained from the Arrhenius dependence of the decay time constant on temperature, is (1.12 ± 0.11) eV and the photo-oligomers decompose at ∼130 °C, being more fragile than the crystalline polymers of C 60 .

Rare-earth (RE) fullerides are an intriguing family of materials in which electronic instabilities on the RE sublattice couple to the electronic and lattice degrees-of-freedom of the strongly-correlated fulleride sublattice. In particular, insulating Sm2.75C60 adopts an orthorhombic superstructure, arising from long-range ordering of Sm partial vacancies, and can be driven to a lattice-collapsed metallic state due to a valence transition towards Sm3+ upon pressurization. Here we use synchrotron X-ray absorption spectroscopy (XAS) at the Sm L3 edge at ambient conditions to authenticate the mixed valence character of the material by identifying two features due to distinct Sm2+ and Sm3+ components – their relative intensity allows a direct measure of the average Sm valence in Sm2.75C60 at +2.07(3). We then attempt to mimic the physical pressure effect on the electronic properties by co-intercalation of the smaller-size valence-precise Ca2+ ion to form the series of ternary solid solutions, (Sm1-xCax)2.75C60 (0 ≤ x ≤ ⅔). XAS measurements in their high-resolution partial fluorescence yield (PFY) variance find that chemical pressure leads to an increase of the Sm3+ contribution to the average valence by >10% in the most contracted member, (Sm⅓Ca⅔)2.75C60 of the present study with the average valence reaching a value of +2.33(2). Assuming full charge transfer between the metal ions and C60, the charge on the C60 units remains invariant throughout at approximately −5.78. This opens the possibility that the system can be tuned further towards the higher average valences needed for the high-pressure insulator-to-metal transition in Sm2.75C60 to be shifted to ambient pressure with a single-valence Sm3+ state accessible at a Ca content of x ~0.9.

Raman spectra of the C120 crystalline fullerene dimers, synthesized by high-pressure/high-temperature (HPHT) treatment of the C60 fullerite, were measured at ambient and elevated temperatures (T > 130 °C) in order to study the kinetics of their thermal decomposition. Measurements exhibit an intensity decrease of the dimer-related pentagon pinch (PP) mode and an increase of the monomer’s one. The relative intensity of the dimer’s PP mode decreases exponentially with the thermal treatment time and becomes faster at elevated temperatures. The activation energy EA of the dimer decomposition, obtained from the Arrhenius dependence of the exponential decay time constant on temperature, is (1.71 ± 0.06) eV.

The photopolymerization process and the stability of the C60 photo-oligomers at elevated temperature in the molecular donor-acceptor fullerene complex {Pt(dbdtc)2} ·C60 (C60 complex with platinum dibenzyldithiocarbamate) and pristine fullerite C60 are studied by Raman spectroscopy. Fast polymerization, manifested by the appearance of additional peaks in the frequency region of the A g (2) pentagon-pinch (PP) mode of the C60 molecule, was observed upon sample illumination at 514.5 and 532 nm, even at low laser power density as well as at 785 nm at higher power density. The frequencies of the new peaks are in accordance with the empirical dependence of the PP-mode frequency on the number of the sp3-like coordinated carbon atoms per molecular cage. The temperature dependence of the polymer content under constant laser power density reveals the decomposition of the photo-oligomers to monomers at ~ 350 K in the fullerene complex {Pt(dbdtc)2} ·C60 and at ~ 410 K in the case of the pristine C60. These values are considerably smaller than the decomposition temperature of 525 565 K for the crystalline polymers of C60.

In this study, we examined the influence of microstructured charcoal (MC) when added to ammonium nitrate fuel oil (ANFO) samples. We performed a study that investigated ANFOs structure, crystallinity, and morphology by utilizing infrared spectroscopy (IR), X-ray diffraction (XRD), and scanning electron microscopy (SEM), respectively. MC characteristics were probed by Raman spectroscopy and SEM analysis. SEM analysis indicated how fuel oil (FO) covered ammonium nitrate prill. Moreover, the surface of the MC was covered by specific microfibers and microtubes. The disordered graphitic structure of the MC was also confirmed by Raman spectroscopy. Simulation of blasting properties revealed that the addition of MC should decrease blasting parameters like heat explosion, detonation pressure, and detonation temperature. However, the obtained differences are negligible in comparison with the regular ANFO. All analyses indicated that MC was a good candidate as an additive to ANFO.

The structural stability and electronic properties of [Formula: see text] are probed by means of high-pressure Raman spectroscopy using two different pressure transmitting media that lead to practically identical results. Although [Formula: see text] is isostructural with the rare-earth metal fulleride, [Formula: see text] of the same stoichiometry, the pressure coefficients of characteristic intramolecular [Formula: see text] modes are larger than those in the [Formula: see text] counterpart but similar to those in the pristine [Formula: see text] solid. Since the reduced pressure coefficients in the Sm fulleride have been attributed to strong [Formula: see text] coupling, our findings for the isostructural Ca fulleride are compatible with a reduced orbital mixing and [Formula: see text] coupling.

The growth of GaN nanocrystals in an amorphous SiO2 matrix by sequential Ga and N implantation and rapid thermal annealing is reported. The effect of the implantation and annealing conditions on the distribution of the implanted ions, as well as the size, static disorder, and stability of the grown GaN nanocrystals, is studied by means of transmission electron microscopy, Rutherford backscattering spectrometry, Raman scattering, and extended X-ray absorption fine structure spectroscopies. It is found that the optimum temperature range for the post-implantation annealing of the nanocrystals, with a size that ranges from about 3 to 12 nm, is 1000–1100 °C. Higher temperatures result in the dissociation of the nanocrystals and out-diffusion of N and Ga, whereas lower temperatures are insufficient for the growth of GaN nanocrystals. Annealing for 30–90 s is optimum in order to avoid considerable loss of N and Ga. However, upon annealing at higher temperatures within the optimum range, up to 1100 °C, or for longer times, up to 120 s, larger GaN nanocrystals are grown and/or lower static disorder is observed.

The high pressure response of type-I collagen from bovine Achilles tendon is investigated with micro-Raman spectroscopy. Fluorinert™ and methanol-ethanol mixtures were used as pressure transmitting media (PTM) in a diamond anvil cell. The Raman spectrum of collagen is dominated by three bands centred at approximately 1450, 1660 and 2930 cm-1 , attributed to C-H deformation, C=O stretching of the peptide bond (amide-I band) and C-H stretching modes respectively. Upon pressure increase, using Fluorinert™ as PTM, a shift towards higher frequencies of the C-H stretching and deformation peaks is observed. Contrary, the amide-I band peaks are shifted to lower frequencies with moderate pressure slopes. On the other hand, when using the alcohol mixture as PTM, the amide-I band exhibits more pronounced C=O bond softening, deduced from the shift to lower frequencies, suggesting a strengthening of the hydrogen bonds between glycine and proline residues of different collagen chains due to the presence of the polar alcohol molecules. Furthermore, some of the peaks exhibit abrupt changes in their pressure slopes at approximately 2 GPa, implying a variation in the compressibility of the collagen fibres. This could be attributed to a pitch change from 10/3 to 7/2, sliding of the tropocollagen molecules, twisting variation at the molecular level and/or elimination of the D-gaps induced by kink compression. All spectral changes are reversible upon pressure release, which indicates that denaturation has not taken place. Finally, a minor lipid phase contamination was detected in some sample spots. Its pressure response is also monitored.

A facile and low-cost method for structuring carbon-encapsulated cobalt nanoparticles (Co@C) is presented. Three samples were solvothermally prepared in one step at 220 °C and one in two steps at 200 °C. Three different polyols such as propylene glycol, triethylene glycol, and tetraethylene glycol were used as carbon sources, solvents, and reducing agents. The samples were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and Raman spectroscopy. Concerning the crystal structure of the particles, a mixture of hcp/fcc Co phases was obtained in three of the samples, independently of the polyol used. The coexistence of cubic and hexagonal phases was revealed both from XRD and high-resolution TEM (HRTEM). The formation of the cubic fcc structure, despite the relatively low reaction temperature, is attributed to the role of the interface between carbon coating and metallic core. The presence of carbon coating was demonstrated by Raman spectrometry, exhibiting the characteristic D and G graphitic bands, and by HRTEM observations. All samples showed ferromagnetic behavior with saturation magnetization up to 158 emu/g and coercivity up to 206 Oe. From the magnetic particle hyperthermia measurements recorded at a frequency of 765 kHz, a maximum SLP value of 241 W/g was obtained.

The effectiveness of a low cost sorbent produced by thermal modification of ammonium heptamolybdate (AHM) in adsorption of radionuclides and heavy metals was investigated. The product was characterized by XRD, SEM and Raman spectroscopy. Sorption experiments were performed in Pb, U, Cs, Ba and Eu solutions (pH 2.0–6.0). The obtained isotherms were simulated by Langmuir and Freundlich isotherms and kinetics data were used in order to evaluate the sorption mechanism. The results showed the high and selective efficiency of the AHM-derived MoO3 especially in Pb and U removal whereas the desorption experiments revealed its environmental applicability under real conditions for the investigated metal cations.

Amylose or pea starch‐indomethacin systems are prepared using two different methods: The alkaline method, where the samples are prepared by mixing alkaline aqueous solutions of glucan and indomethacin at pH 12, and the sonication method, where the samples are prepared at pH 7 by mixing a glucan aqueous solution with indomethacin dispersed in water in the presence of cholate salts using sonication. The aim is to assess whether V‐amylose complexes can be formed with the drug indomethacin as the guest molecule. Experimental techniques, such as Raman Spectroscopy, X‐ray Diffraction, Differential Scanning Calorimetry, Optical Microscopy, and Confocal Laser Scanning Microscopy, verify the presence of the drug molecules in the examined systems. The results indicate that the sonication method is more effective for the complex preparation. However, even in this case, a very limited complexation is achieved. The bioavailability of the systems is evaluated using in vitro methods, simulating gastric, and intestinal conditions. It is shown that the systems matrix provided only limited protection to indomethacin molecules up to their release in the small intestine. Thus, it is concluded that indomethacin molecules are rather physically entrapped within the amylose or starch matrix than in the interior of the amylose helices.

This study reports a novel approach for growing multilayer thin films consisting of alternate layers of carbon nanotubes (CNT) and nickel on Si (1 0 0) substrates and justifies their use in thin film temperature sensors. A low pressure chemical vapor deposition system was employed for synthesizing CNT films, while Ni films were deposited by electrodeposition. Porous-Si was used as substrate to increase adhesion between the layers of the multilayer structure. The structure of the multilayer films and the quality of the CNT grown were analyzed using several characterization methods, including scanning electron microscopy, x-ray photoelectron spectroscopy, x-ray auger electron spectroscopy and Raman spectroscopy. The electrical characteristics were investigated using a van der Pauw setup and the effect of the increasing number of CNT layers in the multilayer structure was studied. The sensitivity of the multilayer film was found to increase with increasing number of CNT layers, despite the decrease of the temperature coefficient of resistance. On the other hand, the initial resistance was found to increase. Results indicated that these multilayer structures are appropriate for fabricating highly sensitive thin film gauges that can detect lower heat fluxes with more accuracy.

The effect of 700 keV In implantation and subsequent annealing on GaN was studied by Rutherford Backscattering spectroscopy, Raman spectroscopy and nanο-indentation as a function of the ion fluence (F) ranging from 5 × 1013 to 1 × 1016 cm− 2. Symmetry allowed and disorder activated Raman scattering peaks were analyzed using the spatial correlation model, allowing their assignment to phonon branches of crystalline GaN or defects and the estimation of the corresponding phonon coherence length (L). The L values decrease abruptly at a critical fluence of approximately 2 × 1014 cm− 2. After a slight increase in the nano-hardness (H) and reduced elastic modulus (Er) values at low implantation fluences, they exhibit a steep reduction. These variations are accompanied by changes in the shape of the load–displacement curves, which are indicative of elasto-plastic behavior up to a critical F, whereas they approach the ideal plastic behavior at higher fluences. Annealing at 1000 °C of the sample implanted with 1 × 1015 ions/cm2 results in efficient recovery of its structural and nano-mechanical properties. However, annealing of specimens implanted at higher fluences causes partial recovery that starts mainly from the transition region between the heavily damaged and the underlying undamaged GaN. The highly correlated behavior of L, H and Er on the implantation fluence implies a common origin of the studied effects.

The pressure-assisted photopolymerization in the fullerene complex {Cd(dedtc)2} 2·C60 (fullerene complex with cadmium diethyldithiocarbamate) observed in the pressure region between 2.24 and 5.99 GPa was studied in detail. After a phase transition near ~ 2 GPa, the Raman spectra exhibit time-dependent changes under prolonged laser illumination regarding the appearance of new peaks in the frequency region of the A g (2) mode of the C60 monomer. These peaks are related to the fullerene oligomers with a different number of sp3-like coordinated carbon atoms per molecular cage. The polymer content increases with the laser power density and exposure time, while for a fixed laser power, its saturated value is independent of pressure. Outside the pressure range 2.24 5.99 GPa, photopolymerization is suppressed.

The strain anisotropy of a-plane GaN epilayers is studied by polarization-dependent Raman spectroscopy. The intensity dependence of the A1(TO), E1(TO) and Raman peaks for an almost strain-free epilayer is well explained by using Raman tensors of C6v symmetry. However, the corresponding angular dependence for anisotropically strained GaN with |exx − eyy|∼6 × 10−3 (where x||a and y||m axes) dictates the use of a perturbation term of C2v symmetry that accounts for the orthorhombic distortion of the hexagonal unit cell. The consideration of this term elucidates the appearance of the mode for such epilayer orientations where it is forbidden by the hexagonal symmetry.

Raman spectra of hydrogenated and fluorinated single-wall carbon nanotubes (SWCNTs) are measured at ambient temperature before and after heat treatment. The spectra of the as-prepared hydrogenated SWCNTs show a giant structureless band in the visible region that screens the Raman peaks related to the carbon atom vibrations. The onset of this strong band follows the excitation laser line, which is typical of hot luminescence. The intensity of the luminescence background decreases exponentially with the annealing time, while the dependence of the luminescence decay time constant on the annealing temperature is of the Arrhenius type with the activation energy Ea = 465 ± 44 meV. The luminescence background in the Raman spectra of the fluorinated SWCNTs is comparable with the Raman peak intensity and decreases exponentially with the annealing time. The dependence of the decay time constant on the temperature is again of the Arrhenius type with the activation energy Ea = 90 ± 8 meV. The appearance of hot luminescence is related to the upshift of the fundamental energy gap in functionalized SWCNTs and the structural disorder induced by random binding of hydrogen or fluorine atoms. The luminescence background disappears upon annealing in vacuum or in air after removal of hydrogen (fluorine), while the annealed samples still demonstrate large structural disorder.

The high-pressure response of the Sm2.75C60 fulleride is probed by Raman spectroscopy. The Raman spectrum of Sm2.75C60 and its pressure evolution differ significantly from those of pristine C60. The initial well-resolved Raman spectrum of the fulleride disappears above 4 GPa. This change is reversible; however, the original low-pressure Raman profiles are recovered only below 2 GPa. These observations are in line with the pressure-induced hysteretic phase transition of the compound observed earlier by X-ray diffraction and the proposed insulator to metal transition.

Raman spectroscopy is employed to study the high-pressure response of carbon nanofibers exhibiting a unique morphology of stacked, truncated conical graphene layers (cups) along the longitudinal fiber axis (stacked-cup carbon nanofibers). The pressure evolution of the observed Raman peaks is smooth and reversible, and their pressure coefficients suggest an intermediate structural morphology between graphite and multiwall carbon nanotubes. The pressure coefficients are similar to those exhibited by the pressure-induced collapsed structures of large-diameter nanofibers and macroscopic fibers, suggesting the enhanced size-related rigidity of the studied system.

Raman spectra of purified arc-discharge single-walled carbon nanotubes (SWCNTs) were measured at temperatures up to 750 K. The temperature-induced frequency shift is reversible for the tangential G modes and irreversible for the radial breathing modes (RBMs). The residual softening of the RBMs increases with the tube diameter, whereas its dependence on the treatment temperature exhibits a threshold-like character. The mode softening can be attributed to removal of adsorbents and/or destruction of random C–C bonds between adjacent nanotubes caused by the high temperature treatment (HTT).

Raman spectra of the two-dimensional rhombohedral (2D-R) polymer of C60 were measured at ambient conditions after 0.5 hour of treatment at various elevated temperatures in order to study the process of polymer degradation. The 2D-R polymer is stable up to ∼510 K, while at higher temperatures an intermediate state appears where the initial 2D-R polymer coexists with inclusions of tetragonal-like (T-like) and orthorhombic-like (O-like) oligomers, as well as C60 dimers and monomers. The polymeric material changes drastically its composition after treatment at ∼560 K resulting in the domination of C60 monomers.

Raman spectra of single crystalline two-dimensional rhombohedral (2D-R) polymer of C 60 were measured at ambient conditions after its high temperature treatment (HTT) in order to study the polymer decomposition process. The data obtained indicate that the 2D-R polymer remains stable after 0.5 h treatment up to ∼503 K, while at higher temperatures a material transformation takes place. New Raman lines appear in the Raman spectrum after HTT in the range of 513–553 K, related to the A g (2) pentagon pinch (PP) mode of 2D tetragonal-like (2D-T-like) and 1D orthorhombic-like (1D-O-like) oligomers as well as to C 60 dimers and monomers, typical for an intermediate state of partially decomposed 2D-R polymer. Above 553 K, the material changes completely and its new composition is dominated by C 60 monomers with some possible inclusion of C 60 dimers. The activation energy of the 2D-R polymer decomposition, obtained from the dependence of the decomposition time on the treatment temperature, is E A = 1.76 ± 0.07 eV/molecule.

The effect of Indium (In) implantation in n-type GaN is studied using Raman spectroscopy and Rutherford backscattering (RBS). The RBS analysis reveals that the 700 keV In implantation results in the formation of a subsurface defective region that extends to a depth of 400 nm. An abrupt increase (∼93%) of the maximum defect concentration is observed for fluences in the range 1.5 and 5×1014 cm-2. A further increase of the fluence to 5×1015 cm-2 renders the implanted layer amorphous. In the Raman spectra recorded in the backscattering geometry only the E22 peak is resolved since the A1(LO) is completely damped due to plasmon - phonon coupling. As the fluence increases, the characteristic sharp peaks of the as-grown sample broaden due to relaxation of the q-selection rules allowing phonons with q ≠ 0 to contribute in the Raman scattering. Furthermore, three additional broad peaks are detected in the implanted samples even after implantation with the fluence of 5×1013 cm-2. They are ascribed to disorder activated Raman scattering or acoustic overtones (300 cm-1, 420 cm-1) and the formation of point defects (670 cm-1), respectively. Rapid thermal annealing at 1000 °C causes partial recovery of the lattice. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

InxAl1-xN (0001) wurtzite layers with 0.2 0.45. In the case of the Al rich samples, an additional broad feature appears. The Raman spectra are fitted using the spatial correlation model providing the extent of the phonon confinement imposed by the alloy potential fluctuations is estimated. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The pressure response of the tangential G band of double-wall carbon nanotubes (DWCNTs) synthesised by means of catalytic chemical vapour deposition is compared with that of their peapod-derived analogues. For both samples, the screening of the pressure exerted on the internal tubes is reflected in the pressure response of the corresponding G peaks. The different nanotube diameter and intratube spacing distributions in the two studied DWCNT materials differentiate the pressure dependence of several G band components.

Bundled single-walled carbon nanotubes (SWCNTs) were studied as a function of temperature by means of Raman spectroscopy. The Raman modes exhibit negative temperature shift, reversible for the G band and partially irreversible for the radial breathing modes (RBMs). The softening of the latter is larger for larger diameter tubes, resulting in a better separation of the RBMs after high temperature treatment (HTT). The RBM residual softening vs. treatment temperature demonstrates threshold-like behavior. The temperature-induced changes may be associated with an irreversible weakening of the tube–tube (intertube) interaction possibly due to adsorbent removal or destruction of random intertube C–C bonds.

This work focuses on the high pressure Raman study of carbon nanostuctures comprising of singleor double-wall carbon nanotubes. The detailed examination of the Raman peaks, especially those attributed to the radial breathing modes of the carbon nanotubes, as a function of pressure provides a wealth of information concerning the pressure response of individual nanotubes as well as the internal-external tube (intratube) interactions. The radial breathing modes of both the internal and the external tubes in double-wall carbon nanotubes show reduced pressure slope values as compared to the corresponding in single-wall carbon nanotubes. The reduced slopes for the internal tubes reflect the pressure screening effect inside the external tubes, while those for the external tubes their structural reinforcement due to the encapsulation of smaller diameter tubes in their interior. Moreover, the magnitude of the pressure screening effect depends strongly on the intratube spacing and thus on the intratube interaction. All the experimental observations are well reproduced qualitatively by means of theoretical calculations based on a simple phenomenological model.

The pressure response of carotene-encapsulating single-wall carbon nanotubes is investigated by means of Raman spectroscopy. The pressure evolution of the tangential G band frequencies of the carbon nanotubes is linear without any specific features. On the other hand, the pressure response of the carotene's ν 1 mode frequency is quite distinct, having a smaller low pressure slope than that reported in the literature for the molecule. This behaviour is compatible with the pressure screening effect in the interior of carbon nanotubes. For pressure higher than 2 GPa, the pressure slope becomes even smaller, an effect which can be attributed to the theoretically predicted cross-section deformation of the encapsulating tubes.

High-pressure Raman studies of double-wall carbon nanotubes (DWCNTs) and their parent single-wall carbon nanotubes provide experimental evidence of the structural support of carbon nanotubes due to the encapsulation of smaller diameter tubes in their interior. The structural support is manifested by the reduced slope of the radial breathing mode frequency of the external tubes in DWCNTs, which further decreases at higher pressures as the inner–outer tube (intratube) interaction increases.

Stability of the linear orthorhombic polymer of C60 under pressure and laser irradiation is studied by Raman scattering and X-ray diffraction measurements. The Raman spectrum at ambient pressure remains unchanged, in the time scale of the experiment, up to an intensity of 3200 W/cm2 of the 514.5 nm line of an Ar+ laser, but irreversible changes are observed at higher intensities. The Raman spectra recorded at increased pressure show similar irreversible changes even at the laser intensity as low as 470 W/cm2. The X-ray diffraction and Raman measurements of the pressure-treated samples, performed after pressure release, show that the nonirradiated material does not exhibit any changes in the crystal structure and phonon spectra. This behavior indicates a pressure-enhanced photo-induced transformation to a new polymeric phase characterized by a Raman spectrum that differs from those of the other known polymeric phases of C60. The Raman spectra of the phototransformed linear orthorhombic polymer of C60 were measured at a pressure of up to 29 GPa. The pressure dependence of the Raman mode frequencies show singularities near 4 GPa and 15 GPa, respectively, related to a reversible phase transition and an irreversible transformation to a metastable disordered phase. The diffuse Raman spectrum of the disordered phase does not exhibit substantial changes with an increase in pressure up to 29 GPa. The high-pressure phase transforms to a mixture of pristine and dimerized C60, after pressure release and exposure to ambient conditions for 30 h.