Raman Peak Shift Research Articles

Nanoscale Strain Mapping in SIMOX 3-D Sculpted Silicon Waveguides Using Tip-Enhanced Raman Spectroscopy

Strain in silicon plays a significant role in exploring electro-optical material, boosting transistor performance, tuning birefringence of optical silicon waveguides, and so on. In this paper, we measured, for the first time, the nanoscale strain in the SIMOX 3-D sculpted silicon waveguides using tip-enhanced Raman spectroscopy (TERS). A model, which relates the observed Raman peak shifts to the localized stresses for our TERS experiments, was presented. The tip-induced electric-field enhancements, tip-induced depolarization of incident light, and oblique incidence geometry of the TERS system were included in the model. Both polarizations of incident light and Raman scattered light are selected appropriately with the guidance of the model for obtaining enough electric-field enhancements and accurately calculate the stresses. A 2-D stress map inside the silicon waveguide with spatial resolution of about 20 nm was obtained, and corresponding strains were calculated based on Hooke's law. We observed that the stresses are compressive, and the strains show inhomogeneity. The origins of strain and the strain-induced second-order optical susceptibility inside the SIMOX 3-D sculpted buried silicon waveguides are discussed and analyzed. The mapping of 2-D nanoscale strain and the analysis of second-order optical susceptibility in this work suggest that the SIMOX 3-D sculpted strained silicon might be a potential metamaterial for electro-optical modulation and optical signal processing. Moreover, the presented TERS model could be a valuable tool for probing strain in strained silicon devices.

Optical Diagnostics of Porous Silicon Nanoparticles Biodegradation

SUMMARY Optical methods such as Raman micro-spectroscopy and photoluminescence were employed for diagnostics of biodegradation of porous silicon nanoparticles (SiNPs) in phantom suspensions and breast cancer cells (MCF-7 cell line) in-vitro.Two types of SiNPs, with and without photoluminescence in the visible spectral range, were investigated. The biodistribution of photoluminescent SiNPs within the cells obtained by Raman imaging was additionally verified by high-resolution structured-illumination optical microscopy (HR-SIM). Almost complete degradation of SiNPs inside the living cells and aqueous suspensions was observed after 2 weeks of storage. The results reveal new prospects of multi-modal optical characterization of SiNPs during their dissolution in vitro. 1. INTRODUCTION SiNPs are well-known to be degradable in physiological fluids and in living tissues due to dissolution process resulting in formation of orthosilicic acid [1]. Usually several week are sufficient for complete release of SiNPs from the body [1]. Nonetheless, the SiNP degradation rate depends on the particle size, porosity, surface coverage, pH value and ambience and can vary from a few days up to several months [2]. The SiNP biodegradation is associated usually with the disappearance of their PL property. It can also be assessed by histological methods or by the analysis of silicon content in the tissues by inductively coupled plasma optical emission spectrometry. However, these methods of analysis are not very precise, fast or/and straightforward. Mesoporous SiNPs do not possess efficient PL, therefore we used two optical methods: PL and Raman spectroscopy for characterization of different types of PSiNPs. 2. EXPERIMENTAL RESULTS We have prepared 100 nm SiNPs by grinding of meso- and microporous silicon films (PSi). Both types of the films were obtained by electrochemical etching of Si wafers in HF-based solutions. Micro PSiNPs have demonstrated efficient PL properties, whereas meso PSiNPs have not, but they provided better contrast in Raman imaging. Degradation of micro PSiNPs in suspensions was investigated during 2 week in order to determine influence of size, concentration, pH level influence on degradation rate. We used centrifugation to obtain micro PSiNPs samples with different size of NPs in order to find size dependency of degradation rate. Meso PSiNPs were tested in the same regime by Raman spectroscopy. Dialysis was applied to enhance degradation. Both methods showed size shrinking of nanoparticles, since PL peak positions is determined by quantum confinement in nanocrystals and Raman peak shifts in small nanocryslals due to the confinement of phonons. Then degradation was examined in vitro. The uptake of silicon nanoparticles by MCF-7 breast cancer cells was observed for time intervals between 6 hours and 2 weeks. The 3D HR-SIM revealed the localization of PL-SiNPs inside cells. Staining of the cell organelles proved the accumulation of nanoparticles mostly in the cytoplasm and in the nucleus periphery (see left Fig.). The Raman images for SiNPs are shown in central Fig. SiNPs exhibited a characteristic peak of Raman scattering at 520 cm-1, which is due to the presence of nanocrystalline silicon in the cells (see right Fig.). The strongly highlighted signal from SiNPs shows presence of SiNPs inside the cell structure without being overlapped by the surrounding signals from the cell organelles. To investigate time-depending modifications of SiNPs the detailed analyses of Raman imaging data for the timeframe of 2 weeks were performed in-vitro. The chemical changes of SiNPs in MCF-7 cell interior determining the biodegradation processes of nanoparticles were evaluated from the corresponding shifts and changes of the Raman spectra and intensity during increased incubation time. Based on the performed investigations the model of SiNPs uptake by cancer cells and biodegradation is proposed. 3. CONCLUSIONS The photolumescent and Raman spectroscopies were used to visualize the intracellular localization and subsequent biodegradation of SiNPs in cancer cells for the first time. The obtained results are important for the development of new methods of ex-vivoexpress-diagnosis of early stages of cancer. REFERENCES Park J.-H., Gu L., von Maltzahn G., Ruoslahti E., Bhatia S.N., Sailor M.J. Nat. Mater. 8(4), 331–336 (2009).Shabir Q. Biodegradability of Porous Silicon. In: Handbook of Porous Silicon. Canham L. (Ed.). Springer Int. Publ., 395–401 (2014). Figure 1

Crystallization processes of SrTiO3 films prepared by PVP-modified sol–gel method

Crystallization processes of sol–gel derived SrTiO3 films have been investigated systematically. The crystallization processes included two stages, firstly, the coordination of the cations changed from the carboxylate groups to the carbonate groups; secondly, the resulting pervskite SrTiO3 was crystallized by the decomposition of the carbonate groups. The intermediate with carbonate groups has also been observed in the SrTiO3 films annealed at 500 °C by the Raman peak shift near 1071 cm−1. The stoichiometry of the intermediate, close to Sr2Ti2O5CO3, has been further confirmed by the TG-DSC and XPS results.

A comparative study of the effect of Pd-doping on the structural, optical, and photocatalytic properties of sol–gel derived anatase TiO2 nanoparticles

Pd-doped anatase TiO2 nanoparticles were synthesized by a modified sol–gel deposition technique. The synthetic strategy is applicable to other transition and post-transition metals to obtain phase-pure anatase titania nanoparticles. This is important in the sense that anatase titania forms the most hydroxyl radicals (compared to other polymorphs like rutile, brookite, etc.) for better photocatalytic performance. XRD and Raman data confirm the phase-pure anatase formation. Doping of Pd2+ into Ti4+ sites (for substitutional doping) or interstitial sites (for interstitial doping) creates strain within the nanoparticles and is reflected in the XRD peak broadening and Raman peak shifts. This is because of the ionic radii difference between Ti4+(∼68pm) and Pd2+(∼86pm). XPS data confirm the formation of high surface titanol groups at the nanoparticle surface and a large number of loosely bound Ti3+–O bonds, both of which considerably enhance the photocatalytic activity of the doped nanoparticles. A comparative study with other metal doping (Ga) shows that TiO2: Pd nanoparticles have more Ti3+–O bonds, which enhance the charge transfer rate and hence improve the photocatalytic activity compared to other transition and post-transition metal-doped titania nanostructures.

Morphology dependent PL quenching of multi-zone nanoporous silicon: Size variant silicon nanocrystallites on a single chip

Fabrication and optical sensing studies of single plane multi-zone nano-porous silicon (n-PS) prepared using laser-induced electrochemical etching technique is presented. Single plane multi-zone pertains to lateral formation of zones in silicon bearing step pore- and nano-crystallites size on the same plane. Different morphologies assembled in the form of a spiral shaped pattern on n-PS. Such novel pattern was a consequence of coupling between laser illumination and spiral shaped counter electrode used during silicon etching. The morphology analysis was done by recording profiles of characteristic LO phonon mode of silicon Raman spectra. The asymmetry and Raman peak shift helped in discerning the multi-zone morphology and it was complimented by Scanning Electron Microscopy (SEM) and photoluminescence (PL) studies. A wide range alcohol concentration (10–200ppm) was tested using PL quenching technique. A direct correlation between morphology of n-PS and ethanol sensitivity was ascertained. Maximum sensing response of 40% was achieved at the centre and it decreased towards the periphery of the spiral pattern. The present simple and low cost fabrication technique allows fabrication of multiple morphologies on a single chip in one step and enables preparation of optimized n-PS for desirable applications.

Raman Shifts in Electron-Irradiated Monolayer MoS2.

We report how the presence of electron-beam-induced sulfur vacancies affects first-order Raman modes and correlate the effects with the evolution of the in situ transmission-electron microscopy two-terminal conductivity of monolayer MoS2 under electron irradiation. We observe a red-shift in the E' Raman peak and a less pronounced blue-shift in the A'1 peak with increasing electron dose. Using energy-dispersive X-ray spectroscopy and selected-area electron diffraction, we show that irradiation causes partial removal of sulfur and correlate the dependence of the Raman peak shifts with S vacancy density (a few %). This allows us to quantitatively correlate the frequency shifts with vacancy concentration, as rationalized by first-principles density functional theory calculations. In situ device current measurements show an exponential decrease in channel current upon irradiation. Our analysis demonstrates that the observed frequency shifts are intrinsic properties of the defective systems and that Raman spectroscopy can be used as a quantitative diagnostic tool to characterize MoS2-based transport channels.

폴리올과 붕산의 착화합물 형성원리를 이용한 수용액 중의 보론 제거에 관한 라만 분광학 연구

해수 중에 보론은 주로 붕산(boric acid, <TEX>$B(OH)_3$</TEX>)으로 존재하며 그 크기가 역삼투압(RO, reverse osmosis) 공정의 막의 공칭공경(nominal pore size)만큼 작아 이를 제거하기가 쉽지 않다. 이에 본 연구에서는 수용액 중 보론 화합물의 크기를 역삼투압 공정에서 제거가 용이하도록 키우기 위한 방법으로 <TEX>$B(OH)_3$</TEX>가 폴리올과 착화합물을 형성하는 원리를 이용하고자하며 착화합물의 형성 여부를 라만 분광학 연구를 통해 확인하고자 하였다. 먼저 <TEX>$B(OH)_3$</TEX>와 붕산염(borate ion, <TEX>${B(OH)_4}^-$</TEX>) 이온의 대칭(symmetric) B-O 신축운동 모드(stretching vibrational mode)의 진동수를 확인하기 위하여 pH를 증가시키며 라만 스펙트럼을 측정한 결과 <TEX>$877cm^{-1}$</TEX>에서 <TEX>$730cm^{-1}$</TEX>으로 피크의 이동이 관찰되었다. 이는 수용액 중의 <TEX>$B(OH)_3$</TEX>가 pH가 증가하면서 <TEX>${B(OH)_4}^-$</TEX>로 전환됨을 나타내고 이러한 피크의 이동은 진동수 계산(frequency calculation)에 의한 예측과 정확하게 일치하였다. 반면 <TEX>$B(OH)_3$</TEX> 수용액에 폴리올을 첨가한 경우 pH가 증가하여도 <TEX>${B(OH)_4}^-$</TEX>의 특성 진동수인 <TEX>$730cm^{-1}$</TEX>가 나타나지 않았으며 이는 <TEX>$B(OH)_3$</TEX>가 <TEX>${B(OH)_4}^-$</TEX>로 전환되는 것이 아니라 폴리올과 착화합물을 형성함을 간접적으로 보여주고 있다. Boron is difficult to be removed from seawater by simple RO (reverse osmosis) membrane process, because the size of boric acid (<TEX>$B(OH)_3$</TEX>), the major form of aqueous boron, is as small as the nominal pore size of RO membrane. Thus, the complexation of boric acid with polyols was suggested as an alternative way to increase the size of aqueous boron compounds and the complexation behavior was investigated with Raman spectroscopy. As a reference, the Raman peak for symmetric B-O stretching vibrational mode both in boric acid and borate ion (<TEX>${B(OH)_4}^-$</TEX>) was selected. A Raman peak shift (<TEX>$877cm^{-1}{\rightarrow}730cm^{-1}$</TEX>) was observed to confirm that boric acid in water is converted to borate ion as the pH increases, which is also correctly predicted by frequency calculation. Meanwhile, the Raman peak of borate ion (<TEX>$730cm^{-1}$</TEX>) did not appear as the pH increased when polyols were applied into aqueous solution of boric acid, suggesting that the boric acid forms complexing compounds by combining with polyols.

Comparative Raman spectroscopic study of phase stability and anharmonic effects in AZr2(PO4)3 (A = K, Rb and Cs)

AZr2(PO4)3 (A=Na, K, Rb, Cs) are a set of framework structured compounds that exhibit tunable ultralow thermal expansion over the wide temperature range of 293–1273K. We report a systematic Raman spectroscopic investigation on AZr2(PO4)3 (A=K, Rb and Cs) compounds as a function of temperature in the range 80–860K and pressures of up to 32GPa. To get insight into the thermal expansion property, phonon anharmonicity has been investigated by studying the temperature and pressure dependence of Raman peak shifts and line widths and computed bulk modulus. We have compared the phase transition and amorphization pressures of the various members of AZr2(PO4)3 to account for the stability of the ambient rhombohedral phase. We find that unlike most of the anomalous thermal expansion materials, in AZr2(PO4)3 (A=K, Rb and Cs), the phonons that are anharmonic with temperature do not necessarily exhibit anharmonicity with pressure.

Raman spectra measurements on DEPC liposome and cell membrane of living neuron under xenon pressure

The Raman spectra of liposomes were measured under xenon pressures and low temperatures to observe the spectra changes accompanying the gel to liquid crystalline phase transition of the liposomes. C–H stretching bonds of the lipids in the liposome were slightly red shifted at approximately 285 K and atmospheric pressure, which coincided well with the phase transition condition. This Raman peak shift was observed at lower temperatures and related linearly to the xenon pressures. The xenon pressure dependence on the phase transition temperature was in good agreement with the DSC measurements, and the red shifts of Raman peaks supported the molecular mechanism of interaction between xenon and phospholipid bilayers suggested by the MD simulations. The phase transition measurements under xenon pressure with the microscopic Raman spectroscopy were applied to cultured neuronal networks to observe the interaction of dissolved xenon with the cell membrane and the surrounding water.

Raman-Infrared (IR) Spectroscopy Study of Natural Cordierites from Kalahandi, Odisha

Abstract A combined Raman and IR spectroscopic study has been carried out on natural cordierite samples from Kalahandi district, Odisha to understand the effect of Mg-Fe2+ exchange on Raman peak shift and to identify the volatile species within these cordierite crystals. In the field, the cordierites are hosted by silica-saturated quartz-feldspathic rocks, mafic granulites and also by the silica-undersaturated Mg-Al granulites. X-ray Diffraction (XRD), Raman spectroscopy and microprobe analyses were initially used to characterize the samples and to obtain chemical composition respectively. XRD of the gem quality cordierite reveals perfect orthorhombic symmetry, supported by Raman analyses that deduce the extent of Al-Si ordering in this mineral. Microprobe data indicate that most cordierites are Mg-rich (XMg = 0.93-0.94), however, a variation in Mg/Fe concentration of cordierite from different locations is observed. The samples also show high Na content that are associated with quartzo-feldspathic rocks intruded by pegmatites, than that of the Mg-Al granulites. This result suggests temperature variance in cordierite crystallization among different host rocks. Raman spectra of these cordierites define structurally resolved Raman vibrational modes where the magnitude of peak shift of most bands towards lower wavenumber than pure Mg-cordierite is proportional with Fe concentration, and are linked with the extent of Mg-Fe exchange within cordierite structure. FTIR study confirms the presence of both type-I and type-II waters along with significant amount CO2 as channel constituents, however, type-I H2O and CO2 concentrations vary within a single crystal. The FTIR spectroscopic evidence strongly supports a H2O and CO2 bearing fluid composition during crystallization of cordierite from these localities.

Optical Properties and Raman Scattering Investigation of Ag Doped ZnO Thin Film Prepared by Two-Step Solution-Based Deposition Method

Mist-atomization deposition method was applied in order to grow ZnO nanoparticles on Au-seeded glass substrates acting as seeded template. Ag doped ZnO thin films were deposited on ZnO seeded templates by solution-immersion method. The influence of Ag doping content on the optical and Raman scattering properties of ZnO films were systematically investigated by UV-Vis transmittance measurement measured by ultra-violet visible spectroscopy (UV-Vis) and Raman scattering spectrum measured by Raman spectroscopy under room temperature. From UV-Vis transmittance measurement, the incorporation of Ag dopant to the ZnO makes the transmittance wavelength shifted to the shorter wavelength as compared to the pure ZnO. From Raman spectra, 4 cm-1 downshift is observed in Ag-doped thin films as compared to pure ZnO thin films. This Raman peak shift shows that a tensile stress existed in the Ag-doped ZnO film.

Influence of applied current density on the nanostructural and light emitting properties of n-type porous silicon

Effects of current density on nanostructure and light emitting properties of porous silicon (PS) samples were investigated by field emission scanning electron microscope (FE-SEM), gravimetric method, Raman and photoluminescence (PL) spectroscopy. FE-SEM images have shown that below 60 mA/cm2, macropore and mesopore arrays, exhibiting rough morphology, are formed together, whose pore diameter, pore depth and porosity are about 265–760 nm, 58–63 μ m and 44–61%, respectively. However, PS samples prepared above 60 mA/cm2display smooth and straight macropore arrays, with pore diameter ranging from 900–1250 nm, porosity of 61–80% and pore depth between 63–69 μ m . Raman analyses have shown that when the current density is increased from 10 mA/cm2to 100 mA/cm2, Raman peaks of PS samples shift to lower wavenumbers by comparison to crystalline silicon (c-Si). The highest Raman peak shift is found to be 3.2 cm-1for PS sample, prepared at 90 mA/cm2, which has the smallest nanocrystallite size, about 5.2 nm. This sample also shows a pronounced PL, with the highest blue shifting, of about 12 nm. Nanocrystalline silicon, with the smallest nanocrystallite size, confirmed by our Raman analyses using microcrystal model (MCM), should be responsible for both the highest Raman peak shift and PL blue shift due to quantum confinement effect (QCE).

Quantitative analysis of the phonon confinement effect in arbitrarily shaped Si nanocrystals decorated on Si nanowires and its correlation with the photoluminescence spectrum

Arrays of single‐crystalline Si nanowires (NWs) decorated with arbitrarily shaped Si nanocrystals (NCs) are grown by a metal‐assisted chemical etching process using silver (Ag) as the noble metal catalyst. The metal‐assisted chemical etching‐grown Si NWs exhibit strong photoluminescence (PL) emission in the visible and near infrared region at room temperature. Quantum confinement of carriers in the Si NCs is believed to be primarily responsible for the observed PL emission. Raman spectra of the Si NCs decorated on Si NWs exhibit a red shift and an asymmetric broadening of first‐order Raman peak as well as the other multi‐phonon modes when compared with that of the bulk Si. Quantitative analysis of confinement of phonons in the Si NCs is shown to account for the measured Raman peak shift and asymmetric broadening. To eliminate the laser heating effect on the phonon modes of the Si NWs/NCs, the Raman measurement was performed at extremely low laser power. Both the PL and Raman spectral analysis show a log‐normal distribution for the Si NCs, and our transmission electron microscopy results are fully consistent with the results of PL and Raman analyses. We calculate the size distribution of these Si NCs in terms of mean diameter (D0) and skewness (σ) by correlating the PL spectra and Raman spectra of the as‐grown Si NCs decorated on Si NWs. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Ultrafine Pt nanoparticle induced doping/strain of single layer graphene: experimental corroboration between conduction and Raman characteristics

The doping/strain induced by ultrafine sputtered Pt nanoparticles (NPs) of different sizes on single layer graphene is studied through conduction channel modification of graphene-based field-effect transistors and subsequent Raman characterization. For sub-nm (0.5 nm) sized Pt NPs, a substantial Dirac point shift is observed in the I–V characteristics, suggestive of n-type doping of the large area single layer graphene through the process of charge transfer and chemical interaction. Conversely, for larger (1.1 nm) Pt NPs, minimal Dirac point shift is observed, indicating lack of the charge transfer induced doping effect. The representative Raman signatures corroborate with the electrical characterization results and indicate while charge transfer dominates Raman peak shift for the 0.5 nm Pt NP decorated graphene, strain effect dominates in case of the larger 1.1 nm Pt NP.

Homoepitaxial growth and stress analysis of (111) diamond film with embedded gold islands

The internal stress in high-quality (111) homoepitaxial diamond film grown on high-pressure high temperature (HPHT) synthesized single crystal diamond substrate by chemical vapor deposition (CVD) can be reduced effectively by embedding Au islands in diamond. Au islands formed from an Au layer deposited on the diamond substrate by electron beam evaporation can be obtained after hydrogen plasma annealing. Transmission electron microscopy and X-ray diffraction results show that the Au islands covered with CVD diamond have a size in a few hundreds of nanometers and are oriented with diamond in the orientation relationship of {111}Au//{111}Dia and <110 > Au//<110 > Dia. The surfaces of the CVD diamond films grown on substrate with and without Au coating exhibit cracks when the film thickness reaches 3.5 μm. As evaluated from the Raman peak shift, it is shown that the internal tensile stress in the film with Au islands is less than in the same thick film on substrate without Au coating. A crack-free (111) homoepitaxial diamond film in the same thickness can be obtained by insertion of multilayers of Au islands in CVD diamond.

Observation of laser-driven shock propagation by nanosecond time-resolved Raman spectroscopy

An improved nanosecond time-resolved Raman spectroscopy is performed to observe laser-driven shock propagation in the anthracene/epoxy glue layer. The digital delay instead of optical delay line is introduced for sake of unlimited time range of detection, which enables the ability to observe both shock loading and shock unloading that always lasts several hundred nanoseconds. In this experiment, the peak pressure of shock wave, the pressure distribution, and the position of shock front in gauge layer were determined by fitting Raman spectra of anthracene using the Raman peak shift simulation. And, the velocity of shock wave was calculated by the time-dependent position of shock front.

Structure and phase change in Cu-Ge3Sb2Te5 films for use in phase change random access memory

The Cu-Ge3Sb2Te5 thin films with different Cu contents were prepared by magnetron sputtering method. The dependence of film resistance on temperature is measured in situ by using the four-point probe heating platform. The crystal structure, microstructure, optical gap, and bond states of the Cu-Ge3Sb2Te5 films are investigated by X-ray diffraction, transmission electron microscopy, transmission and Raman spectra, respectively. It is shown that the crystallization temperature and activation energy of crystallization increase with increasing Cu content, suggesting the improvement in thermal stability and data retention ability, while optical gap decreases with increasing Cu concentration. It is observed that the Raman peak shifts from 129 cm-1 to 127 cm-1, which may be ascribed to the vibration of polar Cu–Te bonds. The Cu-Ge3Sb2Te5 crystallizes into the embedded Cu2Te and Ge2Sb2Te5 phases with evenly grown grains.

Fatigueless response of spider draglines in cyclic torsion facilitated by reversible molecular deformation

We demonstrate that spider draglines exhibit a fatigueless response in extreme cyclic torsion up to its breaking limit. The well defined Raman bands at 1095 and 1245 cm–1 shifted linearly towards lower wavenumbers versus increasing twist in both clockwise and counter-clockwise directions. Under thousands of continuous loading cycles of twist strain approaching its breaking limit, all the Raman bands were preserved and the characteristic Raman peak shifts were found to be reversible. Besides, nanoscale surface profile of the worked silk appeared as good as the pristine silk. This unique fatigueless twist response of draglines, facilitated by reversible deformation of protein molecules, could find applications in durable miniatured devices.

Raman investigation of chemical reaction product in thermal‐treated SiCf/C/Mo/Ti6Al4V composite

SiC fiber‐reinforced titanium matrix composite (TMC) is an interesting material for aerospace industry because of its excellent properties. Characterization of their interfacial reaction product is principal to further optimization of the TMCs. Here we report application of Raman spectroscopy to identify reaction products and their microstructural details in thermal‐treated SiCf/C/Mo/Ti6Al4V composite. Meanwhile TEM is performed to help explain phenomena in Raman result. Raman line scanning along interface indicates thickness of two sublayers (Ti5Si3(Cx) layer next to SiC fiber and TiCx layer next to matrix). The main Raman result of phase distribution is confirmed by TEM. While a 300‐nm Ti3SiC2 layer whose Raman features are similar with nearby Ti5Si3(Cx) layer is also detected. Raman peakshift in Ti5Si3(Cx) layer possibly results from residual stress or/and microstructural evolution caused by carbon solution. No evidence indicates Mo participation of interfacial reactions. However, Mo diffusion changes phase distribution of matrix alloy and affects interfacial reaction indirectly. Meanwhile, TEM and Raman results indicate that particles are TiCx and defective Ti3AlC2. Raman features of Ti3AlC2 particles differ from that of bulk material, which is attributed to defects. Although Ti3AlC2 formation mechanism is ambiguous, it possibly relates to TiCx formation nearby. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Compressive and tensile response of CFRP cylinders induced by multi-walled carbon nanotubes

Abstract Compressive and tensile response of filament wound carbon fiber reinforced epoxy (CFRP) cylinders induced by adding various multi-walled carbon nanotubes (MWCNTs) were systematically evaluated in details. The addition of various MWCNTs significantly enhanced the compressive modulus of CFRP cylinders while barely affecting tensile modulus. Specifically, MWCNTs–NH 2 endowed highest enhancement on compressive modulus of the cylinders by 63.7% due to their uniform dispersion and excellent interfacial adhesion compared with MWCNTs–COOH and raw MWCNTs. Moreover, specific energy absorption of CFRP cylinders was also enhanced by MWCNTs as a result of their positive effect on microcrack initiation and the corresponding enhancement was more obvious under compressive load than tensile load. Acoustic emission detection illustrated that MWCNTs effectively triggered abundant microcracks by inducing local stresses fluctuations around the fibers, but prevented macrocrack formation by their crack bridging effect, subsequently delaying cylinder collapse at ultrahigh AE energy. Additionally, Raman peak shift revealed that all layers of MWCNTs showed their whole performance under compression, while only the outer nanotube layers played a role through interfacial friction with the resin matrix under tension, which resulted in significant enhancement of the compressive modulus and related energy absorption compared to corresponding tensile values.