Raman Peak Shift Research Articles

Temperature and Strain Effects in Micro-Raman Thermometry for Measuring In-Plane Thermal Conductivity of Thin Films

ABSTRACT Micro-Raman thermometry is an effective method for measuring thermal conductivity of thin films. It features noncontact and nondestructive probing and convenience of sample preparation. However, there is a concern of its accuracy when using the Raman peak shift as the temperature transducer since it responds to both temperature and strain upon optical heating. In this work, a series of detailed experiments are carried out to evaluate contributions to Raman signals from temperature only vs. from thermomechanical strain. It is shown that using proper calibration, contributions to Raman signals from temperature only and from thermomechanical strain can be decoupled and thermal conductivity can be evaluated correctly. These procedures are then applied to bismuth telluride thin films to illustrate measurement of thin film thermal conductivity.

Study on the effect of Ni co-doping on structural, micro-structural and optical properties of transparent AZO thin films

Abstract Optically transparent Zn0.97-xAl0.03NixO thin films were prepared using spin coating technique. The role of Ni concentration on the structural, microstructural, composition and optical properties were studied by means of XRD, SEM-EDS, RAMAN, UV–Visible spectroscopy. The prepared preferred crystalline orientation along the (002) plane (c-axis) with Ni concentration is seen in the prepared films. The findings of FESEM –EDX demonstrates the homogeneous, uniform and smooth texture of the prepared films with strong adherence to the glass substrate and the presence of nominal values of elements. In addition, the findings of Raman also confirm the absence of Ni related impurity phases. Furthermore, Raman peak shift and intensity variations of Raman spectra suggests that the prepared films have a high degree of crystallinity with lower residual stresses. Optical results suggested that spin coated thin films have optical transparency nearly 90% in the visible wavelength region. It was also observed that the energy bang-gap decreases with the concentration of Ni ions in the host ZnO matrix. Results examined indicate that spin-coated thin films are possible candidates for TCO applications.

Evaluation of Strain-Shift Coefficients for SiSn by Raman Spectroscopy

1. Introduction Silicon tin (SiSn) is a new promising candidate material for next-generation optical devices since its energy band-gap is theoretically expected to a direct band-gap as Sn fraction increases [1, 2]. The lattice constant difference (strain states) between the substrate and the SiSn thin film directly affects a band-gap, a carrier mobility, and device design. Therefore, it is important to evaluate strain states in SiSn thin film and accurate strain evaluation techniques are indispensable.Raman spectroscopy is one of the powerful strain evaluation techniques because it is a high spatial resolution and nondestructive measurement. However, the strain shift coefficient of SiSn has not been experimentally investigated in contrast to silicon germanium, germanium tin, and highly accurate strain measurement cannot be performed by Raman spectroscopy. In this study, Raman measurement was performed to extract the strain-shift coefficient of SiSn thin films, accurately. 2. Experimental method SiSn thin films (Sn fraction: 0.50, 0.90, 1.8, 2.0, and 6.0%) were grown on (001)-Si substrate by molecular beam epitaxy. Their thickness was set to 50 nm. Sn fraction and in-plane biaxial strain were confirmed by X-ray diffraction (XRD).The Si1-x Sn x thin films were evaluated by Raman spectroscopy. Excitation source of ultraviolet laser (λ = 355 nm) was used and focal length of the Raman spectrometer was 2,000 mm. Wavenumber resolution is approximately 0.1 cm-1. The Raman spectra of the Si1-x Sn x thin films for Si-Si vibration mode were measured to determine the strain-shift coefficient. 3. Results and Discussion Figure 1 shows Raman spectra of Si1-x Sn x with x of 0.06 and bulk Si (Si-Si mode) for comparison. As a result, asymmetrical broadening on the low-wavenumber side with slight peak shift in the Raman spectrum for the SiSn thin film were observed. In the Raman scattering, this broadening is often explained using the so-called spatial correlation model, which reproduces the relaxation of momentum conservation due to random atom positions.Figure 2 shows the relationship between Raman peak shift of SiSn for Si-Si mode (Δω LO) and in-plane strain estimated by reciprocal space mapping using XRD. In this study, D’Costa model (see below equation) was used to obtain strain-free Raman shift for Si-Si mode [3]: ω 0 = 520 – 141.8x. (1)It was revealed that the relationship between Raman peak shift of SiSn for Si-Si mode and in-plane strain has clear linear dependence. From the slope of the straight line which calculated by linear approximation as shown in Fig. 2, the value of the strain-shift coefficient b was found to be -732 cm-1. This value shows good agreement with that of strained Si [4] and SiGe [5]. On the basis of the result, it is suggested that the strain-shift coefficient b is not affected by random atom positions (alloy state), and the value of b may not change by composition and strain state.In conclusion, these insights play an important role in the strain evaluation for the next-generation SiSn device by Raman spectroscopy and in the understanding the relationship between phonon behavior and strain. Acknowledgements This work was supported partly the Japan Society for the Promotion of Science (JSPS) (19K21971 and 17J08240).

Effect of patterned silicon nitride substrate on Raman scattering and stress of graphene

Graphene is widely used for nano-devices due to its distinctive band structure and fascinating properties. The substrates could significantly affect the properties of graphene and related devices. In this work, we investigate the effect of surface morphology and roughness of patterned silicon nitride substrates on Raman scattering and stress of graphene. We find that the Raman scattering of graphene depend strongly on surface morphology and roughness of patterned substrates. It is concluded that the peak red-shifts in 2D and G bands was due to the strain induced by patterns with different surface morphology (holes and trenches) and roughness. Furthermore, the effects of morphology of patterned area are much greater than the role of surface roughness in the induced strain of graphene. Due to the larger surface area (about 1.65 times), the strain in the grooves is greater than in holes, in spite of greater surface roughness in holes. Our results also reveal that the effect of pattern depth should be taken into account to understand the Raman peak shift and the strain change of graphene. Our work is fundamentally important for understanding the graphene properties on dependence of surface morphology of substrates and enhancing the interfacial strength of graphene-based devices.

Performance Boosts in n-Type Lateral Double-Diffused MOSFET With Process-Induced Strain Using Contact Etch Stop Layer Stressor

In this brief, the contact etch stop layer (CESL) stressor is introduced to improve the performance of n-type lateral double-diffused MOSFET (nLDMOSFET) with various operating voltages. Three groups of nLDMOSFETs were studied to demonstrate the effects of the CESL stressor. The electrical properties were carefully characterized, and the tip-enhanced Raman spectroscopy measurements were carried out to examine the process-induced strain directly. It is found that nLDMOSFETs with the strained SiN CESL have larger output current, transconductance (g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> ), and higher breakdown voltage (BV). The strained SiN CESL introduces tensile strain in the device and results in the performance boosts, which are verified by negative Raman peak shift mappings and TCAD simulations. The strained SiN CESL could effectively decrease the specific ON-resistance (Ron) and improve the BV of the nLDMOSFET, due to the mobility enhancement.

Residual Stress Measurements in PVD Coatings of Carbide Cutting Tools Directly in the Cutting Edge

Residual stress measurements directly in the coated cutting edge are not possible with X-ray diffraction (XRD) due to the diameter of the X-ray beam. On the other hand, Raman microscopy enables measurements on the micrometer scale. Parameter variations in the PVD process were used to provide different residual stress states in (Al,Ti)N coatings on carbide cutting tools. They were examined by XRD in regions that can be reliably measured. The same area was then examined by Raman microscopy to determine the relationship of Raman peaks to the residual stress. Local high-resolution Raman measurements were then taken at the cutting edge and further influences on the Raman peak position besides residual stresses were excluded. In order to analyze the relationship between Raman peak shift and residual stress state, measurements were performed during a bending load. Finally, an outlook on further investigations is given.

Raman peak shifts by applied magnetic field in InSb/Al x In1−x Sb superlattices

InSb/Al x ln1−x Sb superlattices (SLs) are grown by molecular beam epitaxy on (001) InSb substrate and Raman scattering spectroscopy of the samples under magnetic field is investigated. Al contents in AlInSb of the samples are varied. All samples are characterized by atomic force microscopy (AFM), X-ray diffraction and Raman scattering spectroscopy. The Raman spectroscopy is done by using excitation laser with 633 nm wavelength and 2 μm beam spot under applied magnetic field from 0 to 170 mT. Both TO and LO Raman peaks from InSb are detected from all samples. There are Raman peak shift of both TO and LO by applied magnetic field. Stronger magnetic effect is found in LO than TO phonon modes. We attribute this effect to the symmetry breaking of the InSb/AlInSb interfaces since the observed roughness of the top InSb layer can qualitatively correlate with the shift.

Investigation of thermal residual stresses during laser ablation of tantalum carbide coated graphite substrates using micro-Raman spectroscopy and COMSOL multiphysics

Laser ablation of high-temperature ceramic coatings results in thermal residual stresses due to which the coatings fail by cracking and debonding. Hence, the measurement of such residual stresses during laser ablation process holds utmost importance from the view of performance of coatings in extreme conditions. The present research aims at investigating the effect of laser parameters such as laser pulse energy, scanning speed and line spacing on thermal residual stresses induced in tantalum carbide-coated graphite substrates. Residual stresses were measured using micro-Raman spectroscopy and correlated with Raman peak shifts. Transient thermal analysis was performed using COMSOL Multiphysics to model the single ablated track and residual stresses were reported at low, moderate and high pulse energy regimes. The results showed that the initial laser conditions caused higher tensile residual stresses. Moderate pulse energy regime comprised higher compressive residual stresses due to off centre overlapping of the laser pulses. Higher pulse energy (250 μJ), higher scanning speed (1000 mm/s) and moderate line spacing (20 μm) caused accumulation of tensile residual stresses during the final stage of laser ablation. The deviation of experimental residual stresses from COMSOL numerical model was attributed to unaccounted additional stresses induced during thermal spraying process and deformation potentials in the numerical model.

Evaluation of Thermal Conductivity Characteristics in Polycrystalline Silicon - The Effect of Nanostructure in the Grains

1.Introduction Polycrystalline silicon (poly-Si) is a promising candidate for channel materials such as thin film transistors (TFTs). Moreover, poly-Si is also expected for the next-generation thermoelectric device materials. It has been reported that poly-Si has low thermal conductivity due to their grain boundaries and defects, and so on [1,2]. We have previously confirmed that nanostructures exist in poly-Si grains, and these nanostructures become the phonon scatters [3]. However, the detailed effect of annealing on the nanostructure size has not been sufficiently. In this study, we focused on only the nanostructure size by changing the additional annealing conditions during poly-Si thin film fabrication with keeping the same grain size, and evaluated the thermal conductivity characteristics of the poly-Si thin film. 2.Experiments The 100 nm thick SiO2 films were thermally grown on Si substrates. The 150 nm thick Amorphous Si (a-Si) thin films were deposited at 510 °C by low pressure chemical vapor deposition (LPCVD) using the mono-silane (SiH4) gases under the pressure of 0.4 Torr. The a-Si thin films on SiO2/Si substrate were then annealed at 700 °C 2 hrs (Sample A), 700 °C 2hrs + 900 oC 2hrs (Sample B) and 700 °C 2 hrs +1100 °C 2 hrs (Sample C), respectively. The grain size is determined by the first annealing. Therefore, the grain size of each sample is almost the same at 600 nm.The fabricated samples were measured by UV Raman spectroscopy for the investigation of thermal conductivity characteristics. The excitation source was the UV laser (λ=355 nm), and the focal length of the spectrometer was 2,000 mm. The laser power was controlled by a variable neutral density (ND) filter in the incident light path from 1 to 10 mW in 1 mW steps. Five-point Raman spectra measurements were performed on each sample to evaluate the thermal conductivity characteristics. 3.Results and Discussion Figure 1 shows the laser-power-dependent Raman spectra of Sample A. It was confirmed that the higher laser power resulted in the higher Raman spectral intensity. In addition, it was confirmed the Raman spectrum tends to shift toward lower wavenumber as the laser power increases. It has been reported that the Raman spectrum for Si-Si mode shift toward lower wavenumber due to the thermal effect as temperature increases. Therefore, it is considered that the change in the Raman shift is due to the temperature change caused by local laser heating. Table 1 shows the average nanostructure size of each sample. The nanostructure size is calculated by the full width at half maximum (FWHM) of the UV Raman spectroscopy [4]. Figure 2 shows that the laser-power-dependent Raman peak shift from the poly-Si thin films. It was confirmed that there is a difference in zero power intercept due to phonon confinement effect. It is considered that the Raman spectrum for sample A shifted due to the phonon confinement effect possibly caused by the smaller nanostructures inside the grain. In addition, it was also confirmed that the discrepancy in the Raman shifts between each sample becomes larger as the laser power increases, and it indicates that there is a difference in the temperature change for each sample. The relation between Raman shift and temperature are described by following Eq. (1) [5].dω/dT = -0.024 cm-1/K (1)Figure 3 shows that temperature in poly-Si thin film measured by Si Raman peak shift. It was revealed that Sample B has lower thermal conductivity despite the nanostructure size is larger. It may need to consider not only size but also density of the nanostructure to understand these phenomena. In conclusion, we clearly indicated that not only the average grain size but also the nanostructures inside grains should be carefully considered to control thermal conductivities. REFERENCE Y. Nakamura, Sci. Technol. Adv. Mater. 19, 31 (2018).K. Valalaki, N. Vouroutzis, and A. G. Nassiopoulou, J. Phys. D: Appl. Phys. 49, 315104 (2016).H. Takeuchi, R. Yokogawa, K. Takahashi, K. Komori, T. Morimoto, N. Sawamoto and A. Ogura, 236th ECS Meeting. G04-1210 (2019).H. Yamazaki, M. Koike, M. Saitoh, M. Tomita, R. Yokogawa, N. Sawamoto, M. Tomita, D. Kosemura, and A. Ogura, Sci. Rep. 7,16549 (2017).D. Fan, H. Sigg, R. Spolenak, and Y. Ekinci, Phys. Rev. B 96, 115307 (2017). Figure 1

Evaluation of Strain-Shift Coefficients for SiSn by Raman Spectroscopy

We report on the strain-shift coefficient of silicon tin (SiSn) alloys obtained by ultraviolet (UV) Raman spectroscopy. The values of the Raman peak shift of the Si-Si mode for the SiSn (Sn fraction: 0.5, 0.9, 1.8, 2.2, and 6.0%) thin films were found to increase with Sn fraction and it indicates that compressive strain is induced in the SiSn films. The strain-shift coefficient of the Si-Si mode obtained from linear fits to the measurement data (UV Raman spectroscopy and X-ray diffraction reciprocal space mapping) has a good agreement with the values of the strain-shift coefficients about strained Si and strained silicon germanium, and commercial high-purity Si reported by previous studies. The strain-shift coefficient determined by in this work contribute to realize strain measurements for the next-generation SiSn devices such as near-infrared optical and thermoelectric devices.

Lead‐Free Cs3Sb2Br9 Single Crystals for High Performance Narrowband Photodetector

AbstractLead‐free single crystal perovskite materials exhibit impressive characteristics, such as high carrier mobility, low trap density, and long diffusion length. Herein, the high‐performance blue light photodetectors are reported based on lead‐free all‐inorganic Cs3Sb2Br9 perovskite single crystals. These millimeter‐sized Cs3Sb2Br9 single crystals have small thermal activation energy of 56.8 meV estimated by temperature‐dependent photoluminescence study. There is no obvious structural phase transition of the as‐obtained Cs3Sb2Br9 single crystals since no Raman peak shift is observed with temperature increasing from 80 to 300 K. The as‐constructed high quality Cs3Sb2Br9 single crystals photodetectors have an excellent performance of a responsivity of 2.29 A W−1, a sharp detectivity of 3.77 × 1012 Jones, and an external quantum efficiency (EQE) peak of 1.8 × 103%. Moreover, the photodetectors exhibit a fast response time (&lt;0.2 ms) and the full width at half maximum (FWHM) of the sharp EQE peak is as narrow as 15 nm. This work provides a promising strategy in the design of lead‐free, stable, and high‐performance perovskites for photodetector devices.

Comparative Study of Boron Precursors for Chemical Vapor‐Phase Deposition‐Grown Hexagonal Boron Nitride Thin Films

Two different boron precursors, diborane (B2H6) and trimethyl boron ((CH3)3B, TMB), are investigated for chemical vapor‐phase deposition (CVD)‐grown hexagonal boron nitride (h‐BN) on α‐Al2O3 (0001) substrates. The BN layer grown using TMB includes a large amount (2 × 1020 cm−3) of carbon atoms, which is 60 times higher than that in the BN layer grown using B2H6. The X‐ray diffraction 2θ/ω scans for BN film grown using B2H6 exhibit the h‐BN (002) peak. The BN film obtained using TMB includes turbostratic BN (t‐BN). The E2g Raman peak frequencies in B2H6 and TMB h‐BN are observed at 1368.8 and 1369.7 cm−1, respectively. The Raman peak shift to a higher frequency indicates that a larger compressive strain is induced using TMB than using B2H6. The full width at half maximum of the B2H6 and TMB Raman peak frequencies is 21.8 and 42.7 cm−1, respectively. The cathodoluminescence spectra of B2H6 h‐BN show the band‐edge emissions at 225 and 232 nm, whereas only a 300 nm broadband is obtained in TMB h‐BN. It is suggested that the carbon atoms in TMB prevent the formation of highly crystalline h‐BN thin films.

Influence of hydrogen dilution and doping gas on the material properties of plasma-deposited polycrystalline silicon thin films

We studied the effects of precursor gas composition and the addition of dopant gas, PH3, on polycrystalline silicon films deposited using plasma-enhanced chemical vapor deposition. Spectroscopic ellipsometry measurement and modeling results revealed that the poly-Si films consist of a subsurface layer and a bulk layer. The sample deposited under greater hydrogen dilution exhibited a fully crystallized subsurface layer and a denser bulk layer. We also studied the effects of various dopant gas flow rates on structural and electrical properties of the poly-Si films. Ellipsometry, X-ray diffraction, and Raman analyses revealed that the film deposited using a large dopant-gas flow rate exhibits decreased grain size and increased void fraction. Furthermore, the doped poly-Si films show a trend of Raman peak shift, which was attributed to tensile stress. The stress of the doped poly-Si films increases with higher dopant-gas flow rate. Measurement of the temperature-dependent dark conductivity shows saturation of the electrical conductivity of heavily doped films.

Application of calcite, Mg‐calcite, and dolomite as Raman pressure sensors for high‐pressure, high‐temperature studies

AbstractThe Raman spectra of calcite, Mg‐calcite, and dolomite were measured under ambient and high pressure–temperature (P‐T) conditions using a hydrothermal diamond anvil cell, for the purpose of developing new pressure sensors suited for experiments investigating the physicochemical properties of carbonate minerals. By fitting the Raman vibrational frequencies as functions of pressure and temperature, pressure (P, in MPa) can be determined from relative frequency shifts (in cm−1) of the symmetric stretching (ν1) and librational (νL) lattice vibrations of calcite: P = 229(1) × (ν1 calcite, HP − ν1 calcite, ref), P = 162(1) × (νL calcite, HP − νL calcite, ref), or from the translational (νT) and librational (νL) lattice vibrations of dolomite: P = 371(3) × [(νL dolomite, HP − νT dolomite, HP) − (νL dolomite, ref − νT dolomite, ref)], where νref is the value under ambient P‐T conditions. Under elevated temperatures, correction for the effect of temperature (T, in °C) on the Raman frequency shifts can be accomplished through ν1 calcite, HT = ν1 calcite, ref − 6.8(5) × 10−6 × T2–0.0051(3) × T + 0.12, νL calcite, HT = νL calcite, ref − 1.07(12) × 10−5 × T2–0.00341(7) × T + 0.76, νL dolomite, HT − νT dolomite, HT = (νL dolomite, ref − νT dolomite, ref) − 0.0198(3) × T + 0.45. Application of the calcite and dolomite Raman pressure sensors should be made on condition that no phase transitions or breakdown reactions occur under high P‐T conditions, with errors of ±50 MPa and ± 5% at pressures below and above 1.0 GPa, respectively. Results from an additional experiment showed that pressures determined using alternate Raman pressure calibration methods were self‐consistent and in excellent agreement with the results determined using the ν1 Raman peak shifts of aragonite.

Anharmonic Effects in Single-Walled Carbon Nanotubes Analyzed through Low-Temperature Raman Imaging

The high thermal conductivity of single-walled carbon nanotubes (SWCNTs) has gained much attention for their applications in potential thermal devices. Here, we investigate anharmonic effects, originated from phonon interactions, of SWCNT bundles by temperature dependent Raman imaging using our home-built mini cryostat system. The cryostat system is small enough to be mounted on a piezo scanner that suppresses thermal drift, enabling Raman imaging at different temperatures. We obtained Raman spectral images of several SWCNT bundles with a spatial resolution of a few hundred nanometers at different temperatures. We found that different bundles show different temperature dependences of Raman peak intensity, shift, and width. The temperature dependence was further elucidated by considering the sample topography observed by atomic force microscopy, where bundle effects seem to play an important role to influence the anharmonicity. The temperature-dependent Raman analysis based on spatially resolved imaging will be a powerful tool to investigate anharmonic effects of advanced carbon nanomaterials as well as to realize in situ visualization of thermal properties for future thermal devices.

High‐Electric‐Field‐Induced Phase Transition and Electrical Breakdown of MoTe2

Abstract2D molybdenum ditelluride (MoTe2) has recently received significant attention due to its unique phase transition and ambipolar behavior as well as thickness‐dependent bandgap. The phase transition and electrical breakdown of various thickness MoTe2 field‐effect transistors observed under high electric fields are addressed. Interestingly, the MoTe2 exhibits phase transition from a semiconducting 2H phase to a metallic 1T′ almost simultaneously with electrical breakdown, and this is confirmed by a Raman peak of 1T′‐MoTe2 at 125 cm−1. Using Raman mapping results of MoTe2 FETs obtained after the breakdown, it is revealed that the phase transition is initiated from the metal contacting electrode regions of source and drain. All the Raman peaks of MoTe2 shifted to low frequency with increasing drain voltage. Based on the Raman peak shifts, the temperature change in the MoTe2 FETs while device operation is in progress is estimated. The maximum temperature and dissipated power of a tri‐layer MoTe2 device are found to reach 495 K and 5.85 mW, respectively, at an electric field of 6.5 V µm−1. This research provides guidelines for circuit design toward the application of 2D semiconductor devices, related to the energy dissipation and electrical breakdown unique to 2D phase transitional materials.

Exploiting optical properties of nanopolycrystalline diamond in high pressure experiments

ABSTRACTWe investigated the optical properties (absorption, luminescence and Raman spectra) of nanopolycrystalline diamond (NPD) aiming at exploring its capabilities as a pressure sensor and as a pressure-cell anvil for combined X-ray/neutron and optical studies. Notably, we analysed the Raman peak shift and broadening with pressure using a Moissanite Anvil Cell (MAC). The results are compared with those obtained in a DAC, where Raman signals from NPD chips and diamond anvils strongly overlap. Its pressure behaviour in the hydrostatic and non-hydrostatic regimes were investigated. We showed that the nanopolycrystalline structure induces remarkable differences in the peak shift and broadening between NPD and natural type IIa single-crystal diamond, making NPD suitable as pressure gauge for pressure determination and testing hydrostaticity of pressure transmitting medium.

Fabrication of metal nanoparticles-graphene nanocomposites and study of the charge transfer effect

Abstract Composites fabricated by metal nanoparticles supported on graphene sheets are promising for many technological applications ranging from sensing, energy production and storage, catalysis to electronics and optoelectronics. This is due to the benefits offered by the properties of both components. In particular, charge transfer effects at graphene-nanoparticles interface are the basis for the operation of several devices. Here we present an approach to fabricate hybrid composites consisting of graphene-noble metal nanoparticles. Mono- and bimetallic platinum and palladium nanoparticles are produced by laser ablation in a liquid environment and their morphology is characterized by transmission electron microscopy. In addition, in order to fabricate low-dimensional hybrid composites, the nanoparticles are loaded on graphene layer by spin coating of colloidal solutions and the density of the nanoparticles on graphene was evaluated by scanning electron microscopy. The nanoparticles-graphene charge transfer was studied by employing Raman spectroscopy and conductive atomic force microscopy. In particular, the degree of the G and 2D Raman peak shifts (evidenced by the Raman Spectroscopy measurements) and the characteristics of the current-voltage curves (evidenced by conductive atomic force microscopy) allowed inferring an n-type doping effect of the metal nanoparticles on the graphene properties, i. e. electrons transfer from the nanoparticles to the graphene layers. A combined analysis of these results allow us to demonstrate that the chemical composition of the metal nanoparticles is a key parameter in determining the charge transfer phenomenon in low-dimensional systems.

Wide-Span Multi-Wavelength High-Power Diode-Laser Pumping of Fiber Raman Laser

A multimode silica-core fiber Raman laser was pumped directly by five wavelength-combined multimode diode lasers. The pump wavelengths were spread over a bandwidth of ~700 cm−1, namely, at 976, 969, 950, 940, and 915 nm. This is larger than the Raman peak shift of 490 cm−1. The output power reached 31.5 W with an overall slope efficiency of 42% at the wavelength of 1018 nm when pumped with the maximum launched power of 175 W. According to simulations, the fiber was under-length and the output power could double in a longer fiber. Our results suggest that pumping with spectrally combined diode lasers is a promising approach to high-power fiber Raman lasers, even when the pump wavelengths are not optimized.

In situ monitoring of the crystalline state of active pharmaceutical ingredients during high-shear wet granulation using a low-frequency Raman probe

Optimization of manufacturing processes based on scientific evidence is important in the quality control of active pharmaceutical ingredients (APIs) and drug products, particularly when crystal forms change during production, which could affect subsequent drug performance. In this study, we verified crystalline states using various crystal faces and excipients during high-shear wet granulation based on non-contact low-frequency (LF) Raman probe monitoring. Four model drugs [indomethacin (IND), acetaminophen (APAP), theophylline (TP), and caffeine (CAF) polymorphs and cocrystals] were mixed with microcrystalline cellulose and hydroxypropyl cellulose with the addition of water over time. The LF Raman probe showed comparatively high sensitivity in monitoring 5–20% APAP and IND in a wet mass. Notably, as observed from the characteristic LF Raman peak shifts, form I TP and CAF and their cocrystals were more susceptible to transformation to the monohydrate form than form II. This method was also shown to be applicable in monitoring a commercial formulation of eight excipients and revealed crystalline transformations after 15 min of mixing. Therefore, probe-type LF Raman spectroscopy can be successfully employed to distinguish and monitor the crystalline state of APIs in real time during high-shear wet granulation, in which there is a risk of crystal transformation.