The dynamic surface chemistry during the interaction of CO with ceria captured by Raman spectroscopy

The interaction of CO with ceria under conditions typically used to measure the oxygen storage capacity (OSC) of automotive three way catalysts (TWC) has been investigated by in situ Raman spectroscopy. During exposure of the ceria to CO at 623 K vibrational bands at 1582–1600 and 1331–1340 cm⁻¹ appeared; these bands increased with increasing time of exposure to CO. The band positions are consistent with phonon modes of carbon; however, assignment to carboxylate species or carbonate species cannot be excluded. Subsequent exposure to O₂ at room temperature resulted in a decrease in the intensities of the 1582–1600 and 1331–1340 cm⁻¹ bands by more than 90%. As well, exposure to O₂ at room temperature also resulted in the appearance of Raman modes characteristic of formate and peroxide surface species. The mechanism by which formate forms upon room temperature O₂ exposure is discussed in the context of the assignment of the 1582–1600 and 1331–1340 cm⁻¹ bands to carbon phonon modes which result from the disproportionation of CO on reduced ceria.     

In situ IR,Raman, and UV-Vis DRS spectroscopy of supported vanadium oxide catalysts during methanol oxidation

The application of in situ Raman, IR, and UV-Vis DRS spectroscopies during steady-state methanol oxidation has demonstrated that the molecular structures of surface vanadium oxide species supported on metal oxides are very sensitive to the coordination and H-bonding effects of adsorbed methoxy surface species. Specifically, a decrease in the intensity of spectral bands associated with the fully oxidized surface (V⁵⁺) vanadia active phase occurred in all three studied spectroscopies during methanol oxidation. The terminal V = O (∼1030 cm⁻¹) and bridging V–O–V (∼900–940 cm⁻¹) vibrational bands also shifted toward lower frequency, while the in situ UV-Vis DRS spectra exhibited shifts in the surface V⁵⁺ LMCT band (>25,000 cm⁻¹) to higher edge energies. The magnitude of these distortions correlates with the concentration of adsorbed methoxy intermediates and is most severe at lower temperatures and higher methanol partial pressures, where the surface methoxy concentrations are greatest. Conversely, spectral changes caused by actual reductions in surface vanadia (V⁵⁺) species to reduced phases (V³⁺/V⁴⁺) would have been more severe at higher temperatures. Moreover, the catalyst (vanadia/silica) exhibiting the greatest shift in UV-Vis DRS edge energy did not exhibit any bands from reduced V³⁺/V⁴⁺ phases in the d–d transition region (10,000–30,000 cm⁻¹), even though d–d transitions were detected in vanadia/alumina and vanadia/zirconia catalysts. Therefore, V⁵⁺ spectral signals are generally not representative of the percent vanadia reduction during the methanol oxidation redox cycle, although estimates made from the high temperature, low methoxy surface coverage IR spectra suggest that the catalyst surfaces remain mostly oxidized during steady-state methanol oxidation (15–25% vanadia reduction). Finally, adsorbed surface methoxy intermediate species were easily detected with in situ IR spectroscopy during methanol oxidation in the C–H stretching region (2800–3000 cm⁻¹) for all studied catalysts, the vibrations occurring at different frequencies depending on the specific metal oxide upon which they chemisorb. However, methoxy bands were only found in a few cases using in situ Raman spectroscopy due to the sensitivity of the Raman scattering cross-sections to the specific substrate onto which the surface methoxy species are adsorbed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Carotenoids from red palm methyl esters by nanofiltration

Palm oil contains high concentrations of carotenoids and tocopherols that can be recovered by first converting them to methyl esters and then applying membrane technology to separate the carotenoids from the methyl esters. Several solvent-stable nanofiltration membranes were investigated for this application. Flux with a model red palm methyl ester solution ranged from 0.5 to 10 Lm⁻²h⁻¹, and rejection of β-carotene was 60–80% at a transmembrane pressure of 2.76 MPa and 40°C. A multistage membrane process was designed for continuous production of palm carotene concentrate and decolorized methyl esters. With a feed rate of 10 tons per hour of red palm methyl esters containing 0.5 gL⁻¹ β-carotene, the process could produce 3611 L·h⁻¹ of carotene concentrate containing 1.19 gL⁻¹ carotene and 7500 Lh⁻¹ of decolorized methyl esters containing less than 0.1 gL⁻¹ β-carotene. The economics of this process is promising.     

Characterization of edible oils,butters and margarines by Fourier transform infrared spectroscopy with attenuated total reflectance

The combination of attenuated total reflectance (ATR) and mid-infrared spectroscopy (MIRS) with statistical multidimensional techniques made it possible to extract relevant information from MIR spectra of lipid-rich food products. Wavenumber assignments for typical functional groups in fatty acids were made for standard fatty acids: Absorption bands around 1745 cm⁻¹, 2853 cm⁻¹, 2954 cm⁻¹, 3005 cm⁻¹, 966 cm⁻¹, 3450 cm⁻¹ and 1640 cm⁻¹ are due to absorption of the carbonyl group, C−H stretch, =CH double bonds of lipids and O−H of lipids, respectively. In lipid-rich food products, some bands are modified. Water strongly absorbs in the region of 3600–3000 cm⁻¹ and at 1650 cm⁻¹ in butters and margarines, allowing one to rapidly differentiate the foods as function of their water content. Principal component analysis was used to emphasize the differences between spectra and to rapidly classify 27 commercial samples of oils, butters and margarines. As the MIR spectra contain information about carbonyl groups and double bonds, the foods were classified with ATR-MIR, in agreement with their degree of esterification and their degree of unsaturation as determined from gas-liquid chromatography analysis. However, it was difficult to differentiate the studied food products in terms of their average chainlength.     

Quantitative analysis of palm carotene using fourier transform infrared and near infrared spectroscopy

β-Carotene content is usually determined by using ultraviolet (UV)-visible spectrophotometry at 446 nm. In this study, two spectroscopic techniques, namely, Fourier transform infrared (FTIR) and near infrared (NIR) spectroscopy, have been investigated and compared to UV-visible spectrophotometry to measure the β-carotene content of crude palm oil (CPO). Calibration curves ranging from 200 to 800 ppm were prepared by extracting β-carotene from original CPO using open-column chromatography. Separate partial least squares calibration models were developed for predicting β-carotene based on the spectral region from 976 to 926 cm⁻¹ for FTIR spectroscopy and 546 to 819 nm for NIR spectroscopy. The correlation coefficient (R ²) and standard error of calibration obtained were 0.972 and 25.2 for FTIR and 0.952 and 23.6 for NIR techniques, respectively. The validation set gave R ² of 0.951 with standard error of performance (SEP) of 25.78 for FTIR technique and R ² of 0.979 with SEP of 19.96 for NIR technique. The overall reproducibility and accuracy did not give comparable results to that of spectrophotometric method; however, the standard deviation of prediction was still within ±5% β-carotene content over the range tested. Because of their rapidness and simplicity, both FTIR and NIR techniques provide alternative means of measuring β-carotene content in CPO. In addition, these two spectroscopic techniques are environmentally friendly since no solvent is involved.     

Infrared Study of Benzene Hydrogenation on Pt/SiO2 Catalyst by Co-adsorption of CO and Benzene

FT-IR spectra of the co-adsorption of benzene and CO have been performed to identify the preferred adsorption sites of hydrogen and benzene on a Pt/SiO₂ catalyst for hydrogenation of benzene. Results of CO adsorbed on atop sites on Pt/SiO₂ includes: an α peak at 2091 cm⁻¹, a β peak at 2080 cm⁻¹ and a γ peak at 2067 cm⁻¹ indicating three kinds of adsorption sites for dissociative hydrogen on Pt/SiO₂. The site of lowest CO stretching frequency offers stronger adsorbates–metal interaction for benzene and hydrogen. Hydrogen binding on the site of lowest CO stretching frequency before benzene adsorption significantly enhances the reaction rate of benzene hydrogenation.     

Quantitative determination of low density lipoprotein oxidation by FTIR and chemometric analysis

This study was conducted to develop a quantitative FTIR spectroscopy method to measure LDL lipid oxidation products and determine the effect of oxidation on LDL lipid and protein. In vitro LDL oxidation at 37°C for 1 h produced a range of conjugated diene (CD) (0.14–0.26 mM/mg protein) and carbonyl contents (0.9–3.8 μg/g protein) that were used to produce calibration sets. Spectra were collected from the calibration set and partial least squares regression was used to develop calibration models from spectral regions 4000-650, 3750-3000, 1720-1500, and 1180-935 cm⁻¹ to predict CD and carbonyl contents. The optimal models were selected based on their standard error of prediction (SEP), and the selected models were performance-tested with an additional set of LDL spectra. The best models for CD prediction were derived from spectral regions 4000-650 and 1180-935 cm⁻¹ with the lowest SEP of 0.013 and 0.013 mM/mg protein, respectively. The peaks at 1745 (cholesterol and TAG ester C=O stretch), 1710 (carbonyl C-O stretch), and 1621 cm⁻¹ (peptide C=O stretch) positively correlated with LDL oxidation. FTIR and chemometrics revealed protein conformation changes during LDL oxidation and provided a simple technique that has potential for rapidly observing structural changes in human LDL during oxidation and for measuring primary and secondary oxidation products.     

On the structure of glasses in the Ge-S-Br and Ge-Se-Br systems

The structure of the vitreous GeSBr₂ and GeSeBr₂ compounds has been investigated using Raman scattering spectroscopy. The Raman spectra of the GeSBr₂ compound contain bands at 235 and 113 cm⁻¹, which are attributed to vibrations in the GeBr₄ molecule, and bands at 288, 254, 161, and 147 cm⁻¹, which are absent in the Raman spectra of binary compounds. The Raman spectrum of the GeSeBr₂ glass has common features with the spectra of the GeSe₂ and GeBr₄ compounds but also involves a number of new bands intermediate in position between the bands at 265 cm⁻¹ for the GeSe₂ compound and the bands at 325 cm⁻¹ for the GeBr₄ compound. The spectra obtained confirm the existence of equilibria between the formation and dissociation of ternary structural units in melts of the thiobromide and selenobromide systems.     

Structural and electrochemical impedance spectroscopic studies on reactive magnetron sputtered titanium oxynitride (TiON) thin films

Titanium oxynitride films were deposited onto commercially pure titanium substrates by direct current reactive magnetron sputtering method using Ti targets and an Ar–N₂–O₂ mixture discharge gas. The X-ray photoelectron spectroscopy survey spectra on the etched surfaces of TiON films exhibited the characteristic Ti 2p, N 1s, and O 1s peaks at the corresponding binding energies 454.5, 397.0, and 530.7 eV, respectively. The surface topography of these coatings was studied using atomic force microscopy. The characteristic Raman peaks at 200 and 641 cm⁻¹ for the TiN bonds and at 148, 398 ,and 518 cm⁻¹ for the TiO₂ bonds were observed from the Laser Raman spectrometer. The potentiodynamic polarization studies in simulated bodily fluid were performed and the results are reported in this article.     

β-Carotene transport in human lipoproteins. Comparisons with a-tocopherol

The purpose of this study was to investigate the temporal relationships of the transport of β-carotene in human lipoproteins. We administered 60 mg β-carotene with breakfast to nine fasting subjects, then blood samples were collected at intervals of up to 75 h, lipoproteins were isolated, and β-carotene was quantitated. β-Carotene concentrations in chylomicrons and very low density lipoproteins (VLDL) peaked at 6 and 9 h, respectively. Nonetheless, at all time points the majority of plasma β-carotene was contained in low density lipoproteins (LDL), while high density lipoproteins (HDL) carried a smaller portion (at 24 h, 73±8% in LDL as compared with 23±5% in HDL). In three subjects, transport of β-carotene was compred with the results of earlier studies on the transport of stereoisomers of α-tocopherol. Unlike plasmaRRR-α-tocopherol concentrations, which are maintained by the preferential incorporation ofRRR-α-tocopherol into VLDL by the liver, β-carotene increased and decreased in VLDL similarly toSRR-α-tocopherol, a stereoisomer whose concentrations are not maintained in plasma. In conclusion, β-carotene is primarily transported in the plasma in LDL, but its incorporation by the liver into lipoproteins does not appear to be enhanced.     

Rapid Determination of Free Fatty Acid in Extra Virgin Olive Oil by Raman Spectroscopy and Multivariate Analysis

We introduce a visible Raman spectroscopic method for determining the free fatty acid (FFA) content of extra virgin olive oil with the aid of multivariate analysis. Oleic acid was used to increase the FFA content in extra virgin olive oil up to 0.80% in order to extend the calibration span. For calibration purposes, titration was carried out to determine the concentration of FFA for the investigated oil samples. As calibration model for the FFA content (FFA%), a partial least squares (PLS) regression was applied. The accuracy of the Raman calibration model was estimated using the root mean square error (RMSE) of calibration and validation and the correlation coefficient (R ²) between actual and predicted values. The calibration curve of actual FFA% obtained by titration versus predicted values based on Raman spectra was established for different spectral regions. The spectral window (945–1600 cm⁻¹), which includes carotenoid bands, was found to be a useful fingerprint region being statistically significant for the prediction of the FFA%. High R ² and small RMSE values for calibration and validation could be obtained, respectively.     

Free fatty acid formation and lipid oxidation on milled rice

Milled rice was stored at 37°C and 70% humidity and sampled regularly for 50 d. Rice surface lipid was extracted with isopropanol and analyzed for free fatty acids (FFA) and conjugated diene (CD) contents. Diffuse reflectance Fourier transform infrared (DRIFTS) spectra of the rice samples were also obtained. FFA and CD levels increased together during rice storage and exhibited three distinct phases. DRIFTS identified a decrease in intensity at 1746 cm⁻¹ (ester, −C=O) and increases in intensity at 1731 cm⁻¹ (aldehyde, −CO) and 1714 cm⁻¹ (fatty acid, −C=O) during storage, which correlated well with the chemical analysis data. DRIFTS spectral data were analyzed by a partial least squares regression method to identify spectral regions that correlate strongly with measured FFA and construct prediction models. Overall, the mid-infrared region (4000–400 cm¹) gave the best model (R=0.98, root mean square error of cross-validation=0.05) and also predcted the FFA content of milled rice well. The DRIFTS technique has potential for use in studying qualitative chemical changes on the milled rice surface lipids and for predicting FFA on milled rice.     

Milled rice surface lipid measurement by diffuse reflectance fourier transform infrared spectroscopy (DRIFTS)

Diffuse reflectance Fourier transform infrared spectroscopy was investigated as a method for rice surface lipid determination. Long- and medium-grain rice was milled at four degrees of milling to obtain samples with various levels of residual bran, and total lipids were determined by solvent extraction. Fourier transform infrared spectra were collected between 4000 and 400 cm⁻¹. Weighted regression analysis identified changes in surface chemical functional groups with bran removal. Groups typical of lipids increased with bran content whereas those typical of carbohydrates and protein decreased. Partial least squares (PLS) regression analysis showed a high degree of correlation between the spectra in the 4000–400 cm⁻¹ range and extracted lipids of long-grain rice (R ²=0.96) and medium-grain rice (R ²=0.96); a high degree of correlation was also observed when long- and medium-grain rice data were combined (R ²=0.96). There was a high positive correlation between the spectra and extracted lipids in the 1300–1000 cm⁻¹ range for the long-grain rice (R ²=0.98), medium-grain rice (R ²=0.98), and combined long-/medium-grain rice data (R ²=0.94). PLS selected spectral regions that correlated positively with functional groups of lipid/lipid oxidation products and negatively with functional groups of protein and carbohydrates.     

Effects of quenching mechanisms of carotenoids on the photosensitized oxidation of soybean oil

The effects of 0, 1.0 × 10”⁻⁵, 2.5 × 10⁻⁵, and 5.0 × 10⁻⁵ M β-apo-8'-carotenal, β-carotene, and canthaxanthin on the photooxidation of soybean oil in methylene chloride containing 3.3 × 10⁻⁹ M chlorophyll b were studied by measuring peroxide values and conjugated diene content. β-Apo-8'-carotenal, β-carotene, and canthaxanthin contain 10,11, and 13 conjugated double bonds, respectively. The peroxide values and conjugated diene contents of oils containing the carotenoids were significantly lower (P<0.05) than those of control oil containing no carotenoid. As the number of conjugated double bonds of the carotenoids increased, the peroxide values of soybean oils decreased significantly (P<0.05). The quenching mechanisms and kinetics of the carotenoids in the photosensitized oxidation of soybean oil were studied by measuring peroxide values. The steady-state kinetics study showed that carotenoids quenched singlet oxygen to reduce chlorophyll-sensitized photooxidation of soybean oil. The singlet-oxygen quenching rate constants ofβ- apo-8'-carotenal, β-carotene, and canthaxanthin were 3.06 × 10⁹, 4.60 × 10⁹, and 1.12 × 10¹⁰ M⁻¹sec⁻¹, respectively.     

Red pigment-forming substances from autoxidized linolenate: Identification of prostaglandin-like substances

The chemical structures of lipid degradation products capable of reacting with amino acids and forming red pigments were investigated. The red pigment-forming substances (RPS's) derived from autoxidized linolenate in triglyceride of linseed oil were purified successively by gel chromatography on Sephadex LH-20, column chromatography and TLC on Silica gel 60, and HPLC on μ-Porasil. Consequently, three types of RPS's were isolated. IR spectra of RPS's were similar, except for slight differences in the fingerprint region (1300—650 cm⁻¹). These substances included the OH group (3500 cm⁻¹ region), conjugated aldehyde (νC=0 1688 cm⁻¹, νC=C 1635 cm⁻¹) and ketone (νC=0 1740 cm⁻¹) in their molecules. RPS's were analyzed by GLC and GC-MS after derivatization with dimethylhydrazine and/or trimethylsilyl reagents, before and after the reduction with NaBH₄ and/or hydrogenation with PtO₂. The fragmentation patterns indicated the presence of an ethyl group in addition to the functional groups described above, and the molecular formula was estimated to be C₁₀H₁₄O₃. Further elucidation of the structures was obtained by¹³C- and¹H-NMR analyses, and evidence was obtained for the presence of a hydroxypentanone ring, a PG-like structure. The sequence of the protons on the ring carbons was unequivocally deduced from the double resonance experiments. All the data taken together suggested that the RPS's were the stereoisomer of 3-(2-ethyl-5-hydroxy-3-oxo) cyclopentanyl-2-propenal. Presented at the General Meeting of JSSF held in Tokyo University of Fisheries, Tokyo, April 1983.     

Detection of lard mixed with body fats of chicken, lamb, and cow by fourier transform infrared spectroscopy

Fourier transform infrared (FTIR) spectroscopy provides a simple and rapid means of detecting lard blended with chicken, lamb, and cow body fats. The spectral bands associated with chicken, lamb, and cow body fats and their lard blends were recorded, interpreted, and identified. Qualitative differences between the spectra are proposed as a basis for differentiating between the pure animal fats and their blends. A semiquantitative approach is proposed to measure the percent of lard in blends with lamb body fat (LBF) on the basis of the frequency shift of the band in the region 3009–3000 cm⁻¹, using the equation y=0.1616x+3002.10. The coefficient of determination (R ²) was 0.9457 with a standard error (SE) of 1.23. The percentage of lard in lard/LBF blends was also correlated to the absorbance at 1417.89 and 966.39 cm⁻¹ by the equations y=0.0061x+0.1404 (R ²=0.9388, SE=0.018) and y=0.004x+0.1117 (R ²=0.9715, SE=0.009), respectively. For the qualitative determination of lard blended with chicken body fat (CF), the FTIR spectral bands in the frequency ranges of 3008–3000, 1418–1417, 1385–1370, and 1126–1085 cm⁻¹ were employed. Semiquantitative determination by measurement of the absorbance at 3005.6 cm⁻¹ is proposed, using the equation y=0.0071x+0.1301 (R ²=0.983, SE=0.012). The percentage of lard in lard/GF blends was also correlated to the absorbance at 1417.85 cm⁻¹ (y=0.0053x+0.0821, with R ²=0.9233, SE=0.019) and at 1377.58 cm⁻¹ (y=0.0069x+0.1327, with R ²=0.9426, SE=0.022). For blends of lard with cow body fat (CBF) bands in the range 3008–3006 cm⁻¹ and at 1417.8 and 966 cm⁻¹ were used for qualitative detection. The equation y=−0.005x+0.3188 with R ²=0.9831 and SE=0.0086 was obtained for semiquantitative determination at 966.22 cm⁻¹.     

Chia seeds as a source of natural lipid antioxidants

Chia (Salvia sp) seeds were investigated as a source of natural lipid antioxidants. Methanolic and aqueous extracts of defatted chia seeds possessed potent antioxidant activity. Analysis of 2 batches of chia-seed oils demonstrated marked difference in the fatty acid composition of the oils. In both batches, the oils had high concentrations of polyunsaturated fatty acids. The major antioxidant activity in the nonhydrolyzed extract was caused by flavonol glycosides, chlorogenic acid (7.1 × 10⁻⁴ mol/kg of seed) and caffeic acid (6.6 × 10⁻³ m/kg). Major antioxidants of the hydrolyzed extracts were flavonol aglycones/kaempferol (1.1 × 10⁻³ m/kg), quercetin (2.0 × 10⁻⁴ m/kg) and myricetin (3.1 × 10⁻³ m/kg); and caffeic acid (1.35 × 10⁻² m/kg). Two methods were used to measure antioxidant activities. Both were based on measuring bleaching ofβ-carotene in the coupled oxidation ofβ-carotene and linoleic acid in the presence of added antioxidants.     

Electrochemical study of the codeposition of Mg–Li–Al alloys from LiCl–KCl–MgCl<Subscript>2</Subscript>–AlCl<Subscript>3</Subscript> melts

This work presents a novel electrochemical study on the codeposition of Mg, Li and Al on a molybdenum electrode in LiCl–KCl–MgCl₂–AlCl₃ melts at 943 K to form Mg–Li–Al alloys. Cyclic voltammograms (CVs) showed that the underpotential deposition (UPD) of magnesium on pre-deposited aluminum leads to the formation of a liquid Mg–Al solution, and the succeeding underpotential deposition of lithium on pre-deposited Mg–Al leads to the formation of a liquid Mg–Li–Al solution. Chronopotentiometric measurements indicated that the codeposition of Mg, Li and Al occurs at current densities lower than −0.47 A cm⁻² in LiCl–KCl–MgCl₂ (0.525 mol kg⁻¹) melts containing 0.075 mol kg⁻¹ AlCl₃. Chronoamperograms demonstrated that the onset potential for the codeposition of Mg, Li and Al is −2.100 V, and the codeposition of Mg, Li and Al is formed when the applied potentials are more negative than −2.100 V. The diffusion coefficient of aluminum ions in the melts was determined by different electrochemical techniques. X-ray diffraction and inductively coupled plasma analysis indicated that α, α + β and β Mg–Li–Al alloys with different lithium and aluminum contents were obtained via potentiostatic and galvanostatic electrolysis.     

n-heptane reforming over Pt supported on beta zeolite exchanged with Cs and Li cations

Raman spectra of SO_x adsorbed on γ-alumina and Pt/γ-alumina model catalysts have been obtained with a 244 nm Raman spectrometer. Strong peaks in the 980–1380 cm^-1 region characteristic of adsorbed sulfates are clearly portrayed in the spectra, which contrast with fluorescence-dominated scans obtained using visible excitation. Broad bands are also observed in the 3500–3700 cm^-1 O–H stretch region on the γ-alumina, which belong to weakly-bound physisorbed water and more strongly-bound surface hydroxyls. These features are monitored as the samples are heated up to 600°C in the presence of nitrogen. The sulfate peaks vary in position depending on whether or not the γ-alumina is loaded with platinum, hydrated, or dehydrated. Platinum appears to inhibit the physisorption of water and the formation of hydroxyls on the γ-alumina surface, as evidenced by the absence of O–H stretch vibrations on the Pt-loaded sample. Our spectral data demonstrate that UV Raman spectroscopy is a useful technique for analytical studies of adsorbed SO_x on γ-alumina, and holds promise for future in situ investigations of other adsorbed species on catalytic substrates of automotive interest. This revised version was published online in July 2006 with corrections to the Cover Date.     

Spectroscopic Investigation of Quantum Confinement Effects in Ion Implanted Silicon-on-Sapphire Films

Crystalline Silicon-on-Sapphire (SOS) films were implanted with boron (B⁺) and phosphorous (P⁺) ions. Different samples, prepared by varying the ion dose in the range 10¹⁴–5 × 10¹⁵ and ion energy in the range 150–350 keV, were investigated by the Raman spectroscopy, photoluminescence (PL) spectroscopy and glancing angle x-ray diffraction (GAXRD). The Raman results from dose dependent B⁺ implanted samples show red-shifted and asymmetrically broadened Raman line-shape for B⁺ dose greater than 10¹⁴ ions cm⁻². The asymmetry and red shift in the Raman line-shape is explained in terms of quantum confinement of phonons in silicon nanostructures formed as a result of ion implantation. PL spectra shows size dependent visible luminescence at ∼1.9 eV at room temperature, which confirms the presence of silicon nanostructures. Raman studies on P⁺ implanted samples were also carried out as a function of ion energy. The Raman results show an amorphous top SOS surface for sample implanted with 150 keV P⁺ ions of dose 5 × 10¹⁵ ions cm⁻². The nanostructures are formed when the P⁺ energy is increased to 350 keV by keeping the ion dose fixed. The GAXRD results show consistency with the Raman results.