碳纤维在电化学处理中的拉曼光谱研究

采用激光拉曼光谱研究了电化学改性处理过程中聚丙烯腈基碳纤维的表面微结构变化,分析了不同处理时间下碳纤维的一级拉曼光谱特性。结果表明： 碳纤维的一级拉曼光谱可以拟合为4个峰,即D(D₁),G,D₂和D₃,表征碳纤维表面微结构变化的拉曼参数主要有D线和G线的积分面积比R(I_D/I_G),D₂线与G线的积分面积比I_D3/I_G,D₃线与G线比I_D3/I_G以及所有无序结构积分面积总和与G线积分面积的比值I_DS/I_G。电化学处理后,碳纤维表面无序度增大,D线和G线交叠度减小,R增大,I_D3/I_G增大,I_D2/I_G减小。随着处理时间的增加,I_DS/I_G不断增大,它与R值的变化趋势基本一致,并且可以更全面表征碳纤维表面结构有序性的变化。因此,利用激光拉曼光谱可以研究电化学改性处理过程中碳纤维表面的微结构变化规律。     

PAN基碳纤维在表面处理中的拉曼光谱研究

采用激光拉曼光谱研究了PAN基碳纤维在表面处理中的微结构变化,分析了表面处理前后碳纤维的一级拉曼光谱特性。结果表明：拉曼光谱中主要的D峰和G峰的拉曼频移、半高宽以及各个不同拉曼频移位置对应肩峰的积分面积比是表征碳纤维物相结构变化的重要参数。经过不同的表面处理,PAN基碳纤维的一级拉曼光谱参数发生了一定程度变化,D峰和G峰的拉曼峰位向高波数偏移,表征石墨微晶尺寸的R值有所提高,这说明在表面处理后碳纤维的石墨微结构受到刻蚀,微晶尺寸有所减小,石墨微晶的边界活性增大;此外,表征碳纤维结构有序程度和缺陷多少的D峰和G峰的半高宽均有减小,表征无定型碳结构或某种有机官能团的A峰和D″峰的相对积分面积减小,这说明与乱层石墨结构相比,碳纤维中存在的无定型碳结构更容易被刻蚀,经过表面处理之后无定型碳的物相比例减小,这与碳纤维XRD图谱中表观结晶度提高的规律相一致。因此,利用激光拉曼光谱可研究碳纤维物相结构的变化规律。     

用RAMAN光谱研究碳纤维皮芯结构随热处理温度的演变规律

用Raman光谱研究碳纤维经不同温度热处理后其皮芯结构的演变规律。结果发现：随着热处理温度的提高,碳纤维表面和内部的Raman光谱具有相似的变化趋势。同时,表征碳纤维表面和内部石墨化程度的R_s与 R_c值均越来越小,且R_s值减小得更快,说明碳纤维的石墨化程度越来越高,并且表面的石墨化程度提高的更快,这是因为碳纤维表面和内部的碳有着不同的石墨化物性。前者接近于软碳,易于石墨化;后者接 近于硬碳,难于石墨化,可能是树脂碳。文章提出并采用皮芯结构因子R_sc(＝R_s/R_c)来表征了碳纤维的皮芯结构程度。当R_sc等于1时,碳纤维是完全均质的。随着热处理温度的升 高,碳纤维的R_sc趋向于零,说明其皮芯结构越来越严重。碳纤维的皮芯结构加重是最终导致其抗拉强度不断降低的原因之一。     

傅里叶变换红外光谱在胃癌淋巴结转移诊断中的应用研究

观察傅里叶变换红外光谱技术无创、原位、快速诊断胃癌淋巴结转移的可行性。联合使用衰减全反射探头及傅里叶变换红外光谱仪测量新鲜离体胃周淋巴结红外光谱,发现每条光谱在吸收波长3 000～1 000 cm-1之间循序出现13条谱带,依据病理检测结果将淋巴结分为转移组及非转移组,比较两组淋巴结红外光谱的峰位和相对峰强等指标结果,最后进行标准统计学分析。36例胃癌患者,共检测淋巴结720枚,其中转移性淋巴结180枚,未转移540枚;与非转移淋巴结相比,转移淋巴结红外光谱有如下特征：(1)与核酸相关的峰强比I_{1 240}/I_{1 460}(p=0.015)和I_{1 080}/I_{1 460}(p=0.034)显著升高,提示转移淋巴结细胞的核酸含量增多;(2)与蛋白相关的I_{1 640}/I_{1 460}(p=0.001)和I_{1 546}/I_{1 460}(p=0.027)峰强比值升高,表明转移淋巴结组织的蛋白质含量明显升高;(3)与脂类相关的I_{2 855}/I_{1 460}和I_{1 740}/I_{1 460}显著降低(p＜0.001),提示癌组织脂类含量相对减少;(4)I_{1 160}/I_{1 460}(p=0.023)显著降低,表明恶性细胞糖类物质的减少。研究结果显示,傅里叶变换红外光谱分析技术有望成为术中原位、在体和快速诊断胃癌淋巴结转移的新方法。     

钠磷酸盐精细结构的拉曼光谱解析

构建了钠磷酸盐精细结构团簇,应用量子化学从头计算方法,采用闭壳层Hatree-Fock(RHF)方法和6-31G(d, p)基组优化构型,进行了拉曼光谱的模拟计算。引入SIT应力指数标识磷酸盐局部微观精细结构,讨论和分析了磷酸盐在高频区的非桥氧对称伸缩振动的特征谱峰。结果表明SIT值与相应结构特征谱峰的拉曼位移呈良好相关性。采用高温拉曼光谱仪测定了Na₅P₃O₁₀固态及熔体的变温拉曼光谱,观察到了Na₅P₃O₁₀在873～1 073 K间的相变。Na₅P₃O₁₀晶体的微结构单元为Q2₁与Q11₂, 其理论含量比例为2∶1。随着温度升高,Na₅P₃O₁₀的主要峰包中心向低频移动,熔融后体系中出现了Q₀,Q1₁,Q2₁,Q11₂,Q12₂,Q22₂等多种精细结构单元,导致其拉曼光谱的展宽与不对称性的出现。这些概念的建立和运用为磷酸盐熔体及玻璃的拉曼光谱的定量分析奠定了基础。     

胆管癌新鲜离体组织的傅里叶变换红外光谱研究

该研究探讨了运用傅里叶变换红外(FTIR)光谱技术对胆管癌进行术中原位、无创和快速诊断的可行性。联合应用傅里叶变换红外光谱仪和衰减全反射(ATR)探头,测定了26例胆管癌和43例良性胆管疾病新鲜离体组织的红外吸收光谱,发现每条光谱在3 800～1 000 cm-1之间循序出现了12个谱带。测量各个谱带的峰位、峰强和峰面积值,然后计算出各谱带的相对峰强和相对峰面积比值,最后进行标准统计学分析。比较胆管癌与良性胆管组织的光谱发现有以下特征：(1)2 925 cm-1谱带明显地向低波数移位(P=0.033);(2)峰强比I_{1 083}/I_{1 460}(P=0.005)和峰面积比S1 083/S_{1 460}(P=0.001),S_{1 240}/S_{1 460}(P=0.025)明显升高,说明癌组织中核酸相对脂类含量明显增加;(3)峰强比I_{1 550}/I_{1 083}(P=0.000)和峰面积比S_{1 550}/S_{1 083}(P=0.000)明显下降,提示蛋白质相对核酸的含量下降。研究结果表明,FTIR有望成为一种术中原位、在体和快速诊断胆管癌的新方法。     

红外光谱法测定杉木/聚丙烯复合材料中木粉和塑料含量

木塑复合材料(wood plastic composites, WPCs)中木材和塑料的配比影响其性能和价格,传统的热化学方法尚不能快速准确地测定WPCs中木塑配比。为探究红外光谱法定量分析WPCs中木粉和塑料的可行性,以杉木、聚丙烯(PP)以及各种添加剂为原料,经过木粉改性、混料和挤出造粒制备出13种不同杉木含量(9.8%～61.5%)的WPCs。采用KBr压片法对制得的样品进行红外光谱分析,通过对比WPCs、杉木、PP以及其他添加剂的红外谱图,确定杉木特征吸收峰为1 059,1 033和1 740 cm-1,1 377,2 839和841 cm-1表征PP特征峰。建立木粉含量、PP含量和二者特征吸收峰峰高比之间的相关关系,结果表明,木粉含量与I_{1 059}/I_{1 377}和I_{1 033}/I_{1 377}之间均存在极强的线性相关,R2分别为0.992和0.993,PP含量与I_{1 377}/I_{1 740}和I_{2 839}/I_{1 740}之间存在高度线性相关,R2分别为0.985和0.981,形成了杉木/PP复合材料中木粉和PP含量的红外光谱定量分析方法,木粉含量预测方程依次为y=53.297x-9.107和y=55.922x-10.238,PP含量预测方程依次为y=6.828 5x+5.403 6和y=8.719 7x+3.295 8。方法精密性和准确性检验表明,方法可重复性强、准确度高,木粉与塑料含量预测平均相对误差约为5%,与传统热化学方法相比,预测精度有较大提高,更重要的是红外光谱法操作更为简便。该研究为杉木/PP复合材料中木粉及塑料含量的测定提供了一种简便、快速、准确的方法。     

非晶碳薄膜振动拉曼光谱的第一性原理研究

采用基于第一性原理的赝势平面波方法,对3个不同密度(2.6,2.9和3.2 g·cm-3)非晶碳结构的振动态密度和振动拉曼光谱进行了研究。结构模型由快速“液体-淬火”方法模拟得到,振动频率和本征模由线性响应理论决定,拉曼耦合张量由有限电场方法计算。计算结果表明：当密度从2.6增加到3.2 g·cm-3时,sp3碳含量从50%增加到84.4%,G峰向高频区偏移,D峰和G峰的强度之比I_D/I_G减小,T峰向低频区偏移且T峰和G峰的强度之比I_T/I_G增大。该结果与实验结果显示出很好的一致性。依据原子振动的分析结果证实：拉曼光谱的G峰和D峰均来自于sp2碳原子的振动贡献,且G峰是由任何成对的sp2碳原子的伸缩振动产生的,T峰来自于sp3杂化碳原子的振动贡献,G峰和T峰峰位随结构的色散是由键长变化导致的。     

组织细胞DNA降解与死亡时间的相关性的显微拉曼光谱分析

为了给死亡时间推断的研究提供新的途径与数据, 探讨了人死亡后组织细胞DNA含量变化与死后时间间隔关系。将离体肾、肝组织置于特定环境中,在不同时间点提取离体组织, 利用激光共焦显微拉曼光谱技术和统计学方法, 在拉曼位移测试范围内, 对死后不同时间肾、肝组织DNA含量变化进行拉曼光谱检测与统计学分析。结果显示: 人死亡后48～72 h, 随着死亡时间的推移, 肾、肝组织Raman光谱的主要散射峰峰位没有明显变化, 而其峰高有明显差异;所测组织的激光拉曼光谱特征峰的相对峰强值(I_{1 094}/I_{2 923})随死亡时间的推移而减小。因此可以得出结论: 人死亡后肾、肝组织细胞DNA含量随死亡时间延长呈下降趋势, 两者之间存在线性关系。     

非平衡磁控溅射法制备的Cr-DLC薄膜真空退火的Raman光谱研究

利用非平衡磁控溅射法制得厚度达到2.23 μm的掺铬含氢类金刚石(Cr-DLC)碳膜。采用Raman光谱和XPS对制得的薄膜进行了结构和热稳定性等表征。结果表明：室温时,薄膜在1 544 cm-1附近的Raman“G”峰归属于石墨结构中C—C键的伸缩振动,即E_2g 模式;而1 367 cm-1附近的“D”峰归属于sp2碳环的“呼吸”振动模式,即A_1g模式;计算得到薄膜sp3键的相对含量约为48at.%。加热至300 ℃,薄膜的Raman谱图与室温时相似,表明此温度段薄膜的结构稳定,未发生明显改变;至400 ℃时,I_D/I_G值迅速增大,sp2键含量升高, 表明此时DLC膜发生了明显的结构变化,开始发生石墨化。继续升温,膜中I_D/I_G比率增加,“G”峰位向高波数方向位移,表明 sp2/sp3比率逐渐增大,薄膜石墨化程度加强,sp2键的无序度逐渐降低,最终导致薄膜的摩擦系数和磨损率等逐渐增大, 热稳定性逐渐降低。退火600 ℃时,I_D/I_G值以及sp2键含量达到最大值,DLC薄膜失效。     

Raman Spectroscopic Characterization of Graphene

Abstract

The recent progress using Raman spectroscopy and imaging of graphene is reviewed. The intensity of the G band increases with increased graphene layers, and the shape of 2D band evolves into four peaks of bilayer graphene from a single peak of monolayer graphene. The G band will blue shift and become narrow with both electron and hole doping, whereas the 2D band will blue shift with hole doping and red shift with electron doping. Frequencies of the G and 2D band will downshift with increasing temperature. Under compressed strain, the upshift of the G and 2D bands can be found. Moreover, the strong Raman signal of monolayer graphene is explained by interference enhancement effect. As for epitaxial graphene, Raman spectroscopy can be used to identify the superior and inferior carrier mobility. The edge chirality of graphene can be determined by using polarized Raman spectroscopy. All results mentioned here are closely relevant to the basic theory of graphene and application in nanodevices.     

Raman and X‐ray diffraction analysis on unburned carbon powder refined from fly ash

The bonding and crystalline structures of oil‐fried fly ash collected from a power plant were analyzed by using Raman spectroscopy and X‐ray diffraction (XRD), respectively. These carbon powders underwent a series of annealing treatment for graphitization and crystallization. In Raman spectra, the refined, unburned carbon contains clearly the D, G and D′ peaks under 2000 or 2700 °C treatment. The Raman spectral line shape of refined, unburned carbon heated at 2700 °C is similar to that of commercial graphite made from graphitization process. In the XRD spectra, the refined, unburned carbon contains (002), (100) and (004) diffraction peaks under heating at 2000 or 2700 °C. The XRD spectral line shape of refined, unburned carbon heated at 2700 °C is similar to that of a commercial graphite bar. The quantitative graphitization level from Raman spectra and crystallization degree from XRD spectra on refined, unburned carbon powders serve as preliminary guide for the qualitative evaluation of these unburned carbon powders. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman scattering characterization of a carbon coating after low-energy argon ion bombardment

The characteristic of Raman scattering spectra of a carbon coating, which was modified by radio frequency argon plasma, has been investigated. The argon ion bombardment causes changes in the microstructure and amount of stress in the coating. Raman scattering spectra are discussed in terms of intensity, bandwidth and wavenumber. The evolvement of Raman spectra shows the following behavior with increasing bombardment time: the intensity changes of the disordered D band, amorphous D″ band and graphite G band could be separated into several stages; low-energy argon ion bombardment over a short period can reduce the number of defects in the carbon coating, while a larger bombardment period can increase the number of defects; the widths of the D and G bands both increase, while that of the D″ band decreases; the wavenumbers of all the three bands fluctuate according to the changes in electronic configuration and amount of stress in the carbon coating.     

Raman validity for crystallite size La determination on reticulated vitreous carbon with different graphitization index

The graphitization index provided by X-ray diffraction (XRD) and Raman spectrometry for reticulated vitreous carbon (RVC) substrates, carbonized at different heat treatment temperatures (HTT), is investigated. A systematic study of the dependence between the disorder-induced D and G Raman bands is presented. The crystallite size L_a was obtained for both X-ray diffraction and Raman spectrometry techniques. Particularly, the validity for L_a determination, from Raman spectra, is pointed out comparing the commonly used formula based on peaks amplitude ratio (I_D/I_G) and the recent proposed equation that uses the integrated intensities of D and G bands. The results discrepancy is discussed taken into account the strong contribution of the line broadening presented in carbon materials heat treated below 2000 °C.     

不同煤级煤的Raman谱特征及与XRD结构参数的关系

11种Cdaf在57.58%～94.01%的不同变质程度煤的拉曼光谱实验表明不同变质程度煤的拉曼光谱一级模都存在两个明显的振动峰,分别为较为宽缓的D峰(1 340～1 380 cm-1)和相对较为尖锐的G峰(1 580～1 600 cm-1)。将800～1 800 cm-1范围的谱图拟合为两个洛仑兹峰,每个峰的峰位置,峰强度以及半峰宽等拉曼参数与碳含量的相关关系分析结果显示：D峰位置和G峰位置随碳含量的增加分别向低波数和高波数区域移动;两峰的峰位差随碳含量的增加而增加;两峰的半峰宽FWHM-D,FWHM-G及两峰强度比I_D/I_G在碳含量75％～94％范围内与碳含量线性相关。发现XRD分析获得的d002和L_c与拉曼谱中的G峰位置及半峰宽存在着良好的相关性。与X射线衍射得到的晶粒尺寸L_a值相关性分析表明用Cancado公式和KW公式对L_a进行估算均是不合理的。     

Raman evidence of the interaction between multiwalled carbon nanotubes and nanostructured TiO2

Nanocomposites of carbon nanotubes and titanium dioxide (TiO₂) have attracted much attention due to their photocatalytic properties. Although many examples in the literature have visualized these nanocomposites by electron microscopic images, spectroscopic characterization is still lacking with regard to the interaction between the carbon nanotube and TiO₂. In this work, we show evidence of the attachment of nanostructured TiO₂ to multiwalled carbon nanotubes (MWNTs) by Raman spectroscopy. The nanostructured TiO₂ was characterized by both full‐width at half‐maximum (FWHM) and the Raman shift of the TiO₂ band at ca 144 cm⁻¹, whereas the average diameter of the crystallite was estimated as approximately 7 nm. Comparison of the Raman spectra of the MWNTs and MWNTs/TiO₂ shows a clear inversion of the relative intensities of the G and D bands, suggesting a substantial chemical modification of the outermost tubes due to the attachment of nanostructured TiO₂. To complement the nanocomposite characterization, scanning electronic microscopy and X‐ray diffraction were performed. Copyright © 2011 John Wiley & Sons, Ltd.     

Characterization of carbon nanotube filters and other carbonaceous materials by Raman spectroscopy—II: study on dispersion and disorder parameters

Recently, we have reported on the characterization of various carbonaceous materials including multiwalled carbon nanotube (MWCNT) filters, which have specific molecular filtering capabilities and good mechanical strength and can be produced in bulk as highly aligned arrays of bundles of CNTs. We have extended our studies using Fourier transform‐Raman spectroscopy with 1064 nm excitation wavelength and a rotating sample holder in the region 1000–2800 cm⁻¹, in addition to 532 and 785 nm, which were used for Raman excitation in our previous study. Raman spectra were analyzed for band positions and line shape with special emphasis on the D‐, G‐ and G′‐ bands. For the single‐walled species, Carbotrap and graphite spectra were also recorded with 488 nm excitation. A dispersion study has been made from the Raman data available with the different excitation wavelengths. Slight band shifts and band broadening could be observed under the two sample conditions, one with the stationary sample and the other with sample rotation. The spectral changes are related to the excessive heating caused in a stationary sample by laser irradiation. Based on our findings in this study combined with our earlier study, we can state that only a careful line shape analysis and study of intensity pattern of the D‐ and G‐Raman bands under well‐defined measurement conditions lends itself as a good measure of degree of alignment in the MWCNT bundles. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of Gold Nanoparticles and Unwanted Residues on Raman Spectra of Graphene Sheets

We report the effect of gold nanoparticles (AuNPs) and unwanted sodium citrate residues (UnR) left after deposition of AuNPs by drop-casting method on the Raman spectra of graphene sheets (GS). The AuNPs solution was deposited on three different substrates: 5.0 wt% Yb³⁺-doped (Q5) phosphate glass, silica glass (S1), and Si/SiO₂-300 nm (S2) substrates. For Q5 substrate, a slight increase in intensity of the G peak was observed, mostly for thinner layers, which can be attributed to a weak SERS effect shielded by UnR. The combination of the following aspects: a blue shift of the G band position, a slight increase in the FWHM (Full Width at Half Maximum), and a slight increase of the Raman intensities of both G and 2D bands in other GS without UnR supports the argument of shielded SERS effect. On the other hand, the effects of UnR on the S1 and S2 substrates produce a decrease on the Raman intensities of G and 2D bands, opposite to the effect produced by the AuNPs; this result was found more intense for the S2 substrate in relation to S1. This is possibly caused by the greater amount of UnR accumulated on the Si/SiO₂ substrate, due to its higher hydrophilicity in relation to other samples. Additional Raman measurements reveal that the Raman intensity of GS in all substrates is unaffected by the presence of a possible humidity on GS, revealing the effect of UnR. Hence, it is vital to understand how residues influence the salient features of GS/AuNPs.