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New Lines in the Raman Spectra of Carbons and Graphite
Journal of the American Ceramic Society
Abstract
An extensive survey of the Raman spectral activity of a wide variety of carbon materials has produced experimental evidence for at least five structure-sensitive lines or bands. In addition to the well-known, always present 1580 cm−1 graphite line and the 1360 cm−1 disordered carbon line, there is a disorder line at ∼1620 cm−1 that is responsible for the apparent blue-shift of the graphite line in very disordered carbons; and there are lines at ∼2700 and ∼2735 cm−1 that are strong in graphite and annealed carbons but absent in very disordered carbons. These additional lines increase the capability of Raman spectroscopy to characterize carbon materials.
... The T peak (* 1060 cm -1 ) is an indicator for sp 3 bonded carbon in the sample. The D' peak is an indicator of the grain size of the carbon material, located at 1620 cm -1 [41][42][43][44]. This D' peak becomes more prominent as the grain size increases, which in the case of glassy carbons is associated with an increase in carbonization temperature. ...
... 2000-3500 cm -1 range were present but at low intensity and merged. All these Raman characteristics are typical of low HTT glassy carbon from the literature [38,39,42,43,46,47]. ...
... This increase in I(D/G) with an increase in number of pulses is analogous to behaviour observed in the literature with increases in the heat treatment temperature when producing glassy carbon [39] since more pulses means higher material temperature. From the 'Three stage model' presented by Ferrari et al. [45,46], it is known that that the combination of a G peak location between 1580 and 1600 cm -1 coinciding with an I(D/ G) value ranging between 0.5 and 2.0 indicates a dominance of sp 2 bonded carbon [38,39,42,43,46,47]. Hence, the Raman spectroscopy data show that carbon coatings produced using thermal heat treatment and photonic curing methods both predominantly consisted of sp 2 bonded carbon. ...
Photonic curing was explored as a rapid method for producing glassy carbon coatings, reducing processing time from ~ 20 h for conventional thermal processing down to ~ 1 min. A resole-type thermoset polymer resin coated on steel foil was used as a precursor, placed in a nitrogen purged container and exposed to high energy light (~ 27 J/cm ² per pulse for up to 20 pulses). Comparison samples were produced at 800 °C using a conventional nitrogen purged thermal route. For both photonic and conventionally produced coatings, Raman spectroscopy and primary peak XPS data showed sp ² bonded carbon, indicative of bulk glassy carbon. This transformation evolved with increasing number of pulses, and therefore amount of energy transferred to the coating. The produced coatings were resilient, highly smooth, with no evidence of surface defects. XPS analysis indicated greater sp ³ content at the immediate surface (5–10 nm) for photonic cured carbon compared with thermally cured carbon, likely due to the local environment (temperature, atmosphere) around the surface during conversion. The ability to rapidly manufacture glassy carbon coatings provides new opportunities to expand the window of applications of glassy carbons in coatings towards large-scale high volume applications.
... It is caused by a double resonance effect created by defects in the ideal graphite structure (Thomsen and Reich 2000). This band is referred to as the 'D' band-D standing for disorder (Tuinstra and Koenig 1970;Vidano and Fischbach 1978;Wang et al. 1990). In graphitic carbons, the positions of the D and G band, as well as the relative height of the D band compared to the height of the G band (i.e. the D/G height ratio H D /H G ) depends on the amount of defects in the graphitic crystal structure (e.g. ...
... In graphitic carbons, the positions of the D and G band, as well as the relative height of the D band compared to the height of the G band (i.e. the D/G height ratio H D /H G ) depends on the amount of defects in the graphitic crystal structure (e.g. Tuinstra and Koenig 1970;Vidano and Fischbach 1978;Wang et al. 1989;Beyssac et al. 2003), the size of the crystals (Tuinstra and Koenig 1970;Wang et al. 1990), the orientation of the crystal relative to the Raman laser beam (Wang et al. 1989) and the temperature and pressure of formation (e.g. Beyssac et al. 2002Beyssac et al. , 2003. ...
... In micromorphological thin sections, the molecular structure of its components could be altered by mechanical polishing during sample preparation. It is well known that polishing graphitic carbon changes its Raman spectrum: Polishing induces more defects in its crystal structure and increases the height of the D band relatively to the height of the G band (Vidano and Fischbach 1978;Wang et al. 1989;Beyssac et al. 2003). The influence of polishing on the structure of chars, lacking a crystal structure, is lesser known. ...
Burned or charred organic matter in anthropogenic combustion features may provide important clues about past human activities related to fire. To interpret archaeological hearths, a correct identification of the organic source material is key. In the present work, Raman spectroscopy is applied to characterise the structural properties of char produced in laboratory heating- and open-fire experiments. This reference data set is compared to analyses of three different archaeological sites with Middle Palaeolithic combustion contexts. The results show that it is possible to determine whether a charred fragment is the product of burning animal-derived matter (e.g. meat) or plant-derived matter (e.g. wood) by plotting a few Raman spectral parameters (i.e. position of G and D bands, and intensity ratios HD/HG and HV/HG) against one another. The most effective parameters for discriminating animal- from plant-derived matter are the position of the G band and the HV/HG intensity ratio. This method can be applied on raw sample material and on uncovered micromorphological thin sections. The latter greatly compliments micromorphology by providing information about char fragments without any clear morphological characteristics. This study is the first of its kind and may provide archaeologists with a robust new method to distinguish animal- from plant-derived char in thin sections.
Supplementary information:
The online version contains supplementary material available at 10.1007/s12520-020-01263-3.
... More conductive materials exhibit stronger electron-phonon interaction than semi-conductive ones. A low intensive band at 2451 cm -1 called by D'' by Vidano and Fischbach [17,18], consists of the sum of D and D 1 modes (D 1 -sp 3 at 1060-1080 cm -1 ). In our case of composites "TEG -CNTs", the position of G-mode at 1581cm -1 does testify the formation of good crystalline structure of composites "TEG -CNTs" (its theoretical value for graphite and graphene is 1580 cm -1 ), relative intensity I 2D /I G = 1.12. ...
... The analysis of fitted data for 2D mode suggests that the obtained composites "expanded graphite-CNTs" are of good crystalline structure and exhibit the metal-like conductive properties (inharmonic of 2D mode is about 10 cm -1 ) [18]. Fig. 3 shows IR absorption spectra of composites "TEG -CNTs" at 1% of CNTs in the spectral area 0-8000 cm -1 with 5 intensive negative absorption peaks at 2000 cm -1 (two peaks), 2500 and 4000 cm -1 (two peaks). ...
We investigated influence of multiwalled carbon nanotubes (CNTs) on spectral characteristics of composites “thermo-expanded graphite – carbon nanotubes (TEG–CNTs)”. The introduction of CNTs in an amount of 0-3% by weight of TEG composites results in a significant increase in the strength characteristics and thermal stability of the composites. This result indicates that CNTs is ideal filler for composites based on TEG compositions and structures. Measurements the giant two-polar oscillations with very small half-width 0.5 cm–1 testify the strong interaction of surface polaritons with photons. When frequencies of local oscillations of surface bonds of carbon nanotubes and modes along “nanotube-TEG” boundaries matches, then the light absorption increases 102–105 times. Thus, IR absorption with two-polar oscillations was measured at 0% of nanotubes in TEG at frequency of 2750 cm–1. It is own optical mode in the thermally expanded graphite. 5 peaks with two-polar oscillations were measured in the IR absorption spectra at 1% of carbon nanotubes. And 8 peaks with two-polar oscillations were measured at 3 % of carbon nanotubes at optical mode frequencies along the boundaries of thermally expanded graphite - carbon nanotubes. When frequencies of local oscillations of carbon nanotubes and composite’s modes matches, then the light absorption extremely increases (in 102–105 times), and two-polar IR absorption oscillations with negative components are formed. In general, two-photon interference is a result of quantum entanglement of dipole-active oscillations and splitting of photons according to the Hong-Ou-Mendel (HOM) quantum effect. Two-photon entanglement is built on the basis of the most entanglement states, also known as Bell's states. The HOM–quantum effect on composites “expanded graphite-carbon nanotubes” is promising for the development of highly coherent optical quantum computers.
... The carbon-related band additionally observed in the Si electron lens irradiated with an acceleration voltage of 20 keV electron beam for 24 h was confirmed by analyzing the Raman spectra based on the sample deposited by sputtering carbon on the surface of the carbon rod (Cressington, UK) and the Si electron lens. In this case, carbon allotropes, such as carbon rods and carbon nanotubes (CNTs), as well as phonon peaks corresponding to the D-band, G-band, and 2D-band, were identified and commonly observed [14][15][16][17][18][19][20][21]. Figure 4 shows the Raman spectra of the carbon-related material prepared using various methods. Figure 4a shows the Raman spectrum of a typical carbon rod. ...
... The carbon-related band additionally observed in the Si electron lens irradiated with an acceleration voltage of 20 keV electron beam for 24 h was confirmed by analyzing the Raman spectra based on the sample deposited by sputtering carbon on the surface of the carbon rod (Cressington, Watford, UK) and the Si electron lens. In this case, carbon allotropes, such as carbon rods and carbon nanotubes (CNTs), as well as phonon peaks corresponding to the D-band, G-band, and 2D-band, were identified and commonly observed [14][15][16][17][18][19][20][21]. Figure 4 shows the Raman spectra of the carbon-related material prepared using various methods. Figure 4a shows the Raman spectrum of a typical carbon rod. ...
Microcolumns have a stacked structure composed of an electron emitter, electron lens (source lens), einzel lens, and a deflector manufactured using a micro electro-mechanical system process. The electrons emitted from the tungsten field emitter mostly pass through the aperture holes. However, other electrons fail to pass through because of collisions around the aperture hole. We used Raman scattering measurements and X-ray photoelectron spectroscopy analyses to investigate the influence of electron beam bombardment on a Si electron lens irradiated by acceleration voltages of 0, 20, and 30 keV. We confirmed that the crystallinity was degraded, and carbon-related contamination was detected at the surface and edge of the aperture hole of the Si electron lens after electron bombardment for 24 h. Carbon-related contamination on the surface of the Si electron lens was verified by analyzing the Raman spectra of the carbon-deposited Si substrate using DC sputtering and a carbon rod sample. We report the crystallinity and the origin of the carbon-related contamination of electron Si lenses after electron beam bombardment by non-destructive Raman scattering and XPS analysis methods.
... Pristine (Fig. 4a-i) shows a prominent peak of G-band at 1580 cm −1 , attributed to E 2g mode due to the in-plane vibrations of carbon atoms, and a trace of D-band at 1340 cm −1 corresponding to A 1g mode due to the break of symmetry occurring at the edge planes and defects in the graphene sheets and structural disordering. 11,[25][26][27] We utilize the intensity ratio of D-band (I D ) to G-band (I G ) as a measure of structural disorder. 11,[25][26][27] The lower the ratio, the greater structural preservation. ...
... 11,[25][26][27] We utilize the intensity ratio of D-band (I D ) to G-band (I G ) as a measure of structural disorder. 11,[25][26][27] The lower the ratio, the greater structural preservation. The I D /I G ratio (Fig. 4b) increases from pristine (0.096) to cycled anodes, due to structural disordering. ...
Lithium-ion batteries (LIBs) are ubiquitous power sources and demand for higher energy and higher performance LIBs than state-of-the-art ones continues to increase for longer range use of electric mobility and energy-storage systems. Performance of conventional LIBs is often limited or failed in tough working environments, particularly, subzero-temperatures because of reduced ionic conductivity of electrolyte and diffusion kinetics of both anode and cathode, causing lithium metal plating and dendrite growth and finally safety issue and death of LIBs. Herein, for the first time we report a lithium metal plating-free and unprecedented high-performance graphite∥LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) full-cell under subzero-temperature of −10 °C and high-voltage of 4.45 V through the construction of robust solid electrolyte interphase (SEI) layers at both anode and cathode and their structural stabilization in 1 M LiPF 6 and nonflammable electrolyte. Subzero-temperature operation of commercial electrolyte-based full-cell however results in a drastic performance failure in early cycles and shows distinguishing marks such as lithium metal plating at graphite anode and irreversible phase transformation of NCM811 to disordered H3 phase with a large volume contraction. The strong correlation between anode-electrolyte and cathode-electrolyte interfacial stabilization, bulk structural stabilization of both anode and cathode, and highly reversible cycling performance under subzero-temperature is clearly demonstrated.
... The degree of graphitization in carbon-related materials can be expressed by measuring the D-G peak intensity ratio (I D /I G ), whereas the number of defective sites proportionally increases to this value. 33,175,176 Laser-induced surface modification of metal oxide films is also generally used to provide oxygen vacancies and defects during the rapid photoexcitation process. 55,177,178 A strategy to control the defect densities on Co 3 O 4 nanosheets via laser annealing was recently proposed by Lu et al. 152 First, a simple hydrothermal method was used to prepare the Ni foam with Co(OH) 2 nanosheets, followed by lowtemperature calcination (250 C, 3 h) to obtain tightly anchored Co 3 O 4 nanosheets on the Ni foam electrode. ...
Nanomaterials synthesized through laser irradiation have numerous applications in the field of energy storage and conversion. Conventional methods for fabricating nanomaterials often involve extended reaction times, making them susceptible to issues such as reproducibility, impurities, and inhomogeneity. To address these issues, a novel strategy of synthesizing nanomaterials via solvent-free laser irradiation in the gas phase is proposed as a potential solution. This innovative strategy offers ultrafast heating and cooling processes compared to conventional time-consuming methods, resulting in the formation of homogeneous nanosystems within femto- to nanosecond timeframes. The focused laser beam induces rapid photothermal and photochemical effects in either air or an inert gas atmosphere, enabling the rapid production of nanomaterials with precise control over geometry, chemistry, crystallinity, and defect density by adjusting processing conditions and sintering mediums. This review provides insights into the rapid solvent-free laser-assisted synthesis of nanomaterials using natural carbon-based materials, polymers, metal–organic frameworks, and inorganic species in both air and inert atmospheres. The introduction of photo-irradiation across a wide range of precursors facilitates phase transitions and surface functionalization in the resulting nanoproducts. We also discuss the effects of altering laser wavelengths, pulse widths, fluences, and repetition rates on both surface and bulk properties of the final products. Finally, we explore the applications of laser-induced nanomaterials in areas such as rechargeable batteries, supercapacitors, solar cells, and catalysis.
... 1580 cm -1 ) and the D band (ca. 1360 cm -1 ) (e.gTuinstra and Koenig 1970; Nakamizo et al. 1974;Vidano and Fischbach 1978;Wang et al. 1990), bands which have also been observed for seaweed chars (Cao et al. 2021). The G band, or graphite band, corresponds to the E2g2 vibrational mode and is observed alone in graphite crystals (Tunistra and Koenig 1970). ...
The use of seaweed as fuel has been mentioned in ethnographic and historical sources of different coastal regions. Nevertheless, the archaeological record of seaweed burning is still limited to contexts where preservation is exceptional and macroscopic discrimination of charred remains is possible. Here, we evaluate the effectiveness of Raman spectroscopy in discriminating seaweed vs. plant/wood char. Our dataset (N = 92) consists of modern and archaeological seaweed and plant/wood charred remains, including specimens of unknown origin from the Atacama Desert coast, Northern Chile. The charred samples were processed to obtain 13 parameters which were then fed into five supervised machine learning models. The models, built on samples of known origin (seaweed and plant/wood), performed remarkably well in terms of accuracy, kappa, sensitivity, and specificity. The models were used for final predictions on 10 non-identified archaeological charcoals. Our results suggest that Raman spectroscopy combined with machine learning techniques is a robust methodology for discriminating seaweed and plant/wood charred remains in the archaeological record. The predictions on unknown samples confirm that seaweed was used as fuel in a specific funerary ritual in the southern Atacama Desert coast around 5000 cal BP. Furthermore, charred specimens of Lessonia spp. recovered from combustion features in other northern Chile coastal settlements, suggest that seaweed pyrotechnology developed by Atacama Desert coast people is likely a long-term process. As for coastal archaeology, this work encourages new research on seaweed as an alternative/main fuel in coastal deserts and evaluates possible bias for chronologies from coastal archaeological settlements around the globe.
... The two peaks became barely distinguishable at lower temperatures due to structural disorder-related broadening, but, following its attribution, we did not see a physical reason to rule out the second peak. -As far as the D contribution is concerned, the presence of the smaller contribution on the left tail is supported by (i) literature reports [13][14][15][16][17][18] and (ii) by the presence of slope changes in the spectrum shape that a single peak cannot justify. ...
First of all, we thank Dr. Meier for his thorough reading and constructive remarks [...]
... All compositions contained carbon, primarily along grain boundaries, evenly distributed throughout the microstructure. The carbon was identified as primarily graphitic from Raman spectra (not shown), using the analysis discussed elsewhere [15,[34][35][36]. Boron carbide was also observed in 0-ZrC as ~1 µm, equiaxed grains, identified from the Raman spectra (not shown) with analysis discussed elsewhere [36,37]. ...
The thermal conductivity of ZrB2 with 0 to 10 vol.% ZrC was studied from 25 to 2000°C. The ZrB2-ZrC ceramics were prepared by attrition milling the starting powders and adding 0.5 wt.% C as a sintering aid. The ceramics were hot-pressed to full density at 1900°C for 30 min in a flowing Ar atmosphere. The ceramics contained graphitic carbon as a secondary phase, with ZrB2 and ZrC grain sizes of approx. 3.5 and 1.5 μm, respectively. At room temperature, thermal conductivity was 75 W/m·K for monolithic ZrB2, increasing to 79 W/m·K for 2.5 vol.% ZrC, and decreasing to 72 W/m·K for 10 vol.% ZrC. At 2000°C, thermal conductivity was 72 W/m·K for ZrB2, decreasing to 69 W/m·K for 10 vol.% ZrC. Electrical resistivity behavior was similar to thermal conductivity, decreasing with the addition of ZrC up to 2.5 vol.% (9.9 µΩ·cm at 25°C), then increasing with further ZrC additions. The increase in thermal conductivity with ZrC addition up to 2.5 vol.% was the result of preferential segregation of W from the ZrB2 phase to the ZrC phase. The reduction in thermal conductivity with greater ZrC additions was due to the lower thermal conductivity of ZrC.
... The G band, normally at ~1580 cm −1 , is a common feature of all sp 2 carbon forms due to an in-plane vibration mode or the C-C bond strain in graphitic materials. Thus, it is an indication of the presence of a carbon graphitic structure [31][32][33][34][35] in the samples. We noted from the Figure 4 that both showed a sharp G band which is slightly blue-shifted to ~1600 cm −1 which could be interpreted as the evolution of sample from graphene multilayers to nanocrystalline and the presence of sp 3 bonding [35]. ...
Graphene growth at low temperatures was investigated by integrating a hot wire cell made from coil-shaped tungsten into a plasma-enhanced chemical vapour deposition (PECVD) system. It was found that the suitable position of the hot wire was such that the precursor gas comes out of the end of the gas pipeline and directly flows into the hot wire along its axis. This position puts the gas pipeline outside of plasma area, yielding uninterrupted plasma. The obtained films, which were grown at a low temperature between 290 °C to 300 °C, showed the presence of sharp G band in Raman spectra, indicating the presence of graphitic carbon structure and was confirmed by X-Ray Diffraction data. Also, sharp D band was detected in Raman spectra, which indicated that the film contains many defects. In addition to the nature of ion bombardment in the PECVD process, the defects were due to the addition of O-H functional groups and the formation of sp3 C-H in the samples, as shown in the FTIR spectra. Due to these defects, the Raman spectra obtained of the films showed very weak 2D bands, suggesting that our samples were in the form of graphene oxide.
... This could be interpreted as a D peak [29]. The structural distortion might be a reason for this [30]. ...
... Meanwhile, the Raman spectrometer was equipped with a density filter to avoid the thermal decomposition of samples. Each spectral analysis was conducted with LabSpec 5 (LS5) software (Version LS5: 2.02, Horiba, Paris, France) [41,42]. ...
The Lutang graphite deposit in Chenzhou, Hunan province, China, is a well-known coal seam-derived graphite (graphite formed from coal during its natural evolution) deposit with proven reserves of 9.5 million tons and prospective reserves of around 20 million tons (2015 data). The graphite occurs at an andalusite bearing sericite quartz chlorite metamorphic mudstone around a c. 530 km2 Qitianling granite intrusion. A set of coal seam-derived graphite samples from the Lutang graphite deposit in Hunan was examined by geochemical, crystallographic, and spectroscopic techniques to assess changes in the degree of graphitization approaching the intrusion. The carbon content, degree of graphitization, and Raman spectral parameters of series coal seam-derived natural graphite samples show a fluctuating increase with increasing proximity to the granite intrusion. The profile of geological structural features has a close spatial correlation with the variations in the degree of graphitization of series coal seam-derived natural graphite, and a strain-enhanced graphitization model is proposed. Moreover, the geographical distribution and the degree of graphitization are positively related to changes in the iron content of chlorite, suggesting a graphitization process promoted by mineral catalysis during metamorphism. A close spatial relationship exists between graphite mineral and chlorite occurrences when approaching the intrusive mass. The results of this research are important for understanding the role of tectonic stress and mineral catalysis on the genesis of coal-derived graphite.
... Furthermore, as shown in Fig. 1f, the Raman spectra of both the NG and the KG exhibit a Raman active feature of the doubly degenerate E 2g phonon mode (the G band) at 1582 cm −1 [43]. However, the NG has more pronounced disorder-induced D and D ⸍ bands at 1350 cm −1 and 1620 cm −1 , respectively, compared to the KG. ...
Graphite intercalation compounds (GICs) are widely known for their remarkable multifold physico-chemical properties and their numerous state-of-the-art applications, such as energy storage, sensors, lubrication, catalysis, magneto-optics, superconductivity, etc. However, the properties of GICs largely depend on the synthesis technique, structure, and morphology of the graphite; the size and properties of the intercalant species and its concentration in the host material. Accordingly, in the field of electrochemical energy storage, the appearance of novel ionic systems and detailed investigations of GICs are highly desired. In this study, two different types of graphite, natural graphite (NG) and kish graphite (KG), were used to gain insights into the intercalation of the ClO4⁻ anion in graphite from a concentrated Al(ClO4)3 aqueous electrolyte solution through extensive electrochemical studies and various in situ and ex situ spectroscopic characterization techniques. An analysis of cyclic voltammograms indicated the presence of surface-controlled charge storage along with diffusion-controlled ion intercalation into the interlayer spaces in NG and KG. Additionally, a comparative study on the electrochemical behavior of these two types of graphite showed differences that can be correlated with their structural properties. These findings open new perspectives for GIC formation in concentrated aqueous electrolytes and applications in electrochemical energy storage.
... The manifestation of the intense G′ band at 2690 cm −1 further proves the higher degree of graphitic ordering for the ECS-2402. 41 This analysis of the Raman spectra corroborates the XRD results, further suggesting that the ECS-2402 sample is more graphitized compared to ECS-4601 and ECS-3701. For the Pt/ECS Raman spectra, essentially no major change in the Raman spectra from the respective carbon support is observed, indicating that the platinization process did not affect the structure of the host carbons. ...
... Non-invasive measurements of inelastic light scattering give an insight into the phonon structure of graphene. The analysis of graphene G and 2D band parameters provides information about the number of graphene layers, strain, and carrier concentration [11][12][13][14][15]. Furthermore, in defected graphene, D and D' defect bands are also observed and their intensity values are related to the concentration of defects and their types [16][17][18][19][20]. Thus, careful statistical studies of Raman spectra allow to determine how the substrate impacts graphene properties and, consequently, modifies the efficiency of graphene-based structures. ...
We present detailed Raman studies of graphene deposited on gallium nitride nanowires with different variations in height. Our results indicate that different density and height of nanowires impact graphene properties such as roughness, strain, and carrier concentration as well as density and type of induced defects. Tracing the manifestation of those interactions is important for the application of novel heterostructures. A detailed analysis of Raman spectra of graphene deposited on different nanowire substrates shows that bigger differences in nanowires height increase graphene strain, while a higher number of nanowires in contact with graphene locally reduces the strain. Moreover, the value of graphene carrier concentration is found to be correlated with the density of nanowires in contact with graphene. The lowest concentration of defects is observed for graphene deposited on nanowires with the lowest density. The contact between graphene and densely arranged nanowires leads to a large density of vacancies. On the other hand, grain boundaries are the main type of defects in graphene on rarely distributed nanowires. Our results also show modification of graphene carrier concentration and strain by different types of defects present in graphene. Therefore, the nanowire substrate is promising not only for strain and carrier concentration engineering but also for defect engineering.
... The most intense-D band, which is located near 1350 cm −1 -is connected to sp 3 carbons and arises usually from the defects and disorders in the carbon lattice [25]. The G band with a maximum at ca. 1580 cm −1 corresponds to the Raman-allowed E 2g optical phonon [26] and is a typical feature of all graphitic materials. The deconvolution revealed the presence of three other signals of different symmetries. ...
Graphene oxide (GO) is one of the most exciting and widely used materials. A new method of nanographene oxide (n-GO) formation is presented. The described unique sequence of ultrasonication in dimethyl sulfoxide solution allows us to obtain different sizes of n-GO sheets by controlling the timing of the cutting and re-aggregation processes. The obtained n-GO exhibits only minor spectral changes, mainly due to the formation of S-containing surface groups; thus, it can be concluded that the material is not reduced during the process. Maintaining the initial oxygen functionalities together with the required nano-size (down to 200 nm) and high homogeneity are beneficial for extensive applications of n-GO. Moreover, we prove that the obtained material is evidently biocompatible. The calculated half-maximal effective concentration (EC50) increases by 5-fold, i.e., from 50 to 250 µg/mL, when GO is converted to n-GO. As a consequence, the new n-GO neither disturbs blood flow even in the narrowest capillaries nor triggers a toxic influence in surrounding cells. Thus, it can be a serious candidate for drugs and biomolecule carriers administered systemically.
... They combined the calculation results and found that the 1620 cm −1 band corresponded to a maximum in the vibrational density of states of graphite and attributed it to a splitting of the degenerate E 2g modes of crystalline graphite, which was certified by Vidano and Fischbach experimentally. 45 They found that the G band would become asymmetric and a shoulder at about 1620 cm −1 appeared when the glass carbon was heat-treated above 1600°C. They defined it as the D′ band as it always existed with the presence of the D band and attributed it to the defect of graphite. ...
Raman spectroscopy, as a rapid, high-precision, and nondestructive tool, can be used for analyzing the samples from gas to solid, from ex situ to in situ, from organic macromolecule to minerals. It has been demonstrated as a powerful tool for characterizing carbonaceous solid fuels and their thermal conversion products. This review provides a systematic overview of the application of Raman spectroscopy for investigating the entire thermochemical processing of coal, biomass, and wastes. After introducing the fundamentals of Raman spectroscopy, its application for characterizing the feedstock (raw coals, biomass, and wastes) is reviewed. Then, using the Raman spectroscopy for ex situ characterization of the products (char and ash) after reactions and in situ diagnostic during reactions are discussed. Besides, some potential advanced Raman spectroscopy techniques are further briefly introduced. Lastly, the challenges and prospects of using Raman spectroscopy to study thermochemical processes are discussed.
... Second-order RSs of graphene materials have a long and rich history. Initially discovered in different graphite materials in the form of doublet of bands at~2720 cm −1 (strong) and 3248 cm −1 (very weak) [63,64], designated as G (then 2D) and 2G, respectively, this region of the spectrum, demonstrating interesting properties, since that has been actively analyzed [65][66][67][68] (references are representative rather than exhaustive). Referring the reader to an excellent review of the state of art in this area [6], we will focus only on two features of the 2D band, which are important for further discussion. ...
The standard D-G-2D pattern of Raman spectra of sp2 amorphous carbons is considered from the viewpoint of graphene domains presenting their basic structure units (BSUs) in terms of molecular spectroscopy. The molecular approximation allows connecting the characteristic D-G doublet spectra image of one-phonon spectra with a considerable dispersion of the C=C bond lengths within graphene domains, governed by size, heteroatom necklace of BSUs as well as BSUs packing. The interpretation of 2D two-phonon spectra reveals a particular role of electrical anharmonicity in the spectra formation and attributes this effect to a high degree of the electron density delocalization in graphene domains. A size-stimulated transition from molecular to quasi-particle phonon consideration of Raman spectra was experimentally traced, which allowed evaluation of a free path of optical phonons in graphene crystal.
... In graphene, the G Raman mode corresponds to a one-phonon Raman process of an LO phonon from the center of the Brillouin-zone, whereas the D mode corresponds to higher-order resonant Raman processes involving a phonon close to the K or K' point of the Brillouin-zone and scattering by a structural defect. This notation is applied even in the amorphous phase as the two Raman bands observed for amorphous carbon evolve into the graphenelike signals on annealing [35,36]. The evolution of the Raman spectra with an increasing heat-treatment temperature between 1300 C and 3000 C observed from our data aligns with the literature. ...
The preparation of carbons for technical applications is typically based on a treatment of a precursor, which is transformed into the carbon phase with the desired structural properties. During such treatment the material passes through several different structural stages, for example, starting from precursor molecules via an amorphous phase into crystalline-like phases. While the structure of non-graphitic and graphitic carbon has been well studied, the transformation stages from molecular to amorphous and non-graphitic carbon are still not fully understood. Disordered carbon often contains a mixture of sp³-, sp²-and sp¹-hybridized bonds, whose analysis is difficult to interpret. We systematically address this issue by studying the transformation of purely sp³-hybridized carbons, that is, nanodiamond and adamantane, into sp²-hybridized non-graphitic and graphitic carbon. The precursor materials are thermally treated at different temperatures and the transformation stages are monitored. We employ Raman spectroscopy, WAXS and TEM to characterize the structural changes. We correlate the intensities and positions of the Raman bands with the lateral crystallite size La estimated by WAXS analysis. The behavior of the D and G Raman bands characteristic for sp²-type material formed by transforming the sp³-hybridized precursors into non-graphitic and graphitic carbon agrees well with that observed using sp²-structured precursors.
... The D band, which is located at 1330-1350 cm −1 , arises from the defects and disorders in the carbon lattice and the double resonant processes near the K point of the Brillouin Zone (BZ) boundary [28]. The G band at 1583 cm −1 corresponds to the Ramanallowed E 2g optical phonon [29]. The D'' band at 1500-1550 cm −1 , is related to the amorphous phase and its intensity is inversely related to the crystallinity [30]. ...
Reduced graphene oxide (rGO) is a graphene-like material that exhibits high productivity for a wide range of industrial applications. To promote the application of rGO, it is important to not only produce high-quality rGO but also precisely evaluate the output. The intensity ratio of the D to G band in the Raman scattering is commonly used to assess the defect density of the carbon materials; however, this ratio is limited to evaluate the reduction degree of rGO because of the ambiguity arising from the superposition of the bands. In this study, we investigate the relationship between the intensity ratio of D* to G band and the reduction of graphene oxide (GO) to evaluate the degree of reduction of rGO. The spectral analysis of GO and rGO, along with systematic research of the thermally reduced GO synthesized via thermal treatment (100–900 °C) revealed a strong linkage between the D*/G intensity ratio and the C/O atomic ratio. The atomic vibrational relationships were elucidated by the assignment of the D* band, based on the density functional perturbation theory calculations. These findings explain the atomic vibrational properties of rGO and provide an indicator of the quality of rGO to optimize its performance for applications.
... The pristine anode (Figure 10a-i) has a sharp G-band (E 2g ) only at 1580 cm À 1 , characteristic of highly ordered graphene layers. In all electrolytes (Figure 10a-ii,iii,iv), after F1, D-band (A 1g ) at 1340 cm À 1 , attributed to due to lattice defects and disordered carbon, [49][50][51] newly forms at the expense of G-band. In particular, the D-band in commercial electrolyte (Figure 10a-ii) is relatively stronger than those in other electrolytes, which is due to higher structural disorder of graphite. ...
The formation of a robust solid‐electrolyte interphase (SEI) layer at the surface of a graphite anode by electrolyte control is a key technology for high‐performance lithium‐ion batteries. Although propylene carbonate (PC) offers a lower melting point than ethylene carbonate, its combination with the graphite anode without additive is a worse choice, owing to co‐intercalation of PC and Li⁺ ion into graphite, exfoliation of graphene sheets, and death of the battery. This study reports a graphite anode with an unprecedentedly high initial coulombic efficiency of 94 %, close to theoretical capacity, and excellent capacity retention of 99 % after 100 cycles in a PC‐based electrolyte system, even at an unusually high rate of 0.2 C, which is generally attainable only at a very low rate of below 0.05 C in commercial electrolyte. The SEI stabilization for a graphite anode in PC‐based electrolyte provides a new avenue for high‐energy and high‐performance batteries in widened range of working temperatures. A strong correlation between anode‐electrolyte interfacial stabilization and highly reversible cycling performance is clearly demonstrated.
In this study, we introduce a pioneering methodology for crafting silicon oxycarbonitride materials (SiOCN) by harnessing the intricate synergy between allyl-substituted hydrido polycarbosilane (AHPCS) and a novel triazine-based dendron, serving as a nitrogen-containing polymeric precursor. The synthetic journey involves meticulous hydrosilylation reactions between AHPCS's Si–H moieties and the –CH 00000000 00000000 00000000 00000000 11111111 00000000 11111111 00000000 00000000 00000000 CH2 groups embedded within the triazine dendritic architecture, followed by controlled pyrolysis under an argon atmosphere at temperatures up to 900 °C. Through systematic variations in reaction durations and pyrolytic temperatures, we uncover the prevalence of SiC4−xOx motifs within the material matrix, with oxygen content modulation observed in samples under extended reaction times and heightened pyrolysis temperatures. Nitrogen-based bonding's paramount importance within the N-containing polymeric precursor is also established, revealing a preference for retaining N sp²–C over N sp³–C bonds due to intricate nitrogen–AHPCS interactions that yield robust Si–N linkages. This inquiry not only advances our fundamental understanding but also charts a course for tailoring silicon oxycarbonitride –SiOCN– material properties. Promisingly, these advancements position such materials as prospective candidates for high-energy silicon oxycarbonitride-based supercapacitors, bridging pioneering materials science with sustainable energy storage technology.
The demand for versatile and sustainable energy materials is on the rise, given the importance of developing novel clean technologies for transition to a net zero economy. Here, we present the synthesis, characterization, and application of lignin-derived ordered mesoporous carbons with various pore sizes (from 5 to approximately 50 nm) as anodes in sodium-ion batteries. We have varied the pore size using self-synthesized PEOn-b-PHAm block copolymers with different PEO and PHA chain lengths, applying the “soft templating” approach to introduce isolated spherical pores of 20 to 50 nm in diameters. The pore structure was evaluated by transmission electron microscopy (TEM), nitrogen physisorption, and small-angle X-ray scattering (SAXS). We report the microstructure analysis of such mesoporous lignin-based carbons using Raman spectroscopy and wide-angle X-ray scattering (WAXS). In comparison with nontemplated carbon and carbons templated employing commercial Pluronic F-127 and PIB50-b-PEO45, which created accessible channels and spherical pores up to approximately 10 nm in diameter, the carbon microstructure analysis revealed that templating with all applied polymers significantly impedes graphitization upon thermal treatment. Furthermore, the gained knowledge of similar carbon microstructures regardless of the type of template allowed the investigation of the influence of different pore morphologies in carbon applied as an anode material in sodium-ion batteries, supporting the previous theories in the literature that closed pores are beneficial for sodium storage while providing insights into the importance of pore size.
The design of a material porous microstructure with interconnected micro-meso-macropores is a key issue for the successful development of carbon-derived materials for supercapacitor applications. Another important issue is the nature of these carbon materials. For those reasons, in this study, novel hierarchical micro-meso-macroporous silicon oxycarbide-derived carbon (SiOC-DC) was obtained via chlorine etching of carbon-enriched SiOC prepared via pyrolysis (1100–1400 °C) of sol-gel triethoxysilane/dimethyldiphenysiloxane hybrids. In addition, and for the first time, non-conventional Raman parameters combined with the analysis of their microstructural characteristics were considered to establish their relationships with their electrochemical response. The sample pyrolyzed at 1100 °C showed planar and less-defective carbon domains together with the largest specific surface area (SSA) and the highest volume of micro-meso-macropores, which upgraded their electrochemical response. This sample has the highest specific capacitance (Cs = 101 Fg−1 (0.2 Ag−1)), energy (Ed = 12–7 Wh−1 kg−1), and power densities (Pd = 0.32–35 kw kg−1), showing a good capacitance retention ratio up to 98% after 10,000 charge–discharge cycles at 0.5 Ag−1. At a pyrolysis temperature ≥ 1200 °C, the carbon domains were highly ordered and tortuous with a high degree of interconnection. However, SSA and pore volumes (micro-meso-macropores) were significantly reduced and downgraded the Cs, Ed, and Pd values.
In this work, waste medical masks collected from daily life usage were pyrolyzed and catalytically decomposed with perovskite-type La0.6Ca0.4Co1–xFexO3−δ pre-catalysts for co-production of carbon nanomaterials and H2. The influences of catalysis reaction temperature and Co/Fe ratio in the investigated pre-catalysts on the yields and selectivity of the gaseous products and carbon deposition were systematically studied. The physicochemical characteristics of the produced carbon nanomaterials were comprehensively characterized by the state-of-the-art techniques. La0.6Ca0.4Co0.2Fe0.8O3–δ possessed the highest hydrogen and carbon nanomaterials yields at 850 °C among all the investigated pre-catalysts. Especially, this pre-catalyst showed an excellent performance during the 10 cycles of successive deconstruction of plastic wastes with the highest hydrogen yield of 34.33 mmol/gplastic at the 7th cycle. More importantly, carbon nanotubes generated had higher graphitic characteristics and fewer defects. The presented results demonstrated that the developed perovskite-type pre-catalyst is a promising candidate for the production of hydrogen and carbon nanotube composites for energy storge applications from medical waste plastics.
Due to the complicated nature of carbon dots (CDs), fluorescence mechanism of near-infrared (NIR) fluorescent CDs is still unrevealed and features highly controversial. Reliable and effective strategies for manipulating the NIR fluorescence of CDs are urgently needed. Herein, CDs with one-photon (622 nm, QYs ≈ 17%) and two-photon (629 nm) NIR fluorescence are prepared by acidifying o-phenylenediamine-based reaction sediments. Systematic analysis reveals that the protonation of amino groups increases the particle surface potential, disperse the bulk sediments into nano-scale CDs. In the meanwhile, amino protonation of pyridinic nitrogen (-N=) structure inserts numerous n orbital energy levels between the π → π* transition, narrows the gap distance for photon transition, and induces NIR fluorescence emission on CDs. Present research reveals an effective pathway to activate CDs reaction sediments and trigger NIR emission, thus may open a new avenue for developing CDs with ideal optical properties and promising application prospects.
Moderate-pressure microwave plasmas are used to prepare nitrogen-incorporated carbon nanowalls (CNWs) by chemical vapor deposition using acetylene and methane as precursor gases. The growth temperature range for acetylene is shown to be totally lower than that (
$>$
1000
$^{\circ}$
C) for methane, which is attributed to the difference in degree of hydrogenation of radical species in the two plasmas. The structural order and cluster size of sp
$^{2}$
carbon phase in CNWs characterized by the Raman spectroscopy increase initially and, then, decrease with temperature in each temperature range, showing the same trend as the inverse of the sheet resistance of CNWs. The results indicate that the carrier transport in CNWs depends exclusively on the microstructure of sp
$^{2}$
carbon phase, despite a large difference in the growth temperature range depending on the precursor gas.
In the last 30 to 40 years, various new types of carbon materials have been engineered for multiple industrial uses. It is now well-known that the Raman spectrum is sensitive to the structure, even though the spectrum is rather uncomplicated. Because Raman spectroscopy now has a reputation for providing good information, potential users of Raman equipment can request information on the quality of their sample. However, they are often not able to define clearly what they mean by “quality.” If they are growing diamond films, they may or may not want interstitial sp2 carbon to glue polycrystalline diamond together. If they are growing hard diamond-like carbon (DLC) films, they may want to correlate the spectral characteristics with physical characteristics of the film. In this column, I explain how the Raman characteristics can aid in characterization of carbon materials.
A kinetic study of graphene oxide (GO) synthesis using electrochemical exfoliation of graphite in the acidic and alkaline electrolyte has been carried out. The effects of temperature (301-333K), sulfuric acid concentration (0.3-0.6M), pH (0.3-11.2), current density (12-40 mA/cm²), and graphite density (1.72-1.92 g/cc) on the rate of GO formation have been examined. The GO exfoliation rate was found to be unaffected by graphite density; therefore, all the kinetic was studied with the graphite density of 1.82 g/cc. The GO exfoliation rate increased with a sulfuric acid concentration in the electrolyte. The temperature was seen to enhance the rate of GO synthesis. The activation energy of GO exfoliation was found to be 33.53 kJ/mol in a temperature range of 301-333K. Based on the findings the mechanism was proposed and the rate law was deduced. . The surface reaction of anions during intercalation and de-intercalation in the interstices of graphite has been found to be the rate-controlling step. Synthesized GO was characterized with transmission electron microscopy (TEM), Raman spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The kinetic model has been developed to fit the GO exfoliation rate within a pH range of 0.3-1.1.
In this paper, the waste mercuric chloride catalysts (WMCC) were successfully recycled and then modified by ferrum (Fe) loading. Various analysis techniques were used to study the reaction mechanism of Fe loading modified regenrated activated carbon (RAC). Results show that the absorbed organic matter is the main reason causing the WMCC inactivation and it will thoroughly decompose beyond 334 °C. With assistance of microwave energy, the WMCC can be activated by roasting at 500 °C for 30 mins. At this moment, the base material of the RAC still maintained the graphite structure. The experimental results of the adsorption performance of Fe-loaded RAC that prepared from different Fe loading additions on arsenic (As) in arsenic-containing wastewater show that: the Fe-loaded RAC with Fe loading addition of 12.51 wt% has a maximum As (V) removal efficiency of 86.76%. The main phase composition of the Fe-loaded RAC is Fe2O3 and Fe3O4, and its defect density is the largest, which is considered to be the main reason for the effective adsorption of As (V).
Thermally altered coals affect the safety and efficiency of coal mining and utilization, but most studies of thermally altered coal have only focused on the whole coal instead of on different macerals. Thermally altered coals have complex and special maceral components; not only intrinsic macerals but also newly formed macerals such as pyrolytic carbon can be observed. The shape and texture of intrinsic macerals also change significantly after thermal alteration, especially for vitrinite. Therefore, employing an in situ testing method to study the macerals in thermally altered coals is necessary. Herein, a confocal Raman imaging microscope was used. Results show that macerals become coked in samples adjacent to the sill, and circular mosaic texture is the most common texture observed in this series of samples. In samples away from the sill, inertinite is isotropic, while in samples closest to the sill, anisotropic inertinite can be found. The Raman spectra of inertinite and vitrinite (mosaic texture) are significantly different. For vitrinite, the D and G peaks are closer, and the height of D is lower than for inertinite. The Raman spectra of thermally altered coal include 13 bands after curve fitting. Curved-fitted results show that for vitrinite, polycondensation provides the nucleation of mesophase spheres, and newly formed aromatics take part in the growth of mesophase spheres. However, for inertinite, excessive amorphous carbon and substituents, such as aromatic alkyl and aryl–alkyl ether, form cross-linked structures and hinder the anisotropic development of inertinite.
CrMoV steel was exposed to 500, 550, and 600 °C for up to 120 h in 0.1 and 10 MPa CO2. A significant change in carbon deposition content was not observed in the 0.1 MPa CO2, in contrast to the high carbon content at 550 °C and 10 MPa CO2. The formation of internal Fe-rich M3C carbides and super saturation of steel grains with dissolves carbon at 550 °C but not at 500 and 600 °C may be responsible for this difference. The effect of carbon deposition on the outward Fe diffusion via vacancy or interstitial sites was also discussed.
Cheap, abundant and easily-obtained carbon fillers such as graphite (GR), carbon black (CB), lamp black and active carbon were successfully incorporated into a silicon oxycarbide (SiOC) matrix using attrition milling followed by spark plasma sintering to obtain dense crack-free bulk composites. Carbon-enriched SiOC composites (C-SiOC) showed enhanced electrical (σ) and thermal (k) conductivities. Values as high as 667 Sm⁻¹ for σ and an increase of 63% for k compared with SiOCs were obtained when GR flakes were incorporated into the SiOC. Very interesting values were also achieved (250 Sm⁻¹ and a 46% increase) when CB was used, due to the formation of a percolating network of highly-interconnected tortuous graphene-like carbon domains which promoted phonon/electron transport.
Raman parameters such as the tortuosity index, 3D ordering of graphene layers and the I2D/IG ratio, in conjunction with AB stacking, were crucial for understanding the electronic and/or phonon transport.
The Raman spectra of graphene‐based matter exhibit a set of defect/disorder‐induced bands. The D band, which exhibits a strong dispersion up to ~50 cm−1/eV, comes from transverse optical phonons around K or K′ in the first Brillouin zone and involves an intervalley double resonance (DR) Raman process. In the present work, resonant Raman scattering (lines ranging from 1.58 to 3.81 eV) is used to study the unusual behavior of the one‐phonon Raman band of a carbonaceous material (anthracene‐based carbon which is one of the graphitizable carbons) upon its secondary carbonization stage (450°C–1000°C). While the G band appears to be nondispersive, the D band exhibits a change in both position and intensity. Its dispersion progressively rises from ~6 cm−1/eV to values close to what is usually observed in defected graphene‐based systems when anthracene‐based carbon becomes almost pure. This evolution appears to be correlated with a release of hydrogen (fixed on the edges of polyaromatic layers) questioning their role in changing the D band resonance conditions.
The oxidation behavior of CrMoV steel in 0.1, 5, and 10 MPa CO2 was studied at 550 °C for 500 h. Reaction rates decreased from 0.1 to 5 MPa, and breakaway occurred sooner with increasing pressure. Amorphous carbon was identified within the inner layer in all CO2 pressure values, while graphite was mainly detected under 5 and 10 MPa. Carbon deposition may link to the formation of Fe- and (Fe, Ni)-rich M3C carbides at the oxide/steel interface, which catalyzed the Boudouard reaction. A high external CO2 pressure and the oxidation of Cr-rich carbides within the steel may favor carbon depositions.
The last decade has witnessed an explostion of technological applications driven by the development of fabrication methods and the discovery of several new classes of pure carbon. Structural diversity exhibited by the carbon atoms is key to understanding their physical and chemical properties and in furture material developement. This feature summarizes the use of Raman spectroscopy as a principal tool to investigate the vibrational dynamics of carbon materials and to provide indirect structural characterization of their short-, medium-, and long-range order.
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Structural changes in Ceylon natural graphite with grinding were studied by Raman spectroscopy along with X-ray diffraction. The natural graphite shows a single Raman band at 1580 cm−1, but the ground graphite samples exhibit two Raman bands at 1360 and 1620 cm−1 in addition to the 1580 cm−1 graphite band. The 1360 cm−1 band increases in intensity with increasing grinding time, and becomes much stronger than the 1580 cm−1 band after 200-hr grinding. Raman results are compared with structural parameters such as effective Debye parameter and C0 spacing obtained from X-ray diffraction measurements, and discussed in terms of structural defects introduced into the crystal lattice of natural graphite. A linear relationship was obtained for the ground graphite when the relative intensity of the 1360 cm−1 band is plotted as a function of effective Debye parameter. The slope of the linear plot is different for the ground graphite from that for the graphitized cokes, indicating a difference in the type of structural defects involved.
CALCIUM fluoride occurs in Nature as the crystal form known as fluorite. It can, however, be grown artificially as single crystals, and when doped with suitable impurities it is widely used as a laser material1,2. For this purpose, calcium fluoride is usually doped with rare-earth impurities or uranium and grown by either the Czochralski3 or Stockbarger4 techniques. The Czochralski technique is inherently a high temperature-gradient method of growth, in which the crystal is pulled directly from the melt, whereas the Stockbarger process, in which the molten material is crystallized inside a crucible in a controlled manner, involves much lower temperature gradients. During etching investigations on crystals grown by these techniques, it was noticed that certain similarities and differences existed in the dislocation arrangements induced by the method of growth, and that some of these could be modified by subsequent annealing. These features are described and compared with the dislocation arrays observed in crystals of other materials grown using the Czochralski technique.
The crystal perfection of O° Czochralski grown sapphire was examined by a PbOPbF2 etchant and quantitative x-ray measurements. The (0001) planes from different sections of a large boule contained a minimum etch pit density of 104/cm2 and a maximum of 105/cm2. The misorientations in (1120) planes by Laue case diffraction were 0.2–3 min. For (00.12) planes by Bragg case diffraction, the maximum mis-orientation is 0.5 min. These data are 10 − 100 times lower than reported results on Verneuil grown material.
Raman spectra are reported from single crystals of graphite and other graphite materials. Single crystals of graphite show one single line at 1575 cm−1. For the other materials like stress‐annealed pyrolitic graphite, commercial graphites, activated charcoal, lampblack, and vitreous carbon another line is detected at 1355 cm−1. The Raman intensity of this band is inversely proportional to the crystallite size and is caused by a breakdown of the k‐selection rule. The intensity of this band allows an estimate of the crystallite size in the surface layer of any carbon sample. Two in‐plane force constants are calculated from the frequencies.
The stress-strain curves and the defect structure of corundum single crystals (sapphire and ruby) were studied. The influence of impurity (Cr) presence, crystallographic orientation, temperature, and deformation rate was investigated. Chromium makes corundum harder and causes a yield point phenomenon. The yield point was also increased by the transition from 60° to 90° orientation of the specimens, by lowering the temperature, and by an increase in the deformation rate. In 60°-specimens the deformation occurs by means of gliding on basal planes in 〈1120〉 and 〈1010〉 directions. In 90°-samples beside this one gliding in (1010), (1011), (2021) and (2243) is found.[Russian Text Ignored.]
Chemical polishing and etching techniques were used to reveal the dislocation structures of sapphire and ruby crystals grown by the flame-fusion and flux techniques. The average density of edge dislocations lying in prism planes was 3.0 × 105 per cm2, which could be changed only slightly by chromium additions and annealing at 2000°C. An average basal dislocation density of 2 × 105 per cm2 decreased 35 to 80% on annealing. Crystal orientation (i.e., angle between the c axis and the growth axis) showed no effect on dislocation density but a pronounced effect on subboundary arrangement and density. The substructure of 0° crystals was more complex than that of 90° crystals; 60° crystals possessed a structure intermediate between 0° and 90°. Principal observations included (1) prismatic and basal slip on all as-grown crystals; (2) profuse basal slip, readily polygonized on annealing; (3) dislocation densities of flux crystals lower than those of Verneuil crystals; and (4) a rare form of basal twinning, composition plane , on all flux crystals.
Single crystals of ruby (Al2O3: 0.05 wt% Cr) were grown by the Czochralski method as 60° type rods. Crystal slices were taken at 30°, 60°, and 90° to the boule axis. Dislocations were observed by Lang X-ray transmission topographs. All sections revealed a relatively defective central region with a dislocation density of about 104/cm2. Examples were found of polygenization and small-angle boundaries emanating from the center. Areas near the circumference of the boule had easily resolved dislocation lines and densities as low as 102/cm2. These regions also showed a Frank-type network with node formation. On all slices distinct parallel groups of dislocation lines were observed. Burgers vector, b, for these dislocations was examined by contrast methods involving alternate orientations of the diffraction vector, g. Burgers vector lay along . A simple model of basal slip of the type (0001) was used to explain these dislocations.
Sapphire single crystals exhibit the same qualitative creep properties over the temperature range 900° to 1400°C. as do comparable metal single crystals at room temperature. The creep of sapphire under constant load has four portions: (a) a period of increasing creep rate, (b) a period of decreasing creep rate, (c) a period of constant creep rate, and (d) a final period of increasing creep rate. The stress required to initiate creep falls smoothly from about 780 kg. per sq. cm. at 900°C. to about 130 kg. per sq. cm. at 1400°C. After creep is initiated, it will continue at a lower stress (the addition of chromia increases the stress required to initiate creep). The electrical resistivity of sapphire is apparently increased by plastic deformation and decreased by subsequent heating near 1800°C. Slip lines in periclase and rutile were studied and slip systems were identified.
Two techniques are described by which single crystals of sapphire may be grown. One is a development of the vertical-pulling technique for the production of scatter-free, lowdislocation-density material, whilst the other is an extension of a floating-zone, recrystallisation technique previously used for calcium tungstate. The origin and control of defects in crystals grown by these techniques are discussed.
Raman spectroscopy is used to characterize the fiber surface of graphite and carbon fibers. A correlation exists between the Raman spectrum of the fiber surface and the shear strength of the composite. Effects of surface treatments are reflected in the Raman spectrum as well as the shear strength of the composite. Many graphite fibers have a weak surface layer where the graphite planes are oriented paallel to the surface.
Zinc tungstate crystals were grown by the Czochralski method and the effect of growth parameters on crystal perfection was studied. Of the (010) and (100) slip planes, Berg-Barrett photographs showed that the (100) slip plane appeared to be the most active during crystal growth. Observations made on crystals grown in a steep temperature gradient showed that strain due to thermal gradients was responsible for the high dislocation densities in these crystals.
Studies on seeding showed that if no widening occurred, then the perfection of the region of the crystal after seeding was much higher than the seed; the changes in temperature employed to widen the crystal gave rise to very high dislocation densities. X-ray examination verified the observations made by chemical etching. Crystals grown under nearly isothermal temperature conditions provided material with dislocation densities between 0 and 500/cm2. These crystals propagated with facets at the solid-liquid interface which gave rise to impurity distributions similar to those observed in semiconductor crystals. The conditions for growing low-dislocation-density Czochralski crystals of zinc tungstate are similar to those for growing low-dislocation-density semiconductor crystals.
The Raman spectrum of glassy carbon has been measured. Two broad lines are observed at 1340 and 1590 cm<sup>-1</sup>. These results are consistent with the turbostratic structure, which has been suggested for glassy carbon, with a particle size L a of approximately 30 Å.
Laser Raman spectra were studied of natural graphite (SP-1) and carbonaceous materials including pyrolytic graphite, carbon black, glassy carbon, coal, “white” carbon and sputtered carbon. All of these carbons have two Raman bands at 1580 cm−1 and 1360 cm−1, except for natural graphite which has a single sharp Raman band at 1580 cm−1. The relative intensity of the 1360 cm−1 band to the 1580 cm−1 band and the half band width increase going from graphite through glassy carbon to carbon black. The 1360 cm−1 band in glassy carbon becomes sharper and stronger with the increase of heat-treatment temperature (HTT), while the addition of iron to the glassy carbon matrices results in a decrease in intensity and half band width of this band with increasing HTT and iron content. Sputtered carbon and “white” carbon, prepared from graphite irradiated by a high power laser, showed an additional broad band around 2140cm−1. This band is believed to originate from conjugated acetylenic bands (—CC—)n.
Surface Distributions of Dislocations in Metals RamanSuectrumofGraohite
- Ibf C Frank
IBF. C. Frank, Carnegie InstituteofTechnology SymposiumonthePlastic Deforma-tion of Crystalline Solids (Pittsburgh Report, 1950); pp. 150-51. Office of Naval Research Rept. No. NAVEXOS-P-834. lS C. J. Ball and P. B. Hirsch, " Surface Distributions of Dislocations in Metals, " Philos. Mag., 46 [12] 1343-52 (1955). 2o S. Amelinckx and W. Dekeyser; pp. 325-84 in Solid State Physics, Val. 8. Edited by Frederick Seitz and David Turnbull. Academic Press, New York, 1959. 21 J. P. Hinh and J. Lothe, TheoryofDislocations; pp. 637-78. McGraw-Hill, New York, 1968. References F. Tuinstra and J. L. Koenie. " RamanSuectrumofGraohite. " J. Chem. Phvs.. 53 1 (31 1126-30 (1970).
Formation of Bubbles in Crystals of Corundum Grown from the Melt
- M I Musatov
M. I. Musatov, " Formation of Bubbles in Crystals of Corundum Grown from the Melt, " Sov. J. Opt. Technol., 41 [4] 217-19 (1974).
Growth Faulting and Reorientation of Czochralski-Grown Sapphire Single Crystals " ; presented at the 3rd American Association for Crystal Growth Conference at Stanford, Calif Growth Defects in Calcium Tungstate Single Crystals
- H Strock
- P Kotval
H. Strock and P. Kotval, " Growth Faulting and Reorientation of Czochralski-Grown Sapphire Single Crystals " ; presented at the 3rd American Association for Crystal Growth Conference at Stanford, Calif., July 1975. B. Cockayne, D. S. Robertson, and W. Bardsle, " Growth Defects in Calcium Tungstate Single Crystals, " Br. J. Appl. Phys., 15 [lo] 1165-69 (1964).
Some Consideration on the Fields of Stress Connected with DislocationsinaRegularLattice Kro:xrg, " Plastic Deformation of Single Crystals of Sapphire: Basal Slip and Twinning, Acfa Mefall
- M Burgers
M. Burgers, " Some Consideration on the Fields of Stress Connected with DislocationsinaRegularLattice, " Proc. K. Ned. Akod. Wef., 42 [4]293-325 (1939). a M. L. Kro:xrg, " Plastic Deformation of Single Crystals of Sapphire: Basal Slip and Twinning, Acfa Mefall., 5 [9] 507-24 (1957).
Dislocations in Ruby Laser Crystals Dislocation Reactions and Cavitation Studies in Melt-Grown Sapphire
- K R Janowski
- H Conrad
I I K. R. Janowski and H. Conrad, " Dislocations in Ruby Laser Crystals, " Trans. AIME, 230 [6] 717-25 (1964). l2 C. A. May and J. S. Shah, " Dislocation Reactions and Cavitation Studies in Melt-Grown Sapphire, " J. Mater. Sci., 4 [2] 179-87 (1%9).
Surface Structure in Corundum: I, " ibid
- R Scheuplein
- P Gibbs
R. Scheuplein and P. Gibbs, " Surface Structure in Corundum: I, " ibid., 43 [9] 458-72 (1960).
Laser Raman Spectral Investigation of Coals
- R A Friedel
- G L Carlson
' R. A. Friedel and G. L. Carlson, " Laser Raman Spectral Investigation of Coals, " Chem. Ind. (London). 40 1101 1128-29 11971).
Microfilms (Ann Arbor, Mich.) Order No. 74-29,371
- Univ
Univ. Microfilms (Ann Arbor, Mich.) Order No. 74-29,371; Diss. Abstr. Int. B, 35
127-29 in Carbon '72 (%prints or the 1st International Carbon Conference
- R L Beatty
- B Fischbach
(a) R. L. Beatty and B. Fischbach; pp. 127-29 in Carbon '72 (%prints or the
1st International Carbon Conference held June 25-30, 1972, in Baden-Badin).
- Raman Spectroscopy
Raman Spectroscopy," J. Compos. Mater., 4 [lo] 492-99 (1970).
M. Nakamizo; private communicationRaman Spectrum of Ground Natural Graphite
- M Nakamizo
- M Inagaki
- H Kakiyama
- H Honda
171 3299-3300 (1975); also Tech. Rept. ORNL-TM 4504, Aug. 1975.
" M. Nakamizo; private communication.
'' M. Nakamizo, M. Inagaki, H. Kakiyama, and H. Honda, "Raman Spectrum of
Ground Natural Graphite," Bienn. Conf. Carbon. Ext. Abstr. Program, 13th 1977
pp. 269-70.
Long Wavelength Optical Vibration Modes of Graphite
Long Wavelength Optical Vibration Modes of Graphite," J. Phys. Chem. Solids
Suppl., 32 187-93 (1971).
- T G Miller
- D B Fischbach
- J M Macklin
J. t p p l. Phys., 45 [5] 2370 (1974).
(a) T. G. Miller, D. B. Fischbach, and J. M. Macklin, "Struchwal Characterization of Carbon Materials by Laser Raman Spectroscopy," Bienn. Con$ Carbon. Ext.
Laser Raman Spectral Investigation of Coals
- Friedeland R. A.
72 (Preprints or the 1st International Carbon Conference
- R L B Beattyandd
- Fischbach