Perspectives On Carbon Nanotubes And Graphene Raman Spectroscopy Pdf

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Updated to include expanded coverage of the preparation, purification, structural characterization, and common application areas of single- and multi-walled CNT structures, this work compares, contrasts, and, where appropriate, unitizes CNT to graphene.

Characterization techniques for graphene-based materials in catalysis

Carbon nanotubes CNTs possess remarkable nonlinear optical properties; a particular application is to function as a mode locker used in ultrafast fiber lasers to produce ultrashort optical pulses.

In this review, typical fabrication process and development of CNT SAs are discussed and we highlight the recent investigation and progress of state-of-the-art ultrafast fiber lasers covering GHz, bidirectional ultrafast fiber lasers, vectorial mode fiber lasers, comb systems, and mode-locking dynamics.

In the past few decades, ultrafast fiber lasers have gained enormous attention and found applications covering broad fields from fundamental research to industrial process, based on their salient advantages, including maintenance-free operation, compactness, cost-effective design, high beam quality, high-efficient heat dissipation and rather low price [ 1 ], [ 2 ], [ 3 ].

The diversity of rare-earth-doped fiber gain medium is identified as a key element in the fiber resonator cavity and essential to produce various operation wavelengths ranging from near infrared to mid infrared [ 4 ], [ 5 ], [ 6 ], [ 7 ]. Typically, commercial ultrafast fiber laser systems dominate in 1.

Other wavelengths that are sensitive to different molecules may have potential in establishment of precise monitoring systems [ 8 ]. Ultrashort pulses are generally produced by inserting a nonlinear optical element into a resonator cavity as an intensity discriminator, which is called a saturable absorber SA.

The basic function of SA is to suppress low incident intensity beam while support higher intensity spikes and the working mechanism has been revealed in other Ref [ 10 ]. CNTs possess multiple excellent properties and advantages that are well fitted with the requirements of a good SA.

The recovery time was measured to be composed with a fast intraband carrier relaxation time of 0. Mature growth process greatly reduces the price of raw materials and meanwhile research cost. More importantly, the development of CNT SAs over the past 15 years clear the path to all-fiber integration configuration, and extensive studies have verified its broad operation wavelength range which is an intrinsic drawback of commercial SESAMs.

CNT SAs have subsequently been rapidly adopted by many research groups and until now. The development of CNT SAs based on fiber laser may be summarized as: 1 The initial demonstration of CNT SAs for different gain medium, operation wavelength, operation states Q -switching, mode locking to ensure the feasibility; 2 In view of the superior properties as an SA, effective modification of cavity design gains more interests including wavelength-tuning, wavelength-switching, multiwavelength, pulse-shaping regime switching, etc.

These phenomena assure the stability and compatibility of CNT SAs; 3 The recent cases pay more attention to advanced applications and research platforms as physical mechanism. There are some review articles focusing on the nonlinear optical properties and the success as SAs for ultrafast laser pulses [ 10 ], [ 49 ], [ 50 ], [ 51 ].

Compared with commercial fiber lasers, the biggest challenges of CNT mode-locked fiber lasers met mainly come from energy and stability. Broad operational wavelength range has been confirmed previously. The intrinsic high-power handing of CNT ensures the possibilities to generate high-energy pulses and mature chirped pulses amplification technique is able to produce commercial-grade energy pulses.

This study will emphasize more on the state-of-the-art ultrafast fiber lasers based on CNT mode locker, including the fabrication and characteristics of a CNT SA, especially detailed dispersion theory, Raman mapping results and uniformity, stability discussion.

Besides, recent progress and applications of CNT-based ultrafast fiber laser is highlighted, involving GHz fiber lasers, comb systems, vectorial mode fiber lasers, bidirectional mode-locked fiber lasers and mode-locking dynamics of fiber lasers.

Finally, conclusions and perspectives are given. The high temperature of anode sublimates carbon and evaporates it; besides, the high energy accompanied with the medium leads to disruption of carbon vapors and carbon ions formation. The carbon vapors are then directed toward the cold collector as the gas flows.

In CVD, the synthesis of CNTs is processed by decomposition of hydrocarbon vapor over the catalyst particle or without a catalyst. When the CNT precursor is vapored and the vapor is contacted with heated metal catalyst, it is first decomposed into carbon and hydrogen.

Hydrogen leaves with the passing carrier gas or reducing gas, whereas the carbon dissolves in the metal catalyst. When the temperature reaches the carbon solubility limit of the metal, the decomposed carbon particles precipitate and crystallize to form CNTs. Based on different interactions between the catalyst and the substrate, such growth mechanism can be concluded as two parts: tip growth and root growth.

Besides, its derivatives can be widely used to grow vertically aligned CNTs and allows more chirality controlling. The iron particles are decomposed from the catalyst precursor and act as growth nucleation site, where CNTs are grown around the catalyst cluster. Another attractive alternative to the CVD processes is the catalytic decomposition of a carbon-containing molecule on substrate-supported catalyst particles Co and Mo.

This process involves the detailed characterization of the different phases in the catalyst preparation stage to ensure selective production of CNTs. These growth processes have been reviewed elsewhere [ 52 ], [ 53 ], [ 54 ], [ 55 ], [ 56 ], [ 57 ], [ 58 ] and the results turn to be that HiPco and CoMoCAT methods are more favorable due to mass production, high purity, and small diameter distribution.

CNTs as good SAs have been widely demonstrated in various types of ultrafast fiber laser systems. The principle of how to choose a suitable CNT as a desirable SA for the desired laser performance is still under investigation. An SWNT consists of a single graphene layer rolled into a seamless cylinder, whereas DWNTs and MWNTs are composed of two and more concentric cylindrical graphene shells coaxially arrayed around a central hollow core and separated with van der Waals forces between adjacent layers.

Such structures complicate the nonlinear optical properties of SAs meanwhile extremely hard to control during fabrication. In this review article, we will focus on SWNTs as SAs, including selection, dispersion, characterizations and applications in ultrafast fiber lasers.

As described previously, many methods have been applied to produce SWNTs, but there are still considerable impurities involved in the final products. This may influence the optical properties and increase the scattering loss, meanwhile weaken the SA effect. Owing to the typical semiconductor characteristic, optical absorption at a given wavelength produces electron—hole pairs. A higher incident power will lead to conduction band filling or valence band depleting, as well as photobleaching, due to Pauli blocking principle [ 66 ].

This is also called absorption saturation. Moreover, the absorbed wavelength corresponding to the band gap energy usually decides the final operation wavelength. In addition, armchair nanotubes packed in bundles have large pseudogaps [ 69 ]. The m -SWNTs are responsible for the optical absorption mainly in the visible spectral range labeled as M 11 , but the optical absorption with energy lower than the van Hove singularities is also possible due to the excitation effects [ 70 ] and hot Dirac fermions [ 71 ].

Extremely strict growth environment or complicated follow-up treatment [ 75 ], [ 76 ], [ 77 ], [ 78 ], [ 79 ], [ 80 ], [ 81 ], [ 82 ], [ 83 ] makes the cost ultrahigh 75 times or higher than the original SWNTs powder, such conditions somehow limit its applications. Practically, the choice of a mixture is favorable. Apart from purity and chirality selection of SWNTs, diameter distribution is also an important factor affecting the laser performance and operation condition.

First, saturable absorption at a specific wavelength depends on the tube diameter and keeps proportional relationship. For instance, the SWNTs with a diameter range of 0. It is essential to match absorption spectra with the operation wavelength. SWNTs acting as an SA can also be realized at other wavelengths away from the peak resonance where they have appreciable optical absorption. Narrow diameter distribution and sharp absorption peak may enhance nonlinear optical properties and decrease the saturated light intensity or the threshold of mode locking.

However, such excellent performances are restricted by the fact that pristine SWNTs have the tendency to spontaneously agglomerate into large bundles or ropes in the form of an entangled state. Moreover, SWNTs are considered insoluble in all known solvent. These will weaken electrical, optical, thermal, mechanical properties, so the preparation of effective dispersion of SWNTs in different solvent and polymer matrix presents a major premise to extension and utilization of SWNTs in ultrafast fiber laser systems.

Dispersion of SWNTs in different solvent medium features various methods, from physical treatment to surface modification. There are already several reviews describing this [ 88 ], [ 89 ], [ 90 ], [ 91 ], [ 92 ], [ 93 ], [ 94 ]; here, we will pay attention to some typical approaches utilized to fabricate CNT SAs.

Ultrasonication is often used to disperse SWNTs in aqueous solution and has been proved to be the most promising and effective technique to obtain good dispersion. Large SWNT bundles in the solvent are separated by the energy transferred from ultrasound wave through the medium.

The provided sonication energy is important for the final quality of the dispersed samples; therefore, the sonication energy applied should be able to overcome the binding energy of CNT aggregates but less than the amount required to fracture a tube to maintain the morphology of individual SWNT [ 91 ].

Hence, research reveals that the optimal sonication energy depends on the tube diameter rather than the amount of SWNTs or surfactant, surface functional groups and SWNT length [ 95 ]. Nowadays, the most effective ultrasonication type is based on ultrasonication probe tip.

The operation mechanism can be expressed as following: the probe will shock at a certain frequency meanwhile forming a conical field in the solvent. This is responsible for the nucleation and collapse of bubbles. Shear force is created by such process and dominates the separation of SWNT bundles. The wand tip vibrations along with the rapid generation and collapse of bubbles will introduce a flow recirculating between the probe and the forming conical field to enhance the dispersion effect [ 90 ], [ 96 ].

Several factors can affect the area of conical zone and local velocity field, including boiling point, relative viscosity of solvent, sonication energy, structure of cell and location of probe.

To be summarized, lower boiling point, lower viscosity, higher sonication energy and specific cell can improve the circulation efficiency and the rate at which bubbles are generated and collapsed, further promote dispersion quality. The result of the probe-like ultrasonication configuration is that substantial heat can be generated rapidly; thus for some volatile solvent, such as ethanol and acetone, fast evaporation will weaken the dispersing ability; besides, the increased temperature will enhance the Brownian motion giving large collision probability of separated SWNTs to form bundles again.

Hence, the samples normally require external temperature control. Moreover, the sonication process must be operated in short intervals. The entire dispersion process of SWNTs in aqueous solutions majorly contains two parts, dispersion and stabilization. Simple ultrasonication process will offer shear force to obtain effect of disperse.

However, the van der Waals attractions between tubes do exist and will lead to re-aggregation. Hence, in the real process of making SWNT SAs, the combination of ultrasonication and noncovalent surface modification is always applied.

In accordance with different polymer matrix, dispersion medium can be classified as aqueous solution and organic solvents. In aqueous solution, surfactants are widely utilized as dispersant to separate SWNTs and they are demonstrated to be one of the simple and most effective ways to nondestructively enhance the dispersibility. The most significant reason of surfactants with such function is an amphiphilic molecule structure, which possesses a hydrophobic head group attached to the side walls of tube and a hydrophilic tail interacted with the polar solvent [ 97 ], [ 98 ].

The ionic surfactants are more favorable and effective in aqueous solvent, whereas nonionic surfactants are more suitable for organic solvent. The use of surfactants is usually combined with ultrasonic treatment and it is revealed that shear forces applied on CNTs play a more critical role than the surfactant.

Dispersion of CNTs with surfactants. However, on removal of the high shear force, the van der Waals between individual CNTs would assemble themselves to a new equilibrium state of low energy, through reaggregation process. The stability is preserved by electrostatic or steric repulsion [ 91 ]. In addition, the high curvature of the small tubular geometry makes the surface increasingly electrophilic, and an external dispersant is necessary to incorporate into the medium for dispersing SWNTs.

In all solvents described previously, NMP is experimentally proved to be unique. The van der Waals attraction between nanotubes in close state is still strongly attracted. Therefore, a stable solution can only be achieved in low-concentration dispersion to increase the interaction distance, and these limitations may influence desired performance for SA application, that is, modulation depth.

Polyvinylpyrrolidone has been verified to perform as perfect assistance to increase loading and stability of SWNTs in NMP [ ], [ ], [ ]. Various methods have been used to characterize the dispersion effect and nonlinear optical properties of SWNTs.

For example, UV—Vis-IR optical absorption spectroscopy is a powerful tool to determine the structure of CNTs and study the influence of ultrasonication process. Power-dependent characterization can be implemented by Z -scan open and closed aperture which can be applied to measure the nonlinear optical characteristics saturable absorption and optical limiting.

Photoluminescence spectroscopy can be used to identify different species of SWNTs in the sample and is also widely used to monitor the quality of dispersion, SWNTs bundling and enrichment of specific chirality. Pump probe spectroscopy is commonly utilized to measure the recovery time as well as excitation relaxation time.

Detailed description about these techniques has been reviewed elsewhere [ 68 ], [ 77 ], [ 78 ], [ ], [ ], [ ], [ ], [ ], [ ], [ ], [ ], [ ], [ ], [ ], [ ], [ ], [ ], [ ], [ ], [ ], [ ], [ ], [ ]. The fitted curve can be expressed as. Power-dependent transmission measurement.

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Surface Functionalization of Carbon Nanotubes for Energy Applications

Raman spectroscopy has been already established as a powerful tool for characterizing the different types of carbon nanostructures , ranging from the highly ordered two-dimensional graphene and one-dimensional nanotubes , down to disordered materials, like nanographite and charcoal. Here we focus on the recent advances of Raman spectroscopy within carbon nanoscience. We discuss in situ nano-manipulation and Raman imaging for addressing controlled perturbations; multi-technique work for the development of nanometrology; crossing the diffraction limit with near-field optics for high resolution imaging. Finally, the applications of Raman spectroscopy in cross-referenced fields, like biotechnology and soil science, are discussed. If you are not the author of this article and you wish to reproduce material from it in a third party non-RSC publication you must formally request permission using Copyright Clearance Center.

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Lattice vibrations and Raman scattering in two-dimensional layered materials beyond graphene

Characterization techniques for graphene-based materials in catalysis[J].

Carbon Nanotubes and Graphene

We review lattice vibrational modes in atomically thin two-dimensional 2D layered materials, focusing on 2D materials beyond graphene, such as group VI transition metal dichalcogenides, topological insulator bismuth chalcogenides, and black phosphorus. Although the composition and structure of those materials are remarkably different, they share a common and important feature, i. Black phosphorus , including crystalline structures and stacking order. We then review the studies on vibrational modes of layered materials and nanostructures probed by the powerful yet nondestructive Raman spectroscopy technique. Based on studies conducted before , recent investigations using more advanced techniques have pushed the studies of phonon modes in 2D layered materials to the atomically thin regime, down to monolayers.

Carbon nanotubes CNTs possess remarkable nonlinear optical properties; a particular application is to function as a mode locker used in ultrafast fiber lasers to produce ultrashort optical pulses. In this review, typical fabrication process and development of CNT SAs are discussed and we highlight the recent investigation and progress of state-of-the-art ultrafast fiber lasers covering GHz, bidirectional ultrafast fiber lasers, vectorial mode fiber lasers, comb systems, and mode-locking dynamics. In the past few decades, ultrafast fiber lasers have gained enormous attention and found applications covering broad fields from fundamental research to industrial process, based on their salient advantages, including maintenance-free operation, compactness, cost-effective design, high beam quality, high-efficient heat dissipation and rather low price [ 1 ], [ 2 ], [ 3 ]. The diversity of rare-earth-doped fiber gain medium is identified as a key element in the fiber resonator cavity and essential to produce various operation wavelengths ranging from near infrared to mid infrared [ 4 ], [ 5 ], [ 6 ], [ 7 ]. Typically, commercial ultrafast fiber laser systems dominate in 1. Other wavelengths that are sensitive to different molecules may have potential in establishment of precise monitoring systems [ 8 ]. Ultrashort pulses are generally produced by inserting a nonlinear optical element into a resonator cavity as an intensity discriminator, which is called a saturable absorber SA.

Carbon nanotubes CNTs are receiving a great deal of attention as a catalyst support for different energy applications, due to their high surface area and high conductivity. Recent literature studies have shown that the application of CNTs mainly depends on their surface functionalization process. Typically, pristine CNTs as produced have no functional groups, which is usually considered as an obstacle to their widespread application. In this chapter, we highlight the different techniques used to functionalize the surface of CNTs, including physical and chemical functionalization processes. We show the advantages and the drawbacks of the different functionalization processes.

Description

Бринкерхофф кивнул и двинулся следом за Мидж. Фонтейн вздохнул и обхватил голову руками. Взгляд его черных глаз стал тяжелым и неподвижным. Возвращение домой оказалось долгим и слишком утомительным. Последний месяц был для Лиланда Фонтейна временем больших ожиданий: в агентстве происходило нечто такое, что могло изменить ход истории, и, как это ни странно директор Фонтейн узнал об этом лишь случайно. Три месяца назад до Фонтейна дошли слухи о том, что от Стратмора уходит жена. Он узнал также и о том, что его заместитель просиживает на службе до глубокой ночи и может не выдержать такого напряжения.

Perspectives on carbon nanotubes and graphene Raman spectroscopy.

О принципе Бергофского Сьюзан узнала еще в самом начале своей карьеры. Это был краеугольный камень метода грубой силы. Именно этим принципом вдохновлялся Стратмор, приступая к созданию ТРАНСТЕКСТА.

 - Она выдержала паузу.  - Постараюсь побыстрее. - А лучше еще быстрее.  - Стратмор положил трубку.

Он достаточно долго проработал бок о бок с директором и знал, что перерыв не относился к числу поощряемых им действий - особенно когда дело касалось ТРАНСТЕКСТА. Фонтейн заплатил за этого бегемота дешифровки два миллиарда и хотел, чтобы эти деньги окупились сполна. Каждая минута простоя ТРАНСТЕКСТА означала доллары, спущенные в канализацию. - Но, Мидж… - сказал Бринкерхофф.

КОД ОШИБКИ 22 Сьюзан вздохнула с облегчением. Это была хорошая весть: проверка показала код ошибки, и это означало, что Следопыт исправен. Вероятно, он отключился в результате какой-то внешней аномалии, которая не должна повториться.

Стратмор медленно приближался к застывшему в гротескной лозе телу, не сводя с него глаз. Он схватил убитого за запястье; кожа была похожа на обгоревший пенопласт, тело полностью обезвожено. Коммандер зажмурился, сильнее сжал запястье и потянул. Труп сдвинулся на несколько сантиметров.

В данный момент мы ничего не знаем про Северную Дакоту, кроме анонимного адреса. - Возможно, это приманка, - предположила Сьюзан. Стратмор вскинул брови. - С какой целью. - Танкадо мог посылать фиктивные сообщения на неиспользованный адрес в надежде, что мы его обнаружим и решим, что он обеспечил себе защиту.

Он упал.

 Спокойно, Джабба, - предупредил директор. - Директор, - сказал Джабба, - Энсей Танкадо владеет нашим банком данных. Дайте ему то, чего он требует. Если он хочет, чтобы мир узнал о ТРАНСТЕКСТЕ, позвоните в Си-эн-эн и снимите штанишки.

Отключение невозможно. Но. Увы, она уже знала ответ. Так вот какова месть Танкадо. Уничтожение ТРАНСТЕКСТА.

Он совсем забыл про кольцо на пальце, забыл, для чего приехал в Севилью. Он посмотрел на приближающуюся фигуру, затем перевел взгляд на кольцо. Из-за чего погибла Меган. Неужели ему предстояло погибнуть по той же причине. Человек неумолимо приближался по крутой дорожке.

Он не заметил отражения, мелькнувшего за оконным стеклом рядом с. Крупная фигура возникла в дверях директорского кабинета. - Иису… - Слова застряли у Бринкерхоффа в глотке.

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  1. CalГ­nica B.

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