Use of carbon nanotubes for VLSI interconnects

The requirements for using carbon nanotubes as interconnects in future integrated circuits are defined. Growth techniques and some methods of their characterisation are described. The need to grow nanotubes on conducting metal substrates is pointed out and this effort is starting.     

Carbon nanotubes growth in AlPO4-5 zeolites: Evidence for density dependent field emission characteristics

We report on the correlation between the concentration of Fe-catalyst, doped in the aluminum phosphate (AlPO₄-5) zeolite and the resulting density of carbon nanotubes (CNTs) to obtain the optimum electron field emission conditions from the CNTs. Initially, AlPO₄-5 crystallites were impregnated, for a period of ∼ 10–60 min, in the Fe-catalyst solution and subjected to Electron Spectroscopy for Chemical Analysis (E.S.C.A.). The analysis revealed that the concentration of Fe-catalyst, C_Fe, was increased from ∼ 1.7% to ∼ 8.6%, respectively, with increase in impregnation time, I_T. The HRTEM results showed that Fe nano-clusters, with diameter ∼ 7–10 nm, were formed in the surface region of the crystallites. These crystallites were sprayed on the conducting substrates, under identical spraying conditions. SEM study revealed that the coverage of the crystallites on the substrates was ∼ 10³–10⁴ crystallites/cm². These substrates were subjected to direct current plasma enhanced chemical vapor deposition (dc-PECVD) process, to grow CNTs. The SEM micrographs were recorded for the CNT-grown substrates and the average areal density of CNTs, (σ_T)_av, on the crystallites (t/cm²) was estimated. The analysis indicated that (σ_T)_av increased from ∼ 6.24 ± 0.19 × 10¹⁰ to 2.04 ± 0.61 × 10¹¹ t/cm² with gradual increase in C_Fe. The field emission study of the samples revealed that the optimum values of the turn-on electric field, ∼ 3.69 V/μm and the field emission current density, ρ_d, ∼ 1.78 × 10³ μA/cm² were achieved for (σ_T)_av, ∼ 6.24 ± 0.19 × 10¹⁰ t/cm², at a concentration of Fe, C_Fe, ∼ 3.0%, encapsulated in the AlPO₄-5 crystallites.     

The density of water in carbon nanotubes

In this paper, the density of water confined in carbon nanotubes of different sizes and chirality is calculated. Molecular dynamics is used to simulate the spontaneous filling of the nanotube with water molecules coming from an external bath. Three H₂O filling modes are found and a correlation, which relates the density with the nanotube diameter, is proposed.     

Meeting the challenge of formulating for the future

The history of the paint market shows that change quickly follows new technical advances or governmental regulation. Restrictions on the use of volatile organic compounds (VOCs) in architectural coatings are no exception. This paper examines the history of VOC regulations and resin technology in Europe compared to the U.S. Despite differences in formulations, substrates, and test methods, there are lessons that can be applied by U.S. paint makers and their suppliers. Other new directions in polymer synthesis and technology which may impact the paint industry are also discussed. Presented at the 78th FSCT Annual Meeting, November 5, 2001, in Atlanta, GA 7201 Hamilton Blvd., Allentown PA.     

生物柴油及其面临的挑战

生物柴油是可再生的清洁能源。简述了生物柴油及国内外生物柴油产业发展现状,阐述了生物柴油的性质,并分析了生物柴油产业未来面临的挑战。     

Carbon nanotubes: dynamics of synthesis processes

Heat and mass transport are obtained in a solar reactor using ‘in situ’ measurements linked to numerical simulation and allow the interpretation of the vaporization process as well as the determination of the cooling regime. Comparison with other processes (laser ablation or electric arc) point out some common behavior like the great influence of the cooling rate of vapors on the structure and yield of nanostructured carbon material. We also investigate the growth mechanisms of single wall carbon nanotubes (SWNTs) produced by the solar method as a function of the nature of catalysts and the temperature variation in the condensing area. The Raman spectra clearly show that the change of catalyst induces differences in the diameter of SWNT whereas TEM pictures enhance the change of both length and diameter of the bundles. All these results are explained considering that the key parameter is the temperature at which the SWNTs are formed. This temperature range can be related to the sublimation temperature of the target and to the eutectic temperature of the binary phase diagram. Finally we propose a new mechanism to explain the nucleation process and segregation rate which seems to depend on the capacity of catalyst to form carbide.     

集成电路制备中化学机械全局平面化(CMP)后的表面清洗技术

论述了集成电路制备中CMP过程带来污染的重大危害,介绍了目前CMP后清洗所面临的两大新挑战,同时对CMP后清洗的现状做出了分析,提出了存在的问题,并且对未来清洗的方向进行了展望。     

Short communication: Carbon nanotubes as flame retardants for polymers

Flame retardant nanocomposites were synthesized by melt‐blending ethylene‐vinyl acetate copolymer (EVA) with multi wall carbon nanotubes. Fire property measurements by cone calorimeter revealed that the incorporation of multi wall carbon nanotubes into EVA significantly reduced the peak heat release rates compared with the virgin EVA. Peak heat release rates of EVA with multi‐wall carbon nanotubes were slightly improved compared with EVA nanocomposites based on modified layered silicates. Char formation is the main important factor for these improvements. There was also a synergistic effect by the combination of carbon nanotubes and organoclays resulting in an overall more perfect closed surface with improved heat release values. Copyright © 2002 John Wiley & Sons, Ltd.     

Fabrication of bimetallic nanoparticles/multi-walled carbon nanotubes composites for microelectronic circuits

A method for the fabrication of electrically-conducting polymer composites has been developed by mixing modified multi-walled carbon nanotubes (MWCNTs) functionalized by bimetallic nanoparticles (Ag/Ni/MWCNTs) into a UV curable resin. MWCNTs were treated by a concentrated H₂SO₄/HNO₃ mixture followed by ultrasonication with AgNO₃ and NiSO₄ in an ethylene glycol solution, producing MWCNTs decorated with Ag and Ni nanoparticles. The microstructure and surface morphology of the Ag/Ni/MWCNTs were investigated by scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray spectrometry. It was found that the addition sequences of NiSO₄ and AgNO₃ influence the morphology of the Ag/Ni/MWCNTs. The electrically-conducting polymer composites were obtained by dispersing the prefabricated Ag/Ni/MWCNTs in UV curable resin, the curing process of which was tracked by Fourier transform infrared spectroscopy, and the electrical resistance was measured using the four-probe method. The fabrication of microelectronic patterns made by screen printing on different substrates was described.     

打破绿色壁垒:未来石化新挑战

分析了“绿色壁垒”产生的原因、背景及企业打破绿色壁垒的紧迫性 ,并提出了石化企业迎战“绿色壁垒”的对策     

The formation of electric circuits with carbon nanotubes and copper using tin solder

A Sn coated single multi-walled carbon nanotube (MWCNT) was connected between Cu terminals and with other MWCNTs using tin solder. HRTEM micrographs showed the interconnections between two sides as well as on one side of a Cu grid. MWCNTs not only formed straight connections but also bent in the middle with little damage to the graphenes of nanotubes. The process also joined a single nanotube with other nanotubes at their tips as well as in the middle, and in various modes including series and parallel. The connections were found to be stable in air and under TEM observations, and could be made by both small and large diameter MWCNTs. The process uses existing Sn-based soldering technology and provides a way for the development of CNT-based nanochips.     

Carbon nanotubes: Amino functionalization and its application in the fabrication of Al-matrix composites

Al-matrix composites reinforced with amino-functionalized multiwalled carbon nanotubes (fCNTs) have been fabricated using the powder metallurgy process. Using this method fCNTs (1.5 wt.%) were dispersed in Al powder by high energy ball milling. Al–fCNTs composites (1.5 wt.%) were fabricated by the consolidation of powders at 550 MPa followed by sintering at 620 °C under a vacuum of 10^? 2 Torr for 2 h. Functionalization of the nanotubes was carried out by ball milling multi-walled carbon nanotubes (MWCNTs) in the presence of ammonium bicarbonate. It was observed that the dispersion of fCNTs in Al-matrix was much higher than those of non-functionalized MWCNTs. Microhardness measurements showed that a microhardness value of about 400 kg/mm² could be obtained for Al-matrix composites loaded with 1.5 wt.% fCNTs. Microstructure observations using scanning electron microscopy (SEM) and high-resolution electron microscopy (HRTEM) confirmed that the sintered composites had a good dispersion of fCNTs in Al matrix and they do not agglomerate with each other. Further, the HRTEM characterization of these composites revealed the formation of a thin transition layer of Al₄C₃ between fCNTs and Al matrix, which is believed to be responsible for load transfer from Al matrix to fCNTs. A thorough characterization of MWCNTs and fCNTs synthesized in the present work was carried out using XRD, SEM, TGA, HRTEM, FTIR, SIMS and Raman spectroscopy.     

碳纳米管负载络合铂催化苯乙烯硅氢加成反应

研究了碳纳米管负载聚乙二醇络合铂催化剂的制备及其催化苯乙烯与甲基二氯硅烷硅氢加成反应的反应规律。该催化剂在常温常压下有很高的催化活性,络合剂聚乙二醇能非常有效地提高β-加成产物苯乙基甲基二氯硅烷的选择性,30℃温度下反应195min,甲基二氯硅烷的转化率可达83 33%,β-加成产物选择性为100%;硅氢加成反应有一个明显的诱导期,诱导期过后反应迅速进行,反应温度等因素对诱导期有重要影响;催化剂性能稳定,回收使用3次无明显失活。     

The weight and density of carbon nanotubes versus the number of walls and diameter

The weight and density of carbon nanotubes are calculated as a function of their characteristics (inner diameter, outer diameter, and number of walls). The results are reported in the form of diagrams which may be useful to other researchers, in particular in the fields of synthesis/production, materials and composites, health/toxicity studies.     

Mixed oxide nanotubes in nanomedicine: A dead-end or a bridge to the future?

Nanomedicine has seen a significant rise in the development of new research tools and clinically functional devices. In this regard, significant advances and new commercial applications are expected in the pharmaceutical and orthopedic industries. For advanced orthopedic implant technologies, appropriate nanoscale surface modifications are highly effective strategies and are widely studied in the literature for improving implant performance. It is well-established that implants with nanotubular surfaces show a drastic improvement in new bone creation and gene expression compared to implants without nanotopography. Nevertheless, the scientific and clinical understanding of mixed oxide nanotubes (MONs) and their potential applications, especially in biomedical applications are still in the early stages of development. This review aims to establish a credible platform for the current and future roles of MONs in nanomedicine, particularly in advanced orthopedic implants. We first introduce the concept of MONs and then discuss the preparation strategies. This is followed by a review of the recent advancement of MONs in biomedical applications, including mineralization abilities, biocompatibility, antibacterial activity, cell culture, and animal testing, as well as clinical possibilities. To conclude, we propose that the combination of nanotubular surface modification with incorporating sensor allows clinicians to precisely record patient data as a critical contributor to evidence-based medicine.     

Carbon nanotube-based heterostructures for high-performance photodetectors: Recent progress and future prospects

Unique optical, electrical and chemical properties make carbon nanotubes (CNTs) an excellent candidate for potential applications in the next-generation optoelectronics. Especially, the optoelectronic properties of CNTs can be enhanced dramatically by constructing heterostructures with other materials, in which the charge separation efficiency is enhanced and the recombination probability of excitons is suppressed significantly. Therefore, the CNT-based heterostructures have been widely used as active materials in high-performance photoelectronic devices. Herein, the recent progress of the CNT-based heterostructure photodetectors is reviewed. Firstly, the working mechanisms and typical figures-of-merits are introduced. Secondly, different type CNT-based heterostructures and related photodetectors are highlighted, such as van der Waals heterostructures, all-carbon heterostructures, and bulk heterostructures. Finally, we give the current challenges and future prospects for the development of this emerging field.     

Growth of dense single-walled carbon nanotubes in nano-sized silicon dioxide holes for future microelectronics

Dense and aligned single-walled carbon nanotubes (SWCNTs) were synthesised in nano-sized silicon dioxide holes patterned using electron beam lithography for microelectronics applications. Carbon nanotubes are new materials with potential uses for interconnects and field effect transistors (FETs) of LSI. As single-walled carbon nanotubes have lower resistance than multi-walled carbon nanotubes in close-packed arrangements and show both metallic and semiconducting behaviour, there is a great deal of interest in using dense SWCNTs for low resistive interconnects and high current transistors. Here, we report not only a method for fabrication of SWCNTs in nano-sized holes, but also differences in growth rate and Raman spectroscopy of CNTs in holes of various sizes. The growth rate of CNTs in the holes decreased as the hole size was reduced, due to the amount of carbon radicals diffusing to the catalyst particles at the bottom of the holes.     

Carbon nanotubes produced by fluidized bed catalytic CVD: first approach of the process

Multi-walled carbon nanotubes have been produced with high yield on an iron supported catalyst by catalytic chemical vapor deposition in a fluidized bed reactor. The choice of such a technique allows to reach high selectivity towards the desired material. A remarkable feature of this process is the huge bed expansion observed during the nanotubes growth that affects the fluidization regime due to the evolution of the apparent density of the composite powder. The catalytic powder, the composite material and the purified nanotubes have been analyzed by SEM, TEM and BET nitrogen adsorption.     

Properties of vapor-deposited borophosphorosilicate glass layers employed in technology of silicon integrated circuits

The data of investigations on the physicochemical and electrophysical properties of borophosphosilicate glass layers deposited from mixtures of tetraethoxysilane and esters of boric and phosphoric acids in an oxygen-ozone medium (temperature, 400–440°C; atmospheric and subatmospheric pressures) have been generalized. The empirical relationships are obtained for determining the boundaries of the optimum dopant concentration region when the glass is used as a reflow interlayer dielectric in integrated circuit technology. The assumption is made that the structure of borophosphosilicate glass layers is formed by a porous network involving dopant clusters.