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The growth of multiwalled carbon nanotubes (MWCNTs) produced by a catalytic chemical vapor deposition (CCVD) process has been monitored using a tapered element oscillating microbalance (TEOM) probe. This technique displays a high sensitivity (<1 μg). Growths in the TEOM microreactor are investigated with catalytic particles (Fe, Ni) dispersed on different supports. First, high surface area Fe/Al2O3 or Fe (Ni) exchanged on zeolite powders is used. Second, growths are performed on array of nickel dots or Fe/Si-nc particles dispersed on large holes patterned on Si(100) substrates. An accurate monitoring of the early stages of growth permits a precise evaluation of the growth rates and shows substantial differences between these samples which greatly differ by the surface area. On catalysts dispersed on Si(100) the mass uptake is linear throughout the process. On high surface area catalysts, however, a saturation of the mass uptake is indifferently observed. This saturation is explained either by diffusion limitation by the growing MWCNTs or by internal diffusion through the pores or external diffusion through the grains of the catalyst. The kinetic dependence with partial pressure of the incoming C2H6:H2 gas mixture is then explored on the Fe/Al2O3 catalyst. A linear dependence of the MWCNT growth an (PC2H6/PH2)1/2 is found. A simple model is then developed that accounts for this dependence only if an associative and competitive adsorption of ethane is the rate determining step of the overall process. These results thus bring insight to improve and control the CCVD growth kinetics of MWCNTs. [ABSTRACT FROM AUTHOR]

Presents information on a study which examined nucleation and growth kinetics of chemical vapor deposition diamond thin films on silicon. Background of the study; Methodology of the study; Results and discussion.

Abstract: This paper reports on the kinetics of diamond nucleation and growth on polycrystalline copper investigated by in situ Auger Electron Spectroscopy and Scanning Electron Microscopy. Copper is a reference substrate to study the diamond nucleation from graphite. The substrate is first treated with diamond paste. However the diamond seeds let on the surface by the pre-treatment are almost completely transformed into graphite. The nucleation of CVD diamond can be well described in the framework of carbon phase transformations. Diamond seeds deposited on the substrate are first transformed into graphitic layers. A process occurring on the edges site of graphite is subsequently postulated, in agreement with the Lambrecht model. [Copyright &y& Elsevier]

Abstract: Iron-based nanoparticles are prepared by a laser-induced chemical vapor deposition (CVD) process. They are characterized as body-centered Fe and Fe2O3 (maghemite/magnetite) particles with sizes ≤5 and 10nm, respectively. The Fe particles are embedded in a protective carbon matrix. Both kind of particles are dispersed by spin-coating on SiO2/Si(100) flat substrates. They are used as catalyst to grow carbon nanotubes by a plasma- and filaments-assisted catalytic CVD process (PE-HF-CCVD). Vertically oriented and thin carbon nanotubes (CNTs) were grown with few differences between the two samples, except the diameter in relation to the initial size of the iron particles, and the density. The electron field emission of these samples exhibit quite interesting behavior with a low turn-on voltage at around 1V/μm. [Copyright &y& Elsevier]

During the last decade silicon nanocrystals (Si-nc) have received widespread interest because of their high quantum efficiency for light emission at room temperature. However, the challenge still ahead is to study and apply these to single Si-ncoptoelectronics, i.e., solving problems linked with connection and manipulation. In this letter we report on connecting (wiring) single Si-nc with conducting multi-walled carbon nanotubes (MWNTs). We have been able to establish a strong mechanical connection by direct growth of MWNTs on Si-nc used as support of iron nanoparticles, by catalytic chemical vapor deposition (CCVD). To monitor the initial stage of the MWNTs growth process, we used a tapered element oscillating microbalance (TEOM). We compared the growth process on Si-nc coated by iron (Fe/Si-nc) to the standard process of growing MWNTs on alumina as support for iron (Fe/Al). The results showed that in the case of Fe/Si-nc catalyst, we obtained three times larger diameter of multi-walled CNTs compared to Fe/Al. This was mainly due to the Si-nc size. The diameter of the CNTs only depended on the size of the Si-nc particles that rested stuck on the tip of the MWNTs. The connected Si-nc kept their photoluminescence properties at room temperature. The present findings open new opportunities in the development of nanodevices for the optoelectronic application field. [ABSTRACT FROM AUTHOR]

Polycrystalline diamond films with a predominant (100) texture were deposited onto silicon substrates using hot-filament chemical vapor deposition. During film deposition, different temperature gradients were created and imposed laterally across the substrate materials. Films grown under a gradient of 100 °C cm-1 displayed large (100) oriented grains. No crystallite (100) orientation was observed in the as-grown films prepared without a temperature gradient. It was observed that the diamond grain size varied as a /unction of the gradient. The lower gradient resulted in smaller grains and vice versa. Furthermore, the size of the grains was a function of the deposition time. The orientation of the diamond grains changed gradually across the substrate from (100) to (110) orientation as we scanned from the high-temperature to the low-temperature zone. The films were characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and Fourier transform infrared (FTIR) spectroscopy. XRD showed strong (400) reflections in the oriented samples. SEM results indicated the presence of smooth diamond surfaces consisting of predominantly (100) oriented platelets. As the (100) oriented diamond grains were grown on top of the (100) oriented silicon substrates, the faces were mostly aligned parallel to the substrate surface resulting in the deposition of a smooth diamond surface. AFM observations revealed the presence of steps located at the boundaries of the oriented grains. FTIR results showed the characteristic difference in hydrogen bonding in the oriented samples and gave useful information about mechanisms responsible for the orientation. Quantitative analysis was carried out to measure the H content in the films, and it was found that the oriented films contained less hydrogen. Our findings suggest that high saturation of carbon and a concentration gradient of sp³ CH2 species can be the key... [ABSTRACT FROM AUTHOR]

Abstract: The deposition of carbon has been studied at high temperature on polycrystalline nickel by hot filaments activated chemical vapor deposition (HFCVD). The sequences of carbon deposition are studied by surface analyses: Auger electron spectroscopy (AES), electron loss spectroscopy (ELS), X-ray photoelectron spectroscopy (XPS) in a chamber directly connected to the growth chamber. A general scale law of the (C/Ni) intensity lines is obtained with a reduced time. Both, shape analysis of the AES C KVV line and the C1s relative intensity suggest a three-step process: first formation of graphene and a highly graphitic layer, then multiphase formation with graphitic, carbidic and diamond-like carbon and finally at a critical temperature that strongly depends on the pretreatment of the polycrystalline nickel surface, a rapid transition to diamond island formation. Whatever the substrate diamond is always the final product and some graphene layers the initial product. Moreover it is possible to stabilize a few graphene layers at the initial sequences of carbon deposition. The duration of this stabilization step is strongly depending however on the pre-treatment of the Ni surface. [Copyright &y& Elsevier]

In this paper, the growth of thin and dense films of vertically aligned carbon nanotubes (CNTs) on Fe-Co/TiN/Si(100) substrates is reported. Special attention is held to the preparation of the TiN buffer layers. This layer is deposited by pulse laser deposition at high temperature with a high texturation according to [TiN(100)//Si(100)]. Further ammonia heat treatment is performed at 623 K to control a Ti:N stoichiometry and remove oxygen impurity. Fe and Co as catalysts are subsequently deposited at high temperature (923 K) at the monolayer level with two ultrahigh vacuum evaporator cells. The growth of CNTs is performed by a direct-current plasma-enhanced and hot filaments-assisted catalytic chemical vapor deposition (dc HF CCVD) process. Highly dense films of CNTs, are obtained with only 0.5 nm Fe(Co) evaporated. Observations by transmission electron microscopy show that most of the CNTs display sizes in the 2.5-6 nm range, most of them with a double-wall (DW). This is in agreement with spectral features of the Raman radial breathing modes (RBM) in the 70-130 cm-1 range. Generally, these large-diameter DWCNTs display a high defect density with morphologies partially collapsed into flattened twisted shapes. [ABSTRACT FROM AUTHOR]

Abstract We investigate the influence of carbon nanotubes (CNT) aligned array on the magnetic properties of ensemble of densely packed Co nanoparticles (NPs) embedded inside CNT. Each CNT contains only one nanosized Co. Such a special structure was formed by catalyst chemical vapor deposition (CCVD) activated by current discharge plasma and hot filament. The Co NPs, previously deposited onto SiO 2 /Si substrate, acted as a catalyst. By varying the parameters of the CCVD process, we were able to also sputter the substrate instead of CNT growth. Co NPs were used as a mask and the structure of Si-based nanocones with Co NPs on the top of each cone was formed. Exhaustive investigation of the structural, morphology and crystalline properties of Co nanoparticles were performed. The magnetic properties of two kinds of samples, Co on the Si-based nanocone and Co inside CNT, were differ drastically. In the former case, the magnetic anisotropy of thin-film-type has been observed with large magnetic domains. Whereas for the Co-CNT samples ferromagnetic NPs were magnetically isolated. It was established that the magnetic anisotropy of nanosized Co plays more dominant role than the dipole interaction between Co NPs. The role of the CNT container in this is discussed. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

In this work, we present a practical approach for controlling single walled carbon nanotubes (SWCNTs) diameter distribution through thin film Ru catalyst, coupled with hydrogen pre-treatment. Uniform and stable Ru nanoclusters were obtained after dewetting the Ru thin films under atomic hydrogen pre-treatment. SWCNTs were synthetized by double hot filament chemical vapor deposition (d-HFCVD) on SiO 2 /Si substrates at different temperatures. We found that the temperature is an important synthesis parameter that influences the diameter distribution of the final SWCNTs. Statistical analysis of the Raman radial breathing modes evidences the growth of highly enriched semi-conducting SWCNTs (about 90%) with narrow diameter distribution that correlates directly with the catalyst particle size distribution. Electrical measurement results on as-grown SWCNTs show good thin-film transistor characteristics. [ABSTRACT FROM AUTHOR]

Abstract: In this work, we investigate magnetic properties of iron based nanoparticles (NP) intercalated into carbon nanotube (CNT) aligned arrays synthesized by injection chemical vapor deposition. We have analyzed the temperature (T) and the ferrocene concentration (C F) dependences of the macroscopic magnetic parameters. From these experiments a weaker interaction between magnetic moments of NP was obtained for low C F values. The random anisotropy model for the experimental data analysis was applied and micromagnetic parameters were evaluated. The law of the approach to magnetic saturation (LAS) was analyzed using the general expression with the correlation function C(r=x/R a) of magnetic axes, R a being the magnetic anisotropy correlation length. We obtained that, while for C F =0.5% C(r) is a step-like (C(r <10)=1, C(r >10)=0), for C F ⩾1% C(r) decays rapidly on a short range, (2-3)R a. Such extended correlations for C F =0.5% could be associated with the dominant role of the coherent anisotropy, which is caused by the influence of the alignment of CNT. When the aligned CNTs for C F =0.5% are destroyed into powder, the LAS is changed to H −1/2, which means the dominant role of the exchange mechanism. [Copyright &y& Elsevier]

Abstract: Single crystal diamond films of varying quality are deposited using microwave plasma chemical vapor deposition (MPCVD) apparatus. Unpolished natural diamond seeds are used as substrates in the temperature (T s) range 850–1200 °C. The gas mixture of methane (CH4), hydrogen (H2) and oxygen (O2) is used for the deposition of diamond. The deposition pressure is varied in the range 90 to 150 Torr. The films are characterized using scanning electron microscopy (SEM), Atomic force microscopy (AFM) and Raman spectroscopy techniques. The growth morphology of the films is found to be a sensitive function of the deposition parameters. The crystalline nature of the films change from polycrystalline to single crystal as we increase T s and for a certain set of parameters the filamentary growth of the diamond crystals can be seen. The films are polycrystalline in the range of substrate temperatures 850–900 °C and oriented grains of diamond crystals are evident as the T s increases. The single crystal diamond growth is observed to proceed via the step growth mechanism with the evidence of bunching of the steps. Our study explores evolution of the growth of single crystal diamond in a wide range of parameters. [Copyright &y& Elsevier]

A new hot filament chemical vapor deposition with direct current plasma assistance (DC HFCVD) chamber has been designed for an intense nucleation and subsequent growth of diamond films on Si(100). Growth process as well as the I=f(V) characteristics of the DC discharge are reported. Gas phase constituents activation was obtained by a stable glow discharge between two grid electrodes coupled with two sets of parallel hot filaments settled in-between and polarised at the corresponding plasma potential. The sample is negatively biased with a small 10–15 V extraction potential with respect to the cathode grid. Such design allows to create a high density of both ions and radicals that are extracted and focussed onto the surface of the sample. The current density onto the sample can be finely tuned independently of the primary plasma. A homogeneous plasma fully covering the sample surface is visualized. Consequently, a high-density nucleation (&ges;1010 cm−2) occurs. [Copyright &y& Elsevier]