Carpet Growth Research Articles

Direct synthesis and chemical vapor deposition of 2D carbide and nitride MXenes.

Two-dimensional transition-metal carbides and nitrides (MXenes) are a large family of materials actively studied for various applications, especially in the field of energy storage. MXenes are commonly synthesized by etching the layered ternary compounds, called MAX phases. We demonstrate a direct synthetic route for scalable and atom-economic synthesis of MXenes, including compounds that have not been synthesized from MAX phases, by the reactions of metals and metal halides with graphite, methane, or nitrogen. The direct synthesis enables chemical vapor deposition growth of MXene carpets and complex spherulite-like morphologies that form through buckling and release of MXene carpet to expose fresh surface for further reaction. The directly synthesized MXenes showed excellent energy storage capacity for lithium-ion intercalation.

Influence estimation of recreation pressure on the forest trail "Buchyna" NNP "Skolivski Beskydy"

Complex studies of the impact of recreational pressure on the forest trail "Buchina" of NNP "Skolivski Beskydy" were carried out. It was found that the air microclimatic parameters across the all transects were shown to fluctuate. The air temperature was stable, as well as the humidity changed very slightly. The wind force gradually decreased from the middle of the forest trail to the margins. The difference in the illumination of the soil surface on the trail and adjacent areas is the most noticeable. The impact of recreational activities on the microclimatic parameters of soils is more significant than this in the air. The temperature and humidity of the soil was decreased and the density of the structure was increased towards the center of the trail. Changes in water-physical parameters of soils let us identify the initial stages of digression in the studied recreational-pressed forest ecosystems. Brioindication studies have shown that the forest area on both sides of the route, which does not experience recreational pressure, is characterized by extremely weak development of moss cover. It was represented by 5 species of mosses such as Atrichum undulatum, Polytrichum formosum, Plagiomnium undulatum, Eurhynchium angustirete and E. striatum. Those species were represented by toll turf, dendroides and rough carpet growth forms. Species diversity at the trail edges were doubled. There were founded 10 spesies of bryobionta: A. undulatum, P. formosum, Plagiomnium cuspidatum, P. ellipticum, P. undulatum, E. angustirete, Pseudoscleropodium purum, Thuidium delicatulum, T. tamariscinum, Calliergonella cuspidatа, were represented by toll turf, dendroides, rough mats and weft growth forms. In the zone of intensive trampling on the forest trail, the moss cover was completely absent. Bryophytes, which were recorded in trail margins, marked the initial stages of recreational digression (I-II) and were belonging to the group of sensitive forest species. The strongest pressure was recorded on the central part of the forest trail. However, the density of the soil structure, even in this area, didn't overtop the indicator rate for the category of "very loose soils". Our study suggests that the organization of recreational activities for the planning of permanent tourist routes (so-called "ecological trails'') in the areas of spruce-beech forests haven't cause extremely pressure on the park ecosystems (equally for soil and vegetation cover) in NNP "Skolivski Beskydy". As a preventive measure, we recommend regulating the number of visitors to reduce the mechanical trampling on the forest trails and the arrangement of different fences, decks, etc.

Hierarchical nanostructured surface design for robust and flexible multifunctional devices

This paper investigates structural and functional properties of a hierarchical hybrid flexible material with nanostructured surface architecture. These solids comprise of carpet-like arrays of covalently bonded carbon nanotubes (CNT) on the surface of strong and flexible carbon fabric. In-depth analysis of the multi-scale morphology of this structure is provided, with emphasis on structure-property relationships relevant to surface-interaction related applications such as catalysis, sensing, microfluidics and bio-scaffolding devices. A two-step process is used to anchor carbon nanotubes directly on the surface of carbon fiber cloth, and its morphology, structure and surface chemistry analyzed in detail. Surface structure model from structural and physical property measurements predict over 2000 times increase in specific surface area (SSA) of the fabric due to CNT carpet growth. This estimate is in good agreement with direct SSA measurement using Brunauer–Emmett–Teller (BET) gas-adsorption technique, indicating full utilization of the CNT surface sites, which can be used for adsorption, functionalization, thermal or electrical transport. Electrical measurement of these materials shows a systematic increase of sheet conductivity of the fabric with increasing CNT carpet height. These results indicate that this type of material design can combine the structural durability and flexibility of advanced fabrics with the enhanced surface activity of nanomaterials for a wide variety of surface interaction devices of the future.

Magnesia and Magnesium Aluminate Catalyst Substrates for Carbon Nanotube Carpet Growth

Carbon nanotube (CNT) carpet growth behavior is systematically investigated on a pristine and ion beam-bombarded family of basic catalyst substrates: MgAl2O4 (100), MgAl2O4 (110), MgAl2O4 (111), an...

Enhancement of catalytic effect for CNT growth at low temperature by PECVD

Lowering the temperature of CNT synthesis before any attempts of integration is a technical challenge. The improvement of CNT carpet growth on Ni/TiN/SiO2/Si by previously reducing the size of Ni particles using H2 plasma prior to be exposed to H2:C2H4 plasma is studied. Different techniques, SEM, in situ Raman, NEXAFS, XPS and TEM were combined to investigate the growth rate and the quality of CNT films. An original use of in situ Raman spectroscopy allowed us to determine the increase of sample surface temperature in contact with H2 plasma through Si anharmonicity. Finally it was possible to grow CNT carpets by PECVD with a process temperature of 480 °C.

(Invited) Modification and Analysis of Carbon Based Structures By Metal Nanoparticulate Ions

Our collaborative work to create and soft land ionized gas phase single crystalline metal nanoparticulate ions onto substrates was motivated by Robert Hauge’s wish to produce templates for carbon nanotube carpet growth. Ionwerks created a machine to do this but, as is often the case, funding was found first for alternative applications. One such has been low energy (500 eV) injection of 8 nm silver nanoparticulate ions (AgNP-) into the near surface of bio-polymers. A uniform layer (70 e15 Ag atoms/cm2) of these implanted particles serve to assist the laser desorption of intact biomolecules from a brain tissue sample into the gas phase. Some of these desorbed molecules are ionized and can be transported into a mass spectrometer and uniquely identified by their exact mass to charge (m/z). By scanning a 50 micron focused laser across the surface of an AgNP implanted rat brain tissue sections, a complete mass spectrum can be acquired at each of several hundred thousand laser locations. Images of specific biomolecules can be derived from these spectra. Putative molecular biomarkers can then be identified by inter-comparing the numerous molecular images from each animal grouping within an animal study. Images from the same brain levels between injured (or diseased) and uninjured rats define histological micro domains in which elevated or decreased molecular ion intensities correlate with other measures of injury/disease state severity. Imaging of these biomarker ions is becoming useful in preclinical screening of drug candidates and should ultimately enter clinical settings. The AgNP enhanced mass spectral imaging has been also applied to the surface analysis of synthetic polymers, fullerenes, and nanotubes. A third application uses 30 keV, 15 nm AgNP ion impacts to form otherwise unattainable controlled nano-sized holes in graphene—especially “rebar” graphene. Alternatively, low energy soft landing at lower energy can form nanostructures upon the graphene which have implications for device formation. However, before departure, Bob made it clear that we needed to get back to carpet growth and other ideas which he outlined in extensive and explicit discussions—mostly at outdoor cafes and coffee shops. His dictates and imprimatur remain.

Abiotic tooth enamel.

Tooth enamel comprises parallel microscale and nanoscale ceramic columns or prisms interlaced with a soft protein matrix. This structural motif is unusually consistent across all species from all geological eras. Such invariability-especially when juxtaposed with the diversity of other tissues-suggests the existence of a functional basis. Here we performed ex vivo replication of enamel-inspired columnar nanocomposites by sequential growth of zinc oxide nanowire carpets followed by layer-by-layer deposition of a polymeric matrix around these. We show that the mechanical properties of these nanocomposites, including hardness, are comparable to those of enamel despite the nanocomposites having a smaller hard-phase content. Our abiotic enamels have viscoelastic figures of merit (VFOM) and weight-adjusted VFOM that are similar to, or higher than, those of natural tooth enamels-we achieve values that exceed the traditional materials limits of 0.6 and 0.8, respectively. VFOM values describe resistance to vibrational damage, and our columnar composites demonstrate that light-weight materials of unusually high resistance to structural damage from shocks, environmental vibrations and oscillatory stress can be made using biomimetic design. The previously inaccessible combinations of high stiffness, damping and light weight that we achieve in these layer-by-layer composites are attributed to efficient energy dissipation in the interfacial portion of the organic phase. The in vivo contribution of this interfacial portion to macroscale deformations along the tooth's normal is maximized when the architecture is columnar, suggesting an evolutionary advantage of the columnar motif in the enamel of living species. We expect our findings to apply to all columnar composites and to lead to the development of high-performance load-bearing materials.

Catalytic CVD growth of millimeter-tall single-wall carbon nanotube carpets using industrial gaseous waste as a feedstock

A gaseous product mixture from Fischer-Tropsch synthesis (FTS-GP) was utilized as an efficient feedstock for growth of high-quality, well-aligned single-wall carbon nanotube (SWCNT) carpets of millimeter-scale heights on Fe and (sub) millimeter-scale heights on Co catalysts via chemical vapor deposition (CVD). Although the SWCNT carpets were grown over a wide temperature range (between 650 and 850 °C), growth conducted at optimal temperatures for Co (850 °C) and Fe (750 °C) yielded predominantly SWCNTs that were straight and clean, with sidewalls largely free of amorphous carbon. Growth on Fe is characterized by a relatively high growth rate (∼50 μm/min) and long catalyst lifetime (>90 min), with the catalyst showing no decay of activity, while growth on a Co catalyst shows a lifetime of ∼60 min, with a slower growth rate of ∼7 μm/min. The resulting area densities of SWCNT carpets grown on Fe and Co, determined by the weight-gain method, were 1.0 × 1012 and 6.0 × 1012 cm−2, respectively — among the highest achieved for SWCNT carpets on standard catalysts. Unlike SWCNT carpet growth involving conventional feedstocks, growth rate and density of SWCNTs on Fe are less sensitive to the FTS-GP fraction and thus allow for relatively easy optimization and scale-up.

Impacts of rearing techniques on growth, survival and bacterial microbiota of carpet shell clam (Ruditapes decussatus) larvae

In this study, we investigate the impacts of two water treatment regimes, the closed aquaculture system (CAS) and flow-through system (FTS), on the carpet shell clam (Ruditapes decussatus) larval microbiota, growth and survival. A bacteriological barrier (B) was created among breeder stage treated by florfenicol (FF, 8 mg L−1day−1 per 5 days). After spawning, larvae were maintained in five different rearing techniques: CAS; FTS; B + CAS; B + FTS and B + CAS + FF (8 mg L−1 day−1 per 3 days). Significant decrease was observed in both total bacterial count and presumptive Vibrio count (PVC) in FF-treated breeders. Besides, larvae reared in B + FTS showed significantly lower PVC than larvae maintained in other rearing techniques. It was also determined that growth and survival of larvae reared in B + CAS + FF and B + FTS were significantly better than those reared in other systems. One hundred and twelve Vibrio strains, isolated from breeders, eggs and larvae, were subjected to some bacteriological tests (API 20E strips, vibriostatic agent O/129, growth at different temperatures and salinity). Vibrio alginolyticus was the predominant isolated species (36.61 %), followed by V. fluvialis (25 %), V. vunificus (17.86 %), V. cholera (13.39 %) and V. paraheamolyticus (7.14 %). These results may contribute to the understanding of the effect of rearing techniques on the bacterial load, survival and growth of early life stages of R. decussatus larvae.

Oyster Shells As Recorders of Short-Term Oscillations of Salinity and Temperature During Deposition of Coral Bioherms and Reefs In the Miocene Lorca Basin, SE Spain

Abstract: We use δ 18 O and δ 13 C of oyster shells, inferred seawater δ 18 O (δ w ), and temperature tolerance ranges of modern zooxanthellate coral communities to constrain and model paleo-salinities of marginal-marine waters of the Miocene Lorca Basin, Spain. Salinities ranged from 22 to 32 PSU during growth of coral bioherms and carpets of the Soriana and Parrilla formations, and from 35 to 39 PSU during deposition of the Hondo Formation reef complex. The periods with lower modeled salinities correspond with deltaic and alluvial-fan sedimentation in the area. The modeling is supported by 87 Sr/ 86 Sr data and provides new insights into the evolution of the local depositional settings. Departures of Sr-isotope values from the global oceanic curve occur within the intervals with the lowest modeled salinities, and the non-oceanic 87 Sr/ 86 Sr preserved in individual oyster shells was probably sourced from uplifted Aquitanian–Burdigalian limestones. 87 Sr/ 86 Sr values that plot along the global ocean Sr-isotope curve for the late Miocene indicate a Tortonian age for the upper part of the Soriana Formation and the Parrilla Formation, and a Messinian age for the Hondo Formation. More generally, we demonstrate how the chemical analyses of oyster shells provide additional information regarding short-term oscillations of salinity and temperature of seawater beyond what can be obtained by traditional paleoecological methods.

Gaseous product mixture from Fischer-Tropsch synthesis as an efficient carbon feedstock for low temperature CVD growth of carbon nanotube carpets.

Low-temperature chemical vapor deposition (CVD) growth of carbon nanotube (CNT) carpets from Fe and Fe-Cu catalysts using a gaseous product mixture from Fischer-Tropsch synthesis (FTS-GP) as a superior carbon feedstock is demonstrated. This growth approach addresses a persistent issue of obtaining thick CNT carpets on temperature-sensitive substrates at low temperatures using a non-plasma CVD approach without catalyst pretreatment and/or preheating of the carbon feedstock. The efficiency of the process is evidenced by the highly dense, vertically aligned CNT structures from both Fe and Fe-Cu catalysts even at temperatures as low as 400 °C - a record low growth temperature for CNT carpets obtained via conventional thermal CVD. The grown CNTs exhibit a straight morphology with hollow interior and parallel graphitic planes along the tube walls. The apparent activation energies for CNT carpet growth on Fe and Fe-Cu catalysts are 0.71 and 0.54 eV, respectively. The synergistic effect of Fe and Cu show a strong dependence on the growth temperature, with Cu being more influential at temperatures higher than 450 °C. The low activation energies and long catalyst lifetimes observed are rationalized based on the unique composition of FTS-GP and Gibbs free energies for the decomposition reactions of the hydrocarbon components. The use of FTS-GP facilitates low-temperature growth of CNT carpets on traditional (alumina film) and nontraditional substrates (aluminum foil) and has the potential of enhancing CNT quality, catalyst lifetime, and scalability.

Fast Imaging of Carbon Nanotube Carpet Growth by Environmental TEM

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Influence of support morphology on the bonding of molecules to nanoparticles

Supported metal nanoparticles form the basis of heterogeneous catalysts. Above a certain nanoparticle size, it is generally assumed that adsorbates bond in an identical fashion as on a semiinfinite crystal. This assumption has allowed the database on metal single crystals accumulated over the past 40 years to be used to model heterogeneous catalysts. Using a surface science approach to CO adsorption on supported Pd nanoparticles, we show that this assumption may be flawed. Near-edge X-ray absorption fine structure measurements, isolated to one nanoparticle, show that CO bonds upright on the nanoparticle top facets as expected from single-crystal data. However, the CO lateral registry differs from the single crystal. Our calculations indicate that this is caused by the strain on the nanoparticle, induced by carpet growth across the substrate step edges. This strain also weakens the CO-metal bond, which will reduce the energy barrier for catalytic reactions, including CO oxidation.

In situ time resolved wide angle X-ray diffraction study of nanotube carpet growth: Nature of catalyst particles and progressive nanotube alignment

Catalytic chemical vapor deposition is the most promising process to obtain vertically aligned carbon nanotube (VACNT) carpets. Live analysis of growing VACNT is crucial to reveal their nucleation and growth mechanisms. We present novel time resolved in situ X-ray diffraction (XRD) analysis on growing macroscopic VACNT carpets enabling us to get statistical information on catalytic phase together with nanotube progressive alignment. A specific synthesis set-up has been developed to perform such in situ synchrotron XRD experiments. Nucleation kinetics of the different phases are evidenced: first, orthorhombic Fe3C crystalline phase is formed, followed by the formation of CNTs and finally of γ-Fe, demonstrating that Fe3C particles are the nucleation seeds for CNT growth. The additional formation of Fe3C or γ-Fe nanowires inside CNTs is associated with capillary forces and mobility of them at 850°C. Experiments also reveal the progressive formation and alignment of VACNT carpets during the continuous precursor injection. Quantification of the alignment degree allows one to get a better understanding of the effect of precursor injection rate and CNT length on VACNT alignment. The overall results are key issues for the scaling-up of VACNT synthesis and their applications towards commercialization.

Fast Imaging of Carbon Nanotube Nucleation and Growth Processes using Environmental TEM

Carbon nanotubes (CNT), an allotrope of carbon, are made out of seamlessly rolled cylindrical sheets of graphene. There are number of possible ways to seamlessly roll a sheet of graphene into a nanotube. Hence, each single walled carbon nanotube (SWCNT) is characterized by a chirality vector. CNTs exhibit varying properties depending on their structure and morphology such as outer and inner diameters, number of walls, length and chirality. As a result it becomes vital to grow tubes with predetermined structure and morphology for any potential application. The typical growth process of CNTs involves iron catalyst particles being deposited over a SiO 2 or Al 2O3 substrate, reduced in the presence of hydrogen and exposed to a source of carbon at a temperature. Under hydrocarbon decomposition conditions a CNT nucleates on a catalytic particle and grows via the vapor-liquid-solid (VLS) mechanism. If majority of particles undergo a nucleation process then so called carpet growth is

Wetting behavior and activity of catalyst supports in carbon nanotube carpet growth

A simple, reliable, and non-destructive approach based on contact angle measurements is described for predicting the activity of catalyst supports in carbon nanotube (CNT) carpet growth. The basic component of the surface free energy of different alumina supports - determined from the van Oss-Good-Chaudhury model and the Young-Dupré equation - was found to correlate with the activity of Fe catalyst during water-assisted CVD growth of CNT carpets.

Coulomb attraction during the carpet growth mode of NaCl

The submonolayer growth of NaCl bilayer high-rectangular shaped islands on Ag(111) is investigated at around room temperature by using low temperature scanning tunneling microscopy. The growth at the step edges is preferred. Two kinds of islands are observed. They either grow with their non-polar edge at the step edge of Ag(111) or the islands overgrow in a carpet-like mode with the polar direction parallel to the edge. In the latter case, the Ag step is rearranged and considerable, while the NaCl layer is bent. This study clarifies the nature of the interaction of an alkali halide nanostructure with a metal step edge.

Catalyst–support interactions and their influence in water-assisted carbon nanotube carpet growth

We report results from characterization studies focused on a diverse selection of catalyst support materials in order to understand what makes a good catalyst support during carbon nanotube (CNT) carpet growth via water-assisted chemical vapor deposition. The growth and catalyst morphological changes occurring for thin Fe layers deposited on Al2O3, MgO, TiN, and ZrO2 are compared. The growth behaviors of the catalyst substrates were evidently different, with Al2O3/Fe supporting CNT carpet growth and showing the highest activity and longest lifetime. The TiN/Fe catalyst also supported CNT carpet growth, albeit with much lower activity, shorter lifetime, and lower CNT quality while MgO/Fe and ZrO2/Fe did not support CNT carpet growth under standard growth conditions. Studies using a combination of atomic force microscopy and X-ray photoelectron spectroscopy revealed a general correlation between the catalyst behavior (activity and lifetime) and the 3D evolution of the catalyst for active catalysts (Al2O3/Fe and TiN/Fe). Analysis of inactive catalysts under standard conditions (MgO/Fe and ZrO2/Fe) raise interesting questions related to additional chemical interactions between the substrate and catalyst that could influence nucleation and CNT growth. This work provides a step toward understanding the challenges that arise in engineering efficient CNT growth processes on a desired substrate.

Comparison of the efficiency of various substrates in growing vertically aligned carbon nanotube carpets

Vertically aligned multi-walled carbon nanotube (VACNT) carpets have been synthesized on metal and isolating thin films without the use of a pre-deposited catalyst. We used ferrocene as precursor powder catalyst and acetylene as a carbon source to grow VACNT carpets using three-temperature-zone chemical vapor deposition (TTZ-CVD). Tuning the carrier gas Ar flow rate and the sublimation time of ferrocene in the TTZ-CVD extended the lifetime of the catalyst, increasing the efficiency of growth. Increasing the number of ferrocene loads increased the growth height of VACNT carpets on metal and isolating thin films. The effective growth rates of VACNT carpets were 10.4, 7.13, 4.8, 3, 2, 9.55, 7.6, 13.3, and 32.32 μm/min, respectively, on Cu, Ti, Au, Pt, Mo, Cr, Ag, Ni, and Si. VACNT carpets such as SiO 2 and Al 2O 3 also grew on the isolating thin films with growth rates of 37.28 and 23.8 μm/min, respectively. By controlling the growth parameters, the growth of VACNT carpets on selective substrates can be controlled.

Effect of ammonia gas etching on growth of vertically aligned carbon nanotubes/nanofibers

The etching effect of ammonia (NH 3) on the growth of vertically aligned nanotubes/nanofibers (CNTs) was investigated by direct-current plasma enhanced chemical vapor deposition (DC-PECVD). NH 3 gas etches Ni catalyst layer to form nanoscale islands while NH 3 plasma etches the deposited amorphous carbon. Based on the etching effect of NH 3 gas on Ni catalyst, the differences of growing bundles of CNTs and single strand CNTs were discussed; specifically, the amount of optimal NH 3 gas etching is different between bundles of CNTs and single strand CNTs. In contrast to the CNT carpet growth, the single strand CNT growth requires shorter etching time (5 min) than large catalytic patterns (10 min) since nano dots already form catalyst islands for CNT growth. Through removing the plasma pretreatment process, the damage from being exposed at high temperature substrate occurring during the plasma generation time is minimized. High resolution transmission electron microscopy (HTEM) shows fishbone structure of CNTs grown by PECVD.