Laser-induced Chemical Vapor Deposition Research Articles

Innovative accident tolerant fuel concept enabled through direct manufacturing technology

Nuclear energy is one of the largest sources of carbon-free electricity in the world. Some countries are looking at new ways to support and revitalize the nuclear sector since the Fukushima disaster. The accident tolerant fuel program is geared toward improving the safety of nuclear energy by investigating materials that can replace or modify the current uranium-dioxide nuclear fuel and zirconium-based cladding. This research program is being supported by all major nuclear countries since 2011. The practical limitations on allowable uranium enrichment has taken the focus away from the most promising fuels with high radioactivity retention such as tristructural isotropic particle fuel. To overcome such enrichment limitation, a new fuel concept is proposed using advanced ceramic direct manufacturing with laser-induced chemical vapor deposition. The fuel-as-fiber concept is an accident-tolerant fuel design that features high thermal conductivity, strong capability of radioactivity retention and most importantly requires reasonable enrichment levels with uranium nitride as the fuel. In this work, the initial fabrication of uranium-based fuel with laser-induced chemical vapor deposition technology is demonstrated. Then an advanced multi-physics guided modeling approach based on finite element analysis codes and informed by the manufacturing capabilities is developed to accelerate the advancement of fuel-as-fiber concept for use in current light-water reactor technology. The detailed thermomechanical analysis showed promising results for viability of the innovative fuel-as-fiber concept. The predicted stresses in the fuel structural materials were similar to the case of tristructural isotropic particle fuel experience base that has shown excellent reliability in retention of fuel radioactivity at high temperatures.

Structural and mechanical characterization of carbon fibers grown by laser induced chemical vapor deposition at hyperbaric pressures

Laser induced chemical vapor deposition (LCVD) of freestanding carbon fibers from ethylene at hyperbaric pressures was investigated. Relationships between processing conditions, growth behavior, microstructure, and mechanical properties of the carbon fibers were established. It is found that the fiber growth rates are limited by surface reaction kinetics at low temperatures and limited by gas phase nucleation at high temperatures. At higher pressures and intermediate temperatures, growth becomes mass transport limited whereupon the fibers exhibit drastic changes in morphology and microstructure from a core-shell, smooth appearance to nodular formations. The tensile strengths of the carbon fibers grown by LCVD are generally poor due to the nature of graphitic carbon deposits. However, the Weibull modulus among the LCVD grown carbon fibers was found to be very high. Effects of processing conditions and microstructure on the fiber strengths are observed and discussed.

Femtosecond laser-induced chemical vapor deposition of tungsten quasi-periodic structures on silicon substrates

A rapid, maskless deposition technique for writing conductive tracks via femtosecond laser-induced chemical vapor deposition has been developed. The technique can be used for a range of applications, one example being writing conductive tracks for the construction of microelectronic devices. The process uses pulsed ultrafast laser with 300 fs pulse length and 1030 nm wavelength for the direct deposition of tungsten tracks on silicon substrates from metal organic tungsten hexacarbonyl precursors. The written tracks consisted of wavy quasi-periodic walls with thickness of 200 nm and a periodicity of 500 nm, aligned perpendicular to the linear polarization of the laser beam. Fixed number of pulses spot dwell experiments revealed that a thin film formed before quasi-periodic structures grew on top of that thin film. The peak intensity threshold for the deposition process (8.64 × 1010 W/cm2) was lower than the threshold for surface modification on the silicon substrate (3.34 × 1011 W/cm2) at the same scanning speed of 10 μm/s and repetition rate of 502 kHz. Negligible damage to the underlying substrate was observed in the cross section. Scan speeds up to 100 μm s−1 were achieved in the process. The elemental composition of the deposits was measured to be 80% by weight tungsten in energy-dispersive x-ray spectroscopy methods and the resistivity of the deposit was measured to be 290 μΩ cm using the transfer length method.

Formation mechanisms of boron oxide films fabricated by large-area electron beam-induced deposition of trimethyl borate.

Boron-containing materials are increasingly drawing interest for the use in electronics, optics, laser targets, neutron absorbers, and high-temperature and chemically resistant ceramics. In this article, the first investigation into the deposition of boron-based material via electron beam-induced deposition (EBID) is reported. Thin films were deposited using a novel, large-area EBID system that is shown to deposit material at rates comparable to conventional techniques such as laser-induced chemical vapor deposition. The deposition rate and stoichiometry of boron oxide fabricated by EBID using trimethyl borate (TMB) as precursor is found to be critically dependent on the substrate temperature. By comparing the deposition mechanisms of TMB to the conventional, alkoxide-based precursor tetraethyl orthosilicate it is revealed that ligand chemistry does not precisely predict the pathways leading to deposition of material via EBID. The results demonstrate the first boron-containing material deposited by the EBID process and the potential for EBID as a scalable fabrication technique that could have a transformative effect on the athermal deposition of materials.

Dual-Wavelength In Situ Pyrometry During Additive Formation of Fibers by Laser-Induced Deposition

A dual-wavelength pyrometry system has been demonstrated for measuring the reaction zone temperature for a series of carbon and SiC fibers grown additively by hyperbaric-pressure laser-induced chemical vapor deposition. The results demonstrate an inverse relationship between reaction zone size and temperature measurement noise. Though the noise can obscure transient effects associated with unstable growth, use of individual wavelength signals has been demonstrated as a means to deconvolute these features. Consequently, the use of in situ temperature measurements helps to link the final morphology of the fiber to its real-time growth behavior.

The study of nitrogen inclusion in carbon nanotubes obtained by catalytic laser-induced chemical vapour deposition (C-LCVD)

Nitrogen doped carbon nanotubes were grown on Fe2O3 nanoparticles deposited on silicon substrates, by laser-induced chemical vapour deposition of acetylene/ammonia mixtures. The concentration of the nitrogen has been controlled in the range 1–6 atomic% by adjusting the flow rate of ammonia, pressure and laser power. XPS and Raman spectroscopy were used to quantitatively assess the compositional and structural properties of the nitrogen-doped carbon nanotubes (NCNTs). First order Raman spectra were deconvoluted assuming five vibrational modes and the integrated peak intensity ratio ID/IG and I2D/IG of all samples are displayed. We demonstrate that the relative amount of sp2 CC carbon has the same trend as ID4/IG and the pyrrolic relative amount exhibits the same trend as I2D4/IG. The high resolution TEM images are consistent with the Raman and XPS results, revealing that the surface of the NCNTs outer walls becomes more distorted at the highest content of N while the inner walls of the nanotube preserve a high crystallinity, corresponding to the lowest ID/IG ratio.

Laser-induced reduction and in-situ optical spectroscopy of individual plasmonic copper nanoparticles for catalytic reactions

Copper (Cu) can provide an alternative to gold (Au) for the development of efficient, low-cost and low-loss plasmonic nanoparticles (NPs), as well as selective nanocatalysts. Unlike Au, the surface oxidation of Cu NPs can be an issue restricting their applicability. Here, we selectively reduce the Cu NPs by low power laser illumination in vacuum and use dark-field scattering to reveal in real time the optical signatures of the reduction process and its influence on the Cu NP plasmonic resonance. We then study reactive processes at the single particle level, using individual Cu catalyst nanoparticles for the selective laser-induced chemical vapour deposition of germanium nanostructures.

Fabrication of highly ultramicroporous carbon nanofoams by SF6-catalyzed laser-induced chemical vapor deposition

We have developed a laser-induced chemical vapor deposition (LCVD) method for preparing nanocarbons with the aid of SF6. This method would offer advantages for the production of aggregates of nanoscale foams (nanofoams) at high rates. Pyrolysis of the as-grown nanofoams induced the high surface area (1120m2g−1) and significantly enhanced the adsorption of supercritical H2 (16.6mgg−1 at 77K and 0.1MPa). We also showed that the pyrolized nanofoams have highly ultramicroporous structures. The pyrolized nanofoams would be superior to highly microporous nanocarbons for the adsorption of supercritical gases.

Structure and optical properties of conglobate hydrogenated amorphous carbon films prepared by pulsed laser-induced chemical vapor deposition

The hydrogenated amorphous carbon films were prepared by pulsed laser-induced chemical vapor deposition at room temperature. In the proposed technique, the styrene with no catalyst was used as a carbon source. The conglobate microstructure of the films was observed. The influence of various laser repetition rates on the structure and optical properties of the films was investigated. With the increase of laser repetition rate, the films possessed more aromatic bonds, more sp3 carbon and less sp2 clustering. A broader optical band gap and lower photoluminescence intensity was simultaneously found. The results were attributed to the different distribution of electronic localization around the level edge with different laser repetition rates. Therefore, we can tune the structure and optical properties of the films according to change the laser repetition rates.

Controlling Nanowire Growth by Light.

Individual Au catalyst nanoparticles are used for selective laser-induced chemical vapor deposition of single germanium nanowires. Dark-field scattering reveals in real time the optical signatures of all key constituent growth processes. Growth is initially triggered by plasmonic absorption in the Au catalyst, while once nucleated the growing Ge nanowire supports magnetic and electric resonances that then dominate the laser interactions. This spectroscopic understanding allows real-time laser feedback that is crucial toward realizing the full potential of controlling nanomaterial growth by light.

(Invited) UV Excimer Laser Assisted Heteroepitaxy of (Si)GeSn on Si(100)

Fabrication of Photonic Integrated Circuits (PICs) using CMOS compatible direct bandgap Group-IV heterostructures is of increasing concern from scientific, technological, and economic point of view. Growth of group IV alloys, such as the Silicon-Germanium-Tin (Si-Ge-Sn) binaries and ternaries through CMOS compatible techniques is therefore of particular interest. This contribution presents UV-Laser based processes, such as Laser induced Chemical Vapor Deposition (LCVD) and Pulsed Laser Induced Epitaxy (PLIE) combined with conventional processing techniques, for material synthesis as well as results obtained growing different (Si)GeSn binary and ternary systems for material and lattice engineering. Synthesis of epitaxial (Si)GeSn alloys with above 10% Sn in large areas and of SiGeSn/GeSn micropatterns, through scanning and mask projection assisted PLIE, respectively, will be discussed. Emphasis will be placed on the influence of processing parameters on compositional and structural properties of the epitaxial alloys.

(Invited) UV Excimer Laser Assisted Heteroepitaxy of (Si)GeSn on Si(100)

The perspective to achieve Photonic Integrated Circuits (PICs) using CMOS compatible direct bandgap Group-IV heterostructures is highly attractive from scientific, technological, and economic point of view. Research activities on modeling, growing and processing adequate Group-IV materials and heterostructures for developing new emitters, waveguides and detectors have therefore been intensified over the last decade.Several approaches directed to material and strain engineering of Silicon and Germanium micro- or nanostructures were studied and already led to significant progress in this field. However, to ensure further prospects, more versatile material systems would be of interest and theoretical as well as experimental studies in this direction identified the Silicon-Germanium-Tin (SiGeSn) ternary as an attractive but also challenging system. These studies converged finally to the intensive exploration on how to produce and process Germanium-Tin (GeSn) binary and Silicon containing Germanium-Tin (Si)GeSn alloys, that are heteroepitaxially grown on Silicon wafers or virtual Germanium (v-Ge) substrates. As a result, the possibility to tune independently band gap and lattice constant over a wide range and to achieve, by adjusting strain and composition, the predicted direct bandgap material within this system, is currently explored. As a consequence, (Si)GeSn is now expected to boost the development of new high speed micro- and nanoelectronic components, as well as of CMOS compatible opto-electronic devices and of new GeSn and SiGeSn strain platforms on conventional Si wafers, as successfully employed in Si(Ge) technology [1-4].Major issues in growing and processing these binary and ternary (Si)GeSn alloys are the large mismatch between the lattices of the pure elements (0.54nm for Si, 57nm for Ge, and 0.69nm for a-Sn), the very low solid phase solubility of Sn in Ge of less than 1% and the tendency of Sn to cluster and to form surface precipitates, when subjected to thermal treatment [5-7].Due to these interconnected issues, increased attention has been devoted to, Si-technology compatible, non-equilibrium growth techniques that allow such an independent adjustment of lattice parameters and band gaps in a precise and cost efficient way. Among several well established techniques, like low temperature Molecular Beam Epitaxy (MBE) and Chemical Vapor Deposition (CVD), also Pulsed Laser Induced Epitaxy (PLIE) using Excimer lasers has been identified as a promising candidate.This contribution will give an overview on recent achievements obtained through 193 nm ArF-Excimer Laser PLIE of (Si)GeSn alloys on v-Ge substrates and on Si wafers. The technique itself is based on local rapid melting and solidification processes, that are induced by 25 ns short ArF-Excimer laser pulses and are completed within an ultra-short time scale (<500 ns). Applying these heat treatments to Si, Ge and Sn heterostructures that are grown on Si(100), leads to epitaxial alloys with gradients in composition and strain that depend on the intermixing of these elements in the molten phase and ultimately on the thermal gradients produced by adjusting “precursor-heterostructure”, laser energy density and number of laser pulses [8-11].This contribution will give an overview on the following PLIE approaches that have been used to obtain the binary and ternary alloys with different crystallinity, strain and stoichiometry, including Sn content of up to 20% and their respective advantages or drawbacks:i) PLIE treatment of low cost precursor heterostructures, like thermally evaporated Sn on Si(100) or on v-Ge.ii) PLIE of v-Ge wafers coated with Sn films through Molecular Beam Epitaxy (MBE).iii) PLIE of Boron doped or intrinsic a-Si:H or a-Ge:H films, produced by Laser Induced Chemical Vapour Deposition (LCVD) and MBE, on Sn/v-Ge.iv) Scanning of the substrate through the laser beam to achieve large area treatment.v) Production of micro-patterns by Mask Projection Assisted PLIE. Acknowledgment This work was partially financed by Spanish (MAT2008-02350, MAT2011-24077), Galician (2010/83) and local P.P.00VI131H64102 (UVigo) grants, co-financed by FEDER funds.

Co-catalytic Absorption Layers for Controlled Laser-Induced Chemical Vapor Deposition of Carbon Nanotubes

The concept of co-catalytic layer structures for controlled laser-induced chemical vapor deposition of carbon nanotubes is established, in which a thin Ta support layer chemically aids the initial Fe catalyst reduction. This enables a significant reduction in laser power, preventing detrimental positive optical feedback and allowing improved growth control. Systematic study of experimental parameters combined with simple thermostatic modeling establishes general guidelines for the effective design of such catalyst/absorption layer combinations. Local growth of vertically aligned carbon nanotube forests directly on flexible polyimide substrates is demonstrated, opening up new routes for nanodevice design and fabrication.

Support Vector Machine Classification of Single Walled Carbon Nanotube Growth Parameters

ABSTRACTSelective single-walled carbon nanotube (SWNT) growth is a challenging problem, limiting their use in a wide variety of applications. Significant degrees of freedom in these experiments may lead to synthesis of multi-walled carbon nanotubes (MWNTs), which are less preferred. Thus, a method for constraining the synthesis results to only SWNTs is desired. A machine learning based approach for selectively growing SWNTs using a laser-induced chemical vapor deposition growth system is introduced. This approach models the complex relationships between the associated synthesis parameters to predict SWNT growth. The parameters under consideration include argon, ethylene, hydrogen and carbon dioxide partial pressures, growth temperature, and water vapor concentration. The catalyst consists of 10 nm of alumina and 1 nm of nickel deposited onto 10 µm diameter silicon pillars with a height of 10 µm. Determination of SWNT growth is performed through in-situ Raman spectroscopy using a 532 nm excitation laser. A total of 121 experiments are used to train a SWNT vs. MWNT classifier with a resulting model accuracy of 94.21%. The classifier model is applied to a range of simulated inputs, and the subset of these inputs that meet a &gt;90% probability of SWNT growth are investigated further. The simulated inputs consist of 531,201,645 unique growth parameter combinations spanning the entire parameter space. A reduced dataset of 449,117 growth parameter combinations define 90% probability of SWNT growth according to the model. Randomly selected input parameters from this reduced dataset were tested experimentally, resulting in SWNT growth for all performed experiments validating the classifier model. This approach maps input growth conditions to SWNT growth selectivity using a limited set of experimental data and allows for further investigation into SWNT growth rates and chiral dependencies.

Effect of the manufacturing parameters on the structure of nitrogen-doped carbon nanotubes produced by catalytic laser-induced chemical vapor deposition

Nitrogen-containing carbon nanotubes (CNx-NTs), with a relatively high level of nitrogen doping were prepared by the catalytic laser-induced CVD method. The nanotubes were catalytically grown directly on a silicon substrate from C2H2/NH3 gaseous precursors. X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) give firm evidence for the nitrogen doping. As determined by XPS, the N concentration for the prepared CNx-NTs increases from 3.6 to 30.6 at.% with increasing ammonia concentration and pressure. TEM images indicate that the nanotubes are bamboo like. As the nitrogen content increases, there is a transition from the bamboo shape with few defects and little distortion to a corrugated structure with a much larger number of defects. Raman spectroscopy revealed that with increasing nitrogen concentration, there is more disorder and defects, together with an increase in ID/IG ratio. By energy-filtering TEM, a higher N concentration was found on the outer amorphous nanolayer than in the compartment core of the nanotubes.

Carbon Nanotubes Grown by CO2 Laser-Induced Chemical Vapor Deposition on Quartz

Carbon Nanotubes Grown by CO2 Laser-Induced Chemical Vapor Deposition on Quartz

Optical feedback mechanisms in laser induced growth of carbon nanotube forests

We study optical feedback mechanisms occurring during growth of multi-walled carbon nanotube forests on transparent substrates. Growth is realised via laser-induced chemical vapour deposition using iron nanoparticle catalysts. In situ Raman and reflection spectroscopy employed clearly distinguish three growth phases. In the initial seed phase, growth of carbon nanostructures increases the laser absorption and this feedback enables growth of radially orientated carbon nanotubes. Understanding the laser interaction with the growing nanostructure holds the key towards controlled growth and opens up new routes to nanostructure and nanodevice design and fabrication.

A Molecular Dynamics Study on the Constraint Conditions of the Particle Growth Process in Laser Synthesis of Nanopowders

Laser-induced chemical vapor deposition (LICVD) is a nanopowder synthesis method in which the nanoparticles of a synthetic product undergo nucleation, growth, and agglomeration. The growth process is crucial because it directly determines the growth rate and final size of nanoparticles. In this paper, the nanoparticle growth process is analyzed through a molecular dynamics study, and the process is divided into five steps. In addition, this study explains the microscopic heat and mass transfer processes that occur in the surrounding space and on the particulate surface. Three constraint conditions that may restrict the growth process, namely, transfer constraint, surface constraint, and temperature constraint conditions, are proposed and modeled. To calculate the final diameter and the nanoparticle growth rate, formulae for the constraint conditions are developed. The behavior of four gases in the particulate growth zone is discussed in detail.

Fast growth of graphene patterns by laser direct writing

Rapid single-step fabrication of graphene patterns was developed using laser-induced chemical vapor deposition (LCVD). A laser beam irradiates a thin nickel foil in a CH4 and H2 environment to induce a local temperature rise, thereby allowing the direct writing of graphene patterns in precisely controlled positions at room temperature. Line patterns can be achieved with a single scan without pre- or postprocesses. Surprisingly, the growth rate is several thousand times faster than that of general CVD methods. The discovery and development of the LCVD growth process provide a route for the rapid fabrication of graphene patterns for various applications.

Laser direct writing of graphene patterns

ABSTRACTRapid growth of single-layer graphene using laser-induced chemical vapor deposition (LCVD) with a visible CW laser (λ = 532 nm) irradiation at room temperature was investigated. In this study, an optically-pumped solid-state laser with a wavelength of 532 nm irradiates a thin nickel foil to induce a local temperature rise, thereby allowing the direct writing of graphene patterns about ~10 μm in width with high growth rate on precisely controlled positions. It is demonstrated that the fabrication of graphene patterns can be achieved with a single scan for each graphene pattern using LCVD with no annealing or preprocessing of the substrate. The scan speed reaches to about ~50 um/s, which indicates that the graphene pattern with 1:1 aspect ratio (x:y) can be grown in 0.2 sec. The patterned graphene on nickel was transferred to SiO2/Si substrate for fabrication of electrical circuits and sensor devices.