Monolithic material fabrication by chemical vapour deposition

The subatmospheric pressure chemical vapour deposition (CVD) process has been used to fabricate theoretically dense, highly pure, void free and large area infrared-optical and ceramic materials such as ZnS, ZnSe, CdS, CdZnTe, Si and SiC. In this paper, an overview of a large scale CVD process is presented emphasizing the important technical and engineering issues such as control of material properties, injector heating and its effect on growth, selection of an appropriate mandrel material, grain growth, material bowing, nodular growth, and storage, transport and scrubbing of a large quantity of hazardous chemicals. Further, the flow pattern in our CVD reactors is described and its importance in achieving good control over thickness and composition uniformity over large areas is discussed.     

Low-temperature fabrication of superconducting FeSe thin films by pulsed laser deposition

Superconducting FeSe thin films were prepared at a substrate temperature of 320 °C by pulsed laser deposition. X-ray diffraction and transmission electron microscopic analyses showed that highly c-axis-orientated and high-quality films were obtained on various substrate materials, including single-crystal MgO, LaAlO₃, SrTiO₃ and (100)-Si, and amorphous-SiO_x, at such low temperature. From transport measurements all the films showed low-temperature structural phase transition at ∼ 60-90 K and superconducting transition at onset temperature varies from ∼ 7 K to < 2 K, depending on the substrate used. The transport property of FeSe film on Si was found most different from all the others, in spite of their similarity in structural analysis. Chemical analysis demonstrated that Fe and Se homogeneously distributed in the film and the stoichiometry of FeSe and the bonding states of Fe and Se are as well uniform along the film growth direction.     

Study of the fabrication of infrared-transparent dielectric aspheric deposits by continuous-wave laser deposition

The fabrication of dielectric aspheric deposits with optical refractive functionality by a continuous-wave laser deposition technique is reported for the particular case of an amorphous As-S alloy. The influence of both the laser power and fabrication times in the deposit thickness profile is studied from the measurements performed by a mechanical profilometer. The use of press-powder tablets as starting material have been found to have a significant effect in the deposition efficiency, and indications of a transition from a discrete to a continuous nature of the target, have also been observed. A notable reproducibility has been found both in the material stoichiometry and thickness profiles. The optical function of the fabricated refractive aspheric deposits has been measured to be similar to one performed by axicon lenses.     

Powder effects in SiC matrix layered structures fabricated using selective area laser deposition vapor infiltration (SALDVI)

Silicon carbide has been deposited by laser-induced chemical vapor infiltration from the gas precursor tetramethylsilane, Si(CH₃)₄, into loosely packed powder layers of SiC, ZrO₂-Y₂O₃, or Mo. The goal is to produce dense layered structures of arbitrary shape by computer controlled laser scanning where the pore spaces between the powder particles are filled with solid material deposited from the gas phase using the selective area laser deposition vapor infiltration (SALDVI) process. Layered samples were fabricated for each powder material using both single line (bar) and multiple line (slab) laser scan patterns and 10 Torr Si(CH₃)₄, 2.5 m/s scan speed, 1000°C target temperature, and 120 m layer thickness. Samples of SiC and ZrO₂-Y₂O₃ are prone to surface cracking in the bar geometry, and cracking and delamination of layers in the slab geometry. Samples fabricated with Mo powder have no cracks or delamination defects in either bar or slab geometry as well as a better surface appearance.     

Additive particle deposition and selective laser processing-a computational manufacturing framework

Many additive manufacturing technologies involve the deposition of particles onto a surface followed by selective, targeted, laser heating. This paper develops a modular computational framework which combines the various steps within this overall process. Specifically, the framework synthesizes the following:

• particle dynamics, which primarily entails: (a) the movement of the particles induced by contact with the surface, (b) particle-to-particle contact forces and (c) near-field interaction and external electromagnetic fields.
• laser-input, which primarily entails: (a) absorption of laser energy input and (b) beam interference (attenuation) from particles and
• particle thermodynamics, which primarily entails: (a) heat transfer between particles in contact by conduction and (b) subsequent thermal softening of the particles.

Numerical examples are provided and extensions are also addressed for two advanced processing scenarios involving solid-liquid-gas phase transformations.     

Microstructure and properties of Ti/Al lightweight graded material by direct laser deposition

A novel Ti/Al lightweight graded material was fabricated successfully using the direct laser deposition process, with the composition continuously changing from 100 vol.-% Ti6Al4V to 100 vol.-% AlSi10Mg. Microstructures and phase transformations were characterised, and the mechanical properties of the Ti/Al lightweight graded material were investigated. It was found that element concentrations followed a nearly linear relationship along the compositional gradient. The maximum hardness reached 619 HV in the ‘II’ zones, and then it decreased gradually to 214 HV at the outermost layer, with the increase in the proportion of AlSi10Mg. The values for the ultimate tensile strength were above 400?MPa, and the fracture surfaces indicated a transition from ductile to brittle fracture along the graded direction.     

Optimization of selective emitter fabrication method for solar cells using a laser grooving

In this paper, screen-printing laser grooved buried contact (LGBC) method was applied, which is compatible with the existing screen-printed solar cell equipment and facilities. Experiments were performed in order to optimize short circuit current (I(sc)), open circuit voltage (V(oc)) and fill factor of high efficiency solar cells. To enhance I(sc), V(oc) and efficiency, heavy doping was performed at low sheet resistance in the laser grooved region of the cell. In contrast, light doping was carried out at a high sheet resistance in the non-laser grooved region. To increase fill factor, porous silicon found on the wafer after dipping in an HF solution to remove SiN(x), was cleared. The fabricated screen-printing LGBC solar cell using a 125 mm x 125 mm single crystalline silicon wafer exhibited an efficiency of 17.2%. The results show that screen-printing LGBC method can be applied for high efficiency solar cells.     

Facile fabrication of transparent superhydrophobic surfaces by spray deposition

Herein, we present a one-step facile spray-deposition process for fabricating a new superhydrophobic surface with a novel statistical copolymer. The polymeric material is relatively inexpensive, easily prepared, transparent, solvent-processable, very simple, and applicable to rugged substrates. The materials presented herein also feature a near-perfect superhydrophobic surface with a static water contact angle of 178° and a transmittance of higher than 75% at 550 nm wavelength.     

Preparation of cubic alumina and scandia doped zirconia and its thin film fabrication by pulsed laser deposition technique

Alumina and scandia doped zirconia was prepared through a soft chemistry synthesis route and sintered at 1873 K. X-ray diffraction patterns indicate a pure cubic phase for the composition of 0.88ZrO₂-0.112Sc₂O₃-0.008Al₂O₃. Thin films were fabricated on Al₂O₃ 〈0001〉 substrates using pulsed laser deposition technique. Dense films of 0.941 μm thickness were obtained at 873 and 1023 K substrate temperatures at an oxygen partial pressure of 15 Pa. The ionic conductivity of both thin film and sintered pellet was measured using ac impedance spectroscopy in air. The conductivity values are higher for thin films compared to that of sintered pellets.     

Fabrication of material patterns by grid-assisted deposition

We developed a simple patterning approach where a grid with micrometer rule is used in order to control the deposition of a solute. Ordered patterns were obtained, over large areas, in a few seconds. The patterning process we propose here is fast and low cost. It can also be applied to diverse soluble molecular and supramolecular species. We also investigated what parameters have to be changed in order to have total control on the final tridimensional architecture of the material.     

一种潜在的激光制冷介质-罗丹明B掺杂PMMA

报道了罗丹明B掺杂PMMA材料制作过程及材料吸收和荧光光谱实验。吸收光谱表明，PMMA样品从紫外到近红外范围存在较小的吸收。罗丹明B／PMMA样品吸收光谱主要反映罗丹明B的吸收特征，其吸收峰中心波长位于550nm。荧光光谱显示，以630nm激发，反斯托克斯荧光峰位于595nm，能量差为0．11eV。该材料辐射反斯托克斯荧光，可用于激光制冷领域的研究。     

Low-temperature deposition of iridium thin films by pulsed laser deposition

Extremely smooth iridium (Ir) thin films were deposited on Si(1 0 0) substrate at lower temperature than 300 °C by pulsed laser deposition (PLD) technique using Ir target in a vacuum atmosphere. The crystal orientation, surface morphology, and resistivity of the Ir thin films were systematically determined as a function of substrate temperature. Well-crystallized and single-phase Ir thin films with (1 1 1) preferred orientation were obtained at substrate temperature of 200-300 °C. The surface roughness increased with the increasing of substrate temperature. Likewise, the room-temperature resistivity of Ir thin films decreased with increasing substrate temperature, showing a low value of (10.7±0.1) μΩ cm at 300 °C.     

Organic nanowire-templated fabrication of alumina nanotubes by atomic layer deposition

Alumina nanotubes were fabricated by a template method. Tris-(8-hydroxyquinoline) gallium (GaQ3) organic nanowires were used as a soft template for coating with alumina using an atomic layer deposition technique. The deposition was conducted at 25 degrees C by using trimethylaluminum and distilled water as the precursors of Al2O3. Amorphous alumina nanotubes were obtained after removing the GaQ3 by dissolving in toluene or by heat treatment at 350 degrees C. The amorphous nanotubes could be crystallized by heating at 900 degrees C for 1 h in vacuum.     

Solid freeform fabrication by extrusion and deposition of semi-solid alloys

Solid Freeform Fabrication (SFF) refers to techniques that create prototypes by a layer wise deposition of material. There are several techniques available, none of which allows the production of metallic prototypes without post processing, such as debinding or sintering. One of the SFF techniques, Fused Deposition Modeling (FDM®), is a well established process for thermoplastic materials such as for example ABS. Based on the FDM® technique, a process is being developed that allows the extrusion and deposition of semi-solid metals (EDSSM). The microstructure of an alloy in the semi-solid state has been investigated as a function of parameters used for rapid prototyping with SFF techniques. The extrusion and deposition processes are dependent on the rheological properties of the semi-solid metal, which in turn are dependent on the microstructure. The effect of microstructure and rheological properties on the extrusion and deposition processes is discussed.     

Freeform fabrication by controlled droplet deposition of powder filled melts

A method of directly delivering highly filled hot-melt particulate suspensions using piezoelectric droplet generators is presented. Highly fluid suspensions of alumina in a mixture of long and short chain n-alkanes containing up to 40% by volume solids have been prepared. These fluids were subsequently used to deposit ceramic objects using a commercial ink-jet printer. These objects were then successfully sintered to near full density. The deposition mechanism is controlled by the propagation of acoustic waves in a droplet generating chamber. We have observed the change in resonance of this chamber with the introduction of particles into a fluid. A simple model is developed to explain these observations in terms of changes in the speed of sound of the fluid on the addition of solid particles in suspension.     

Influence of laser deposition patterns on part distortion, interior quality and mechanical properties by laser solid forming (LSF)

Present work applied a kind of new deposition pattern, fractal deposition pattern, in the LSF process. The influences of different depositing patterns (fractal, offset and raster) on the parts’ deformation, interior quality and mechanical properties are also investigated. The finite element method (FEM) simulation results show that the offsetout (the offset from the outside to the inside) and fractal deposition patterns generate the temperature distribution with the circular and eccentric circle symmetry at the end of deposition process, respectively. There are smaller temperature gradients using these two kinds of deposition patterns than those by the raster and offsetin (the offset from the inside to the outside) deposition patterns. It is also found that the magnitude of the transient temperature gradient has a critical effect on part distortion during LSF process. The fractal deposition pattern generates the smallest parts’ deformation, followed by offsetout. The parts interior quality investigation with fractal and offsetout deposition patterns shows that the overlap should be increased to 50% to avoid pore defects. Moreover, we find that adopting arc path instead of square path at the corner locations and “semi-spot vibration” strategy for the offset and fractal deposition patterns respectively can produce better LSFed parts’ quality.     

Trabecular-like Ti-6Al-4V scaffolds for orthopedic: fabrication by selective laser melting and in vitro biocompatibility

Porous metal scaffolds play an important role in the orthopedic field, due to their wide applications in prostheses implantation. Some previous studies showed that the scaffolds with trabecular bone structure reconstructed via computed tomography had satisfactory biocompatibility. However, the reverse modeling scaffolds were inflexible for customized design. Therefore, a top-down designing biomimetic bone scaffold with favorable mechanical performances and cytocompatibility is urgently demanded for orthopedic implants. An emerging additive manufacturing technique, selective laser melting, was employed to fabricate the trabecular-like porous Ti-6Al-4 V scaffolds with varying irregularities (0.05-0.5) and porosities (48.83%–74.28%) designed through a novel Voronoi-Tessellation based method. Micro-computed tomography and scanning electron microscopy were used to characterize the scaffolds’ morphology. Quasi-static compression tests were performed to evaluate the scaffolds’ mechanical properties. The MG63 cells culture in vitro experiments, including adhesion, proliferation, and differentiation, were conducted to study the cytocompatibility of scaffolds. Compressive tests of scaffolds revealed an apparent elastic modulus range of 1.93–5.24 GPa and an ultimate strength ranging within 44.9–237.5 MPa, which were influenced by irregularity and porosity, and improved by heat treatment. Furthermore, the in vitro assay suggested that the original surface of the SLM-fabricated scaffolds was favorable for osteoblasts adhesion and migration because of micro scale pores and ravines. The trabecular-like porous scaffolds with full irregularity and higher porosity exhibited enhanced cells proliferation and osteoblast differentiation at earlier time, due to their preferable combination of small and large pores with various shapes. This study suggested that selective laser melting-derived Ti-6Al-4 V scaffold with the trabecular-like porous structure designed through Voronoi-Tessellation method, favorable mechanical performance, and good cytocompatibility was a potential biomaterial for orthopedic implants.