scispace - formally typeset
Search or ask a question
Author

Douglas M. Smith

Other affiliations: University of New Mexico, Lucideon
Bio: Douglas M. Smith is an academic researcher from Los Alamos National Laboratory. The author has contributed to research in topics: Laser ablation & Nitride. The author has an hindex of 3, co-authored 3 publications receiving 113 citations. Previous affiliations of Douglas M. Smith include University of New Mexico & Lucideon.

Papers
More filters
Journal ArticleDOI
TL;DR: In this paper, an aluminum target was laser ablated in an oxygen (O2) atmosphere, producing nanosize alumina (Al2O3) powder with surface areas between 135 and 250 m2/g, corresponding to primary particle sizes ranging from 7 to 3 nm in radius.
Abstract: An aluminum (Al) target was laser ablated in an oxygen (O2) atmosphere, producing nanosize alumina (Al2O3) powder. The powder surface area decreased (and the particle size increased) with both increasing oxygen pressure and laser fluence. All powders produced had surface areas between 135 and 250 m2/g, corresponding to primary particle sizes ranging from 7 to 3 nm in radius. Phase evolution with temperature was studied via X-ray diffraction. These powders showed a direct transformation from γ- to α-alumina at approximately 1200°C, bypassing other transition alumina phases, while still maintaining small particle size ( 30 nm). Despite the nanosize particles, green densities equal to 54% of the skeletal density (i.e., true density of the solid phase) were obtained by uniaxial pressing at 40 MPa.

87 citations

Journal ArticleDOI
TL;DR: In this paper, an aluminum target was laser ablated in a nitrogen (N2) atmosphere, producing aluminum nitride (AlN) powder, which was calcined at 900°C for 2 h.
Abstract: An aluminum (Al) target was laser ablated in a nitrogen (N2) atmosphere, producing aluminum nitride (AlN) powder. These powders were calcined at 900°C for 2 h. Powders were produced at various nitrogen pressures, and the calcined powders were tested for unreacted aluminum content, using differential thermal analysis (DTA). The AlN powder, produced at a laser fluence of 12 J/cm2 and a nitrogen pressure of 10.0 kPa (75 torr), showed no evidence of unreacted aluminum by DTA and was phase-pure AlN by X-ray diffraction (XRD). The surface area of this powder is 82 m2/g, corresponding to a particle size of ∼11 nm, which is in good agreement with TEM observations.

30 citations

Journal ArticleDOI
TL;DR: In this article, an aluminum target was laser ablated in a nitrogen (N2) atmosphere, producing aluminum nitride (AlN) powder, which was calcined at 900°C for 2 h.
Abstract: An aluminum (Al) target was laser ablated in a nitrogen (N2) atmosphere, producing aluminum nitride (AlN) powder. These powders were calcined at 900°C for 2 h. Powders were produced at various nitrogen pressures, and the calcined powders were tested for unreacted aluminum content, using differential thermal analysis (DTA). The AlN powder, produced at a laser fluence of 12 J/cm2 and a nitrogen pressure of 10.0 kPa (75 torr), showed no evidence of unreacted aluminum by DTA and was phase-pure AlN by X-ray diffraction (XRD). The surface area of this powder is 82 m2/g, corresponding to a particle size of ∼11 nm, which is in good agreement with TEM observations.

4 citations


Cited by
More filters
Journal ArticleDOI
08 Aug 1997-Science
TL;DR: In this article, it was shown that α-Al 2 O 3 is the thermodynamically stable phase of coarsely crystalline aluminum oxide and becomes thermodynamic stable at surface areas greater than 125 square meters per gram at 800 kelvin.
Abstract: Corundum, α-Al 2 O 3 , is the thermodynamically stable phase of coarsely crystalline aluminum oxide, but syntheses of nanocrystalline Al 2 O 3 usually result in γ-Al 2 O 3 . Adsorption microcalorimetry, thermogravimetric analyses, and Brunauer-Emmett-Teller adsorption experiments, coupled with recently reported high-temperature solution calorimetry data, prove that γ-Al 2 O 3 has a lower surface energy than α-Al 2 O 3 and becomes energetically stable at surface areas greater than 125 square meters per gram and thermodynamically stable at even smaller surface areas (for example, 75 square meters per gram at 800 kelvin). The results are in agreement with recent molecular dynamics simulations and provide conclusive experimental evidence that differences in surface energy can favor the formation of a particular polymorph.

818 citations

Journal ArticleDOI
TL;DR: In this article, the main applications of current interest including some discussions of the underlying phenomena are dealt with, including some experiments for synthesizing nanoparticles in the gas phase aiming at any of the above mentioned functional applications.

713 citations

Book
14 Dec 1998
TL;DR: A review of recent advances in aerosol generation of materials is presented in this article, where gas-to-particle and spray processes (spray pyrolysis) for powder generation and various routes for film generation are discussed from the experimental and theoretical perspectives.
Abstract: Recent advances in aerosol generation of materials are reviewed Gas-to-particle and spray processes (spray pyrolysis) for powder generation and various routes for film generation are discussed from the experimental and theoretical perspectives The range of materials generated by these routes has increased in recent years to include fullerenes and ceramic superconductors Many metals and various oxide and nonoxide ceramics have also been added to the list of materials generated by gas-phase routes Established aerosol routes such as vapor condensation have found widespread applications for generation of nanophase materials The formation of quantum dots via aerosol approaches has also been demonstrated The theoretical understanding of gas-to-particle conversion routes has advanced to include the finite rate of particle fusion or sintering occurring after collisions of particles The modeling of spray pyrolysis systems has provided insight into the control of particle morphology and reactor design In th

526 citations

Journal ArticleDOI
TL;DR: Corundum, α-Al2O3, appears to be the thermodynamically stable phase of aluminum oxide at all common pressure and temperature conditions, but attempted syntheses of nanocrystalline Al 2O3 usually res...
Abstract: Corundum, α-Al2O3, appears to be the thermodynamically stable phase of aluminum oxide at all common pressure and temperature conditions, but attempted syntheses of nanocrystalline Al2O3 usually res...

243 citations

Journal ArticleDOI
TL;DR: In this paper, the properties of nanoparticle aerosols of size ranging from 4.9 to 13 nm, generated by laser ablation of solid surfaces are described, where the authors used a pulsed excimer laser to irradiate a rotating target mounted in a cylindrical chamber 4'cm in diameter and 18'cm long.
Abstract: The properties of nanoparticle aerosols of size ranging from 4.9 nm to 13 nm, generated by laser ablation of solid surfaces are described. The experimental system consisted of a pulsed excimer laser, which irradiated a rotating target mounted in a cylindrical chamber 4 cm in diameter and 18-cm long. Aerosols of oxides of aluminum, titanium, iron, niobium, tungsten and silicon were generated in an oxygen carrier gas as a result of a reactive laser ablation process. Gold and carbon aerosols were generated in nitrogen by non-reactive laser ablation. The aerosols were produced in the form of aggregates of primary particles in the nanometer size range. The aggregates were characterized using a differential mobility analyzer and electron microscopy. Aggregate mass and number concentration, electrical mobility size distribution, primary particle size distribution and fractal dimension were measured. System operating parameters including laser power (100 mJ/pulse) and frequency (2 Hz), and carrier gas flow rate (1 l/min) were held constant. A striking result was the similarity in the properties of the aerosols. Primary particle size ranged between 4.9 and 13 nm for the eight substances studied. The previous studies with flame reactors produced a wider spread in primary particle size, but the order of increasing primary particle size follows the same trend. While the solid-state diffusion coefficient probably influences the size of the aerosol in flame reactors, its effect is reduced for aerosols generated by laser ablation. It is hypothesized that the reduced effect can be explained by the collision-coalescence mechanism and the very fast quenching of the laser generated aerosol.

199 citations