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24 Jun 2002

Volume 80, Issue 25, pp. 4687-4873

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High-contrast photoluminescent patterns in lithium fluoride crystals produced by soft x-rays from a laser-plasma source

G. Baldacchini, F. Bonfigli, F. Flora, R. M. Montereali, D. Murra, E. Nichelatti, A. Faenov, and T. Pikuz

Appl. Phys. Lett. 80, 4810 (2002); http://dx.doi.org/10.1063/1.1486476 (3 pages) | Cited 18 times

Online Publication Date: 17 June 2002

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A technique using soft x-rays and extreme ultraviolet light generated by a laser-plasma source has been investigated for producing low-dimensionality photoluminescent patterns based on active color centers in lithium fluoride (LiF) crystals. Strong visible photoluminescence at room temperature has been observed in LiF crystals from fluorescent patterns obtained by masking the incoming radiation. This technique is able to produce colored patterns with high spatial resolution on large areas and in short exposure times as compared with other coloration methods. © 2002 American Institute of Physics.
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78.55.Fv Solid alkali halides
61.72.J- Point defects and defect clusters
61.80.Cb X-ray effects
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
71.55.Ht Other nonmetals
61.82.Ms Insulators
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Field emission from open ended aluminum nitride nanotubes

V. N. Tondare, C. Balasubramanian, S. V. Shende, D. S. Joag, V. P. Godbole, S. V. Bhoraskar, and M. Bhadbhade

Appl. Phys. Lett. 80, 4813 (2002); http://dx.doi.org/10.1063/1.1482137 (3 pages) | Cited 115 times

Online Publication Date: 17 June 2002

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This letter reports the field emission measurements from the nanotubes of aluminum nitride which were synthesized by gas phase condensation using the solid-vapor equilibria. A dc arc plasma reactor was used for producing the vapors of aluminum in a reactive nitrogen atmosphere. Nanoparticles and nanotubes of aluminum nitride were first characterized by transmission electron microscope and tube dimensions were found to be varying from 30 to 200 nm in diameter and 500 to 700 nm in length. These tubes were mixed with nanoparticles of size range between 5 and 200 nm in diameter. Tungsten tips coated with these nanoparticles and tubes were used as a field emitter. The field emission patterns display very interesting features consisting of sharp rings which were often found to change their shapes. The patterns are attributed to the open ended nanotubes of aluminum nitride. A few dot patterns corresponding to the nanoparticles were also seen to occur. The Fowler–Nordheim plots were seen to be nonlinear in nature, which reflects the semi-insulating behavior of the emitter. The field enhancement factor is estimated to be 34 500 indicating that the field enhancement due to the nanometric size of the emitter is an important cause for the observed emission. © 2002 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
61.46.-w Structure of nanoscale materials
81.07.De Nanotubes

Controlled alignment of carbon nanofibers in a large-scale synthesis process

Vladimir I. Merkulov, A. V. Melechko, M. A. Guillorn, M. L. Simpson, D. H. Lowndes, J. H. Whealton, and R. J. Raridon

Appl. Phys. Lett. 80, 4816 (2002); http://dx.doi.org/10.1063/1.1487920 (3 pages) | Cited 61 times

Online Publication Date: 17 June 2002

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Controlled alignment of catalytically grown carbon nanofibers (CNFs) at a variable angle to the substrate during a plasma-enhanced chemical vapor deposition process is achieved. The CNF alignment is controlled by the direction of the electric field lines during the synthesis process. Off normal CNF orientations are achieved by positioning the sample in the vicinity of geometrical features of the sample holder, where bending of the electric field lines occurs. The controlled growth of kinked CNFs that consist of two parts aligned at different angles to the substrate normal also is demonstrated. © 2002 American Institute of Physics.
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81.07.De Nanotubes
61.46.-w Structure of nanoscale materials
81.05.U- Carbon/carbon-based materials
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth

Oxygen and ozone oxidation-enhanced field emission of carbon nanotubes

Sheng-Chin Kung, Kuo Chu Hwang, and I. Nan Lin

Appl. Phys. Lett. 80, 4819 (2002); http://dx.doi.org/10.1063/1.1485315 (3 pages) | Cited 43 times

Online Publication Date: 17 June 2002

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Vertically aligned carbon nanotube (CNT) arrays were grown on p-type silicon wafer using acetylene and iron phthalocyanine as the sources of hydrocarbons and catalysts, respectively. The CNT arrays were treated by chemical reagents, such as oxygen (O2), ozone (O3), bromine, and acids. When treated by O2 and O3, the emission current of the CNT array was increased ∼800% along with a decrease of the onset field emission voltage from 0.8 to 0.6 V/μm. Other chemical treatments, e.g., bromination and acid oxidation, lead to poorer field emission performance. The effects of these chemical processes on the field emission properties of CNT arrays will be discussed. © 2002 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.65.Mq Oxidation
61.46.-w Structure of nanoscale materials

Structure study of Se species in channels of AlPO4-5 crystals

Irene L. Li and Z. K. Tang

Appl. Phys. Lett. 80, 4822 (2002); http://dx.doi.org/10.1063/1.1489100 (3 pages) | Cited 5 times

Online Publication Date: 17 June 2002

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The thermal adsorption/desorption process of selenium species in the channels of AlPO4-5 (AFI) single crystals is studied by simultaneous thermogravimetry (TG) and differential scanning calorimetry (DSC). There exist two peaks in the TG and DSC curves, indicating that two different structures of Se species, helical chain and 8-member ring, coexist in the AFI channels. Polarized Raman and optical absorption spectra show that the helical chains are highly aligned along the channel direction, while the Se8 rings are randomly oriented in the channels. The helical chains have a lowest optical absorption band at 2.6 eV, which is strongly polarization dependent, while the 8-member rings have a lowest absorption band at 3.0 eV that varies slowly with the light polarization. © 2002 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
68.43.Mn Adsorption kinetics
78.30.-j Infrared and Raman spectra
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
68.43.Vx Thermal desorption

Triplex molecular layers with nonlinear nanomechanical response

V. V. Tsukruk, H.-S. Ahn, D. Kim, and A. Sidorenko

Appl. Phys. Lett. 80, 4825 (2002); http://dx.doi.org/10.1063/1.1486267 (3 pages) | Cited 7 times

Online Publication Date: 17 June 2002

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The molecular design of surface structures with built-in mechanisms for mechanical energy dissipation under nanomechanical deformation and compression resistance provided superior nanoscale wear stability. We designed robust, well-defined trilayer surface nanostructures chemically grafted to a silicon oxide surface with an effective composite modulus of about 1 GPa. The total thickness was within 20–30 nm and included an 8 nm rubber layer sandwiched between two hard layers. The rubber layer provides an effective mechanism for energy dissipation, facilitated by nonlinear, giant, reversible elastic deformations of the rubber matrix, restoring the initial status due to the presence of an effective nanodomain network and chemical grafting within the rubber matrix. © 2002 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
81.07.Bc Nanocrystalline materials
62.25.-g Mechanical properties of nanoscale systems
07.10.Cm Micromechanical devices and systems
61.46.-w Structure of nanoscale materials
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
62.20.F- Deformation and plasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
62.20.Qp Friction, tribology, and hardness
81.40.Pq Friction, lubrication, and wear
68.35.Af Atomic scale friction
62.20.D- Elasticity

Patterning surfaces with colloidal particles using optical tweezers

J. P. Hoogenboom, D. L. J. Vossen, C. Faivre-Moskalenko, M. Dogterom, and A. van Blaaderen

Appl. Phys. Lett. 80, 4828 (2002); http://dx.doi.org/10.1063/1.1488690 (3 pages) | Cited 44 times

Online Publication Date: 17 June 2002

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A method for positioning colloidal particles on surfaces in any designed pattern is described. Optical tweezers are used to bring particles from a reservoir to the substrate where opposite surface charges are used to immobilize particles on the surface. Both chemical surface modification and polyelectrolyte coating of either substrate or colloids make the method generally applicable. We show that using this technique large, two-dimensional patterns can be created that can be dried without distortions by critical point drying. As an example we show the positioning of 79 nm radius metallodielectric particles and we show how two-dimensional patterns can be used to direct three-dimensional epitaxial crystal growth. The method is inexpensive, relatively fast, and can be fully automated. © 2002 American Institute of Physics.
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68.35.Dv Composition, segregation; defects and impurities
82.70.Dd Colloids

Self-organized, ordered array of coherent orthogonal column nanostructures in epitaxial La0.8Sr0.2MnO3 thin films

J. C. Jiang, E. I. Meletis, and K. I. Gnanasekar

Appl. Phys. Lett. 80, 4831 (2002); http://dx.doi.org/10.1063/1.1489078 (3 pages) | Cited 16 times

Online Publication Date: 17 June 2002

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We report direct transmission electron microscopy evidence of self-organized, ordered array of coherent orthogonal column nanostructures in epitaxial La0.8Sr0.2MnO3 (LSMO) thin films grown on (001) LaAlO3 (LAO) using pulsed-laser ablation. The orthogonal column nanostructures have an orthorhombic structure and are epitaxially grown on a continuous cubic perovskite LSMO thin-film layer that is epitaxially grown on (001) LAO substrate. The orthogonal column nanostructures exhibit a narrow size distribution, with the short edges having a length of about 25 nm and the long edge (growth direction) of ∼ 70 nm. The short edges are parallel to the [100] and [010] directions of LAO. All columns are encapsulated by uniformly thick amorphous-like grain boundaries and are “quasi” periodically arranged along the [100] and [010] directions of LAO. The continuous epitaxial layer of cubic perovskite structure grows along the [001] direction with an in-plane orientation relationship with respect to the substrate of 〈100〉LSMOC∥〈100〉LAO, while the orthorhombic column structures grow along its [1math0] direction with an in-plane orientation relationship of [110]LSMOO∥[100]LAO and [001]LSMOO∥[010]LAO. The spontaneous formation of such self-organized, coherent column nanostructures can be considered to follow a type of Stranski–Krastanov growth mode without Oswald ripening. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
75.70.Ak Magnetic properties of monolayers and thin films
61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
81.15.Fg Pulsed laser ablation deposition
61.72.Mm Grain and twin boundaries

Photoluminescence of size-separated silicon nanocrystals: Confirmation of quantum confinement

G. Ledoux, J. Gong, F. Huisken, O. Guillois, and C. Reynaud

Appl. Phys. Lett. 80, 4834 (2002); http://dx.doi.org/10.1063/1.1485302 (3 pages) | Cited 134 times

Online Publication Date: 17 June 2002

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Silicon nanocrystals with diameters between 2.5 and 8 nm were prepared by pulsed CO2 laser pyrolysis of silane in a gas flow reactor and expanded through a conical nozzle into a high vacuum. Using a fast-spinning molecular-beam chopper, they were size-selectively deposited on dedicated quartz substrates. Finally, the photoluminescence of the silicon nanocrystals and their yield were measured as a function of their size. It was found that the photoluminescence follows very closely the quantum-confinement model. The yield shows a pronounced maximum for sizes between 3 and 4 nm. © 2002 American Institute of Physics.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Ap Elemental semiconductors
81.15.Fg Pulsed laser ablation deposition
61.46.-w Structure of nanoscale materials
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.07.Bc Nanocrystalline materials
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