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7 Mar 2005

Volume 86, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 86, 103102 (2005); http://dx.doi.org/10.1063/1.1875734 (3 pages)

Tadashi Kawazoe, Kiyoshi Kobayashi, and Motoichi Ohtsu
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Sensitivity of exciton spin relaxation in quantum dots to confining potential

S. Mackowski, T. Gurung, H. E. Jackson, L. M. Smith, W. Heiss, J. Kossut, and G. Karczewski

Appl. Phys. Lett. 86, 103101 (2005); http://dx.doi.org/10.1063/1.1875763 (3 pages) | Cited 11 times

Online Publication Date: 28 February 2005

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We observe a strong dependence of the exciton spin relaxation in CdTe quantum dots on the average dot size and the depth of the confining potential. After rapid thermal annealing, which increases the average dot size and leads to weaker confinement, we measure the spin relaxation time of the quantum dot excitons to be 1.5 ns, as compared to 4.8 ns found previously for the as-grown CdTe quantum dots. The annealed CdTe quantum dots exhibit also smaller values of the absolute polarization of the quantum dot emission. This dramatic enhancement of the spin scattering efficiency upon annealing is attributed to increased mixing between different spin states in larger CdTe quantum dots.
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73.21.La Quantum dots
71.35.-y Excitons and related phenomena
78.67.Hc Quantum dots
78.55.Et II-VI semiconductors
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
61.72.Cc Kinetics of defect formation and annealing

Optical nanofountain: A biomimetic device that concentrates optical energy in a nanometric region

Tadashi Kawazoe, Kiyoshi Kobayashi, and Motoichi Ohtsu

Appl. Phys. Lett. 86, 103102 (2005); http://dx.doi.org/10.1063/1.1875734 (3 pages) | Cited 24 times

Online Publication Date: 28 February 2005

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We have proposed and demonstrated a nanophotonic device, which concentrates optical energy in a nanometric region. We call this device an “optical nanofountain,” which uses the energy transfer among quantum dots and acts like a light-harvesting photosynthetic system. We experimentally concentrated optical energy in a nanometric area less than 20 nm by using the optical nanofountain which was composed of CuCl quantum dots embedded in a NaCl matrix. Its focal diameter of 20 nm corresponds to the numerical aperture of 12.
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87.80.Cc Optical trapping
42.82.Gw Other integrated-optical elements and systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
87.50.W- Optical/infrared radiation effects
37.10.Vz Mechanical effects of light on atoms, molecules, and ions

Fabrication and optical investigation of a high-density GaN nanowire array

T. Wang, F. Ranalli, P. J. Parbrook, R. Airey, J. Bai, R. Rattlidge, and G. Hill

Appl. Phys. Lett. 86, 103103 (2005); http://dx.doi.org/10.1063/1.1879110 (3 pages) | Cited 14 times

Online Publication Date: 28 February 2005

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A high-density GaN nanowire array has been successfully fabricated through self-organized nanometer-sized holes as mask appearing in InGaN layer. The self-organized nanometer-sized holes are naturally formed during InGaN epitaxial growth using metalorganic chemical vapor deposition technology by modifying growth parameters. Scanning electron microcopy and atomic force microcopy have been used to characterize them. Optical investigation was carried out by room-temperature photoluminescence, which indicated that strong emission from an n-GaN nanowire array was observed at 367 nm, the near-band edge emission wavelength for n-type GaN. The results show that excellent optical properties of the GaN nanowire array can be obtained by this technique. It is important to point out that GaN-based nanolaser or nano-light-emitting diodes with different emission wavelengths can be potentially achieved using this technology.
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81.05.Ea III-V semiconductors
81.07.Bc Nanocrystalline materials
81.16.Dn Self-assembly
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Cr III-V semiconductors
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Ps Atomic force microscopy (AFM)
61.46.-w Structure of nanoscale materials
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.16.Nd Micro- and nanolithography
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Raman scattering and field-emission properties of RuO2 nanorods

C. L. Cheng, Y. F. Chen, R. S. Chen, and Y. S. Huang

Appl. Phys. Lett. 86, 103104 (2005); http://dx.doi.org/10.1063/1.1879106 (3 pages) | Cited 24 times

Online Publication Date: 28 February 2005

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We report Raman scattering and field emission properties of rutile RuO2 nanorods obtained by metalorganic chemical vapor deposition. The RuO2 nanorods have lengths up to several micrometers and diameters in the range of 10–50 nm. The nanosize dependencies of the peak shift and the broadening of the three first-order Raman modes agree well with those calculated on the basis of the phonon confinement model. The unique geometrical features of RuO2 nanorods exhibit a strong effect on field enhancement (β ∼ 1153), which results in a low threshold field (Eth ∼ 4.9 V/μm) defined at the beginning of emission. The low turn-on field for driving a current of 10 μA/cm2 is about 10.3 V/μm, which is comparable with amorphous carbon film. Our results indicate that RuO2 nanorods provide an excellent alternative for field emitter due to several advantages, including nanometer structure, natural conductor, enhanced resistance to oxidation, and long-term stability.
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81.07.Bc Nanocrystalline materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.30.Hv Other nonmetallic inorganics
79.70.+q Field emission, ionization, evaporation, and desorption
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.16.-c Methods of micro- and nanofabrication and processing

Optoelectronic properties of three-dimensional ZnO hybrid structure

Min-Chang Jeong, Byeong-Yun Oh, Woong Lee, and Jae-Min Myoung

Appl. Phys. Lett. 86, 103105 (2005); http://dx.doi.org/10.1063/1.1872209 (3 pages) | Cited 22 times

Online Publication Date: 28 February 2005

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Three-dimensional (3D) ZnO hybrid structure was fabricated by growing a ZnO buffer layer, a ZnO nanowire array, and a ZnO film continuously through the control of supersaturation conditions. Lower and upper ends of vertically aligned nanowires in this hybrid structure formed seamless interfacial contacts with the buffer layer and the film for current conduction. Photocurrent was generated only when the ultraviolet (UV) light (λ = 350 nm) was irradiated. This structure also exhibited different atmosphere-dependent responses to the UV light. The optoelectronic properties of the 3D structure are attributed to the photogenerated carriers and the surface reaction of negatively charged oxygen species in ZnO nanowires.
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85.60.-q Optoelectronic devices
73.50.Pz Photoconduction and photovoltaic effects
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
61.46.-w Structure of nanoscale materials
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
61.82.Rx Nanocrystalline materials

Highly ordered CdS nanoparticle arrays on silicon substrates and photoluminescence properties

Y. Lei, W. K. Chim, H. P. Sun, and G. Wilde

Appl. Phys. Lett. 86, 103106 (2005); http://dx.doi.org/10.1063/1.1869545 (3 pages) | Cited 24 times

Online Publication Date: 1 March 2005

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Highly ordered cadmium sulphide (CdS) nanoparticle (NP) arrays were fabricated on silicon (Si) substrates using ultrathin alumina membranes as evaporation masks. The CdS NPs are polycrystalline and are composed of ultrasmall closely packed nanocrystallites. These crystallites increase in size as the duration of the CdS evaporation process increases. When the thickness of the NPs changes from about 10 to 50 nm, the size of the crystallites increases from about 5–14 to 20–40 nm. Photoluminescence measurements on the CdS NP arrays show a strong emission spectrum with two subbands that are attributed to band-edge and surface-defect emissions. The peak position and width of the band-edge emission band are closely related to the size of the crystallites in the CdS NPs.
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81.05.Dz II-VI semiconductors
81.16.-c Methods of micro- and nanofabrication and processing
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors
85.40.Hp Lithography, masks and pattern transfer
61.46.-w Structure of nanoscale materials

Self-assembly of faceted Ni nanodots on Si(111)

D. Aurongzeb, S. Patibandla, M. Holtz, and H. Temkin

Appl. Phys. Lett. 86, 103107 (2005); http://dx.doi.org/10.1063/1.1880452 (3 pages) | Cited 8 times

Online Publication Date: 2 March 2005

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We report the formation of Ni nanodots on Si(111). Island density is varied by annealing temperature and time and is studied using atomic force microscopy (AFM) and magnetic force microscopy. Activation energies of 0.09±0.02 and 0.31±0.05 eV are observed for the formation of these islands. These are associated with Ni surface self-diffusion across the (111) and (110) Ni facets, respectively. For brief 500 °C anneals, regular nanodots are observed with self-limiting sizes of height ∼ 16 nm and area 180 nm×260 nm, while density exhibits a power-law time dependence with exponent 1.13±0.12. AFM analysis reveals a “truncated hut” shape consistent with (110) top and (111) sidewall surfaces.
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75.50.Cc Other ferromagnetic metals and alloys
81.07.Bc Nanocrystalline materials
81.16.Dn Self-assembly
81.40.Gh Other heat and thermomechanical treatments
75.50.Tt Fine-particle systems; nanocrystalline materials
61.46.-w Structure of nanoscale materials
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.35.Fx Diffusion; interface formation
66.30.Fq Self-diffusion in metals, semimetals, and alloys

Shape recovery of nanoscale imprints in a thermoset “shape memory” polymer

Brent A. Nelson, William P. King, and Ken Gall

Appl. Phys. Lett. 86, 103108 (2005); http://dx.doi.org/10.1063/1.1868883 (3 pages) | Cited 15 times

Online Publication Date: 2 March 2005

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This letter reports temperature-dependent recovery of atomic force microscope tip-formed indentations in a thermoset shape memory polymer. The indentations are made at both room temperature and 69 °C, and then recovered at temperatures between 40 °C and 70 °C. The shape recovery is more complete for higher anneal temperatures, and is relatively independent of time for 102–104 s. The experiments show shape memory in the 1–100 nm size scale.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.40.Jj Elasticity and anelasticity, stress-strain relations
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
61.46.-w Structure of nanoscale materials
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Gy Mechanical properties; surface strains
62.20.D- Elasticity
62.20.M- Structural failure of materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Gh Other heat and thermomechanical treatments
68.37.Ps Atomic force microscopy (AFM)

First-principles study of Ti-doped sodium alanate surfaces

Jorge Íñiguez and Taner Yildirim

Appl. Phys. Lett. 86, 103109 (2005); http://dx.doi.org/10.1063/1.1881787 (3 pages) | Cited 25 times

Online Publication Date: 3 March 2005

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We have performed first-principles calculations of thick slabs of Ti-doped sodium alanate (NaAlH4), which allows one to study the system energetics as the dopant progresses from the surface to the bulk. Our calculations predict that Ti stays on the surface, substitutes for Na, and attracts a large number of H atoms to its vicinity. Molecular dynamics simulations suggest that the most likely product of the Ti doping is the formation of H-rich TiAln(n>1) compounds on the surface, and hint at the mechanism by which Ti enhances the reaction kinetics of NaAlH4.
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71.15.Nc Total energy and cohesive energy calculations
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
61.72.up Other materials
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)

Freezing/melting of Lennard-Jones fluids in carbon nanotubes

F. R. Hung, K. E. Gubbins, R. Radhakrishnan, K. Szostak, F. Béguin, G. Dudziak, and M. Sliwinska-Bartkowiak

Appl. Phys. Lett. 86, 103110 (2005); http://dx.doi.org/10.1063/1.1862786 (3 pages) | Cited 4 times

Online Publication Date: 3 March 2005

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We report molecular simulation and experimental results for the freezing/melting behavior of Lennard-Jones fluids adsorbed in pores of cylindrical geometry, using simple models for multiwalled carbon nanotubes (MWNTs) of inner diameter 5 nm. For cylindrical pores, our results for a D = 9.7σff MWNT show no formation of regular three-dimensional crystalline structures. They also suggest that the outer layers experience an increase in the freezing temperature, while the inner layers provoke a depression in the freezing temperature with respect to the bulk freezing point. Dielectric relaxation spectroscopy shows a solid-fluid transition at 234 K for CCl4 in these MWNTs that is in qualitative agreement with that determined in our simulations for the inner adsorbed layers.
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64.70.D- Solid-liquid transitions
68.43.Mn Adsorption kinetics
68.43.De Statistical mechanics of adsorbates
61.25.Em Molecular liquids
68.43.Hn Structure of assemblies of adsorbates (two- and three-dimensional clustering)
61.46.-w Structure of nanoscale materials

Direct micromachining of quartz glass plates using pulsed laser plasma soft x-rays

Tetsuya Makimura, Hisao Miyamoto, Youichi Kenmotsu, Kouichi Murakami, and Hiroyuki Niino

Appl. Phys. Lett. 86, 103111 (2005); http://dx.doi.org/10.1063/1.1882750 (3 pages) | Cited 17 times

Online Publication Date: 3 March 2005

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We have investigated direct micromachining of quartz glass, using pulsed laser plasma soft x-rays (LPSXs) having a potential capability of nanomachining because the diffraction limit is ∼ 10 nm. The LPSX’s were generated by irradiation of a Ta target with 532 nm laser light from a conventional Q switched Nd:YAG laser at 700 mJ/pulse. In order to achieve a sufficient power density of LPSX’s beyond the ablation threshold, we developed an ellipsoidal mirror to obtain efficient focusing of LPSXs at around 10 nm. It was found that quartz glass plates are smoothly ablated at 45 nm/shot using the focused and pulsed LPSX’s.
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42.70.Ce Glasses, quartz
42.62.-b Laser applications
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.79.Bh Lenses, prisms and mirrors
41.50.+h X-ray beams and x-ray optics
52.77.-j Plasma applications
52.38.Mf Laser ablation
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Ms Insulators
61.80.Cb X-ray effects
61.82.-d Radiation effects on specific materials

Formation mechanism of fivefold deformation twins in nanocrystalline face-centered-cubic metals

Y. T. Zhu, X. Z. Liao, and R. Z. Valiev

Appl. Phys. Lett. 86, 103112 (2005); http://dx.doi.org/10.1063/1.1879111 (3 pages) | Cited 37 times

Online Publication Date: 3 March 2005

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Fivefold deformation twins have been recently observed in nanocrystalline face-centered-cubic (fcc) metals and alloys synthesized by severe plastic deformation techniques. However, numerous molecular dynamics simulations in the literature have not observed fivefold deformation twins in nanocrystalline fcc metals. The discrepancy between experimental observations and molecular dynamics simulations has raised an issue on their formation mechanism and conditions. Here we propose a sequential twinning mechanism that provides a clear path for the formation of fivefold deformation twins. The mechanism requires an orientation change of applied stresses, which explains why molecular dynamics simulations under a constant load orientation do not produce fivefold deformation twins.
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81.05.Bx Metals, semimetals, and alloys
81.07.Bc Nanocrystalline materials
61.72.Mm Grain and twin boundaries
61.72.Bb Theories and models of crystal defects
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
62.25.-g Mechanical properties of nanoscale systems
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Role of the microstructure on the magnetic properties of Co-doped ZnO nanoparticles

B. Martínez, F. Sandiumenge, Ll. Balcells, J. Arbiol, F. Sibieude, and C. Monty

Appl. Phys. Lett. 86, 103113 (2005); http://dx.doi.org/10.1063/1.1880433 (3 pages) | Cited 23 times

Online Publication Date: 3 March 2005

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We report on the magnetic and structural properties of Co-doped ZnO nanoparticles prepared by the vaporization-condensation method in a solar reactor. X-ray diffraction data and high-resolution electron microscopy (HREM) confirm the total absence of metallic Co clusters or any other phase different from würtzite-type ZnO. Electron energy loss spectroscopy analyses performed on several particles indicate that the oxidation state of Co is +2 and yield an average Co concentration of 4.5 at. %, in good agreement with the nominal composition. Transmission electron microscopy micrographs show that shape and size of the particles are strongly dependent on the preparation conditions, as well as the microstructure as evidenced by HREM. Ferromagnetism is only found in samples prepared in vacuum revealing a close correlation between microstructure and magnetic properties.
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75.50.Pp Magnetic semiconductors
75.50.Tt Fine-particle systems; nanocrystalline materials
61.46.-w Structure of nanoscale materials
81.05.Dz II-VI semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.75.-c Magnetic properties of nanostructures
81.16.Pr Micro- and nano-oxidation
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.07.Bc Nanocrystalline materials
68.37.Lp Transmission electron microscopy (TEM)
79.20.Uv Electron energy loss spectroscopy
81.65.Mq Oxidation

Covalently linked deoxyribonucleic acid with multiwall carbon nanotubes: Synthesis and characterization

Weiwei Chen, Chi Hung Tzang, Jianxin Tang, Mengsu Yang, and Shuit Tong Lee

Appl. Phys. Lett. 86, 103114 (2005); http://dx.doi.org/10.1063/1.1880439 (3 pages) | Cited 9 times

Online Publication Date: 3 March 2005

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We have developed a multistep method to covalently link functionalized multiwall carbon nanotubes (MWNT) to deoxyribonucleic acid (DNA) oligonucleotides. X-ray photoelectron spectroscopy was used to characterize the initial chemical modification to form amine-terminated MWNTs, which were then covalently combined with DNA. The morphology recorded by atomic force microscopy gave direct and explicit imaging of the resulting DNA-MWNT adducts, showing that chemical functionalization occurred at the ends and sidewalls of MWNTs. The present methodology is an important first step in realizing a DNA-guided self-assembly process for carbon nanotubes.
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87.14.G- Nucleic acids
81.07.De Nanotubes
81.16.Be Chemical synthesis methods
87.85.J- Biomaterials
61.46.-w Structure of nanoscale materials
87.15.B- Structure of biomolecules
81.16.Ta Atom manipulation
79.60.Jv Interfaces; heterostructures; nanostructures
87.85.Qr Nanotechnologies-design
87.85.Rs Nanotechnologies-applications
87.64.Dz Scanning tunneling and atomic force microscopy
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ps Atomic force microscopy (AFM)
68.37.Xy Scanning Auger microscopy, photoelectron microscopy
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
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