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24 May 2010

Volume 96, Issue 21, Articles (21xxxx)

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Appl. Phys. Lett. 96, 213701 (2010); http://dx.doi.org/10.1063/1.3431628 (3 pages)

Satish Rao, Saurabh Raj, Stefan Balint, Carlota Bardina Fons, Susana Campoy, Montserrat Llagostera, and Dmitri Petrov
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Silicon nanocrystals dispersed in water: Photosensitizers for molecular oxygen

B. Goller, S. Polisski, H. Wiggers, and D. Kovalev

Appl. Phys. Lett. 96, 211901 (2010); http://dx.doi.org/10.1063/1.3432349 (3 pages) | Cited 2 times

Online Publication Date: 24 May 2010

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We report on the synthesis of freestanding silicon spheres having sizes in the range of 3–10 nm. As-prepared luminescent silicon nanocrystals have H-passivated surface. Therefore, energy transfer from excitons confined in Si nanocrystals to oxygen molecules is found to be efficient. It is demonstrated that a termination of silicon nanocrystal H-passivated hydrophobic surface by lipids provides their water solubility. We found that this procedure preserves photosensitizing ability of silicon nanocrystals. Therefore, this material system can potentially be employed for a variety of biomedical applications.
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73.22.-f Electronic structure of nanoscale materials and related systems
61.46.-w Structure of nanoscale materials
33.50.Hv Radiationless transitions, quenching
82.37.Vb Single molecule photochemistry

Hyperfine fields in nanocrystalline Fe–Zr–B probed by 57Fe nuclear magnetic resonance spectroscopy

Marcel Miglierini, Adriana Lančok, and Jaroslav Kohout

Appl. Phys. Lett. 96, 211902 (2010); http://dx.doi.org/10.1063/1.3431612 (3 pages)

Online Publication Date: 24 May 2010

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In nanocrystalline Fe90Zr7B3, hyperfine fields belonging to the amorphous residual matrix are distinguished from those of bcc-Fe nanograins by nuclear magnetic resonance spectroscopy on 57Fe nuclei. With this technique, the nanograins located in magnetic domains can be distinguished from those positioned in domain walls. Structural features of core and surface regions of both types of nanograins are described. Presence of small ( ∼ 0.2%) inclusions of Zr was identified in the core of nanograins.
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71.70.Jp Nuclear states and interactions
76.60.-k Nuclear magnetic resonance and relaxation
75.50.Tt Fine-particle systems; nanocrystalline materials
75.75.Fk Domain structures in nanoparticles
75.60.Ch Domain walls and domain structure

Stress control in polycrystalline thin films—reduction in adatoms diffusion into grain boundaries via surfactants

Yi Yang, Hanchen Huang, S. K. Xiang, and Eric Chason

Appl. Phys. Lett. 96, 211903 (2010); http://dx.doi.org/10.1063/1.3435473 (3 pages) | Cited 2 times

Online Publication Date: 25 May 2010

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The diffusion of adatoms into grain boundaries (GBs) of polycrystalline thin film during vapor deposition affects the stress that develops and the film’s subsequent performance. This Letter reports a proposed mechanism of modifying the stress by controlling adatom diffusion into GBs through the use of surfactants. Based on polycrystalline kinetic Monte Carlo simulations of Cu〈111〉 thin films with In surfactant, the authors demonstrate that the proposed mechanism is feasible. Further, the authors show that the reduction is due to the decrease in effective adatom diffusivity, which dominates over the increase in adatom concentration.
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68.60.Bs Mechanical and acoustical properties
66.30.Lw Diffusion of other defects
61.72.Mm Grain and twin boundaries
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Ultrafast dynamics of excitons in delafossite CuScO2 thin films

Fucai Liu, T. Makino, H. Hiraga, T. Fukumura, Yongfa Kong, and M. Kawasaki

Appl. Phys. Lett. 96, 211904 (2010); http://dx.doi.org/10.1063/1.3436548 (3 pages) | Cited 1 time

Online Publication Date: 25 May 2010

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Ultrafast carrier dynamics were investigated in a delafossite CuScO2, a material with a remarkably large binding energy of exciton ( ∼ 0.4 eV), using femtosecond transient transmission spectroscopy. Differential transmission spectra showed dispersive structures in the excitonic resonance energies. We have observed a delayed rise-up on a time scale of 10 ps, suggesting slow carrier cooling. It is followed by a slower decay, time constant of which corresponds to the lifetime of exciton (approximately 0.75 ns). These results were analyzed in terms of the generalized many-body Elliott model, accounting for a screening effect of excitons.
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78.66.Nk Insulators
71.35.-y Excitons and related phenomena
78.30.Hv Other nonmetallic inorganics
78.40.Ha Other nonmetallic inorganics
78.47.jb Transient absorption
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

The role of Zn interstitials in cobalt-doped ZnO diluted magnetic semiconductors

Tongfei Shi, Zhenguo Xiao, Zhijun Yin, Xinhua Li, Yuqi Wang, Hongtao He, Jiannong Wang, Wenshen Yan, and Shiqiang Wei

Appl. Phys. Lett. 96, 211905 (2010); http://dx.doi.org/10.1063/1.3437082 (3 pages) | Cited 3 times

Online Publication Date: 26 May 2010

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Co-doped ZnO samples Zn1−xCoxO and CoyZn1−yO were prepared by the sol-gel and magnetron sputtering methods, respectively. Although the Co K-edge extended x-ray absorption fine structure spectra show that the doped Co ions are located at the Zn substitutional sites for both Zn1−xCoxO (x ≤ 0.05) and CoyZn1−yO (y ≤ 0.05) samples, magnetic measurements show paramagnetism in Zn1−xCoxO (x ≤ 0.05) and high temperature ferromagnetism in CoyZn1−yO (y ≤ 0.05). An experimental and numerical study of the O K-edge x-ray absorption near-edge structure spectra reveals that the incorporation of the Zn interstitials in the lattice is crucial to the appearance of high temperature ferromagnetism in CoyZn1−yO (y ≤ 0.05) samples.
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75.50.Pp Magnetic semiconductors
61.72.jj Interstitials
75.50.Dd Nonmetallic ferromagnetic materials
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
75.20.Ck Nonmetals
78.70.Dm X-ray absorption spectra

Polarization control of electroluminescence from vertically stacked InAs/GaAs quantum dots

Tomoya Inoue, Masaki Asada, Nami Yasuoka, Osamu Kojima, Takashi Kita, and Osamu Wada

Appl. Phys. Lett. 96, 211906 (2010); http://dx.doi.org/10.1063/1.3441403 (3 pages) | Cited 5 times

Online Publication Date: 27 May 2010

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We have developed a technique to control the polarization dependence of quantum dot (QD)-semiconductor optical amplifiers (SOAs) using vertically stacked self-assembled InAs QDs with moderately thick intermediate layers. By increasing the number of stacking layers, the transverse magnetic polarization component of electroluminescence (EL) from the cleaved edge surface of the SOA has been enhanced dramatically. Broadband and almost isotropic EL with a polarization difference of less than 1.2 dB has been demonstrated in a 1.3 μm optical communication band for nine-layer stacked QDs in the active region of the SOA.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
78.60.Fi Electroluminescence
81.16.Dn Self-assembly
68.18.-g Langmuir-Blodgett films on liquids

Dispersion measurements of a 1.3 μm quantum dot semiconductor optical amplifier over 120 nm of spectral bandwidth

M. Bagnell, J. Davila-Rodriguez, A. Ardey, and P. J. Delfyett

Appl. Phys. Lett. 96, 211907 (2010); http://dx.doi.org/10.1063/1.3430742 (3 pages) | Cited 1 time

Online Publication Date: 27 May 2010

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Group delay and higher order dispersion measurements are conducted on a 1.3 μm quantum dot semiconductor optical amplifier at various injection currents. White-light spectral interferometry is performed, along with a wavelet transform to recover the group delay. The group delay, group velocity dispersion, and higher order dispersion terms are quantified. The measurement spans both ground state and first excited state transitions, ranging from 1200 to 1320 nm. The group velocity dispersion, β2, is found to be −6.3×103 fs2 (7.6 fs/nm) at an injection current of 500 mA.
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42.55.Px Semiconductor lasers; laser diodes
07.60.Ly Interferometers
02.30.Uu Integral transforms

Surface-passivation effects on the photoluminescence enhancement in ZnS:Mn nanoparticles by ultraviolet irradiation with oxygen bubbling

Dae-Ryong Jung, Jongmin Kim, and Byungwoo Park

Appl. Phys. Lett. 96, 211908 (2010); http://dx.doi.org/10.1063/1.3431267 (3 pages) | Cited 9 times

Online Publication Date: 28 May 2010

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This study examined the effects of surface-passivation on the photoluminescence (PL) properties of ZnS:Mn nanoparticles treated by ultraviolet (UV) irradiation with oxygen bubbling. Compared to the pristine Mn-doped zinc-sulfide nanocrystals (quantum efficiency: ∼ 16%), the UV-irradiated ZnS:Mn showed significantly enhanced luminescence properties (quantum efficiency: ∼ 35%). The photoinduced surface passivation was characterized by x-ray diffraction, x-ray photoelectron spectroscopy, and time-resolved PL. The optimum thickness of the passivation layer for the quantum efficiency was examined considering the nanocrystal size, local strain, and radiative/nonradiative recombination rates.
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81.65.Rv Passivation
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
73.63.Bd Nanocrystalline materials
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Near infrared optical materials from polymeric amorphous carbon synthesized by collisional plasma process

M. Rybachuk, A. Hertwig, M. Weise, M. Sahre, M. Männ, U. Beck, and J. M. Bell

Appl. Phys. Lett. 96, 211909 (2010); http://dx.doi.org/10.1063/1.3431292 (3 pages) | Cited 4 times

Online Publication Date: 28 May 2010

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The synthesis of polymerlike amorphous carbon (a-C:H) thin-films by microwave excited collisional hydrocarbon plasma process is reported. Stable and highly aromatic a-C:H were obtained containing significant inclusions of poly(p-phenylene vinylene) (PPV). PPV confers universal optoelectronic properties to the synthesized material. That is a-C:H with tailor-made refractive index are capable of becoming absorption-free in visible (red)-near infrared wavelength range. Production of large aromatic hydrocarbon including phenyl clusters and/or particles is attributed to enhanced coagulation of elemental plasma species under collisional plasma conditions. Detailed structural and morphological changes that occur in a-C:H during the plasma synthesis are also described.
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42.70.-a Optical materials
81.15.Jj Ion and electron beam-assisted deposition; ion plating
68.55.A- Nucleation and growth
68.55.J- Morphology of films
78.66.Nk Insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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