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1 Jul 2012

Volume 112, Issue 1, Articles (01xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 112, 013503 (2012); http://dx.doi.org/10.1063/1.4730908 (9 pages)

Ajing Cao and Jianmin Qu
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back to top Nanoscale Science and Design

Effects of internal strain and external pressure on electronic structures and optical transitions of self-assembled InxGa1−xAs/GaAs quantum dots: An experimental and theoretical study

Yuan Wen, Mou Yang, S. J. Xu, L. Qin, and Z. X. Shen

J. Appl. Phys. 112, 014301 (2012); http://dx.doi.org/10.1063/1.4730628 (5 pages)

Online Publication Date: 2 July 2012

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The optical emissive transitions from the ground and excited states of the self-assembled InxGa1−xAs/GaAs quantum dots (QDs) at room temperature were experimentally measured as a function of the external hydrostatic pressure by means of the confocal micro-photoluminescence technique. The ground state transition is very weak under zero external pressure and the photoluminescence is dominant by the excited state transition. However, the intensity of the ground state transition monotonically increases with increasing the external pressure and eventually become the dominant transition. Their pressure coefficients (PCs) were determined to be 6.8 and 7.1 meV/kbar, respectively, which were astonishingly smaller than those of GaAs bulk and the InGaAs/GaAs reference quantum well. The emission peak from the higher order excited states had a much smaller PC (∼0.5 meV/kbar). The influence of the built-in strain and external hydrostatic pressure on the electronic structures and optical transitions of various InxGa1−xAs/GaAs QDs was theoretically investigated by using the eight-band k·p method. Good agreement between the theoretical and experimental results was achieved, firmly revealing that the internal built-in strain in the dot system is mainly responsible for the experimental findings.
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73.21.La Quantum dots
78.55.Cr III-V semiconductors
78.67.Hc Quantum dots
71.20.Nr Semiconductor compounds

Gibbs free energy approach to the prediction of melting points of isolated, supported, and embedded nanoparticles

Wenhua Luo, Wangyu Hu, Kalin Su, and Kemin Li

J. Appl. Phys. 112, 014302 (2012); http://dx.doi.org/10.1063/1.4730919 (7 pages)

Online Publication Date: 2 July 2012

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By means of the thermodynamic and thermophysical properties of bulk materials, the Gibbs free energies for isolated, supported, and embedded nanoparticles were obtained and used to elucidate the sized-dependent melting phenomenon of the nanoparticles. To account for the substrate effect upon the melting point of nanoparticles, the interfacial energy of binary immiscible systems was studied in detail. It was found that the interfacial energy of a binary immiscible system including carbon can be replaced almost entirely by the contribution from carbon; thus, the reason why the melting model of isolated nanoparticles can be applied to research the melting of the supported nanoparticles was clarified. Moreover, a new approach to achieving the diameter of the smallest crystalline nanoparticles was proposed based on the melting behavior of embedded nanoparticles.
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64.70.dj Melting of specific substances
65.40.gd Entropy
65.40.gp Surface energy
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
68.35.Md Surface thermodynamics, surface energies

Dielectric studies and band gap tuning of ferroelectric Cr-doped ZnO nanorods

Manoj K. Gupta, Nidhi Sinha, and Binay Kumar

J. Appl. Phys. 112, 014303 (2012); http://dx.doi.org/10.1063/1.4730933 (4 pages) | Cited 2 times

Online Publication Date: 2 July 2012

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Effect of Cr-doping on the optical behavior of ZnO nanorods (NRs) (size: diameter ∼ 40 nm and length ∼ 400 nm) is reported. Significant red shift of 18 nm was observed in UV-Vis studies, i.e., a band gap tuning is achieved by Cr doping. In photoluminescence studies, a very remarkable blue shift of 16 nm in green emission was observed. Significant shifts in various modes of Raman spectra of Cr-doped ZnO nanorods are observed in low and high wavenumber region, along with appearance and disappearance of other peaks. The results suggest that Cr-doping can affect the defects and oxygen vacancies in ZnO nanomaterials giving the possibility of fine band gap tuning for tailor made applications of nano-optoelectronics devices. A very high dielectric constant (950) at low frequency side and ferroelectric phase transition (69 °C) were found for Cr-doped ZnO NR, which make it suitable for charge storage and nanoscale memory devices.
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77.80.B- Phase transitions and Curie point
78.67.Qa Nanorods
77.22.Ch Permittivity (dielectric function)
78.30.Fs III-V and II-VI semiconductors
78.55.Et II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
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Nanofluidic preconcentration and detection of nanoparticles

Anirban Mitra, Filipp Ignatovich, and Lukas Novotny

J. Appl. Phys. 112, 014304 (2012); http://dx.doi.org/10.1063/1.4731250 (5 pages)

Online Publication Date: 2 July 2012

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The fast detection and characterization of nanoparticles, such as viruses or environmental pollutants, are important in fields ranging from biosensing to quality control. However, most existing techniques have practical throughput limitations, which significantly limit their applicability to low analyte concentrations. Here, we present an integrated nanofluidic scheme for preconcentration and subsequent detection of nanoparticle samples within a continuous flow-through system. Using a Brownian ratchet mechanism, we increase the nanoparticle concentration ∼27-fold. Single nanoparticles are subsequently detected and characterized by optical heterodyne interferometry. A wide range of potential applications can be foreseen, including real-time analysis of clinically relevant virus samples and contamination control of processing fluids used in the semiconductor industry.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
87.80.-y Biophysical techniques (research methods)
07.10.Cm Micromechanical devices and systems
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

High resolution x-ray diffraction methodology for the structural analysis of one-dimensional nanostructures

M. C. Martínez-Tomás, D. N. Montenegro, V. Sallet, and V. Muñoz-Sanjosé

J. Appl. Phys. 112, 014305 (2012); http://dx.doi.org/10.1063/1.4730403 (10 pages) | Cited 2 times

Online Publication Date: 2 July 2012

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We present a systematic high-resolution x-ray diffraction (HRXRD) methodology for the analysis of one-dimensional nanostructures, in order to give answer to some of the frequently found problems in the literature. Regarding the assessment of structural properties, it is well known that high resolution x-ray diffraction measurements can provide qualitative and quantitative information on several intrinsic parameters of the material. However when nanostructures are present, the difficulties in analyzing the diffracted signals coming from nanostructures and the homolayer on which they usually grow have led to a reduced use of this technique, one of the most powerful methods for structural analysis. The aim of this paper is to develop a methodology for the analysis of one-dimensional structures based on the mosaic model similar to the one used in the x-ray diffraction methods for layers and films. On this basis, it has been possible by making a careful and systematic application of HRXRD to obtain separated structural information of nanostructures and the layer/block/grain underneath. In addition, the existence of a long-range ordering of nanostructures has been studied from the detection and analysis of forbidden reflections. The HRXRD experimental work has been particularized on ZnO nanorods grown by catalyst-free metal organic chemical deposition on c-sapphire substrates.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
81.16.-c Methods of micro- and nanofabrication and processing
81.05.Dz II-VI semiconductors

Disappearance and recovery of luminescence in GdPO4:Eu3+ nanorods: Propose to water/OH• release under near infrared and gamma irradiations

Niroj Kumar Sahu, R. S. Ningthoujam, and D. Bahadur

J. Appl. Phys. 112, 014306 (2012); http://dx.doi.org/10.1063/1.4731644 (12 pages) | Cited 5 times

Online Publication Date: 3 July 2012

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Luminescence intensity of rare-earth doped materials can be varied depending on shape of particles, capping agent, and heat-treatment. This is related to the non-radiative rate possessed by the material. Here, we observed the high quenching of the luminescence intensity of Eu3+ doped GdPO4 prepared in water (H2O) medium. On the contrary, in ethylene glycol (EG) medium, it shows high luminescence. Luminescence intensity is recovered when Eu3+ doped GdPO4 nanorods prepared in H2O medium is heated above 700 °C. This transforms hexagonal to monoclinic structure following the removal of water. Luminescence intensity is enhanced by changing the medium from H2O to D2O and also if core-shell formation occurs. Also, we found significant variation in bending and stretching vibrations of O-H and microstructure in this material prepared in H2O and EG. Two types of O-H stretching frequencies are observed at 3450 and 3520 cm−1 in H2O medium prepared sample which are assigned to the O-H having the hydrogen bonding (surface water) and the confined water, respectively. The formation of nanorods is due to the presence of water on the surface of particles or/and inside the pores of compound. The available water in the nanoparticles pores can be utilized for the efficient killing of mass cells tumor by generating reactive free radicals (H· and OH·) through the application of laser near infrared (NIR) source and the subsequent irradiation of gamma ray. This proposed mechanism is quite different from the conventional treatment of mass cell/malignant tumor using gamma ray radiation. Sample is highly paramagnetic and it will be useful for magnetic resonance imaging contrast agent.
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78.55.Hx Other solid inorganic materials
61.80.Ed γ-ray effects
81.40.Gh Other heat and thermomechanical treatments
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
61.82.Rx Nanocrystalline materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Size and alloying induced changes in lattice constant, core, and valance band binding energy in Pd-Ag, Pd, and Ag nanoparticles: Effect of in-flight sintering temperature

Saurabh K. Sengar, B. R. Mehta, and Govind

J. Appl. Phys. 112, 014307 (2012); http://dx.doi.org/10.1063/1.4731714 (8 pages)

Online Publication Date: 3 July 2012

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In the present study, we report the growth of size selected Pd, Ag, and Pd-Ag alloy nanoparticles by an integrated method comprising of the gas phase synthesis, electrical mobility size selection, and in-flight sintering steps. Effect of temperature during in-flight sintering on nanoparticle size, crystal structure, and electronic properties has been studied. XRD studies show lattice expansion in Pd and Ag nanoparticles and lattice contraction in Pd-Ag alloy nanoparticles on increasing the sintering temperatures. In case of Pd and Ag nanoparticles, size induced changes in lattice constants are consistent with the changes in the binding energy positions with respect to bulk values. In case of Pd-Ag alloy nanoparticles, change in nanoparticle size and composition on sintering affect the lattice constant and binding energy positions. Large changes in Pd4d valance band centroid in Pd-Ag nanoparticles are due to size and alloying effects. The results of this study are important for understanding the correlation between electronic properties and Pd-H interaction in Pd alloy nanoparticles.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.07.Wx Nanopowders
81.16.-c Methods of micro- and nanofabrication and processing
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
71.20.Be Transition metals and alloys

Abnormal pseudospin-degenerate states in a graphene quantum dot with double vacancy defects

Aiping Zhou and Weidong Sheng

J. Appl. Phys. 112, 014308 (2012); http://dx.doi.org/10.1063/1.4732075 (5 pages) | Cited 1 time

Online Publication Date: 3 July 2012

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We study valley-polarized states in an armchair graphene quantum dot with double vacancy defects. Half-filled doubly degenerate states are found in the middle of the gap only when two vacancies occupy certain specific sites in each of the sublattices of the quantum dot. The doubly degenerate states forming around the vacancies are shown to be entirely localized in their respective sublattice, which results in that the two parallel-spin electrons in the degenerate Fermi level carry purely opposite valley pseudospins. Surprisingly, the pseudospin-degenerate states are found to be symmetric even when the reflection symmetry of the structure has been broken by the vacancies. It is further shown that the pseudospin degeneracy, similar to the Kramer’s degeneracy lifted by a magnetic field, can be removed by an applied electric field. Like the Zeeman effect, the split states would retain their original valley pseudospins and exhibit linear splitting energy with respect to the applied field.
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73.22.Pr Electronic structure of graphene
71.20.Tx Fullerenes and related materials; intercalation compounds
71.55.Ht Other nonmetals
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
73.21.La Quantum dots
61.72.jd Vacancies

Spin-electron beam splitters based on magnetic barrier nanostructures

Mao-Wang Lu, Gui-Lian Zhang, and Sai-Yan Chen

J. Appl. Phys. 112, 014309 (2012); http://dx.doi.org/10.1063/1.4730784 (5 pages) | Cited 3 times

Online Publication Date: 3 July 2012

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With the help of stationary phase method, we investigate the Goos-Hänchen (GH) effect of electrons in nanostructures consisting of realistic magnetic barriers (MB) created by lithographic patterning of ferromagnetic (FM) or superconducting films. Due to intrinsic symmetry, only nanostructures with symmetric magnetic field possess a considerable spin-dependent GH effect, and GH shifts of transmitted spin beams are found to depend upon the incident angle and the incident energy of electrons as well as the size and position of the FM stripe. These interesting properties may provide an effective scheme to realize spin injection into semiconductor and also give rise to a type of spin beam splitters based on MB nanostructures.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Controlled facile synthesis, growth mechanism, and exothermic properties of large-area Co3O4 nanowalls and nanowires on silicon substrates

Zhiqiang Qiao, Daguo Xu, Fude Nie, Guangcheng Yang, and Kaili Zhang

J. Appl. Phys. 112, 014310 (2012); http://dx.doi.org/10.1063/1.4731798 (9 pages)

Online Publication Date: 3 July 2012

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Co3O4 nanowalls and nanowires have been synthesized onto silicon substrates by low-temperature thermal oxidation of sputtered Co thin films in static air. The synthesis method is very simple and suitable for large-scale fabrication. The effects of the thermal oxidation temperature and duration on the size, amount, and length of the nanowires and nanowalls are systematically investigated both by scanning electron microscopy characterization and differential scanning calorimetry thermal analysis. It is found that the Co/CoO oxidation and Co3O4 decomposition are important factors contributing to the growth of the Co3O4 nanowalls and nanowires. The mechanical adhesion between the Co3O4 nanowalls/nanowires/film and the silicon substrate is observed to be very strong, which is beneficial for many practical applications. Based on the experimental observations, the detailed growth mechanisms of the nanowalls and nanowires are presented. Finally, the promising novel exothermic reaction properties of the Co3O4 nanowalls and nanowires with Al are investigated by thermal analysis.
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81.16.-c Methods of micro- and nanofabrication and processing
68.35.Np Adhesion
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
75.50.Pp Magnetic semiconductors

Application of hydrogenation to low-temperature cleaning of the Si(001) surface in the processes of molecular-beam epitaxy: Investigation by scanning tunneling microscopy, reflected high-energy electron diffraction, and high resolution transmission electron microscopy

L. V. Arapkina, L. A. Krylova, K. V. Chizh, V. A. Chapnin, O. V. Uvarov, and V. A. Yuryev

J. Appl. Phys. 112, 014311 (2012); http://dx.doi.org/10.1063/1.4732073 (7 pages)

Online Publication Date: 5 July 2012

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Structural properties of the clean Si(001) surface obtained as a result of low-temperature (470–650 °C) pre-growth annealings of silicon wafers in a molecular-beam epitaxy chamber have been investigated. To decrease the cleaning temperature, a silicon surface was hydrogenated in the process of a preliminary chemical treatment in HF and NH4F aqueous solutions. It has been shown that smooth surfaces composed of wide terraces separated by monoatomic steps can be obtained by dehydrogenation at the temperatures ≳600 °C, whereas clean surfaces obtained at the temperatures <600 °C are rough. It has been found that there exists a dependence of structural properties of clean surfaces on the temperature of hydrogen thermal desorption and the process of the preliminary chemical treatment. The frequency of detachment/attachment of Si dimers from/to the steps and effect of the Ehrlich-Schwoebel barrier on ad-dimer migration across steps have been found to be the most probable factors determining a degree of the resultant surface roughness.
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81.65.Cf Surface cleaning, etching, patterning
68.55.ag Semiconductors
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.43.Vx Thermal desorption
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.40.Gh Other heat and thermomechanical treatments

Photocurrent of lead-free (K0.5Na0.5)(Mn0.005Nb0.995)O3 ferroelectric nanotubes

Jungmin Park, Chang Won Ahn, and Ill Won Kim

J. Appl. Phys. 112, 014312 (2012); http://dx.doi.org/10.1063/1.4732455 (6 pages) | Cited 1 time

Online Publication Date: 5 July 2012

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We fabricated (K0.5Na0.5)(Mn0.005Nb0.995)O3 (KNMN) nanotubes using (K0.5Na0.5)(Mn0.005 Nb0.995)O3 sol on an anodic aluminum oxide (AAO) template. The highly ordered AAO template was fabricated by a two-step anodization process. Lead-free (K0.5Na0.5)(Mn0.005Nb0.995)O3 ferroelectric nanotubes were fabricated by infiltration with KNMN sol inside the AAO template by a sol-gel process. The outer diameter and thickness of the wall in the KNMN nanotube were about 70 nm and 5 nm, respectively. The crystalline structure, surface morphology, and ferroelectric and photocurrent properties were investigated. The maximum power conversion efficiencies (η) of KNMN nanotubes were higher than that of KNMN film due to the greater effective area (KNMN nanotubes: η = 0.02%, KNMN film: η = 0.008%).
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72.40.+w Photoconduction and photovoltaic effects
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.60.Jv Interfaces; heterostructures; nanostructures
81.16.Be Chemical synthesis methods
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
61.46.Fg Nanotubes

Optically engineered ultrafast pulses for controlled rotations of exciton qubits in semiconductor quantum dots

Angela Gamouras, Reuble Mathew, and Kimberley C. Hall

J. Appl. Phys. 112, 014313 (2012); http://dx.doi.org/10.1063/1.4731723 (8 pages)

Online Publication Date: 6 July 2012

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Shaped ultrafast pulses designed for controlled-rotation (C-ROT) operations on exciton qubits in semiconductor quantum dots are demonstrated using a quantum control apparatus operating at ∼1 eV. Optimum pulse shapes employing amplitude and phase shaping protocols are implemented using the output of an optical parametric oscillator and a programmable pulse shaping system, and characterized using autocorrelation and multiphoton intrapulse interference phase scan techniques. We apply our pulse characterization results and density matrix simulations to assess the fundamental limits on the fidelity of the C-ROT operation, providing a benchmark for the evaluation of sources of noise in other quantum control experiments. Our results indicate the effectiveness of pulse shaping techniques for achieving high fidelity quantum operations in quantum dots with a gate time below 1 ps.
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81.07.Ta Quantum dots
78.67.Hc Quantum dots
71.35.-y Excitons and related phenomena

A model of an artificial one-dimensional quasicrystal composed of semiconductor quantum dots

Wen-Long Ma and Shu-Shen Li

J. Appl. Phys. 112, 014314 (2012); http://dx.doi.org/10.1063/1.4733314 (4 pages)

Online Publication Date: 6 July 2012

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A model is presented of an artificial one-dimensional quasicrystal composed of semiconductor quantum dots (QDs) arranged in a Fibonacci sequence. Compared to the typical one-dimensional quasicrystal, the major advantage of this artificial system is that its electronic properties can be tuned by controlling the number of dots in the system. A self-similar hierarchy of energy gaps is found in the energy spectra of this system just as in the one-dimensional quasicrystal and the localized states may appear quite symmetrically in the two main energy gaps of the energy spectra. Numerical calculations show that whether the localized states exist or not, but depends on the number of dots in a way quite similar to the generation of a Fibonacci sequence. Such an artificial structure may offer new research directions in semiconductor QD devices.
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71.23.Ft Quasicrystals
61.44.Br Quasicrystals
71.23.An Theories and models; localized states

Macroscopic and microscopic defects and nonlinear optical properties of KH2PO4 crystals with embedded TiO2 nanoparticles

Valentin G. Grachev, Ian A. Vrable, Galina I. Malovichko, Igor M. Pritula, Olga N. Bezkrovnaya, Anna V. Kosinova, Vasyl O. Yatsyna, and Vladimir Ya. Gayvoronsky

J. Appl. Phys. 112, 014315 (2012); http://dx.doi.org/10.1063/1.4733301 (11 pages) | Cited 1 time

Online Publication Date: 10 July 2012

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Results from the successful growth of high quality KH2PO4 (KDP) crystals with incorporated TiO2 anatase nanoparticles and the characterization of these crystals using several complementary methods are presented. The study allowed the nature and distribution of macroscopic and microscopic defects in the KDP:TiO2 crystals to be clarified. The relationship between these defects and the distribution of TiO2 nanoparticles, and the influence of incorporated nanoparticles on the nonlinear optical properties of composite crystals in comparison with pure crystals were also elucidated. Visual observations, transmission and scanning electron microscopy have shown that the anatase nanoparticles were captured mainly by the pyramidal growth sector and, to a considerably lesser extent, by the prismatic growth sector. Energy dispersive x-ray analysis was able to confirm that the growth layer stacks contain the TiO2 particles. Fourier transformation infrared spectra have clearly shown the presence of an absorption band at about 800 cm−1 in both KDP:TiO2 and TiO2, and the disappearance of the band, associated with hydroxyl OH− groups on the TiO2 surface in KDP:TiO2. Significant variation in the imaginary and real parts of the cubic nonlinear optical susceptibilities and refractive index changes at continuous wave excitation were found in prism and pyramid parts of pure KDP and KDP:TiO2 samples. Deciphering complicated electron paramagnetic resonance spectra in KDP:TiO2 and comparison with published data permitted the identification of paramagnetic defects along with their associated g-factors and zero-field splitting parameters (in some cases for the first time). It was found that the dominant lines belong to four different centers FeA3+, FeB3+, CrR3+, and CrGB3+. From analysis of line intensities it was concluded that the concentration of intrinsic defects like potassium and hydrogen vacancies in KDP:TiO2 is comparatively small, that the concentration of non-controlled impurities in nominally pure KDP samples is several times larger than in KDP:TiO2, and that the concentration of non-controlled impurities in the prismatic part of the KDP:TiO2 boule is approximately twice as large as in the pyramid part.
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76.30.Fc Iron group (3d) ions and impurities (Ti-Cu)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Hv Other nonmetallic inorganics
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
61.72.jd Vacancies
42.65.An Optical susceptibility, hyperpolarizability

The effects of doping and shell thickness on the optical and magnetic properties of Mn/Cu/Fe-doped and Co-doped ZnS nanowires/ZnO quantum dots/SiO2 heterostructures

Jian Cao, Jinghai Yang, Lili Yang, Maobin Wei, Bo Feng, Donglai Han, Lin Fan, Bingji Wang, and Hao Fu

J. Appl. Phys. 112, 014316 (2012); http://dx.doi.org/10.1063/1.4733948 (8 pages) | Cited 3 times

Online Publication Date: 10 July 2012

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In this paper, we demonstrated the encapsulation of Mn/Cu/Fe-doped and co-doped ZnS nanowires (NWs) and ZnO quantum dots (QDs) with a layer of mesoporous SiO2 shell for the purpose of integrating dual emission and ferromagnetism property into one common nanostructure at room temperature. Within the ZnS:Mn2+Cu2+Fe2+/ZnO@SiO2 nanocomposites, ZnS:Mn2+Cu2+Fe2+ NWs and ZnO QDs provided color-tunable visible emission and UV emission, respectively. The color-tunable visible emission in the ZnS:Mn2+Cu2+Fe2+ NWs can be obtained by adjusting the concentrations of Mn2+, Cu2+, and Fe2+ ions. The ferromagnetism of the ZnS:Mn2+Cu2+Fe2+ NWs was observed around room temperature, the mechanism of which was explained by the super-exchange mechanism. The results of the effect of the ZnO QDs shell thickness on the optical properties of the ZnS:Mn2+/ZnO@SiO2 nanocomposites showed that the luminescence intensity of the yellow-orange emission and UV emission reached the highest value when the ratio of ZnS:Mn2+/ZnO equaled 1:5.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
61.72.uj III-V and II-VI semiconductors
61.72.U- Doping and impurity implantation
78.66.Hf II-VI semiconductors
78.67.Hc Quantum dots
78.60.-b Other luminescence and radiative recombination

Phonon thermal conductivity of GaN nanotubes

Gang Zhou and Liangliang Li

J. Appl. Phys. 112, 014317 (2012); http://dx.doi.org/10.1063/1.4736421 (8 pages) | Cited 1 time

Online Publication Date: 10 July 2012

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We theoretically investigated the phonon thermal conductivity of gallium nitride (GaN) nanotubes with diameters ranging from a few nanometers to 120 nanometers using the Boltzmann transport equation and took into account the phonon dispersion relations of the nanotubes and the influence of boundary scattering on the non-equilibrium phonon distribution. The calculation results show that the phonon thermal conductivity of GaN nanotubes is much lower than that of the bulk counterpart and it depends on the thickness, inner and outer diameters, and surface roughness of the nanotubes. A small thickness or a large surface roughness leads to a small thermal conductivity. The reduction of the phonon thermal conductivity of the nanotubes is mainly due to the decrease of the phonon group velocity, change of the phonon relaxation rate, and enhancement of phonon boundary scattering. The understanding and results on the thermal conductivity obtained in this work are important for the optoelectronic devices based on GaN nanotubes and nanowires, and the developed calculation method on the phonon thermal conductivity is generally applicable and can be used for other nanotube systems.
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66.70.Df Metals, alloys, and semiconductors
68.35.bg Semiconductors
61.46.Fg Nanotubes
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Giant enhancement in ferromagnetic properties of Pd nanoparticle induced by intentionally created defects

P. K. Kulriya, B. R. Mehta, D. C. Agarwal, Praveen Kumar, S. M. Shivaprasad, J. C. Pivin, and D. K. Avasthi

J. Appl. Phys. 112, 014318 (2012); http://dx.doi.org/10.1063/1.4733950 (7 pages) | Cited 1 time

Online Publication Date: 11 July 2012

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The important central question related to origin of ferromagnetic properties in the non-magnetic materials at nano-dimensions has been investigated by a novel approach of studying the evolution of magnetic properties by intentionally creating defects. The ferromagnetic response of Pd is found to increase by 20 times for nanoparticle (NP) dispersed in carbon matrix and increase by about 3.5 times in case of Pd nanoparticles dispersed in SiO2 matrix on exposure to swift heavy ion irradiation. Ferromagnetic response is found to increase by about 9.3 times on subjecting the Pd nanoparticles to hydrogen loading-deloading cycle. Ferromagnetic properties of Pd nanoparticles dispersed in carbon and SiO2 matrices, despite having same size and concentration, are observed to be vastly different due to matrix effect. These changes in ferromagnetic properties are correlated to the change in the electronic structure due to matrix, nanoparticle size, and creation of defects in the nanoparticle core and at NP-matrix interface during post deposition treatments. Giant enhancement in the magnetic properties and change in electronic properties point toward a core and surface magnetic structure in metal nanoparticle.
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75.75.Lf Electronic structure of magnetic nanoparticles
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.50.Cc Other ferromagnetic metals and alloys
75.50.Tt Fine-particle systems; nanocrystalline materials
71.55.Ak Metals, semimetals, and alloys
73.20.Hb Impurity and defect levels; energy states of adsorbed species

In-plane mapping of buried InGaAs quantum rings and hybridization effects on the electronic structure

M. D. Teodoro, A. Malachias, V. Lopes-Oliveira, D. F. Cesar, V. Lopez-Richard, G. E. Marques, E. Marega, Jr., M. Benamara, Yu. I. Mazur, and G. J. Salamo

J. Appl. Phys. 112, 014319 (2012); http://dx.doi.org/10.1063/1.4733964 (9 pages) | Cited 1 time

Online Publication Date: 11 July 2012

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This work reports the investigation on the structural differences between InAs quantum rings and their precursor quantum dots species as well as on the presence of piezoelectric fields and asymmetries in these nanostructures. The experimental results show significant reduction in the ring dimensions when the sizes of capped and uncapped ring and dot samples are compared. The iso-lattice parameter mapped by grazing-incidence x-ray diffraction has revealed the lateral extent of strained regions in the buried rings. A comparison between strain and composition of dot and ring structures allows inferring on how the ring formation and its final configuration may affect optical response parameters. Based on the experimental observations, a discussion has been introduced on the effective potential profile to emulate theoretically the ring-shape confinement. The effects of confinement and strain field modulation on electron and hole band structures are simulated by a multiband k.p calculation.
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71.20.Nr Semiconductor compounds
73.21.Fg Quantum wells
77.65.-j Piezoelectricity and electromechanical effects
71.15.-m Methods of electronic structure calculations
61.46.-w Structure of nanoscale materials

Simulated thermal conductivity of silicon-based random multilayer thin films

Anthony Frachioni and B. E. White, Jr.

J. Appl. Phys. 112, 014320 (2012); http://dx.doi.org/10.1063/1.4733351 (4 pages) | Cited 1 time

Online Publication Date: 11 July 2012

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Reverse nonequilibrium molecular dynamics simulations have been used to quantify the impact of randomly placed mass-altered atomic planes, such as those produced in pseudomorphically grown heterostructures, on the thermal conductivity of silicon. The results indicate that the room temperature thermal conductivity of these silicon-based structures can be reduced to values below 0.050 W/m-K. These values are significantly less than those found in random alloy or superlattice structures containing the same percentage of mass-altered atoms and are attributed to Anderson localization of phonons. Such low lattice thermal conductivity in these silicon-based structures could dramatically improve the thermoelectric efficiency of this earth abundant material.
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66.70.Df Metals, alloys, and semiconductors
63.20.Pw Localized modes
72.20.Pa Thermoelectric and thermomagnetic effects
73.21.Cd Superlattices
73.61.Cw Elemental semiconductors
63.22.Np Layered systems

Effect of Y-doping on the electrical transport properties of nanocrystalline BiFeO3

A. Mukherjee, S. Basu, G. Chakraborty, and M. Pal

J. Appl. Phys. 112, 014321 (2012); http://dx.doi.org/10.1063/1.4734005 (8 pages) | Cited 1 time

Online Publication Date: 12 July 2012

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Effect of yttrium doping on the electrical transport properties of sol-gel prepare nanocrystalline BiFeO3 was investigated. A comprehensive state-of-the art sophisticated instruments like x-ray diffraction, differential thermal analyzer, field emission scanning electron microscope, and HRTEM were utilized to characterize the BiFeO3 nanoparticles. It was observed that the values of dc activation energy calculated from Arrhenius relation increase with increase of yttrium content. The variation of ac conductivity with frequency and temperature exhibits a correlated barrier hopping conduction mechanism. The dielectric permittivity of the sample reveals an increasing tendency with the concentration of yttrium and depends on both the grain and the interfacial grain boundary resistance. The activation energies for the dielectric relaxation estimated from the modulus spectra were found to be reasonably good agreement with those obtained from dc conductivity study.
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81.07.Bc Nanocrystalline materials
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
77.22.Gm Dielectric loss and relaxation
77.22.Ch Permittivity (dielectric function)
73.63.Bd Nanocrystalline materials
72.20.Ee Mobility edges; hopping transport

Electrostatic effects in coupled quantum dot-point contact-single electron transistor devices

S. Pelling, E. Otto, S. Spasov, S. Kubatkin, R. Shaikhaidarov, K. Ueda, S. Komiyama, and V. N. Antonov

J. Appl. Phys. 112, 014322 (2012); http://dx.doi.org/10.1063/1.4736419 (5 pages) | Cited 1 time

Online Publication Date: 12 July 2012

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We study the operation of a system where quantum dot (QD) and point contact (PC) defined in a two-dimensional electron gas of a high-mobility GaAs/AlGaAs heterostructure are capacitively coupled to each other and to metallic single electron transistor (SET). The charge state of the quantum dot can be probed by the point contact or single electron transistor. These can be used for sensitive detection of terahertz radiation. In this work, we explore an electrostatic model of the system. From the model, we determine the sensitivity of the point contact and the single electron transistor to the charge excitation of the quantum dot. Nearly periodic oscillations of the point contact conductance are observed in the vicinity of pinch-off voltage. They can be attributed to Coulomb blockade effect in a quasi-1D channel because of unintentional formation of small quantum dot. The latter can be a result of fluctuations in GaAs quantum well thickness.
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85.30.Hi Surface barrier, boundary, and point contact devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.35.Ds Quantum interference devices
85.35.Gv Single electron devices

Interparticle coupling of plasmon fields due to reorganization of Au nanoparticles in Langmuir-Blodgett film

Sarathi Kundu

J. Appl. Phys. 112, 014323 (2012); http://dx.doi.org/10.1063/1.4736546 (4 pages) | Cited 1 time

Online Publication Date: 12 July 2012

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Dodecanethiol-encapsulated Au nanoparticles have been deposited on Si(001) and quartz substrates by Langmuir-Blodgett method at different surface pressures for producing layer-by-layer structure. Out-of-plane structural reorganization and optical absorption spectra have been obtained from x-ray reflectivity and UV-Vis spectroscopy measurements, respectively. With time, positions of the nanoparticles reorganize so that films become more compact and thickness decreases. Localized surface plasmon resonance peaks show that coupling between Au nanoparticles occur as the interparticle distance decreases after reorganization and as a result, a redshift in the plasmon peak wavelength takes place. Variation in redshift depends upon the deposition pressure or layer number.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.40.Kc Metals, semimetals, and alloys
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.68.+m Optical properties of surfaces
81.16.-c Methods of micro- and nanofabrication and processing

Influence of impurity propagation and concomitant enhancement of impurity spread on excitation profile of doped quantum dots

Nirmal Kr Datta, Suvajit Pal, and Manas Ghosh

J. Appl. Phys. 112, 014324 (2012); http://dx.doi.org/10.1063/1.4732137 (8 pages) | Cited 2 times

Online Publication Date: 13 July 2012

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We investigate the excitation behavior of a repulsive impurity doped quantum dot under the combined influence of dopant drift and associated time variation in its spatial spread. We have considered Gaussian impurity centers. In order to make the investigation rational, the time-dependence of the spatial spread has been connected with the instantaneous location of the dopant. Looking at the general applicability of the findings, we have considered linear and random propagation of the dopant. For a systematic analysis, we have proceeded in a stepwise manner during the investigation. Thus, at first we have not considered the time-dependence of spatial spread of dopant and concentrated only on the dopant drift. Subsequently, we have introduced time-dependence in the spatial spread and observed the outcome. Although the incorporation of time-dependence in spatial stretch makes the calculation much more tedious and involved, yet this adequately describes the role played by the time-varying impurity domain exclusively in modulating the excitation rate. The varied nature of dopant propagation interplays delicately with the time-dependent modulation of its spatial stretch giving some important insight into the physics underlying the excitation process.
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61.72.up Other materials
73.21.La Quantum dots
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