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14 Mar 2011

Volume 98, Issue 11, Articles (11xxxx)

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Appl. Phys. Lett. 98, 111101 (2011); http://dx.doi.org/10.1063/1.3561770 (3 pages)

Mike Woerdemann, Christina Alpmann, and Cornelia Denz
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Enhanced photoluminescence around 1540 nm from erbium doped silicon coimplanted with hydrogen and silver

Sebastian Naczas, Perveen Akhter, and Mengbing Huang

Appl. Phys. Lett. 98, 113101 (2011); http://dx.doi.org/10.1063/1.3562959 (3 pages) | Cited 1 time

Online Publication Date: 14 March 2011

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This work reports on an approach based on coimplantation of hydrogen and silver for improving luminescence around 1540 nm from erbium doped silicon. As a result of H induced nanocavities and their gettering of implanted Ag ions, Ag nanostructures are formed in Si doped with erbium and oxygen. The presence of such nanostructures can lead to an enhancement of more than a factor of 2 in Er photoluminescence, compared to the control sample. In addition, analysis of PL data suggests that both the Er excitation cross section and the Er optical activation are increased by the formation of Ag nanostructures. We discuss possible mechanisms for these findings.
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78.66.Db Elemental semiconductors and insulators
78.55.Ap Elemental semiconductors
61.72.U- Doping and impurity implantation
61.46.-w Structure of nanoscale materials
81.16.-c Methods of micro- and nanofabrication and processing

Thermometry based on phonon confinement effect in nanoparticles

Junwei Wang and Liping Huang

Appl. Phys. Lett. 98, 113102 (2011); http://dx.doi.org/10.1063/1.3565250 (3 pages)

Online Publication Date: 14 March 2011

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Raman spectra of TiO2 nanoparticles (NPs) have a very strong finite-size dependency due to the phonon confinement effect. This provides a convenient way to characterize NPs size by simply using Raman spectroscopy. Together with fast grain growth kinetics and high stability under high temperature and pressure, these NPs have the potential to forensically retain the complete thermal history (temperature and time) of an event that they went through. Here, we demonstrate that both temperature and time can be determined simultaneously by using these thermosensors in the range of 400–700 °C and 5–60 s, assuming that the temperature is constant (a step-function approximation to a thermal spike) during a thermal event.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
06.30.Ft Time and frequency
63.22.Kn Clusters and nanocrystals
07.20.Dt Thermometers
78.30.Hv Other nonmetallic inorganics
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Medium energy ion scattering of Gr on SiC(0001) and Si(100)

M. Copel, S. Oida, A. Kasry, A. A. Bol, J. B. Hannon, and R. M. Tromp

Appl. Phys. Lett. 98, 113103 (2011); http://dx.doi.org/10.1063/1.3565968 (3 pages) | Cited 1 time

Online Publication Date: 14 March 2011

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Depth profiling of graphene with high-resolution ion beam analysis is a practical method for analysis of monolayer thicknesses of graphene. Not only is the energy resolution sufficient to resolve graphene from underlying SiC but by use of isotope labeling it is possible to tag graphene generated from reacted ethylene. Furthermore, we are able to analyze graphene supported by oxidized Si(100) substrates, allowing the study of graphene films grown by chemical vapor deposition on metal and transferred to silicon. This introduces a powerful method to explore the fundamentals of graphene formation.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth

Enhanced Sb incorporation in InAsSb nanowires grown by metalorganic vapor phase epitaxy

B. Mattias Borg, Kimberly A. Dick, Joël Eymery, and Lars-Erik Wernersson

Appl. Phys. Lett. 98, 113104 (2011); http://dx.doi.org/10.1063/1.3566980 (3 pages) | Cited 2 times

Online Publication Date: 14 March 2011

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We demonstrate metalorganic vapor phase epitaxy of InAs1−xSbx nanowires (x = 0.08–0.77) for applications in high-speed electronics and long-wavelength optical devices. The composition of the InAsSb nanowires and InAsSb epilayers on the same sample is independently determined using lab-setup high resolution x-ray diffraction, by making use of the size-dependent in-plane broadening of the nanowire Bragg peak. We find that the incorporation of Sb into the nanowires is significantly higher than for planar epitaxy under the same growth conditions. Thermodynamic calculations indicate that this is due to a dramatically decreased effective V/III ratio at the particle/nanowire interface.
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81.16.-c Methods of micro- and nanofabrication and processing
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.07.Gf Nanowires
81.07.Vb Quantum wires
81.05.Ea III-V semiconductors
68.65.La Quantum wires (patterned in quantum wells)

Ultrathin body InAs tunneling field-effect transistors on Si substrates

Alexandra C. Ford, Chun Wing Yeung, Steven Chuang, Ha Sul Kim, Elena Plis, Sanjay Krishna, Chenming Hu, and Ali Javey

Appl. Phys. Lett. 98, 113105 (2011); http://dx.doi.org/10.1063/1.3567021 (3 pages) | Cited 6 times

Online Publication Date: 15 March 2011

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An ultrathin body InAs tunneling field-effect transistor on Si substrate is demonstrated by using an epitaxial layer transfer technique. A postgrowth, zinc surface doping approach is used for the formation of a p+ source contact which minimizes lattice damage to the ultrathin body InAs compared to ion implantation. The transistor exhibits gated negative differential resistance behavior under forward bias, confirming the tunneling operation of the device. In this device architecture, the ON current is dominated by vertical band-to-band tunneling and is thereby less sensitive to the junction abruptness. The work presents a device and materials platform for exploring III–V tunnel transistors.
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85.30.Tv Field effect devices

Near-field radiative transfer based thermal rectification using doped silicon

Soumyadipta Basu and Mathieu Francoeur

Appl. Phys. Lett. 98, 113106 (2011); http://dx.doi.org/10.1063/1.3567026 (3 pages) | Cited 10 times

Online Publication Date: 15 March 2011

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In this letter, we have designed a near-field thermal rectifier using a film and a bulk of doped silicon, with different doping levels, separated by a vacuum gap. We examine the origin of nonlinearities in thermal rectification associated with near-field heat transfer, and investigate closely the effects of varying the vacuum gap and the film thickness on rectification. For a 10 nm thick film, rectification greater than 0.5 is achieved for vacuum gaps varying from 1 nm to 50 nm with the hot and cold temperatures of the terminals of the rectifier being 400 K and 300 K, respectively. The results obtained from this study may benefit future research in thermal management and energy harvesting.
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66.70.Df Metals, alloys, and semiconductors
61.72.uf Ge and Si

Chirality and thickness-dependent thermal conductivity of few-layer graphene: A molecular dynamics study

Wei-Rong Zhong, Mao-Ping Zhang, Bao-Quan Ai, and Dong-Qin Zheng

Appl. Phys. Lett. 98, 113107 (2011); http://dx.doi.org/10.1063/1.3567415 (3 pages) | Cited 6 times

Online Publication Date: 15 March 2011

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The thermal conductivity of graphene nanoribbons (layer from 1 to 8 atomic planes) is investigated by using the nonequilibrium molecular dynamics method. We present that the room-temperature thermal conductivity decays monotonically with the number of the layers in few-layer graphene. The superiority of zigzag graphene in thermal conductivity is only available in high temperature region and disappears in multilayer case. It is explained that the phonon spectral shrink in high frequency induces the change in thermal conductivity. It is also reported that single-layer graphene has better ballistic transport property than the multilayer graphene.
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81.05.ue Graphene
81.07.Bc Nanocrystalline materials
73.23.Ad Ballistic transport
72.20.Ht High-field and nonlinear effects
66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
63.22.Rc Phonons in graphene

Wavelength-sized GaAs optomechanical resonators with gigahertz frequency

L. Ding, C. Baker, P. Senellart, A. Lemaitre, S. Ducci, G. Leo, and I. Favero

Appl. Phys. Lett. 98, 113108 (2011); http://dx.doi.org/10.1063/1.3563711 (3 pages) | Cited 4 times

Online Publication Date: 15 March 2011

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We report on wavelength-sized GaAs optomechanical disk resonators showing ultrastrong optomechanical interaction. We observe optical transduction of a disk mechanical breathing mode with 1.4 GHz frequency and effective mass of ∼ 2 pg. The measured vacuum optomechanical coupling rate reaches g0 = 0.8 MHz, with a related differential optomechanical coupling factor gom = 485 GHz/nm. The disk Brownian motion is optically resolved with a sensitivity of 10−17 m/√Hz at room temperature and pressure.
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84.40.Az Waveguides, transmission lines, striplines
85.30.-z Semiconductor devices

Temperature stress on pristine ZnO nanowire field effect transistor

Kyoungwon Kim, Pulak Chandra Debnath, Sangsig Kim, and Sang Yeol Lee

Appl. Phys. Lett. 98, 113109 (2011); http://dx.doi.org/10.1063/1.3567795 (3 pages) | Cited 2 times

Online Publication Date: 15 March 2011

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We have investigated the effect of the temperature dependency on the device stability of pristine ZnO nanowires (NWs) field effect transistor (FET). Pristine ZnO NW FET shows a large threshold voltage (Vth) shift by 6.5 V after increasing the measured temperature from 323 to 363 K. This large shift in Vth is mainly due to thermally activated process. Thermally activated electrons from the deep level trap site can be free carriers which results in the shift in Vth in negative direction. Also, activation energy of ZnO NW FET is derived to be about 1.432 eV based on thermally activated Arrhenius model.
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85.30.Tv Field effect devices
73.61.Ga II-VI semiconductors
71.55.Gs II-VI semiconductors

Colloidal quantum dot photodetectors enhanced by self-assembled plasmonic nanoparticles

Ludan Huang, Chang-Ching Tu, and Lih Y. Lin

Appl. Phys. Lett. 98, 113110 (2011); http://dx.doi.org/10.1063/1.3567514 (3 pages)

Online Publication Date: 16 March 2011

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Self-assembled colloidal plasmonic silver nanoparticles monolayers were integrated into solution-processed colloidal quantum dot (QD) photodetectors. We observed plasmon enhancement of photodetector responsivity over a board spectrum range (400–600 nm), with a 1.2–1.6 fold enhancement for a 440-nm-thick QD film device and a 2.4–3.3 fold enhancement for a 100-nm-thick QD device. The enhancement behavior was wavelength dependent with higher enhancement factor at longer wavelengths. The origins of responsivity enhancement were discussed.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Nanorod solar cell with an ultrathin a-Si:H absorber layer

Yinghuan Kuang, Karine H. M. van der Werf, Z. Silvester Houweling, and Ruud E. I. Schropp

Appl. Phys. Lett. 98, 113111 (2011); http://dx.doi.org/10.1063/1.3567527 (3 pages) | Cited 2 times

Online Publication Date: 16 March 2011

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We propose a nanostructured three-dimensional (nano-3D) solar cell design employing an ultrathin hydrogenated amorphous silicon (a-Si:H) n-i-p junction deposited on zinc oxide (ZnO) nanorod arrays. The ZnO nanorods were prepared by aqueous chemical growth at 80 °C. The photovoltaic performance of the nanorod/a-Si:H solar cell with an ultrathin absorber layer of only 25 nm is experimentally demonstrated. An efficiency of 3.6% and a short-circuit current density of 8.3 mA/cm2 were obtained, significantly higher than values achieved for planar or even textured counterparts with three times thicker ( ∼ 75 nm) a-Si:H absorber layers.
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88.40.jj Silicon solar cells
88.40.hj Efficiency and performance of solar cells

Plasmonic concentrators for enhanced light absorption in ultrathin film organic photovoltaics

A. E. Ostfeld and D. Pacifici

Appl. Phys. Lett. 98, 113112 (2011); http://dx.doi.org/10.1063/1.3567543 (3 pages) | Cited 2 times

Online Publication Date: 16 March 2011

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We report on experimental absorption enhancement in 24 and 150-nm-thick bulk heterojunctions of the conducting polymer poly(3-hexylthiophene) and the fullerene (6,6)-phenyl C61 butyric acid methyl ester. By using periodic and quasiperiodic hole arrays as nanoengineered plasmonic concentrators milled in a silver film, a spectrally broad, omnidirectional, and polarization-insensitive absorption enhancement is observed over that of a reference layer deposited on a flat film. As the result of increased absorption, an enhancement in the polymer fluorescence intensity is also observed. This demonstrates the potential of plasmonic concentrators for improved energy harvesting in ultrathin film solar cells.
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85.60.-q Optoelectronic devices
81.07.Pr Organic-inorganic hybrid nanostructures
81.05.ub Fullerenes and related materials
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
78.55.-m Photoluminescence, properties and materials

Comparison of the spectral and temporal emission characteristics of homoepitaxial and heteroepitaxial ZnO nanowires

C. Pfüller, O. Brandt, T. Flissikowski, H. T. Grahn, T. Ive, J. S. Speck, and S. P. DenBaars

Appl. Phys. Lett. 98, 113113 (2011); http://dx.doi.org/10.1063/1.3567548 (3 pages)

Online Publication Date: 16 March 2011

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Using metalorganic chemical vapor deposition, we have grown ZnO nanowires (NWs) on ZnO(0001) as well as on Al2O3(0001) and Si(111) substrates. The optical properties of these NWs are studied by continuous-wave and time-resolved photoluminescence spectroscopy. Both the spectral and the temporal characteristics of the NWs are found to be virtually identical despite the different substrates and the different morphology of the NWs. This study thus provides strong experimental evidence for the hypothesis that NWs remove the constraints introduced by the substrate.
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78.55.Et II-VI semiconductors
81.07.Gf Nanowires
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.07.Vb Quantum wires
81.05.Dz II-VI semiconductors
78.67.Uh Nanowires

First principle study of the thermal conductance in graphene nanoribbon with vacancy and substitutional silicon defects

Jin-Wu Jiang, Bing-Shen Wang, and Jian-Sheng Wang

Appl. Phys. Lett. 98, 113114 (2011); http://dx.doi.org/10.1063/1.3567768 (3 pages) | Cited 2 times

Online Publication Date: 16 March 2011

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The thermal conductance in graphene nanoribbon with a vacancy or silicon point defect is investigated by nonequilibrium Green’s function (NEGF) formalism combined with first-principles calculations of density-functional theory with local density approximation. The thermal conductance is very sensitive to the position of the vacancy defect, while insensitive to the position of silicon defect. A vacancy defect situated at the center of the nanoribbon generates a saddlelike surface, which greatly reduces the thermal conductance by strong scattering to all phonon modes; while an edge vacancy defect only results in a further reconstruction of the edge and slightly reduces the thermal conductance.
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73.61.Wp Fullerenes and related materials
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
61.72.jd Vacancies

In situ doping of graphene by exfoliation in a nitrogen ambient

Kevin Brenner and Raghu Murali

Appl. Phys. Lett. 98, 113115 (2011); http://dx.doi.org/10.1063/1.3562018 (3 pages) | Cited 1 time

Online Publication Date: 17 March 2011

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We present an in situ method of n-doping graphene by exfoliating in an N-ambient. By exfoliating single-layer graphene in a nitrogen-rich environment, the dopant specie plays an active role in minimizing C–C reconstruction that typically occurs at the moment of defect generation. Employing such in situ methods provides an efficient mechanism of passivating defects produced during graphene growth and transfer, as well as a means of controllably incorporating dopant species into the graphene lattice.
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81.05.ue Graphene
81.65.Rv Passivation
61.72.up Other materials

Theory of optical emission enhancement by coupled metal nanoparticles: An analytical approach

G. Sun and J. B. Khurgin

Appl. Phys. Lett. 98, 113116 (2011); http://dx.doi.org/10.1063/1.3565170 (3 pages)

Online Publication Date: 17 March 2011

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We present an analytical “coupled mode” model explaining enhancement of emission by an emitter placed within complexes of metal nanoparticles and apply it for an important case of an emitter placed inside the gap of two coupled Au nanospheres. This approach has dual advantages of exposing the underling physics of the enhancement and revealing a straightforward path toward optimization.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Bz Metals and metallic alloys

High quality, transferrable graphene grown on single crystal Cu(111) thin films on basal-plane sapphire

Kongara M. Reddy, Andrew D. Gledhill, Chun-Hu Chen, Julie M. Drexler, and Nitin P. Padture

Appl. Phys. Lett. 98, 113117 (2011); http://dx.doi.org/10.1063/1.3569143 (3 pages) | Cited 4 times

Online Publication Date: 17 March 2011

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The current method of growing large-area graphene on polycrystalline Cu surfaces (foils or thin films) and its transfer to arbitrary substrates is technologically attractive. However, the quality of graphene can be improved significantly by growing it on single-crystal Cu surfaces. Here we show that high quality, large-area graphene can be grown on epitaxial single-crystal Cu(111) thin films on reusable basal-plane sapphire [α-Al2O3(0001)] substrates for transfer to another substrate. While enabling graphene growth on Cu single-crystal surfaces, this method has the potential to avoid the high cost and extensive damage to graphene associated with sacrificing bulk single-crystal Cu during graphene transfer.
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81.05.ue Graphene
68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Field emission from GeSe2 nanowalls

Yanjun Zhang, Hui Li, Li Jiang, Huibiao Liu, Chunying Shu, Yuliang Li, and Chunru Wang

Appl. Phys. Lett. 98, 113118 (2011); http://dx.doi.org/10.1063/1.3569147 (3 pages)

Online Publication Date: 17 March 2011

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Single-crystalline GeSe2 nanowalls were prepared via a chemical vapor deposition process. Field-emission (FE) properties of as-prepared GeSe2 nanowalls were investigated. The FE properties could be observed in the GeSe2 nanowalls. The electron emission process from GeSe2 nanowalls is a quantum tunneling process, which follows the Fowler–Nordheim behavior. Their turn-on fields and current densities are comparable to those of many other semiconductor nanomaterials. The field enhancement factor for a single GeSe2 nanowall is estimated to be as high as 527 and 1054 with the average spacing between the electrodes is 100 μm and 200 μm, respectively. These results indicate that GeSe2 nanostructures are promising candidates for applications in field emitter.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.16.-c Methods of micro- and nanofabrication and processing
81.07.Bc Nanocrystalline materials
73.63.Bd Nanocrystalline materials
73.40.Gk Tunneling
61.46.-w Structure of nanoscale materials

Plasmonic core-shell gold nanoparticle enhanced optical absorption in photovoltaic devices

Di Qu (曲迪), Fang Liu (刘仿), Jiafan Yu (于嘉钒), Wanlu Xie (谢婉露), Qi Xu (许骐), Xiangdong Li (李向东), and Yidong Huang (黄翊东)

Appl. Phys. Lett. 98, 113119 (2011); http://dx.doi.org/10.1063/1.3559225 (3 pages) | Cited 2 times

Online Publication Date: 18 March 2011

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The enhancement effect of optical absorption with core-shell gold nanoparticles on the surface of wafer-based silicon photovoltaic devices has been studied. The obvious enhanced photocurrent is observed, especially when the wavelength is above 800 nm, and the highest enhancement value is about 14% around the wavelength of 1100 nm. The simulation results indicate that the presence of dielectric coating shell could improve the surface plasmon based scattering effect at longer wavelength range, which provides a good understanding of the experiment results.
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81.16.-c Methods of micro- and nanofabrication and processing
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
72.40.+w Photoconduction and photovoltaic effects
79.60.Bm Clean metal, semiconductor, and insulator surfaces
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
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