1
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Multiple Exciton Generation in 3D-Ordered Networks of Ge Quantum Wires in Alumina Matrix. MATERIALS 2022; 15:ma15155353. [PMID: 35955285 PMCID: PMC9369923 DOI: 10.3390/ma15155353] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/14/2022] [Revised: 07/14/2022] [Accepted: 07/28/2022] [Indexed: 12/10/2022]
Abstract
Thin films containing 3D-ordered semiconductor quantum wires offer a great tool to improve the properties of photosensitive devices. In the present work, we investigate the photo-generated current in thin films consisting of an interconnected 3D-ordered network of Ge quantum wires in an alumina matrix. The films are prepared using nitrogen-assisted magnetron sputtering co-deposition of Ge and Al2O3. We demonstrate a strong photocurrent generation in the films, much stronger than in similar films containing Ge quantum dots. The enhanced photocurrent generation is the consequence of the multiple exciton generation and the films’ specific structure that allows for efficient carrier transport. Thin film with the largest nitrogen content showed enhanced performance compared to other thin films with 1.6 excitons created after absorption of a single photon at an energy nearly equal to the double bandgap value. The bandgap value depends on the geometrical properties of the quantum wires, and it is close to the maximum of the solar irradiance in this case. In addition, we show that the multiple exciton generation is the most pronounced at the photon energy values equal to multiple values of the thin film bandgap.
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2
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Dushaq G, Paredes B, Rasras M. Strong enhancement of direct transition photoluminescence at room temperature for highly tensile-strained Ge decorated using 5 nm gold nanoparticles. NANOTECHNOLOGY 2020; 31:315201. [PMID: 32303009 DOI: 10.1088/1361-6528/ab8a8d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Strain engineering of germanium has recently attracted tremendous research interest. The primary goal of this approach is to exploit mechanical strain to tune the electrical and optical properties of Ge to ultimately achieve an on-chip light source compatible with silicon technology. Additionally, this can result in enhanced electrical performance for high-speed optoelectronic applications. In this paper, we demonstrate the formation of highly tensile-strained Ge islands grown on a pre-patterned (110) GaAs substrate using a depth controlled nanoindentation process. Results show that a biaxial tensile strain, up to ∼2%, can be transferred from the mechanically stamped substrate to Ge islands by optimizing the parameters of the nanoindentation process. We verified our measurements by observing the islands' photoluminescence (PL) emission properties. A strong emission at room-temperature was observed around the wavelength of 1.9 µm (650 meV). This strain-induced redshift of the PL spectra is consistent with theoretical predictions, revealing a direct Ge bandgap formation. Furthermore, we demonstrate a significant 6.5x enhancement in the PL emission signal of the direct-transition when the Ge islands are decorated by 5 nm gold nanoparticles. This is attributed to a longer optical path length interaction and a plasmonic induced high-field enhancement which increases the light absorption in the Ge islands. Furthermore, results show that GNPs can significantly modulate the energy band structure and the carrier's transportation at the nanoscale metal-germanium Schottky interface. This maskless physical approach can offer a pathway towards a practical CMOS-compatible integrated laser. Additionally, it opens possibilities for designing innovative optoelectronic devices.
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3
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Mechanical Nano-Patterning: Toward Highly-Aligned Ge Self-Assembly on Low Lattice Mismatched GaAs Substrate. Sci Rep 2019; 9:14221. [PMID: 31578380 PMCID: PMC6775282 DOI: 10.1038/s41598-019-50633-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2019] [Accepted: 09/11/2019] [Indexed: 12/04/2022] Open
Abstract
Low-dimensional semiconductor structurers formed on a substrate surface at pre-defined locations and with nano-precision placement is of vital interest. The potential of tailoring their electrical and optical properties will revolutionize the next generation of optoelectronic devices. Traditionally, highly aligned self-assembly of semiconductors relies on Stranski- Krastanov growth mode. In this work, we demonstrate a pathway towards ordered configuration of Ge islands on low lattice mismatch GaAs (110) substrate patterned using depth-controlled nanoindentation. Diamond probe tips with different geometries are used to nano-mechanically stamp the surface of GaAs (110). This creates nanoscale volumes of dislocation-mediated deformation which acts to bias nucleation. Results show that nanostamped GaAs exhibits selective-nucleation of Ge at the indent sites. Ge islands formed on a surface patterned using cube corner tip have height of ~10 nm and lateral size of ~225 nm. Larger islands are formed by using Vickers and Berkovich diamond tips (~400 nm). The strain state of the patterned structures is characterized by micro-Raman spectroscopy. A strain value up to 2% for all tip geometries has been obtained. Additionally, strong room temperature photoluminescence (PL) emission is observed around 1.9 µm (650 meV). The observed strain-induced enhancement in the light-emission efficiency is attributed to direct conduction to heavy-hole (cΓ-HH) and conduction to light-hole (cΓ-LH) transitions. The inherent simplicity of the proposed method offers an attractive technique to manufacture semiconductor quantum dot structures for future electronic and photonic applications.
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4
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Kravtsova AN, Guda LV, Polozhentsev OE, Pankin IA, Soldatov AV. Xanes Specroscopic Diagnostics of the 3D Local Atomic Structure of Nanostructured Materials. J STRUCT CHEM+ 2018. [DOI: 10.1134/s0022476618070259] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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5
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Pivac B, Dubček P, Dasović J, Popović J, Radić N, Bernstorff S, Zavašnik J, Vlahovic B. Stress Evolution during Ge Nanoparticles Growth in a SiO 2 Matrix. Inorg Chem 2018; 57:14939-14952. [DOI: 10.1021/acs.inorgchem.8b02760] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Branko Pivac
- Materials Physics, R. Bošković Institute, Bijenička 54, Zagreb 10000, Croatia
| | - Pavo Dubček
- Materials Physics, R. Bošković Institute, Bijenička 54, Zagreb 10000, Croatia
| | - Jasna Dasović
- Materials Physics, R. Bošković Institute, Bijenička 54, Zagreb 10000, Croatia
| | - Jasminka Popović
- Materials Physics, R. Bošković Institute, Bijenička 54, Zagreb 10000, Croatia
| | - Nikola Radić
- Materials Physics, R. Bošković Institute, Bijenička 54, Zagreb 10000, Croatia
| | - Sigrid Bernstorff
- Elettra-Sincrotrone Trieste, SS 14, Km 163.5, in AREA Science Park, Basovizza 34149, Trieste, Italy
| | - Janez Zavašnik
- Jožef Stefan Institute, Jamova Cesta 39, Ljubljana 1000, Slovenia
- Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Straße 1, Düsseldorf 40237, Germany
| | - Branislav Vlahovic
- North Carolina Central University, Durham, North Carolina 27707, United States
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6
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Rudd R, Hall C, Murphy PJ, Reece PJ, Charrault E, Evans D. Decoupling the effects of confinement and passivation on semiconductor quantum dots. Phys Chem Chem Phys 2018; 18:19765-72. [PMID: 27385513 DOI: 10.1039/c6cp03438a] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Semiconductor (SC) quantum dots (QDs) have recently been fabricated by both chemical and plasma techniques for specific absorption and emission of light. Their optical properties are governed by the size of the QD and the chemistry of any passivation at their surface. Here, we decouple the effects of confinement and passivation by utilising DC magnetron sputtering to fabricate SC QDs in a perfluorinated polyether oil. Very high band gaps are observed for fluorinated QDs with increasing levels of quantum confinement (from 4.2 to 4.6 eV for Si, and 2.5 to 3 eV for Ge), with a shift down to 3.4 eV for Si when oxygen is introduced to the passivation layer. In contrast, the fluorinated Si QDs display a constant UV photoluminescence (3.8 eV) irrespective of size. This ability to tune the size and passivation independently opens a new opportunity to extending the use of simple semiconductor QDs.
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Affiliation(s)
- Roya Rudd
- Future Industries Institute, University of South Australia, Mawson Lakes, South Australia, 5095, Australia.
| | - Colin Hall
- Future Industries Institute, University of South Australia, Mawson Lakes, South Australia, 5095, Australia.
| | - Peter J Murphy
- Future Industries Institute, University of South Australia, Mawson Lakes, South Australia, 5095, Australia.
| | - Peter J Reece
- School of Physics, University of New South Wales, Sydney, NSW 2052, Australia.
| | - Eric Charrault
- Future Industries Institute, University of South Australia, Mawson Lakes, South Australia, 5095, Australia.
| | - Drew Evans
- Future Industries Institute, University of South Australia, Mawson Lakes, South Australia, 5095, Australia.
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7
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Lee M, Park YH, Kang EB, Chae A, Choi Y, Jo S, Kim YJ, Park SJ, Min B, An TK, Lee J, In SI, Kim SY, Park SY, In I. Highly Efficient Visible Blue-Emitting Black Phosphorus Quantum Dot: Mussel-Inspired Surface Functionalization for Bioapplications. ACS OMEGA 2017; 2:7096-7105. [PMID: 30023540 PMCID: PMC6044902 DOI: 10.1021/acsomega.7b01058] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/25/2017] [Accepted: 10/11/2017] [Indexed: 05/28/2023]
Abstract
The preparation of blue-emitting black phosphorus quantum dots (BPQDs) is based on the liquid-phase exfoliation of bulk BP. We report the synthesis of soluble BPQDs showing a strong visible blue-light emission. Highly fluorescent (photoluminescence quantum yield of ≈5% with the maximum emission (λmax) at ≈437 nm) and dispersible BPQDs in various organic solvents are first prepared by simple ultrasonication of BP crystals in chloroform in the ambient atmosphere. Furthermore, simple mussel-inspired surface functionalization of BPQDs with catechol-grafted poly(ethylene glycol) in basic buffer afforded water-soluble blue-emitting BPQDs showing long-term fluorescence stability, very low cytotoxicity, and excellent fluorescence live cell imaging capability.
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Affiliation(s)
- Miyeon Lee
- Department
of Chemistry, KAIST, Yuseong-gu, Daejeon 34141, South Korea
| | - Young Ho Park
- Department
of Energy System Engineering, DGIST, Daegu 42988, South Korea
| | - Eun Bi Kang
- Department of Chemical
& Biological Engineering, Department of Polymer Science and
Engineering, and Department of IT Convergence (Brain Korea PLUS 21), Korea National University of Transportation, 50 Daehak-ro, Chungju-si, Chungbuk 27909, South Korea
| | - Ari Chae
- Department of Chemical
& Biological Engineering, Department of Polymer Science and
Engineering, and Department of IT Convergence (Brain Korea PLUS 21), Korea National University of Transportation, 50 Daehak-ro, Chungju-si, Chungbuk 27909, South Korea
| | - Yujin Choi
- Department of Chemical
& Biological Engineering, Department of Polymer Science and
Engineering, and Department of IT Convergence (Brain Korea PLUS 21), Korea National University of Transportation, 50 Daehak-ro, Chungju-si, Chungbuk 27909, South Korea
| | - Seongho Jo
- Department of Chemical
& Biological Engineering, Department of Polymer Science and
Engineering, and Department of IT Convergence (Brain Korea PLUS 21), Korea National University of Transportation, 50 Daehak-ro, Chungju-si, Chungbuk 27909, South Korea
| | - Yu Jin Kim
- Center for
Nanoscale Materials, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Soo-Jin Park
- Department
of Chemistry, Inha University, Incheon 402-751, South Korea
| | - Byunggak Min
- Department of Chemical
& Biological Engineering, Department of Polymer Science and
Engineering, and Department of IT Convergence (Brain Korea PLUS 21), Korea National University of Transportation, 50 Daehak-ro, Chungju-si, Chungbuk 27909, South Korea
| | - Tae Kyu An
- Department of Chemical
& Biological Engineering, Department of Polymer Science and
Engineering, and Department of IT Convergence (Brain Korea PLUS 21), Korea National University of Transportation, 50 Daehak-ro, Chungju-si, Chungbuk 27909, South Korea
| | - Jihoon Lee
- Department of Chemical
& Biological Engineering, Department of Polymer Science and
Engineering, and Department of IT Convergence (Brain Korea PLUS 21), Korea National University of Transportation, 50 Daehak-ro, Chungju-si, Chungbuk 27909, South Korea
| | - Su-Il In
- Department
of Energy System Engineering, DGIST, Daegu 42988, South Korea
| | - Sang Youl Kim
- Department
of Chemistry, KAIST, Yuseong-gu, Daejeon 34141, South Korea
| | - Sung Young Park
- Department of Chemical
& Biological Engineering, Department of Polymer Science and
Engineering, and Department of IT Convergence (Brain Korea PLUS 21), Korea National University of Transportation, 50 Daehak-ro, Chungju-si, Chungbuk 27909, South Korea
| | - Insik In
- Department of Chemical
& Biological Engineering, Department of Polymer Science and
Engineering, and Department of IT Convergence (Brain Korea PLUS 21), Korea National University of Transportation, 50 Daehak-ro, Chungju-si, Chungbuk 27909, South Korea
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8
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Gu T, Gao J, Ostroumov EE, Jeong H, Wu F, Fardel R, Yao N, Priestley RD, Scholes GD, Loo YL, Arnold CB. Photoluminescence of Functionalized Germanium Nanocrystals Embedded in Arsenic Sulfide Glass. ACS APPLIED MATERIALS & INTERFACES 2017; 9:18911-18917. [PMID: 28485911 DOI: 10.1021/acsami.7b02520] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Embedding metallic and semiconductor nanoparticles in a chalcogenide glass matrix effectively modifies the photonic properties. Such nanostructured materials could play an important role in optoelectronic devices, catalysis, and imaging applications. In this work, we fabricate and characterize germanium nanocrystals (Ge NCs) embedded in arsenic sulfide thin films by pulsed laser ablation in aliphatic amine solutions. Unstable surface termination of aliphatic groups and stable termination by amine on Ge NCs are indicated by Raman and Fourier-transform infrared spectroscopy measurements. A broad-band photoluminescence in the visible range is observed for the amine functionalized Ge NCs. A noticeable enhancement of fluorescence is observed for Ge NCs in arsenic sulfide, after annealing to remove the residual solvent of the glass matrix.
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Affiliation(s)
- Tingyi Gu
- Electrical and Computer Engineering, University of Delaware , Newark, Delaware 19716, United States
| | - Jia Gao
- Department of Chemical and Biological Engineering, Princeton University , Princeton, New Jersey 08544, United States
| | - Evgeny E Ostroumov
- Department of Chemistry, Princeton University , Princeton, New Jersey 08544, United States
| | - Hyuncheol Jeong
- Department of Chemical and Biological Engineering, Princeton University , Princeton, New Jersey 08544, United States
| | - Fan Wu
- Princeton Institute for the Science and Technology of Materials, Princeton University , Princeton, New Jersey 08544, United States
| | - Romain Fardel
- Princeton Institute for the Science and Technology of Materials, Princeton University , Princeton, New Jersey 08544, United States
- Department of Mechanical and Aerospace Engineering, Princeton University , Princeton, New Jersey 08544, United States
| | - Nan Yao
- Princeton Institute for the Science and Technology of Materials, Princeton University , Princeton, New Jersey 08544, United States
| | - Rodney D Priestley
- Department of Chemical and Biological Engineering, Princeton University , Princeton, New Jersey 08544, United States
- Princeton Institute for the Science and Technology of Materials, Princeton University , Princeton, New Jersey 08544, United States
| | - Gregory D Scholes
- Department of Chemistry, Princeton University , Princeton, New Jersey 08544, United States
- Princeton Institute for the Science and Technology of Materials, Princeton University , Princeton, New Jersey 08544, United States
| | - Yueh-Lin Loo
- Department of Chemical and Biological Engineering, Princeton University , Princeton, New Jersey 08544, United States
- Andlinger Center for Energy and the Environment, Princeton University , Princeton, New Jersey 08544, United States
| | - Craig B Arnold
- Princeton Institute for the Science and Technology of Materials, Princeton University , Princeton, New Jersey 08544, United States
- Department of Mechanical and Aerospace Engineering, Princeton University , Princeton, New Jersey 08544, United States
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9
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McLeod JA, Zhao J, Yang L, Liu Y, Liu L. Structural evolution of reduced GeO x nanoparticles. Phys Chem Chem Phys 2017; 19:3182-3191. [PMID: 28083591 DOI: 10.1039/c6cp07354a] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
GeOx nanoparticles (NPs) are of growing interest in lithium storage and optoelectronics. GeOx NPs prepared by chemical reduction, exposed to air or retained under N2, then annealed under H2 at various temperatures are studied herein using soft X-ray spectroscopy. We find that fresh and air-exposed GeOx NPs evolve rather differently under annealing. The fresh GeOx NPs start as a very amorphous heterogeneous mixture of GeOx and Ge, and during annealing both the valence band and conduction band edges evolve. In contrast, the air-exposed GeOx NPs initially contain quartz-phase GeO2, and during annealing only the conduction band edge evolves due to increased oxygen vacancies forming unoccupied defect states (the valence band does not change until annealing at high temperture, at which point almost all of the GeO2 is removed). These findings suggest a preparation and annealing strategy that could be used to tailor GeOx NPs for their intended use in lithium storage or optoelectronic applications.
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Affiliation(s)
- John A McLeod
- Institute of Functional Nano and Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Soochow University, Suzhou, Jiangsu 215123, China.
| | - Jia Zhao
- Institute of Functional Nano and Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Soochow University, Suzhou, Jiangsu 215123, China.
| | - Linju Yang
- Institute of Functional Nano and Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Soochow University, Suzhou, Jiangsu 215123, China.
| | - Yi Liu
- Institute of Functional Nano and Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Soochow University, Suzhou, Jiangsu 215123, China.
| | - Lijia Liu
- Institute of Functional Nano and Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Soochow University, Suzhou, Jiangsu 215123, China.
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10
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Di Bartolomeo A, Passacantando M, Niu G, Schlykow V, Lupina G, Giubileo F, Schroeder T. Observation of field emission from GeSn nanoparticles epitaxially grown on silicon nanopillar arrays. NANOTECHNOLOGY 2016; 27:485707. [PMID: 27804921 DOI: 10.1088/0957-4484/27/48/485707] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We apply molecular beam epitaxy to grow GeSn-nanoparticles on top of Si-nanopillars patterned onto p-type Si wafers. We use x-ray photoelectron spectroscopy to confirm a metallic behavior of the nanoparticle surface due to partial Sn segregation as well as the presence of a superficial Ge oxide. We report the observation of stable field emission (FE) current from the GeSn-nanoparticles, with turn on field of [Formula: see text] and field enhancement factor β ∼ 100 at anode-cathode distance of ∼0.6 μm. We prove that FE can be enhanced by preventing GeSn nanoparticles oxidation or by breaking the oxide layer through electrical stress. Finally, we show that GeSn/p-Si junctions have a rectifying behavior.
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Affiliation(s)
- Antonio Di Bartolomeo
- Physics Department 'E. R. Caianiello', University of Salerno, via Giovanni Paolo II, I-84084, Fisciano, Italy
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11
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Origin of the Photoluminescence Quantum Yields Enhanced by Alkane-Termination of Freestanding Silicon Nanocrystals: Temperature-Dependence of Optical Properties. Sci Rep 2016; 6:36951. [PMID: 27830771 PMCID: PMC5103264 DOI: 10.1038/srep36951] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2016] [Accepted: 10/21/2016] [Indexed: 02/08/2023] Open
Abstract
On the basis of the systematic study on temperature dependence of photoluminescence (PL) properties along with relaxation dynamics we revise a long-accepted mechanism for enhancing absolute PL quantum yields (QYs) of freestanding silicon nanocrystals (ncSi). A hydrogen-terminated ncSi (ncSi:H) of 2.1 nm was prepared by thermal disproportination of (HSiO1.5)n, followed by hydrofluoric etching. Room-temperature PL QY of the ncSi:H increased twentyfold only by hydrosilylation of 1-octadecene (ncSi-OD). A combination of PL spectroscopic measurement from cryogenic to room temperature with structural characterization allows us to link the enhanced PL QYs with the notable difference in surface structure between the ncSi:H and the ncSi-OD. The hydride-terminated surface suffers from the presence of a large amount of nonradiative relaxation channels whereas the passivation with alkyl monolayers suppresses the creation of the nonradiative relaxation channels to yield the high PL QY.
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12
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Pivac B, Dubček P, Popović J, Dasović J, Bernstorff S, Radić N, Zavašnik J. Influence of stress on the properties of Ge nanocrystals in an SiO2matrix. J Appl Crystallogr 2016. [DOI: 10.1107/s1600576716014175] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
In this work, self-assembled Ge quantum dot (QD) formation in a dielectric matrix is explored. Of particular interest were their structural and optical properties, in order to understand the stress build-up in such a process and its impact on the material properties during processing. To this end, thin films consisting of (Ge + SiO2)/SiO2multilayers grown by RF magnetron sputtering were deposited at room temperature. Annealing of such films at 873 K in inert N2atmosphere produced, at the position of the Ge-rich SiO2layers, a high lateral density (about 1012 cm−2) of Ge QDs with a good crystallinity. SiO2spacer layers separated the adjacent Ge-rich layers, where the Ge QDs were formed with a diameter of about the size of the (Ge + SiO2) as-deposited layer thickness, and created a good vertical repeatability, confirmed by the appearance of a Bragg sheet in two-dimensional small-angle X-ray scattering patterns. The structural analysis, by wide-angle X-ray diffraction, grazing-incidence small-angle X-ray scattering and transmission electron microscopy, has shown that the described processing of the films induced large compressive stress on the formed QDs. Optical analysis by time-resolved photoluminescence (PL) revealed that the high density of crystalline Ge QDs embedded in the amorphous SiO2matrix produced a strong luminescence in the visible part of the spectrum at 2–2.5 eV photon energy. It is shown that the decay dynamics in this energy range are very fast, and therefore the transitions that create such PL are attributed to matrix defects present in the shell surrounding the Ge QD surface (interface region with the matrix). The measured PL peak, though wide at its half-width, when analysed in consecutive short spectral segments showed the same decay dynamics, suggesting the same mechanism of relaxation.
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Stavarache I, Maraloiu VA, Prepelita P, Iordache G. Nanostructured germanium deposited on heated substrates with enhanced photoelectric properties. BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2016; 7:1492-1500. [PMID: 27826525 PMCID: PMC5082716 DOI: 10.3762/bjnano.7.142] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2016] [Accepted: 09/28/2016] [Indexed: 06/01/2023]
Abstract
Obtaining high-quality materials, based on nanocrystals, at low temperatures is one of the current challenges for opening new paths in improving and developing functional devices in nanoscale electronics and optoelectronics. Here we report a detailed investigation of the optimization of parameters for the in situ synthesis of thin films with high Ge content (50 %) into SiO2. Crystalline Ge nanoparticles were directly formed during co-deposition of SiO2 and Ge on substrates at 300, 400 and 500 °C. Using this approach, effects related to Ge-Ge spacing are emphasized through a significant improvement of the spatial distribution of the Ge nanoparticles and by avoiding multi-step fabrication processes or Ge loss. The influence of the preparation conditions on structural, electrical and optical properties of the fabricated nanostructures was studied by X-ray diffraction, transmission electron microscopy, electrical measurements in dark or under illumination and response time investigations. Finally, we demonstrate the feasibility of the procedure by the means of an Al/n-Si/Ge:SiO2/ITO photodetector test structure. The structures, investigated at room temperature, show superior performance, high photoresponse gain, high responsivity (about 7 AW-1), fast response time (0.5 µs at 4 kHz) and great optoelectronic conversion efficiency of 900% in a wide operation bandwidth, from 450 to 1300 nm. The obtained photoresponse gain and the spectral width are attributed mainly to the high Ge content packed into a SiO2 matrix showing the direct connection between synthesis and optical properties of the tested nanostructures. Our deposition approach put in evidence the great potential of Ge nanoparticles embedded in a SiO2 matrix for hybrid integration, as they may be employed in structures and devices individually or with other materials, hence the possibility of fabricating various heterojunctions on Si, glass or flexible substrates for future development of Si-based integrated optoelectronics.
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Affiliation(s)
- Ionel Stavarache
- National Institute of Materials Physics, 405A Atomistilor Street, 077125 Magurele, Ilfov, Romania
| | - Valentin Adrian Maraloiu
- National Institute of Materials Physics, 405A Atomistilor Street, 077125 Magurele, Ilfov, Romania
| | - Petronela Prepelita
- National Institute for Laser, Plasma and Radiation Physics, 409 Atomistilor Street, 077125 Magurele, Ilfov, Romania
| | - Gheorghe Iordache
- National Institute of Materials Physics, 405A Atomistilor Street, 077125 Magurele, Ilfov, Romania
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Zhang Y, Ersoy O, Karatutlu A, Little W, Sapelkin A. Local structure of Ge quantum dots determined by combined numerical analysis of EXAFS and XANES data. JOURNAL OF SYNCHROTRON RADIATION 2016; 23:253-259. [PMID: 26698071 DOI: 10.1107/s160057751501913x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/23/2015] [Accepted: 10/10/2015] [Indexed: 06/05/2023]
Abstract
The sensitivity of X-ray absorption near-edge structure (XANES) to the local symmetry has been investigated in small (∼4 nm) matrix-free Ge quantum dots. The FDMNES package was used to calculate the theoretical XANES spectra that were compared with the experimental data of as-prepared and annealed nanoparticles. It was found that XANES data for an as-prepared sample can only be adequately described if the second coordination shell of the diamond-type structural model is included in the FDMNES calculations. This is in contrast to the extended X-ray absorption fine-structure data that show only the first-shell signal. These results suggest that, despite the high degree of disorder and a large surface-to-volume ratio, as-prepared small Ge quantum dots retain the diamond-type symmetry beyond the first shell. Furthermore, we utilized this sensitivity of XANES to the local symmetry to study annealed Ge quantum dots and found evidence for significant structural distortion which we attribute to the existence of surface disorder in the annealed oxygen-free Ge quantum dots.
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Affiliation(s)
- Yuanpeng Zhang
- School of Physics and Astronomy, Queen Mary, University of London, Mile End Road, London E1 4NS, UK
| | - Osman Ersoy
- School of Physics and Astronomy, Queen Mary, University of London, Mile End Road, London E1 4NS, UK
| | - Ali Karatutlu
- School of Physics and Astronomy, Queen Mary, University of London, Mile End Road, London E1 4NS, UK
| | - William Little
- School of Physics and Astronomy, Queen Mary, University of London, Mile End Road, London E1 4NS, UK
| | - Andrei Sapelkin
- School of Physics and Astronomy, Queen Mary, University of London, Mile End Road, London E1 4NS, UK
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15
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Zhao J, Yang L, McLeod JA, Liu L. Reduced GeO2 Nanoparticles: Electronic Structure of a Nominal GeOx Complex and Its Stability under H2 Annealing. Sci Rep 2015; 5:17779. [PMID: 26634908 PMCID: PMC4669506 DOI: 10.1038/srep17779] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2015] [Accepted: 11/04/2015] [Indexed: 11/23/2022] Open
Abstract
A nominal GeOx (x ≤ 2) compound contains mixtures of Ge, Ge suboxides, and GeO2, but the detailed composition and crystallinity could vary from material to material. In this study, we synthesize GeOx nanoparticles by chemical reduction of GeO2, and comparatively investigate the freshly prepared sample and the sample exposed to ambient conditions. Although both compounds are nominally GeOx, they exhibit different X-ray diffraction patterns. X-ray absorption fine structure (XAFS) is utilized to analyse the detailed structure of GeOx. We find that the two initial GeOx compounds have entirely different compositions: the fresh GeOx contains large amorphous Ge clusters connected by GeOx, while after air exposure; the Ge clusters are replaced by a GeO2-GeOx composite. In addition, the two GeOx products undergo different structural rearrangement under H2 annealing, producing different intermediate phases before ultimately turning into metallic Ge. In the fresh GeOx, the amorphous Ge remains stable, with the GeOx being gradually reduced to Ge, leading to a final structure of crystalline Ge grains connected by GeOx. The air-exposed GeOx on the other hand, undergoes a GeO2→GeOx→Ge transition, in which H2 induces the creation of oxygen vacancies at intermediate stage. A complete removal of oxides occurs at high temperature.
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Affiliation(s)
- Jia Zhao
- Jiangsu Key Laboratory for Carbon-Based Functional Materials &Devices, Institute of Functional Nano and Soft Materials (FUNSOM), Soochow University-Western University Center for Synchrotron Radiation Research, Soochow University, Suzhou, Jiangsu, 215123 China
| | - Linju Yang
- Jiangsu Key Laboratory for Carbon-Based Functional Materials &Devices, Institute of Functional Nano and Soft Materials (FUNSOM), Soochow University-Western University Center for Synchrotron Radiation Research, Soochow University, Suzhou, Jiangsu, 215123 China
| | - John A McLeod
- Jiangsu Key Laboratory for Carbon-Based Functional Materials &Devices, Institute of Functional Nano and Soft Materials (FUNSOM), Soochow University-Western University Center for Synchrotron Radiation Research, Soochow University, Suzhou, Jiangsu, 215123 China
| | - Lijia Liu
- Jiangsu Key Laboratory for Carbon-Based Functional Materials &Devices, Institute of Functional Nano and Soft Materials (FUNSOM), Soochow University-Western University Center for Synchrotron Radiation Research, Soochow University, Suzhou, Jiangsu, 215123 China
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16
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Corsini NRC, Zhang Y, Little WR, Karatutlu A, Ersoy O, Haynes PD, Molteni C, Hine NDM, Hernandez I, Gonzalez J, Rodriguez F, Brazhkin VV, Sapelkin A. Pressure-Induced Amorphization and a New High Density Amorphous Metallic Phase in Matrix-Free Ge Nanoparticles. NANO LETTERS 2015; 15:7334-7340. [PMID: 26457875 DOI: 10.1021/acs.nanolett.5b02627] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Over the last two decades, it has been demonstrated that size effects have significant consequences for the atomic arrangements and phase behavior of matter under extreme pressure. Furthermore, it has been shown that an understanding of how size affects critical pressure-temperature conditions provides vital guidance in the search for materials with novel properties. Here, we report on the remarkable behavior of small (under ~5 nm) matrix-free Ge nanoparticles under hydrostatic compression that is drastically different from both larger nanoparticles and bulk Ge. We discover that the application of pressure drives surface-induced amorphization leading to Ge-Ge bond overcompression and eventually to a polyamorphic semiconductor-to-metal transformation. A combination of spectroscopic techniques together with ab initio simulations were employed to reveal the details of the transformation mechanism into a new high density phase-amorphous metallic Ge.
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Affiliation(s)
- Niccolo R C Corsini
- Department of Physics, Blackett Laboratory, Imperial College London , Exhibition Road, London SW7 2AZ, United Kingdom
| | - Yuanpeng Zhang
- School of Physics and Astronomy, Queen Mary University of London , Mile End Road, London E1 4NS, United Kingdom
| | - William R Little
- School of Physics and Astronomy, Queen Mary University of London , Mile End Road, London E1 4NS, United Kingdom
| | - Ali Karatutlu
- School of Physics and Astronomy, Queen Mary University of London , Mile End Road, London E1 4NS, United Kingdom
- Electrical and Electronics Engineering, Yildirim Campus, Bursa Orhangazi University , 16245 Yildirim, Bursa, Turkey
| | - Osman Ersoy
- School of Physics and Astronomy, Queen Mary University of London , Mile End Road, London E1 4NS, United Kingdom
| | - Peter D Haynes
- Department of Physics, Blackett Laboratory, Imperial College London , Exhibition Road, London SW7 2AZ, United Kingdom
| | - Carla Molteni
- Department of Physics, King's College London , Strand, London WC2R 2LS, United Kingdom
| | - Nicholas D M Hine
- TCM Group, Cavendish Laboratory, University of Cambridge , JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom
- Department of Physics, University of Warwick , Coventry CV4 7AL, United Kingdom
| | - Ignacio Hernandez
- Malta Consolider Team, Departmento CITIMAC, Universidad de Cantabria , Avenida Los Castros s/n, 39005 Santander, Spain
| | - Jesus Gonzalez
- Malta Consolider Team, Departmento CITIMAC, Universidad de Cantabria , Avenida Los Castros s/n, 39005 Santander, Spain
| | - Fernando Rodriguez
- Malta Consolider Team, Departmento CITIMAC, Universidad de Cantabria , Avenida Los Castros s/n, 39005 Santander, Spain
| | - Vadim V Brazhkin
- High Pressure Physics Institute, RAS , 142190 Troitsk, Moscow Region, Russia
| | - Andrei Sapelkin
- School of Physics and Astronomy, Queen Mary University of London , Mile End Road, London E1 4NS, United Kingdom
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17
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Millo O, Balberg I, Azulay D, Purkait TK, Swarnakar AK, Rivard E, Veinot JGC. Direct Evaluation of the Quantum Confinement Effect in Single Isolated Ge Nanocrystals. J Phys Chem Lett 2015; 6:3396-3402. [PMID: 26275992 DOI: 10.1021/acs.jpclett.5b01541] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
To address the yet open question regarding the nature of quantum confinement in Ge nanocrystals (Ge NCs) we employed scanning tunneling spectroscopy to monitor the electronic structure of individual isolated Ge NCs as a function of their size. The (single-particle) band gaps extracted from the tunneling spectra increase monotonically with decreasing nanocrystal size, irrespective of the capping ligands, manifesting the effect of quantum confinement. Band-gap widening of ∼1 eV with respect to the bulk value was observed for Ge-NCs 3 nm in diameter. The picture emerging from comparison with theoretical calculations and other experimental results is discussed.
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Affiliation(s)
- Oded Millo
- Racah Institute of Physics and the Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem , Jerusalem 91904, Israel
| | - Isacc Balberg
- Racah Institute of Physics and the Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem , Jerusalem 91904, Israel
| | - Doron Azulay
- Racah Institute of Physics and the Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem , Jerusalem 91904, Israel
| | - Tapas K Purkait
- Department of Chemistry, University of Alberta , 11227 Saskatchewan Drive NW, Edmonton, Alberta T6G 2G2, Canada
| | - Anindya K Swarnakar
- Department of Chemistry, University of Alberta , 11227 Saskatchewan Drive NW, Edmonton, Alberta T6G 2G2, Canada
| | - Eric Rivard
- Department of Chemistry, University of Alberta , 11227 Saskatchewan Drive NW, Edmonton, Alberta T6G 2G2, Canada
| | - Jonathan G C Veinot
- Department of Chemistry, University of Alberta , 11227 Saskatchewan Drive NW, Edmonton, Alberta T6G 2G2, Canada
- NRC-National Institute for Nanotechnology , 11421 Saskatchewan Drive NW, Edmonton, Alberta T6G 2M9, Canada
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