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Search Results (386)

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Keywords = super-lattice

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12 pages, 1916 KiB  
Article
A Revisiting to Re-Effects on Dislocation Slip Mediated Creeps of the γ′-Ni3Al Phase at High Temperature via a Hybrid Model
by Zhuangzhuang Kong, Jianing Luo, Yunlei Xu and Ping Peng
Metals 2025, 15(2), 103; https://doi.org/10.3390/met15020103 - 22 Jan 2025
Viewed by 352
Abstract
The anomalous flow behavior of the γ′-Ni3Al phase at high temperature is closely related to a cross-slip of 1/2110111 super-partial dislocations. The acceleration of cross-slips induced by the addition of rhenium (Re) is known as Re-effects. In [...] Read more.
The anomalous flow behavior of the γ′-Ni3Al phase at high temperature is closely related to a cross-slip of 1/2110111 super-partial dislocations. The acceleration of cross-slips induced by the addition of rhenium (Re) is known as Re-effects. In this work, by means of a series of lattice transitions, a hybrid model including a preexisting anti-phase boundary APB111 was constructed to assess the difficulty of cross-slips of 1/2110111 super-partial dislocations from 111 planes to 001 planes in the γ′-Ni3Al phases, and the impact of the addition of Re on these dislocation mediated creep resistances was reinvestigated by first-principles calculations. The results showed that the addition of Re at preferential Al sublattice sites was indeed beneficial for the cross-slip of the first leading 1/2110111 super-partial dislocations, and the existence of APB111 could promote cross-slip of second leading 1/2110111 super-partial dislocations. A detailed calculation of stacking fault energies demonstrated that an obvious Suzuki segregation of Re existed at APB111 and APB001, and Re preferentially occupied Ni sublattice sites. It is found Re-segregations at APB111 were disadvantageous for the cross-slip of new 1/2110111 super-partial dislocations, but the formation of more Kear-Wilsdorf dislocation locks could benefit from Re-segregations at APB001. Full article
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21 pages, 8328 KiB  
Article
Impact of Buffer Layer on Electrical Properties of Bow-Tie Microwave Diodes on the Base of MBE-Grown Modulation-Doped Semiconductor Structure
by Algirdas Sužiedėlis, Steponas Ašmontas, Jonas Gradauskas, Aurimas Čerškus, Aldis Šilėnas and Andžej Lučun
Crystals 2025, 15(1), 50; https://doi.org/10.3390/cryst15010050 - 3 Jan 2025
Viewed by 429
Abstract
Bow-tie diodes on the base of modulation-doped semiconductor structures are often used to detect radiation in GHz to THz frequency range. The operation of the bow-tie microwave diodes is based on carrier heating phenomena in an epitaxial semiconductor structure with broken geometrical symmetry. [...] Read more.
Bow-tie diodes on the base of modulation-doped semiconductor structures are often used to detect radiation in GHz to THz frequency range. The operation of the bow-tie microwave diodes is based on carrier heating phenomena in an epitaxial semiconductor structure with broken geometrical symmetry. However, the electrical properties of bow-tie diodes are highly dependent on the purity of the grown epitaxial layer—specifically, the minimal number of defects—and the quality of the ohmic contacts. The quality of MBE-grown semiconductor structure depends on the presence of a buffer layer between a semiconductor substrate and an epitaxial layer. In this paper, we present an investigation of the electrical and optical properties of planar bow-tie microwave diodes fabricated using modulation-doped semiconductor structures grown via the MBE technique, incorporating either a GaAs buffer layer or a GaAs–AlGaAs super-lattice buffer between the semi-insulating substrate and the active epitaxial layer. These properties include voltage sensitivity, electrical resistance, I–V characteristic asymmetry, nonlinearity coefficient, and photoluminescence. The investigation revealed that the buffer layer, as well as the illumination with visible light, strongly influences the properties of the bow-tie diodes. Full article
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15 pages, 3988 KiB  
Article
Performance Study of Ultraviolet AlGaN/GaN Light-Emitting Diodes Based on Superlattice Tunneling Junction
by Zhuang Zhao, Yang Liu, Peixian Li, Xiaowei Zhou, Bo Yang, Yingru Xiang and Junchun Bai
Micromachines 2025, 16(1), 28; https://doi.org/10.3390/mi16010028 - 28 Dec 2024
Viewed by 455
Abstract
In this study, we aim to enhance the internal quantum efficiency (IQE) of AlGaN-based ultraviolet (UV) light-emitting diodes (LEDs) by using the short-period AlGaN/GaN superlattice as a tunnel junction (TJ) to construct polarized structures. We analyze in detail the effect of this polarized [...] Read more.
In this study, we aim to enhance the internal quantum efficiency (IQE) of AlGaN-based ultraviolet (UV) light-emitting diodes (LEDs) by using the short-period AlGaN/GaN superlattice as a tunnel junction (TJ) to construct polarized structures. We analyze in detail the effect of this polarized TJ on the carrier injection efficiency and investigate the increase in hole and electron density caused by the formation of 2D hole gas (2DHG) and 2D electron gas (2DEG) in the superlattice structure. In addition, a dielectric layer is introduced to evaluate the effect of stress changes on the tunneling probability and current spread in TJ. At a current of 140 mA, this method demonstrates effective current expansion. Our results not only improve the performance of UV LEDs but also provide an important theoretical and experimental basis for future research on UV LEDs based on superlattice TJ. In addition, our study also highlights the key role of group III nitride materials in achieving efficient UV luminescence, and the polarization characteristics and band structure of these materials are critical for optimizing carrier injection and recombination processes. Full article
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16 pages, 5835 KiB  
Article
LA-ICP-MS Trace Element Characteristics and Geological Significance of Stibnite in the Zhaxikang Pb–Zn–Ag–Sb Deposit, Southern Tibet, SW China
by Zijun Qiu, Jinchao Wu, Panagiotis Voudouris, Stylianos Tombros, Jiajun Liu and Degao Zhai
Minerals 2024, 14(12), 1294; https://doi.org/10.3390/min14121294 - 20 Dec 2024
Viewed by 588
Abstract
Discovered within the North Himalayan Metallogenic Belt (NHMB), the Zhaxikang Pb–Zn–Ag–Sb deposit stands as the sole super-large scale ore deposit in the region. This deposit holds significant quantities of Pb and Zn (2.066 million tons at 6.38% average grade), Ag (2661 tons at [...] Read more.
Discovered within the North Himalayan Metallogenic Belt (NHMB), the Zhaxikang Pb–Zn–Ag–Sb deposit stands as the sole super-large scale ore deposit in the region. This deposit holds significant quantities of Pb and Zn (2.066 million tons at 6.38% average grade), Ag (2661 tons at an average of 101.64 g/t), and Sb (0.235 million tons at 1.14% average grade), making it one of China’s foremost Sb–polymetallic deposits. Stibnite represents the main carrier of Sb in this deposit and has been of great attention since its initial discovery. However, the trace element composition of stibnite in the Zhaxikang deposit has not yet been determined. This study carried out an analysis of the distribution patterns and substitution processes of trace elements within stibnite gathered from the Zhaxikang deposit, aiming to provide crucial information on ore-forming processes. Utilizing high-precision laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), we discovered that the studied stibnite is notably enriched in arsenic (~100 ppm) and lead (~10 ppm). Furthermore, the notably consistent time-resolved profiles suggest that elements such as Fe, Cu, As, In, Sn, Hg, and Pb predominantly exist as solid solutions within stibnite. Consequently, it is probable that the enrichment of Cu, Pb, and Sn in stibnite is due to isomorphic substitution reactions, including 3Pb2+↔2Sb3+, Cu+ + Pb2+↔Sb3+, and In3+ + Sn3+↔2Sb3+. Apart from that, Mn, Pb, and Hg with the spiky signals indicate their existence within stibnite as micro-inclusions. Overall, we found that the trace element substitutions in stibnite from the Zhaxikang Pb–Zn–Ag–Sb deposit are complicated. Incorporations of trace elements such as Pb, Cu, and In into stibnite are largely influenced by a variety of factors. The simple lattice structure and constant trace elements in studied stibnite indicate a low-temperature hydrothermal system and a relatively stable process for stibnite formation. Full article
(This article belongs to the Special Issue Ag-Pb-Zn Deposits: Geology and Geochemistry)
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18 pages, 13730 KiB  
Article
Additive Manufacturing of Biomimetic Near-Zero CTE Optical Structures
by Shuang Bai, David Cheng and Jian Liu
Machines 2024, 12(12), 933; https://doi.org/10.3390/machines12120933 - 20 Dec 2024
Viewed by 467
Abstract
Super invar, with its near-zero coefficient of thermal expansion (CTE), has a great potential to be used in the design and fabrication of high-precision optical structures, such as optical mirror substrates. In order to reduce the weight and maintain the strength of the [...] Read more.
Super invar, with its near-zero coefficient of thermal expansion (CTE), has a great potential to be used in the design and fabrication of high-precision optical structures, such as optical mirror substrates. In order to reduce the weight and maintain the strength of the mirror substrate, several biomimetic lattice designs were investigated in this paper. The static modeling provides a systematic study on different types of biomimetic mirror substrates. The impact of structure parameters, such as the wall thickness, lattice unit length, height of the lattice structure, and the thickness of the side plate, are also studied. It turns out that the three-layer lattice-structured composite mirror substrate has the best performance. With AM techniques, three-layer gyroid optical structures, which are not possible to fabricate with conventional manufacturing technology, were designed and printed with our in-house-built AM machine. The stiffness test of the gyroid specimens was in good agreement with the modeling results. The gyroid structure shows about a 20% improvement over the honeycomb structure. The gyroid design reduces the equivalent density to 1.8 g/cm3 and has an order-of-magnitude improvement on the thermal deformation, while maintaining a comparable strength with that of beryllium. Full article
(This article belongs to the Special Issue Recent Advances in 3D Printing in Industry 4.0)
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18 pages, 6740 KiB  
Article
Integrating Experimental and Computational Insights: A Dual Approach to Ba2CoWO6 Double Perovskites
by Ramesh Kumar Raji, Tholkappiyan Ramachandran, Muthu Dhilip, Vivekanandan Aravindan, Joseph Stella Punitha and Fathalla Hamed
Ceramics 2024, 7(4), 2006-2023; https://doi.org/10.3390/ceramics7040125 - 18 Dec 2024
Viewed by 739
Abstract
Double perovskite materials have emerged as key players in the realm of advanced materials due to their unique structural and functional properties. This research mainly focuses on the synthesis and comprehensive characterization of Ba2CoWO6 double perovskite nanopowders utilizing a high-temperature [...] Read more.
Double perovskite materials have emerged as key players in the realm of advanced materials due to their unique structural and functional properties. This research mainly focuses on the synthesis and comprehensive characterization of Ba2CoWO6 double perovskite nanopowders utilizing a high-temperature conventional solid-state reaction technique. The successful formation of Ba2CoWO6 powders was confirmed through detailed analysis employing advanced characterization techniques. Rietveld refinement of X-ray diffraction (XRD) and Raman data established that Ba2CoWO6 crystallizes in a cubic crystal structure with the space group Fm-3m, indicative of a highly ordered perovskite lattice. The typical crystallite size, approximately 65 nm, highlights the nanocrystalline nature of the material. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) discovered a distinctive morphology characterized by spherical shaped particles, suggesting a complex particle formation process influenced by synthesis conditions. To probe the electronic structure, X-ray Photoelectron Spectroscopy (XPS) identified cobalt and tungsten valence states, critical for understanding dielectric properties associated with localized charge carriers. The semiconducting character of the synthesized Ba2CoWO6 nanocrystalline material was confirmed through UV-Visible analysis, which revealed an energy bandgap value of 3.3 eV, which aligns well with the theoretical predictions, indicating the accuracy and reliability of the experimental results. The photoluminescence spectrum exhibited two distinct emissions in the blue-green region. These emissions were attributed to the transitions 3P03H4, 3P03H5, and 3P03H6, primarily resulting from the contributions of Ba2+ ions. The dielectric characteristics of the compound were analyzed across a different range of frequencies, spanning from 1 kHz to 1 MHz. Magnetic characterization using Vibrating Sample Magnetometry (VSM) revealed antiferromagnetic behavior of Ba2CoWO6 ceramics at room temperature, attributed to super-exchange interactions between Co3+ and W5+ ions mediated by oxygen ions in the perovskite lattice. Additionally, first-principles calculations based on the Generalized Gradient Approximation (GGA+U) with a modified Becke–Johnson (mBJ) potential were employed to gain a deeper understanding of the structural and electronic properties of the materials. This approach involved systematically varying the Hubbard U parameter to optimize the description of electron correlation effects. These results deliver an extensive understanding of the structural, optical, morphological, electronic, and magnetic properties of Ba2CoWO6 ceramics, underscoring their potential for electronic and magnetic device applications. Full article
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20 pages, 21853 KiB  
Article
Thermal Evolution of Expanded Phases Formed by PIII Nitriding in Super Duplex Steel Investigated by In Situ Synchrotron Radiation
by Bruna Corina Emanuely Schibicheski Kurelo, João Frederico Haas Leandro Monteiro, Gelson Biscaia de Souza, Francisco Carlos Serbena, Carlos Maurício Lepienski, Rodrigo Perito Cardoso and Silvio Francisco Brunatto
Metals 2024, 14(12), 1396; https://doi.org/10.3390/met14121396 - 5 Dec 2024
Viewed by 699
Abstract
The Plasma Immersion Ion Implantation (PIII) nitriding was used to form a modified layer rich in expanded austenite (γN) and expanded ferrite (αN) phases in super duplex steel. The thermal stability of these phases was investigated through the in [...] Read more.
The Plasma Immersion Ion Implantation (PIII) nitriding was used to form a modified layer rich in expanded austenite (γN) and expanded ferrite (αN) phases in super duplex steel. The thermal stability of these phases was investigated through the in situ synchrotron X-ray diffraction. All the surfaces were analyzed by SEM, EDS, and nanoindentation. During the heating stage of the thermal treatments, the crystalline structure of the γN phase expanded thermally up to a temperature of 350 °C and, above this temperature, a reduction in the lattice parameter was observed due to the diffusion of nitrogen into the substrate. During the isothermal heating, the gradual diffusion of nitrogen continued and the lattice parameter of the γN phase decreased. Increasing the treatment temperature from 450 °C to 550 °C, a greater reduction in the lattice parameter of the γN phase occured and the peaks related to the CrN, α, and αN phases became more evident in the diffractograms. This phenomenon is associated with the decomposition of the γN phase into CrN + α + αN. After the heat treatments, the thickness of the modified layers increased and the hardness values close to the surface decreased, according to the diffusion of the nitrogen to the substrate. Full article
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10 pages, 3798 KiB  
Article
750 V Breakdown in GaN Buffer on 200 mm SOI Substrates Using Reverse-Stepped Superlattice Layers
by Shuzhen You, Yilong Lei, Liang Wang, Xing Chen, Ting Zhou, Yi Wang, Junbo Wang, Tong Liu, Xiangdong Li, Shenglei Zhao, Jincheng Zhang and Yue Hao
Micromachines 2024, 15(12), 1460; https://doi.org/10.3390/mi15121460 - 30 Nov 2024
Viewed by 989
Abstract
In this work, we demonstrated the epitaxial growth of a gallium nitride (GaN) buffer structure on 200 mm SOI (silicon-on-insulator) substrates. This epitaxial layer is grown using a reversed stepped superlattice buffer (RSSL), which is composed of two superlattice (SL) layers with different [...] Read more.
In this work, we demonstrated the epitaxial growth of a gallium nitride (GaN) buffer structure on 200 mm SOI (silicon-on-insulator) substrates. This epitaxial layer is grown using a reversed stepped superlattice buffer (RSSL), which is composed of two superlattice (SL) layers with different Al component ratios stacked in reverse order. The upper layer, with a higher Al component ratio, introduces tensile stress instead of accumulative compressive stress and reduces the in situ curvature of the wafer, thereby achieving a well-controlled wafer bow ≤ ±50 µm for a 3.3 µm thick buffer. Thanks to the compliant SOI substrate, good crystal quality of the grown GaN layers was obtained, and a breakdown voltage of 750 V for a 3.3 µm thick GaN buffer was achieved. The breakdown field strength of the epitaxial GaN buffer layer on the SOI substrate is estimated to be ~2.27 MV/cm, which is higher than the breakdown field strength of the GaN-on-Si epitaxial buffer layer. This RSSL buffer also demonstrated a low buffer dispersion of less than 10%, which is good enough for the further processing of device and circuit fabrication. A D-mode GaN HEMT was fabricated on this RSSL buffer, which showed a good on/off ratio of ~109 and a breakdown voltage of 450 V. Full article
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13 pages, 4441 KiB  
Article
Design and Growth of P-Type AlGaN Graded Composition Superlattice
by Yang Liu, Xue Yang, Xiaowei Zhou, Peixian Li, Bo Yang, Zhuang Zhao, Yingru Xiang and Junchun Bai
Micromachines 2024, 15(12), 1420; https://doi.org/10.3390/mi15121420 - 26 Nov 2024
Viewed by 666
Abstract
A graded composition superlattice structure is proposed by combining simulation with experimentation. The structural factors affecting graded symmetric superlattices and graded asymmetric superlattices and their action modes are simulated and analyzed. A Mg-doped graded symmetric superlattice structure with high Al content, excellent structural [...] Read more.
A graded composition superlattice structure is proposed by combining simulation with experimentation. The structural factors affecting graded symmetric superlattices and graded asymmetric superlattices and their action modes are simulated and analyzed. A Mg-doped graded symmetric superlattice structure with high Al content, excellent structural quality, good surface morphology and excellent electrical properties was grown by MOCVD equipment. The AlxGa1−xN superlattice with Al composition of 0.7 in the barrier exhibits a hole concentration of approximately 5 × 1015 cm−3 and a resistivity of 66 Ω·cm. Full article
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8 pages, 3741 KiB  
Article
Etching Processing of InGaAs/InAlAs Quantum Cascade Laser
by Qi Wu, Yana Zhu, Dongxin Xu, Zaijin Li, Yi Qu, Zhongliang Qiao, Guojun Liu, Zhibin Zhao, Lina Zeng, Hao Chen and Lin Li
Coatings 2024, 14(11), 1448; https://doi.org/10.3390/coatings14111448 - 13 Nov 2024
Viewed by 885
Abstract
The 3–5 μm mid-infrared band is the atmospheric window band, where there are absorption peaks of many molecules. It plays an important role in trace gas detection, directional infrared countermeasures, biomedicine, and free-space optical communications. The wet etching process of the designed InGaAs/InAlAs [...] Read more.
The 3–5 μm mid-infrared band is the atmospheric window band, where there are absorption peaks of many molecules. It plays an important role in trace gas detection, directional infrared countermeasures, biomedicine, and free-space optical communications. The wet etching process of the designed InGaAs/InAlAs quantum cascade laser with superlattice structure was explored to provide a good experimental basis for the research and development of lasers. The HBr:HNO3:H2O series of etching solutions were selected for corrosion experiments, and the surface morphology was observed by scanning electron microscopy (SEM) and metallographic microscopy to obtain the corrosion rate of the etching solution. The experimental results show that the etching liquid ratio is HBr:HNO3:H2O = 1:1:10, and the etching rate is 0.6 μm/min. A quantum cascade laser that works continuously at room temperature was prepared, with an injection strip width of 7 μm, a cavity length of 4mm, and an operating temperature of 20 °C. The device works in continuous mode (CW), with a maximum continuous output power of about 186 mW, a threshold current of about 0.4 A, a threshold current density of about 1.428 kA/cm2, a device center wavelength of about 4424 nm, a side mode suppression ratio of 28 dB, and a spectrum full width at half maximum of 2 nm. Full article
(This article belongs to the Special Issue Advancements in Lasers: Applications and Future Trends)
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10 pages, 2113 KiB  
Article
Kondo Versus Fano in Superconducting Artificial High-Tc Heterostructures
by Gaetano Campi, Gennady Logvenov, Sergio Caprara, Antonio Valletta and Antonio Bianconi
Condens. Matter 2024, 9(4), 43; https://doi.org/10.3390/condmat9040043 - 31 Oct 2024
Viewed by 954
Abstract
Recently, the quest for high-Tc superconductors has evolved from the trial-and-error methodology to the growth of nanostructured artificial high-Tc superlattices (AHTSs) with tailor-made superconducting functional properties by quantum design. Here, we report the growth by molecular beam epitaxy (MBE) of a superlattice of [...] Read more.
Recently, the quest for high-Tc superconductors has evolved from the trial-and-error methodology to the growth of nanostructured artificial high-Tc superlattices (AHTSs) with tailor-made superconducting functional properties by quantum design. Here, we report the growth by molecular beam epitaxy (MBE) of a superlattice of Mott insulator metal interfaces (MIMIs) made of nanoscale superconducting layers of quantum confined-space charge in the Mott insulator La2CuO4 (LCO), with thickness L intercalated by normal metal La1.55Sr0.45CuO4 (LSCO) with period d. The critical temperature shows the superconducting dome with Tc as a function of the geometrical parameter L/d showing the maximum at the magic ratio L/d = 2/3 where the Fano–Feshbach resonance enhances the superconducting critical temperature. The normal state transport data of the samples at the top of the superconducting dome exhibit Planckian T-linear resistivity. For L/d > 2/3 and L/d < 2/3, the heterostructures show a resistance following Kondo universal scaling predicted by the numerical renormalization group theory for MIMI nanoscale heterostructures. We show that the Kondo temperature, TK, and the Kondo scattering amplitude, R0K, vanish at L/d = 2/3, while TK and R0K increase at both sides of the superconducting dome, indicating that the T-linear resistance regime competes with the Kondo proximity effect in the normal phase of MIMIs. Full article
(This article belongs to the Special Issue Superstripes Physics, 3rd Edition)
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17 pages, 5669 KiB  
Article
Stacking Fault Nucleation in Films of Vertically Oriented Multiwall Carbon Nanotubes by Pyrolysis of Ferrocene and Dimethyl Ferrocene at a Low Vapor Flow Rate
by Ayoub Taallah, Shanling Wang, Omololu Odunmbaku, Lin Zhang, Xilong Guo, Yixin Dai, Wenkang Li, Huanqing Ye, Hansong Wu, Jiaxin Song, Jian Guo, Jiqiu Wen, Yi He and Filippo S. Boi
C 2024, 10(4), 91; https://doi.org/10.3390/c10040091 - 12 Oct 2024
Viewed by 1114
Abstract
Recent observations of superconductivity in low-dimensional systems composed of twisted, untwisted, or rhombohedral graphene have attracted significant attention. One-dimensional moiré superlattices and flat bands have interestingly been identified in collapsed chiral carbon nanotubes (CNTs), opening up new avenues for the tunability of the [...] Read more.
Recent observations of superconductivity in low-dimensional systems composed of twisted, untwisted, or rhombohedral graphene have attracted significant attention. One-dimensional moiré superlattices and flat bands have interestingly been identified in collapsed chiral carbon nanotubes (CNTs), opening up new avenues for the tunability of the electronic properties in these systems. The nucleation of hexagonal moiré superlattices and other types of stacking faults has also been demonstrated in partially collapsed and uncollapsed carbon nano-onions (CNOs). Here, we report a novel investigation on the dynamics of stacking fault nucleation within the multilayered lattices of micrometer-scale vertically oriented films of multiwall CNTs (MWCNTs), resulting from the pyrolysis of molecular precursors consisting of ferrocene or dimethyl ferrocene, at low vapor flow rates of ~5–20 mL/min. Interestingly, local nucleation of moiré-like superlattices (as stacking faults) was found when employing dimethyl ferrocene as the pyrolysis precursor. The morphological and structural properties of these systems were investigated with the aid of scanning and transmission electron microscopies, namely SEM, TEM, and HRTEM, as well as X-ray diffraction (XRD) and Raman point/mapping spectroscopy. Deconvolution analyses of the Raman spectra also demonstrated a local surface oxidation, possibly occurring on defect-rich interfaces, frequently identified within or in proximity of bamboo-like graphitic caps. By employing high-temperature Raman spectroscopy, we demonstrate a post-growth re-graphitization, which may also be visualized as an alternative way of depleting the oxygen content within the MWCNTs’ interfaces through recrystallization. Full article
(This article belongs to the Special Issue Characterization of Disorder in Carbons (2nd Edition))
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10 pages, 5839 KiB  
Article
The Influence of Etching Method on the Occurrence of Defect Levels in III-V and II-VI Materials
by Kinga Majkowycz, Krzysztof Murawski, Małgorzata Kopytko, Krzesimir Nowakowski-Szkudlarek, Marta Witkowska-Baran and Piotr Martyniuk
Nanomaterials 2024, 14(19), 1612; https://doi.org/10.3390/nano14191612 - 9 Oct 2024
Cited by 1 | Viewed by 1059
Abstract
The influence of the etching method on the occurrence of defect levels in InAs/InAsSb type-II superlattice (T2SLs) and MCT photodiode is presented. For both analyzed detectors, the etching process was performed by two methods: wet chemical etching and dry etching using an ion [...] Read more.
The influence of the etching method on the occurrence of defect levels in InAs/InAsSb type-II superlattice (T2SLs) and MCT photodiode is presented. For both analyzed detectors, the etching process was performed by two methods: wet chemical etching and dry etching using an ion beam (RIE—reactive ion etching). The deep-level transient spectroscopy (DLTS) method was used to determine the defect levels occurring in the analyzed structures. The obtained results indicate that the choice of etching method affects the occurrence of additional defect levels in the MCT material, but it has no significance for InAs/InAsSb T2SLs. Full article
(This article belongs to the Special Issue Nanoelectronics: Materials, Devices and Applications (Second Edition))
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25 pages, 2762 KiB  
Article
Impact of Acoustic and Optical Phonons on the Anisotropic Heat Conduction in Novel C-Based Superlattices
by Devki N. Talwar and Piotr Becla
Materials 2024, 17(19), 4894; https://doi.org/10.3390/ma17194894 - 5 Oct 2024
Viewed by 1175
Abstract
C-based XC binary materials and their (XC)m/(YC)n (X, Y ≡ Si, Ge and Sn) superlattices (SLs) have recently gained considerable interest as valuable alternatives to Si for designing and/or exploiting nanostructured electronic devices (NEDs) in the growing high-power application needs. [...] Read more.
C-based XC binary materials and their (XC)m/(YC)n (X, Y ≡ Si, Ge and Sn) superlattices (SLs) have recently gained considerable interest as valuable alternatives to Si for designing and/or exploiting nanostructured electronic devices (NEDs) in the growing high-power application needs. In commercial NEDs, heat dissipation and thermal management have been and still are crucial issues. The concept of phonon engineering is important for manipulating thermal transport in low-dimensional heterostructures to study their lattice dynamical features. By adopting a realistic rigid-ion-model, we reported results of phonon dispersions ωjSLk of novel shortperiod XCm/(YC)n001 SLs, for m, n = 2, 3, 4 by varying phonon wavevectors kSL along the growth k|| ([001]), and in-plane k ([100], [010]) directions. The SL phonon dispersions displayed flattening of modes, especially at high-symmetry critical points Γ, Z and M. Miniband formation and anti-crossings in ωjSLk lead to the reduction in phonon conductivity κz along the growth direction by an order of magnitude relative to the bulk materials. Due to zone-folding effects, the in-plane phonons in SLs exhibited a strong mixture of XC-like and YC-like low-energy ωTA, ωLA modes with the emergence of stop bands at certain kSL. For thermal transport applications, the results demonstrate modifications in thermal conductivities via changes in group velocities, specific heat, and density of states. Full article
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9 pages, 2124 KiB  
Article
Friedel Oscillations and He-He Interactions in Mo
by Xuepeng Shen, Enzhi Liang, Qian Zhan, Wei Wang and Wen Tong Geng
Crystals 2024, 14(10), 834; https://doi.org/10.3390/cryst14100834 - 25 Sep 2024
Viewed by 692
Abstract
Helium ions implanted into metals can form ordered bubbles that are isomorphic to the host lattice. While long-range elastic interactions are generally believed to drive bubble superlattice formation, the interactions between individual helium solutes are not yet fully understood. Our first-principles calculations reveal [...] Read more.
Helium ions implanted into metals can form ordered bubbles that are isomorphic to the host lattice. While long-range elastic interactions are generally believed to drive bubble superlattice formation, the interactions between individual helium solutes are not yet fully understood. Our first-principles calculations reveal that in molybdenum, Friedel oscillations induced by individual helium atoms generate potential barriers and wells that influence helium pairing and clustering at short He-He distances. These repulsive and attractive interactions at high concentrations provide thermodynamic driving forces that align randomly distributed helium atoms into Mo-He superlattices. Friedel oscillations may have broad impacts on solute–solute interactions in alloys. Full article
(This article belongs to the Section Crystal Engineering)
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