Article
Optics
Linxuan Li, Siqi Zhu, Lu Cheng, Hongsheng Qi, Yu Fan, Wei Zheng
Summary: Raman and infrared reflectance spectroscopy were used to study GaN single crystals with different doping types and carrier concentrations. The characteristic spectra related to the carrier concentration were observed and fitted to obtain the accurate carrier concentration of the GaN crystals, which agreed well with the results from Hall measurement.
JOURNAL OF LUMINESCENCE
(2022)
Article
Materials Science, Multidisciplinary
Mohsen Sabbaghi, Tobias Stauber, Hyun-Woo Lee, J. Sebastian Gomez-Diaz, George W. Hanson
Summary: This work investigates the in-plane optical phonon modes of current-carrying single-layer graphene and identifies the effects of DC current on the frequency shifts and the breaking of rotational symmetry.
Article
Thermodynamics
Wenlong Bao, Zhaoliang Wang, Dawei Tang
Summary: The study focused on investigating the interfacial thermal transport between GaN and AlN, revealing a higher thermal conductivity compared to other interfaces. Structural similarity and interfacial phonon modes were employed to uncover the heat transfer mechanism, along with calculations of temperature and wave-resolved spectral heat flux. This research contributes to an effective understanding and improvement of thermal management in GaN-based devices.
INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER
(2022)
Article
Materials Science, Multidisciplinary
Yanbo Dong, Enling Li, Zhen Cui, Yang Shen, Deming Ma, Fangping Wang, Zhihao Yuan, Kunqi Yang
Summary: The electronic structure, charge transfer, and photon scattering of buckled and planar few-layer 2D GaN have been investigated using first-principles calculations. The results show that buckled GaN with H passivation has a direct band gap, which decreases with increasing number of atomic layers. Planar GaN has an indirect band gap, which remains relatively stable as the number of atomic layers increases. Charge transfer occurs between adjacent layers in buckled structures, while it occurs within the layers in planar structures. The lattice vibration modes and Raman spectra of buckled and planar GaN are affected by the symmetry and interactions between atomic layers, with peak positions shifting with the number of atomic layers.
Article
Nanoscience & Nanotechnology
J. L. Cuevas, M. Ojeda, M. Calvino, A. Trejo, F. Salazar, A. Miranda, L. A. Perez, M. Cruz-Irisson
Summary: This study investigates the phonon modes of Gallium Antimonide nanowires (GaSbNWs) using density functional theory. The results show that the red-shift of the highest frequency modes of GaSb is hindered by low frequency H bond bending modes. Three distinguishable frequency intervals were observed, and it was found that the radial breathing mode decreases with increasing nanowire diameter, while the specific heat exhibits the opposite trend.
PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES
(2022)
Article
Physics, Multidisciplinary
Dao-Sheng Tang, Li-Min Zhang
Summary: In order to effectively regulate thermal transport for the near-junction thermal management of GaN electronics, this study comprehensively investigates the phonon characteristics and topological phonon properties of GaN nanostructures. The phonon modes, including the dispersion relation, density of states, and participation ratio, are calculated for six GaN superlattices. Weyl phonons with a Chern number of 1(-1) are found in all six GaN superlattices, and their distribution in the Brillouin zone increases with the number of phonon branches. The effects of strain on Weyl phonons in GaN/AlN and AlGaN/GaN superlattices are also investigated, revealing the persistence of Weyl phonons in large strain states. The findings of this work contribute to a deeper understanding of phonon properties and the topological effects in GaN nanostructures.
Article
Chemistry, Physical
Meenu Sharma, Sonam Rani, Devesh K. Pathak, Ravi Bhatia, Rajesh Kumar, I Sameera
Summary: A temperature dependent Raman spectromicroscopic study was conducted on multiwall carbon nanotubes to investigate anharmonic effects, revealing non-linear shifts in the peak position of Raman D- and G-bands with temperature. Phonon softening and hardening of Raman modes were observed over a wide temperature range, with the G-peak shift explained by anharmonic properties of the graphite lattice. The width variation of the G-peak appeared to be nearly independent of temperature due to competing effects from electron-phonon coupling and anharmonic contributions.
Article
Nanoscience & Nanotechnology
Edson P. Bellido, Isobel C. Bicket, Gianluigi A. Botton
Summary: This study investigates the significant effects of bends on surface plasmon resonances in nanowires and isolated edges of planar structures, revealing energy shifts, mode intersection, and antinode splitting as key phenomena that must be considered in the design of optical devices.
Article
Optics
Maoji Wang, Lauren R. Richey-Simonsen, Jordan M. Gerton
Summary: To investigate the optical modes in nanophotonic devices, researchers demonstrated a probe-free, far-field method to characterize the optical modes within GaN nanowires, observing spectral signatures resulting from lateral leakage of waveguide modes. By using an analytical model coupled with finite element simulations, they were able to accurately deduce the transverse dimension of the nanowires from hyperspectral images.
Article
Materials Science, Multidisciplinary
Benjamin M. Janzen, Piero Mazzolini, Roland Gillen, Andreas Falkenstein, Manfred Martin, Hans Tornatzky, Janina Maultzsch, Oliver Bierwagen, Markus R. Wagner
Summary: The study investigates the phonon modes of beta-Ga2O3 in different oxygen isotope compositions and reveals that the substitution of oxygen isotopes affects the Raman frequencies. By conducting experiments and theoretical calculations, the study identifies the atomistic origin of Raman modes and presents a blueprint for future identification of different point defects in Ga2O3 using Raman spectroscopy.
JOURNAL OF MATERIALS CHEMISTRY C
(2021)
Article
Materials Science, Multidisciplinary
Ajay Tiwari, D. Chandrasekhar Kakarla, Bommareddy Poojitha, Priyambada Sahoo, H. L. Liu, A. Dixit, C. W. Wang, T. W. Yen, M. -j. Hsieh, J. -y. Lin, Jyothinagaram Krishnamurthy, Y. C. Lai, H. Chou, T. W. Kuo, Arkadeb Pal, H. D. Yang
Summary: A two-dimensional honeycomb-structured magnet Ni2Te3O8 with intriguing physical properties was synthesized, characterized, and comprehensively investigated. The study revealed a long-range commensurate antiferromagnetic ordering at TN ≈ 35 K and observed spin-lattice coupling and magnetodielectric effect.
Article
Chemistry, Multidisciplinary
Galia Pozina, Carl Hemmingsson, Natalia Abrikossova, Elizaveta I. Girshova, Erkki Lahderanta, Mikhail A. Kaliteevski
Summary: This study investigates the optical spectroscopy properties of hybrid structures composed of colloidal Ag nanoparticles and planar GaN nanowires. A new emission line at 3.36 eV is observed near the Ag nanoparticles. The experimental results are explained using the Frohlich resonance approximation model and the effective medium approach.
Article
Nanoscience & Nanotechnology
Thomas Auzelle, Florian Ullrich, Sebastian Hietzschold, Chiara Sinito, Stefan Brackmann, Wolfgang Kowalsky, Eric Mankel, Oliver Brandt, Robert Lovrincic, Sergio Fernandez-Garrido
Summary: The optoelectronic properties of GaN surfaces were studied after functionalization with phosphonic acid derivatives, showing significant changes in GaN work function and impacting surface band bending. The internal quantum efficiency of GaN layers and nanowires was significantly affected by the covalent bonding of phosphonic acids, with modifications to internal electric fields and surface states. Phosphonate chemistry shows potential for selective sensing applications in surface functionalization of GaN.
ACS APPLIED MATERIALS & INTERFACES
(2021)
Article
Chemistry, Physical
Jing Yu, Zhonglin Li, Jie Jiang, Wenjun Liu, Shuai Guo, Yao Liang, Bo Zhong, Yingying Wang, Mingqiang Zou
Summary: In this work, temperature-dependent polarized Raman spectroscopy was used to investigate the anisotropic thermal properties of atomically thin ReS2 flakes. It was found that the Raman modes of ReS2 redshift with increasing temperature and that the temperature coefficients differ along different crystal axes. Additionally, the broadening of phonon modes was attributed to phonon decay. This study will contribute to the understanding of thermal anisotropy in two-dimensional anisotropic materials.
CHEMICAL PHYSICS LETTERS
(2023)
Article
Chemistry, Physical
Swayam Kesari, Rekha Rao, Samatha Bevara, S. N. Achary
Summary: The study reveals multiple structural phase transitions of metastable Zn4V2O9 under high pressure, some of which are reversible and some are irreversible; as pressure increases, Raman spectra show an increase in coordination of vanadium atoms and features of structural disorder.
JOURNAL OF ALLOYS AND COMPOUNDS
(2022)
Article
Nanoscience & Nanotechnology
Bruno Daudin, Fabrice Donatini, Catherine Bougerol, Bruno Gayral, Edith Bellet-Amalric, Remy Vermeersch, Nathaniel Feldberg, Jean-Luc Rouviere, Maria Jose Recio Carretero, Nuria Garro, Saul Garcia-Orrit, Ana Cros
Summary: The study reveals that GaN can grow epitaxially on muscovite mica, showing a specific nucleation mechanism for GaN on mica and the potential for obtaining almost pure ZB GaN epitaxial layers at high growth temperatures.
Article
Nanoscience & Nanotechnology
Bruno Daudin, Alexandra-Madalina Siladie, Marion Gruart, Martien den Hertog, Catherine Bougerol, Benedikt Haas, Jean-Luc Rouviere, Eric Robin, Maria-Jose Recio-Carretero, Nuria Garro, Ana Cros
Summary: The spontaneous growth of GaN nanowires in the absence of catalyst is controlled by Ga flux, with diffusion barriers causing an uneven distribution of Ga adatoms at the top surface leading to GaN accumulation in the periphery. This promotes the formation of superlattices in InGaN and AlGaN nanowires, while the presence of Mg enhances Al diffusion length along the sidewalls in AlN nanowires, inducing the formation of AlN nanotubes.
Article
Nanoscience & Nanotechnology
A. Cros, A. Garcia Cristobal, K. Hestroffer, B. Daudin, J. Wang, F. Demangeot, R. Pechou
Summary: Analysis of electron-phonon coupling in GaN/AlN core-shell nanowires using Raman scattering excited at various UV wavelengths revealed different vibration modes of phonons under different excitations. The thickness of the AlN shell can be adjusted to tune the energy and character of the electronic bands in these nanowires.
Article
Polymer Science
Diana Favero, Victoria Marcon, Carlos A. Figueroa, Clara M. Gomez, Ana Cros, Nuria Garro, Maria J. Sanchis, Marta Carsi, Otavio Bianchi
Summary: This research aimed to investigate the effect of different chain extenders on the properties of soybean polyurethane, including morphology, thermal behavior, viscoelasticity, and dielectric properties. It was found that the choice of chain extender influenced the organization of PU structure and the interaction between hard and soft domains, resulting in different molecular motions and transitions. Additionally, the phase-separated morphology at high temperatures was attributed to the Maxwell-Wagner-Sillars interfacial polarization process.
JOURNAL OF APPLIED POLYMER SCIENCE
(2021)
Article
Materials Science, Multidisciplinary
J. Cardoso, G. Jacopin, D. Nd Faye, A. M. Siladie, B. Daudin, E. Alves, K. Lorenz, T. Monteiro, M. R. Correia, N. Ben Sedrine
Summary: The optical properties of Eu3+-implanted and annealed AlxGa1-xN nanowires were studied, showing successful red emission for all samples after rapid thermal annealing. Differences in spectral shape were observed due to the presence of multiple optically active Eu3+ centers, with the most stable luminescence intensity observed in AlN nanowires after RTA at 1200 °C. Additionally, the GaN/AlN interface was found to play a key role in Eu3+ optical activation.
APPLIED MATERIALS TODAY
(2021)
Article
Physics, Applied
Remy Vermeersch, Eric Robin, Ana Cros, Gwenole Jacopin, Bruno Daudin, Julien Pernot
Summary: Investigation of Si doping in AlN nanowires grown by plasma assisted molecular beam epitaxy was conducted for the purpose of fabricating efficient AlN based deep ultra-violet light-emitting-diodes. Si donors were found to exist in both shallow and deep DX states, with a favorable formation of shallow Si donors discussed in terms of Fermi level pinning on nanowires sidewalls.
APPLIED PHYSICS LETTERS
(2021)
Article
Physics, Applied
Ece N. Aybeke, Alexandra-Madalina Siladie, Remy Vermeersch, Eric Robin, Oleksandr Synhaivskyi, Bruno Gayral, Julien Pernot, Georges Bremond, Bruno Daudin
Summary: Practical semiconductor nanowire optoelectronic devices require controlling their electrical transport properties. This study quantitatively measured the local carrier density in doped GaN nanowires using scanning spreading resistance microscopy. The results reveal the presence of a conductive shell and resistive core in Mg-doped p-type nanowires, while Si-doped n-type nanowires exhibit a resistive shell and conductive core.
JOURNAL OF APPLIED PHYSICS
(2022)
Article
Nanoscience & Nanotechnology
Jose P. S. Cardoso, Maria Rosario Correia, Remy Vermeersch, Dirkjan Verheij, Gwenole Jacopin, Julien Pernot, Teresa Monteiro, Susana Cardoso, Katharina Lorenz, Bruno Daudin, Nabiha Ben Sedrine
Summary: Europium-implanted AlN nanowire pn junctions were annealed at 1000 degrees C and showed increased Eu3+ luminescence intensity with higher fluence, while the contribution from defect-related emissions decreased. This study demonstrates the potential of using Eu-implanted AlN NWs for developing red LEDs with improved luminescence properties.
ACS APPLIED NANO MATERIALS
(2022)
Article
Physics, Applied
Remy Vermeersch, Gwenole Jacopin, Bruno Daudin, Julien Pernot
Summary: The electrical properties of silicon doped AlN nanowires grown by plasma assisted molecular beam epitaxy were investigated. The behavior of electrical properties changes with the doping level and is consistent with the theory of space-charge limited current assisted by traps.
APPLIED PHYSICS LETTERS
(2022)
Article
Polymer Science
Diana Favero, Victoria Marcon, Lucas Dall Agnol, Clara M. Gomez, Ana Cros, Nuria Garro, Maria J. Sanchis, Marta Carsi, Carlos A. Figueroa, Otavio Bianchi
Summary: This study investigates the effect of different chain extenders on the structure-property relationships of soy-based polyurethanes during hydrolytic degradation. It is found that the addition of chain extenders accelerates the degradation of flexible domains, resulting in a stiffer and more brittle polymer. Hydrolytic degradation also leads to the formation of new infrared absorption peaks and increased phase separation.
JOURNAL OF APPLIED POLYMER SCIENCE
(2022)
Article
Nanoscience & Nanotechnology
Alexandre Concordel, Joel Bleuse, Gwenole Jacopin, Bruno Daudin
Summary: The optical properties of nanowire-based InGaN/GaN multiple quantum wells (MQWs) heterostructures grown by plasma-assisted molecular beam epitaxy were investigated, with a focus on the effect of an InGaN underlayer grown below the active region and the influence of surface recombination. It was found that the InGaN underlayer demonstrated a beneficial effect due to the trapping of point defects transferred from the pseudo-template to the active region. Surface recombination was found to be dominated by the formation of additional point defects during the growth of the heterostructure for large InN molar fraction. Inhomogeneous luminescence of single nanowires at the nanoscale highlighted a spatial distribution of non-radiative recombination centers identified as intrinsic point defects created during the growth of MQWs. These findings have implications for improving the performance of microLEDs in the visible range.
Article
Physics, Applied
Remy Vermeersch, Gwenole Jacopin, Eric Robin, Julien Pernot, Bruno Gayral, Bruno Daudin
Summary: We have demonstrated that intentional Ga doping of AlN nanowires in the range of 0.01%-0.5% results in the formation of nanometric carrier localization centers. This leads to the observation of sharp cathodoluminescence lines in the wavelength range of 220-300 nm for single nanowires. Additionally, an ensemble of Ga-doped AlN nanowires exhibits wide-band cathodoluminescence emission, paving the way for efficient UV-C light emitting diodes covering a wide part of the DNA absorption band.
APPLIED PHYSICS LETTERS
(2023)
Article
Nanoscience & Nanotechnology
Remy Vermeersch, Gwenole Jacopin, Florian Castioni, Jean-Luc Rouviere, Alberto Garcia-Cristobal, Ana Cros, Julien Pernot, Bruno Daudin
Summary: The growth and optical properties of GaN quantum disks in AlN nanowires were studied via molecular beam epitaxy to control the emission wavelength of AlN nanowire-based LEDs. In addition to GaN quantum disks with thickness ranging from 1 to 4 monolayers, focus was given to incomplete GaN disks with lateral confinement. Their emission spectrum consists of sharp lines extending down to 215 nm near the AlN band edge. The room temperature cathodoluminescence intensity of GaN quantum disks embedded in AlN nanowires is about 20% of the low temperature value, highlighting the potential of ultrathin/incomplete GaN quantum disks for deep UV emission.
