ORCID Profile
0000-0003-3203-7935
Current Organisation
Linköping University
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Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9NR02354B
Abstract: We report the synthesis and characterization of a new laminated i-MAX phase, (V 2/3 Sc 1/3 ) 2 AlC, with in-plane chemical ordering between the M-elements. We also produce V 2−x C MXene with only 24 h etching time using HF and MXene scrolls using LiF + HCl.
Publisher: American Chemical Society (ACS)
Date: 11-12-2014
DOI: 10.1021/NL503564K
Abstract: Chirality, tailored by external morphology and internal composition, has been realized by controlled curved-lattice epitaxial growth of In(x)Al(1-x)N nanospirals. The curved morphology of the spiral segments is a result of a lateral compositional gradient while maintaining a preferred crystallographic growth direction, implying a lateral gradient in optical properties. In idual nanospirals show an asymmetric core-shell structure with curved basal planes. Mueller matrix spectroscopic ellipsometry shows that the tailored chirality is manifested in the polarization state of light reflected off the nanospirals.
Publisher: American Physical Society (APS)
Date: 24-05-2018
Publisher: Springer Science and Business Media LLC
Date: 05-2018
Publisher: Elsevier BV
Date: 2017
Publisher: American Association for the Advancement of Science (AAAS)
Date: 13-08-2021
Abstract: A range of two-dimensional (2D) materials, including graphene and hexagonal boron nitride, have been synthesized and studied because of the unusual properties that occur when one dimension becomes very small. MXenes are a family of materials made of layers of inorganic transition metal carbides and nitrides that are a few atoms thick and are manufactured by selective etching. Attempts to make similar boridene materials have been challenging because of the reactive nature of boride phases and because the parent materials tend to dissolve rather than selectively etch. Zhou et al . synthesized boridene in the form of single-layer 2D molybdenum boride sheets by selective etching in aqueous hydrofluoric acid to produce sheets with ordered metal vacancies, opening up an additional family of materials for study. —MSL
Publisher: Trans Tech Publications, Ltd.
Date: 03-2009
DOI: 10.4028/WWW.SCIENTIFIC.NET/MSF.615-617.275
Abstract: We have performed 2D X-ray diffraction mapping of the SiC lattice basal plane orientation over full 2” SiC substrates. Measurements of the omega angle were made in two perpendicular directions -20 and -100 , which gives the complete vectorized tilt of the basal planes. The Mapping revealed two characteristic bending behaviors on measured commercial wafers. The first is characterized by large variations in omega angle across the wafer in both crystallographic directions. The continuously changing omega angle in both directions gives the wafer an apparent rotationally symmetric bending which is concave towards the growth direction. The second characteristic behavior is seen in wafers with lower degree of omega angle variation. The variations in this type of wafers are not changing linearly, but are bending the basal planes with two-fold symmetry.
Publisher: Elsevier BV
Date: 02-2016
Publisher: Wiley
Date: 18-02-2020
Publisher: Informa UK Limited
Date: 08-03-2022
Publisher: Elsevier BV
Date: 08-2021
Publisher: Wiley
Date: 04-2018
Abstract: The exploration of 2D solids is one of our time's generators of materials discoveries. A recent addition to the 2D world is MXenes that possses a rich chemistry due to the large parent family of MAX phases. Recently, a new type of atomic laminated phases (coined i-MAX) is reported, in which two different transition metal atoms are ordered in the basal planes. Herein, these i-MAX phases are used in a new route for tailoriong the MXene structure and composition. By employing different etching protocols to the parent i-MAX phase (Mo
Publisher: AIP Publishing
Date: 17-08-2009
DOI: 10.1063/1.3211124
Abstract: Highly oriented ZnO nanotubes were fabricated on a silicon substrate by aqueous chemical growth at low temperature (& °C) by trimming of ZnO nanorods. The yield of nanotubes in the s le was 100%. Photoluminescence spectroscopy of the nanotubes reveals an enhanced and broadened ultraviolet (UV) emission peak, compared with the initial nanorods. This effect is attributed to whispering gallery mode resonance. In addition, a redshift of the UV emission peak is also observed. Enhancement in the deep defect band emission in the nanotubes compared to nanorods was also manifested as a result of the increased surface area.
Publisher: MDPI AG
Date: 23-07-2020
Abstract: Selective-area grown, catalyst-free GaN nanorod (NR) arrays grown on Si substrates have been realized using liquid-target reactive magnetron sputter epitaxy (MSE). Focused ion beam lithography (FIBL) was applied to pattern Si substrates with TiNx masks. A liquid Ga target was sputtered in a mixture gas of Ar and N2, ranging the N2 partial pressure (PN₂) ratio from 100% to 50%. The growth of NRs shows a strong correlation with PN₂ on the selectivity, coalescence, and growth rate of NRs in both radial and axial directions. The growth rate of NRs formed inside the nanoholes increases monotonically with PN₂. The PN₂ ratio between 80% and 90% was found to render both a high growth rate and high selectivity. When the PN₂ ratio was below 80%, multiple NRs were formed in the nanoholes. For a PN₂ ratio higher than 90%, parasitic NRs were grown on the mask. An observed dependence of growth behavior upon the PN₂ ratio is attributed to a change in the effective Ga/N ratio on the substrate surface, as an effect of impinging reactive species, surface diffusivity, and residence time of adatoms. The mechanism of NR growth control was further investigated by studying the effect of nanoholes array pitch and growth temperature. The surface diffusion and the direct impingement of adatoms were found to be the dominant factors affecting the lateral and axial growth rates of NR, respectively, which were well elucidated by the collection area model.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 17-03-2023
Abstract: Intercalated layered materials offer distinctive properties and serve as precursors for important two-dimensional (2D) materials. However, intercalation of non–van der Waals structures, which can expand the family of 2D materials, is difficult. We report a structural editing protocol for layered carbides (MAX phases) and their 2D derivatives (MXenes). Gap-opening and species-intercalating stages were respectively mediated by chemical scissors and intercalants, which created a large family of MAX phases with unconventional elements and structures, as well as MXenes with versatile terminals. The removal of terminals in MXenes with metal scissors and then the stitching of 2D carbide nanosheets with atom intercalation leads to the reconstruction of MAX phases and a family of metal-intercalated 2D carbides, both of which may drive advances in fields ranging from energy to printed electronics.
Publisher: IOP Publishing
Date: 04-10-2012
DOI: 10.1088/0022-3727/45/42/422001
Abstract: Reactive magnetron sputtering was used to deposit Y x Al 1− x N thin films, 0 ⩽ x ⩽ 0.22, onto Al 2 O 3 (0 0 0 1) and Si(1 0 0) substrates. X-ray diffraction and analytical electron microscopy show that the films are solid solutions. Lattice constants increase with Y concentration, in agreement with ab initio calculations. Spectroscopic ellipsometry measurements reveal a band gap decrease from 6.2 eV ( x = 0) down to 4.5 eV ( x = 0.22). Theoretical investigations within the special quasirandom structure approach show that the wurtzite structure has the lowest mixing enthalpy for 0 ⩽ x ⩽ 0.75.
Publisher: IOP Publishing
Date: 20-11-2014
DOI: 10.1088/0957-4484/25/49/495702
Abstract: Indium segregation in a narrow InGaN single quantum well creates quantum dot (QD) like exciton localization centers. Cross-section transmission electron microscopy reveals varying shapes and lateral sizes in the range ∼1-5 nm of the QD-like features, while scanning near field optical microscopy demonstrates a highly inhomogeneous spatial distribution of optically active in idual localization centers. Microphotoluminescence spectroscopy confirms the spectrally inhomogeneous distribution of localization centers, in which the exciton and the biexciton related emissions from single centers of varying geometry could be identified by means of excitation power dependencies. Interestingly, the biexciton binding energy (E(b)xx) was found to vary from center to center, between 3 to -22 meV, in correlation with the exciton emission energy. Negative binding energies are only justified by a three-dimensional quantum confinement, which confirms QD-like properties of the localization centers. The observed energy correlation is proposed to be understood as variations of the lateral extension of the confinement potential, which would yield smaller values of E(b)xx for reduced lateral extension and higher exciton emission energy. The proposed relation between lateral extension and E(b)xx is further supported by the exciton and the biexciton recombination lifetimes of a single QD, which suggest a lateral extension of merely ∼3 nm for a QD with strongly negative E(b)xx = -15.5 meV.
Publisher: American Chemical Society (ACS)
Date: 02-12-2209
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/C9RA10007E
Abstract: Reduction of thermal conductivity of sputtered CaMn 1−x Nb x O 3 thin films by secondary Ruddlesden–Popper phase and grain size optimization.
Publisher: MDPI AG
Date: 07-04-2018
DOI: 10.3390/NANO8040223
Abstract: GaN nanorods, essentially free from crystal defects and exhibiting very sharp band-edge luminescence, have been grown by reactive direct-current magnetron sputter epitaxy onto Si (111) substrates at a low working pressure of 5 mTorr. Upon diluting the reactive N2 working gas with a small amount of Ar (0.5 mTorr), we observed an increase in the nanorod aspect ratio from 8 to ~35, a decrease in the average diameter from 74 to 35 nm, and a two-fold increase in nanorod density. With further dilution (Ar = 2.5 mTorr), the aspect ratio decreased to 14, while the diameter increased to 60 nm and the nanorod density increased to a maximum of 2.4 × 109 cm−2. Yet, lower N2 partial pressures eventually led to the growth of continuous GaN films. The observed morphological dependence on N2 partial pressure is explained by a change from N-rich to Ga-rich growth conditions, combined with reduced GaN-poisoning of the Ga-target as the N2 gas pressure is reduced. Nanorods grown at 2.5 mTorr N2 partial pressure exhibited a high intensity 4 K photoluminescence neutral donor bound exciton transitions (D0XA) peak at ~3.479 eV with a full-width-at-half-maximum of 1.7 meV. High-resolution transmission electron microscopy corroborated the excellent crystalline quality of the nanorods.
Publisher: American Chemical Society (ACS)
Date: 30-05-2018
Publisher: Elsevier BV
Date: 09-2016
Publisher: IOP Publishing
Date: 21-03-2014
Publisher: Elsevier BV
Date: 2017
Publisher: Elsevier BV
Date: 02-2021
Publisher: Elsevier BV
Date: 11-2020
Publisher: AIP Publishing
Date: 16-09-2013
DOI: 10.1063/1.4820581
Abstract: Using in situ high-temperature (1073–1173 K) transmission electron microscopy, we investigated the thermal stability of Pt and Mo in contact with polycrystalline ZrB2 thin films deposited on Al2O3(0001). During annealing, we observed the diffusion of cubic-structured Pt1−xMox (with x = 0.2 ± 0.1) along the length of the ZrB2 layer. From the time-dependent increase in diffusion lengths, we determined that the Pt1−xMox does not react with ZrB2, but diffuses along the surface with a constant temperature-dependent velocity. We identify the rate-limiting step controlling the observed phenomenon as the flux of Mo atoms with an associated activation barrier of 3.8 ± 0.5 eV.
Publisher: AIP Publishing
Date: 04-04-2011
DOI: 10.1063/1.3576912
Abstract: Electronic-grade GaN (0001) epilayers have been grown directly on Al2O3 (0001) substrates by reactive direct-current-magnetron sputter epitaxy (MSE) using a liquid Ga sputtering target in an Ar/N2 atmosphere. The as-grown GaN epitaxial films exhibit low threading dislocation density on the order of ≤1010 cm−2 determined by transmission electron microscopy and modified Williamson–Hall plot. X-ray rocking curve shows narrow full-width at half maximum (FWHM) of 1054 arc sec of the 0002 reflection. A sharp 4 K photoluminescence peak at 3.474 eV with a FWHM of 6.3 meV is attributed to intrinsic GaN band edge emission. The high structural and optical qualities indicate that MSE-grown GaN epilayers can be used for fabricating high-performance devices without the need of any buffer layer.
Publisher: IOP Publishing
Date: 27-10-2011
Publisher: AIP Publishing
Date: 16-01-2014
DOI: 10.1063/1.4861179
Abstract: The early stages of InGaN/GaN quantum well growth for In-reduced conditions have been investigated for varying thickness and composition of the wells. The structures were studied by monochromated scanning transmission electron microscopy–valence electron energy loss spectroscopy spectrum imaging at high spatial resolution. It is found that beyond a critical well thickness and composition, quantum dots (width & nm) are formed inside the well. These are buried by compositionally graded InGaN, which is formed as GaN is grown while residual In is incorporated into the growing structure. It is proposed that these dots act as carrier localization centers inside the quantum wells.
Publisher: Elsevier BV
Date: 11-2022
Publisher: Wiley
Date: 04-11-2018
Abstract: Global warming caused by burning of fossil fuels is indisputably one of mankind's greatest challenges in the 21st century. To reduce the ever-increasing CO
Publisher: American Vacuum Society
Date: 07-11-2022
DOI: 10.1116/6.0002079
Abstract: InxGa1−x N is a strategically important material for electronic devices given its tunable bandgap, modulated by the In/Ga ratio. However, current applications are hindered by defects caused by strain relaxation and phase separation in the material. Here, we demonstrate growth of homogeneous InxGa1−x N films with 0.3 & x & 0.8 up to ∼30 nm using atomic layer deposition (ALD) with a supercycle approach, switching between InN and GaN deposition. The composition is uniform along and across the films, without signs of In segregation. The InxGa1−x N films show higher In-content than the value predicted by the supercycle model. A more pronounced reduction of GPCInN than GPCGaN during the growth processes of InN and GaN bilayers is concluded based on our analysis. The intermixing between InN and GaN bilayers is suggested to explain the enhanced overall In-content. Our results show the advantage of ALD to prepare high-quality InxGa1−x N films, particularly with high In-content, which is difficult to achieve with other growth methods.
Publisher: Elsevier BV
Date: 08-2018
Publisher: Springer Science and Business Media LLC
Date: 05-11-2018
DOI: 10.1038/S41598-018-34279-W
Abstract: Nanostructure formation via surface-diffusion-mediated segregation of ZrN and AlN in Zr 1−x Al x N films during high mobility growth conditions is investigated for 0 ≤ × ≤ 1. The large immiscibility combined with interfacial surface and strain energy balance resulted in a hard nanolabyrinthine lamellar structure with well-defined (semi) coherent c-ZrN and w-AlN domains of sub-nm to ~4 nm in 0.2 ≤ × ≤ 0.4 films, as controlled by atom mobility. For high AlN contents (x 0.49) Al-rich ZrN domains attain wurtzite structure within fine equiaxed nanocomposite wurtzite lattice. Slow diffusion in wurtzite films points towards crystal structure dependent driving force for decomposition. The findings of unlikelihood of iso-structural decomposition in c-Zr 1−x Al x N, and stability of w-Zr 1−x Al x N (in large × films) is complemented with first principles calculations.
Publisher: Elsevier BV
Date: 02-2011
Publisher: Wiley
Date: 12-01-2022
Abstract: CaMnO 3 is a perovskite with attractive magnetic and thermoelectric properties. CaMnO 3 films are usually grown by pulsed laser deposition or radio frequency magnetron sputtering from ceramic targets. Herein, epitaxial growth of CaMnO 3– y (002) films on a ‐oriented LaAlO 3 substrate using pulsed direct current reactive magnetron sputtering is demonstrated, which is more suitable for industrial scale depositions. The CaMnO 3– y shows growth with a small in‐plane tilt of ≈0.2° toward the (200) plane of CaMnO 3– y and the () with respect to the LaAlO 3 substrate. X‐ray photoelectron spectroscopy of the electronic core levels shows an oxygen deficiency described by CaMnO 2.58 that yields a lower Seebeck coefficient and a higher electrical resistivity when compared to stoichiometric CaMnO 3 . The LaAlO 3 substrate promotes tensile‐strained growth of single crystals. Scanning transmission electron microscopy and electron energy loss spectroscopy reveal antiphase boundaries composed of Ca on Mn sites along and , forming stacking faults.
Publisher: American Chemical Society (ACS)
Date: 05-2018
Abstract: All known materials wear under extended mechanical contacting. Superlubricity may present solutions, but is an expressed mystery in C-based materials. We report negative wear of carbon nitride films a wear-less condition with mechanically induced material inflation at the nanoscale and friction coefficient approaching ultralow values (0.06). Superlubricity in carbon nitride is expressed as C-N bond breaking for reduced coupling between graphitic-like sheets and eventual N
Publisher: IOP Publishing
Date: 11-07-2012
DOI: 10.1088/0957-4484/23/30/305708
Abstract: Growing InGaN quantum dots (QDs) at the apex of hexagonal GaN pyramids is an elegant approach to achieve a deterministic positioning of QDs. Despite similar synthesis procedures by metal organic chemical vapor deposition, the optical properties of the QDs reported in the literature vary drastically. The QDs tend to exhibit either narrow or broad emission lines in the micro-photoluminescence spectra. By coupled microstructural and optical investigations, the QDs giving rise to narrow emission lines were concluded to nucleate in association with a (0001) facet at the apex of the GaN pyramid.
Publisher: AIP Publishing
Date: 05-2012
DOI: 10.1063/1.4714220
Abstract: Piezoelectric wurtzite ScxAl1−xN (x = 0, 0.1, 0.2, 0.3) thin films were epitaxially grown by reactive magnetron co-sputtering from elemental Sc and Al targets. Al2O3(0001) wafers with TiN(111) seed and electrode layers were used as substrates. X-ray diffraction shows that an increase in the Sc content results in the degradation of the crystalline quality. S les grown at 400 °C possess true dielectric behavior with quite low dielectric losses and the leakage current is negligible. For ScAlN s les grown at 800 °C, the crystal structure is poor and leakage current is high. Transmission electron microscopy with energy dispersive x-ray spectroscopy mapping shows a mass separation into ScN-rich and AlN-rich domains for x ≥ 0.2 when substrate temperature is increased from 400 to 800 °C. The piezoelectric response of epitaxial ScxAl1−xN films measured by piezoresponse force microscopy and double beam interferometry shows up to 180% increase by the addition of Sc up to x = 0.2 independent of substrate temperature, in good agreement with previous theoretical predictions based on density-functional theory.
Publisher: Elsevier BV
Date: 04-2019
Publisher: American Vacuum Society
Date: 28-04-2016
DOI: 10.1116/1.4948234
Abstract: DC magnetron sputtering was used to deposit molybdenum boride thin films for potential low-friction applications. The films exhibit a nanocomposite structure with ∼10 nm large MoB2−x (x & 0.4) grains surrounded by a boron-rich tissue phase. The preferred formation of the metastable and substoichiometric hP3-MoB2 structure (AlB2-type) is explained with kinetic constraints to form the thermodynamically stable hR18-MoB2 phase with a very complex crystal structure. Nanoindentation revealed a relatively high hardness of (29 ± 2) GPa, which is higher than bulk s les. The high hardness can be explained by a hardening effect associated with the nanocomposite microstructure where the surrounding tissue phase restricts dislocation movement. A tribological study confirmed a significant formation of a tribofilm consisting of molybdenum oxide and boron oxide, however, without any lubricating effects at room temperature.
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7NR03663A
Abstract: Au-containing nanolaminated carbides Mo 2 AuC and Mo 2 (Au 1−x Ga x ) 2 C were synthesized by a thermally induced substitutional reaction in Mo 2 GaC and Mo 2 Ga 2 C, respectively.
Publisher: Elsevier BV
Date: 09-2020
Publisher: Elsevier BV
Date: 08-2022
Publisher: Elsevier BV
Date: 07-2020
Publisher: American Chemical Society (ACS)
Date: 03-07-2020
DOI: 10.26434/CHEMRXIV.12588479.V1
Abstract: The atomic structure and local composition of high quality epitaxial substoichiometric titaniumdiboride (TiB 1.9 ) thin film, deposited by unbalanced magnetron sputtering, were studied usinganalytical high-resolution scanning transmission electron microscopy, density functional theoryand image simulations. The unmatched Ti is pinpointed to planar defects on {1-100} prismaticplanes and attributed to the absence of B between Ti planes that locally relaxes the structure.This mechanism allows the line compound to accommodate the off-stoichiometry and remaina line compound between defects. The planar defects are embedded in otherwise stoichiometricTiB 2 and are delineated by insertion of dislocations. An accompanied decrease in Ti-Ti bondlengths along and across the faults is observed.Introduction
Publisher: American Physical Society (APS)
Date: 07-12-2011
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D0NR07045A
Abstract: Tailored synthesis method is used to produce higher yield of (Mo 2/3 Y 1/3 ) 2 AlC i -MAX, for realization of 2D Mo 1.33 CT z MXene with ordered vacancies, the latter shows electrochemical performance equivalent to that produced from the Sc containing i -MAX.
Publisher: Wiley
Date: 18-07-2022
Abstract: Solid‐state precipitation can be used to tailor material properties, ranging from ferromagnets and catalysts to mechanical strengthening and energy storage. Thermoelectric properties can be modified by precipitation to enhance phonon scattering while retaining charge‐carrier transmission. Here, unconventional Janus‐type nanoprecipitates are uncovered in Mg 3 Sb 1.5 Bi 0.5 formed by side‐by‐side Bi‐ and Ge‐rich appendages, in contrast to separate nanoprecipitate formation. These Janus nanoprecipitates result from local comelting of Bi and Ge during sintering, enabling an amorphous‐like lattice thermal conductivity. A precipitate size effect on phonon scattering is observed due to the balance between alloy‐disorder and nanoprecipitate scattering. The thermoelectric figure‐of‐merit ZT reaches 0.6 near room temperature and 1.6 at 773 K. The Janus nanoprecipitation can be introduced into other materials and may act as a general property‐tailoring mechanism.
Publisher: American Chemical Society (ACS)
Date: 10-01-2023
Publisher: Elsevier BV
Date: 03-2022
Publisher: American Chemical Society (ACS)
Date: 23-02-2022
Publisher: American Chemical Society (ACS)
Date: 23-09-2019
Publisher: Elsevier BV
Date: 11-2015
Publisher: AIP Publishing
Date: 15-12-2011
DOI: 10.1063/1.3671560
Abstract: We study the effect of high power pulses in reactive magnetron sputter epitaxy on the structural properties of GaN (0001) thin films grown directly on Al2O3 (0001) substrates. The epilayers are grown by sputtering from a liquid Ga target, using a high power impulse magnetron sputtering power supply in a mixed N2/Ar discharge. X-ray diffraction, micro-Raman, micro-photoluminescence, and transmission electron microscopy investigations show the formation of two distinct types of domains. One almost fully relaxed domain exhibits superior structural and optical properties as evidenced by rocking curves with a full width at half maximum of 885 arc sec and a low temperature band edge luminescence at 3.47 eV with the full width at half maximum of 10 meV. The other domain exhibits a 14 times higher isotropic strain component, which is due to the higher densities of the point and extended defects, resulting from the ion bombardment during growth. Voids form at the domain boundaries. Mechanisms for the formation of differently strained domains, along with voids during the epitaxial growth of GaN are discussed.
Publisher: Wiley
Date: 22-12-2010
Publisher: Elsevier BV
Date: 10-2016
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9NA00324J
Abstract: MXenes are an extensive family of 2D transition metal carbides and nitrides, whose properties are strongly affected by surface terminations, typically O and F. Herein, we enable chlorine as a new termination, thereby expanding the property space.
Publisher: Elsevier BV
Date: 2021
Publisher: MDPI AG
Date: 02-09-2017
DOI: 10.3390/EN10091322
Abstract: We demonstrate the versatility of magnetron sputter epitaxy by achieving high-quality GaN nanorods on different substrate/template combinations, specifically Si, SiC, TiN/Si, ZrB2/Si, ZrB2/SiC, Mo, and Ti. Growth temperature was optimized on Si, TiN/Si, and ZrB2/Si, resulting in increased nanorod aspect ratio with temperature. All nanorods exhibit high purity and quality, proved by the strong bandedge emission recorded with cathodoluminescence spectroscopy at room temperature as well as transmission electron microscopy. These substrates/templates are affordable compared to many conventional substrates, and the direct deposition onto them eliminates cumbersome post-processing steps in device fabrication. Thus, magnetron sputter epitaxy offers an attractive alternative for simple and affordable fabrication in optoelectronic device technology.
Publisher: Elsevier BV
Date: 03-2021
Publisher: AIP Publishing
Date: 22-04-2013
DOI: 10.1063/1.4802758
Abstract: Using in situ transmission electron microscopy, we investigated the kinetics of liquid Ga droplet decay on thin amorphous carbon films during annealing at 773 K. The transmission electron microscopy images reveal that liquid Ga forms spherical droplets and undergo coarsening/decay with increasing time. We find that the droplet volumes change non-linearly with time and the volume decay rates depend on their local environment. By comparing the late-stage decay behavior of the droplets with the classical mean-field theory model for Ostwald ripening, we determine that the decay of Ga droplets occurs in the surface diffusion limited regime.
Publisher: Elsevier BV
Date: 12-2020
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D2NA00456A
Abstract: We report single-rod photodetectors with high responsivity and gain based on indium aluminium nitride (In x Al 1− x N) nanorods (NRs). A transition from a positive photoresponse to a negative photoresponse was observed while increasing the In composition.
Publisher: Elsevier BV
Date: 03-2021
Publisher: Elsevier BV
Date: 2019
Publisher: Wiley
Date: 05-08-2021
Abstract: Exploratory theoretical predictions in uncharted structural and compositional space are integral to materials discoveries. Inspired by M 5 SiB 2 (T2) phases, the finding of a family of laminated quaternary metal borides, M ′ 4 M ″SiB 2 , with out‐of‐plane chemical order is reported here. 11 chemically ordered phases as well as 40 solid solutions, introducing four elements previously not observed in these borides are predicted. The predictions are experimentally verified for Ti 4 MoSiB 2 , establishing Ti as part of the T2 boride compositional space. Chemical exfoliation of Ti 4 MoSiB 2 and select removal of Si and MoB 2 sub‐layers is validated by derivation of a 2D material, TiO x Cl y , of high yield and in the form of delaminated sheets. These sheets have an experimentally determined direct band gap of ≈4.1 eV, and display characteristics suitable for supercapacitor applications. The results take the concept of chemical exfoliation beyond currently available 2D materials, and expands the envelope of 3D and 2D candidates, and their applications.
Publisher: Elsevier BV
Date: 12-2012
Publisher: MDPI AG
Date: 04-2021
DOI: 10.3390/MA14071739
Abstract: Several ternary phases are known in the Mo-Fe-B system. Previous ab initio calculations have predicted that they should exhibit a tempting mix of mechanical and magnetic properties. In this study, we have deposited Mo-Fe-B films with a Fe-content varying from 0–37 at.% using non-reactive DC (direct current) magnetron sputtering. The phase composition, microstructure, and mechanical properties were investigated using X-ray diffraction, scanning transmission electron microscopy, and nanoindentation measurements. Films deposited at 300 °C and with at.% Fe are nanocomposites consisting of two amorphous phases: a metal-rich phase and a metal-deficient phase. Hardness and elastic modulus were reduced with increasing Fe-content from ~29 to ~19 GPa and ~526 to ~353 GPa, respectively. These values result in H3/E2 ratios of 0.089–0.052 GPa, thereby indicating brittle behaviour of the films. Also, no indication of crystalline ternary phases was observed at temperatures up to 600 °C, suggesting that higher temperatures are required for such films to form.
Publisher: Elsevier BV
Date: 07-2013
Publisher: Springer Science and Business Media LLC
Date: 25-04-2017
DOI: 10.1038/NCOMMS14949
Abstract: The exploration of two-dimensional solids is an active area of materials discovery. Research in this area has given us structures spanning graphene to dichalcogenides, and more recently 2D transition metal carbides (MXenes). One of the challenges now is to master ordering within the atomic sheets. Herein, we present a top-down, high-yield, facile route for the controlled introduction of ordered acancies in MXenes. By designing a parent 3D atomic laminate, (Mo 2/3 Sc 1/3 ) 2 AlC, with in-plane chemical ordering, and by selectively etching the Al and Sc atoms, we show evidence for 2D Mo 1.33 C sheets with ordered metal acancies and high electrical conductivities. At ∼1,100 F cm −3 , this 2D material exhibits a 65% higher volumetric capacitance than its counterpart, Mo 2 C, with no vacancies, and one of the highest volumetric capacitance values ever reported, to the best of our knowledge. This structural design on the atomic scale may alter and expand the concept of property-tailoring of 2D materials.
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C6NR05168E
Abstract: Recent developments in fabrication techniques and extensive investigations of the physical properties of III-V semiconductor nanowires (NWs), such as GaAs NWs, have demonstrated their potential for a multitude of advanced electronic and photonics applications. Alloying of GaAs with nitrogen can further enhance the performance and extend the device functionality via intentional defects and heterostructure engineering in GaNAs and GaAs/GaNAs coaxial NWs. In this work, it is shown that incorporation of nitrogen in GaAs NWs leads to formation of three-dimensional confining potentials caused by short-range fluctuations in the nitrogen composition, which are superimposed on long-range alloy disorder. The resulting localized states exhibit a quantum-dot like electronic structure, forming optically active states in the GaNAs shell. By directly correlating the structural and optical properties of in idual NWs, it is also shown that formation of the localized states is efficient in pure zinc-blende wires and is further facilitated by structural polymorphism. The light emission from these localized states is found to be spectrally narrow (∼50-130 μeV) and is highly polarized (up to 100%) with the preferable polarization direction orthogonal to the NW axis, suggesting a preferential orientation of the localization potential. These properties of self-assembled nano-emitters embedded in the GaNAs-based nanowire structures may be attractive for potential optoelectronic applications.
Publisher: American Physical Society (APS)
Date: 19-04-2016
Publisher: Springer Science and Business Media LLC
Date: 05-10-2017
DOI: 10.1038/S41598-017-12702-Y
Abstract: Selective-area growth (SAG) of single-crystal wurtzite GaN nanorods (NRs) directly onto Si(001) substrates with un-etched native SiO x amorphous layer, assisted by a patterning TiN x mask fabricated by nanosphere lithography (NSL), has been realized by reactive magnetron sputter epitaxy (MSE). The GaN NRs were grown vertically to the substrate surface with the growth direction along c -axis in the well-defined nano-opening areas. A 5-step structural and morphological evolution of the SAG NRs observed at different sputtering times depicts a comprehensive growth model, listed in sequence as: formation of a polycrystalline wetting layer, predominating c -axis oriented nucleation, coarsening and coalescence of multi-islands, single NR evolution, and finally quasi-equilibrium crystal shape formation. Room-temperature cathodoluminescence spectroscopy shows a strong GaN bandedge emission with a uniform luminescence across the NRs, indicating that the SAG NRs are grown with high quality and purity. In addition, single-longitudinal-mode lasing, attributed to well-faceted NR geometry forming a Fabry–Pérot cavity, was achieved by optical pumping, paving a way for fabricating high-performance laser optoelectronics using MSE.
Publisher: Elsevier BV
Date: 07-2022
Publisher: AIP Publishing
Date: 22-06-2015
DOI: 10.1063/1.4922877
Abstract: A high mobility of 2250 cm2/V·s of a two-dimensional electron gas (2DEG) in a metalorganic chemical vapor deposition-grown AlGaN/GaN heterostructure was demonstrated. The mobility enhancement was a result of better electron confinement due to a sharp AlGaN/GaN interface, as confirmed by scanning transmission electron microscopy analysis, not owing to the formation of a traditional thin AlN exclusion layer. Moreover, we found that the electron mobility in the sharp-interface heterostructures can sustain above 2000 cm2/V·s for a wide range of 2DEG densities. Finally, it is promising that the sharp-interface AlGaN/GaN heterostructure would enable low contact resistance fabrication, less impurity-related scattering, and trapping than the AlGaN/AlN/GaN heterostructure, as the high-impurity-contained AlN is removed.
Publisher: Elsevier BV
Date: 08-2015
Publisher: AIP Publishing
Date: 11-11-2013
DOI: 10.1063/1.4830044
Abstract: Nucleation mechanism of catalyst-free GaN nanorod grown on Si(111) is investigated by the fabrication of uniform and narrow (& nm) nanorods without a pre-defined mask by molecular beam epitaxy. Direct evidences show that the nucleation of GaN nanorods stems from the sidewall of the underlying islands down to the Si(111) substrate, different from commonly reported ones on top of the island directly. Accordingly, the growth and density control of the nanorods is exploited by a “narrow-pass” approach that only narrow nanorod can be grown. The optimal size of surrounding non-nucleation area around single nanorod is estimated as 88 nm.
Publisher: American Chemical Society (ACS)
Date: 13-10-2020
DOI: 10.1021/JACS.0C08113
Publisher: The Electrochemical Society
Date: 25-09-2009
DOI: 10.1149/1.3207674
Abstract: AlxGa1-xN multiple quantum wells (MQW) were grown on AlN epilayer grown on 4H-SiC substrate. The growth was performed without interruption in a horizontal hot-wall MOCVD reactor using a mixture of hydrogen and nitrogen as carrier gases. The precursors were ammonia, trimethylaluminum and trimethylgallium. Results obtained from X-ray diffraction and infra-red reflectance were used to obtain the composition of the films when growing simple AlxGa1 xN layer. Visible reflectance was used to evaluate the thickness of the films. Finally the MQW parameters as thicknesses and composition variation were obtained by scanning transmission electron microscopy and demonstrated an agreement with the growth parameters used
Publisher: American Physical Society (APS)
Date: 20-09-2018
Publisher: Wiley
Date: 06-04-2018
Abstract: Structural design on the atomic level can provide novel chemistries of hybrid MAX phases and their MXenes. Herein, density functional theory is used to predict phase stability of quaternary i-MAX phases with in-plane chemical order and a general chemistry (W
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C8NR01986J
Abstract: We investigated the presence of adsorbed species on Nb 2 C MXene surfaces and their influence on the structural stability over time.
No related grants have been discovered for Justinas Palisaitis.