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| 2. |
- Alnoor, Hatim, et al.
(författare)
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Exploring MXenes and their MAX phase precursors by electron microscopy
- 2021
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Ingår i: Materials Today Advances. - : Elsevier. - 2590-0498. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- This review celebrates the width and depth of electron microscopy methods and how these have enabled massive research efforts on MXenes. MXenes constitute a powerful recent addition to 2-dimensional materials, derived from their parent family of nanolaminated materials known as MAX phases. Owing to their rich chemistry, MXenes exhibit properties that have revolutionized ranges of applications, including energy storage, electromagnetic interference shielding, water filtering, sensors, and catalysis. Few other methods have been more essential in MXene research and development of corresponding applications, compared with electron microscopy, which enables structural and chemical identification at the atomic scale. In the following, the electron microscopy methods that have been applied to MXene and MAX phase precursor research are presented together with research examples and are discussed with respect to advantages and challenges.
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| 3. |
- Chang, Jui-Che, et al.
(författare)
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HiPIMS-grown AlN buffer for threading dislocation reduction in DC-magnetron sputtered GaN epifilm on sapphire substrate
- 2023
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Ingår i: Vacuum. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0042-207X .- 1879-2715. ; 217
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Tidskriftsartikel (refereegranskat)abstract
- Gallium nitride (GaN) epitaxial films on sapphire (Al2O3) substrates have been grown using reactive magnetron sputter epitaxy with a liquid Ga target. Threading dislocations density (TDD) of sputtered GaN films was reduced by using an inserted high-quality aluminum nitride (AlN) buffer layer grown by reactive high power impulse magnetron sputtering (R-HiPIMS) in a gas mixture of Ar and N2. After optimizing the Ar/N2 pressure ratio and deposition power, a high-quality AlN film exhibiting a narrow full-width at half-maximum (FWHM) value of the double-crystal x-ray rocking curve (DCXRC) of the AlN(0002) peak of 0.086° was obtained by R-HiPIMS. The mechanism giving rise the observed quality improvement is attributed to the enhancement of kinetic energy of the adatoms in the deposition process when operated in a transition mode. With the inserted HiPIMS-AlN as a buffer layer for direct current magnetron sputtering (DCMS) GaN growth, the FWHM values of GaN(0002) and (10 1‾ 1) XRC decrease from 0.321° to 0.087° and from 0.596° to 0.562°, compared to the direct growth of GaN on sapphire, respectively. An order of magnitude reduction from 2.7 × 109 cm−2 to 2.0 × 108 cm−2 of screw-type TDD calculated from the FWHM of the XRC data using the inserted HiPIMS-AlN buffer layer demonstrates the improvement of crystal quality of GaN. The result of TDD reduction using the HiPIMS-AlN buffer was also verified by weak beam dark-field (WBDF) cross-sectional transmission electron microscopy (TEM).
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| 4. |
- El Ghazaly, Ahmed, et al.
(författare)
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Enhanced supercapacitive performance of Mo1.33C MXene based asymmetric supercapacitors in lithium chloride electrolyte
- 2021
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Ingår i: Energy Storage Materials. - : Elsevier. - 2405-8289 .- 2405-8297. ; 41, s. 203-208
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Tidskriftsartikel (refereegranskat)abstract
- Two-dimensional (2D) Mo1.33C MXene renders great potential for energy storage applications and is mainly studied in the sulfuric acid (H2SO4) electrolyte. However, H2SO4 limits the electrode potential to 0.9 V for symmetric devices and 1.3 V for asymmetric devices. Herein, we explore the electrochemical behavior of Mo1.33C MXene in LiCl electrolyte. In comparison to H2SO4, LiCl electrolyte is a neutral salt with high solubility at room temperature and low hazardousness. The analysis shows a volumetric capacitance of 815 Fcm(-3) at a scan rate of 2 mVs(-1) with a large operating potential window of -1.2 to +0.3V (vs. Ag/AgCl). This is further exploited to construct MXene-based asymmetric supercapacitors Mo1.33C//MnxOn, and the electrochemical performance is evaluated in 5M LiCl electrolyte. Owing to the wide voltage widow of the Mo1.33C//MnxOn devices (2V) and high packing density of the electrodes, we have achieved a volumetric energy density of 58 mWh/cm(3), a maximum power density of 31 Wcm(-3) and retained 92% of the initial capacitance after 10,000 charge/discharge cycles at 10 A g(-1). One of the main value propositions of this work, aside from the high energy density, is the outstanding columbic efficiency (100%), which ensures excellent cyclic stability and is highly desirable for practical applications.
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| 5. |
- El Ghazaly, Ahmed, et al.
(författare)
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Improved charge storage performance of a layered Mo1.33C MXene/MoS2/graphene nanocomposite
- 2021
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Ingår i: Nanoscale Advances. - : Royal Society of Chemistry (RSC). - 2516-0230. ; 3:23, s. 6689-6695
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Tidskriftsartikel (refereegranskat)abstract
- The construction of nanocomposite electrodes based on 2D materials is an efficient route for property enrichment and for exploitation of constituent 2D materials. Herein, a flexible Mo1.33C i-MXene/MoS2/graphene (MOMG) composite electrode is constructed, utilizing an environment-friendly method for high-quality graphene and MoS2 synthesis. The presence of graphene and MoS2 between MXene sheets limits the commonly observed restacking, increases the interlayer spacing, and facilitates the ionic and electronic conduction. The as-prepared MOMG electrode delivers a volumetric capacitance of 1600 F cm(-3) (450 F g(-1)) at the scan rate of 2 mV s(-1) and retains 96% of the initial capacitance after 15 000 charge/discharge cycles (10 A g(-1)). The current work demonstrates that the construction of nanocomposite electrodes is a promising route towards property enhancement for energy storage applications.
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| 6. |
- Gangaprasad Rao, Smita, et al.
(författare)
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Phase formation in CrFeCoNi nitride thin films
- 2023
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Ingår i: Physical Review Materials. - : AMER PHYSICAL SOC. - 2475-9953. ; 7:4
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Tidskriftsartikel (refereegranskat)abstract
- As a single-phase alloy, CrFeCoNi is a face centered cubic (fcc) material related to the archetypical highentropy Cantor alloy CrFeCoNiMn. For thin films, CrFeCoNi of approximately equimolar composition tends to assume an fcc structure when grown at room temperature by magnetron sputtering. However, the single-phase solid solution state is typically not achieved for thin films grown at higher temperatures. The same holds true for Cantor alloy-based ceramics (nitrides and oxides), where phase formation is extremely sensitive to process parameters such as the amount of reactive gas. This study combines theoretical and experimental methods to understand the phase formation in nitrogen-containing CrFeCoNi thin films. Density functional theory calculations considering three competing phases (CrN, Fe-Ni and Co) show that the free energy of mixing, Delta G of (CrFeCoNi)(1-x)N-x solid solutions has a maximum at x = 0.20-0.25, and AG becomes lower when x < 0.20 and x > 0.25. Thin films of (CrFeCoNi)1-xNx (0.14 >= x <= 0.41) grown by magnetron sputtering show stabilization of the metallic fcc when x <= 0.22 and the stabilization of the NaCl B1 structure when x > 0.33, consistent with the theoretical prediction. In contrast, films with intermediate amounts of nitrogen (x = 0.22) grown at higher temperatures show segregation into multiple phases of CrN, Fe-Ni-rich and Co. These results offer an explanation for the requirement of kinetically limited growth conditions at low temperature for obtaining single-phase CrFeCoNi Cantor-like nitrogen-containing thin films and are of importance for understanding the phase-formation mechanisms in multicomponent ceramics. The results from the study further aid in making correlations between the observed mechanical properties and the crystal structure of the films.
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| 7. |
- Zheng, Wei, et al.
(författare)
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Flexible Free-Standing MoO3/Ti3C2Tz MXene Composite Films with High Gravimetric and Volumetric Capacities
- 2021
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Ingår i: Advanced Science. - : Wiley. - 2198-3844. ; 8:3
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Tidskriftsartikel (refereegranskat)abstract
- Enhancing both the energy storage and power capabilities of electrochemical capacitors remains a challenge. Herein, Ti3C2Tz MXene is mixed with MoO3 nanobelts in various mass ratios and the mixture is used to vacuum filter binder free, open, flexible, and free-standing films. The conductive Ti3C2Tz flakes bridge the nanobelts, facilitating electron transfer; the randomly oriented, and interconnected, MoO3 nanobelts, in turn, prevent the restacking of the Ti3C2Tz nanosheets. Benefitting from these advantages, a MoO3/Ti3C2Tz film with a 8:2 mass ratio exhibits high gravimetric/volumetric capacities with good cyclability, namely, 837 C g−1 and 1836 C cm−3 at 1 A g−1 for an ≈ 10 µm thick film; and 767 C g−1 and 1664 C cm−3 at 1 A g−1 for ≈ 50 µm thick film. To further increase the energy density, hybrid capacitors are fabricated with MoO3/Ti3C2Tz films as the negative electrodes and nitrogen-doped activated carbon as the positive electrodes. This device delivers maximum gravimetric/volumetric energy densities of 31.2 Wh kg−1 and 39.2 Wh L−1, respectively. The cycling stability of 94.2% retention ratio after 10 000 continuous charge/discharge cycles is also noteworthy. The high energy density achieved in this work can pave the way for practical applications of MXene-containing materials in energy storage devices.
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