Udit Kumar, Ayush Arunachalam, Corbin Feit, S. Novia Berriel, Kanad Basu, Parag Banerjee, Sudipta Seal
CeO2 nanostructures have been utilized for various biomedical, sensor, and catalysis applications owing to their unique defect structure, enabling them to have regenerative oxidative properties. Defect engineering in CeO2 nanostructures has major importance, enabling them to be utilized for specific applications. Despite various synthesis methods, it is challenging to have precise and reversible control over defect structures. Against this backdrop, in the current work, we have explored machine learning (ML) enhanced defect engineering of CeO2 nanofilms. In our earlier work [J. Vac. Sci. Technol. A 39, 060405 (2021)], we have developed an atomic layer deposition process for CeO2 using in situ ellipsometry measurements. In the current work, data collected through in situ spectroscopic ellipsometry and ex situ XPS have been correlated using two ML algorithms (gradient boost and random forest regressor) to exert better control over the chemical properties. Defect structures are one of the desired properties in CeO2 nanomaterials, characterized by the Ce3+/Ce4+ oxidation state ratio leading to its regenerative properties. We have shown that the defect structure of the CeO2 nanofilms can be predicted using in situ ellipsometry data in real time using a trained ML algorithm using two different methods. The first method involves an indirect approach of thickness prediction using an ML algorithm (k-nearest neighbors) followed by Ce3+/Ce4+ estimation using an experimental calibration curve. The second method with a more direct approach involves Ce3+/Ce4+ prediction using real-time ellipsometry data (amplitude ratio ψ and phase difference Δ) using gradient boost and random forest regressor.
{"title":"Real-time artificial intelligence enhanced defect engineering in CeO2 nanostructures","authors":"Udit Kumar, Ayush Arunachalam, Corbin Feit, S. Novia Berriel, Kanad Basu, Parag Banerjee, Sudipta Seal","doi":"10.1116/6.0002912","DOIUrl":"https://doi.org/10.1116/6.0002912","url":null,"abstract":"CeO2 nanostructures have been utilized for various biomedical, sensor, and catalysis applications owing to their unique defect structure, enabling them to have regenerative oxidative properties. Defect engineering in CeO2 nanostructures has major importance, enabling them to be utilized for specific applications. Despite various synthesis methods, it is challenging to have precise and reversible control over defect structures. Against this backdrop, in the current work, we have explored machine learning (ML) enhanced defect engineering of CeO2 nanofilms. In our earlier work [J. Vac. Sci. Technol. A 39, 060405 (2021)], we have developed an atomic layer deposition process for CeO2 using in situ ellipsometry measurements. In the current work, data collected through in situ spectroscopic ellipsometry and ex situ XPS have been correlated using two ML algorithms (gradient boost and random forest regressor) to exert better control over the chemical properties. Defect structures are one of the desired properties in CeO2 nanomaterials, characterized by the Ce3+/Ce4+ oxidation state ratio leading to its regenerative properties. We have shown that the defect structure of the CeO2 nanofilms can be predicted using in situ ellipsometry data in real time using a trained ML algorithm using two different methods. The first method involves an indirect approach of thickness prediction using an ML algorithm (k-nearest neighbors) followed by Ce3+/Ce4+ estimation using an experimental calibration curve. The second method with a more direct approach involves Ce3+/Ce4+ prediction using real-time ellipsometry data (amplitude ratio ψ and phase difference Δ) using gradient boost and random forest regressor.","PeriodicalId":17490,"journal":{"name":"Journal of Vacuum Science & Technology A","volume":"16 5","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135934526","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Michael A. Collings, Marcel Junige, Andrew S. Cavanagh, Victor Wang, Andrew C. Kummel, Steven M. George
Ruthenium (Ru) thin films were deposited utilizing electron-enhanced atomic layer deposition (EE-ALD). Sequential exposures of Ru(DMBD)(CO)3 (DMBD = 2,3-dimethylbutadiene) and low-energy electrons at ∼125 eV were used to grow the Ru films at temperatures ≤160 °C. The electrons were obtained from a hollow cathode plasma electron source that provided an electron current of ∼200 mA over a surface area of ∼4 cm2. Low-energy electrons can desorb surface ligands derived from Ru(DMBD)(CO)3, such as CO, through electron-stimulated desorption. The desorbed surface ligands leave chemically reactive sites for subsequent Ru(DMBD)(CO)3 precursor absorption. Ru EE-ALD film growth was monitored utilizing in situ spectroscopic ellipsometry (SE). The electron exposures resulted in rapid Ru film nucleation and growth. Under saturation conditions at 160 °C, the growth rate for Ru EE-ALD was 0.2 Å/cycle. The electron efficiency factor for Ru EE-ALD was ∼21 500 electrons/deposited Ru atom. There was no film growth without electron exposures. Ru growth was observed on various substrates including silicon with native oxide and titanium. Ru growth was also obtained on insulating substrates such as 400 nm thick thermal SiO2 substrates. XPS analysis measured <1 at. % oxygen in the deposited Ru films. XRD, x-ray reflectivity, and SE were used to characterize the Ru films before and after forming gas anneal (FGA). FGA successfully removed carbon impurities from the as-deposited Ru films. The resistivity of the Ru EE-ALD films after FGA was determined to be as low as 17 μΩ cm for a film thickness of 6.7 nm. SE measurements of the imaginary part of the pseudodielectric function, 〈ɛ2〉, were utilized to characterize the as-deposited Ru films and the high purity Ru films after FGA. The low resistivity of the Ru films after FGA was consistent with a prominent Drude absorption in the ⟨ε2⟩ spectrum at ≤1 eV. Various reactive background gases such as H2, NH3, and H2O were utilized during EE-ALD to attempt to remove the carbon from the as-deposited Ru EE-ALD films.
{"title":"Electron-enhanced atomic layer deposition of Ru thin films using Ru(DMBD)(CO)3 and effect of forming gas anneal","authors":"Michael A. Collings, Marcel Junige, Andrew S. Cavanagh, Victor Wang, Andrew C. Kummel, Steven M. George","doi":"10.1116/6.0002938","DOIUrl":"https://doi.org/10.1116/6.0002938","url":null,"abstract":"Ruthenium (Ru) thin films were deposited utilizing electron-enhanced atomic layer deposition (EE-ALD). Sequential exposures of Ru(DMBD)(CO)3 (DMBD = 2,3-dimethylbutadiene) and low-energy electrons at ∼125 eV were used to grow the Ru films at temperatures ≤160 °C. The electrons were obtained from a hollow cathode plasma electron source that provided an electron current of ∼200 mA over a surface area of ∼4 cm2. Low-energy electrons can desorb surface ligands derived from Ru(DMBD)(CO)3, such as CO, through electron-stimulated desorption. The desorbed surface ligands leave chemically reactive sites for subsequent Ru(DMBD)(CO)3 precursor absorption. Ru EE-ALD film growth was monitored utilizing in situ spectroscopic ellipsometry (SE). The electron exposures resulted in rapid Ru film nucleation and growth. Under saturation conditions at 160 °C, the growth rate for Ru EE-ALD was 0.2 Å/cycle. The electron efficiency factor for Ru EE-ALD was ∼21 500 electrons/deposited Ru atom. There was no film growth without electron exposures. Ru growth was observed on various substrates including silicon with native oxide and titanium. Ru growth was also obtained on insulating substrates such as 400 nm thick thermal SiO2 substrates. XPS analysis measured &lt;1 at. % oxygen in the deposited Ru films. XRD, x-ray reflectivity, and SE were used to characterize the Ru films before and after forming gas anneal (FGA). FGA successfully removed carbon impurities from the as-deposited Ru films. The resistivity of the Ru EE-ALD films after FGA was determined to be as low as 17 μΩ cm for a film thickness of 6.7 nm. SE measurements of the imaginary part of the pseudodielectric function, 〈ɛ2〉, were utilized to characterize the as-deposited Ru films and the high purity Ru films after FGA. The low resistivity of the Ru films after FGA was consistent with a prominent Drude absorption in the ⟨ε2⟩ spectrum at ≤1 eV. Various reactive background gases such as H2, NH3, and H2O were utilized during EE-ALD to attempt to remove the carbon from the as-deposited Ru EE-ALD films.","PeriodicalId":17490,"journal":{"name":"Journal of Vacuum Science & Technology A","volume":"17 2","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135272586","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Tenghao Jiang, Hong Zhao, Kostadinos Tsoutas, Lixian Sun, Hongwei Liu, Yanping Liu, Fanjun Xu, Zhong Zheng, Marcela M. Bilek, Zongwen Liu
In the past two decades, high entropy alloy (HEA) coatings have attracted great attention due to their superior mechanical properties, outstanding corrosion and oxidation resistance, and exceptionally high thermal stability. In comparison to HEA thin films, high entropy nitrides (HENs) exhibit higher mechanical strength and chemical inertness. In this work, AlCrFeCoNiCu0.5 HEA and HEN thin films were fabricated using a filtered cathodic arc. By regulating the deposition pressure from 0.0005 Pa (HEA thin film) to 0.05 Pa, the nitrogen concentration in each thin film was precisely controlled to tune the mechanical properties. Scanning transmission electron microscopy-energy dispersive spectroscopy revealed that the nitrogen concentration of the films was up to 21.2 at. % at the pressure of 0.05 Pa. The reduced effect of preferential sputtering increased aluminum concentration from 8.3 ± 1.5 to 12.9 ± 2.2 at. % as pressure increased up to 0.05 Pa. X-ray photoelectron spectroscopy further confirmed the formation of AlN and CrN at pressures of 0.01–0.05 Pa. The highest hardness and elastic modulus of the HEN film were 12.4 ± 0.6 and 347.3 ± 17.7 GPa, respectively, which were 84.8% and 131.4% higher than those of the HEA thin film.
{"title":"Effect of nitrogen pressure on the fabrication of AlCrFeCoNiCu0.5 high entropy nitride thin films via cathodic arc deposition","authors":"Tenghao Jiang, Hong Zhao, Kostadinos Tsoutas, Lixian Sun, Hongwei Liu, Yanping Liu, Fanjun Xu, Zhong Zheng, Marcela M. Bilek, Zongwen Liu","doi":"10.1116/6.0003064","DOIUrl":"https://doi.org/10.1116/6.0003064","url":null,"abstract":"In the past two decades, high entropy alloy (HEA) coatings have attracted great attention due to their superior mechanical properties, outstanding corrosion and oxidation resistance, and exceptionally high thermal stability. In comparison to HEA thin films, high entropy nitrides (HENs) exhibit higher mechanical strength and chemical inertness. In this work, AlCrFeCoNiCu0.5 HEA and HEN thin films were fabricated using a filtered cathodic arc. By regulating the deposition pressure from 0.0005 Pa (HEA thin film) to 0.05 Pa, the nitrogen concentration in each thin film was precisely controlled to tune the mechanical properties. Scanning transmission electron microscopy-energy dispersive spectroscopy revealed that the nitrogen concentration of the films was up to 21.2 at. % at the pressure of 0.05 Pa. The reduced effect of preferential sputtering increased aluminum concentration from 8.3 ± 1.5 to 12.9 ± 2.2 at. % as pressure increased up to 0.05 Pa. X-ray photoelectron spectroscopy further confirmed the formation of AlN and CrN at pressures of 0.01–0.05 Pa. The highest hardness and elastic modulus of the HEN film were 12.4 ± 0.6 and 347.3 ± 17.7 GPa, respectively, which were 84.8% and 131.4% higher than those of the HEA thin film.","PeriodicalId":17490,"journal":{"name":"Journal of Vacuum Science & Technology A","volume":"73 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135871480","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Gallium nitride (GaN) has attracted significant interest as a next-generation semiconductor material with various potential applications. During metalorganic chemical vapor deposition (MOCVD) of GaN using trimethyl gallium (TMG) and NH3, dimeric precursors are produced by gas-phase reactions such as adduct formation or thermal decomposition. In this work, the surface adsorption reactions of monomeric and dimeric Ga molecules including TMG, [(CH3)2Ga(NH2)]2, and [(CH3)GaNH]2 on the GaN surface are investigated using density functional theory calculations. It is found that [(CH3)2Ga(NH2)]2 is the most predominant form among the various dimeric precursors under typical GaN MOCVD process conditions. Our results indicate that the dimeric [(CH3)GaNH]2 precursor, which is generated through the thermal decomposition of [(CH3)2Ga(NH2)]2, would have higher reactivity on the GaN surface. Our work provides critical insights that can inform the optimization of GaN MOCVD processes, leading to advancements in GaN-based high-performance semiconductors.
{"title":"Adsorption mechanism of dimeric Ga precursors in metalorganic chemical vapor deposition of gallium nitride","authors":"Hankyu Kim, Miso Kim, Bumsang Kim, Bonggeun Shong","doi":"10.1116/6.0002966","DOIUrl":"https://doi.org/10.1116/6.0002966","url":null,"abstract":"Gallium nitride (GaN) has attracted significant interest as a next-generation semiconductor material with various potential applications. During metalorganic chemical vapor deposition (MOCVD) of GaN using trimethyl gallium (TMG) and NH3, dimeric precursors are produced by gas-phase reactions such as adduct formation or thermal decomposition. In this work, the surface adsorption reactions of monomeric and dimeric Ga molecules including TMG, [(CH3)2Ga(NH2)]2, and [(CH3)GaNH]2 on the GaN surface are investigated using density functional theory calculations. It is found that [(CH3)2Ga(NH2)]2 is the most predominant form among the various dimeric precursors under typical GaN MOCVD process conditions. Our results indicate that the dimeric [(CH3)GaNH]2 precursor, which is generated through the thermal decomposition of [(CH3)2Ga(NH2)]2, would have higher reactivity on the GaN surface. Our work provides critical insights that can inform the optimization of GaN MOCVD processes, leading to advancements in GaN-based high-performance semiconductors.","PeriodicalId":17490,"journal":{"name":"Journal of Vacuum Science & Technology A","volume":"17 19","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135863985","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Xi Su, Zexin Tu, Liwei Ji, Hao Wu, Hongxing Xu, Chang Liu
Nickel oxide (NiO) films were prepared on ITO-coated glass substrates by atomic layer deposition at different temperatures. NiO films exhibit good anodic electrochromic properties because of their polycrystalline structures. The optical modulation observed at 550 nm was around 44%, changing color from transparent to black. The largest coloration efficiency at 550 nm was calculated to be 31.7 cm2/C.
{"title":"Electrochromic properties of NiO films prepared by atomic layer deposition","authors":"Xi Su, Zexin Tu, Liwei Ji, Hao Wu, Hongxing Xu, Chang Liu","doi":"10.1116/6.0003040","DOIUrl":"https://doi.org/10.1116/6.0003040","url":null,"abstract":"Nickel oxide (NiO) films were prepared on ITO-coated glass substrates by atomic layer deposition at different temperatures. NiO films exhibit good anodic electrochromic properties because of their polycrystalline structures. The optical modulation observed at 550 nm was around 44%, changing color from transparent to black. The largest coloration efficiency at 550 nm was calculated to be 31.7 cm2/C.","PeriodicalId":17490,"journal":{"name":"Journal of Vacuum Science & Technology A","volume":"67 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136067495","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Farahani, T. Kozák, A. D. Pajdarová, A. Bahr, H. Riedl, P. Zeman
A combination of time-averaged mass spectroscopy (MS), time-averaged optical emission spectroscopy (OES), and plasma transport modeling was employed to understand the transport processes of ions and atoms in high-power impulse magnetron sputtering discharges resulting in changes in the stoichiometry of NbCx films during their deposition from a stoichiometric NbC compound target at different repetition frequencies and duty cycles. Mass spectrometry showed that the fluxes of ions originating from the elements of the target increase with increasing pulse power density (and decreasing pulse length) due to an increasing electron density and, thus, electron-impact ionization probability. Due to the higher ionization energy and much lower ionization cross section of C (compared to Nb), it was found that the contribution of C+ ions to the deposition flux is practically negligible. Additionally, OES tracked the densities of ions and atoms at different distances from the target. The OES analysis revealed that the atom densities decreased as the pulse power density increased. In contrast, the ion densities exhibited an increase, which is consistent with the findings of MS. Using the data from MS, OES, and modeling, we were able to estimate the fluxes of atoms to the substrate. Our observations demonstrated a transition from C-rich toward Nb-rich flux of film-forming species with increasing pulse power density, corresponding to changes in the film composition. We further discuss the role of internal plasma processes that are responsible for this transition.
{"title":"Understanding ion and atom fluxes during high-power impulse magnetron sputtering deposition of NbCx films from a compound target","authors":"M. Farahani, T. Kozák, A. D. Pajdarová, A. Bahr, H. Riedl, P. Zeman","doi":"10.1116/6.0002944","DOIUrl":"https://doi.org/10.1116/6.0002944","url":null,"abstract":"A combination of time-averaged mass spectroscopy (MS), time-averaged optical emission spectroscopy (OES), and plasma transport modeling was employed to understand the transport processes of ions and atoms in high-power impulse magnetron sputtering discharges resulting in changes in the stoichiometry of NbCx films during their deposition from a stoichiometric NbC compound target at different repetition frequencies and duty cycles. Mass spectrometry showed that the fluxes of ions originating from the elements of the target increase with increasing pulse power density (and decreasing pulse length) due to an increasing electron density and, thus, electron-impact ionization probability. Due to the higher ionization energy and much lower ionization cross section of C (compared to Nb), it was found that the contribution of C+ ions to the deposition flux is practically negligible. Additionally, OES tracked the densities of ions and atoms at different distances from the target. The OES analysis revealed that the atom densities decreased as the pulse power density increased. In contrast, the ion densities exhibited an increase, which is consistent with the findings of MS. Using the data from MS, OES, and modeling, we were able to estimate the fluxes of atoms to the substrate. Our observations demonstrated a transition from C-rich toward Nb-rich flux of film-forming species with increasing pulse power density, corresponding to changes in the film composition. We further discuss the role of internal plasma processes that are responsible for this transition.","PeriodicalId":17490,"journal":{"name":"Journal of Vacuum Science & Technology A","volume":"279 3","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136261865","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
An on-lattice kinetic Monte Carlo model is constructed to investigate microscopic nucleation behavior during the submonolayer epitaxial growth of GaN islands, where the Ga and N atoms are treated as the basic particles. The input kinetic parameters of Ga and N, including their surface diffusion energy barriers, were obtained from previous ab initio calculations. Furthermore, a simple and effective bond counting rule is applied in our kinetic Monte Carlo model, and the statistics of the GaN islands on the surface are realized via the application of the Hoshen–Kopelman algorithm. The growth temperature range covers the typical growth temperatures used in the molecular beam epitaxy of GaN. The results obtained show that triangular GaN flakes are observed and that the shapes of the GaN islands remain triangular when the growth temperature is changed. Additionally, the power law for the maximum density of islands versus the ratio of the effective diffusion to the deposition rate is obtained; the exponent of this law is −0.506 ± 0.006, indicating that these triplets represent the seeds required for further nucleation. Finally, the coexistence of the Ga-edge and N-edge types of triangular GaN islands is observed. The island formation mechanism is attributed to a local monomer density misbalance, and it is also shown that a slight variation in the Ga/N ratio in the deposition flux changes the proportion of the Ga-edge and N-edge type triangles; this represents a further indication that controllable GaN morphologies can be obtained by tuning the chemical potentials of the constituent elements.
{"title":"Microscopic study of submonolayer nucleation characteristics during GaN (0001) homoepitaxial growth","authors":"Peng Su, Wensen Ai, Xuejiang Chen, Lijun Liu","doi":"10.1116/6.0003115","DOIUrl":"https://doi.org/10.1116/6.0003115","url":null,"abstract":"An on-lattice kinetic Monte Carlo model is constructed to investigate microscopic nucleation behavior during the submonolayer epitaxial growth of GaN islands, where the Ga and N atoms are treated as the basic particles. The input kinetic parameters of Ga and N, including their surface diffusion energy barriers, were obtained from previous ab initio calculations. Furthermore, a simple and effective bond counting rule is applied in our kinetic Monte Carlo model, and the statistics of the GaN islands on the surface are realized via the application of the Hoshen–Kopelman algorithm. The growth temperature range covers the typical growth temperatures used in the molecular beam epitaxy of GaN. The results obtained show that triangular GaN flakes are observed and that the shapes of the GaN islands remain triangular when the growth temperature is changed. Additionally, the power law for the maximum density of islands versus the ratio of the effective diffusion to the deposition rate is obtained; the exponent of this law is −0.506 ± 0.006, indicating that these triplets represent the seeds required for further nucleation. Finally, the coexistence of the Ga-edge and N-edge types of triangular GaN islands is observed. The island formation mechanism is attributed to a local monomer density misbalance, and it is also shown that a slight variation in the Ga/N ratio in the deposition flux changes the proportion of the Ga-edge and N-edge type triangles; this represents a further indication that controllable GaN morphologies can be obtained by tuning the chemical potentials of the constituent elements.","PeriodicalId":17490,"journal":{"name":"Journal of Vacuum Science & Technology A","volume":"66 2","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136381538","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this study, we report the structural, energetic, mechanical, electronic, thermal, and magnetic properties of W1−xTaxN6, W1−xMoxN6, and Mo1−xTaxN6 (0 ≤ x ≤ 1) alloys in a hexagonal structure (space group: R3¯m) determined using density functional theory–based first-principles calculations. These compounds are mechanically stable, whereas W0.33Ta0.66N6 is vibrationally unstable. Among both mechanically and vibrationally stable compounds, W0.66Ta0.33N6 and W0.66Mo0.33N6 have the highest hardness of 55 GPa, while the softest alloy (Mo0.33Ta0.66N6) exhibits 46 GPa, indicating new potential super hard materials. The high hardness in these materials is attributed to the combined effect of covalent N–N bonding of hexagonal rings and a metal to nitrogen charge transfer. Only two alloys, W0.33Mo0.66N6 and W0.66Mo0.33N6, are semiconducting alloys with electronic bandgaps of 1.82 and 1.92 eV, respectively. A significant magnetic moment of 0.82 μB per unit metal was calculated for W0.66Mo0.33N6.
{"title":"Density functional theory calculations of mechanical and electronic properties of W1−xTaxN6, W1−xMoxN6, and Mo1−xTaxN6 (0 ≤ x ≤ 1) alloys in a hexagonal structure","authors":"S. R. Kandel, D. Gall, S. V. Khare","doi":"10.1116/6.0002923","DOIUrl":"https://doi.org/10.1116/6.0002923","url":null,"abstract":"In this study, we report the structural, energetic, mechanical, electronic, thermal, and magnetic properties of W1−xTaxN6, W1−xMoxN6, and Mo1−xTaxN6 (0 ≤ x ≤ 1) alloys in a hexagonal structure (space group: R3¯m) determined using density functional theory–based first-principles calculations. These compounds are mechanically stable, whereas W0.33Ta0.66N6 is vibrationally unstable. Among both mechanically and vibrationally stable compounds, W0.66Ta0.33N6 and W0.66Mo0.33N6 have the highest hardness of 55 GPa, while the softest alloy (Mo0.33Ta0.66N6) exhibits 46 GPa, indicating new potential super hard materials. The high hardness in these materials is attributed to the combined effect of covalent N–N bonding of hexagonal rings and a metal to nitrogen charge transfer. Only two alloys, W0.33Mo0.66N6 and W0.66Mo0.33N6, are semiconducting alloys with electronic bandgaps of 1.82 and 1.92 eV, respectively. A significant magnetic moment of 0.82 μB per unit metal was calculated for W0.66Mo0.33N6.","PeriodicalId":17490,"journal":{"name":"Journal of Vacuum Science & Technology A","volume":"26 2","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136381800","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Alyson Spitzig, Jennifer E. Hoffman, Jason D. Hoffman
Bulk VO2 undergoes an insulator-to-metal transition (IMT) with up to five orders of magnitude change in the resistance at 340 K. However, when VO2 is deposited as a film on a substrate, the strain from the substrate can alter the IMT temperature, resistivity ratio of IMT, and hysteresis. Here, we present single-phase VO2 ultrathin films (thickness less than 20 nm) grown using oxygen plasma molecular beam epitaxy (MBE) on TiO2 (001) and Al2O3 (0001) substrates. First, we modify existing recipes employing ozone MBE and reproduce the best films from literature on TiO2 (001), maintaining an almost three orders of magnitude transition in a 12 nm thick film with TIMT of 308 K (296 K) upon warming (cooling). We then extend our recipe to Al2O3 (0001) substrates where we stabilize a 12 nm thin single-phase VO2 film and observe two orders of magnitude transition at 337 K (329 K) upon warming (cooling), expanding the possible growth methods for ultrathin VO2 films on Al2O3 (0001).
大块VO2经历绝缘体到金属的转变(IMT)，在340 K时电阻变化高达五个数量级。然而，当VO2作为薄膜沉积在衬底上时，衬底的应变会改变IMT的温度、电阻率和迟滞率。在这里，我们用氧等离子体分子束外延(MBE)在TiO2(001)和Al2O3(0001)衬底上生长了单相VO2超薄膜(厚度小于20 nm)。首先，我们利用臭氧MBE修改了现有的配方，并在TiO2(001)上重现了文献中最好的薄膜，在加热(冷却)时，在TIMT为308 K (296 K)的12 nm厚薄膜中保持了近三个数量级的转变。然后，我们将我们的配方扩展到Al2O3(0001)衬底，在那里我们稳定了12 nm薄的单相VO2薄膜，并在337 K (329 K)加热(冷却)时观察到两个数量级的转变，扩展了在Al2O3(0001)上超薄VO2薄膜的可能生长方法。
{"title":"Ultrathin VO2 grown with oxygen plasma molecular beam epitaxy on TiO2 (001) and Al2O3 (0001)","authors":"Alyson Spitzig, Jennifer E. Hoffman, Jason D. Hoffman","doi":"10.1116/6.0003096","DOIUrl":"https://doi.org/10.1116/6.0003096","url":null,"abstract":"Bulk VO2 undergoes an insulator-to-metal transition (IMT) with up to five orders of magnitude change in the resistance at 340 K. However, when VO2 is deposited as a film on a substrate, the strain from the substrate can alter the IMT temperature, resistivity ratio of IMT, and hysteresis. Here, we present single-phase VO2 ultrathin films (thickness less than 20 nm) grown using oxygen plasma molecular beam epitaxy (MBE) on TiO2 (001) and Al2O3 (0001) substrates. First, we modify existing recipes employing ozone MBE and reproduce the best films from literature on TiO2 (001), maintaining an almost three orders of magnitude transition in a 12 nm thick film with TIMT of 308 K (296 K) upon warming (cooling). We then extend our recipe to Al2O3 (0001) substrates where we stabilize a 12 nm thin single-phase VO2 film and observe two orders of magnitude transition at 337 K (329 K) upon warming (cooling), expanding the possible growth methods for ultrathin VO2 films on Al2O3 (0001).","PeriodicalId":17490,"journal":{"name":"Journal of Vacuum Science & Technology A","volume":"498 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135111503","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Won-Jun Jang, Min Hui Chang, Min Jeong Kang, Young Jae Song, Se-Jong Kahng
Standing wave patterns are formed near potential barriers or steps due to the interference of incident and reflected waves. Graphene systems show standing wave patterns near atomic step edges, defects, and impurities in scanning tunneling microscopy; however, there are still unexplored examples. In this study, we present our experimental results for graphene directly grown on hexagonal-BN/Cu by chemical vapor deposition. Standing wave patterns were observed in our scanning tunneling microscopy and spectroscopy, revealing linear dispersion relations with a Fermi velocity of about 106 m/s. Our study shows that graphene grown on hexagonal-BN/Cu provides a useful platform to study the electronic characteristics of graphene systems.
{"title":"Standing wave patterns in graphene systems studied using scanning tunneling spectroscopy","authors":"Won-Jun Jang, Min Hui Chang, Min Jeong Kang, Young Jae Song, Se-Jong Kahng","doi":"10.1116/6.0003075","DOIUrl":"https://doi.org/10.1116/6.0003075","url":null,"abstract":"Standing wave patterns are formed near potential barriers or steps due to the interference of incident and reflected waves. Graphene systems show standing wave patterns near atomic step edges, defects, and impurities in scanning tunneling microscopy; however, there are still unexplored examples. In this study, we present our experimental results for graphene directly grown on hexagonal-BN/Cu by chemical vapor deposition. Standing wave patterns were observed in our scanning tunneling microscopy and spectroscopy, revealing linear dispersion relations with a Fermi velocity of about 106 m/s. Our study shows that graphene grown on hexagonal-BN/Cu provides a useful platform to study the electronic characteristics of graphene systems.","PeriodicalId":17490,"journal":{"name":"Journal of Vacuum Science & Technology A","volume":"63 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135779249","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：