TY  - JOUR
AU  - Chesnyak, Valeria
AU  - Stavrić, Srđan
AU  - Panighel, Mirco
AU  - Comelli, Giovanni
AU  - Peressi, Maria
AU  - Africh, Cristina
PY  - 2022
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/10208
AB  - The influence on the growth of cobalt (Co)-based nanostructures of a surface carbide (Ni2C) layer formed at the Ni(100) surface is revealed via complementary scanning tunneling microscopy (STM) measurements and first-principles calculations. On clean Ni(100) below 200 °C in the sub-monolayer regime, Co forms randomly distributed two-dimensional (2D) islands, while on Ni2C it grows in the direction perpendicular to the surface as well, thus forming two-atomic-layers high islands. We present a simple yet powerful model that explains the different Co growth modes for the two surfaces. A jagged step decoration, not visible on stepped Ni(100), is present on Ni2C. This contrasting behavior on Ni2C is explained by the sharp differences in the mobility of Co atoms for the two cases. By increasing the temperature, Co dissolution is activated with almost no remaining Co at 250 °C on Ni(100) and Co islands still visible on the Ni2C surface up to 300 °C. The higher thermal stability of Co above the Ni2C surface is rationalized by ab initio calculations, which also suggest the existence of a vacancy-assisted mechanism for Co dissolution in Ni(100). The methodology presented in this paper, combining systematically STM measurements with first-principles calculations and computational modelling, opens the way to controlled engineering of bimetallic surfaces with tailored properties.
T2  - Nanoscale
T1  - Carbide coating on nickel to enhance the stability of supported metal nanoclusters
VL  - 14
IS  - 9
SP  - 3589
EP  - 3598
DO  - 10.1039/D1NR06485A
ER  - 

@article{
author = "Chesnyak, Valeria and Stavrić, Srđan and Panighel, Mirco and Comelli, Giovanni and Peressi, Maria and Africh, Cristina",
year = "2022",
abstract = "The influence on the growth of cobalt (Co)-based nanostructures of a surface carbide (Ni2C) layer formed at the Ni(100) surface is revealed via complementary scanning tunneling microscopy (STM) measurements and first-principles calculations. On clean Ni(100) below 200 °C in the sub-monolayer regime, Co forms randomly distributed two-dimensional (2D) islands, while on Ni2C it grows in the direction perpendicular to the surface as well, thus forming two-atomic-layers high islands. We present a simple yet powerful model that explains the different Co growth modes for the two surfaces. A jagged step decoration, not visible on stepped Ni(100), is present on Ni2C. This contrasting behavior on Ni2C is explained by the sharp differences in the mobility of Co atoms for the two cases. By increasing the temperature, Co dissolution is activated with almost no remaining Co at 250 °C on Ni(100) and Co islands still visible on the Ni2C surface up to 300 °C. The higher thermal stability of Co above the Ni2C surface is rationalized by ab initio calculations, which also suggest the existence of a vacancy-assisted mechanism for Co dissolution in Ni(100). The methodology presented in this paper, combining systematically STM measurements with first-principles calculations and computational modelling, opens the way to controlled engineering of bimetallic surfaces with tailored properties.",
journal = "Nanoscale",
title = "Carbide coating on nickel to enhance the stability of supported metal nanoclusters",
volume = "14",
number = "9",
pages = "3589-3598",
doi = "10.1039/D1NR06485A"
}

Chesnyak, V., Stavrić, S., Panighel, M., Comelli, G., Peressi, M.,& Africh, C.. (2022). Carbide coating on nickel to enhance the stability of supported metal nanoclusters. in Nanoscale, 14(9), 3589-3598.
https://doi.org/10.1039/D1NR06485A

Chesnyak V, Stavrić S, Panighel M, Comelli G, Peressi M, Africh C. Carbide coating on nickel to enhance the stability of supported metal nanoclusters. in Nanoscale. 2022;14(9):3589-3598.
doi:10.1039/D1NR06485A .

Chesnyak, Valeria, Stavrić, Srđan, Panighel, Mirco, Comelli, Giovanni, Peressi, Maria, Africh, Cristina, "Carbide coating on nickel to enhance the stability of supported metal nanoclusters" in Nanoscale, 14, no. 9 (2022):3589-3598,
https://doi.org/10.1039/D1NR06485A . .

TY  - JOUR
AU  - Stavrić, Srđan
AU  - Chesnyak, Valeria
AU  - Panighel, Mirco
AU  - Comelli, Giovanni
AU  - Africh, Cristina
AU  - Peressi, Maria
PY  - 2022
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/10704
AB  - Transition metal atoms are commonly used in catalysis and photo-catalysis, but their potential reactivity reduces with aggregation and alloying. We investigate in particular whether Cobalt adatoms float on Ni surfaces or dissolve into the metal. Density functional theory calculations have been performed in order to evaluate the stability of different Cobalt adsorption configurations on Nickel surfaces, mainly at (100) terraces and steps, and the relevant energy barriers for diffusion on terraces and across steps, segregation and dissolution into the substrate. The simulations have been compared with variable temperature scanning tunneling microscopy and low energy electron diffraction. The results show that the Cobalt adatoms and small aggregates are unstable with respect to the formation of Co-Ni alloys, but the presence of a carbide monolayer on Ni surface improve their stability. © 2022 Societa Italiana di Fisica. All rights reserved.
T2  - Il Nuovo Cimento C
T1  - Cobalt on nickel surfaces and the role of carbide on its stability
VL  - 45
IS  - 6
DO  - 10.1393/ncc/i2022-22177-5
ER  - 

@article{
author = "Stavrić, Srđan and Chesnyak, Valeria and Panighel, Mirco and Comelli, Giovanni and Africh, Cristina and Peressi, Maria",
year = "2022",
abstract = "Transition metal atoms are commonly used in catalysis and photo-catalysis, but their potential reactivity reduces with aggregation and alloying. We investigate in particular whether Cobalt adatoms float on Ni surfaces or dissolve into the metal. Density functional theory calculations have been performed in order to evaluate the stability of different Cobalt adsorption configurations on Nickel surfaces, mainly at (100) terraces and steps, and the relevant energy barriers for diffusion on terraces and across steps, segregation and dissolution into the substrate. The simulations have been compared with variable temperature scanning tunneling microscopy and low energy electron diffraction. The results show that the Cobalt adatoms and small aggregates are unstable with respect to the formation of Co-Ni alloys, but the presence of a carbide monolayer on Ni surface improve their stability. © 2022 Societa Italiana di Fisica. All rights reserved.",
journal = "Il Nuovo Cimento C",
title = "Cobalt on nickel surfaces and the role of carbide on its stability",
volume = "45",
number = "6",
doi = "10.1393/ncc/i2022-22177-5"
}

Stavrić, S., Chesnyak, V., Panighel, M., Comelli, G., Africh, C.,& Peressi, M.. (2022). Cobalt on nickel surfaces and the role of carbide on its stability. in Il Nuovo Cimento C, 45(6).
https://doi.org/10.1393/ncc/i2022-22177-5

Stavrić S, Chesnyak V, Panighel M, Comelli G, Africh C, Peressi M. Cobalt on nickel surfaces and the role of carbide on its stability. in Il Nuovo Cimento C. 2022;45(6).
doi:10.1393/ncc/i2022-22177-5 .

Stavrić, Srđan, Chesnyak, Valeria, Panighel, Mirco, Comelli, Giovanni, Africh, Cristina, Peressi, Maria, "Cobalt on nickel surfaces and the role of carbide on its stability" in Il Nuovo Cimento C, 45, no. 6 (2022),
https://doi.org/10.1393/ncc/i2022-22177-5 . .

TY  - JOUR
AU  - Stavrić, Srđan
AU  - del Puppo, Simone
AU  - Šljivančanin, Željko
AU  - Peressi, Maria
PY  - 2021
UR  - https://vinar.vin.bg.ac.rs/handle/123456789/9561
AB  - Recent experiments indicate that the reactivity of metal surfaces changes profoundly when they are covered with two-dimensional (2D) materials. Nickel, the widespread catalyst choice for graphene (G) growth, exhibits complex surface restructuring even after the G sheet is fully grown. In particular, due to excess carbon segregation from bulk nickel to surface upon cooling, a nickel carbide (Ni2C) phase is detected under rotated graphene (RG) but not under epitaxial graphene (EG). Motivated by this experimental evidence, we construct different G/Ni(111) interface models accounting for the two types of G domains. Then, by applying density functional theory, we illuminate the microscopic mechanisms governing the structural changes of nickel surface induced by carbon segregation. A high concentration of subsurface carbon reduces the structural stability of Ni(111) surface and gives rise to the formation of thermodynamically advantageous Ni2C monolayer. We show the restructuring of the nickel surface under RG cover and reveal the essential role of G rotation in enabling high density of favorable C binding sites in the Ni(111) subsurface. As opposed to RG, the EG cover locks the majority of favorable C binding sites preventing the build-up of subsurface carbon density to a phase transition threshold. Therefore we confirm that the conversion of C-rich Ni surface to Ni2C takes place exclusively under RG cover, in line with the strong experimental evidence. © 2021 American Physical Society.
T2  - Physical Review Materials
T1  - First-principles study of nickel reactivity under two-dimensional cover: Ni2 C formation at rotated graphene/Ni(111) interface
VL  - 5
IS  - 1
SP  - 014003
DO  - 10.1103/PhysRevMaterials.5.014003
ER  - 

@article{
author = "Stavrić, Srđan and del Puppo, Simone and Šljivančanin, Željko and Peressi, Maria",
year = "2021",
abstract = "Recent experiments indicate that the reactivity of metal surfaces changes profoundly when they are covered with two-dimensional (2D) materials. Nickel, the widespread catalyst choice for graphene (G) growth, exhibits complex surface restructuring even after the G sheet is fully grown. In particular, due to excess carbon segregation from bulk nickel to surface upon cooling, a nickel carbide (Ni2C) phase is detected under rotated graphene (RG) but not under epitaxial graphene (EG). Motivated by this experimental evidence, we construct different G/Ni(111) interface models accounting for the two types of G domains. Then, by applying density functional theory, we illuminate the microscopic mechanisms governing the structural changes of nickel surface induced by carbon segregation. A high concentration of subsurface carbon reduces the structural stability of Ni(111) surface and gives rise to the formation of thermodynamically advantageous Ni2C monolayer. We show the restructuring of the nickel surface under RG cover and reveal the essential role of G rotation in enabling high density of favorable C binding sites in the Ni(111) subsurface. As opposed to RG, the EG cover locks the majority of favorable C binding sites preventing the build-up of subsurface carbon density to a phase transition threshold. Therefore we confirm that the conversion of C-rich Ni surface to Ni2C takes place exclusively under RG cover, in line with the strong experimental evidence. © 2021 American Physical Society.",
journal = "Physical Review Materials",
title = "First-principles study of nickel reactivity under two-dimensional cover: Ni2 C formation at rotated graphene/Ni(111) interface",
volume = "5",
number = "1",
pages = "014003",
doi = "10.1103/PhysRevMaterials.5.014003"
}

Stavrić, S., del Puppo, S., Šljivančanin, Ž.,& Peressi, M.. (2021). First-principles study of nickel reactivity under two-dimensional cover: Ni2 C formation at rotated graphene/Ni(111) interface. in Physical Review Materials, 5(1), 014003.
https://doi.org/10.1103/PhysRevMaterials.5.014003

Stavrić S, del Puppo S, Šljivančanin Ž, Peressi M. First-principles study of nickel reactivity under two-dimensional cover: Ni2 C formation at rotated graphene/Ni(111) interface. in Physical Review Materials. 2021;5(1):014003.
doi:10.1103/PhysRevMaterials.5.014003 .

Stavrić, Srđan, del Puppo, Simone, Šljivančanin, Željko, Peressi, Maria, "First-principles study of nickel reactivity under two-dimensional cover: Ni2 C formation at rotated graphene/Ni(111) interface" in Physical Review Materials, 5, no. 1 (2021):014003,
https://doi.org/10.1103/PhysRevMaterials.5.014003 . .