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Papers by naila jabeen

IOSR Journal Of Humanities And Social Science, 2013

Archives of Agronomy and Soil Science, 2015

Journal of the American Chemical Society, 2016

The atomistic understanding of the dissociation mechanisms for large molecules adsorbed on surfac... more The atomistic understanding of the dissociation mechanisms for large molecules adsorbed on surfaces is still a challenge in heterogeneous catalysis. This is especially true for polycyclic aromatic hydrocarbons, which represent an important class of organic compounds used to produce novel graphene-based architectures. Here, we show that coronene molecules adsorbed on Ir(111) undergo major conformational changes during dissociation. They first tilt upward with respect to the surface, still keeping their planar configuration, and subsequently experience a rotation, which changes the molecular axis orientation. Upon lifting, the internal C-C strain is initially relieved; as the dehydrogenation proceeds, the molecules experience a progressive increase in the average interatomic distance and gradually settle to form dome-shaped nanographene flakes. Our results provide important insight into the complex mechanism of molecular breakup, which could have implications in the synthesis of new carbon-based nanostructured materials.

Metal patterns were fabricated by metal liftoff photolithography. Positive photoresist was spin-c... more Metal patterns were fabricated by metal liftoff photolithography. Positive photoresist was spin-coated onto YSZ substrates at 2,000 to 3,000 rpm and baked at 115 °C for 150 s. The sample was then aligned with the glass plate mask using a Karl Suss MJB 3 contact aligner and exposed to UV

Catalysis Today, 2015

Please cite this article in press as: F. Bernardi, et al., Control of the surface atomic populati... more Please cite this article in press as: F. Bernardi, et al., Control of the surface atomic population of Rh 0.5 Pd 0.5 bimetallic nanoparticles supported on CeO 2 , Catal. Today (2015), http://dx.a b s t r a c t Rh 0.5 Pd 0.5 /CeO 2 bimetallic nanoparticles were subjected to reducing and oxidizing atmospheres at different temperatures and characterized by means of the Ambient Pressure X-Ray Photoelectron Spectroscopy (AP-XPS). The surface atomic population is calculated for all cases. By using a high temperature pretreatment at 480 • C in H 2 atmosphere, it was possible to control the surface atomic population with Pd atoms frozen at the skin layer even in an oxidizing atmosphere, which is not observed without high temperature pre-treatment (Rh atoms at the skin layer). The change of the Rh/Pd surface segregation behavior after the high temperature pre-treatment is attributed to the geometrical factor of Strong Metal Support Interaction (SMSI) effect, i.e., the occurrence of the ceria capping layer around nanoparticles.

Carbon, 2015

ABSTRACT Here we show that by using a combined experimental and theoretical approach it is possib... more ABSTRACT Here we show that by using a combined experimental and theoretical approach it is possible to separate the contributions to the interaction strength between epitaxial graphene and transition metal surfaces arising from the geometrical and chemical properties of the supporting surfaces. This has been achieved by performing photoelectron measurements and numerical simulations of the C1s core level spectral distribution for a large number of graphene–metal systems, which have been obtained by systematic intercalation of different metals (Co, Rh, Ir and Ru) at the graphene–Ir(1 1 1) and graphene–Ru(0 0 0 1) interfaces. We demonstrate that the chemical species of the substrate’s topmost layer plays a major role in determining the coupling between graphene and its substrate. Moreover, we show that both the experimental and the theoretical C1s spectral centres of mass are in linear relationship with the d-band centre of the transition metal substrate, which is considered a reliable descriptor of the graphene–substrate interaction strength. Our results provide a simple method to determine and tailor the properties of graphene–metal contacts.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2011

In this report, we briefly describe the general design principles and construction of a newly dev... more In this report, we briefly describe the general design principles and construction of a newly developed ambient pressure X-ray photoelectron spectroscopy system. This system provides an imaging mode with o 20 mm spatial resolution in one dimension as well as an angle-resolved mode. The new imaging mode enables us to study structured surfaces under catalytically and environmentally relevant conditions. To illustrate this capability, in situ studies on a Au-SiO 2 heterojunction and Rh-TiO 2 metal-support system are presented. This new system can probe structured surfaces near ambient pressure as a function of temperature, pressure, electrical potential, local position, and time. It is a valuable in situ tool to detect material transformations at the micrometer scale.

Journal of the American Chemical Society, 2013

Through the use of ambient pressure X-ray photoelectron spectroscopy (APXPS) and a single-sided s... more Through the use of ambient pressure X-ray photoelectron spectroscopy (APXPS) and a single-sided solid oxide electrochemical cell (SOC), we have studied the mechanism of electrocatalytic splitting of water (H2O + 2e(-) → H2 + O(2-)) and electro-oxidation of hydrogen (H2 + O(2-) → H2O + 2e(-)) at ∼700 °C in 0.5 Torr of H2/H2O on ceria (CeO2-x) electrodes. The experiments reveal a transient build-up of surface intermediates (OH(-) and Ce(3+)) and show the separation of charge at the gas-solid interface exclusively in the electrochemically active region of the SOC. During water electrolysis on ceria, the increase in surface potentials of the adsorbed OH(-) and incorporated O(2-) differ by 0.25 eV in the active regions. For hydrogen electro-oxidation on ceria, the surface concentrations of OH(-) and O(2-) shift significantly from their equilibrium values. These data suggest that the same charge transfer step (H2O + Ce(3+) <-> Ce(4+) + OH(-) + H(•)) is rate limiting in both the forward (water electrolysis) and reverse (H2 electro-oxidation) reactions. This separation of potentials reflects an induced surface dipole layer on the ceria surface and represents the effective electrochemical double layer at a gas-solid interface. The in situ XPS data and DFT calculations show that the chemical origin of the OH(-)/O(2-) potential separation resides in the reduced polarization of the Ce-OH bond due to the increase of Ce(3+) on the electrode surface. These results provide a graphical illustration of the electrochemically driven surface charge transfer processes under relevant and nonultrahigh vacuum conditions.

Current Applied Physics, 2012

We report Ambient pressure X-ray Photoelectron Spectroscopy Endstation with an integrated chemica... more We report Ambient pressure X-ray Photoelectron Spectroscopy Endstation with an integrated chemical analytical system that consists of a residual gas analyzer in the 2nd differential pumping stage and a new low-reactive sample holder heating assembly. This system has a linear response to the reaction chamber gas pressure. The sample heating assembly also has a low dark reaction rate up to 400 C for H 2 and CO oxidation. We expect this chemical analytical system will expand our capabilities in conducting inoperando catalysis research.

Chemistry of Materials, 2012

Substoichiometric tungsten oxide films of approximately 10 nm thickness deposited with pulsed las... more Substoichiometric tungsten oxide films of approximately 10 nm thickness deposited with pulsed laser ablation on single-crystal TiO 2 substrates with (001) and (110) orientation show defect states near the Fermi energy in the valence-band X-ray photoelectron spectroscopy (XPS) spectra. The spectral weight of the defect states is particularly strong for the film grown on the (001) surface. In situ XPS under an oxygen pressure of 100 mTorr shows that the spectral weight of the defect states decreases significantly at 500 K for the film on the (110) substrate, whereas that of the film grown on the (001) substrate remains the same at a temperature up to 673 K. Furthermore, diffusion of titanium from the substrate to the film surface is observed on the (110) substrate, as is evidenced by the sudden appearance of the Ti 2p core level signature above 623 K and below 673 K. The film grown on the (001) surface does not show such an interdiffusion effect, which suggests that the orientation of the substrate can have a significant influence on the high-temperature integrity of the tungsten oxide films. Quantitative analysis of the O 1s core level XPS spectra shows that chemisorbed water from sample storage under ambient conditions is desorbed during heating under oxygen exposure.

Chemistry of Materials, 2012

Metal patterns were fabricated by metal liftoff photolithography. Positive photoresist was spin-c... more Metal patterns were fabricated by metal liftoff photolithography. Positive photoresist was spin-coated onto YSZ substrates at 2,000 to 3,000 rpm and baked at 115 °C for 150 s. The sample was then aligned with the glass plate mask using a Karl Suss MJB 3 contact aligner and exposed to UV

IOSR Journal Of Humanities And Social Science, 2013

Archives of Agronomy and Soil Science, 2015

Journal of the American Chemical Society, 2016

The atomistic understanding of the dissociation mechanisms for large molecules adsorbed on surfac... more The atomistic understanding of the dissociation mechanisms for large molecules adsorbed on surfaces is still a challenge in heterogeneous catalysis. This is especially true for polycyclic aromatic hydrocarbons, which represent an important class of organic compounds used to produce novel graphene-based architectures. Here, we show that coronene molecules adsorbed on Ir(111) undergo major conformational changes during dissociation. They first tilt upward with respect to the surface, still keeping their planar configuration, and subsequently experience a rotation, which changes the molecular axis orientation. Upon lifting, the internal C-C strain is initially relieved; as the dehydrogenation proceeds, the molecules experience a progressive increase in the average interatomic distance and gradually settle to form dome-shaped nanographene flakes. Our results provide important insight into the complex mechanism of molecular breakup, which could have implications in the synthesis of new carbon-based nanostructured materials.

Metal patterns were fabricated by metal liftoff photolithography. Positive photoresist was spin-c... more Metal patterns were fabricated by metal liftoff photolithography. Positive photoresist was spin-coated onto YSZ substrates at 2,000 to 3,000 rpm and baked at 115 °C for 150 s. The sample was then aligned with the glass plate mask using a Karl Suss MJB 3 contact aligner and exposed to UV

Catalysis Today, 2015

Please cite this article in press as: F. Bernardi, et al., Control of the surface atomic populati... more Please cite this article in press as: F. Bernardi, et al., Control of the surface atomic population of Rh 0.5 Pd 0.5 bimetallic nanoparticles supported on CeO 2 , Catal. Today (2015), http://dx.a b s t r a c t Rh 0.5 Pd 0.5 /CeO 2 bimetallic nanoparticles were subjected to reducing and oxidizing atmospheres at different temperatures and characterized by means of the Ambient Pressure X-Ray Photoelectron Spectroscopy (AP-XPS). The surface atomic population is calculated for all cases. By using a high temperature pretreatment at 480 • C in H 2 atmosphere, it was possible to control the surface atomic population with Pd atoms frozen at the skin layer even in an oxidizing atmosphere, which is not observed without high temperature pre-treatment (Rh atoms at the skin layer). The change of the Rh/Pd surface segregation behavior after the high temperature pre-treatment is attributed to the geometrical factor of Strong Metal Support Interaction (SMSI) effect, i.e., the occurrence of the ceria capping layer around nanoparticles.

Carbon, 2015

ABSTRACT Here we show that by using a combined experimental and theoretical approach it is possib... more ABSTRACT Here we show that by using a combined experimental and theoretical approach it is possible to separate the contributions to the interaction strength between epitaxial graphene and transition metal surfaces arising from the geometrical and chemical properties of the supporting surfaces. This has been achieved by performing photoelectron measurements and numerical simulations of the C1s core level spectral distribution for a large number of graphene–metal systems, which have been obtained by systematic intercalation of different metals (Co, Rh, Ir and Ru) at the graphene–Ir(1 1 1) and graphene–Ru(0 0 0 1) interfaces. We demonstrate that the chemical species of the substrate’s topmost layer plays a major role in determining the coupling between graphene and its substrate. Moreover, we show that both the experimental and the theoretical C1s spectral centres of mass are in linear relationship with the d-band centre of the transition metal substrate, which is considered a reliable descriptor of the graphene–substrate interaction strength. Our results provide a simple method to determine and tailor the properties of graphene–metal contacts.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2011

In this report, we briefly describe the general design principles and construction of a newly dev... more In this report, we briefly describe the general design principles and construction of a newly developed ambient pressure X-ray photoelectron spectroscopy system. This system provides an imaging mode with o 20 mm spatial resolution in one dimension as well as an angle-resolved mode. The new imaging mode enables us to study structured surfaces under catalytically and environmentally relevant conditions. To illustrate this capability, in situ studies on a Au-SiO 2 heterojunction and Rh-TiO 2 metal-support system are presented. This new system can probe structured surfaces near ambient pressure as a function of temperature, pressure, electrical potential, local position, and time. It is a valuable in situ tool to detect material transformations at the micrometer scale.

Journal of the American Chemical Society, 2013

Through the use of ambient pressure X-ray photoelectron spectroscopy (APXPS) and a single-sided s... more Through the use of ambient pressure X-ray photoelectron spectroscopy (APXPS) and a single-sided solid oxide electrochemical cell (SOC), we have studied the mechanism of electrocatalytic splitting of water (H2O + 2e(-) → H2 + O(2-)) and electro-oxidation of hydrogen (H2 + O(2-) → H2O + 2e(-)) at ∼700 °C in 0.5 Torr of H2/H2O on ceria (CeO2-x) electrodes. The experiments reveal a transient build-up of surface intermediates (OH(-) and Ce(3+)) and show the separation of charge at the gas-solid interface exclusively in the electrochemically active region of the SOC. During water electrolysis on ceria, the increase in surface potentials of the adsorbed OH(-) and incorporated O(2-) differ by 0.25 eV in the active regions. For hydrogen electro-oxidation on ceria, the surface concentrations of OH(-) and O(2-) shift significantly from their equilibrium values. These data suggest that the same charge transfer step (H2O + Ce(3+) <-> Ce(4+) + OH(-) + H(•)) is rate limiting in both the forward (water electrolysis) and reverse (H2 electro-oxidation) reactions. This separation of potentials reflects an induced surface dipole layer on the ceria surface and represents the effective electrochemical double layer at a gas-solid interface. The in situ XPS data and DFT calculations show that the chemical origin of the OH(-)/O(2-) potential separation resides in the reduced polarization of the Ce-OH bond due to the increase of Ce(3+) on the electrode surface. These results provide a graphical illustration of the electrochemically driven surface charge transfer processes under relevant and nonultrahigh vacuum conditions.

Current Applied Physics, 2012

We report Ambient pressure X-ray Photoelectron Spectroscopy Endstation with an integrated chemica... more We report Ambient pressure X-ray Photoelectron Spectroscopy Endstation with an integrated chemical analytical system that consists of a residual gas analyzer in the 2nd differential pumping stage and a new low-reactive sample holder heating assembly. This system has a linear response to the reaction chamber gas pressure. The sample heating assembly also has a low dark reaction rate up to 400 C for H 2 and CO oxidation. We expect this chemical analytical system will expand our capabilities in conducting inoperando catalysis research.

Chemistry of Materials, 2012

Substoichiometric tungsten oxide films of approximately 10 nm thickness deposited with pulsed las... more Substoichiometric tungsten oxide films of approximately 10 nm thickness deposited with pulsed laser ablation on single-crystal TiO 2 substrates with (001) and (110) orientation show defect states near the Fermi energy in the valence-band X-ray photoelectron spectroscopy (XPS) spectra. The spectral weight of the defect states is particularly strong for the film grown on the (001) surface. In situ XPS under an oxygen pressure of 100 mTorr shows that the spectral weight of the defect states decreases significantly at 500 K for the film on the (110) substrate, whereas that of the film grown on the (001) substrate remains the same at a temperature up to 673 K. Furthermore, diffusion of titanium from the substrate to the film surface is observed on the (110) substrate, as is evidenced by the sudden appearance of the Ti 2p core level signature above 623 K and below 673 K. The film grown on the (001) surface does not show such an interdiffusion effect, which suggests that the orientation of the substrate can have a significant influence on the high-temperature integrity of the tungsten oxide films. Quantitative analysis of the O 1s core level XPS spectra shows that chemisorbed water from sample storage under ambient conditions is desorbed during heating under oxygen exposure.

Chemistry of Materials, 2012

Metal patterns were fabricated by metal liftoff photolithography. Positive photoresist was spin-c... more Metal patterns were fabricated by metal liftoff photolithography. Positive photoresist was spin-coated onto YSZ substrates at 2,000 to 3,000 rpm and baked at 115 °C for 150 s. The sample was then aligned with the glass plate mask using a Karl Suss MJB 3 contact aligner and exposed to UV