| 1. |
- Chaudhary, Shilpi, et al.
(författare)
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Adsorption of 3-(triethoxysilyl)propionitrile on a rutile TiO2(110) surface : An X-ray photoelectron spectroscopy study
- 2020
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Ingår i: DAE Solid State Physics Symposium 2019. - : AIP Publishing. - 1551-7616 .- 0094-243X. - 9780735420250 ; 2265
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Konferensbidrag (refereegranskat)abstract
- The adsorption of 3-(triethoxysilyl)propionitrile (TESP) on a reduced rutile TiO2(110) surface has been investigated using synchrotron-based X-ray photoelectron spectroscopy in ultrahigh vacuum (UHV). We have studied TESP adsorption on two surface preparation of rutile TiO2 (110) to explore the role of surface defects. In the first preparation, the adsorption of TESP was studied on reduced TiO2 (110) surface at room temperature. In the second experiment TESP was adsorbed on the oxygen-treated TiO2 surface to quench the oxygen vacancies generated by UHVannealing of the TiO2 crystal. The molecular footprints of the TESP molecules confirms the adsorption on both types of TiO2(110) surfaces. In the case of the reduced surface, temperature-dependent XPS measurements show the thermal stability of TESP molecules up to 600 °C. The comparison of the nitrogen and carbon lineshapes for both preparations suggests different adsorption geometries on the reduced and oxygen-dosed surfaces. To the best of our knowledge, the UHV preparations and measurements of TESP adsorption on rutile TiO2 (110) in the present study are reported for the first time.
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| 2. |
- Chaudhary, Shilpi, et al.
(författare)
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Controlled short-linkage assembly of functional nano-objects
- 2014
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Ingår i: Applied Surface Science. - : Elsevier BV. - 1873-5584 .- 0169-4332. ; 300, s. 22-28
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we report a method that allows the deterministic, photo-controlled covalent assembly of nanoparticles directly on surface. As a model system, we study the conjugation of molecularly imprinted polymer (MIP) nanoparticles on a glass surface and confirm that the immobilized nanoparticles maintain their molecular recognition functionality. The glass slide was first modified with perfluorophenylazide and then used to bind MIP nanoparticles under UV irradiation. After each step the surface was analyzed by water contact angle measurement, fluorescence microscopy, scanning electron microscopy, and/or synchrotron-based X-ray photoelectron spectroscopy. The MIP nanoparticles immobilized on the glass surface remained stable and maintained specific binding for the template molecule, propranolol. The method developed in this work allows MIP nanoparticles to be directly coupled to a flat surface, offering a straightforward means to construct robust chemical sensors. Using the reported photo conjugation method, it is possible to generate patterned assembly of nanoparticles using a photomask. Since perfluorophenylazide-based photochemistry works with all kinds of organic material, the method developed in this work is expected to enable immobilization of not only MIPs but also other kinds of organic and inorganic-organic core-shell particles for various applications involving photon or electron transfer. (C) 2014 The Authors. Published by Elsevier B.V. All rights reserved.
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| 3. |
- Chaudhary, Shilpi
(författare)
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Modification of Oxide Surfaces with Functional Organic Molecules, Nanoparticles, and Hetero-Oxide Layers
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The research work described in this thesis is concerned with the modification of oxide surfaces, as reflected by its title. The surfaces and their modification have been studied using a range of experimental surface characterization tools, in particular x-ray photoelectron spectroscopy (XPS), fluorescence microscopy, scanning electron microscopy, atomic force microscopy, and scanning tunneling microscopy. A large part of the thesis is related to the modification of oxide or metal surfaces with nanoparticles. In particular, three different immobilization schemes for the coupling of molecularly imprinted polymer (MIP) nanoparticles to silicon oxide (SiO2) and gold surfaces were designed and characterized at every step. The first method reports the immobilization of MIPs using a photo-coupling agent in combination with an aminosilane compound. The second method explores an epoxysilane-based coupling agent to directly anchor the nucleophilic core-shell MIP nanoparticle to the surface. Both methods were proven to be non-destructive towards the specific binding sites of the MIP nanoparticles. The third scheme offers the immobilization of nucleophilic core-shell nanoparticles on model gold surfaces using self-assembled monolayers of 11-mercaptoundecanoic acid activated by carbodiimide/N-hydroxysuccinimide. All three coupling methods are quite versatile and can be used in biosensors to couple functional nano-objects with transducer surfaces. In addition to these investigation directly aimed at the immobilization of nanopartciles, more fundamentally oriented studies were carried out on the modification of the rutile TiO2(110) surface with silane molecules to obtain a detailed understanding of adsorption mechanism and geometry of these silanes. The deposition of a different type of nanopartciles, block copolymer reverse micelles loaded gold nanoparticles, on a titanium dioxide surface was tested using electrospray deposition. The study demonstrates that electrospray deposition is a viable method for depositing metal single-size metal nanoparticles onto a surface in vacuum, thereby retaining the clean vacuum conditions. Furthermore, it was shown that the removal of the block copolymer shell after deposition can be achieved both by atomic oxygen and an oxygen plasma, with the atomic oxygen being somewhat more efficient. Overall, it was demonstrated that a TiO2 surface decorated with narrow sized gold nanoparticles could be created, a result of importance in the catalysis domain. The last part of the thesis is concerned with the true in-situ investigation of growth of hetero-oxide layers on oxide surfaces from metal precursors. Tetraethyl orthosilicate (TEOS) was used as precursor for the chemical vapor deposition of silicon oxide on rutile TiO2(110). The growth was monitored in real time using ambient pressure XPS (APXPS), which revealed the dissociative adsorption with the formation of new species in the presence of a TEOS gas phase reservoir. Annealing results in the formation of SiO2 and of a mixed titanium/silicon oxide. Furthermore, tetrakis(dimethylamino)titanium was employed in the atomic layer deposition (ALD) of TiO2 on RuO2. The APXPS results showed evidence was for side reactions beyond the idealized scheme of ALD.
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| 4. |
- Chaudhary, Shilpi, et al.
(författare)
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Real-Time Study of CVD Growth of Silicon Oxide on Rutile TiO2(110) Using Tetraethyl Orthosilicate
- 2015
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:33, s. 19149-19161
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Tidskriftsartikel (refereegranskat)abstract
- The interaction of the ruffle TiO2(110) surface with tetraethyl orthosilicate (TEOS) in the pressure range from UHV to 1 mbar as well as the TEOS-based chemical vapor deposition of SiO2 on the TiO2(110) surface were monitored in real time using near-ambient pressure X-ray photoelectron spectroscopy. The experimental data and density functional theory calculations confirm the dissociative adsorption of TEOS on the surface already at room temperature. At elevated pressure, the ethoxy species formed in the adsorption process undergoes further surface reactions toward a carboxyl species not observed in the absence of a TEOS gas phase reservoir. Annealing of the adsorption layer leads to the formation of SiO2, and an intermediate oxygen species assigned to a mixed titanium/silicon oxide is identified. Atomic force microscopy confirms the morphological changes after silicon oxide formation.
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| 5. |
- Chaudhary, Shilpi, et al.
(författare)
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X-ray photoelectron spectroscopy study of adsorption of (3-mercaptopropyl)trimethoxysilane and n-propyltriethoxysilane on a rutile TiO2(110) surface
- 2015
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Ingår i: Advanced Materials Letters. - 0976-3961. ; 6:4, s. 279-283
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the adsorption of two silane compounds, (3-mercaptopropyl) trimethoxysilane (MPTMS) and n-propyltriethoxysilane (PTES), on a rutile TiO2(110) surface using angle dependent X-ray photoelectron spectroscopy. The observation of the S 2p line, in the case of MPTMS, and the C 1s line for both MPTMS and PTES confirms the adsorption of the molecules. For a dose of 122 Langmuirs of MPTMS we find room temperature coverage of 0.55 monolayers, while for a 60 Langmuir dose of PTES the coverage is found to be 0.89 monolayers. Thus, MPTMS has a considerably lower sticking coefficient on the rutile TiO2(110) surface than PTES. Both PTES and MPTES are found to bind dissociatively to the surface. An analysis of angle dependent data further suggests that for MPTMS the thiol group and thus alkyl chain points away from the surface, while for a 0.5 monolayer coverage of PTES the alkyl chain is oriented towards the surface. A higher coverage, ~1 monolayer, the behavior seems to be reversed for at least a fraction of all molecules. Temperature programed XPS measurements suggest that the oxy groups of both molecules desorb from the surface at 550 K, which is in accordance with literature. The present study thus provides information on how these silane coupling agents bind to titanium oxide and what their molecular orientation is on the surface.
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| 6. |
- Head, Ashley, et al.
(författare)
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Near Ambient Pressure X-ray Photoelectron Spectroscopy Study of the Atomic Layer Deposition of TiO2 on RuO2(110)
- 2016
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:1, s. 243-251
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Tidskriftsartikel (refereegranskat)abstract
- The atomic layer deposition (ALD) of TiO2 on a RuO2(110) surface from tetrakis(dimethylamido) titanium and water at 110 degrees C was investigated using near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) at precursor pressures up to 0.1 mbar. In addition to the expected cyclic surface species, evidence for side reactions was found. Dimethylamine adsorbs on the surface during the TDMAT half-cycle, and a second species, likely methyl methylenimine, also forms. The removal of the amide ligand and the formation of an alkyammonium species during the water half-cycle were found to be pressure dependent. The O 1s, Ru 3d, and Ti 2p spectra show the formation of the Ru-O-Ti interface, and the binding energies are consistent with formation of TiO2 after one full ALD cycle. Dosing TDMAT on the RuO2(110) surface at room temperature promotes a multilayer formation that begins to desorb at 40 degrees C. The imine species is not seen until 60 degrees C. These insights into the ALD mechanism and precursor pressure dependence on reactivity highlight the utility of NAP-XPS in studying ALD processes and interface formation.
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| 7. |
- Head, Ashley R., et al.
(författare)
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In situ characterization of the deposition of anatase TiO2 on rutile TiO2(110)
- 2018
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Ingår i: Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 36:2
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Tidskriftsartikel (refereegranskat)abstract
- Growing additional TiO2 thin films on TiO2 supstrates in ultrahigh vacuum (UHV)-compatible chambers have many applications for sample preparation, such as smoothing surface morphologies, templating, and covering impurities. However, there has been little study into how to control the morphology of TiO2 films deposited onto TiO2 supstrates, especially using atomic layer deposition (ALD) precursors. Here, the authors show the growth of a TiO2 film on a rutile TiO2(110) surface using titanium tetraisopropoxide (TTIP) and water as the precursors at pressures well below those used in common ALD reactors. X-ray absorption spectroscopy suggests that the relatively low sample temperature (175 °C) results in an anatase film despite the rutile template of the supstrate. Using ambient pressure x-ray photoelectron spectroscopy, the adsorption of TTIP was found to be self-limiting, even at room temperature. No molecular water was found to adsorb on the surface. The deposited thickness suggests that an alternate chemical vapor deposition growth mechanism may be dominating the growth process. This study highlights the possibility that metal oxide film deposition from molecular precursors is an option for sample preparations in common UHV-compatible chambers.
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| 8. |
- Huang, Chuixiu, et al.
(författare)
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Breath Figure Patterns Made Easy
- 2014
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 6:8, s. 5971-5976
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Tidskriftsartikel (refereegranskat)abstract
- In this work, a simple breath figure method was proposed to directly fabricate large-area and ordered honeycomb structures on commercial PMMA substrates or PS Petri dishes without the use of an external polymer solution. The obtained honeycomb structure is indeed part of the substrate, providing the honeycomb layer with enough mechanical stability. The breath figure method in this work for the synthesis of honeycomb structure is extremely simple with scale-up capability to large-area production, which offers new insights into surface engineering with great potential in commercial technologies. For example, using the honeycomb-patterned Petri dishes prepared via this method, cells can be easily separated into divided aggregation, which favors understanding of naturally occurring networks in higher organisms and cell cell and cell matrix interactions, and the therapeutic control of genetic circuits.
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| 9. |
- Johansson, Niclas, et al.
(författare)
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Sonogashira cross-coupling over Au(1 1 1): from UHV to ambient pressure
- 2017
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Ingår i: Journal of Physics: Condensed Matter. - 1361-648X. ; 29:44
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the reaction of phenylacetylene (PA) with chloro-, bromo-, and iodobenzene on the Au(1 1 1) surface as a model system for the gold-catalysed Sonogashira cross-coupling. Both ultrahigh vacuum-based and ambient pressure x-ray photoelectron spectroscopy show that iodo- and chlorobenzene (IB and CB) undergo the cross-coupling reaction towards diphenylacetylene. Bromobenzene (BB), in contrast, does not react in the UHV experiments. Further, at ambient pressure signs are found for poisoning of the Au(1 1 1) surface by a carbon species formed in the reaction. The understanding obtained in the reaction experiments are based on a thorough investigation of the adsorption of PA, IB, CB, and BB on the Au(1 1 1) surface by soft x-ray absorption spectroscopy and temperature-dependent x-ray photoelectron spectroscopy. In particular, the experiments provide the orientation of the intact adsorbates with respect to the surfaces at liquid nitrogen temperature. Dissociation in the temperature regime between −80 and −15 °C is observed for iodo- and chlorobenzene, but not for BB, in agreement with that only IB and CB, but not BB, react with PA to form diphenylacetylene. The difference is tentatively attributed to a difference in surface orientation of the different halobenzenes.
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| 10. |
- Kamra, Tripta, et al.
(författare)
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Covalent immobilization of molecularly imprinted polymer nanoparticles on a gold surface using carbodiimide coupling for chemical sensing.
- 2016
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 461, s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- One challenging task in building (bio)chemical sensors is the efficient and stable immobilization of receptor on a suitable transducer. Herein, we report a method for covalent immobilization of molecularly imprinted core-shell nanoparticles for construction of robust chemical sensors. The imprinted nanoparticles with a core-shell structure have selective molecular binding sites in the core and multiple amino groups in the shell. The model Au transducer surface is first functionalized with a self-assembled monolayer of 11-mercaptoundecanoic acid. The 11-mercaptoundecanoic acid is activated by treatment with carbodiimide/N-hydroxysuccinimide and then reacted with the core-shell nanoparticles to form amide bonds. We have characterized the process by studying the treated surfaces after each preparation step using atomic force microscopy, scanning electron microscopy, fluorescence microscopy, contact angle measurements and X-ray photoelectron spectroscopy. The microscopy results show the successful immobilization of the imprinted nanoparticles on the surface. The photoelectron spectroscopy results further confirm the success of each functionalization step. Further, the amino groups on the MIP surface were activated by electrostatically adsorbing negatively charged Au colloids. The functionalized surface was shown to be active for surface enhanced Raman scattering detection of propranolol. The particle immobilization and surface enhanced Raman scattering approach described here has a general applicability for constructing chemical sensors in different formats.
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