| 1. |
- Ali, Amjad, et al.
(författare)
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A potential electrolyte (Ce1-x CaxO2-delta) for fuel cells:Theoretical andexperimental study
- 2018
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Ingår i: Ceramics International. - : ELSEVIER SCI LTD. - 0272-8842 .- 1873-3956. ; 44:11, s. 12676-12683
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Tidskriftsartikel (refereegranskat)abstract
- First-principles calculations are performed using density function theory to explore the effects of dopant Ca in ceria (Ce1-x CaxO2-delta). The impact of oxygen vacancy on band gap and density of states is examined in doped ceria using generalized gradient approximations. Vacancy association and vacancy formation energies of the doped ceria are calculated to reveal the effect of dopant on ion conduction. The experimental study of the sample Ce0.875Ca0.125O2-delta) was performed to compare with the theoretical results. The obtained results from theoretical calculation and experimental techniques show that oxygen vacancy increases the volume, lattice constant (5.47315 angstrom) but decrease the band gap (1.72 eV) and bulk modulus. The dopant radius (1.173 angstrom) and lattice constant (5.4718 angstrom) are also calculated by equations which is close to the DFT lattice parameter. The result shows that oxygen vacancy shifts the density of states to lower energy region. Band gap is decreased due to shifting of valence states to conduction band. Vacancy formation shows a significance increase in density of states near the Fermi level. Density of states at Fermi level is proportional to the conductivity, so an increase in density of states near the Fermi level increases the conductivity. The experimental measured ionic conductivity is found to 0.095 S cm(-1) at 600 degrees C. The microstructural studies is also reported in this work.
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| 2. |
- Fischer, Andreas C., et al.
(författare)
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Layer-by-layer 3D printing of Si micro- and nanostructures by Si deposition, ion implantation and selective Si etching
- 2012
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Ingår i: 12th IEEE Conference on Nanotechnology (IEEE-NANO), 2012. - : IEEE conference proceedings. - 9781467321983 ; , s. 1-4
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Konferensbidrag (refereegranskat)abstract
- In this paper we report a method for layer-by-layer printing of three-dimensional (3D) silicon (Si) micro- and nanostructures. This fabrication method is based on a sequence of alternating steps of chemical vapor deposition of Si and local implantation of gallium (Ga+) ions by focused ion beam (FIB) writing. The defined 3D structures are formed in a final step by selectively wet etching the non-implanted Si in potassium hydroxide (KOH). We demonstrate the viability of the method by fabricating 2 and 3-layer 3D Si structures, including suspended beams and patterned lines with dimensions on the nm-scale.
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| 3. |
- Fraerman, A. A., et al.
(författare)
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Magnetic force microscopy to determine vorticity direction in elliptical Co nanoparticles
- 2004
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Ingår i: Physics of low-Dimensional structures. - 0204-3467. ; 1-2, s. 35-40
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Tidskriftsartikel (refereegranskat)abstract
- We present a magnetic force microscopy investigation into the magnetic properties of arrays of Co nanoparticles fabricated by electron be am lithography. Vorticity directions are determined in zero applied magnetic fields. Experimental dependence of height on stable magnetic states of the particles is investigated. The statistics of the vorticity direction distribution is discussed.
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| 4. |
- Gupta, A., et al.
(författare)
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Synthetic magnetic opals
- 2002
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Ingår i: Pramana (Bangalore). - : Springer Science and Business Media LLC. - 0304-4289 .- 0973-7111. ; 58:06-maj, s. 1051-1059
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Tidskriftsartikel (refereegranskat)abstract
- We present studies of novel nanocomposites of BiNi impregnated into the structure of opals as well as inverse opals. Atomic force microscopy and high resolution elemental analyses show a highly ordered structure and uniform distribution of the BiNi filler in the matrix. These BiNi-based nanocomposites are found to exhibit distinct ferromagnetic-like ordering with transition temperature of about 675 K. As far as we know there exists no report in literature on any BiNi compound which is magnetic.
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| 5. |
- Riazanova, Anastasia, et al.
(författare)
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Gas-assisted electron-beam-induced nanopatterning of high-quality Si-based insulator
- 2014
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 25:15, s. 155301-
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Tidskriftsartikel (refereegranskat)abstract
- An oxygen-assisted electron-beam-induced deposition (EBID) process, in which an oxygen flow and the vapor phase of the precursor, tetraethyl orthosilicate (TEOS), are both mixed and delivered through a single needle, is described. The optical properties of the SiO(2+delta) (-0.04 <= delta <= +0.28) are comparable to fused silica. The electrical resistivity of both single-needle and double-needle SiO(2+delta) are comparable (greater than 7 G Omega cm) and a measured breakdown field is greater than 400 V mu m(-1). Compared to the double-needle process the advantage of the single-needle technique is the ease of alignment and the proximity to the deposition location, which facilitates fabrication of complex 3D structures for nanophotonics, photovoltaics, micro- and nano-electronics applications.
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| 6. |
- Riazanova, Anastasia, et al.
(författare)
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Pattern Shape Control for Heat Treatment Purification of Electron-Beam-Induced Deposition of Gold from the Me2Au(acac) Precursor
- 2012
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 28:14, s. 6185-6191
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Tidskriftsartikel (refereegranskat)abstract
- Gold structures can be created in a scanning electron microscope (SEM) from the Me2Au(acac) precursor by direct writing with the electron beam. The as-deposited purity is usually poor, and a common purification approach is a post-annealing step that indeed is effective but also induces a volume reduction because of carbon loss and an undesirable reconfiguration of the gold structure, resulting in the loss of the original shape. We studied the shape change as a result of such purification, and to minimize this effect, the application of a tantalum and chromium buffer layer was investigated. These buffer materials are well-known for their good adhesion properties. We confirm by dedicated SEM, atomic force microscopy (AFM), and transmission electron microscopy (TEM) analysis that, for the creation of a uniform Au structure, tantalum is a better buffer layer material than chromium. Post-annealing of the Au electron-beam-induced deposition (EBID) patterns for 1 h at 600 degrees C in air resulted in a dramatic purity increase (from 8-12 atomic % Au to above 92 atomic % Au). The uncovered part of the tantalum layer can be easily etched away, resulting in a well-defined, high-purity, gold structure.
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| 7. |
- Bagchi, Sonchita, et al.
(författare)
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Intermediate filament-like proteins in bacteria and a cytoskeletal function in Streptomyces
- 2008
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Ingår i: Molecular Microbiology. - : Wiley. - 0950-382X .- 1365-2958. ; 70:4, s. 1037-1050
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Tidskriftsartikel (refereegranskat)abstract
- Actin and tubulin cytoskeletons are conserved and widespread in bacteria. A strikingly intermediate filament (IF)-like cytoskeleton, composed of crescentin, is also present in Caulobacter crescentus and determines its specific cell shape. However, the broader significance of this finding remained obscure, because crescentin appeared to be unique to Caulobacter. Here we demonstrate that IF-like function is probably a more widespread phenomenon in bacteria. First, we show that 21 genomes of 26 phylogenetically diverse species encoded uncharacterized proteins with a central segmented coiled coil rod domain, which we regarded as a key structural feature of IF proteins and crescentin. Experimental studies of three in silico predicted candidates from Mycobacterium and other actinomycetes revealed a common IF-like property to spontaneously assemble into filaments in vitro. Furthermore, the IF-like protein FilP formed cytoskeletal structures in the model actinomycete Streptomyces coelicolor and was needed for normal growth and morphogenesis. Atomic force microscopy of living cells revealed that the FilP cytoskeleton contributed to mechanical fitness of the hyphae, thus closely resembling the function of metazoan IF. Together, the bioinformatic and experimental data suggest that an IF-like protein architecture is a versatile design that is generally present in bacteria and utilized to perform diverse cytoskeletal tasks.
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| 8. |
- Banuazizi, Seyed Amir Hossein, et al.
(författare)
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Magnetic force microscopy of an operational nanodevice
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We present a new method for probing the spatial profile of an operational magnetic nanodevice using magnetic force microscopy (MFM). We have developed an MFM system by adding a microwave probe station equipped with microwave probe, bias-T, and amplifier to allow electrical and microwave characterization up to 40 GHz during the MFM process. The nanoscale spintronic devices---spin Hall nano-oscillators (SHNOs) based on Pt/NiFe bilayers with a specific design compatible with the developed system---were fabricated and scanned using a Co magnetic force microscopy tip with 10 nm spatial resolution, while a DC current sufficient to exert auto-oscillation flowed. Our results show that this method of developed provides a promising path for the characterization of the spatial profiles of operational nano-oscillators.
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| 9. |
- Belova, Lyubov M., et al.
(författare)
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Rapid electron beam assisted patterning of pure cobalt at elevated temperatures via seeded growth
- 2011
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 22:14, s. 145305-
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Tidskriftsartikel (refereegranskat)abstract
- A new method of direct, rapid nano- to micro-scale patterning of high purity cobalt is presented. The method utilizes a combination of electron beam induced deposition (EBID) and seeded growth at elevated temperatures below the temperature of spontaneous thermal decomposition. Dicobalt octacarbonyl Co-2(CO)(8) is used as the precursor and carbon as a seed layer. Seeded deposition is carried out in the substrate temperature range from 55 to 75 degrees C. Deposition yield is significantly higher than conventional EBID and magnetotransport measurements indicate that resistivity, 22 mu Omega cm, and saturation magnetization, 1.55 T, are much closer to the corresponding values for bulk Co than those for standard EBID.
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| 10. |
- Bhatt, Pramod, et al.
(författare)
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Ferromagnetism above room temperature in nickel-tetracyanoethylene thin films
- 2009
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Ingår i: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 0959-9428 .- 1364-5501. ; 19:36, s. 6610-6615
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Tidskriftsartikel (refereegranskat)abstract
- Room temperature ferromagnetic ordering is reported in Ni-tetracyanoethylene (TCNE) thin films fabricated on Au substrates using physical vapor deposition (PVD) under ultra high vacuum conditions. This technique enables the preparation of very clean films without having any kind of contamination from oxygen-containing species, solvents or precursor molecules. Film stoichiometry was obtained from X-ray photoelectron spectroscopy (XPS) measurements. XPS derived stoichiometry points to a similar to 1 : 2 ratio between Ni and TCNE resulting in Ni(TCNE)(x), x approximate to 2. No evidence of pure Ni metal in the in situ grown films was present in the XPS or the ultraviolet photoelectron spectroscopy (UPS) measurements within the detection limits of the techniques.
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| 11. |
- Costanzi, Barry N., et al.
(författare)
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In situ manufacture of magnetic tunnel junctions by a direct-write process
- 2014
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 104:22, s. 222401-
-
Tidskriftsartikel (refereegranskat)abstract
- In situ construction of Co/SiO2/Co magnetic tunnel junctions using direct-write electron-beam-induced deposition is described. Proof-of-concept devices were built layer by layer depositing the specific components one at a time, allowing device manufacture using a strictly additive process. The devices exhibit a magnetic tunneling signature which agrees qualitatively with the Slonczewski model of magnetic tunneling.
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| 12. |
- Fischer, Andreas C., 1982-, et al.
(författare)
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3D Free-Form Patterning of Silicon by Ion Implantation, Silicon Deposition, and Selective Silicon Etching
- 2012
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Ingår i: Advanced Functional Materials. - : Wiley-VCH Verlagsgesellschaft. - 1616-301X .- 1616-3028. ; 22:19, s. 4004-4008
-
Tidskriftsartikel (refereegranskat)abstract
- A method for additive layer-by-layer fabrication of arbitrarily shaped 3D silicon micro- and nanostructures is reported. The fabrication is based on alternating steps of chemical vapor deposition of silicon and local implantation of gallium ions by focused ion beam (FIB) writing. In a final step, the defined 3D structures are formed by etching the silicon in potassium hydroxide (KOH), in which the local ion implantation provides the etching selectivity. The method is demonstrated by fabricating 3D structures made of two and three silicon layers, including suspended beams that are 40 nm thick, 500 nm wide, and 4 μm long, and patterned lines that are 33 nm wide.
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| 13. |
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| 14. |
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| 15. |
- Guo, Feng, et al.
(författare)
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Nonlinear ferromagnetic resonance shift in submicron Permalloy ellipses
- 2015
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 91:6
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Tidskriftsartikel (refereegranskat)abstract
- We report a systematic study of nonlinearity in the ferromagnetic resonance of a series of submicron Permalloy ellipses with varying aspect ratios. At high excitation powers, the resonances are found to shift to higher or lower applied field. We focus here on the sign of the shift and its dependence on the applied field and shape-induced anisotropy of the ellipses. Using ferromagnetic resonance force microscopy, we find that the measured nonlinear coefficient changes sign as a function of anisotropy field and applied field in qualitative agreement with a macrospin analysis. This macrospin analysis also points to origins of the nonlinearity in a combination of hard-axis in-plane anisotropy and precession ellipticity. In comparison of the macrospin predictions with both experimental and micromagnetic modeling results, we measure/model values of the nonlinear coefficient that are more positive than predicted by the macrospin model. The results are useful in understanding nonlinear physics in nanomagnets and applications of spin-torque oscillators.
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| 16. |
- Gylfason, Kristinn B., 1978-, et al.
(författare)
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Process considerations for layer-by-layer 3D patterning of silicon, using ion implantation, silicon deposition, and selective silicon etching
- 2012
-
Ingår i: Journal of Vacuum Science & Technology B. - : American Vacuum Society. - 1071-1023 .- 1520-8567. ; 30:6, s. 06FF05-
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Tidskriftsartikel (refereegranskat)abstract
- The authors study suitable process parameters, and the resulting pattern formation, in additive layer-by-layer fabrication of arbitrarily shaped three-dimensional (3D) silicon (Si) micro- and nanostructures. The layer-by-layer fabrication process investigated is based on alternating steps of chemical vapor deposition of Si and local implantation of gallium ions by focused ion beam writing. In a final step, the defined 3D structures are formed by etching the Si in potassium hydroxide, where the ion implantation provides the etching selectivity.
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| 17. |
- Hodgkins, Robert P., et al.
(författare)
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Maghemite nanocrystal impregnation by hydrophobic surface modification of mesoporous silica
- 2007
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 23:17, s. 8838-8844
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Tidskriftsartikel (refereegranskat)abstract
- Here, we report the design of a hybrid inorganic/organic mesoporous material through simultaneous pore engineering and hydrophobic surface modification of the intramesochannels to improve the uptake of superparamagnetic maghemite nanocrystals via impregnation techniques. The mesoporous material of the SBA-15 type was functionalized in situ with thiol organo-siloxane groups. Restricting the addition of the thiol organo-siloxane to 2 mol % yielded an inorganic/organic hybrid material characterized by large pores and a well-ordered hexagonal p6mm mesophase. The hydrophobic surface modification promoted the incorporation of 7.5 nm maghemite (gamma-Fe2O3) nanocrystals, prepared through temperature-control led decomposition of iron pentacarbonyl in organic solvents. The hydrophobic, oleic acid capped superparamagnetic maghemite nanocrystals were incorporated into the porous network via wet impregnation from organic suspensions. Combining diffraction, microscopy, and adsorption data confirmed the uptake of the nanocrystals within the intramesochannels of the silica host. Magnetization dependencies on magnetic field at different temperatures show a constriction in the loop around the origin, which indicates immobilization of maghemite nanocrystals inside the thiol-functionalized silica host.
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| 18. |
- Jonas, Kristina, et al.
(författare)
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Roles of curli, cellulose and BapA in Salmonella biofilm morphology studied by atomic force microscopy
- 2007
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Ingår i: BMC Microbiology. - : Springer Science and Business Media LLC. - 1471-2180. ; 7
-
Tidskriftsartikel (refereegranskat)abstract
- Background: Curli, cellulose and the cell surface protein BapA are matrix components in Salmonella biofilms. In this study we have investigated the roles of these components for the morphology of bacteria grown as colonies on agar plates and within a biofilm on submerged mica surfaces by applying atomic force microscopy (AFM) and light microscopy. Results: AFM imaging was performed on colonies of Salmonella Typhimurium grown on agar plates for 24 h and on biofilms grown for 4, 8, 16 or 24 h on mica slides submerged in standing cultures. Our data show that in the wild type curli were visible as extracellular material on and between the cells and as fimbrial structures at the edges of biofilms grown for 16 h and 24 h. In contrast to the wild type, which formed a three-dimensional biofilm within 24 h, a curli mutant and a strain mutated in the global regulator CsgD were severely impaired in biofilm formation. A mutant in cellulose production retained some capability to form cell aggregates, but not a confluent biofilm. Extracellular matrix was observed in this mutant to almost the same extent as in the wild type. Overexpression of CsgD led to a much thicker and a more rapidly growing biofilm. Disruption of BapA altered neither colony and biofilm morphology nor the ability to form a biofilm within 24 h on the submerged surfaces. Besides curli, the expression of flagella and pili as well as changes in cell shape and cell size could be monitored in the growing biofilms. Conclusion: Our work demonstrates that atomic force microscopy can efficiently be used as a tool to monitor the morphology of bacteria grown as colonies on agar plates or within biofilms formed in a liquid at high resolution.
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| 19. |
- Kapilashrami, Mukes, et al.
(författare)
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Understanding the magnetic interaction between intrinsic defects and impurity ions in room-temperature ferromagnetic Mg1-xFexO thin films
- 2016
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 28:15
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the nature and characteristics of the intrinsic defects and impurities in the dielectric barrier separating the ferromagnetic electrodes in a magnetic tunneling junction is of great importance for understanding the often observed 'barrier-breakdown' therein. In this connection, we present herein systematic experimental (SQUID and synchrotron-radiation-based x-ray absorption spectroscopy) and computational studies on the electronic and magnetic properties of Mg1-xFexO thin films. Our studies reveal: (i) defect aggregates comprised of basic and trimer units (Fe impurity coupled to 1 or 2 Mg vacancies) and (ii) existence of two competing magnetic orders, defect- and dopant-induced, with spin densities aligning anti-parallel if the trimer is present in the oxide matrix. These findings open up new avenues for designing tunneling barriers with high endurance and tunneling effect upon tuning the concentration/distribution of the two magnetic orders.
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| 20. |
- Lindberg, Fredrik, et al.
(författare)
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High resolution electron microscopy study on oxide films formed on nickel-base Alloys X-750, 182 and 82 in simulated high flow velocity BWR water conditions
- 2011
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Ingår i: 15th International Conference on Environmental Degradation of Materials in Nuclear Power Systems-Water Reactors 2011. - : John Wiley and Sons Inc.. - 9781622761944 ; , s. 357-369
-
Konferensbidrag (refereegranskat)abstract
- This work contributes to characterization of the oxide films formed on nickel-base alloys (Alloy X-750, Alloy 82 and Alloy 182) under simulated BWR water environments at ∼10 or 18 m/s with or without iron injection. HR SEM/TEM and FIB techniques were applied. The oxide thicknesses on different alloys were substantially different, ranging from 50 nm to 8 μm. For Alloy X-750 and Alloy 182 exposed without iron injection, similar oxide phase compositions consisting of sub-micron Fe2O3 and NiFe 2O4 grains as well as NiO were formed but with substantially different microstructures. For the corroded Alloy X-750 there was an additional dense layer of possibly Ni1.5Cr0.5O 3 in between the NiFe2O4 and NiO layers. On Alloy 82 which contained a relatively low Fe-content only a thin but dense film of Cr1.3Fe0.7O3 was seen. With iron injection the oxide films formed on Alloy 82 were similar to that on the Alloy 182 without iron injection, suggesting that iron injection may play a similar role as if the alloy had an elevated iron content. The implication of the observations for material corrosion behavior in BWRs is elaborated.
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| 21. |
- Mahadeva, Sreekanth K., et al.
(författare)
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A comparative study of room temperature ferromagnetism in MgO films deposited by rf/dc sputtering using high purity Mg and MgO targets
- 2013
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Ingår i: Materials Express. - : American Scientific Publishers. - 2158-5849 .- 2158-5857. ; 3:4, s. 328-334
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of nanocrystalline MgO were deposited on glass/Si substrates by rf/dc sputtering from metallic Mg, and ceramic MgO targets. The purpose of this study is to identify the differences in the properties, magnetic in particular, of MgO films obtained on sputter deposition from 99.99% pure metallic Mg target in a controlled [Nitrogen + Oxygen partial pressure (O(2)pp)] atmosphere as against those deposited using an equally pure ceramic MgO target in argon + identical oxygen ambience conditions while maintaining the same total pressure in the chamber in both cases. Characterization of the films was carried out by X-ray diffraction, focussed ion beam cross sectioning, atomic force microscopy and SQUID-magnetometry. The 'as-obtained' films from pure Mg target are found to be predominantly X-ray amorphous, while the ceramic MgO target gives crystalline films, (002) oriented with respect to the film plane. The films consisted of nano-crystalline grains of size in the range of about 0.4 to 4.15 nm with the films from metallic target being more homogeneous and consisting of mostly subnanometer grains. Both the types of films are found to be ferromagnetic to much above room temperature. We observe unusually high maximum saturation magnetization (MS) values of 13.75 emu/g and similar to 4.2 emu/g, respectively for the MgO films prepared from Mg, and MgO targets. The origin of magnetism in MgO films is attributed to Mg vacancy (V-Mg), and 2p holes localized on oxygen sites. The role of nitrogen in enhancing the magnetic moments is also discussed.
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| 22. |
- Menushenkov, V. P., et al.
(författare)
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Crystalline structure of SmCo5 based alloys
- 2009
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Ingår i: METAL 2009 - 18th International Conference on Metallurgy and Materials, Conference Proceedings. - 9788087294109 ; , s. 394-400
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Konferensbidrag (refereegranskat)abstract
- Microstructure and crystalline structure of SmCo5 based alloys after various heat treatments were studied using X-ray diffraction and metallographic methods. It was established that complicated microstructure of hyperstoichiometric alloys forms in nonequilibrium conditions during crystallization of the ingots and the subsequent cooling to room temperature. XRD study of the lattice parameters of SmCo5 phase in as-cast SmCo5 based alloys after different heat treatments shows evidence of the Sm enrichment of the SmCo5 phase. The behavior of the lattice parameters of SmCo5 phase in Sm-rich alloys when subjected to aging between 1220°C and 700°C can be related to the phase transformation of SmCo5 into SmCo5-x phases.
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| 23. |
- Owens, F. J., et al.
(författare)
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Evidence for high-temperature ferromagnetism in photolyzed C-60
- 2004
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 69:3
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Tidskriftsartikel (refereegranskat)abstract
- C-60 transforms to a polymeric phase where the C-60 molecules are bonded to form a chain structure when it is subjected to ultraviolet radiation at ambient temperature in the absence of oxygen. The electron paramagnetic resonance spectrum of C-60 photolyzed in the presence of a low pressure of oxygen or in air shows a very broad, asymmetric derivative signal at room temperature and at a magnetic field position well removed from g=2.000. With decreasing temperature, the broad line shifts to lower magnetic fields and increases further in linewidth, as expected for a ferromagnetic resonance signal. A low-field nonresonant derivative signal is also observed, consistent with the existence of ferromagnetism. Ferromagnetism up to room temperature in photolyzed C-60 is confirmed unequivocally by superconducting quantum interference device measurements of the dc magnetization as a function of magnetic field. A possible model for the origin of ferromagnetism based on these results and Raman data on photolyzed samples is also proposed.
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| 24. |
- Parekh, Kinnari, et al.
(författare)
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Ternary monodispersed Mn0.5Zn0.5Fe2O4 ferrite nanoparticles : preparation and magnetic characterization
- 2006
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 17:24, s. 5970-5975
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Tidskriftsartikel (refereegranskat)abstract
- A ternary system of Mn0.5Zn0.5Fe2O4 has been synthesized for the first time using thermal decomposition of metal acetylacetonate in the presence of a high temperature boiling point solvent and fatty acids. Unlike the results of synthesis of this material by other techniques, we obtain nearly monodispersed nanoparticles, rendering them ideal for applications like in hyperthermia. The crystal structure and morphology of the particles obtained using x-ray diffraction (XRD) and transmission electron microscopy (TEM) are those of a single phase spinel structure with no other impurity phases. The particles are of 7 nm average diameter, with a very narrow (< 10%) size distribution. The oleic acid surfactant on the particles shows a 28% weight loss in thermo-gravimetric analyses (TGAs), which corresponds to a monolayer thickness of the coating. Magnetic measurements show the particles to be superparamagnetic with a characteristic blocking temperature of around 50 K.
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| 25. |
- Riazanova, Anastasia, et al.
(författare)
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Creation of Patterned Gold Nanostructures via Electron-Beam-Induced Deposition
- 2013
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Ingår i: Materials Research Society Symposium Proceedings. - : Springer Science and Business Media LLC. - 0272-9172 .- 1946-4274. ; 1546
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Tidskriftsartikel (refereegranskat)abstract
- One of the methods to grow nanoscale three-dimensional (3D) Au patterns is to perform local electron-beam-induced deposition (EBID) using the Me2Au(acac) precursor inside the chamber of a scanning electron microscope (SEM). However, due to the organometallic nature of the chemical, the concentration of the metallic constituent in the as-deposited structure is dramatically low, at around 10 at. % of Au. Ex-situ post-annealing of Me2Au(acac) EBIDs is a very promising purification approach, resulting in an Au content of > 92 at. % after annealing at 600 °C. However, in most of the cases it also distorts the geometrical shape of the heat-treated structure, preserving of which is essential for the application. In this paper we present a systematic study of the dependence between the annealing parameters and resulting purity in combination with the shape of the Au structure. Optimized heat treatment conditions for the creation of well-purified high aspect ratio Au pillar array are presented; and for planar continuous structures, the importance of the parameter height to area ratio is identified.
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| 26. |
- Riazanova, Anastasia
(författare)
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Direct Nanoprototyping of Functional Materials via Focused Electron Beam
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- During recent years the demand for nanoscale materials with tailor-made functional properties as bulk species, is continuously and progressively rising for such fields as e.g. micro- and nano-electronics, plasmonics, spintronics, bio-technology, bio-sensing and life sciences. Preserving and / or improving properties of functional materials with their simultaneous size reduction and high-resolution site-specific positioning is indeed very challenging, for both conductors and insulators.One of the advanced nanoprototyping methods that can be utilized for this purpose is the Electron-Beam-Induced Deposition, or shortly EBID. This process is based on a local decomposition by a focused electron beam of a precursor gas molecules adsorbed on the sample’s surface. The beauty of this method is that it gives a unique possibility of rapid creation of site-specific nanoscale 3D structures of precise shape in a single operation. It’s an additive process that can be easily combined with other patterns.However, besides all the benefits, EBID has some constraints, in particular low purity of the deposited materials, due to the organometallic nature of the used precursors. Chemical composition of EBID patterns is strongly dependent on the chosen gas chemistry, the substrate, many deposition parameters and post-treatment processes applied to the deposited structures.In our research we focused on deposition of Co, Au, SiO2, C, W and Pt, their purification and shape control. And this thesis presents an overview of our accomplishments in this field.Depending on the gas chemistry of interest, three major purification approaches of EBID-grown materials were tested out:- Post-deposition annealing: in air and in the controlled atmosphere,- Deposition onto a preheated substrate,- Deposition in the presence of reactive gases.As a result, a dramatic purity improvement was observed and a significant advancement was achieved in creation of high-purity gold, cobalt and silicon dioxide nanoscale structures. In particular:1) For the Me2Au(acac) precursor, we developed a nanofabrication routine combining application of wetting buffer layers, fine tuning of EBID parameters and subsequent post-annealing step, which led to formation of high-purity planar and high aspect ratio periodic Au nanopatterns. We also describe the adopted and gently adjusted wet etching method of undesirable buffer layer removal, required in some cases for the further device application.2) For the Co2(CO)8 precursor, in-situ seeded growth in conjunction with EBID at the elevated substrate temperature resulted in a deposition of pure nanocrystalline Co with magnetic and transport properties close to the bulk material.3) For the tetraethyl orthosilicate precursor, or shortly TEOS, assisting of the deposition process with the additional oxygen supply led to the EBID of carbon-free amorphous insulating Si-oxide, with the absorption and refraction properties comparable to those for fused silica.Several applications of EBID nanopatterns are also discussed.
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| 27. |
- Sharma, P., et al.
(författare)
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Imaging of piezoelectric activity in laser-ablated c-axis-oriented LiNbO3/ZnO thin film multilayer on glass using atomic force microscopy
- 2003
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Ingår i: Journal of Materials Research. - 0884-2914 .- 2044-5326. ; 18:9, s. 2025-2028
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Tidskriftsartikel (refereegranskat)abstract
- A LiNbO3/ZnO multilayer with a preferred c-axis orientation normal to the plane of the substrate was grown on glass and SiO2/Si substrates by laser ablation. The piezoelectric activity in as-deposited films was demonstrated using a novel approach to the atomic force microscope. In the presence of an in-plane, low-frequency (0.1-5 Hz) alternating current electric field, we monitored and imaged the induced piezoelectric response normal to the film plane between two electrodes.
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| 28. |
- Sharma, P., et al.
(författare)
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Piezoelectric activity in c-axis oriented LiNbO3/ZnO bilayers grown by laser ablation technique
- 2005
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Ingår i: Ferroelectrics (Print). - : Informa UK Limited. - 0015-0193 .- 1563-5112. ; 329, s. 969-972
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Tidskriftsartikel (refereegranskat)abstract
- LiNbO3/ZnO multi-layer with a preferred c-axis orientation has been grown on glass and SiO2/Si substrates by laser ablation technique. The piezoelectric activity in as deposited films is demonstrated using a novel approach to the atomic force microscope. In the presence of an in plane low frequency (0.1 to 5 Hz) ac electric field, we monitor and image the induced piezoelectric response normal to the film plane between two electrodes.
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| 29. |
- Shen, Zhijian, et al.
(författare)
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Ferroelectric ceramics with enhanced remnant polarization by ordered coalescence of nano-crystals
- 2012
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Ingår i: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 0959-9428 .- 1364-5501. ; 22:44, s. 23547-23552
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Tidskriftsartikel (refereegranskat)abstract
- An exceptional high ferroelectric remnant polarization (P-r) was observed in BaTiO3 ceramics owing to the formation of micron-sized grains possessing nano-scale mosaicity. Such a structural hierarchy was developed via a novel crystal-growth mechanism, namely ordered coalescence of nano-crystals achieved by synergetic atomic epitaxial growth and self-assembly of nano-crystals. The accommodating lattice defects in sub-grain boundaries due to the imperfect assembly of nano-crystals significantly contribute to the P-r enhancement by stimulating the dynamics of ferroelectric domain formation and switching. This finding defines a new approach to nanopowder sintering leading to enhanced properties sensitive to lattice defects.
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| 30. |
- Shen, Zhijian, et al.
(författare)
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Ordered coalescence of nanocrystals : a path to strong macroporous nanoceramics
- 2010
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 21:20
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Tidskriftsartikel (refereegranskat)abstract
- A versatile approach for integrating two apparently conflicting physical properties, high porosity and high mechanical strength, in polycrystalline bulks is established and demonstrated for the case of alumina ceramics. Macroporous alumina nanoceramics are synthesized by stimulating coalescence-mediated necking, which enables the formation of strong crystallographically coherent necks between adjacent grains. The work places a general emphasis on manipulating crystal growth on the nanoscale and on preparing highly porous polycrystalline bulk ceramics with improved mechanical rigidity.
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| 31. |
- Singh, Veena, et al.
(författare)
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Scalable InkJet-Based Additive Fabrication of Photocatalytic TiO2 Thin Films
- 2022
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Ingår i: ChemPhotoChem. - : Wiley. - 2367-0932. ; 6:3
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Tidskriftsartikel (refereegranskat)abstract
- Photocatalysts for water purification and energy production belong to the class of materials for which there is an urgent need for more environmentally friendly manufacturing. Here we report a high throughput method for inkjet printing of nanostructured photocatalytically active TiO2 films and a detailed analysis of their properties and photocatalytic performance. We show that the inkjet dispersion of TiO2 particles is highly reproducible which leads to a close to linear relation between the number of printed single layers and the thickness of the films. The films here obtained have uniform surfaces and the interfaces with the substrates are free from defects such as grain boundaries, ripples, or discontinuities. This contrasts with films obtained with the traditional doctor blade method. The inkjet printed films have higher photocatalytic performance than the doctor blade films which results in higher catalytic activity per mass of material used. Lifetime tests with wet and dry cycles show that the inkjet films subjected to 10 photocatalytic cycles of 100 minutes each have a loss of performance of only 7 %, while the films made via the doctor blade method have a performance loss of 66 %. These tests revealed additionally that the mechanical stability of the inkjet films is higher than that of the films manufactured via the traditional casting method. This set of results shows that inkjet printing can be an efficient method for the large-scale production of TiO2 photocatalysts.
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| 32. |
- Upadhyay, Ramesh V., et al.
(författare)
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Low-field DC-magnetization study of Ho3+-doped Mn-Zn ferrite ferrofluid
- 2007
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 311:1, s. 106-110
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Tidskriftsartikel (refereegranskat)abstract
- The physical and magnetic properties of magnetic nanoparticles are crucial for their effectiveness and reliability in biomedical applications. In this article, we report the synthesis of a stable Ho-substituted Mn-Zn ferrite ferrofluid and its physical and magnetic properties. Substitution by rare earth metal plays an important role in determining the magneto-crystalline anisotropy in 4f-3d intermetallic compounds. Ho3+ substitution not only enhanced the magnetic anisotropy but also produced strong spin frustration at low temperature. The field dependence of blocking temperature shows H-2/3 dependency in the entire range of field, i.e., 10-700 Oe, indicating the emergence of Ising spins characteristics in the present system.
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| 33. |
- Voit, W., et al.
(författare)
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Application of inkjet technology for the deposition of magnetic nanoparticles to form micron-scale structures
- 2003
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Ingår i: IEE Proceedings - Science Measurement and Technology. - : Institution of Engineering and Technology (IET). - 1350-2344 .- 1359-7094. ; 150:5, s. 252-256
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Tidskriftsartikel (refereegranskat)abstract
- Inkjet printing technique has been applied to the production of magnetic layers and structures consisting of nanosized magnetic particles. These magnetic particles were synthesised by chemical methods and dispersed in suitable fluidic systems. The rheological parameters of the fluids were adjusted for inkjet printing. The resulting micron-scale pattern were obtained with a high reproducibility and structure control. The magnetic local structure of the patterns has been studied by using a new local 'in-plane' susceptibility measurement system as well as magnetic force microscopy. The deposited structures reveal a chain-like self-alignment of the magnetic particles. Potential applications of this fast and versatile process are the production of low- and medium-density magnetic mass storage patterns on almost any kind of substrate and for magnetic character recognition purposes. Printed patterns with minimal structure dimensions in the range of 50-100 mum are discussed. Work is in progress to decrease these dimensions by an order of magnitude by volume reduction of the deposited ink droplets.
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| 34. |
- Wu, Yan, et al.
(författare)
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'In-situ' solution processed room temperature ferromagnetic MgO thin films printed by inkjet technique
- 2011
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Ingår i: Materials Research Society Symposium Proceedings. - : Springer Science and Business Media LLC. - 9781605112695 ; , s. 105-109
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Konferensbidrag (refereegranskat)abstract
- We report on 'in-situ' solution processed homogeneous (200) oriented MgO ∼85nm thin films deposited on Si substrates by inkjet printing. These films are found to show ferromagnetic order beyond room temperature with a saturation magnetization MS as high as ∼0.63 emu/g. X-ray photoelectron spectroscopy investigations show the absence of any possible contamination effects, while the Mg 2p, and O 1s spectra indicate that the role of defect structure at the Mg site is important in the observed magnetism. By controlling the pH values of the precursors the concentration of the defects can be varied and hence tune the magnetization at room temperature. The origin of magnetism in these MgO thin films appears to arise from the cation vacancies.
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