K V Rao

K V Rao
KTH Royal Institute of Technology | KTH · Department of Materials Science and Engineering (MSE)

D.Phil (Oxon)

About

486
Publications
49,738
Reads
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10,214
Citations
Additional affiliations
June 2000 - December 2015
Royal Institute of Technology, also known as Kungliga Tekniska Högskolan
Position
  • over 650 publications related to magnetism, amorphous materials, and materials science in general. Currently involved in magnetic Oxide materials. a paper in Nature Materials since 2003 has been cited over 960 times by now almost one every two days!
September 1984 - November 1990
Position
  • Senior Researcher
Description
  • joint appointment with Adjunct Professorship at KTH
January 1984 - December 2000
Royal Institute of Technology

Publications

Publications (486)
Article
Magnetism in wide band gap materials is of great interests for future spintronic device applications. We prepared MgO and Fe-doped MgO films ‘in-situ’ on substrates by inkjet printing, and investigated the ferromagnetism tuned by the doping of Fe, the annealing temperature and the film thickness. It is found that the Fe-doping improves the crystall...
Article
Solution processed homogeneous (200) oriented MgO∼85 nm thin films deposited on Si substrates were fabricated 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 for the acid ink precursor. X-ray photoelectron spectroscopy investigations show the abs...
Article
Full-text available
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 sync...
Article
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CoFe 2 O 4 nanotubes and porous nanorods were prepared via a simple one-pot template-free hydrothermal method and were used as an adsorbent for the removal of dye contaminants from water. The properties of the synthesized nanotubes and porous nanorods were characterized by electron diffraction, transmission electron microscopy and x-ray powder diff...
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We developed a method to fabricate hybrid magnetic-plasmonic nanorods (Au-Co NRs) via modified seeded mediated method. The only modification is to use cobalt ions instead of Au+3 in the preparation of the seed solution to obtain gold nanorods doped with Co clusters. By adjusting the amount of cobalt seed solution, Au-Co NRs of controlled aspect rat...
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a b s t r a c t The aim of this study is surface modification of Ni-free type Ti based metallic glass (Ti 42 Hf 11 Cu 11 Pd 36 at.%) for increasing calcification by electrochemical treatment. Ni-free type Ti based metallic glass has excel-lent mechanical and chemical properties which are comparable with those of Ti based alloys. Surface of Ti based...
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We have successfully synthesized Fe-doped ZnO nanorods by a new and simple method in which the adopted approach is by using ammonia as a continuous source of O H - for hydrolysis instead of hexamethylenetetramine (HMT). The energy dispersive X-ray (EDX) spectra revealed that the Fe peaks were presented in the grown Fe-doped ZnO nanorods sample...
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We report an unusual robust ferromagnetic order above room temperature upon amorphization of perovskite [YCrO3] in pulsed laser deposited thin films. This is contrary to the usual expected formation of a spin glass magnetic state in the resulting disordered structure. To understand the underlying physics of this phenomenon, we combine advanced spec...
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Optically highly transparent, soft magnetic thin films (4–18 nm thick) of Fe–B–Nb- and Fe–B–Nb–Y-based glassy metal targets were grown on quartz substrates by pulsed laser deposition, and their optical and magneto-optical properties were investigated over the visible spectrum (400–700 nm). All the films found to be fully amorphous in structure were...
Article
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Three-dimensional magnetic photonic crystals were fabricated from silica spheres containing magnetite nano-particles, assembled in a magnetic field. Transmission studies showed significant, sharp features in the magnetic circular dichroism and Faraday rotation, centred on the edge of the third photonic band gap (PBG), but five times narrower than t...
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Thin films of nanocarysalline 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, manetic in paticular, of MgO films obtained on sputter deposition from 99.99% pure metallic Mg target in a aacaontrolled [nitrogen+oxygen p...
Article
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We report a simple, low-cost, single-step inkjet printing method for the fabrication of nanostructured, highly transparent and conductive ITO films, which completely avoids the use of ITO particles in the fabrication process. In our method, the inks are formed from a liquid solution presenting a properly selected mixture of indium and tin acetates....
Article
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We report on preliminary studies of low (14 at.%) and high (53at.%) concentration Mn doped MgO films deposited by co-sputtering from metallic Mn and Mg targets. The structural, surface morphologies and magnetic properties of the films of different thickness were studied. All the as grown films are found to be amorphous and film surfaces are found t...
Conference Paper
Full-text available
We have fabricated by pulse laser deposition very thin (~5-7 nm) and thick (~27-408 nm) films of composition Fe 66 B 24 Nb 4 Ni 6 on silicon and quartz substrates respectively, and studied their magnetic and magneto-optic properties at room temperature. We find that the thicker films on silicon can be tuned by appropriate thermal annealing to explo...
Article
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Abstract: We report a systematic study of room-temperature ferromagnetism (RTFM) in pristine MgO thin films in their amorphous and nano-crystalline states. The as deposited dc-sputtered films of pristine MgO on Si substrates using a metallic Mg target in an O2 containing working gas atmosphere of (N2 + O2) are found to be X-ray amorphous. All these...
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Abstract: We report a systematic study of room-temperature ferromagnetism (RTFM) in pristine MgO thin films in their amorphous and nano-crystalline states. The as deposited dc-sputtered films of pristine MgO on Si substrates using a metallic Mg target in an O 2 containing working gas atmosphere of (N 2 + O 2) are found to be X-ray amorphous. All th...
Article
Full-text available
Direct printing of functional oxide thin films could provide a new route to low-cost, efficient and scalable fabrications of electronic devices. One challenge that remains open is to design the inks with long term stability for effective deposition of specific oxide materials of industrial importance. In this paper, we introduce a reliable method o...
Article
In the past 10 years, ZnO as a semiconductor has attracted considerable attention due to its unique properties, such as high electron mobility, wide and direct band gap and large exciton binding energy. ZnO has been considered a promising material for optoelectronic device applications, and the fabrications of high quality p-type ZnO and p–n juncti...
Article
p-Type ZnO materials: Theory, growth, properties, and devices J.C. Fan, K.M.Sreekanth, Z.Xie, S.L.Chang and K.V. Rao ,abstract In the past 10 years, ZnO as a semiconductor has attracted consid- erable attention due to its unique properties, such as high electron mobility, wide and direct band gap and large exciton binding energy. ZnO has been cons...
Article
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Ink-jet printing technique is used to prepare porous (ZnO)1−x (TiO2) x composite films on indium tin oxide-coated glass substrates. Dye-sensitized solar cells were fabricated using well-characterized printed films of thickness ∼20 and 30 μm, respectively. It is found that the photovoltaic performance of the cells is dependent on the film thickness...
Article
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We present a method to identify bulk glass forming ability by partial substitution of Fe by Ni in FeBNbY based amorphous alloy ribbons and as a consequence obtain enhanced mechanical and soft magnetic properties of bulk glassy rods of diameter as large as 4.5 mm. A detailed investigation of thermal, mechanical, and magnetic properties of (Fe 0.72Àx...
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Mg doped ZnO thin films were prepared by DC/RF magnetron co-sputtering in (Ar+O 2) ambient conditions using metallic Mg and Zn targets. We present a comprehensive study of the effects of film thickness on the structural, optical and magnetic properties. Room temperature ferromagnetism was observed in the films and the saturation magnetization (M S)...
Article
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Mg@ZnO thin films were prepared by DC/RF magnetron co-sputtering in (N2+O2) ambient conditions using metallic Mg and Zn targets. We present a comprehensive study of the effects of film thickness, variation of O2 content in the working gas and annealing temperature on the structural, optical and magnetic properties. The band gap energy of the films...
Article
Full-text available
We report a simple, low-cost, single-step inkjet printing method for the fabrication of nanostructured, highly transparent and conductive ITO films, which completely avoids the use of ITO particles in the fabrication process. In our method, the inks are formed from a liquid solution presenting a properly selected mixture of indium and tin acetates....
Article
Full-text available
Direct printing of functional oxide thin films could provide a new route to low-cost, efficient and scalable fabrications of electronic devices. One challenge that remains open is to design the inks with long term stability for effective deposition of specific oxide materials of industrial importance. In this paper, we introduce a reliable method o...
Article
Full-text available
MgO is a widely used material in ceramic and electronic industry. It is a well known insulator which has been used as a spacer layer in electronic circuits and magnetic tunnel junctions. We report room temperature ferromagnetism in undoped, and V doped MgO nanoparticles of the same size (∼ 39 nm diameter) produced by a two-step chemical process, bu...
Article
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We present herein a soft x-ray spectroscopy study on the electronic and magnetic properties of Mg1�xFexOy thin films. A distinct shoulder feature on the absorption edge reflecting the unoccupied oxygen 2p states is evident in the intrinsic thin films, which diminishes upon Fe doping, while a pre-edge absorption feature (reflecting the O 2p-Fe 3d ac...
Article
Nanotoxicology test of gold nanoparticles (Au NPs) and gold-cobalt (Au-Co) nanoalloy is an important step in their safety evaluation for biomedical applications. The Au and Au-Co NPs were prepared by reducing the metal ions using sodium borohydride (NaBH(4)) in the presence of polyvinyl pyrrolidone (PVP) as a capping material. The average size and...
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Magnetite nanoparticles have been prepared by co-precipitation using a custom-designed jet mixer to achieve rapid mixing (RM) of reactants in a timescale of milliseconds. The quick and stable nucleation obtained allows control of the particle size and size distribution via a more defined growth process. Nanoparticles of different sizes were prepare...
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Room temperature magnetic properties of un-doped, as well as 10 at.% Fe-doped ZnO and MgO single-pass layer of ink-jet printed thin films have been investigated to obtain insight into the role of the band gaps and mechanisms for the origin of ferromagnetic order in these materials. It is found that on doping with Fe, the saturation magnetization is...
Article
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We have investigated the electronic structure of ZnO:Mn and ZnO:Mn,N thin films using x-ray magnetic circular dichroism (XMCD) and resonance-photoemission spectroscopy. From the Mn 2$p$$\rightarrow3d$ XMCD results, it is shown that, while XMCD signals only due to paramagnetic Mn$^{2+}$ ions were observed in ZnO:Mn, nonmagnetic, paramagnetic and fer...
Article
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We demonstrate the impact of rapid mixing of the precursors in a time scale of milliseconds on the reaction rate and magnetic properties of co-precipitated magnetite with a custom-made mixer. The mixed volume is directed into a desk-top AC susceptometer to monitor the magnetic response from the growing particles in real-time. These measurements ind...
Article
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ABSTRACT: The optical properties of multi-functionalized cobalt ferrite (CoFe2O4), cobalt zinc ferrite (Co0.5Zn0.5Fe2O4), and zinc ferrite (ZnFe2O4) nanoparticles have been enhanced by coating them with silica shell using a modified Stöber method. The ferrites nanoparticles were prepared by a modified citrate gel technique. These core/shell ferrite...
Article
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We designed face-centered cubic-structured (fcc) photonic crystals whose lattice parameters were tuned by varying the size of the constituent spherical silica particles in the range 100 to 520 nm. From wide-angle optical transmission investigations and Gaussian fitting of the absorbance spectra over UV-Vis-Near IR range, we found that in these crys...
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Arrays of ferromagnetic circular dots (with diameters ranging from 225 to 420 nm) have been prepared at the surface of atomically ordered paramagnetic Fe60Al40 (at. %) sheets by means of ion irradiation through prelithographed poly(methyl methacrylate) (PMMA) masks. The cumulative effects of consecutive ion irradiation (using Ar+ ions at 1.2 × 1014...
Article
Quantum dots (QDs) are a novel class of inorganic fluorophores which are gaining widespread recognition as a result of their exceptional photophysical properties and their applications as a biomarker and in molecular biomedical imaging. The aim of this study was to evaluate the in vivo genotoxicity in mice exposed to CdSe quantum dots of average si...
Article
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Printing of functional materials requires reliable deposition processes. This work describes the development of printing processes for selected functional materials utilizing industrial-type inkjet printheads. A well-controlled printing process with fluids containing the conductive polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PED...
Article
This indium-doped zinc oxide field effect transistor (IZO-FET) with a large ultraviolet (UV) detection sensitivity has been fabricated by inkjet printing technique. In darkness, the IZO-FETs exhibit a saturation current level of about 10 mA, an incremental mobility as high as 8 cm 2 V À1 s À1 , and a current on/off ratio of 10 4 –10 5 . When illumi...
Article
Abstracf-Cesubstituted Yttrium Iron Garnet films have been epitaxially grown on (lll)-oriented Gadolinium Gallium Garnet substrates by Pulsed Laser Deposition technique. X-ray diffraction measurements show epitaxial growth of the garnet fdm along its [lll] axis. The films were grown at substrate temperature of 790°C and various oxygen partial press...
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Submicron thick Bi, Ga substituted dysprosium iron garnet films were laser deposited on Gd3Ga5O12(GGG) and ceramic glass substrates at room temperature and then post annealed by rapid thermal annealing (RTA). From Faraday rotation studies, the films deposited on glass substrates are found to exhibit perpendicular magnetic anisotropy, Faraday rotati...
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Controlled microstructured thin films with nominal composition Cu95Co5 have been deposited on glass substrates by pulsed laser ablation at room temperature, in vacuum, for different target speed rotation. Atomic Force Microscopy, AFM, studies have shown a surface roughness not higher than 0.5 nm, for the as-deposited samples, which do not exhibit m...
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The lead titanium oxide PbTiO3 (PTO) and High Tc Superconductor YBa2Cu3O7-x (YBCO) capacitor hetero structures have been fabricated by pulsed laser ablation directly on 3C-SiC substrates. X-ray diffraction analysis indicates that both PTO layer and YBCO layer are polycrystalline with a perovskite phase. The zero-field cooling (ZFC) curve of YBCO sh...
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Ferrofluids containing superparamagnetic Fe3O4 nanoparticles have been prepared by a controlled co-precipitation method. The aggregation of the particles was prevented by using a polymeric starch network as a coating agent. Structural and magnetic measurements reveal a particle size of around 6 nm, with a clear evidence of a uniform particle coatin...
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The large values over 300 kA/m at room temperature were found for the coercive field of Nd50Fe40Si10-xAlx (x = 0; 10) amorphous melt-spun ribbons and cast rods. The dependence of the coercive field on the thickness and the preparation method, namely the cooling rate, is ascribed to the existence in the amorphous matrix of very small ferromagnetic c...
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Low field (∿5 Oe)Magneto-Thermo-Gravimetric technique has been used to study the effects of substitution of Nd with Y, Gd, and Dy in melt-spun Fe77Nd15B8 alloys, and also to monitor the changes in the magnetic properties on heat treatment to achieve optimum magnetic hardening in these alloys. From VSM-measurements preliminary studies of the effect...
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Studies of the evolution of electrical resistance in an external applied magnetic field, B, as well as with temperature, T, on Cu 8 6 Co 14 and Cu 92 Co 8 as quenched and annealed melt-spun ribbons, reveal that magnetoresistance, MR, AR(B,T)=R(B)-R(0) scales with B/T. Furthermore, it found that annealing up to 600 °C scales the magnetic moment of t...
Article
In order to elucidate the sensitivity and information that can be obtained from Magneto-Thermo-Gravimetric, MTG, technique, we present a comparative study of our results on structure relaxation as well as crystallization sequences as a function of time and temperature of amorphous Fe90-xSixB10 alloys in the Fe-rich regime, with those obtained from...
Article
We report the first Hall, and electrical resistivity study on rapidly quenched icosahedral Al-based alloys. The Hall coefficient is found to be negative and remains so for i(Al-Mn) alloys even for higher Mn concentrations. The magnitude and temperature coefficient of the electrical resistivity behaviour in these alloys is similar to those observed...
Article
We present a study on the magnetic behavior of nanosized iron oxide particles coated with different surfactants (sodium oleate, PVA and starch) in a ferrofluid. The effect of the coating material, and different particle concentrations in the ferrofluid have been magnetically investigated to determine the effective magnetic particle size and possibl...
Article
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...
Article
Full-text available
Depth sensing nano-indentation investigations have been performed to determine the radial dependence of the hardness through the cross section of a Fe-based bulk glassy rod. We have found the hardness of the material decreases along radius from the centre to the outermost surface. This phenomenon is attributed to the ‘cooling rate induced surface s...
Article
Full-text available
We have succeeded in producing bulk metallic glass by partial substitution of Fe with Ni in Fe-B-Nb alloys which could otherwise be only melt spun into amorphous ribbons. Substitution by Ni in the Fe 72-x B 24 Nb 4 Ni x alloys with (x ~2, 4, 6, 8, 10, 12 and 14) improves the glass forming ability of the materials and as a result rods of same compos...
Article
Full-text available
We have studied the magnetic properties of 100 nm thick ZnO thin films prepared by magnetron sputtering in different oxygen partial pressures (ratio of oxygen pressure to total pressure in deposition chamber, POxy). Only the films fabricated at POxy below ∼ 0.5 show room temperature ferromagnetism. The saturation magnetization at room temperature i...
Article
We have succeeded in producing bulk metallic glass by partial substitution of Fe with Ni in Fe-B-Nb alloys which could otherwise be only melt spun into amorphous ribbons. Substitution by Ni in the Fe 72-xB 24Nb 4Ni x alloys with (x ∼2, 4, 6, 8, 10, 12 and 14) improves the glass forming ability of the materials and as a result rods of same compositi...