Magnetism in C60 Films Induced by Proton Irradiation

2005-03-13

It is shown that polycrystalline fullerene thin films on hydrogen passivated Si(111) substrates irradiated by 2 MeV protons displays ferromagnetic-like behavior at 5 K. At 300 K both the pristine and the irradiated film show diamagnetic behavior. Magnetization data in the temperature range 2 - 300 K, in 1 Tesla applied field, for the irradiated film shows much stronger temperature dependence compared to the pristine film. Possible origin of ferromagnetic-like signals in the irradiated films are discussed.

Author(s): S. Mathew B. Satpati B. Joseph B. N. Dev R. Nirmala S. K. Malik

Crystallographic structure of ultrathin Fe films on Cu(100)

2001-06-19

We report bcc-like crystal structures in 2-4 ML Fe films grown on fcc Cu(100) using scanning tunneling microscopy. The local bcc structure provides a straightforward explanation for their frequently reported outstanding magnetic properties, i.e., ferromagnetic ordering in all layers with a Curie temperature above 300 K. The non-pseudomorphic structure, which becomes pseudomorphic above 4 ML film thickness is unexpected in terms of conventional rules of thin film growth and stresses the importance of finite thickness effects in ferromagnetic ultrathin films.

Author(s): Albert Biedermann Rupert Tscheliessnig Michael Schmid Peter Varga

Ferromagnetism at 300 K in spin-coated films of Co doped anatase and rutile TiO2

2004-09-13

Thin films of Ti1-xCoxO2 (x=0 and 0.03) have been prepared on sapphire substrates by spin-on technique starting from metalorganic precursors. When heat treated in air at 550 and 700 C respectively, these films present pure anatase and rutile structures as shown both by X-ray diffraction and Raman spectroscopy. Optical absorption indicate a high degree of transparency in the visible region. Such films show a very small magnetic moment at 300 K. However, when the anatase and the rutile films are annealed in a vacuum of 1x10-5 Torr at 500 oC and 600 oC respectively, the magnetic moment, at 300 K, is strongly enhanced reaching 0.36 B/Co for the anatase sample and 0.68 B/Co for the rutile one. The ferromagnetic Curie temperature of these samples is above 350 K.

Author(s): R. Suryanarayanan Vaman Naik Parasuram Kharel Punya Talgala Ratna Naik

Ferromagnetism at 300 K in spin-coated anatasea and rutile Ti0.95Fe0.05O2 films

2004-10-14

Thin films of Ti1-xFexO2 (x=0 and 0.05) have been prepared on sapphire substrates by spin-on technique starting from metal organic precursors. When heat treated in air at 550 and 700 degrees C respectively, these films present pure anatase and rutile structures as shown both by X-ray diffraction and Raman spectroscopy. Optical absorption indicate a high degree of transparency in the visible region. Such films show a very small magnetic moment at 300 K. However, when the anatase and the rutile films are annealed in a vacuum of 1x10-5 Torr at 500 degrees C and 600 degrees C respectively, the magnetic moment, at 300 K, is strongly enhanced reaching 0.46 $\mu$B/Fe for the anatase sample and 0.48 $\mu$B/Fe for the rutile one. The ferromagnetic Curie temperature of these samples is above 350 K.

Author(s): R. Suryanarayanan V. M. Naik P. Kharel P. Talgala R. Naik

Frequency-dependent Drude damping in Casimir force calculations

2008-12-11

The Casimir force is calculated between Au thin films that are described by a Drude model with a frequency dependent damping function. The model parameters are obtained from available experimental data for Au thin films. Two cases are considered; annealed and nonannealed films that have a different damping function. Compared with the calculations using a Drude model with a constant damping parameter, we observe changes in the Casimir force of a few percent. This behavior is only observed in films of no more than 300 $\AA$ thick.

Author(s): R. Esquivel-Sirvent

Highly Uniform 300 mm Wafer-Scale Deposition of Single and Multilayered Chemically Derived Graphene Thin Films

2009-12-10

The deposition of atomically thin highly uniform chemically derived graphene (CDG) films on 300 mm SiO2/Si wafers is reported. We demonstrate that the very thin films can be lifted off to form uniform membranes than can be free-standing or transferred onto any substrate. Detailed maps of thickness using Raman spectroscopy and atomic force microscopy (AFM) height profiles reveal that the film thickness is very uniform and highly controllable, ranging from 1-2 layers up to 30 layers. After reduction using a variety of methods, the CDG films are transparent and electrically active with FET devices yielding exceptionally high mobilities of ~ 15 cm2/Vs and sheet resistance of ~ 1 k Ohm/sq at ~ 70 % transparency.

Author(s): Hisato Yamaguchi Goki Eda Cecilia Mattevi HoKwon Kim Manish Chhowalla

Dependence of Zinc Oxide Thin Films Properties on Filtered Vacuum Arc Deposition Parameters

2005-01-17

The micro-properties (structure and composition), and macro-properties (electrical and optical properties) of zinc oxide (ZnO) thin films deposited on glass substrates using a filtere vacuum arc deposition (FVAD) system were investigated as a function of oxygen pressure (0.37 - 0.5 Pa) and arc current (100 - 300 A). Correlations between the various properties were investigated.

Author(s): T. David S. Goldsmith R. L. Boxman

Kinetic stabilization of Fe film on GaAs(100): An in situ x-ray reflectivity Study

2006-03-06

We study the growth of the Fe films on GaAs(100) at a low temperature, 140 K, by $in$-$situ$ UHV x-ray reflectivity using synchrotron radiation. We find rough surface with the growth exponent, $\beta_S$ = 0.51$\pm$0.04. This indicates that the growth of the Fe film proceeds via the restrictive relaxation due to insufficient thermal diffusion of the adatoms. The XRR curves are nicely fit by a model with a uniform Fe film, implying that the surface segregation and interface alloying of both Ga and As are negligible. When the Fe film is annealed to 300 K, however, the corresponding XRR can be fit only after including an additional layer of 9 A thickness between the Fe film and the substrate, indicating the formation of ultrathin alloy near the interface. The confinement of the alloy near the interface derives from the fact that the diffusion of Ga and As from the substrate should proceed via the inefficient bulk diffusion, and hence the overlying Fe film is kinetically stabilized.

Author(s): T. C. Kim J. -M. Lee Y. Kim D. Y. Noh S. -J. OH J. -S. Kim

Large anisotropy in the paramagnetic susceptibility of SrRuO3 films

2003-11-14

By using the extraordinary Hall effect in SrRuO3 films we performed sensitive measurements of the paramagnetic susceptibility in this itinerant ferromagnet, from Tc (~ 150 K) to 300 K. These measurements, combined with measurements of magnetoresistance, reveal that the susceptibility, which is almost isotropic at 300 K, becomes highly anisotropic as the temperature is lowered, diverging along a single crystallographic direction in the vicinity of Tc. The results provide a striking manifestation of the effect of exceptionally large magnetocrystalline anisotropy in the paramagnetic state of a 4d itinerant ferromagnet.

Author(s): Yevgeny Kats Isaschar Genish Lior Klein James W. Reiner M. R. Beasley

300 K Ferromagnetic Magnetic Circular Dichroism in Co2+-doped ZnO Activated by Shallow Donors

2005-07-05

Cobalt-doped ZnO (Co2+:ZnO) films were studied by magnetic circular dichroism (MCD) spectroscopy. A broad 300 K ferromagnetic MCD signal was observed between 1.4 and 4.0 eV after introducing shallow donor states by exposure of paramagnetic Co2+:ZnO films to zinc vapor. The new sub-bandgap ferromagnetic MCD intensity is attributed to low-energy photoionization transitions originating from a spin-split donor impurity band in ferromagnetic Co2+:ZnO.

Author(s): Kevin R. Kittilstved Jialong Zhao William K. Liu J. Daniel Bryan Daniel R. Gamelin

Granularity-induced gapless superconductivity in NbN films: evidence of thermal phase fluctuations

2002-01-17

Using a single coil mutual inductance technique, we measure the low temperature dependence of the magnetic penetration depth in superconducting NbN films prepared with similar critical temperatures around 16 K but with different microstructures. Only (100) epitaxial and weakly granular (100) textured films display the characteristic exponential dependence of conventional BCS s-wave superconductors. More granular (111) textured films exhibit a linear dependence, indicating a gapless state in spite of the s-wave gap. This result is quantitatively explained by a model of thermal phase fluctuations favored by the granular structure.

Author(s): G. Lamura J. C. Villegier A. Gauzzi J. Le Cochec J. Y. Laval B. Placais N. Hadacek J. Bok

Domain structure sequence in ferroelectric Pb(Zr0.2Ti0.8)O3 thin film on MgO

2007-03-23

The structural evolution of a polydomain ferroelectric Pb(Zr0.2Ti0.8)O3 film was studied by temperature dependent X-ray diffraction. Two critical temperatures were evidenced: T*=740K, corresponding to a change in the domain structure (a/c/a/c to a1/a2/a1/a2), and Tc_film = 825K where the film undergoes a ferroelectricparaelectric phase transition. The films remains tetragonal on the whole range of temperature investigated. The evolutions of the domain structure and lattice parameters were found to be in very good agreement with the calculated domain stability map and theoretical temperature-misfit strain phase diagram respectively.

Author(s): Pierre-Eymeric Janolin Françoise Le Marrec Erling Ringgaard Bernard Fraisse Brahim Dkhil

Direct and inverse measurement of thin films magnetostriction

2009-11-10

Two techniques of measurements of thin film magnetostriction are compared: direct, when changes of the substrate curvature caused by the film magnetization are controlled, and inverse ("indirect"), when the modification of the magnetic anisotropy induced by the substrate deformation (usually bending) is measured. We demonstrate how both the elastic strength of the substrate and the effective magneto-mechanical coupling between the substrate deformation and magnetic anisotropy of the film depend on different conditions of bending. Equations to be used for magnetostriction value determination in typical cases are given and critical parameters for the corresponding approximations are identified.

Author(s): J. -Ph. Jay F. Le Berre S. P. Pogossian M. V. Indenbom

Micro-Raman and resistance measurements of epitaxial La0.7Sr0.3MnO3 films

1999-06-23

The Channel-Spark method was used for deposition of highly oriented ferromagnetic La0.7Sr0.3MnO3 films on NdGaO3 substrates. It was found that additional oxygen decreases the film quality suppressing the Curie temperature and metal-insulator transition below the room temperature. To achieve the best quality of the films the samples were either annealed in high vacuum at deposition temperature or even deposited in argon atmosphere with no oxygen annealing. For such films the resistive measurements showed a metallic behaviour in the interval 10-300 K in accordance with the high Curie point (Tc 350 K). Micro-Raman analysis indicate that the La0.7Sr0.3MnO3 films are well ordered, while some outgrowths show stoichiometrical deviations.

Author(s): V. A. Dediu J. Lpez F. C. Matacotta P. Nozar G. Ruani R. Zamboni C. Taliani

Superconducting Mg-B films by pulsed laser deposition in an in-situ two-step process using multi-component targets

2001-03-26

Superconducting thin films have been prepared in a two-step in-situ process, using the Mg-B plasma generated by pulsed laser ablation. The target was composed of a mixture of Mg and MgB2 powders to compensate for the volatility of Mg and therefore to ensure a high Mg content in the film. The films were deposited at temperatures ranging from room temperature to 300 degrees C followed by a low-pressure in-situ annealing procedure. Various substrates have been used and diverse ways to increase the Mg content into the film were applied. The films show a sharp transition in the resistance and have a zero resistance transition temperature of 22-24 K.

Author(s): D. H. A. Blank H. Hilgenkamp A. Brinkman D. Mijatovic G. Rijnders H. Rogalla

Electrical Properties of Crystalline Ba0.5Sr0.5TiO3 Thin Films

2001-07-26

Thin Ba0.5Sr0.5TiO3 (BST) films on p-type Si (100) using The Chemical Solution Deposition (CSD) method. X-ray diffraction (XRD), Scanning electron microscopy (SEM), C-V meter analysis measurement were employed to characterise the films. The growth condition to obtain enough quality epitaxial of Ba0.5Sr0.5TiO3 carried out by spin coating at 3000 rpm for 30 seconds, and then annealing at 900oC for 15 hours. The structure and crystallinity of thin films were investigated by XRD preffered orientation (100), (010); (110), (111), (200), surface analysis by SEM magnification x10000 thin films were heterogen and thickness film 1100 nm; electrical characterization Ba0.5Sr0.5TiO3 at MFS (Metal Ferroelectric Semiconductor) structure in room temperature (300 K) by carried out capacitance flat band (CFB) for frequency 10 KHz and 100 KHz were 206 pF and 187 pF, dielectric constant for frequency 10 KHz and 100 KHz were 132.67 and 117.22, dielectric loss minimum for frequency 10 KHz and 100 KHz were 5.37 % and 6.43 % respectively.

Author(s): Irzaman H. Darmasetiawan M. Nur Indro S. G. Sukaryo M Hikam Na Peng Bo M. Barmawi

Thickness dependence of the properties of epitaxial MgB2 thin films grown by hybrid physical-chemical vapor deposition

2003-04-07

We have studied the effect of deposition rate and layer thickness on the properties of epitaxial MgB2 thin films grown by hybrid physical-chemical vapor deposition on 4H-SiC substrates. The MgB2 film deposition rate depends linearly on the concentration of B2H6 in the inlet gas mixture. We found that the superconducting and normal-state properties of the MgB2 films are determined by the film thickness, not by the deposition rate. When the film thickness was increased, the transition temperature, Tc, increased and the residual resistivity, rho0, decreased. Above about 300 nm, a Tc of 41.8 K, a rho0 of 0.28 mikroOhm.cm, and a residual resistance ratio RRR of over 30 were obtained. These values represent the best MgB2 properties reported thus far.

Author(s): A. V. Pogrebnyakov J. M. Redwing J. E. Jones X. X. Xi S. Y. Xu Q. Li V. Vaithyanathan D. G. Schlom

Electron and lattice structure of ultra thin Ag films on Si(111) and Si(001)

2007-08-30

We studied the low temperature (T<130K) growth of Ag on Si(001) and Si(111) flat surfaces prepared by Si homo epitaxy with the aim to achieve thin metallic films. The band structure and morphology of the Ag overlayers have been investigated by means of XPS, UPS, LEED, STM and STS. Surprisingly a (root3xroot3)R30^o LEED structure for Ag films has been observed after deposition of 2-6 ML Ag onto a Si(111)(root3xroot3)R30^o Ag surface at low temperatures. XPS investigations showed that these films are solid, and UPS measurements indicate that they are metallic. However, after closer STM studies we found that these films consists of sharp Ag islands and (root3xroot3)R30^o Ag flat terraces in between. On Si(001) the low-temperature deposition yields an epitaxial growth of Ag on clean Si(001)2x1 with a twinned Ag(111) structure at coverages as low as 10 ML. Furthermore the conductivity of few monolayer Ag films on Si(100) surfaces has been studied as a function of temperature (40-300 K).

Author(s): V. A. Gasparov M. Riehl-Chudoba

Photoinduced Magnetization in a Thin Fe-CN-Co Film

2003-04-17

The magnetization of a thin Fe-Co cyanide film has been investigated from 5 K to 300 K and in fields up to 500 G. Upon illumination with visible light, the magnetization of the film rapidly increases. The original cluster glass behavior is further developed in the photoinduced state and shows substantial changes in critical temperature and freezing temperature.

Author(s): J. -H. Park Y. D. Huh E. Čižmár S. J. Gamble D. R. Talham M. W. Meisel

Coexistence of Antiferromagnetism and Superconductivity in Electron-doped High-Tc Superconductors

2007-05-30

We present magnetotransport evidence for antiferromagnetism in films of the electron-doped cuprates Pr$_{2-x}$Ce$_x$CuO$_4$. Our results show clear signature of static antiferromagnetism up to optimal doping x=0.15, with a quantum phase transition close to x=0.16, and a coexistence of static antiferromagnetism and superconductivity for 0.12$\le$x$\le$0.15.

Author(s): W. Yu J. S. Higgins P. Bach R. L. Greene