Mariana Diaconu - Academia.edu (original) (raw)

Papers by Mariana Diaconu

Colloids and Surfaces A-physicochemical and Engineering Aspects, 2009

The ability of dried yeast Saccharomyces biomass to remove Cu(II) ions from aqueous solutions was... more The ability of dried yeast Saccharomyces biomass to remove Cu(II) ions from aqueous solutions was investigated by using of batch techniques. The influence of different parameters on copper uptake by dried yeast, such as initial Cu(II) concentration, initial pH of solution and temperature, was studied. The Freundlich, Langmuir, Redlich-Peterson and Sips isotherms were applied to the obtained experimental data. According to Langmuir isotherm the maximum adsorption capacity of investigated non-living biomass was found to be 2.59 mg/g. The thermodynamic parameters (e.g. free energy and enthalpy) were calculated and discussed. The adsorption of Cu(II) onto the dried cells of Saccharomyces cerevisiae is an endothermic process and become more favorable with the increasing of temperature in pH range from 3 to 4. Optimization studies by means of response surface methodology were carried out, which resulted in improvement of the efficiency of sorption removal by using of biomass. The removal efficiency of real wastewater originating from electroplating industry which contains Sn(II) ions was determined and compared with synthetic wastewater obtained in laboratory.

Colloids and Surfaces A-physicochemical and Engineering Aspects, 2009

The ability of dried yeast Saccharomyces biomass to remove Cu(II) ions from aqueous solutions was... more The ability of dried yeast Saccharomyces biomass to remove Cu(II) ions from aqueous solutions was investigated by using of batch techniques. The influence of different parameters on copper uptake by dried yeast, such as initial Cu(II) concentration, initial pH of solution and temperature, was studied. The Freundlich, Langmuir, Redlich-Peterson and Sips isotherms were applied to the obtained experimental data. According to Langmuir isotherm the maximum adsorption capacity of investigated non-living biomass was found to be 2.59 mg/g. The thermodynamic parameters (e.g. free energy and enthalpy) were calculated and discussed. The adsorption of Cu(II) onto the dried cells of Saccharomyces cerevisiae is an endothermic process and become more favorable with the increasing of temperature in pH range from 3 to 4. Optimization studies by means of response surface methodology were carried out, which resulted in improvement of the efficiency of sorption removal by using of biomass. The removal efficiency of real wastewater originating from electroplating industry which contains Sn(II) ions was determined and compared with synthetic wastewater obtained in laboratory.

Acta Crystallographica Section A, 2005

ABSTRACT The L7/L12 stalk of the large ribosomal subunit encompasses protein L10 and multiple cop... more ABSTRACT The L7/L12 stalk of the large ribosomal subunit encompasses protein L10 and multiple copies of L7/L12 and is involved in translation factor related functions. We have determined crystal structures of Thermotoga maritima L10 in complex with L7/L12 N-terminal domains and of an archaeal L10 N-terminal domain in situ on the 50S subunit. A mobile C-terminal α-helix of L10 harbors three consecutive binding sites for L7/L12 dimers in T. maritima and two in E. coli, where the helix is shorter. The N-terminal domain of L10 recognizes the overall fold of the thiostrepton loop of the 23S rRNA and interacts with L11. Together with structures of isolated L7/L12, we devised a complete atomic model of the stalk and reinterpreted the morphology and dynamics of the stalk region as seen in electron microscopic reconstructions of ribosomes. Flexible hinges in both L10 and L7/L12 lead to a high freedom of motion for the L7/L12 C-terminal domains. Our structural data and analysis of L7/L12 mutants by fast kinetics revealed that the L7/L12 C-terminal domains can reach far out into solution to bind translation factors. They thereby promote factor recruitment to the ribosome. The L7/L12 C-termini can then reach back towards ribosome-bound factors to stimulate GTP hydrolysis by stabilization of the factors’ GTPase conformation.

Acta Crystallographica Section A, 2005

ABSTRACT The L7/12 stalk of the large ribosomal subunit comprises protein L10 and multiple copies... more ABSTRACT The L7/12 stalk of the large ribosomal subunit comprises protein L10 and multiple copies of L7/12. It is involved in binding of translation factors and stimulation of factor-dependent GTP hydrolysis. The stalk is disordered in available crystal structures of ribosomes or 50S subunits. We have determined crystal structures of Thermotoga maritima L10 in complex with three L7/12 N-terminal domain (NTD) dimers. The structures are in agreement with a multitude of biochemical data. A globular NTD of L10 encompasses the binding region for 23S rRNA. A long C-terminal helix (alpha 8) of L10 shows a modular design with consecutive binding sites for L7/12 dimers. L10 helix alpha 8 assumes different positions with respect to the NTD in different crystal forms and thus constitutes a mobile platform for the attached L7/12 molecules. The number of L7/12 dimers varies with the length of L10 helix alpha 8 in different species. The structure of the L7/12 NTD dimers agrees with one mode of dimerization observed in isolated L7/12. The hinge region of L7/12 can bind in alpha-helical form to the NTD in isolation but is displaced by L10 upon complex formation and becomes disordered. The organization of the complex supports its function in factor recruitment and GTPase activation.

Acta Crystallographica Section A, 2005

ABSTRACT The L7/L12 stalk of the large ribosomal subunit encompasses protein L10 and multiple cop... more ABSTRACT The L7/L12 stalk of the large ribosomal subunit encompasses protein L10 and multiple copies of L7/L12 and is involved in translation factor related functions. We have determined crystal structures of Thermotoga maritima L10 in complex with L7/L12 N-terminal domains and of an archaeal L10 N-terminal domain in situ on the 50S subunit. A mobile C-terminal α-helix of L10 harbors three consecutive binding sites for L7/L12 dimers in T. maritima and two in E. coli, where the helix is shorter. The N-terminal domain of L10 recognizes the overall fold of the thiostrepton loop of the 23S rRNA and interacts with L11. Together with structures of isolated L7/L12, we devised a complete atomic model of the stalk and reinterpreted the morphology and dynamics of the stalk region as seen in electron microscopic reconstructions of ribosomes. Flexible hinges in both L10 and L7/L12 lead to a high freedom of motion for the L7/L12 C-terminal domains. Our structural data and analysis of L7/L12 mutants by fast kinetics revealed that the L7/L12 C-terminal domains can reach far out into solution to bind translation factors. They thereby promote factor recruitment to the ribosome. The L7/L12 C-termini can then reach back towards ribosome-bound factors to stimulate GTP hydrolysis by stabilization of the factors’ GTPase conformation.

Acta Crystallographica Section A, 2005

ABSTRACT The L7/12 stalk of the large ribosomal subunit comprises protein L10 and multiple copies... more ABSTRACT The L7/12 stalk of the large ribosomal subunit comprises protein L10 and multiple copies of L7/12. It is involved in binding of translation factors and stimulation of factor-dependent GTP hydrolysis. The stalk is disordered in available crystal structures of ribosomes or 50S subunits. We have determined crystal structures of Thermotoga maritima L10 in complex with three L7/12 N-terminal domain (NTD) dimers. The structures are in agreement with a multitude of biochemical data. A globular NTD of L10 encompasses the binding region for 23S rRNA. A long C-terminal helix (alpha 8) of L10 shows a modular design with consecutive binding sites for L7/12 dimers. L10 helix alpha 8 assumes different positions with respect to the NTD in different crystal forms and thus constitutes a mobile platform for the attached L7/12 molecules. The number of L7/12 dimers varies with the length of L10 helix alpha 8 in different species. The structure of the L7/12 NTD dimers agrees with one mode of dimerization observed in isolated L7/12. The hinge region of L7/12 can bind in alpha-helical form to the NTD in isolation but is displaced by L10 upon complex formation and becomes disordered. The organization of the complex supports its function in factor recruitment and GTPase activation.

Mikrochimica Acta, 2006

We report on the high-pressure pulsed laser deposition growth of zinc oxide nanowires containing ... more We report on the high-pressure pulsed laser deposition growth of zinc oxide nanowires containing about 0.2 at.% Co and 0.5 at.% Mn by NiO and Au catalyst. Scanning electron microscopy and X-ray diffraction measurements revealed arrays of parallel-standing nanowires with hexagonal cross section and uniform in-plane epitaxial relations without rotational domains. Elemental analysis was carried out using particle induced X-ray emission and Q-band electron spin resonance. The valence of the incorporated Mn was determined to be 2+. Atomic and magnetic force microscopy measurements indicate that Mn is incorporated preferentially at the nanowire boundaries.

Physical Review B, 2005

X-band electron paramagnetic resonance spectra were recorded for Zn 1− x Mn x O films grown by pu... more X-band electron paramagnetic resonance spectra were recorded for Zn 1− x Mn x O films grown by pulsed laser deposition and a single crystal for comparison. For different Mn concentrations in Zn 1− x Mn x O films we performed measurements in dependence on ...

Solid State Communications, 2006

The ferromagnetism in highly transparent and intrinsically n-type conducting zinc oxide doped wit... more The ferromagnetism in highly transparent and intrinsically n-type conducting zinc oxide doped with 3d transition metals (TM), is predicted to be defect mediated. We investigate the generation of deep defects in n-conducting 1 mm thick ZnO:TM films (TMZCo, Mn, Ti) with a nominal TM content of 0.02, 0.20 and 2.00 at.% grown by pulsed laser deposition on a-plane sapphire substrates using deep level transient spectroscopy. We find that a defect level is generated, independent of the TM content, located 0.31 and 0.27 eV below the conduction band minimum of ZnO:Mn and ZnO:Ti, respectively. Different defect levels are generated in dependence on the Co content in ZnO:Co. This work shows that an optimization of defect-related ferromagnetism in n-conducting ZnO:TM thin films will only be possible if the preparation sensitive formation of deep defects is controlled in the same time. q

Physics Letters A, 2006

We present magnetic properties of Zn(Mn, P)O thin films, with 5 at% Mn, epitaxially grown by puls... more We present magnetic properties of Zn(Mn, P)O thin films, with 5 at% Mn, epitaxially grown by pulsed laser deposition in oxygen atmosphere on a-plane sapphire substrates. Ferromagnetism above room temperature was obtained for films with 0.1 at% P, grown at around 600 • C. Temperaturedependent magnetization curves indicate the presence of an antiferromagnetic coupling between the Mn magnetic moments. After annealing ferromagnetic films for 2 hours at 800 • C in N 2 atmosphere, they became paramagnetic at all temperatures.

Superlattices and Microstructures, 2005

Diluted magnetic semiconductors (DMS), systems formed by replacing cations of the host semiconduc... more Diluted magnetic semiconductors (DMS), systems formed by replacing cations of the host semiconductor material with transition-metal ions, are developed for further use in spintronics. A good combination as a DMS is Zn1−xMnxO due to the ZnO wide band gap (3.37 eV) and the matching ionic radii of Mn2+ and Zn2+. Using electron paramagnetic resonance we determined the valence of Mn ions

Superlattices and Microstructures, 2006

Superlattices and Microstructures, 2006

Room-temperature ferromagnetic Zn1−x(TM)xO semiconductor thin films have been grown by pulsed las... more Room-temperature ferromagnetic Zn1−x(TM)xO semiconductor thin films have been grown by pulsed laser deposition (PLD) on c-plane sapphire substrates and the effect of the substitution of Zn2+ ions by transition metal ions (Mn2+ or Ti2+) has been investigated. In contrast to ZnTiO thin films, the grain size of the ZnMnO thin films can be controlled in a wide range by the

Superlattices and Microstructures, 2005

Diluted magnetic semiconductors (DMS), systems formed by replacing cations of the host semiconduc... more Diluted magnetic semiconductors (DMS), systems formed by replacing cations of the host semiconductor material with transition-metal ions, are developed for further use in spintronics. A good combination as a DMS is Zn1−xMnxO due to the ZnO wide band gap (3.37 eV) and the matching ionic radii of Mn2+ and Zn2+. Using electron paramagnetic resonance we determined the valence of Mn ions

Thin Solid Films, 2005

Epitaxial ZnO thin films were grown by pulsed laser deposition (PLD) in N 2 or N 2 O or O 2 backg... more Epitaxial ZnO thin films were grown by pulsed laser deposition (PLD) in N 2 or N 2 O or O 2 background gas on MgO-buffered a-plane sapphire. The excitonic room-temperature cathodoluminescence (CL) intensity, the carrier concentration and the Hall mobility showed welldefined maxima for films grown at PLD gas pressures of ca. 1 mbar N 2 , N 2 O, and O 2 . However, despite the comparable high CL intensities of the ZnO films grown in the three different background gases, their surface roughness varied considerably. Films with rough surface showed a broadening and splitting of the room-temperature CL peak into maxima at 3.21 and 3.26 eV, which could be due to either grain morphology or spatial variation of the electronic defect structure. D

Thin Solid Films, 2005

The incorporation of 3d transition metals into ZnO can produce ferromagnetism above room temperat... more The incorporation of 3d transition metals into ZnO can produce ferromagnetism above room temperature. For Mn-doped ZnO films grown at low temperatures around 500 8C by pulsed laser deposition, the ferromagnetic behavior is correlated to their textured structure. For optimized films showing homogeneous magnetic domain formation in magnetic force microscopy, the saturation magnetization and coercive field strength amount to 0.013 emu/g and 234 Oe at 300 K, respectively. Compared to undoped ZnO films, the luminescence of Mn-doped ZnO films is strongly quenched. However, luminescence can be observed around antiferromagnetic MnO or MnO 2 clusters that crystallize during the growth process on the film surface. D

Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2006

In this study, ferromagnetic microstructures in highly oriented pyrolytic graphite and superparam... more In this study, ferromagnetic microstructures in highly oriented pyrolytic graphite and superparamagnetic spots in polyimide foils were created by 2.25 MeV proton microbeam irradiation and characterized using atomic and magnetic force microscopy. For this purpose, graphite samples were irradiated with cross-like patterns of 15 lm · 15 lm size using ion fluences in the range of (0.003-2.5) · 10 18 cm À2 . The irradiated crosses showed strong magnetic signals and a complex domain structure in the magnetic images depending on the geometrical dimensions of the crosses. Furthermore, polyimide foils were irradiated with microspots and fluences in the range of (0.016-3.1) · 10 19 cm À2 . Magnetic force microscopy shows very strong phase shifts in these irradiated areas.

Journal of Magnetism and Magnetic Materials, 2006

Ferromagnetic, semi-insulating Mn-alloyed ZnO films with a Curie temperature above 375K have been... more Ferromagnetic, semi-insulating Mn-alloyed ZnO films with a Curie temperature above 375K have been grown by pulsed laser deposition on c-plane sapphire substrates. Antiferromagnetic coupling is revealed by temperature-dependent magnetization measurements. The antiferromagnetic coupling would be compatible with the observed weak ferromagnetism by assuming that the magnetic moments order antiferromagnetically but nonparallel (canted). We find a clear correlation between coercivity and

In this chapter we review the magnetic effects produced by proton irradiation on graphite, disord... more In this chapter we review the magnetic effects produced by proton irradiation on graphite, disordered carbon and fullerene films. The advantage of proton irradiation is twofold: it enables us to make an impurity analysis simultaneously to the implantation of hydrogen. In this chapter we will review the main effects obtained after proton irradiation in different carbon-based structures. This chapter is organized as follows. In section 2 we provide the main characteristics of our irradiation facility. In this section we show an example of element analysis obtained in one of the graphite samples used for the irradiation studies. The irradiation effects are reviewed in section 3. This section is divided in two main subsections that describe the effects in oriented graphite and carbon-based thin films. In section 4 we discuss some of the effects observed after annealing the sample at high temperatures in vacuum or after leaving it at room temperature for a long period of time.

Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2005

ABSTRACT In this study ferromagnetic microstructures in highly oriented pyrolytic graphite (HOPG)... more ABSTRACT In this study ferromagnetic microstructures in highly oriented pyrolytic graphite (HOPG) were created by 2.25 MeV proton microbeam irradiation and characterized using AFM/MFM and SQUID measurements. For this purpose, spots of 1.8 × 1.8 μm2 size as well as cross-like patterns of 15 μm × 15 μm size were irradiated with different ion doses. Furthermore, arrays of 600 μm × 600 μm size containing 100 × 100 micro-spots were produced with ion doses of ∼0.3 nC/μm2. As calculated by SRIM2003 simulations, the corresponding defect densities in the near surface region are between 3 × 1018 cm−3 and 1 × 1021 cm−3 for the range of ion doses used. The irradiated crosses showed strong magnetic signals and a complex domain structure in the MFM images. SQUID measurements on a HOPG sample successively irradiated with micro-spots arrays showed that the irradiation increased the magnetic moment of the sample up to ∼0.6 × 10−5 emu and the remanent magnetization Mr(B = 0) up to 4.5 × 10−4 emu/g. However, annealing effects during irradiation have to be carefully taken into account as they can result in a complete loss of the magnetic ordering in the irradiated areas.

Colloids and Surfaces A-physicochemical and Engineering Aspects, 2009

The ability of dried yeast Saccharomyces biomass to remove Cu(II) ions from aqueous solutions was... more The ability of dried yeast Saccharomyces biomass to remove Cu(II) ions from aqueous solutions was investigated by using of batch techniques. The influence of different parameters on copper uptake by dried yeast, such as initial Cu(II) concentration, initial pH of solution and temperature, was studied. The Freundlich, Langmuir, Redlich-Peterson and Sips isotherms were applied to the obtained experimental data. According to Langmuir isotherm the maximum adsorption capacity of investigated non-living biomass was found to be 2.59 mg/g. The thermodynamic parameters (e.g. free energy and enthalpy) were calculated and discussed. The adsorption of Cu(II) onto the dried cells of Saccharomyces cerevisiae is an endothermic process and become more favorable with the increasing of temperature in pH range from 3 to 4. Optimization studies by means of response surface methodology were carried out, which resulted in improvement of the efficiency of sorption removal by using of biomass. The removal efficiency of real wastewater originating from electroplating industry which contains Sn(II) ions was determined and compared with synthetic wastewater obtained in laboratory.

Colloids and Surfaces A-physicochemical and Engineering Aspects, 2009

The ability of dried yeast Saccharomyces biomass to remove Cu(II) ions from aqueous solutions was... more The ability of dried yeast Saccharomyces biomass to remove Cu(II) ions from aqueous solutions was investigated by using of batch techniques. The influence of different parameters on copper uptake by dried yeast, such as initial Cu(II) concentration, initial pH of solution and temperature, was studied. The Freundlich, Langmuir, Redlich-Peterson and Sips isotherms were applied to the obtained experimental data. According to Langmuir isotherm the maximum adsorption capacity of investigated non-living biomass was found to be 2.59 mg/g. The thermodynamic parameters (e.g. free energy and enthalpy) were calculated and discussed. The adsorption of Cu(II) onto the dried cells of Saccharomyces cerevisiae is an endothermic process and become more favorable with the increasing of temperature in pH range from 3 to 4. Optimization studies by means of response surface methodology were carried out, which resulted in improvement of the efficiency of sorption removal by using of biomass. The removal efficiency of real wastewater originating from electroplating industry which contains Sn(II) ions was determined and compared with synthetic wastewater obtained in laboratory.

Acta Crystallographica Section A, 2005

ABSTRACT The L7/L12 stalk of the large ribosomal subunit encompasses protein L10 and multiple cop... more ABSTRACT The L7/L12 stalk of the large ribosomal subunit encompasses protein L10 and multiple copies of L7/L12 and is involved in translation factor related functions. We have determined crystal structures of Thermotoga maritima L10 in complex with L7/L12 N-terminal domains and of an archaeal L10 N-terminal domain in situ on the 50S subunit. A mobile C-terminal α-helix of L10 harbors three consecutive binding sites for L7/L12 dimers in T. maritima and two in E. coli, where the helix is shorter. The N-terminal domain of L10 recognizes the overall fold of the thiostrepton loop of the 23S rRNA and interacts with L11. Together with structures of isolated L7/L12, we devised a complete atomic model of the stalk and reinterpreted the morphology and dynamics of the stalk region as seen in electron microscopic reconstructions of ribosomes. Flexible hinges in both L10 and L7/L12 lead to a high freedom of motion for the L7/L12 C-terminal domains. Our structural data and analysis of L7/L12 mutants by fast kinetics revealed that the L7/L12 C-terminal domains can reach far out into solution to bind translation factors. They thereby promote factor recruitment to the ribosome. The L7/L12 C-termini can then reach back towards ribosome-bound factors to stimulate GTP hydrolysis by stabilization of the factors’ GTPase conformation.

Acta Crystallographica Section A, 2005

ABSTRACT The L7/12 stalk of the large ribosomal subunit comprises protein L10 and multiple copies... more ABSTRACT The L7/12 stalk of the large ribosomal subunit comprises protein L10 and multiple copies of L7/12. It is involved in binding of translation factors and stimulation of factor-dependent GTP hydrolysis. The stalk is disordered in available crystal structures of ribosomes or 50S subunits. We have determined crystal structures of Thermotoga maritima L10 in complex with three L7/12 N-terminal domain (NTD) dimers. The structures are in agreement with a multitude of biochemical data. A globular NTD of L10 encompasses the binding region for 23S rRNA. A long C-terminal helix (alpha 8) of L10 shows a modular design with consecutive binding sites for L7/12 dimers. L10 helix alpha 8 assumes different positions with respect to the NTD in different crystal forms and thus constitutes a mobile platform for the attached L7/12 molecules. The number of L7/12 dimers varies with the length of L10 helix alpha 8 in different species. The structure of the L7/12 NTD dimers agrees with one mode of dimerization observed in isolated L7/12. The hinge region of L7/12 can bind in alpha-helical form to the NTD in isolation but is displaced by L10 upon complex formation and becomes disordered. The organization of the complex supports its function in factor recruitment and GTPase activation.

Acta Crystallographica Section A, 2005

ABSTRACT The L7/L12 stalk of the large ribosomal subunit encompasses protein L10 and multiple cop... more ABSTRACT The L7/L12 stalk of the large ribosomal subunit encompasses protein L10 and multiple copies of L7/L12 and is involved in translation factor related functions. We have determined crystal structures of Thermotoga maritima L10 in complex with L7/L12 N-terminal domains and of an archaeal L10 N-terminal domain in situ on the 50S subunit. A mobile C-terminal α-helix of L10 harbors three consecutive binding sites for L7/L12 dimers in T. maritima and two in E. coli, where the helix is shorter. The N-terminal domain of L10 recognizes the overall fold of the thiostrepton loop of the 23S rRNA and interacts with L11. Together with structures of isolated L7/L12, we devised a complete atomic model of the stalk and reinterpreted the morphology and dynamics of the stalk region as seen in electron microscopic reconstructions of ribosomes. Flexible hinges in both L10 and L7/L12 lead to a high freedom of motion for the L7/L12 C-terminal domains. Our structural data and analysis of L7/L12 mutants by fast kinetics revealed that the L7/L12 C-terminal domains can reach far out into solution to bind translation factors. They thereby promote factor recruitment to the ribosome. The L7/L12 C-termini can then reach back towards ribosome-bound factors to stimulate GTP hydrolysis by stabilization of the factors’ GTPase conformation.

Acta Crystallographica Section A, 2005

ABSTRACT The L7/12 stalk of the large ribosomal subunit comprises protein L10 and multiple copies... more ABSTRACT The L7/12 stalk of the large ribosomal subunit comprises protein L10 and multiple copies of L7/12. It is involved in binding of translation factors and stimulation of factor-dependent GTP hydrolysis. The stalk is disordered in available crystal structures of ribosomes or 50S subunits. We have determined crystal structures of Thermotoga maritima L10 in complex with three L7/12 N-terminal domain (NTD) dimers. The structures are in agreement with a multitude of biochemical data. A globular NTD of L10 encompasses the binding region for 23S rRNA. A long C-terminal helix (alpha 8) of L10 shows a modular design with consecutive binding sites for L7/12 dimers. L10 helix alpha 8 assumes different positions with respect to the NTD in different crystal forms and thus constitutes a mobile platform for the attached L7/12 molecules. The number of L7/12 dimers varies with the length of L10 helix alpha 8 in different species. The structure of the L7/12 NTD dimers agrees with one mode of dimerization observed in isolated L7/12. The hinge region of L7/12 can bind in alpha-helical form to the NTD in isolation but is displaced by L10 upon complex formation and becomes disordered. The organization of the complex supports its function in factor recruitment and GTPase activation.

Mikrochimica Acta, 2006

We report on the high-pressure pulsed laser deposition growth of zinc oxide nanowires containing ... more We report on the high-pressure pulsed laser deposition growth of zinc oxide nanowires containing about 0.2 at.% Co and 0.5 at.% Mn by NiO and Au catalyst. Scanning electron microscopy and X-ray diffraction measurements revealed arrays of parallel-standing nanowires with hexagonal cross section and uniform in-plane epitaxial relations without rotational domains. Elemental analysis was carried out using particle induced X-ray emission and Q-band electron spin resonance. The valence of the incorporated Mn was determined to be 2+. Atomic and magnetic force microscopy measurements indicate that Mn is incorporated preferentially at the nanowire boundaries.

Physical Review B, 2005

X-band electron paramagnetic resonance spectra were recorded for Zn 1− x Mn x O films grown by pu... more X-band electron paramagnetic resonance spectra were recorded for Zn 1− x Mn x O films grown by pulsed laser deposition and a single crystal for comparison. For different Mn concentrations in Zn 1− x Mn x O films we performed measurements in dependence on ...

Solid State Communications, 2006

The ferromagnetism in highly transparent and intrinsically n-type conducting zinc oxide doped wit... more The ferromagnetism in highly transparent and intrinsically n-type conducting zinc oxide doped with 3d transition metals (TM), is predicted to be defect mediated. We investigate the generation of deep defects in n-conducting 1 mm thick ZnO:TM films (TMZCo, Mn, Ti) with a nominal TM content of 0.02, 0.20 and 2.00 at.% grown by pulsed laser deposition on a-plane sapphire substrates using deep level transient spectroscopy. We find that a defect level is generated, independent of the TM content, located 0.31 and 0.27 eV below the conduction band minimum of ZnO:Mn and ZnO:Ti, respectively. Different defect levels are generated in dependence on the Co content in ZnO:Co. This work shows that an optimization of defect-related ferromagnetism in n-conducting ZnO:TM thin films will only be possible if the preparation sensitive formation of deep defects is controlled in the same time. q

Physics Letters A, 2006

We present magnetic properties of Zn(Mn, P)O thin films, with 5 at% Mn, epitaxially grown by puls... more We present magnetic properties of Zn(Mn, P)O thin films, with 5 at% Mn, epitaxially grown by pulsed laser deposition in oxygen atmosphere on a-plane sapphire substrates. Ferromagnetism above room temperature was obtained for films with 0.1 at% P, grown at around 600 • C. Temperaturedependent magnetization curves indicate the presence of an antiferromagnetic coupling between the Mn magnetic moments. After annealing ferromagnetic films for 2 hours at 800 • C in N 2 atmosphere, they became paramagnetic at all temperatures.

Superlattices and Microstructures, 2005

Diluted magnetic semiconductors (DMS), systems formed by replacing cations of the host semiconduc... more Diluted magnetic semiconductors (DMS), systems formed by replacing cations of the host semiconductor material with transition-metal ions, are developed for further use in spintronics. A good combination as a DMS is Zn1−xMnxO due to the ZnO wide band gap (3.37 eV) and the matching ionic radii of Mn2+ and Zn2+. Using electron paramagnetic resonance we determined the valence of Mn ions

Superlattices and Microstructures, 2006

Superlattices and Microstructures, 2006

Room-temperature ferromagnetic Zn1−x(TM)xO semiconductor thin films have been grown by pulsed las... more Room-temperature ferromagnetic Zn1−x(TM)xO semiconductor thin films have been grown by pulsed laser deposition (PLD) on c-plane sapphire substrates and the effect of the substitution of Zn2+ ions by transition metal ions (Mn2+ or Ti2+) has been investigated. In contrast to ZnTiO thin films, the grain size of the ZnMnO thin films can be controlled in a wide range by the

Superlattices and Microstructures, 2005

Diluted magnetic semiconductors (DMS), systems formed by replacing cations of the host semiconduc... more Diluted magnetic semiconductors (DMS), systems formed by replacing cations of the host semiconductor material with transition-metal ions, are developed for further use in spintronics. A good combination as a DMS is Zn1−xMnxO due to the ZnO wide band gap (3.37 eV) and the matching ionic radii of Mn2+ and Zn2+. Using electron paramagnetic resonance we determined the valence of Mn ions

Thin Solid Films, 2005

Epitaxial ZnO thin films were grown by pulsed laser deposition (PLD) in N 2 or N 2 O or O 2 backg... more Epitaxial ZnO thin films were grown by pulsed laser deposition (PLD) in N 2 or N 2 O or O 2 background gas on MgO-buffered a-plane sapphire. The excitonic room-temperature cathodoluminescence (CL) intensity, the carrier concentration and the Hall mobility showed welldefined maxima for films grown at PLD gas pressures of ca. 1 mbar N 2 , N 2 O, and O 2 . However, despite the comparable high CL intensities of the ZnO films grown in the three different background gases, their surface roughness varied considerably. Films with rough surface showed a broadening and splitting of the room-temperature CL peak into maxima at 3.21 and 3.26 eV, which could be due to either grain morphology or spatial variation of the electronic defect structure. D

Thin Solid Films, 2005

The incorporation of 3d transition metals into ZnO can produce ferromagnetism above room temperat... more The incorporation of 3d transition metals into ZnO can produce ferromagnetism above room temperature. For Mn-doped ZnO films grown at low temperatures around 500 8C by pulsed laser deposition, the ferromagnetic behavior is correlated to their textured structure. For optimized films showing homogeneous magnetic domain formation in magnetic force microscopy, the saturation magnetization and coercive field strength amount to 0.013 emu/g and 234 Oe at 300 K, respectively. Compared to undoped ZnO films, the luminescence of Mn-doped ZnO films is strongly quenched. However, luminescence can be observed around antiferromagnetic MnO or MnO 2 clusters that crystallize during the growth process on the film surface. D

Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2006

In this study, ferromagnetic microstructures in highly oriented pyrolytic graphite and superparam... more In this study, ferromagnetic microstructures in highly oriented pyrolytic graphite and superparamagnetic spots in polyimide foils were created by 2.25 MeV proton microbeam irradiation and characterized using atomic and magnetic force microscopy. For this purpose, graphite samples were irradiated with cross-like patterns of 15 lm · 15 lm size using ion fluences in the range of (0.003-2.5) · 10 18 cm À2 . The irradiated crosses showed strong magnetic signals and a complex domain structure in the magnetic images depending on the geometrical dimensions of the crosses. Furthermore, polyimide foils were irradiated with microspots and fluences in the range of (0.016-3.1) · 10 19 cm À2 . Magnetic force microscopy shows very strong phase shifts in these irradiated areas.

Journal of Magnetism and Magnetic Materials, 2006

Ferromagnetic, semi-insulating Mn-alloyed ZnO films with a Curie temperature above 375K have been... more Ferromagnetic, semi-insulating Mn-alloyed ZnO films with a Curie temperature above 375K have been grown by pulsed laser deposition on c-plane sapphire substrates. Antiferromagnetic coupling is revealed by temperature-dependent magnetization measurements. The antiferromagnetic coupling would be compatible with the observed weak ferromagnetism by assuming that the magnetic moments order antiferromagnetically but nonparallel (canted). We find a clear correlation between coercivity and

In this chapter we review the magnetic effects produced by proton irradiation on graphite, disord... more In this chapter we review the magnetic effects produced by proton irradiation on graphite, disordered carbon and fullerene films. The advantage of proton irradiation is twofold: it enables us to make an impurity analysis simultaneously to the implantation of hydrogen. In this chapter we will review the main effects obtained after proton irradiation in different carbon-based structures. This chapter is organized as follows. In section 2 we provide the main characteristics of our irradiation facility. In this section we show an example of element analysis obtained in one of the graphite samples used for the irradiation studies. The irradiation effects are reviewed in section 3. This section is divided in two main subsections that describe the effects in oriented graphite and carbon-based thin films. In section 4 we discuss some of the effects observed after annealing the sample at high temperatures in vacuum or after leaving it at room temperature for a long period of time.

Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2005

ABSTRACT In this study ferromagnetic microstructures in highly oriented pyrolytic graphite (HOPG)... more ABSTRACT In this study ferromagnetic microstructures in highly oriented pyrolytic graphite (HOPG) were created by 2.25 MeV proton microbeam irradiation and characterized using AFM/MFM and SQUID measurements. For this purpose, spots of 1.8 × 1.8 μm2 size as well as cross-like patterns of 15 μm × 15 μm size were irradiated with different ion doses. Furthermore, arrays of 600 μm × 600 μm size containing 100 × 100 micro-spots were produced with ion doses of ∼0.3 nC/μm2. As calculated by SRIM2003 simulations, the corresponding defect densities in the near surface region are between 3 × 1018 cm−3 and 1 × 1021 cm−3 for the range of ion doses used. The irradiated crosses showed strong magnetic signals and a complex domain structure in the MFM images. SQUID measurements on a HOPG sample successively irradiated with micro-spots arrays showed that the irradiation increased the magnetic moment of the sample up to ∼0.6 × 10−5 emu and the remanent magnetization Mr(B = 0) up to 4.5 × 10−4 emu/g. However, annealing effects during irradiation have to be carefully taken into account as they can result in a complete loss of the magnetic ordering in the irradiated areas.