The structure and magnetism of ultrathin Mn layers grown by molecular beam epitaxy (MBE) on Si(001) are investigated. X-ray absorption fine structure (XAFS) shows that a metastable MnSi phase with a B2-like (CsCl) crystal structure forms and superconducting quantum interference device (SQUID) magnetometry measurements reveal that the B2 structure is ferromagnetic with a Mn moment of 0.33 µB and a Curie temperature TC > 400 K. A change in the Si capping layer growth temperature, TSi, produces a MnSi phase with a B20-like structure, which exhibits a small moment and a TC below 20 K. Surfactant mediated growth of Mn ?-doped Si films and co-deposited Si1-xMnx alloys shows that a Pb surfactant strongly alters the structure and magnetism of these systems. For the ?-doped films, analysis of the crystal structure and magnetic properties over a range of growth parameters identified three distinct Mn-Si phases. With Pb, a sample with a coverage ?Mn = 0.26 monolayer and TSi = 200 ºC develops a ferromagnetic phase with a Mn moment of 1.56 µB and a TC > 400 K, whereas TC drops to zero for a sample grown without Pb. For TSi > 200 ºC, nano-disks with MnSi-B20 type structure form with a TC ? 170 K. A possible correlation exists between the remanent moment and the fraction of Mn occupying Si substitutional sites, which suggests that a dilute Si1-xMnx may be forming in the matrix. Density functional theory (DFT) shows that Pb lowers the formation energy of Si vacancies by 0.92 eV, which enhances the substitutional incorporation of Mn. In the absence of Pb, the co-deposited Si1-xMnx films undergo a 2D spinodal decomposition and form nanocolumns. The nanocolumns are amorphous and paramagnetic. In contrast, in the samples grown with Pb, MnSi1.7 nanorods form in the plane of the films and exhibit two ferromagnetic transitions at TC1 ? 40 K and TC2 > 400 K when x = 0.5%. While TC1 is consistent with TC of bulk MnSi1.7 crystals, TC2 is believed to originate from Mn diluted in the Si matrix.

During the Arctic summer when the anthropogenic influence is limited, the natural marine source of sulfur in the form of gas-phase dimethyl sulfide viz. DMS(g), is of great importance for cloud formation. The harsh environment of the Arctic makes it difficult to perform in situ measurements of DMS(g) and hence regional model simulations can serve as a complement to increase our understanding of DMS related processes in the Arctic. In this thesis a regional scale meteorological forecast model, extended with DMS(g) calculations, is used to provide a consistent three-dimensional time evolving picture of DMS(g) over the pack-ice region. The analysis focus on meteorological aspects on the horizontal and vertical distribution of DMS(g). Our results show that the amount of DMS(g) over an oceanic source region alone does not determine concentration found over the pack-ice, the prevailing wind also exerts a large influence on the horizontal DMS(g) distribution. The modeled DMS(g) concentrations are advected in plumes in over the pack-ice, which, in combination with the photo-chemical decay, explain the large observed temporal variability of DMS(g) over the pack-ice. The modeled vertical structure show episodes with DMS(g) maxima well above the local boundary layer. Also shown is that DMS(g) maxima can be formed adjacent to frontal zones. In the presence of turbulence DMS(g) can be mixed downwards into the local boundary layer and aid growth to local particles and hence contribute to cloud formation in the boundary layer. / At the time of the doctoral defense the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 2: Manuscript. Paper 4: Manuscript.

Sulfur-containing organic solvents or carbon disulfide have been used extensively in semiconductor, TFT-LCD, and synthetic fiber (viscous rayon) industries in the last decades. These compounds can easily be converted into reduced-sulfur ones which exhibit low odor threshold characteristics and arise public complaints once releasing into environments. This paper intended to oxide these compounds by both chemical and biological approaches for the purpose of odor reduction. The first topic was investigations on the oxidation of aqueous DMS (dimethyl sulfide) by using sodium hypochlorite as an oxidant. Results indicated that with an initial DMS concentration of 100 mg/L, it required only 0.75 min or 45 s to convert the DMS completely into its final oxidation product, DMSO2 (dimethyl sulfur dioxide). The required dosage of the oxidant was a little less than the theoretical value. In addition, it was found that initial pH of the batch reaction liquid be kept at around 8.2 for achieving a neutral final solution which emitted only a trace of gaseous chlorine and hydrochloric acid odors. The second one was a trail investigation on the biodegradation of gas-borne hydrogen sulfide and carbon disulfide by a trickling-bed biofilter packed solely with fern chips. Glucose and milk powder were used as main nutrients for microbial film development and enhancer for the biodegradation of sulfides. Results indicated that after an acclimation period of around two months, approximately 99 and 86% of the influent hydrogen sulfide (10-20 ppm) and carbon disulfide (20-60 ppm), respectively, could be removed with an empty bed retention time of around 63 s for the gas in the packed bed. Both neutral or acidic environments were suitable for the biodegradation reaction and the metabolites (mainly, sulfuric acid) could easily be removed from the chips by washing them with water. In the future, efforts should be done to increase the removal capacity of carbon disulfide.

No description available.

In this work, Mn atoms are doped into GaN nanorods by two doping types, homogeneous and delta doping, and GaN nanorods are grown on Si (111) substrate using plasma-assisted MBE. The GaMnN nanorods are characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), high-resolution x-ray diffraction (HR-XRD), Raman scattering, Transmission electron microscopy (TEM), superconducting quantum interference device (SQUID), and x-ray photoelectron spectroscopy (XPS). The Mn delta-doping GaN nanorods with Ga/Mn growth time ratio 20 are approximately 1500 nm in height, grown along the c-axis. The Mn concentration in nanorods is determined to be 0.83% by EDS, without secondary phase formation. The Mn atoms substitute Ga sites in the GaN wurtzite hexagonal structure and, according to the results of Raman, there is no observable Mn-N cluster formation existed. The delta-doping structure, without secondary phase inclusions, can be observed under TEM imaging of the nanorods. The nanorods appear to show ferromagnetic behavior at room temperature, as judged by the M-H with hysteresis curve, however the small the loops are. The delta-doping is adopted in this thesis work to fabricate GaMnN DMS nanorods without secondary phase formation.

This diploma thesis is focused to design, implementation and deployment of a Document Management System in company Xterway, a.s. Thesis is divided into four parts. The first part contains theoretical background necessary for realization. Analysis of current state of the company and its information system is provided in the second part. The last part is dedicated to realization itself followed by an assessment of the achieved results. The new system should simplify work for employees and reduce maintenance costs.

In this work, we have utilized an ion beam process known as gettering to migrate implanted Ni ions much deeper into the bulk substrate than their initial projected end of the range. The projected mean depth is known as Rp. The gettering effect is the most crucial part of the fabrication and we have found that for an H fluence of 3x 1016 cm-2 there is a threshold fluence of approximately 7.5 x 1015 cm-2 that cannot be surpassed if the gettering process is to be completed along with the substrate recovered to the high crystalline quality. This hard threshold is due to the gettering process relaxation induced mechanism that is responsible for migrating the Ni to the Rp/2 location while the H is vacating during the thermal annealing process. If the total number of vacancies produced by the H dissociation is not substantially larger than the total number of implanted Ni atoms the Ni will migrate to the Rp location of the Ni implantation at the amorphous and crystalline interface and toward the surface. When the gettering condition is not met the resulting magnetic responses vary from an exceptionally weak ferromagnetic response to not exhibiting a magnetic response. Additionally, conducting the ion implantation at an elevated substrate temperature does not increase the threshold Ni fluence above our established limit. During the elevated substrate temperature implantation, the hydrogen ions diffuse out to the surface resulting in less migration of the Ni to the initial Rp location within the Ni implantation region. The elevated temperature implantation condition appears to not create a sharp amorphous crystalline interface at the end of the range for the Ni implantation.

Le travail sur le ZnO:Co rapporté dans ce manuscrit, donne une meilleure compréhension des interactions d'échange dans ce composé. La question des interactions spin-spin dans les DMS est abordée à la fois sur le plan théorique et expérimental. Du point de vue théorique, le modèle du superéchange d'Anderson a été utilisé et étendu, afin d'obtenir les valeurs des constantes d'échange sur l'ensemble de la série des DMS II-VI dopés Mn ou Co. Du point de vue expérimental, la combinaison inédite de trois méthodes expérimentales, la diffusion inélastique de neutrons (ou INS), la résonance paramagnétique électronique (ou EPR), et la méthode de mesure des marches d'aimantation sous champ magnétique intense (ou méthode MST), a permis d'établir, pour la première fois, la valeur des dix plus grandes constantes d'échange du ZnO:Co.Les observations faites par INS permettent de mettre en évidence de façon directe une très forte anisotropie spatiale concernant l'intégrale d'échange des premiers voisins. On établit ainsi J(1)=-25,6K et J(2)=-8,5K, correspondant respectivement à la paire des premiers voisins dans le plan (ab), et à la paire des premeirs voisins hors de ce plan. Ce résultat s'explique, en partie, par la présence dans la structure wurtzite d'une contribution ferromagnétique dans le calcul du superéchange, issue d'un chemin formant une boucle et faisant intervenir deux anions distincts.Les mesures effectuées par EPR et par MST permettent d'établir les constantes d'échange entre voisins à plus grande distance. Ainsi, on obtient: J(3)=-1,07K , J(4)=-0,38K , J(5)=0,35K , J(6)=0,17K , J(7)=-0,16K , J(8)=-0,04K , J(9)=-0,03K , |J(10)|=0,013K. / The work performed on ZnO:Co enables a better understanding of exchange constants. The question of the spin-spin interactions in the Diluted Magnetic Semiconducteur (DMS) is studied from both theoretical and experimental approaches. On the théoretical side, a exchange constants for all the II-VI series doped Mn et CO. On the experimental side, the use of three techniques, Inelastic Neutron Scattering (INS), Electron Paramagnetic Resonance (EPR), and the Magnetization Steps (MST) method, has made it possible to establish, for the first time, the ten largest exchange constants in ZnO:Co.The INS experiments show, in direct way, astrong spatial anisotropy of the nearest enighbor exchange integral J(1)=-25.6 K and J(2)=-8.5 K. This result can be explained, in part, by the presence, in the wurtzite structure, of a looped exchange path which involves two distinct anions and is ferromagnetic. To justify this explanation, our model was expanded to cover the entire II-VI series doped Mn and Co. The concurrent results, for the complete series, between the known experimental data and the theoretical exchange values permit the justification and the validation of our hypotheses.The measures performed by EPR and MST enable, for their part, the establisment of the distant neighbor exchange constants. the two techniques give complementary information, and make it possible to directly observe the exchange constants of ZnO:Co going from the third to the tenth largest value, J(3)=-1.07 K ,J(4)=-0.38 K , J(5)=+0.35 K , J(6)=+0.17 K , J(7)=-0.13 K , J(8)=-0.04 K , J(9)=-0.03 K , |J(10)|=0.01 K.

Made available in DSpace on 2014-07-29T15:12:43Z (GMT). No. of bitstreams: 1 Dissertacao Thiago Eduardo Pereira Alves 2010.pdf: 1047109 bytes, checksum: dda1bfd56872ff259ec692829eb6e52b (MD5) Previous issue date: 2010-11-25 / In this work compounds Zn1-xFexO, with 0.00 ≤ x ≤ 0.09, were synthesized by combustion reaction method with two different heating processes, in a thermal blanket and muffle furnace. Chemical analysis of compounds was performed by atomic absorption spectroscopy (AAS) and Fourier transform infrared (FTIR). Structural analysis of the crystalline phase, the diameter of the crystallites and the lattice parameters were checked by X-ray diffraction (XRD, powder method) and refinement software (Unitt and powder X cell). The analysis of surfaces and morphologies were determined by adsorption and desorption of N2 (ASAP, BET model) and transmission electron microscopy (TEM). Finally, Magnetic measurements were performed by vibrating sample magnetometer (VSM). The stoichiometric determined by atomic absorption is in good agreement with the calculated value for all samples. The samples were synthesized in a thermal blanket which corresponds to the wurtzite crystal structure with no secondary phases. The samples synthesized in furnace had wurtzite crystal structure, however, showed a small sample to phase segregation above 5%. The second phases are found with spinel phase indicate that the formation of zinc ferrite. The data of thermal analysis, infrared and X-ray diffraction, we show that the synthesis product in blanket form moving slowly in several stages, while that in the synthesis furnace gets the product directly. We noted the tendency of the formation of smaller particles for the samples from the thermal blanket, as well as high surface areas for these samples, those prepared in a muffle grating. Images by transmission electron microscopy confirm the observations made by x-ray diffraction measurements of surface areas by BET model. The magnetic measurements show ferromagnetic phenomenon only for the sample produced in a muffle. The saturation magnetization was calculated by extrapolation, and their values are promising when compared with the literature. The Curie temperatures were estimated for some samples and all values were well above room temperature. / Neste trabalho compostos de Zn1-xFexO, com 0,00 ≤ x ≤ 0,09, foram sintetizados pelo método da reação de combustão por dois processos de aquecimento diferentes, em manta térmica e forno mufla. A análise química dos compostos foi realizada por espectroscopia de absorção atômica (AAS) e espectroscopia no infravermelho com transformada de Fourrier (FTIR). A análise estrutural da fase cristalina, o diâmetro dos cristalitos e os parâmetros de rede foram verificados por difração de raios X (XRD, método do pó) e softwares de refinamento (powder X e unitt cell). As análises das superfícies e morfologias foram realizadas por adsorção e dessorção de N2 (modelo de BET) e microscopia eletrônica de transmissão. Enfim, medidas magnéticas foram realizadas por magnetometria de amostra vibrante (VSM). A estequiometria determinada por absorção atômica está em boa concordância com o valor calculado para todas as amostras. As amostras sintetizadas em manta térmica apresentaram estrutura cristalina correspondente à wurtzita com ausência de fases secundárias. As amostras sintetizadas em forno mufla apresentaram estrutura cristalina wurtzita, porém, apresentaram uma pequena segregação de fases para amostra acima de 5%. As fases segregadas verificadas correspondem com a fase do espinélio que indicam a formação da ferrita de zinco. Os dados de análise térmica, infravermelho e difração de raios X, nos mostram que a síntese em manta forma o produto passando lentamente em várias etapas, ao passo, que a síntese em mufla obtém o produto de forma direta. Também foi observada a tendência da formação de menores partículas para as amostras provenientes da manta térmica, bem como, áreas superficiais elevadas para essas amostras, em relação àquelas preparadas em mufla. Imagens por microscopia eletrônica de transmissão comprovam as observações realizadas através da difração de raios x e das medidas de áreas superficiais por modelo de BET. As medidas magnéticas apresentaram fenômeno ferromagnético apenas para as amostra produzidas em mufla. As magnetizações de saturação foram calculadas por extrapolação, e seus valores são promissores quando comparados com a literatura. As temperaturas de Curie foram estimadas para algumas amostras e todas apresentaram valores bem acima da temperatura ambiente.

This paper reviews the analytical strategy employed in conventional p-n junction. Then it goes through the analysis of magnetic p-n junction in the same strategy, which makes the review of magnetic p-n junction succinct. I-V equation of magnetic diode is the result of the p-n junction analysis. However, of great importance is to form an acceptable ohmic contact on magnetic diode, which is assumed to be ideal during the magnetic p-n junction analysis. The paper moves on to ohmic contact for magnetic diode, with the example of GaN based magnetic material. With the calculation of the shift of Fermi level in n-GaN with band splitting, conventional ohmic contact structure for n-GaN can be employed to magnetic n-GaN. Experiments from one group prove it. Ohmic contact optimization experiment on n-GaN is present. Ni/Au deposition on n-GaN shows an acceptable ohmic contact. The outlook part points out that the way for research on Schottky diode on magnetic material is partially paved by contents included in this paper.