Transport Properties and Magnetoresistance of Cluster-Assembled Fe-Ge and Fe-Ag Nanocomposites

Granular nanocomposites are composite materials in which grain-like particles with dimensions on the order of nanometers form one of the phases. These nanoparticles are embedded in a second phase, the matrix. Such granular nanocomposites constitute a very promising class of materials with great potential for novel and tailorable properties, making granular nanocomposites especially interesting for scientific endeavor. In the simplest case, granular nanocomposites are synthesized via co-deposition of two immiscible chemical elements. In this approach, nanoparticles grow via incorporation of diffusing atoms of one of the elements forming the prototype material; the remaining atoms of the other element constitute the matrix. This phase segregation process may be assisted by thermal annealing. Another approach used to form granular nanocomposite prototype materials is to ion-implant nanoparticle-type atoms into already grown films or wafer surfaces. However, since these two approaches utilize the immiscibility of the combined materials, they can be applied to such immiscible material systems only. Furthermore, the range of achievable elemental compositions and particle sizes is limited. An interesting alternative strategy to synthesize granular nanocomposites is to deposit the matrix material simultaneously with preformed, spherical nanoparticles. In this approach, the nanoparticles are embedded into the matrix in a direct fashion. The preformed, spherical nanoparticles are called clusters, correspondingly, the created nanomaterials are called cluster-assembled nanocomposites. The great advantage of this special co-deposition approach is that it allows for the creation of nanocomposites out of elements that are at least partially miscible or that can form crystallographic mixed phases—that is, for the creation of so-called nonequilibrium compositions. Embedding the nanoparticles as preformed constituents instead of letting them segregate during the deposition process also increases the degree of control over the deposition process. An ultimate degree of control over the composition is achieved when the clusters are size-selected prior to deposition. This is the strategy pursued in the present thesis. Here, a cluster ion beam deposition system that features a narrow cluster size distribution of ±10% is used to synthesize films of cluster-assembled nanocomposites. Two different nanocomposites are prepared and examined: nanocomposites made of Fe-clusters embedded in Ge-matrices and nanocomposites of Fe-clusters embedded in Ag-matrices. The created Fe-clusters are only a few nanometers in size and, therefore, of superparamagnetic kind. The study of the physical properties of the prepared nanocomposites as a function of cluster size and cluster concentration, in particular, of their transport and magnetoresistive properties, is the central aim of this thesis. First, the Fe-Ge nanocomposites are examined. In this course, also the process of sample preparation and the various performed measurements are discussed. Embedding magnetic Fe nanoparticles into a semiconductor aims for a synthesis of the magnetic and the semiconducting properties, that is, for the creation of so-called magnetic semiconductors. Magnetic semiconductors define a class of materials whose properties can be controlled by means of a magnetic field in addition to—or even instead of—an electric field. For this reason, magnetic semiconductors represent an essential component for the emerging field of spintronics. Two series of Fe-Ge nanocomposites are prepared: one with clusters consisting of 500 ± 50 Fe atoms and one with clusters consisting of 1000 ± 100 Fe atoms. In the course of the analysis, Ge is found to grow in an amorphous structure under the conditions of the co-deposition experiments. A co-deposition sample layout that consists of a co-deposition mask and a complementing sample chip layout is developed. The deposited nanocomposite samples are studied by means of resistance and magnetoresistance measurements in a cryostat, by means of scanning electron microscopy including energy-dispersive X-ray spectroscopy, and by means of SQUID magnetometry. Besides tunneling magnetoresistance, which is negative, of saturating kind, and observed with a magnitude on the order of 1% here, at least one other effect not saturating within the examined magnetic field range of |µ0 H| ≤ 6 T is observed. Several effects that may explain the observed non-saturating behavior are discussed, however, the origin remains unsolved. Furthermore, the resistivity of the Fe-Ge nanocomposites as well as the tunneling magnetoresistance are each found to be a function of the average distance between the surfaces of neighboring clusters rather than the average distance between their centers of mass. Finally, some of the Fe-Ge nanocomposite samples are thermally annealed in vacuum, under the presence of hydrogen gas, and at two different temperatures in various steps. Thermal annealing alters the structure of the as-deposited nanocomposites, which is reflected by changes in the measured physical properties. These changes are identified and discussed. Secondly, the Fe-Ag nanocomposites are examined. In comparison to the Fe-Ge system, the Fe-Ag system is represented in the literature rather well. In particular, it is well-known that the giant magnetoresistance effect can occur in layered as well as in granular Fe-Ag structures. Here, the aim is to confirm that the applied methods give results comparable to those found in the literature and to perhaps even improve upon existing data. Again, two series of nanocomposite samples with clusters consisting of 500 and 1000 Fe atoms, respectively, are fabricated. In addition, a third series of Fe-Ag nanocomposite samples with clusters consisting of 1500 ± 150 Fe atoms is prepared. Giant magnetoresistance of maximum −6% is observed. The giant magnetoresistance effect increases in magnitude with decreasing size of the embedded clusters. Furthermore, an optimum composition of clusters and matrix material for a maximum magnitude of the giant magnetoresistance effect seems to exist. However, no clear dependence of the measured properties on neither the Fe concentration nor the average distance between the surfaces of neighboring clusters is observed. Besides the examination of Fe-Ge and Fe-Ag nanocomposites, a setup that combines laser ablation and inert gas condensation is designed and assembled. In contrast to other techniques, laser ablation features a large fraction of uncharged output particles. Further, laser ablation also allows for the creation of nanoparticles made of electrically insulating materials. Accordingly, the original application considered for the setup lies in the field of matter-wave diffraction experiments. In principle, the setup may be used for the deposition of cluster-assembled materials as well. However, it has never been used for experiments in any of these fields. Nevertheless, the present state of the setup as well as its principle of operation are reviewed. The review is completed with a brief analysis of a test sample of collected Ag clusters prepared with the setup

Development of Nanostructured Glucose Biosensor

With the development of nanotechnology and nanomaterials, biosensors incorporated with novel nanomaterials and nanostructures have shown significant potential in point-of-care medical devices because of their rapid interaction with target analytes and their miniaturized systems. Nanomaterials and nanostructures with special chemical, physical and biological characteristics are able to enhance biosensors’ performance in terms of sensitivity and selectivity. Therefore, my study focused on development of special nanostructures used for advanced glucose biosensor. Monitoring of blood glucose level is essential for diabetes management. However, current methods require people with diabetes to have blood test with 5-8 times per day. Compared to other methods, optical and magnetic techniques have a potential in developing minimally invasive or non-invasive, and continuous glucose monitoring nanostructured biosensors. Consequently, this thesis presented nanostructured optical and magnetic glucose biosensors by incorporating novel nanomaterials and fabricating nanostructures for the next generation of glucose biosensor in the tears. The glucose biorecognition biomolecule used in the biosensors was Concanavalin A (Con A). Con A is a lectin protein that has strong affinity to glucose. Fluorescence resonance energy transfer (FRET) technique was applied to develop optical glucose biosensors. FRET biosensor is a distance-dependent biosensor. The fluorescence emission of a donor molecule could be used to excite acceptor when the distance between donor and acceptor is close enough (\u3c 20 nm). Three different types of nanostructures were developed and used as the donors of the glucose FRET biosensors. The first type of sensor is a ZnO/quantum dots-based glucose biosensors. Hybrid ZnO nanorod array with decoration of CdSe/ZnS quantum dots were prepared and coated on silicone hydrogel which is a common materials of contact lens. The patterned nanostructured FRET sensor could quickly measure rats’ tear glucose in an extremely small amount (2 µL) of diluted tear sample. The second type of biosensor is based on upconversion nanomaterials. Upconversion NaGdF4: Yb, Er nanoparticles with diameter of about 40±5 nm have been prepared by polyol process and coated on silicone hydrogel to directly sense the tear glucose level on the rats’ eye surface. The results show that the upconversion nanomaterials based lens sensor is able to quickly measure glucose in rats’ blood samples. The third type of sensor utilizes the unique optical properties of carbon nanomaterial, fluorescent carbon dots and graphene oxide nanosheets. The carbon dots with tunable fluorescence were developed by a microwave-assisted process. The carbon dots are used as a fluorescence donor in the biosensor, the chitosan coated graphene oxide acts as the fluorescence acceptor to quench the emission of carbon quantum dots. In the presence of glucose, the emission of carbon quantum dots could be restored as a function of the concentration of glucose. Two linear relationships of the restored emission of the sensor and the concentration of glucose were observed, in the range of 0.2 mM to 1 mM, and 1 mM to 10 mM, respectively. On the other hand, a magnetoresistive (MR) nanostructured glucose biosensor has been developed by exploiting hybrid graphene nanosheets decorated with FeCo magnetic nanopartciles. The Fe3O4/silica core/shell nanoparticles are used as the magnetic label of glucose, which could bind onto the surface of FeCo/graphene nanocomposited sensor. The binding of magnetic label onto the hybrid graphene nanosheets can result in the change of the magnetoresistance. The MR signal as a function of the glucose level of diluted rat blood samples is measured in a range of 2 mM to 10 mM. In summary, novel nanomaterials and nanostructures with special fluorescent and magnetoresistive properties are fabricated for developing nanostructured glucose biosensors, which could bring alternative approaches for convenient management diabetes

The influence of ion implantation of iron on the surface, electric and magnetic properties of high density polyethylene

U ovom radu, ispitivana su površinska električna i magnetna svojstva gvožđe-polietilen implantata, sintetisanih jonskom implantacijom pri različitim dozama, u opsegu od 5×1016 jona/cm2 do 5×1017 jona/cm2, i pri energiji od 95 keV. Raderfordovom spektroskopijom rasejanja, Rendgenskom fotoelektronskom spektroskopijom, energijskom disperzivnom spektroskopijom i infracrvenom spektroskopijom, utvrđene su znatne promene sastava površinskog sloja, koje se ogledaju u znatnom udelu gvožđa i nastajanju novih organskih jedinjenja. Mikroskopija atomskih sila je pokazala da je implantacija dovela do promena morfologije površine, i znatno veće površinske hrapavosti. Iz analize transmisionom elektronskom mikroskopijom, utvrđeno je da nakon implantacije dolazi do formiranja nanočestica gvožđa, a da nakon implantacije dozom od 5×1017 jona/cm2 dolazi do formiranja kontinualnog sloja. Merenja slojne otpornosti su pokazala da implantacija gvožđa dovodi do znatnog poboljšanja provodnosti. Magnetna merenja su pokazala da do pojave feromagnetne faze dolazi nakon implantacije dozama od 2×1017 jona/cm2 i 5×1017 jona/cm2. Iz merenja spektroskopskom elipsometrijom se može zaključiti da je nakon implatacije povećan indeks prelamanja i koeficijent apsorpcije u zoni implantacije. Spektroskopija u ultraljubičastoj i vidljivoj oblasti je ukazala na pojavu lokalizovane površinske plazmonske rezonancije čestica gvožđa. Utvrđeno je da površinske energija raste sa implantacionom dozom do doze od 1×1017 jona/cm2, a potom se smanjuje sa povećanjem doze. Pokazano je da su promene hemijskog sastava i morfologije, povezane sa promenama površinskih, električnih i magnetnih svojstava.In this study, the surface electrical and magnetic properties of iron-polyethylene implants, synthesized by ion implantation at different fluences, in the range from 5×1016 ions/cm2 to 5×1017 ions/cm2, and at the energy of 95 keV, were investigated. Rutherford backscattering spectroscopy, X - ray photoelectron spectroscopy, energy dispersive spectroscopy, and infrared spectroscopy have revealed significant changes in the composition of the surface layer, which are reflected in a significant proportion of iron and the formation of new organic compounds. Atomic force microscopy showed that implantation led to changes in surface morphology, and significantly higher surface roughness. From the analysis by transmission electron microscopy, it was determined that after implantation, iron nanoparticles are formed, and that after implantation with a fluence of 5×1017 ions/cm2, a continuous layer is formed. Sheet resistivity measurements have shown that iron implantation leads to a significant improvement in conductivity. Magnetic measurements have shown the occurence of the ferromagnetic phase after implantation at fluences of 2×1017 ions/cm2 and 5×1017 ions/cm2. From the measurements by spectroscopic ellipsometry, it can be concluded that after implantation, the refractive index and the absorption coefficient in the implantation zone increased. Ultraviolet and visible spectroscopy indicated the appearance of localized surface plasmon resonance of iron particles. It was determined that the surface energy increases with the implantation fluence to a fluence of 1×1017 jona/cm2, and then decreases with increasing fluence. It was indicated that the changes in chemical composition and morphology are related to changes in surface, electrical and magnetic properties

Modern Surface Engineering Treatments

Surface engineering can be defined as an enabling technology used in a wide range of industrial activities. Surface engineering was founded by detecting surface features which destroy most of pieces, e.g. abrasion, corrosion, fatigue, and disruption; then it was recognized, more than ever, that most technological advancements are constrained with surface requirements. In a wide range of industry (such as gas and oil exploitation, mining, and manufacturing), the surfaces generate an important problem in technological advancement. Passing time shows us new interesting methods in surface engineering. These methods usually apply to enhance the surface properties, e.g. wear rate, fatigue, abrasion, and corrosion resistance. This book collects some of new methods in surface engineering

Three Dimensional Digital Alloying with Reactive Metal Inks

3D printing of multifunctional components using two or more materials is a rapidly growing area of research. Metallic alloy inks have been used with various 3D printing techniques to create functional components such as antennas, inductors, resistors, and biocompatible implants. Most of these printing techniques use premixed metallic alloy inks or nanoalloy particles with a fixed composition to fabricate the functional part. Since the properties of alloys vary with changes in the elemental composition, a printing process which could digitally dispense alloy inks having specific desired compositions would enable different functionalities and be highly desirable. Using the binary copper-nickel system as an example, the formation of alloy with metal precursor inks is presented. Since copper and nickel both have a face centered cubic (FCC) structure and show complete miscibility in each other, formation of their nanoalloy is, in theory, relatively easy. By printing metal precursor inks rather than nanoparticle suspensions, problems associated with the nanoparticle inks such as ink stability and nozzle clogging can be avoided. Copper and nickel precursor inks were formulated having rheological properties suitable for inkjet printing. Reduction of metal inks was studied under various conditions. The sintered metal and alloy structures were characterized using thermal analysis, infrared spectroscopy, energy-dispersive x-ray spectroscopy (EDS), and x-ray diffraction. Nickel, a ferromagnetic metal, showed novel microstructures such as aligned nanowires and nanowire grids when reduced in the presence of a magnetic field. These microstructures had enhanced anisotropic electrical and magnetic properties along the direction of the nanowire. The reduction of combined ink solutions (copper and nickel) showed formation of a two phase with copper as one phase and a nickel rich alloy as other. These structures demonstrated no change in electrical resistivity when exposed to an oxidation rich environment. To achieve a homogeneous alloy formation, the copper phase and the nickel rich phase were diffused together at high temperatures. Copper nickel alloy inks with ratios Cu30Ni70, Cu50Ni50, and Cu70Ni30 were formulated and reduced at 230 °C and later high temperature diffusion was achieved at 800 °C. The lattice parameter of the alloy phase for the inks with ratio Cu30Ni70 was 3.5533Å, Cu50Ni50 was 3.5658 Å, and Cu70Ni30 was 3.5921 Å. Using Vegard’s law, the composition of the alloy phases for the three samples were estimated to be Cu32Ni68, Cu46Ni54, and Cu75Ni25. This formation of the desired alloy composition can open the door to numerous applications in biomedical and electronics sectors, among other

Advance in Energy Harvesters/Nanogenerators and Self-Powered Sensors

This reprint is a collection of the Special Issue "Advance in Energy Harvesters/Nanogenerators and Self-Powered Sensors" published in Nanomaterials, which includes one editorial, six novel research articles and four review articles, showcasing the very recent advances in energy-harvesting and self-powered sensing technologies. With its broad coverage of innovations in transducing/sensing mechanisms, material and structural designs, system integration and applications, as well as the timely reviews of the progress in energy harvesting and self-powered sensing technologies, this reprint could give readers an excellent overview of the challenges, opportunities, advancements and development trends of this rapidly evolving field

Annual Report 2019 - Institute of Ion Beam Physics and Materials Research

The Institute of Ion Beam Physics and Materials Research conducts materials research for future applications in, e.g., information technology. To this end, we make use of the various possibilities offered by our Ion Beam Center (IBC) for synthesis, modification, and analysis of thin films and nanostructures, as well as of the free-electron laser FELBE at HZDR for THz spectroscopy. The analyzed materials range from semiconductors and oxides to metals and magnetic materials. They are investigated with the goal to optimize their electronic, magnetic, optical as well as structural functionality. This research is embedded in the Helmholtz Association’s programme “From Matter to Materials and Life”. Seven publications from last year are highlighted in this Annual Report to illustrate the wide scientific spectrum of our institute. After the scientific evaluation in the framework of the Helmholtz Programme-Oriented Funding (POF) in 2018 we had some time to concentrate on science again before end of the year a few of us again had to prepare for the strategic evaluation which took place in January 2020, which finally was also successful for the Institute