Chemical mechanical polishing (CMP) has emerged as a critical technique for the manufacture of complex integrated circuits to achieve low surface roughness and high degree of planarization. In particular, the continuous progression of the wafer carrier has been driven by the interest of diminishing the waste on a wafer by reducing the edge of exclusion area, and hence, increasing the amount of chips per wafer. In this thesis,a standard wafer carrier and the state of the art Titan™ wafer carrierare compared and evaluated by planarizing a set of blank wafers with a PECVD oxide film on an IPEC 472 CMP tool. The surface roughness was analyzed before and after the planarization step using an atomic force microscope (AFM) and the nonuniformity across the wafer was characterized by ellipsometry. The material removal rate and the reproducibility of the nonuniformity from wafer to wafer was also observed and compared. A second set of experiments with patterned wafers pla-narized with the Titan™ carrier was also performed. The impact of thepattern density in the step height reduction ratio and surface roughness was analyzed with AFM. The results obtained from the blank wafers planarized with the standard wafer carrier showed a nonuniformity average of ± 6.96% with a 3 mm edge of exclusion, a wafer to wafer nonuniformity of ± 4% and a surface roughness of 0.34 nm. However, the Titan™ carrier delivered a nonuniformity average of ± 2.17%, a wafer to wafer nonuniformity of ± 0.3% and a surface roughness of 0.22 nm. The Titan™ carrier outmatched the standard wafer carrier forcing it to shift the edge of exclusion area to 7mm to be able to achieve a nonuniformity of ± 2.90%. The results for the set of patterned wafers showed a step height reduction ratio (SHRR) average of 98.35%. Thesurface roughness for the oxide above the patterned polysilicon structures decreased from 9.46 nm to 0.33nm and the surface roughness on the recessed areas decreased from 3.70nm to 0.7nm.

Density functional theory was employed to investigate the energetics of ABA, ABC, and intermediary stacked phases for both pristine and s-triazine functionalized graphene trilayers. The energy of the ABC-stacked phase relative to the pristine ABA-stacked ground state showed a 94% increase when s-triazine was adsorbed to the graphene surface, confirming previous studies of the ability of s-triazine to facilitate the ABC to ABA phase-transition. This work is outlined in an enclosed publication titled “Trilayer Graphene as a Candidate Material for Phase Change Memory Applications.” Subsequently, low-pressure CVD was used to synthesize single-crystal graphene trilayers of up to 200 µm, the largest reported thus far. The defect density, stacking density, and morphology of the CVD-grown graphene trilayers are evaluated using Raman spectroscopy. The layers are also shown to be directly discernable as-grown on copper substrates using dark-field optical microscopy even without contrast oxidation of the copper film, representing a quick and reliable method for their identification. Slow-etching of the graphene yielded well-aligned, hexagonal domains further indicating the high-quality, single-crystalline of the graphene.

Silicon heterojunction interdigitated back-contact (SHJ-IBC) solar cells have attracted considerable attention because of their potential to achieve very highly efficiency. However, the back contacting scheme leads to additional fabrication complexity mainly resulting from the formation of interdigitated n- (back surface field (BSF)) and p-type (emitter) hydrogenated amorphous silicon (aSi:H) strips. Photolithography is widely used for patterning of the interdigitated strips, but this is a costly and impractical technique for industrial applications. This work focuses on the development of simple BSF/emitter patterning approaches of SHJ-IBC cells to replace photolithography and two methods, selective deposition (SD) and dry etching of a-Si:H, have been evaluated. Selective deposition of materials is a promising approach for electronic device fabrication, which allows materials deposition on pre-defined areas while no deposition occurs on other parts of the device. As a result, costly lithography and etching steps can be avoided. Selective deposition of a-Si:H at low temperature (~200C) using plasma-enhanced chemical vapor deposition (PECVD) technique, is a novel approach for rear side emitter patterning of SHJ-IBC solar cells. The first target of this study was to selectively deposit a-Si:H on crystalline silicon (c-Si) while avoiding deposition on the SiOx mask. The second target was to achieve a sufficient quality a-Si:H/c-Si interface passivation using selectively deposited silicon film. The SD of a-Si:H was realized by short deposition of a-Si:H followed by etching using hydrogen plasma. Hydrogen atoms can selectively eliminate strained bonds in a-Si:H films. Proper hydrogen plasma exposure allows to discriminate between Si-Si bonds on different substrates. As such, substrate-SD of a-Si:H is possible. Repetition of short deposition followed by hydrogen plasma etching leads to net deposition on one substrate, i.e., c-Si, but not on mask layers, i.e., SiOx. Two deposition approaches were used to develop SD. The first approach is "Time-modulated power"; where deposition and etching is controlled by radio frequency power. The second deposition approach is "Time-modulated SiH4", where film deposition and etching is controlled by pulsed SiH4 flow. Spectroscopic Ellipsometry (SE) and Transmission Electron Microscopy (TEM) were utilized to measure selectivity, film thickness, and morphology. Effective carrier lifetime (τeff) was measured to check the c-Si surface passivation quality using Quasi-steady-state photo-conductance (QSSPC) method and Photoluminescence (PL) image. From TEM it was observed that, although selectivity is achieved in this work, crystallization of the deposited Si film on c-Si results in poor passivation quality, which is probably induced by long hydrogen plasma exposure. To reduce the crystallization rate, NF3 plasma treatment was carried out on c-Si surface before SD. The suppression of silicon epitaxial growth was observed. This is due to the transformation of c-Si surface bonding configurations which was confirmed by measurement of Attenuated total reflectance Fourier transform infrared spectroscopy. The QSSPC and PL results indicated improved passivation quality using NF3 plasma treatment before SD. The other part of this study concerned the etching of a-Si:H (n+) layer in i/n+ a-Si:H stack using hydrogen plasma followed by in-situ re-deposition of a-Si:H(p+) layer. With the aid of in-situ deposition, the vacuum break of PECVD, HF dip of c-Si wafer prior to a-Si:H(p+) deposition, wafer rising and drying can be skipped. A sufficient c-Si surface passivation is here required after the etching and re-deposition processes. According to the SE results, a stable and uniform etching of a-Si:H(n+) film with etching rate of 1.4±0.1 nm/min was achieved. An excellent surface passivation quality with τeff of above 8ms was obtained after etching of a-Si:H(n+) and re-deposition of a-Si:H(p+) layer. A thicker a-Si:H(i) layer was proven to be beneficial to prevent passivation degradation during hydrogen plasma etching. The preliminary results suggest that this is a promising method to replace currently used etching methods that remove the whole a-Si:H(i/n+) stack, significantly simplifying rear side patterning steps for SHJ -IBC solar cell devices.

Hybrid plasmonic (HP) waveguides, a multi-layer waveguide structure supporting a hybrid mode of surface plasmonics and Si photonics, is a compromise way to integrate plasmonic materials into Si or SOI platforms, which can guide optical waves of sub-wavelength size, and with relative low propagation loss. In this thesis, several HP waveguides and devices are developed for the purposes of optical communications and sensing. The single-slot HP ring resonator sensor with 2.6µm radius can give a quality factor (Q factor) of 1300 at the communication wavelength of 1.5µm with a device sensitivity of 102nm/RIU (refractive index unit). The Mach-Zehnder interferometer (MZI) with a 40µm double-slot HP waveguide has a device sensitivity around 474nm/RIU. The partly open silicon side-coupled double-slot HP ring resonator has a device sensitivity of 687.5nm/RIU, with a Q factor over 1000 after optimization. Further, an all-optical switching HP donut resonator with a photothermal plasmonic absorber is developed, utilizing the thermal expansion effect of silicon to shift the resonant peak of the HP resonator. The active area has a radius of 10µm to match the core size of a single-mode fiber. By applying 10mW power of the driving laser to the absorber, the resonator transmitted power can be changed by 15dB, with an average response time of 16µs. Using the same fabrication flow, and removing the oxide materials using hydrogen fluoride wet etching, a hollow HP waveguide is fabricated for liquid sensing applications. The experimentally demonstrated waveguide sensitivity is about 0.68, which is more than twice that of pure Si waveguide device. Microelectromechanical systems (MEMS) can also be integrated into vertical HP waveguides. By tuning the thickness of the air gap, over 20dB transmitted power change was experimentally demonstrated. This can be used for optical switching applications by either changing the absorption or phase of the HP devices. / <p>QC 20170427</p>

In nature, urea is hydrolyzed to ammonia and bicarbonate primarily by enzymes called ureases. As urine waste contains multiple important plant nutrients, there is interest in the waste treatment field to use urine waste products as plant fertilizers. Since urease enzymes are usually found in biofilms, one can prevent nitrogen loss in urine waste by preventing biofilm formation in the surrounding environment. In recent years, many new strategies to prevent microbial growth have been developed, especially within the field of nanoscience. The aim of this master's thesis was to develop a method for growing and analyzing urease-active biofilms and to investigate whether super-acidic metal- oxide surfaces could prevent biofilm growth. In this project, the methods are divided into two sections: methods for producing super-acidic metal-oxide surfaces and methods for growing and analyzing biofilms. The method for growing biofilms was developed through successive experiments, with the results of one experiment being used to design the next. Three batches of antimicrobial plates were manufactured, and seven biofilm experiments were conducted. In these experiments, biofilms were able to grow on antimicrobial plates, but the results were somewhat inconclusive. The biofilms were analyzed by microscopy, since no quantitative analysis method was successful in this study.

Low-dimensional semiconductor structures, such as one-dimensional nanowires (NWs) and zerodimensional quantum dots (QDs), are materials with novel fundamental physical properties and a great potential for a wide range of nanoscale device applications. Here, especially promising are direct bandgap II-VI and III-V compounds and related alloys with a broad selection of compositions and band structures. For examples, NWs based on dilute nitride alloys, i.e. GaNAs and GaNP, provide both an optical active medium and well-shaped cavity and, therefore, can be used in a variety of advanced optoelectronic devices including intermediate band solar cells and efficient light-emitters. Self-assembled InAs QDs formed in the GaAs matrix are proposed as building blocks for entangled photon sources for quantum cryptography and quantum information processing as well as for spin light emitting devices. ZnO NWs can be utilized in a variety of applications including efficient UV lasers and gas sensors. In order to fully explore advantages of nanostructured materials, their electronic properties and lattice structure need to be comprehensively characterized and fully understood, which is not yet achieved in the case of aforementioned material systems. The research work presented this thesis addresses a selection of open issues via comprehensive optical characterization of individual nanostructures using micro-Raman ( -Raman) and micro-photoluminescence ( -PL) spectroscopies. In paper 1 we study polarization properties of individual GaNP and GaP/GaNP core/shell NWs using polarization resolved μ-PL spectroscopy. Near band-edge emission in these structures is found to be strongly polarized (up to 60% at 150K) in the orthogonal direction to the NW axis, in spite of their zinc blende (ZB) structure. This polarization response, which is unusual for ZB NWs, is attributed to the local strain in the vicinity of the N-related centers participating in the radiative recombination and to their preferential alignment along the growth direction, presumably caused by the presence of planar defects. Our findings therefore show that defect engineering via alloying with nitrogen provides an additional degree of freedom to control the polarization anisotropy of III-V nanowires, advantageous for their applications as a nanoscale source of polarized light. Structural and optical properties of novel coaxial GaAs/Ga(N)As NWs grown on Si substrates, were evaluated in papers 2-4. In paper 2 we show by using -Raman spectroscopy that, though nitrogen incorporation shortens a phonon correlation length, the GaNAs shell with [N]&lt;0.6% has a low degree of alloy disorder and weak residual strain. Additionally, Raman scattering by the GaAs-like and GaNlike phonons is found to be enhanced when the excitation energy approaches the E+ transition energy. This effect was attributed the involvement of intermediate states that were created by N-related clusters in proximity to the E+ subband. Recombination processes in these structures were studied in paper 3 by means of μ-PL, μ-PL excitation (μ-PLE), and time-resolved PL spectroscopies. At low temperatures, the alloy disorder is found to localize photo-excited carriers leading to predominance of localized exciton (LE) transitions in the PL spectra. Some of the local fluctuations in N composition are suggested to create three-dimensional confining potentials equivalent to that for QDs, based on the observation of sharp PL lines within the LE contour. In paper 4 we show that the formation of these QD-like confinement potentials is somewhat facilitated in spatial regions of the NWs with a high density of structural defects, based on correlative spatially-resolved structural and optical studies. It is also concluded the principal axis of these QD-like local potentials is mainly oriented along the growth direction and emit light that is linearly polarized in the direction orthogonal to the NW axis. At room temperature, the PL emission is found to be dominated by recombination of free carriers/excitons and their lifetime is governed by non-radiative recombination via surface states. The surface recombination is found to become less severe upon N incorporation due to N-induced modification of the surface states, possibly due to partial surface nitridation. All these findings suggest that the GaNAs/GaAs hetero-structures with the onedimensional geometry are promising for fabrication of novel optoelectronic devices on foreign substrates (e.g. Si). Fine-structure splitting (FSS) of excitons in semiconductor nanostructures has significant implications in photon entanglement, relevant to quantum information technology and spintronics. In paper 5 we study FSS in various laterally-arranged single quantum molecular structures (QMSs), including double QDs (DQDs), quantum rings (QRs), and QD-clusters (QCs), by means of polarization resolved μ-PL spectroscopy. It is found that FSS strongly depends on the geometric arrangements of the QMSs, which can effectively tune the degree of asymmetry in the lateral confinement potential of the excitons and can reduce FSS even in a strained QD system to a limit similar to strain-free QDs. Fabrication of nanostructured ZnO-based devices involves, as a compulsory step, deposition of thin metallic layers. In paper 6 we investigate impact of metallization by Ni on structural quality of ZnO NWs by means of Raman spectroscopy. We show that Ni coating of ZnO NWs causes passivation of surface states responsible for the enhanced intensity of the A1(LO) in the bare ZnO NWs. From the resonant Raman studies, strong enhancement of the multiline Raman signal involving A1(LO) in the ZnO/Ni NWs is revealed and is attributed to the combined effects of the Fröhlich interaction and plasmonic coupling. The latter effect is also suggested to allow detection of carbon-related species absorbed at the surface of a single ZnO/Ni NW, promising for utilizing such structures as efficient nano-sized gas sensors.

Coatings are vital to protect and to increase the productivity of cutting tools in high speed and dry cutting applications. During the cutting operation the temperature may exceed 1000 ºC it is therefore necessary that the coatings withstand high temperatures. A lot of development and research has been carried out during the last 30 years on finding new coating material systems providing enhanced properties such as adhesion, hardness and oxidation resistance at elevated temperatures. This thesis is based on multicomponent alloying of quaternary transition metal nitride hard coatings with a main focus on Ti-Cr-Al-N coatings. Many different coatings and compositions have been deposited using an industrial scale cathodic arc evaporation deposition system. All deposited coatings contain Al as this element is known to increase the hardness and the oxidation resistance of nitride coatings. The deterioration of the hardness in Al-containing nitride coatings is generally attributed to the transformation of cubic Al-N into hexagonal Al-N and the consequent domain coherency relaxation. This thesis investigates these phenomena on an atomic level providing a deeper understanding of and a way to engineer improved hard nitride coatings. The essence of this thesis is that by adding a third metal to a ternary nitride material system, for example one of the most frequently used Ti-Al-N, it is possible to tune and engineer the thermal stability of the cubic structure and the coherency strain which in turn affects the hardness and the oxidation resistance. The key point is that new intermediate phases in the decomposition process are generated so that the eventual detrimental phases are suppressed and delayed. More specifically, when Cr is added to the Ti-Al-N material system the coatings exhibit an age hardening process up to 1000 ºC caused by spinodal decomposition into coherent TiCr- and AlCr-rich cubic Ti-Cr-Al-N domains. This means that the unstable cubic Ti-Cr-Al-N phase decomposes via yet another unstable cubic Cr-Al-N phase before the detrimental hexagonal transformation of AlN takes place. The hardness is therefore retained up to a higher temperature compared to Ti-Al-N coatings. By utilizing multicomponent alloying through addition of Ti to Cr-Al-N coatings the hardness is retained after annealing up to 1100 ºC. This is a dramatic improvement compared to Cr-Al-N coatings. Here the Ti addition promotes the competitive spinodal decomposition into TiCr- and Al-enriched domains suppressing the detrimental hexagonal AlN formation. To investigate the effect of multicomponent alloying for other material systems with different mixing free energies and atomic sizes, Zr-containing, Zr-Cr-Al-N and Zr-Ti-Al-N, quaternary nitride coatings have also been deposited. For high Al- and high Zr-containing coatings the cubic solid solution structure is disrupted into a mix of nano-crystalline hexagonal and cubic phases with significantly lower hardness. The results show that the structure and hardness of these coatings are sensitive to the composition and in order to optimize the hardness and thermal stability the composition has to be fine-tuned. Altogether it is shown that through multicomponent alloying and through the control of the coherency strain it is possible to enhance the hardness and the oxidation resistance compared to the ternary system which may lead to new improved functional hard coatings.

Graphene base transistors (GBTs) are known to be novel devices mingling outstanding properties of graphene, with the concept of hot electron transistors (HETs). According to theoretical calculations, GBTs were predicted to have over 5 orders of magnitude ON/OFF current ratios and THz frequency range operations. This would in fact lead to potential applications in high speed radio frequency (RF) analog devices. Recently, GBTs’ high gain and more than 4 orders of magnitude ON/OFF current ratios have been experimentally proven. However, GBTs still need further improvements before they can be applied in real electronics devices; and that can be done through thickness and barrier height optimization of the tunneling barrier. In this thesis project, we have studied various gate dielectrics for potential applications as tunneling barriers in GBTs. To accomplish this study, we have gone through two rounds of successful cleanroom fabrication processes, where we fabricated fully functional devices. During the first round, we have developed seven different capacitor structures on 4 inch Si wafers with ALD deposited: Al2O3, TiO2, HfO2, “Al2O3+TiO2 mix”, SiO2/HfO2 stack, SiO2/Al2O3 stack and thermally grown SiO2 dielectrics. Whereas in the second batch, BG-GFET structures were fabricated on chip level, with: 2nm SiO2, 5nm SiO2, 10nm SiO2, (2nm/4.2nm) SiO2/HfO2, (2nm/4.5nm) SiO2/”Al2O3+TiO2 mix”, 6nm “Al2O3+TiO2 mix” and 6.6nm TiO2 bottom gates, onto which a single layer graphene was transferred. We have also carried out electrical characterizations of these successfully fabricated devices and making use the encouraging results obtained, we have investigated the associated current injection mechanisms across each barrier / <p>QC 20150115</p>

Artificial opals are self-assembled face centered cubic (fcc) structures of  spherically shaped beads, which interesting applications as photonic band gap materials. Inverse opals are photonic crystals consisting of fcc paced voids of a low refractive index material imbedded in a high refractive index material. Such structures has been used to enhance the photocatalytic effect of different materials and motivates further studies to improve the deposition process of the opal templates and their inversion. We state the fabrication method to design and model metal oxide inverse opals. We have successfully created alumina and alumina-titania inverse opals. With the help of simulations, we engineered inverse opals with self-assembly and atomic layer deposition.

The integration and use of superhydrophobic surfaces to microfluidic systems were investigated in this work. Superhydrophobic surfaces are believed to have the ability to reduce the hydrodynamic resistance of a microchannel, reduce the risk of clogging due to reduced liquid contact with the microchannel walls and reduce the losses in a microfluidic system. Two superhydrophobic surfaces with different fabrication methods were evaluated. It was found that fabrication methods that add material to the microchannel walls do not work well in microchannels. Methods that instead transform a present surface are more suitable for a microfluidic system. To visualize the superhydrophobic surfaces an AFM and SEM were used. By combining the information a good picture of the superhydrophobic surfaces where sometimes achieved. To investigate the impact of the superhydrophobic surfaces, two different designs of microchannels were created on silicon wafers and compared with microchannels created in polydimethylsiloxane. One design used straight channels and the other aimed to maximize the resistance reduction by patterning the walls of the microchannel. Due to manufacturing issues only the straight channels were evaluated, where it was found that superhydrophobic surfaces can increase the flow rate of a microfluidic system. However, the result was not reproduced easily. The reason is currently unknown but believed to originate from flaws in the manufacturing process. A simple version of a device that uses superhydrophobic surfaces to seal microfluidic systems was successfully used and reused. A device with a more refined design could offer the ability to create microfluidic systems with detachable lids. Finally, to further increase the availability of the properly created superhydrophobic surface an alternative functionalization step should be found.