The electron emission characteristics of aluminum, molybdenum and carbon nanotubes were studied. The experiments were setup to study the emission behavior as a function of temperature and exposure to oxygen. Changes in the surface work function as a result of thermal annealing were monitored with low energy ultra-violet photoelectron spectroscopy for flat samples while field emission energy distributions were used on tip samples. The change in the field emission from fabricated single tips exposed to oxygen while in operation was measured using simultaneous Fowler-Nordheim plots and electron energy distributions. From the results a mechanism for the degradation in the emission was concluded. Thermal experiments on molybdenum and aluminum showed that these two materials can be reduced at elevated temperatures, while carbon nanotubes on the other hand show effects of oxidation. To purely reduce molybdenum a temperature in excess of 750 ºC is required. This temperature exceeds that allowed by current display device technology. Aluminum on the other hand shows reduction at a much lower temperature of at least 125 ºC; however, its extreme reactivity towards oxygen containing species produces re-oxidation. It is believed that this reduction is due to the outward diffusion of aluminum atoms through the oxide. Carbon nanotubes on the other hand show signs of oxidation as they are heated above 700 ºC. In this case the elevated temperatures cause the opening of the end caps allowing the uptake of water. Oxygen exposure experiments indicate that degradation in field emission is two-fold and is ultimately dependent on the emission current at which the tip is operated. At low emission currents the degradation is exclusively due to oxidation. At high emission currents ion bombardment results in the degradation of the emitter. In between the two extremes, molybdenum tips are capable of stable emission.

Thermal and flash photolysis studies of ligand-substitution reactions of cis-(pip)(L)M(CO)_4 by L' (pip = piperidine; L, L' = CO, phosphines, phosphites; M = Cr, Mo) implicate square-pyramidal [(L)M(CO)_4], in which L occupies a coordination site in the equatorial plane, as the reactive species. In chlorobenzene (= CB) solvent, the predominant species formed after flash photolysis and a steady-state intermediate for the thermal reaction is cis—[(CB)(L)M(CO)_4], for which rates of CB-dissociation increase with increasing steric demands of coordinated L. Rates of CB-dissociation from trans-[(CB)(L)M(CO)_4] intermediates, formed after photolysis but not thermally, exhibit no observable dependence on the steric properties of the coordinated L.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) show great potential for the future electronics, optoelectronics and energy applications. But, the studies unveiling their interactions with the host substrates are sparse and limits their practical use for real device applications. We report the facile nano-scratch method to determine the adhesion energy of the wafer scale MoS2 atomic layers attached to the SiO2/Si and sapphire substrates. The practical adhesion energy of monolayer MoS2 on the SiO2/Si substrate is 7.78 J/m2. The practical adhesion energy was found to be an increasing function of the MoS2 thickness. Unlike SiO2/Si substrates, MoS2 films grown on the sapphire possess higher bonding energy, which is attributed to the defect-free growth and less number of grain boundaries, as well as less stress and strain stored at the interface owing to the similarity of Thermal Expansion Coefficient (TEC) between MoS2 films and sapphire substrate. Furthermore, we calculated the surface free energy of 2D MoS2 by the facile contact angle measurements and Neumann model fitting. A surface free energy ~85.3 mJ/m2 in few layers thick MoS2 manifests the hydrophilic nature of 2D MoS2. The high surface energy of MoS2 helps explain the good bonding strength at MoS2/substrate interface. This simple adhesion energy and surface energy measurement methodology could further apply to other TMDs for their widespread use.

Supercapacitors are an emerging energy storage device that have gained attention because of the large specific power, at a reasonable specific energy, that they exhibit. These energy storage devices could be used alongside of or in the place of traditional electrochemical battery technologies to power reliable electrical devices. The performance of supercapacitorsis largely determined by electrode properties including the surface area to volume ratio, the electrical conductivity, and the ion diffusivity. Nanomaterial synthesis has been proposed as a method of enhancing the performance of many macroscopic supercapacitor electrodes due to the high surface area to volume ratio and unique tunable properties that are often size or thickness dependent for many materials. Specifically, carbon materials (such as carbon nanotubes), metal organic frameworks, (such as ZIF-8), and transition metal dichalcogenides (such as molybdenum disulfide) have been of interest due to their conductivity, large surface area, and ion diffusivity that they exhibit when one or more of their characteristic lengths is on the order of several nanometers.<div><br></div><div>For the experiments, a carbon nanotube-/ZIF-8-/MoS2framework was synthesized into an electrode material. This process involved first dispersing the carbon nanotubes in DMF using ultrasonication and then modifying the structure with polydopamine to create a binding site for the ZIF-8 to attach to the carbon nanotubes. The ZIF-8 was synthesized by combining 1,2,4-Triazole-3-thiol and ZnCl under 120 degrees Celsius. Afterwards, the MoS2was associated with the carbon nanotube and ZIF-8 framework by a disulfide bond with the sulfur vacancy of the MoS2andthe sulfide group of the ZIF-8. Finally, the sample solution was filtered by vacuum filtration and then annealed at 110 degrees Celsius before being deposited on a nickel foam substrate and tested in a 3-electrode electrochemical cyclic voltammetry study.<br></div><div><br></div><div>The resulting materials were found to have a capacitance of 262.15 F/g with corresponding specific energy and specific power values of 52.4Whr/kg and 1572W/kg. Compared to other supercapacitor research materials, this electrode shows a much larger capacitance than other exclusively carbon materials, and comparable capacitance values to the ZIF-8 and MoS2materialswith the added benefits of an easier and faster manufacturing process. Overall, the electrodes developed in this study, could potentially reduce the cost per farad of the supercapacitor to be more competitive energy storage devices<br></div>

As the family of two−dimensional(2D) materials has grown, two−dimensional heterostructure devices have emerged as great alternatives to replace conventional electronic materials and enable new functionality such as flexible and bendable electronics. The fabrication and performance of these devices depend critically on the understanding and ability to manipulate the mechanical interplay between the stacked materials. In this dissertation, we investigate adhesive interactions and determine the shear modulus of heterostructure devices made from Molybdenum Disulfide (MoS2). MoS2 has been attracting attention recently due to its semiconductor nature (having a direct band gap of 1.9 eV) along with its exceptional mechanical strength and flexibility. As the first step of our research, we suspended MoS2 flakes grown through chemical vapor deposition (CVD) over substrates made of metal (gold, titanium, chromium), semiconductor (germanium, silicon), insulator (silicon oxide), and semi-metal (graphite). Then, by creating pressure differences across the membrane, we forced MoS2 to bulge upward until we observe separation from the surface of the substrates. We demonstrated that MoS2 on graphite has the highest work of separation within the tested surface materials. Furthermore, we measured considerable adhesion hysteresis between the work of separation and the work of adhesion. We proposed that surface roughness and chemical interactions play a role in surface adhesion and separation of 2D materials. These experiments are critical to guiding the future design of electrical and mechanical devices based on 2D materials. Next, we measured the effective shear modulus of MoS2/few−layer graphene (FLG) heterostructures by employing a blister test. Again, by introducing a pressure differential across the suspended MoS2 membrane over the FLG substrate, the MoS2/FLG heterostructure peeled off from the silicon oxide surface once the critical pressure is exceeded. Incorporating a modified free energy model and Hencky’s axisymmetric membrane solution, we determine the average effective shear modulus of the heterostructure. This is the first experimental measurement of the shear modulus of heterostructure devices using a blister test and this platform can be extended to determine the shear modulus of other 2D heterostructures as well. / 2024-05-24T00:00:00Z

Fusion energy is a potential candidate for sustain-able steady-state energy supply. However, a fully functional fusion reactor is not yet available and several remaining challenges need to be addressed before fusion becomes a reliable source. One of the remaining challenges with fusion is the plasma-induced modification of the inner wall of the tokamak, i.e. the structures surrounding hot plasma. Due to the rarity of tritium, an important element in future fusion fuel, the plasma facing component (PFC) should have as low fuel retention as possible. In this thesis, methods for controlling ion accumulation in a material sample have been developed. Using the new system, a molybdenum (42Mo) target has been implanted with deuterium (2H) and the retention has been measured with ion beam analysis. The experiment was carried out using particle accelerators at the Ångström Laboratory at Uppsala University. Following tasks were completed before the experiment took place: (a) automation of the target position regulator, (b) development of control software, and (c) calibration and testing of the system. The deuterium dose was estimated at the level of1.9·1017 atoms/cm2.The deuterium concentration in molybdenum was found to be around 28·1015 atoms/cm2. This corresponds to a retention rate of around (15±3)%. / Fusion är en potentiell kandidat för hållbar kontinuerlig energi. Tyvärr är en fullt fungerande fusionsreaktor inte tillgänglig ännu och flera utmaningar kvarstår att lösa innan det blir en tillförlitlig källa. En av dessa utmaningar är plasma- inducerad modifikation av den inre väggen, dvs. strukturen närmast det heta plasmat i en tokamak. Tritium är en viktig komponent i ett framtida fusionsbränsle och väldigt sällsynt. Därför måste mängden bränsle som fastnar i väggen minimeras. I detta arbete har metoder för jonbestrålning av ett materialprov utvecklats. Med hjälp av det nya systemet har molybden (42Mo) bestrålats med deuterium (2H) och bibehållandet av deuterium har mätts med jonstråleanalys. Experimentet utfördes med hjälp av partikelacceleratorer i Ångströmlaboratoriet vid Uppsala Universitet. Följande uppgifter utfördes innan experimentet ägde rum: (a) automatisering av provmanipulatorn, (b) utveckling av programvara för styrning och (c) kalibrering och test av systemet. I ett avslutande test uppskattades den implanterade dosen till 1, 9 · 1017 atomer/cm2. Proverna var därefter analyserade och med kärnreaktionsanalys hittades ungefär 28 · 1015 atomer/cm2. Detta motsvarar ett bibehållnade på ungefär (12 ± 3)%. / Kandidatexjobb i elektroteknik 2020, KTH, Stockholm

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Increasing global energy demand and environmental concerns have fueled the exploration of sustainable and efficient methods for renewable fuel production. The conversion of cellulosic waste to hydrocarbon fuels using hydrogenated metal oxides presents a novel and eco-friendly approach to sustainably address energy demand. In this study, hydrogenated metal oxides were used as catalysts in a relatively low-temperature and atmospheric-pressure environment to facilitate the conversion of cellulosic waste into hydrocarbon fuels. Hydrogenated metal oxides have been introduced as potential hydrogen transfer catalysts. The expected result is the selective conversion of cellulose to hexane at relatively low temperatures, which significantly reduces energy consumption compared to traditional high temperature conversion techniques. The use of XPell R resulted in 2,000 ppm hexane in dodecane. Although the use of hydrogenated metal oxides for cellulosic waste conversion is promising, ongoing research and optimization efforts are crucial to enhance the catalyst efficiency and increase the yield.