Title Promoter Affiliations Abstract "Bottom-Up generation of atomicalLy precise syntheTIc 2D MATerials for high performance in energy and Electronic applications – A multi-site innovative training action" "Steven De Feyter" "Molecular Imaging and Photonics" "The “graphene rush” has triggered a great interest in the design and fabrication of synthetic 2D materials (S2DMs) excelling in their chemical and physical properties for future emerging technologies addressing numerous societal needs, such as faster and better performing electronics, as well as energy storage and conversion. To match the societal benefits of being at the forefront of new technological and scientific developments, the EC requires a highly skilled scientific and technical workforce that can efficiently finalize the shift to a true knowledge-based society. ULTIMATE will provide to 15 talented young researchers a well-structured training in the burgeoning field of S2DMs by developing their knowledge and understanding on: i) how to generate novel atomically precise 2D materials with defined structure and composition, and ii) how to best exploit their unique and tunable properties for electronics and energy applications. This training-through-research requires an intersectoral approach by specialized and skilled scientists from different (sub-)disciplines including molecular modeling (TUD), organic, macro-/supramolecular synthesis (TUD, HUB, UAM), production of S2DMs (GRA, TUD, UNISTRA, IIT), hierarchical self-assembly (UNISTRA, KUL, HUB, CNR), surface and interface studies (KUL, EMPA, IBM, KFUG, CNR, APE, IIT, UNISTRA), photochemistry and photophysics (UNIME, HUB, UNISTRA, IIT), device fabrication and characterization (IIT, TUD, UNISTRA), and other skills, as well as a strong commitment to the training of young talents with the ultimate goal of achieving scientific breakthroughs in this very topical area of science and technology. The ULTIMATE network will strengthen the EC training efforts by delivering 540 person-months of unprecedented cross-disciplinary and supra-sectoral training that is carefully structured in local, network-wide, and beyond-network training activities, as well as complementary and transferable skills." "Unravelling the mechanism of on-surface 2D polymer formation at the liquid-solid interface: towards reliable and robust synthetic strategies" "Steven De Feyter" "Molecular Imaging and Photonics" "Polymers have permeated almost every sphere of modern life, from packaging to drug delivery, from 3D printing to airplanes. So, after being around for more than a century, what is the next big thing for polymers? The answer lies in the arrival of two-dimensional (2D) materials which have dominated headlines in recent years. Graphene, a single atom thick sheet of carbon isolated at the beginning of the century has several interesting properties and is a valuable material for many applications. Graphene extends in 2D unlike conventional polymers where molecular strings extend only in 1D. Graphene, however, is only the tip of the iceberg. The field of 2D materials is getting crowded and synthetic 2D polymers made by stitching small organic molecules in 2D offer a promising alternative. Unlike known inorganic 2D materials, their properties can be readily manipulated using synthetic organic chemistry. While the premise of the idea appears rather appealing and straightforward, the path forward is not easy given the need to obtain large-area, defect-free films of chemically stable 2D polymers. In this project, we will tackle two important challenges associated with synthetic 2D polymers: (1) the lack of fundamental insight into the mechanism of 2D polymer formation and (2) the poor chemical stability of the prevalent 2D polymer systems." "Plasma Physics and Chemistry Challenges for the Interconnect Technology of 2D Materials." "Stefan De Gendt" "Sustainable Chemistry for Metals and Molecules" "Transition-metal dichalcogenides such as MoS2 or WS2 are semiconducting materials with a layered structure. One single layer consists of a plane of metal atoms terminated on the top and bottom by the chalcogen atoms sulfur, selenium, or tellurium. These layers show strong in-plane covalent bonding, whereas the Van-der-Waals bonds in between adjacent layers are weak. Those weak bonds allow the microcleavage and extraction of a monolayer. Transistors built on such monolayer nanosheets are promising due to high electrostatic controllability in comparison to a bulk semiconductor. This is important for fast switching speed and low-power consumption in the OFF-state. Nonetheless, prototypes of such nanosheet transistors show non-idealities due to the fabrication process. Closed films on a large area cannot be obtained by mechanical exfoliation from mm-sized crystals. For  wafer-level processing, synthetic growth methods are needed. It is a challenge to obtain a few layer thick crystals with large lateral grains or even without grain boundaries with synthetic growth techniques. This requires pre-conditioned monocrystalline substrates, high-temperature deposition, and polymer-assisted transfer to other target substrates after the growth. Such transfer is a source of cracks in the film and degrades the layers’ promising properties by residual polymer from the bond material. Apart from transfer, patterning of the stacked 2D layers is necessary to build devices. The patterning of a 2D material itself or another material on top of it is challenging. The integration of the nanosheets into miniaturized devices cannot be done by conventional continuous-wave dry etching techniques due to the absence of etch stop layers and the vulnerability of these thin layers. To eliminate these issues in growth and integration, we explored the deposition methods on wafer-level and low-damage integration schemes.To this end, we studied the growth of MoS2 by a hybrid physical-chemical vapor deposition for which metal layers were deposited and subsequently sulfurized in H2S to obtain large area 2D layers. The impact of sulfurization temperature, time, partial H2S pressure, and H2 addition on the stoichiometry, crystallinity, and roughness were explored. Furthermore, a selective low-temperature deposition and conversion process at 450 °C for WS2 by the precursors WF6, H2S, and Si was considered. Si was used as a reducing agent for WF6 to deposit thin W films and H2S sulfurized this film in situ. The impact of the reducing agent amount, its surface condition, the temperature window, and the necessary time for the conversion of Si into W and W into WS2 were studied. Further quality improvement strategies on the WS2 were implemented by using extra capping layers in combination with annealing. Capping layers such as Ni and Co for metal-induced crystallization were compared to dielectric capping layers. The impact of the metal capping layer and its thickness on the recrystallization was evaluated. The dielectric capping layer’s property to suppress sulfur loss under high temperature was explored. The annealings, which were done by rapid thermal annealing and nanosecond laser annealing, were discussed.Eventually, the fabrication of a heterostack with a MoS2 base layer and selectively grown WS2 was studied. Atomic layer etching was identified as attractive technique to remove the solid precursor Si from MoS2 in a layer-by-layer fashion. The in-situ removal of native SiO2 and the impact towards MoS2 was determined. The created patterned Si on MoS2 was then converted into patterned WS2 on MoS2 by the selective WF6/H2S process developed earlier. This procedure offers an attractive, scalable way to enable the fabrication of 2D devices with CMOS-compatible processes and contributes essential progress in the field 2D materials technology." "4D materials for synthetic, vascularized, myogenic tissues based on hybrid nanocomposites" "Wim Thielemans" "Chemical Engineering, Kulak Kortrijk Campus, Soft Matter and Biophysics, Development and Regeneration, Kulak Kortrijk Campus" "In this project we aim to develop stimulus responsive, artificial tissues based on polysaccharide nanoparticle-stabilized multiphase materials and optical nanoparticles, together with optical methods allowing in situ mechanostimulation of individual cells and simultaneous readout of cellular responses (i.e., electrical responses, contractility, and inflammation markers (e.g. pH, temperature)). We will explore the ability of these materials to support and guide cell growth by matrix generated mechanical stimuli and to monitor changes in cell activity, in situ, at single cell level, in 3D cultures of electrogenic cells (i.e. myogenic cells). Such optically addressable platforms would provide unique tools for probing cell-matrix interactions and subsequently understand cell and tissue morphogenesis and will find direct applicability in organ-on-chip systems and soft robotics." "Nanoscale characterization and property evaluation of 2D polymers synthesized at the air-water interface" "Steven De Feyter" "Molecular Imaging and Photonics" "Polymers have permeated almost every sphere of modern life, from packaging to drug delivery, from 3D printing to airplanes. They consist of molecular chains in which smaller building blocks are connected via covalent bonds. So what is the next big thing for polymers? The answer lies in the arrival of two-dimensional (2D) materials which have dominated headlines in recent years. Graphene, a single atom thick sheet of carbon isolated at the beginning of the century has several interesting properties and is a valuable material for many applications. The covalent network of graphene extends in 2D unlike conventional polymers where molecular strings extend only in 1D. While graphene research progressed fast in the past decade, challenges associated with its chemical modification have halted its integration in technology. Graphene however, is only the tip of the iceberg. The field of 2D materials is getting crowded and synthetic 2D polymers made by stitching small organic molecules in 2D offer a promising alternative. Unlike known 2D materials, their properties can be readily manipulated using synthetic organic chemistry. In this project the synthesis, nanoscale characterization and property evaluation of different 2D polymers is targeted. The polymers will be synthesized at the air-water interface which will allow their transfer to different solid surfaces thus widening their applicability. The research proposed here will provide access to alternative 2D materials beyond graphene." "Nucleation and Growth Mechanisms of 2D Semiconductor/high-k Dielectric Heterostacks" "Annelies Delabie" "Quantum Chemistry and Physical Chemistry, Quantum Solid State Physics (QSP)" "The extraordinary properties of the diverse two-dimensional (2D) materials are promising to improve existing technologies and create a wide range of new applications. 2D semiconductor/high-k dielectric heterostacks are of interest for applications in nanoelectronics and optoelectronics. Deposition of highly crystalline 2D semiconductors with monolayer thickness control on large-area substrates is essential to enable the applications. However, due to limited understanding on the nucleation and growth mechanisms, it remains challenging to deposit crystalline 2D semiconductors like SnS2 and SnS with monolayer thickness control. In addition, deposition of pin-hole free nm-thin high-k dielectric films on the 2D semiconductors is required. Atomic layer deposition (ALD) can deposit high-k dielectric films with atomic level growth control as it is based on self-limiting surface reactions. However, the surface of an ideal 2D material is reported to be fully self-passivated. Thus, a fundamental question arises as follows, if and how ALD can proceed.Therefore, this Ph.D thesis investigates the nucleation and growth mechanisms of the chemical vapor deposition (CVD) of 2D semiconductors and the ALD of high-k dielectrics on 2D semiconductors.First, we investigate the growth mechanisms of nm-thin 2D SnS2 and SnS crystals by CVD using SnCl4 and H2S. The formation of the SnS phase is favorable at higher temperature and higher H2S/SnCl4 concentration ratio than the SnS2 phase. This is explained by the catalytic decomposition of H2S by SnS2 with formation of H2, where the generated H2 reduces SnS2 to SnS at 350°C or higher temperatures. To explore thickness scaling down to the monolayer level, we investigate the nucleation and growth mechanisms of SnS2 and SnS. Both SnS2 and SnS show initial island growth due to surface diffusion and agglomeration into three-dimensional (3D) islands, different from the layer-by-layer growth for other 2D materials. The initial islands are presumed to be amorphous and crystallize only when reaching a critical size and/or composition, depending on the deposition temperature and substrate. After crystallization, the growth changes to 2D lateral growth, due to the selective incorporation of adatoms at the crystal edges of the 2D SnS2 and SnS crystals.Second, we investigate the nucleation and growth mechanisms of high-k dielectrics ALD on synthetic polycrystalline MoS2. The properties of starting surface determine the nucleation and growth mode of oxide ALD, as such the surface morphology and the point of layer closure of the deposited materials. The nucleation of high-k dielectrics occurs at the grain boundaries at the MoS2 top surface while no nucleation is observed on the basal planes of MoS2. This is attributed to the high reactivity of grain boundaries while the basal planes are more inert. We explore SiO2 functionalization of the MoS2 surface, as the surface hydroxyl groups are known to be reactive sites for metal oxide ALD. Even a sub-nm thin discontinuous SiO2 layer can enable fast layer closure, if it consists of nm-size SiO2 islands with sub-nm spacing. As such, the MoS2 surface gets covered by the lateral and vertical growth of high-k dielectrics ALD, starting with nucleation on the SiO2 islands.Our findings add more knowledge on the nucleation and growth mechanisms of 2D materials. Moreover, the insight into the nucleation of high-k dielectrics and the surface functionalization may be applied to other materials and processes where thin and closed films are required." "2D transition metal dichalcogenides for beyond silicon logic devices: improving the Metal/MoS2 interface through molecular doping." "Marc Heyns" "Surface and Interface Engineered Materials, Sustainable Chemistry for Metals and Molecules" "2D materials have demonstrated enormous potential for a great number of applications such as sensors, spintronic, superconductors, and (photo)electronic devices. From these 2D materials, semiconducting transition metal dichalcogenides (MX2) are of special interest for electronic logic devices such as Field Effect Transistors (FETs), given their interesting properties such as ultra-thin bodies and high electronic band gap that could enable lower standby power dissipations and further boost the performance of devices. MoS2, a member of the semiconducting MX2 family, is normally used as a representative of this family given its robustness under normal environmental conditions, and its natural or synthetic availability. Nevertheless, several challenges need to be addressed before implementing MX2-based devices. Challenges such as understanding and characterizing such devices, reducing high contact resistance, and controlling the doping of such devices.Therefore, this work focuses on understanding and improving the Metal / MoS2 contact resistance and the controllable doping of MoS2-based devices. To achieve this, first the differences of MoS2 FETs compared to conventional inversion FETs are established. Then careful experiments comparing different characterization techniques are carried out to establish the most reliable way for device parameter extraction. The results show that contact resistance was dominated by a Schottky barrier (SB) in the Metal / MoS2 interface leading to high contact resistance of the devices. This contact resistance surpasses the channel resistance for channels smaller than 100nm. It is therefore clear that for further channel length scaling, so as to enhance the performance of the FET, reduction of contact resistance is of primordial interest. The observations from these experiments were then used to carefully model MoS2 FET behavior by using a semi-classical model. Further insight on the nature of high contact resistance was gained with this model and two major trajectories for the electron injection from the metal contact to the MoS2 film were identified. First of all,  a vertical trajectory in which the electrons are injected from the metal to the MoS2 region directly underneath the metal contact, and which are then driven toward the channel through the MoS2 film. Secondly, a lateral trajectory is identified, in which the electrons are injected directly from the border of the metal contact to the MoS2 film in the channel region. These trajectories depend on the height of the SB, the perpendicular, and lateral fields as well as the MoS2 film thickness. For films thinner than 2 layers, it becomes really difficult to accumulate carriers in the MoS2 film underneath the metal contact, and thus the lateral trajectory for injection prevails. It was clear from the model that the MoS2 FET sheet resistance varies greatly spatially, and that the assumption of the same sheet resistance for the whole film does not hold, rather it can be very different in the channel region and under the metal contact, especially for thin MoS2 devices. This introduces an error on the contact transfer length and the contact resistivity of the device when these parameters are extracted using the conventional transfer length method.Additionally, the model revealed that one effective way to reduce contact resistance was to dope the region of the MoS2 film immediately adjacent to the metal contact to enhance the lateral trajectory, which was always the most relevant trajectory. Two sets of experiments were conducted to demonstrate the possibility of effective and controllable surface doping without degrading the carrier mobility, by using two different approaches: self-assembled physisorbed molecules and spin-coating of polymers. Oleylamine (OA) was used for the self-assembly approach and doping was effectively demonstrated together with contact resistance reduction. The advantage of the self-assembly approach lies with the easiness of controlling the spatial distribution and density of carriers through the self-assembly of the molecules. However, the polymer approach is more industry-friendly and robust thermally. The polymer (polyvinyl-alcohol) approach also demonstrated the possibility of doping. After doping, the contact resistance was reduced by 30%. Finally, the relation between the MoS2 film thickness and the surface doping approach were explored, and it was concluded that surface doping is optimal for film thicknesses below 5.2nm.In general, even though an accelerated progress has been observed in MoS2 based devices, still additional work is required for a successful integration in industry. Further reduction of the contact resistance is required and more important, a way to integrate these devices with the additional stages of the manufacturing process, where temperature as high as 400 C are required (i.e. interconnects at the back-end) needs to be addressed." "HITEC - High Temperature Exciton Condensation in 2D Colloidal Nanoplatelets" "Iwan Moreels" "Department of Chemistry" "With the advent of a second quantum revolution in opto-electronics, the quantum nature of light and matter are being exploited for applications in communication, computing and sensing. A condensate of two-dimensional (2D) excitons, bosons comprised of strongly bound electron-hole pairs, is a key building block in this respect, as it can act as a superfluid with low resistance or as a low-power coherent light source. Experimental realization of such condensates at elevated temperatures are often hampered by either limitations to vary the physical parameters of the 2D exciton gas - due to restrictions in materials fabrication - or the limits imposed by existing materials themselves. In HITEC, we will use a combinatory approach to achieve exciton condensation at elevated temperatures. In particular, we will build on a wide suite of early stage physical observations and synthetic methods to design a class optimized 2D excitonic materials, based on so-called colloidal II-VI nanoplatelets. In combination with advanced femtosecond spectroscopy and single particle microscopy, these bottom-up nanomaterials will be optimized using novel core/shell architectures, to obtain specific (multi-)exciton properties and interactions required to achieve high-temperature exciton condensation, a result that will be a breakthrough for both colloidal 2D materials and quantum photonics in general." "Time-resolved optical microscopy techniques to characterize 2D transition metal dichalcogenides" "Valeri Afanasiev" "Semiconductor Physics" "2D transition metal dichalcogenides (TMDs) hold great potential for application in different fields, in particular in nanoelectronics and photonics. In nanoelectronics, large energy dissipation due to heating in chips is unsustainable in terms of both costs and performance drop and 2D TMDs hold great potential to alleviate these problems. In photonics, the integration of 2D TMDs is predicted to enhance the energy harvesting. Towards such applications, it is crucial to develop a controlled, engineered, synthesis at large scale of such materials with high uniformity and to investigate their electronic/optical/thermal dynamics. Among the TMDs, MoS2, MoTe2, WS2 and WTe2 and are the most attractive materials to be investigated. The aim of this project is to synthetize and characterize the 2D TMDs materials and develop ultrafast temporally and spectrally resolved high resolution optical microscopy methods to investigate the electronic and thermo-mechanical aspects of 2D TMDs deposited on a bulk substrate." "From 2D to 3D crystals: a multi-scale, multi-technique and multi-system approach of the crystallization of organic molecules" "Steven De Feyter" "Molecular Imaging and Photonics, MPG - Max-Planck-Gesellschaft, Université de Mons, Université Libre de Bruxelles, Universiteit Antwerpen, Technische Universität Graz" "The occurrence of two or more crystal structures for a given molecule, a phenomenon which is called polymorphism, is ubiquitous to various classes of synthetic and natural compounds. Examples of polymorphism are known in numerous application fields, such as food, explosives, pigments, semiconductors, fertilizers, and pharmaceutical drugs. Different crystal structures, so-called polymorphs, of the same compound exhibit sometimes very different physical properties, chemical reactivity, and biological functions. For instance, the polymorphs might differ in solubility ruining the pharmaceutical effect of one or more of the polymorphs. Understanding and controlling polymorphism is therefore very important. Simple questions, such as ""How many polymorphs has a given compound?"" or ""What drives polymorph selection?"", remain unanswered yet. In this scientific context, scientists have started to explore the occurrence of substrate-induced polymorphism, i.e. the formation of polymorphs that exist only in the vicinity of solid substrates. In particular, 2Dto3D has the ambition to elucidate how positional and orientational order of molecules propagate from the substrate to the upper crystal layers. In this manner, 2Dto3D will gain a fundamental understanding of polymorphism at the interface with solid substrates."