Exotic Substrates Research Articles

Substrate‐Free Transfer of Large‐Area Ultra‐Thin Electronics

AbstractInnovation in materials and technologies has promoted the fabrication of thin‐film electronics on substrates previously considered incompatible because of their chemical or mechanical properties. Indeed, conventional fabrication processes, typically based on photolithography, involve solvents and acids that might harm fragile or exotic substrates. In this context, transfer techniques define a route to overcome the issues related to the nature of the substrate by using supportive carriers in the electronics stack that mitigate or avoid any damages during the fabrication process. Here, a substrate‐free approach is presented for the transfer of ultra‐thin electronics (<150nm‐thick) where no additional layer besides the electronics one remains on the final substrate. Devices are transferred on several surfaces showing good adhesion and an average performance variation of 27%. Furthermore, a sensor bent to a radius of 15.25µm, shows variation in performance of 5%. The technique can also be sequentially repeated for the fabrication of stacked electronics, enabling the development of ultra‐thin devices, compliant on unconventional surfaces.

Bacterial Utilisation of Aliphatic Organics: Is the Dwarf Planet Ceres Habitable?

The regolith environment and associated organic material on Ceres is analogous to environments that existed on Earth 3–4 billion years ago. This has implications not only for abiogenesis and the theory of transpermia, but it provides context for developing a framework to contrast the limits of Earth’s biosphere with extraterrestrial environments of interest. In this study, substrate utilisation by the ice-associated bacterium Colwellia hornerae was examined with respect to three aliphatic organic hydrocarbons that may be present on Ceres: dodecane, isobutyronitrile, and dioctyl-sulphide. Following inoculation into a phyllosilicate regolith spiked with a hydrocarbon (1% or 20% organic concentration wt%), cell density, electron transport activity, oxygen consumption, and the production of ATP, NADPH, and protein in C. hornerae was monitored for a period of 32 days. Microbial growth kinetics were correlated with changes in bioavailable carbon, nitrogen, and sulphur. We provide compelling evidence that C. hornerae can survive and grow by utilising isobutyronitrile and, in particular, dodecane. Cellular growth, electron transport activity, and oxygen consumption increased significantly in dodecane at 20 wt% compared to only minor growth at 1 wt%. Importantly, the reduction in total carbon, nitrogen, and sulphur observed at 20 wt% is attributed to biotic, rather than abiotic, processes. This study illustrates that short-term bacterial incubation studies using exotic substrates provide a useful indicator of habitability. We suggest that replicating the regolith environment of Ceres warrants further study and that this dwarf planet could be a valid target for future exploratory missions.

Wafer-Scale Two-Dimensional MoS2 Layers Integrated on Cellulose Substrates Toward Environmentally Friendly Transient Electronic Devices.

We explored the feasibility of wafer-scale two-dimensional (2D) molybdenum disulfide (MoS2) layers toward futuristic environmentally friendly electronics that adopt biodegradable substrates. Large-area (> a few cm2) 2D MoS2 layers grown on silicon dioxide/silicon (SiO2/Si) wafers were delaminated and integrated onto a variety of cellulose-based substrates of various components and shapes in a controlled manner; examples of the substrates include planar papers, cylindrical natural rubbers, and 2,2,6,6-tetramethylpiperidine-1-oxyl-oxidized cellulose nanofibers. The integrated 2D layers were confirmed to well preserve their intrinsic structural and chemical integrity even on such exotic substrates. Proof-of-concept devices employing large-area 2D MoS2 layers/cellulose substrates were demonstrated for a variety of applications, including photodetectors, pressure sensors, and field-effect transistors. Furthermore, we demonstrated the complete "dissolution" of the integrated 2D MoS2 layers in a buffer solution composed of baking soda and deionized water, confirming their environmentally friendly transient characteristics. Moreover, the approaches to delaminate and integrate them do not demand any chemicals except for water, and their original substrates can be recycled for subsequent growths, ensuring excellent chemical benignity and process sustainability.

(Invited) Wafer-Scale Integration of 2D TMD Heterostructures of Controlled Layer Orientation on Arbitrary Substrates Towards Mechanically-Reconfigurable Electronic Devices

Advancements of modern electronics have demanded to incorporate a diverse set of additional functionalities into device platforms such as high mechanical deformability and improved material/process sustainability. Traditional silicon (Si) wafers-based device manufacturing is intrinsically limited in realizing such novel aspects owing to their rigid/bulky nature as well as complex and unsustainable process schemes. Two-dimensional (2D) transition metal dichalcogenide (TMD) semiconductors are highly promising owing to their extremely large mechanical flexibility and near atom thickness coupled with van der Waals (vdW) attraction-enabled relaxed assembly requirement. Major challenges for realizing such opportunities for emerging electronics have been associated with a lack of reliable manufacturing methods to precisely separate 2D TMD layers from original growth wafers and integrate them on desired functional substrates in a controllable, scalable, and sustainable manner. In this talk, I will discuss recent efforts in my group on exploring viable manufacturing strategies to assemble wafer-scale 2D TMD layers of heterogeneously tailored components on arbitrary substrates. We grew various 2D TMD layers of controlled layer orientation on specially-treated growth substrates with high hydrophilicity or water solubility via a chemical vapor deposition (CVD) process. By taking advantage of the large surface energy contrast between growth substrates vs. grown 2D TMDs, we precisely peel off wafer-scale 2D TMD layers from their original substrates using water preserving their intrinsic structural/chemical integrity. We then integrate them on substrates of virtually unrestricted kinds and shapes in a layer-by-layer fashion, realizing heterogeneously-assembled wafer-scale 2D TMDs layers on a variety of exotic substrates impossible with any conventional approaches. The achieved material quality has been characterized via extensive microscopy/spectroscopy techniques, and the original substrates have been sustainably recycled for sequential growth and integration. Several demonstrations of 2D TMDs-enabled mechanically reconfigurable electronic devices will be presented, which will be impossible with any other traditional materials. This novel manufacturing strategy is believed to greatly broaden the applicability of 2D TMDs in emerging areas of electronics such as three-dimensionally conformal electronic devices of unconventional forms factors.

Automated Assembly of Wafer-Scale 2D TMD Heterostructures of Arbitrary Layer Orientation and Stacking Sequence Using Water Dissoluble Salt Substrates.

We report a novel strategy to assemble wafer-scale two-dimensional (2D) transition metal dichalcogenide (TMD) layers of well-defined components and orientations. We directly grew a variety of 2D TMD layers on "water-dissoluble" single-crystalline salt wafers and precisely delaminated them inside water in a chemically benign manner. This manufacturing strategy enables the automated integration of vertically aligned 2D TMD layers as well as 2D/2D heterolayers of arbitrary stacking orders on exotic substrates insensitive to their kind and shape. Furthermore, the original salt wafers can be recycled for additional growths, confirming high process sustainability and scalability. The generality and versatility of this approach have been demonstrated by developing proof-of-concept "all 2D" devices for diverse yet unconventional applications. This study is believed to shed a light on leveraging opportunities of 2D TMD layers toward achieving large-area mechanically reconfigurable devices of various form factors at the industrially demanded scale.

Solution‐Phase Synthesis of Few‐Layer Hexagonal Antimonene Nanosheets via Anisotropic Growth

Antimonene, an emerging two-dimensional material, has garnered tremendous interest due to its intriguing structure and fascinating electronic properties. However, the synthesis of high-quality few-layer antimonene nanosheets, which can only be produced by exfoliation or epitaxial growth on exotic substrates, has greatly hindered the development of this new field. Herein, few-layer hexagonal and functionalized antimonene nanosheets were successfully prepared from SbCl3 solutions for the first time by exclusively promoting their anisotropic growth in a colloidal solution. Oleylamine was selected as the reducing agent, rather than oleic acid, and dodecylthiol was key to preventing the formation of antimony oxide. Additionally, halide ions adsorbed on the surface also influenced the anisotropic growth of hexagonal antimonene nanosheets. Atomic force microscopy (AFM) revealed that the sheets were ≈5 nm thick; Raman spectroscopy and X-ray diffraction (XRD) revealed a rhombohedral atomic structure (β-Sb) with excellent stability.

Centimeter-scale Green Integration of Layer-by-Layer 2D TMD vdW Heterostructures on Arbitrary Substrates by Water-Assisted Layer Transfer

Two-dimensional (2D) transition metal dichalcogenide (2D TMD) layers present an unusually ideal combination of excellent opto-electrical properties and mechanical tolerance projecting high promise for a wide range of emerging applications, particularly in flexible and stretchable devices. The prerequisite for realizing such opportunities is to reliably integrate large-area 2D TMDs of well-defined dimensions on mechanically pliable materials with targeted functionalities by transferring them from rigid growth substrates. Conventional approaches to overcome this challenge have been limited as they often suffer from the non-scalable integration of 2D TMDs whose structural and chemical integrity are altered through toxic chemicals-involved processes. Herein, we report a generic and reliable strategy to achieve the layer-by-layer integration of large-area 2D TMDs and their heterostructure variations onto a variety of unconventional substrates. This new 2D layer integration method employs water only without involving any other chemicals, thus renders distinguishable advantages over conventional approaches in terms of material property preservation and integration size scalability. We have demonstrated the generality of this method by integrating a variety of 2D TMDs and their heterogeneously-assembled vertical layers on exotic substrates such as plastics and papers. Moreover, we have verified its technological versatility by demonstrating centimeter-scale 2D TMDs-based flexible photodetectors and pressure sensors which are difficult to fabricate with conventional approaches. Fundamental principles for the water-assisted spontaneous separation of 2D TMD layers are also discussed.

Inside view

inside view

Synthesis of Antimonene on Germanium

The lack of large-area synthesis processes on substrates compatible with industry requirements has been one of the major hurdles facing the integration of 2D materials in mainstream technologies. This is particularly the case for the recently discovered monoelemental group V 2D materials which can only be produced by exfoliation or growth on exotic substrates. Herein, to overcome this limitation, we demonstrate a scalable method to synthesize antimonene on germanium substrates using solid-source molecular beam epitaxy. This emerging 2D material has been attracting a great deal of attention due to its high environmental stability and its outstanding optical and electronic properties. In situ low energy electron microscopy allowed the real time investigation and optimization of the 2D growth. Theoretical calculations combined with atomic-scale microscopic and spectroscopic measurements demonstrated that the grown antimonene sheets are of high crystalline quality, interact weakly with germanium, exhibit semimetallic characteristics, and remain stable under ambient conditions. This achievement paves the way for the integration of antimonene in innovative nanoscale and quantum technologies compatible with the current semiconductor manufacturing.

Fungal colonization of exotic substrates in Antarctica

Throughout the history of polar exploration and up to recent times, wood and other exotic materials have been brought to the Antarctic continent and left there. While the possible transportation of exotic fungal species on these materials is sometimes considered, the effects of these exotic substrates on indigenous fungal communities have not been previously evaluated. This study reports results from seven plots where organic materials were used in baiting studies to determine the fungal diversity present in soils. Four plots were on islands in the Palmer Archipelago on the Antarctic Peninsula and three at Ross Island, Antarctica. Samples of sterile wood and cellulose with and without nutrients added were buried in soil and left for either two or four years before being removed and evaluated for fungal colonization. There was a significant increase in fungal colony-forming units (CFU) from soil in direct contact with introduced, sterile wood and cellulose substrates compared to background soil levels. The type of substrate, 2 or 4 year incubation period in the field, or nutrient addition did not have a significant effect on culturable densities in soil. Fungal abundance on soil adhering to substrates was found to be similar to that found in non-polar soils indicating that lack of organic material may be the most significant limiting factor affecting densities of Antarctic fungal populations. Based on a high degree of colonization, these exotic substrates appear to have a significant effect on indigenous soil fungal abundance.

Optimal Conditions for Micromachining $\hbox{Si}_{1 - { \rm x}}\hbox{Ge}_{\rm x}$ at 210 $^{\circ}\hbox{C}$

This paper investigates the possibility of reducing the deposition temperature of silicon-germanium (Si1-xGex) thin films to 210degC and tuning the physical properties of the film locally to achieve optimal mechanical and electrical properties that are suitable for a wide range of microelectromechanical systems that can be postprocessed on top of standard prefabricated electronics or onto more exotic substrates, such as polymer films. First, the effect of the Ge content, layer thickness, and deposition pressure on the mechanical properties of as-deposited Si1-xGex films, which are deposited at 210degC, is analyzed in detail, and the optimal deposition conditions are experimentally determined. Then, the possibility of using pulsed excimer laser annealing to control the electrical and mechanical properties of such films is demonstrated. It is shown that the low deposition temperature imposes many constraints on the laser-annealing conditions, particularly for optimizing the mechanical properties. Moreover, the Ge content and the film thickness have a significant influence on the optimal laser-annealing conditions. It is illustrated that eliminating stress gradient implies very shallow crystallization, which is accompanied by relatively high electrical resistivity. Using the optimal laser-annealing conditions, the stress gradient can be as low as 1 times 10-6 mum-1 for a 0.3-mum-thick film. The optimal electrical resistivity, on the other hand, depends on the Ge content. For 70% Ge, the minimum resistivity is 80 mOmega ldr cm; decreasing the Ge content to 30% results in a resistivity of 3 Omega ldr cm.

The establishment of rumen microbial communities

In young ruminants, the strictly anaerobic bacteria that colonise the rumen are accompanied by a wide range of facultatively-anaerobic organisms, together with some aerobic bacteria. During the development of the rumen, the flora resolves into a spatially-organised set of domains, each populated by characteristic, but to some extent overlapping, consortia. Within and between these consortia, donor/acceptor, predator/prey and competitive relations can be found. The results of experiments on the establishment of functioning microbial communities in gnotobiotic lambs are considered. It seems that any attempt to introduce components of the rumen microflora must take account of the principles of microbial ecology, as they relate to the colonisation of ecosystems. In particular, it is necessary to provide suitable ecological niches for colonisation, which are suitable with respect to sources of energy, carbon, nitrogen minerals and trace nutrients for growth, at ambient pH and Eh values compatible with the tolerance of the desired organisms. The further manipulation of functions that have already been subject to intense natural selective pressure is likely to be particularly difficult. However manipulation to control rumen disorders, utilise exotic substrates or to detoxify toxic compounds produced by plants may be more promising.

Discontinuous RNA synthesis through trans‐splicing

AbstractIn eukaryotic cells intron sequences are usually spliced out with a high degree of precision from heterogenous nuclear RNA (hnRNA) to give functional mRNA with exons in their right order. Provided with the right substrates, cell extracts can achieve the same. With exotic substrates, on the other hand, the same extracts can cut exons from one RNA and join them to exons from another RNA, a process termed trans‐splicing. In vivo, RNA trans‐splicing could lead to faulty, but also to novel proteins and, through reverse transcription, to genomic rearrangements. So far, in living cells trans‐splicing has only been invoked to occur in trypanosomes. In these unicellular organisms most if not all mRNAs are made discontinuously, so that the mature mRNAs carry, at their 5′ end, a common 35‐nucleotide sequence, called a miniexon, encoded separately in the genome. The miniexon is most likely joined to the body of the mRNA by trans‐splicing.