Paper offers a cheap, flexible and biodegradable alternative substrate to silicon for simple electronic devices like disposable sensors. Not only is ordinary copy paper 10,000 times cheaper than silicon, but it also avoids the problems of electronic waste. Van der Waals materials are ideal for this type of device because of their wide-ranging electronic, optical, and mechanical properties. <\/p>\n\n\n\n
\u201cWe have demonstrated a simple, low-cost, and scalable way of depositing layered so-called van der Waals materials, similar to graphite, onto standard paper substrates, […] This method, unlike other widespread approaches, is completely dry and yields films with high electrical conductivity and high-quality optical properties.\u201d<\/p>explains Andres Castellanos-Gomez of Instituto de Ciencia de los Materiales de Madrid, who led the work with Riccardo Frisenda.<\/cite><\/blockquote>\n\n\n\n
Ink-jet printing is commonly used to deposit van der Waals materials, but requires expensive, specialized paper and struggles to produce conductive thin films reliably. By contrast, the dry abrasion-related technique explored by Castellanos-Gomez, Frisenda and their colleagues at Universidad Aut\u00f3noma de Madrid, Northwestern Polytechnical University in China, the Kavli Institute of Nanoscience in the Netherlands, and Universidad Nacional Aut\u00f3noma de M\u00e9xico, is just like writing on paper with a pencil and yields surprisingly good results.<\/p>\n\n\n\n
A powdered van der Waals material is rubbed onto the rough surface of regular paper using a cotton swab. The rubbing action breaks the weak van der Waals inter-layer bonds and forms a thin film of material. By combining the all-dry technique with cut-out masks, more complex device designs can be created.<\/p>\n\n\n\n
\u201cAbrasion-induced deposition could be a universal method to deposit highly conductive films of van der Waals materials, […] This process\u2026 cleaves microcrystals of van der Waals material and leaves an interconnected network of platelets on the surface of the paper.\u201d<\/p>says Castellanos-Gomez.<\/cite><\/blockquote>\n\n\n\n
The approach works with over 40 different van der Waals materials from conductors like graphite to semiconductors like black phosphorus to superconductors like NbSe2<\/sub> or wide bandgap insulators like BN. While the process yields films composed of flakes of varying thickness, which is a disadvantage for high-performance devices, the results are perfectly acceptable for cheap, disposable devices.<\/p>\n\n\n\n
\u201cWe demonstrated that the optical and electrical properties of the van der Waals films deposited through this method are superior to those obtained by conventional wet-based deposition methods like inkjet printing or spray coating,\u201d<\/p>adds Castellanos-Gomez.<\/cite><\/blockquote>\n\n\n\n
As an example, the team created field-effect transistors on paper from four different van der Waals materials and believe the approach is promising for disposable electronics like single-use sensors.<\/p>\n\n\n\n