We use resonance Raman and optical reflection contrast methods to study charge transfer in 1-10 layer (1L-10L) thick graphene samples on which NO(2) has adsorbed. Electrons transfer from the graphene to NO(2), leaving the graphene layers doped with mobile delocalized holes. Doping follows a Langmuir-type isotherm as a function of NO(2) pressure. Raman and optical contrast spectra provide independent, self-consistent measures of the hole density and distribution as a function of the number of layers (N). At high doping, as the Fermi level shift E(F) reaches half the laser photon energy, a resonance in the graphene G mode Raman intensity is observed. We observe a decrease of graphene optical absorption in the near-IR that is due to hole-doping. Highly doped graphene is more optically transparent and much more electrically conductive than intrinsic graphene. In thicker samples, holes are effectively confined near the surface, and in these samples, a small band gap opens near the surface. We discuss the properties and versatility of these highly charge-transfer-doped, few-layer-thick graphene samples as a new class of electronic materials.

Interest in additive manufacturing has recently been spurred by the promise of multi-material printing and the ability to embed functionality and intelligence into objects. Here, we present an alternative to additive manufacturing, introducing an end-to-end workflow in which discrete building blocks are reversibly joined to produce assemblies called digital materials. We describe the design of the bulk-material building blocks and the devices that are assembled from them. Further, we detail the design and implementation of an automated assembler, which takes advantage of the digital material structure to restore positioning errors within a large tolerance. To generate assembly sequences, we use a novel CAD/CAM workflow for designing, simulating, and assembling digital materials. Finally, we evaluate the structures assembled using this process, showing that the joints perform well under varying conditions and that the assembled structures are functionally precise.

Computational flattening algorithms have been successfully applied to X-ray microtomography scans of damaged historical documents, but have so far been limited to scrolls, books, and documents with one or two folds. The challenge tackled here is to reconstruct the intricate folds, tucks, and slits of unopened letters secured shut with “letterlocking,” a practice—systematized in this paper—which underpinned global communications security for centuries before modern envelopes. We present a fully automatic computational approach for reconstructing and virtually unfolding volumetric scans of a locked letter with complex internal folding, producing legible images of the letter’s contents and crease pattern while preserving letterlocking evidence. We demonstrate our method on four letterpackets from Renaissance Europe, reading the contents of one unopened letter for the first time. Using the results of virtual unfolding, we situate our findings within a novel letterlocking categorization chart based on our study of 250,000 historical letters.

No abstract

Extraterrestrial fabrication of spacecraft by current best-practice manufacturing methods is complicated by the need to integrate thousands of unique parts, each made using a diversity of processes and raw materials. Reducing this complexity could enable exponential space exploration via self-replicating spacecraft (known as Von Neumann probes). We propose a hierarchical model for machine design, based on 13 reversiblyassembled part types, reducing the complexity of machine selfreplication and bridging prior work in the areas of in-situ resource utilization (ISRU) and modular robotics. Analogous to amino acids in biological systems, these parts form a basis set for the electronic and mechanical subsystems of an exploratory spacecraft. In simulation we validate representative subsystem designs and develop a hierarchical architecture for the design of mechanisms, actuation, and electronics. By standardizing and modularizing the parts, we drastically reduce the diversity of the required supply chain as well as the minimum viable payload mass. We estimate that a seed launch could contain approximately 10 5 parts, fit within the envelope of a 3U cubesat, and enable the assembly of over one hundred self-replicating assemblers.