Graphene nanoribbons (GNRs) are of enormous research interest as a promising active component in electronic devices, for example, field-effect transistors (FET). The recently developed "bottomup" on-surface synthesis provides an unprecedented approach for the generation of GNRs on metal surfaces with atomic precision. In order to fabricate well-defined GNRs on surfaces, numerous previous works have been focused on the delicate engineering of building blocks. Lateral fusion of polyphenylene chains into GNRs, as a more flexible method, now has received an increasing attention. However, the lateral fusion into GNRs reported to date is merely limited to the straight GNRs. The GNRs with other topologies potentially displaying distinctive electronic properties are rarely reported. In this work, we report the synthesis of armchair-edged graphene nanoribbons (AGNRs) with zigzag topology for the first time via a stepwise polymerization reaction starting from 4,4″-dibromo-m-terphenyl (DMTP) precursor on Au(111). Self-assembled unreacted monomers, covalent dimers, and zigzag polyphenylene chains are observed at different temperatures. Various GNRs with zigzag topology, including 6-AGNRs, 9-AGNRs, and nanoporous AGNRs are eventually produced through lateral fusion of polyphenylene chains. This study further diversifies the GNR family. Confining the zigzag polyphenylene chains in an ideal arrangement for subsequent lateral fusion can be explored in the future.

Abstract-Hardware technologies for trusted computing, or trusted execution environments (TEEs), have rapidly matured over the last decade. In fact, TEEs are at the brink of widespread commoditization with the recent introduction of Intel Software Guard Extensions (Intel SGX). Despite such rapid development of TEE, software technologies for TEE significantly lag behind their hardware counterpart, and currently only a select group of researchers have the privilege of accessing this technology. To address this problem, we develop an open source platform, called OpenSGX, that emulates Intel SGX hardware components at the instruction level and provides new system software components necessarily required for full TEE exploration. We expect that the OpenSGX framework can serve as an open platform for SGX research, with the following contributions. First, we develop a fully functional, instruction-compatible emulator of Intel SGX for enabling the exploration of software/hardware design space, and development of enclave programs. OpenSGX provides a platform for SGX development, meaning that it provides not just emulation but also operating system components, an enclave program loader/packager, an OpenSGX user library, debugging, and performance monitoring. Second, to show OpenSGX's use cases, we applied OpenSGX to protect sensitive information (e.g., directory) of Tor nodes and evaluated their potential performance impacts. Therefore, we believe OpenSGX has great potential for broader communities to spark new research on soon-to-becommodity Intel SGX.

Kagome nanoporous graphenes (NPGs) are fascinating due to their exotic electronic and magnetic properties. The emerging on-surface synthesis (mostly on metal surfaces) provides a new opportunity to fabricate Kagome NPGs...

Selective control on the topology of low-dimensional covalent organic nanostructures in on-surface synthesis has been challenging. Herein, with combined scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS), we report a successful topology-selective coupling reaction on the Cu(111) surface by tuning the thermal annealing procedure. The precursor employed is 1,3,5-tris­(2-bromophenyl)­benzene (TBPB), for which Ullmann coupling is impeded due to the intermolecular steric hindrance. Instead, its chemisorption on the Cu(111) substrate has triggered the ortho C–H bond activation and the following dehydrogenative coupling at room temperature (RT). In the slow annealing experimental procedure, the monomers have been preorganized by their self-assembly at RT, which enhances the formation of dendritic structures upon further annealing. However, the chaotic chirality of dimeric products (obtained at RT) and hindrance from dense molecular island make the fabrication of high-quality porous two-dimensional nanostructures difficult. In sharp contrast, direct deposition of TBPB molecules on a hot surface led to the formation of ordered porous graphene nanoribbons and nanoflakes, which is confirmed to be the energetically favorable reaction pathway through density functional theory-based thermodynamic calculations and control experiments. This work demonstrates that different thermal treatments could have a significant influence on the topology of covalent products in on-surface synthesis and presents an example of the negative effect of molecular self-assembly to the ordered covalent nanostructures.