The advent of devices based on single dopants, such as the single atom transistor 1 , the single spin magnetometer 2,3 and the single atom memory 4 , motivates the quest for strategies that permit to control matter with atomic precision. Manipulation of individual atoms by means of low-temperature scanning tunnelling microscopy 5 provides ways to store data in atoms, encoded either into their charge state 6,7 , magnetization state 8-10 or lattice position 11 . A defining challenge at this stage is the controlled integration of these individual functional atoms into extended, scalable atomic circuits. Here we present a robust digital atomic scale memory of up to 1 kilobyte (8,000 bits) using an array of individual surface vacancies in a chlorine terminated Cu(100) surface. The memory can be read and rewritten automatically by means of atomic scale markers, and offers an areal density of 502 Terabits per square inch, outperforming state-of-the-art hard disk drives by three orders of magnitude. Furthermore, the chlorine vacancies are found to be stable at temperatures up to 77 K, offering prospects for expanding large-scale atomic assembly towards ambient conditions.Since the first demonstration of atom manipulation, 25 years ago 5 , the preferred approach for assembling atomic arrangements has been the lateral positioning of atoms or molecules evaporated onto a flat metal surface, most notably the (111) crystal surface of copper [12][13][14][15] . While ideal for experiments comprising up to several hundreds of constituents, the absence of a large-scale defect-free detectable grid on this surface prohibits the construction of architectures involving correlated lattice-placement of atoms separated by more than a few nanometres. Moreover, thermal motion of the adatoms restricts the technique to temperatures below 10 K. As we demonstrate below, we find that manipulation of missing atoms in a surface (vacancies) 16 , as opposed to additional atoms atop, permits a dramatic leap forward in our capability to build functional devices on the atomic scale.To this purpose, we take advantage of the self-assembly of chlorine atoms on the Cu(100) surface [17][18][19][20] , forming a flat two-dimensional lattice with several convenient properties. First, it provides large areas of a perfect template grid, with a controllable coverage of vacancies. Second, the chlorine lattice remains stable up to a large density of vacancies and up to relatively high temperature (77 K). And third, critical for our purpose, the precise location of the vacancies can be manipulated by STM with a very high level of control (and without the need to pick-up atoms with the tip, i.e. vertical atom manipulation). As we show below, these properties allow us to position thousands of vacancies at predefined atomic sites in a reasonable timeframe.The chlorinated copper surface is prepared in ultra-high vacuum through the evaporation of anhydrous CuCl 2 powder heated to 300 °C onto a clean Cu(100) crystal surface. The crystal is pre-heated to 100-150 °C prior...

Paramagnetic transition-metal complexes assembled on surfaces are of great interest for potential applications in organic spintronics. The magnetochemical interactions of the spin of the metal centers with both ferromagnetic surfaces and optional axial ligands are yet to be understood. We use a combination of X-ray magnetic circular dichroism (XMCD) and quantum-chemical simulations based on density functional theory (DFT+U) to investigate these metal-organic interfaces with chemically tunable magnetization. The interplay between an optional axial ligand (NO, spin S=1/2 or NH 3 , S=0) and Ni and Co ferromagnetic surfaces affecting the spin of Co(II) tetraphenylporphyrin (d 7 , S=1/2), Fe(II) tetraphenylporphyrin (d 6 , S=1), Mn(II) tetraphenylporphyrin (d 5 , S=5/2) and Mn(II) phthalocyanine (d 5 , S=3/2) is studied. We find that the structural trans effect on the surface rules the molecular spin state as well as the sign and strength of the exchange interaction with the substrate. We refer to this observation as the surface spin-trans effect.

Realization of long-range magnetic order in surface-supported two-dimensional systems has been challenging, mainly due to the competition between fundamental magnetic interactions as the short-range Kondo effect and spin-stabilizing magnetic exchange interactions. Spin-bearing molecules on conducting substrates represent a rich platform to investigate the interplay of these fundamental magnetic interactions. Here we demonstrate the direct observation of long-range ferrimagnetic order emerging in a two-dimensional supramolecular Kondo lattice. The lattice consists of paramagnetic hexadeca-fluorinated iron phthalocyanine (FeFPc) and manganese phthalocyanine (MnPc) molecules co-assembled into a checkerboard pattern on single-crystalline Au(111) substrates. Remarkably, the remanent magnetic moments are oriented in the out-of-plane direction with significant contribution from orbital moments. First-principles calculations reveal that the FeFPc-MnPc antiferromagnetic nearest-neighbour coupling is mediated by the Ruderman–Kittel–Kasuya–Yosida exchange interaction via the Au substrate electronic states. Our findings suggest the use of molecular frameworks to engineer novel low-dimensional magnetically ordered materials and their application in molecular quantum devices.

The presence of an oxygen reconstruction on the Cu(001) surface results in the self-metalation of 5,10,15,20-tetraphenylporphyrin (2HTPP) below room temperature (at ~285 K), in contrast to 2HTPP on the bare Cu(001) substrate, where a temperature of ~450 K is required. This study demonstrates the decisive impact of a surface reconstruction on the redox reaction in the solvent-free ultra-high vacuum environment.