can allow the discovery of basic new physical phenomena and the development of new device concepts. [1] The discovery of new vdW quantum materials and their heterostructures starting from graphene, insulators, semiconductors, superconductors, and topological materials has revolutionized both fundamental and applied research. [2,3] The most recent addition to this vdW family is magnets, which have offered various advantages over conventional magnets and opened new perspectives in vdW heterostructure designs. [4][5][6] In addition to the atomically thin and flat nature of vdW magnets, flexibility, gate tunability, strong proximity interactions, and twist angle between the layers can offer a unique degree of freedom and an innovative platform for device functionalities. [4,5] Recently, several vdW magnets have emerged with the discovery of insulating Cr 2 Ge 2 Te 6 , [7] semiconducting (CrI 3 , [8] CrBr 3 [9] ), and metallic Fe x GeTe 2 . [10,11] The insulating vdW magnets are useful for spin-filter tunneling [9,12] and proximityinduced magnetism, [13][14][15] whereas the metallic magnets can be used as electrodes in magnetic tunnel junctions, [16] observationThe discovery of van der Waals (vdW) magnets opened a new paradigm for condensed matter physics and spintronic technologies. However, the operations of active spintronic devices with vdW ferromagnets are limited to cryogenic temperatures, inhibiting their broader practical applications. Here, the robust room-temperature operation of lateral spin-valve devices using the vdW itinerant ferromagnet Fe 5 GeTe 2 in heterostructures with graphene is demonstrated. The room-temperature spintronic properties of Fe 5 GeTe 2 are measured at the interface with graphene with a negative spin polarization. Lateral spin-valve and spin-precession measurements provide unique insights by probing the Fe 5 GeTe 2 /graphene interface spintronic properties via spin-dynamics measurements, revealing multidirectional spin polarization. Density functional theory calculations in conjunction with Monte Carlo simulations reveal significantly canted Fe magnetic moments in Fe 5 GeTe 2 along with the presence of negative spin polarization at the Fe 5 GeTe 2 / graphene interface. These findings open opportunities for vdW interface design and applications of vdW-magnet-based spintronic devices at ambient temperatures.

To obtain reduced specific contact resistivity, iodine donors and silver acceptors were ion-implanted into n-type and p-type (Bi,Sb)2(Se,Te)3 materials, respectively, to achieve >10 times higher doping at the surface. Implantation into n-type materials caused the specific contact resistivity to decrease from 1.7 × 10−6 Ω cm2 to 4.5 × 10−7 Ω cm2. Implantation into p-type materials caused specific contact resistivity to decrease from 7.7 × 10−7 Ω cm2 to 2.7 × 10−7 Ω cm2. For implanted thin-film superlattices, the non-implanted values of 1.4 × 10−7 Ω cm2 and 5.3 × 10−8 Ω cm2 precipitously dropped below the detection limit after implantation, ≤10−8 Ω cm2. These reductions in specific contact resistivity are consistent with an increase in tunneling across the contact.

We investigated the impact of doping group IIIA elements (Al, Ga, In and Tl) on the electronic structure and stability of PbTe by first principles calculations. The impurity-induced defect level changes as a function of the charge state of the impurity. We find that Al and In prefer to act as donors while Ga and Tl tend to act as acceptors in PbTe. Our analysis supports the ‘impurity level’ model where an impurity-induced localized state overlaps either the conduction band or valence band of PbTe, but our results do not agree with ‘mix-valence’ (i.e. 2In2+ → In+ + In3+) or ‘auto-compensation’ (i.e. 2In0 → In+ + In−) models. Our calculations suggest that Tl and In are suitable dopants for improving the thermoelectric efficiency through enhancing the Seebeck coefficient for p- and n-type PbTe, respectively.

Nanoelectrodes with spacing controlled between 1 and 10nm with subnanometer increment have been achieved using atomic layer deposition. Field emission and metal-vacuum-metal tunneling are used to characterize the electrode properties in situ during growth. The current-voltage data is modeled and gives electrode spacing of 1.0±0.2nm, a barrier height of 4.5eV, and electrode radius of 10nm. Temperature variation from 26to235°C changes the spacing by 0.05nm, as calculated from electrical data. This is close to 0.1nm expected from thermal expansion. Exposing to air reduces the barrier height to 2.15eV, which is explained by the growth of a thin metal oxide layer.

We investigate the electronic structures and stability for Ni/Bi2Te3, NiTe/Bi2Te3, Co/Bi2Te3 and CoTe2/Bi2Te3 interfaces by first-principles calculations. It is found that the surface termination strongly affects the band alignment. Ni and Co are found to form Ohmic contacts to Bi2Te3. The interface formation energy for Co/Bi2Te3 interfaces is much lower than that of Ni/Bi2Te3 interfaces. Furthermore, we found that NiTe on Bi2Te3 is more stable than Ni, while the formation energies for Co and CoTe2 on Bi2Te3 are comparable.