Andras Kis

Bio: Andras Kis is an academic researcher from École Polytechnique Fédérale de Lausanne. The author has contributed to research in topics: Monolayer & Semiconductor. The author has an hindex of 67, co-authored 165 publications receiving 53990 citations. Previous affiliations of Andras Kis include École Normale Supérieure & Lawrence Berkeley National Laboratory.

Defect induced, layer-modulated magnetism in ultrathin metallic PtSe 2

Abstract: Defects are ubiquitous in solids and often introduce new properties that are absent in pristine materials. One of the opportunities offered by these crystal imperfections is an extrinsically induced long-range magnetic ordering1, a long-time subject of theoretical investigations1–3. Intrinsic, two-dimensional (2D) magnetic materials4–7 are attracting increasing attention for their unique properties, which include layer-dependent magnetism4 and electric field modulation6. Yet, to induce magnetism into otherwise non-magnetic 2D materials remains a challenge. Here we investigate magneto-transport properties of ultrathin PtSe2 crystals and demonstrate an unexpected magnetism. Our electrical measurements show the existence of either ferromagnetic or antiferromagnetic ground-state orderings that depends on the number of layers in this ultrathin material. The change in the device resistance on the application of a ~25 mT magnetic field is as high as 400 Ω with a magnetoresistance value of 5%. Our first-principles calculations suggest that surface magnetism induced by the presence of Pt vacancies and the Ruderman–Kittel–Kasuya–Yosida (RKKY) exchange couplings across ultrathin films of PtSe2 are responsible for the observed layer-dependent magnetism. Given the existence of such unavoidable growth-related vacancies in 2D materials8,9, these findings can expand the range of 2D ferromagnets into materials that would otherwise be overlooked. Magneto-transport measurements on thin metallic crystals of the transition metal dichalcogenide PtSe2 show signatures of ferro- and antiferromagnetic order depending on the number of layers and first-principles calculations suggest Pt vacancies at the surface as a plausible cause.

MoS2 transistors operating at gigahertz frequencies.

Abstract: The presence of a direct band gap 1−4 and an ultrathin form factor 5 has caused a considerable interest in two-dimensional (2D) semiconductors from the transition metal dichalcogenides (TMD) family with molybdenum disulfide (MoS2) being the most studied representative of this family of materials. While diverse electronic elements, 6,7 logic circuits, 8,9 and optoelectronic devices 12,13 have been demonstrated using ultrathin MoS2, very little is known about their performance at high frequencies where commercial devices are expected to function. Here, we report on top-gated MoS2 transistors operating in the gigahertz range of frequencies. Our devices show cutoff frequencies reaching 6 GHz. The presence of a band gap also gives rise to current saturation, 10 allowing power and voltage gain, all in the gigahertz range. This shows that MoS2 could be an interesting material for realizing high-speed amplifiers and logic circuits with device scaling expected to result in further improvement of performance. Our work represents the first step in the realization of high-frequency analog and digital circuits based on 2D semiconductors.

Shrinking a carbon nanotube.

Abstract: We report a method to controllably alter the diameter of an individual carbon nanotube. The combination of defect formation via electron irradiation and simultaneous resistive heating and electromigration in vacuum causes the nanotube to continuously transform into a high-quality nanotube of successively smaller diameter, as observed by transmission electron microscopy. The process can be halted at any diameter. Electronic transport measurements performed in situ reveal a striking dependence of conductance on nanotube geometry. As the diameter of the nanotube is reduced to near zero into the carbon chain regime, we observe negative differential resistance.

Electrochemical reaction in single layer MoS2: nanopores opened atom by atom

Abstract: Ultrathin nanopore membranes based on 2D materials have demonstrated ultimate resolution toward DNA sequencing. Among them, molybdenum disulphide (MoS2) shows long-term stability as well as superior sensitivity enabling high throughput performance. The traditional method of fabricating nanopores with nanometer precision is based on the use of focused electron beams in transmission electron microscope (TEM). This nanopore fabrication process is time-consuming, expensive, not scalable and hard to control below 1 nm. Here, we exploited the electrochemical activity of MoS2 and developed a convenient and scalable method to controllably make nanopores in single-layer MoS2 with sub-nanometer precision using electrochemical reaction (ECR). The electrochemical reaction on the surface of single-layer MoS2 is initiated at the location of defects or single atom vacancy, followed by the successive removals of individual atoms or unit cells from single-layer MoS2 lattice and finally formation of a nanopore. Step-like features in the ionic current through the growing nanopore provide direct feedback on the nanopore size inferred from a widely used conductance vs. pore size model. Furthermore, DNA translocations can be detected in-situ when as-fabricated MoS2 nanopores are used. The atomic resolution and accessibility of this approach paves the way for mass production of nanopores in 2D membranes for potential solid-state nanopore sequencing.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides.

Abstract: Single-layer metal dichalcogenides are two-dimensional semiconductors that present strong potential for electronic and sensing applications complementary to that of graphene.