Hydrogen atom makes graphene magnetic Graphene has many extraordinary mechanical and electronic properties, but it's not magnetic. To make it so, the simplest strategy is to modify its electronic structure to create unpaired electrons. Researchers can do that by, for example, removing individual carbon atoms or adsorbing hydrogen onto graphene. This has to be done in a very controlled way because of a peculiarity of the graphene's crystal lattice, which consists of two sublattices. Gonzales-Herrero et al. deposited a single hydrogen atom on top of graphene and used scanning tunneling microscopy to detect magnetism on the sublattice lacking the deposited atom (see the Perspective by Hollen and Gupta). Science, this issue p. 437; see also p. 415 Scanning tunneling microscopy shows that a hydrogen atom deposited on graphene makes the complementary sublattice magnetic. [Also see Perspective by Hollen and Gupta] Isolated hydrogen atoms absorbed on graphene are predicted to induce magnetic moments. Here we demonstrate that the adsorption of a single hydrogen atom on graphene induces a magnetic moment characterized by a ~20–millielectron volt spin-split state at the Fermi energy. Our scanning tunneling microscopy (STM) experiments, complemented by first-principles calculations, show that such a spin-polarized state is essentially localized on the carbon sublattice opposite to the one where the hydrogen atom is chemisorbed. This atomically modulated spin texture, which extends several nanometers away from the hydrogen atom, drives the direct coupling between the magnetic moments at unusually long distances. By using the STM tip to manipulate hydrogen atoms with atomic precision, it is possible to tailor the magnetism of selected graphene regions.

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Atomic-scale control of graphene magnetism by using hydrogen atoms

Zero-dimensional (0D) black phosphorus quantum dots (BPQDs) are emerging functional nanomaterials 0D BPQDs are a new form of black phosphorus (BP) nanostructures that were first prepared in 2015; they are different from typical two-dimensional (2D) BP layered nanosheets and one-dimensional (1D) BP nanoribbons Since 2015, numerous studies have been devoted to exploring various synthetic methods, properties and modifications of BPQDs, which exhibit a broad range of applications This review systematically summarizes PBQDs for the first time Different synthetic methods are reviewed, including ultrasonic and electrochemical exfoliation, solvothermal treatment, blender breaking, milling crushing and pulsed laser irradiation We highlight the physicochemical properties of BPQDs from theoretical models and discuss their experimentally observed properties The surface modifications and functionalized combination of BPQDs with other substances are summarized by illustrating different hybrid structures, such as BPQDs/nanosheets hybrids, BPQDs-doping films, BPQDs-molecules complexes, polymers-modified BPQDs, and the assembly of BPQDs in devices The potential applications of BPQDs are demonstrated in current research fields, including bioimaging, fluorescence sensing, nonlinear optical absorbers, cancer therapy, intelligent electronics, photovoltaics, optoelectronics and flexible devices The current status, challenges and future perspectives of PBQDs are discussed rationally This timely overall review should be desirable for broad scientists and facilitate the further development of layered nanostructures-derived QDs and other low-dimensional nanomaterials

Black phosphorus quantum dots: synthesis, properties, functionalized modification and applications.

We have synthesized three new phenylethynylated carbazole boronic acid sensors, which were predicted to display novel d-PeT fluorescence transduction (PeT, photoinduced electron transfer; fluorophore as the electron donor of the electron transfer, ET) by DFT/TDDFT calculations. The d-PeT effect is characterized by a lower background fluorescence at acidic pH than at neutral pH, which is in stark contrast to the normal a-PeT effect (fluorophore as the electron acceptor of the ET) that shows a strong and undesired background fluorescence at acidic pH. Our experimental results confirmed the theoretical predictions and d-PeT was observed for two of the sensors (with p-dimethylaminophenylethynyl substitution at 6- position of the carbazole core). For the third sensor (with phenylethynyl substitution at 6- position of the carbazole core), however, not d-PeT but rather the normal a-PeT was observed. The discrepancy between the DFT/TDDFT calculations and the experimental observations can be rationalized using free energy changes (Rehm-Weller equations) and the rate constants for the ET (k(ET), Marcus equation). These new d-PeT boronic acid sensors show improved photophysical properties compared to the known d-PeT sensor reported previously by us. In particular, the fluorescence transduction efficiency of the new sensors was improved 8-fold when compared to the known d-PeT boronic acid sensors. Novel fluorescence enhancement/reduction was observed for one of the sensors upon binding with mandelic acid or tartaric acid at pH 5.6. The effect of pH as well as the bonding with analytes on the emission of the sensors were rationalized using DFT/TDDFT calculations. We believe that rational sensor design aided by DFT/TDDFT calculations as well as using free energy changes and electron transfer rate constants to study the emission properties of PeT sensors will become an essential tool in the design of new fluorophores or fluorescent sensors with predetermined photophysical properties.

Rational Design of d-PeT Phenylethynylated-Carbazole Monoboronic Acid Fluorescent Sensors for the Se

Effective modulation of physical properties via external control may open various potential nanoelectronic applications of single-layer MoS 2 nanoribbons (MoS 2 NRs). We show by first-principles calculations that the magnetic and electronic properties of zigzag MoS 2 NRs exhibit sensitive response to applied strain and electric field. Tensile strain in the zigzag direction produces reversible modulation of magnetic moments and electronic phase transitions among metallic, half-metallic, and semiconducting states, which stem from the energy-level shifts induced by an internal electric polarization and the competing covalent/ionic interactions. A simultaneously applied electric field further enhances or suppresses the strain-induced modulations depending on the direction of the electric field relative to the internal polarization. These findings suggest a robust and efficient approach to modulating the properties of Mo 2 NRs by a combination of strain engineering and electric field tuning.

Tuning magnetism and electronic phase transitions by strain and electric field in zigzag MoS 2 nanoribbons

Molybdenum disulfide (MoS2) is a promising nonprecious catalyst for the hydrogen evolution reaction (HER) that has been extensively studied due to its excellent performance, but the lack of understanding of the factors that impact its catalytic activity hinders further design and enhancement of MoS2-based electrocatalysts. Here, by using novel porous (holey) metallic 1T phase MoS2 nanosheets synthesized by a liquid-ammonia-assisted lithiation route, we systematically investigated the contributions of crystal structure (phase), edges, and sulfur vacancies (S-vacancies) to the catalytic activity toward HER from five representative MoS2 nanosheet samples, including 2H and 1T phase, porous 2H and 1T phase, and sulfur-compensated porous 2H phase. Superior HER catalytic activity was achieved in the porous 1T phase MoS2 nanosheets that have even more edges and S-vacancies than conventional 1T phase MoS2. A comparative study revealed that the phase serves as the key role in determining the HER performance, as 1T phase MoS2 always outperforms the corresponding 2H phase MoS2 samples, and that both edges and S-vacancies also contribute significantly to the catalytic activity in porous MoS2 samples. Then, using combined defect characterization techniques of electron spin resonance spectroscopy and positron annihilation lifetime spectroscopy to quantify the S-vacancies, the contributions of each factor were individually elucidated. This study presents new insights and opens up new avenues for designing electrocatalysts based on MoS2 or other layered materials with enhanced HER performance.

(Invited) Contributions of Phase, Sulfur Vacancies, and Edges to the Hydrogen Evolution Reaction Catalytic Activity of Porous Molybdenum Disulfide Nanosheets

Using first-principles calculations, we have studied the energetic feasibility and magnetic properties of transition metal (TM) doped PtSe2 monolayers. Our study shows that TM doped PtSe2 layers with 6.25% doping exhibit versatile spintronic behaviour depending on the nature of the dopant TM atoms. Groups IVB and VIII10 TM doped PtSe2 layers are non magnetic semiconductors, while groups IIIB, VB, VIII8, VIII9, IB TM doped PtSe2 layers are half-metals and finally, groups VIB, VIIB and IIB TM doped PtSe2 layers are spin polarized semiconductors. The presence of half-metallic and magnetic semiconducting characteristics suggest that TM doped PtSe2 layers can be considered as a new kind of dilute magnetic semiconductor and thus have the promise to be used in spintronics. By studying the magnetic interactions between two TM dopants in PtSe2 monolayers for dopant concentration of 12.5% and dopant distance of 12.85 [Formula: see text], we have found that in particular, Fe and Ru doped PtSe2 systems are ferromagnetic half-metal having above-room-temperature Curie point of 422 and 379.9 K, respectively. By varying the dopant distance and concentration we have shown that the magnetic interaction is strongly dependent on dopant distance and concentration. Interestingly, the Curie temperature of TM doped PtSe2 layers is affected by the correlation effects on the TM d states and also spin-orbit coupling. We have also studied the magnetic properties of defect complex composed of one TM dopant and one Pt vacancy (TMPt  +  VPt) which shows novel magnetism.

https://iopscience.iop.org/article/10.1088/1361-648X/aaff40/pdf

Engineering the magnetic properties of PtSe2 monolayer through transition metal doping.

Phosphorene quantum dot-fullerene nanocomposites for solar energy conversion: An unexplored inorganic-organic nanohybrid with novel photovoltaic properties

Carbon nanotubes (CNTs) are appealing candidates for solar and optoelectronic applications. Traditionally used as electron sinks, CNTs can also perform as electron donors, as exemplified by coupling with perylenediimide (PDI). To achieve high efficiencies, electron transfer (ET) should be fast, while subsequent charge recombination should be slow. Typically, defects are considered detrimental to material performance because they accelerate charge and energy losses. We demonstrate that, surprisingly, common CNT defects improve rather than deteriorate the performance. CNTs and other low dimensional materials accommodate moderate defects without creating deep traps. At the same time, charge redistribution caused by CNT defects creates an additional electrostatic potential that increases the CNT work function and lowers CNT energy levels relative to those of the acceptor species. Hence, the energy gap for the ET is decreased, while the gap for the charge recombination is increased. The effect is particularly important because charge acceptors tend to bind near defects due to enhanced chemical interactions. The time-domain simulation of the excited-state dynamics provides an atomistic picture of the observed phenomenon and characterizes in detail the electronic states, vibrational motions, inelastic and elastic electron-phonon interactions, and time scales of the charge separation and recombination processes. The findings should apply generally to low-dimensional materials, because they dissipate defect strain better than bulk semiconductors. Our calculations reveal that CNT performance is robust to common defects and that moderate defects are essential rather than detrimental for CNT application in energy, electronics, and related fields.

Common Defects Accelerate Charge Separation and Reduce Recombination in CNT/Molecule Composites: Atomistic Quantum Dynamics.

Recently, inorganic–organic hybrid perovskites have gained immense attention in view of its outstanding performance in solar cell devices. Due to the toxicity of lead, lead-free perovskites are hig...

Moumita Kar

Papers

Engineering the magnetic properties of PtSe2 monolayer through transition metal doping.

Phosphorene quantum dot-fullerene nanocomposites for solar energy conversion: An unexplored inorganic-organic nanohybrid with novel photovoltaic properties

Common Defects Accelerate Charge Separation and Reduce Recombination in CNT/Molecule Composites: Atomistic Quantum Dynamics.

Lead Free Two-Dimensional Mixed Tin and Germanium Halide Perovskites for Photovoltaic Applications

Two-dimensional CP 3 monolayer and its fluorinated derivative with promising electronic and optical properties: A theoretical study