No abstract

The mixed cation compounds Na1–x K x AsSe2 (x = 0.8, 0.65, 0.5) and Na0.1K0.9AsS2 crystallize in the polar noncentrosymmetric space group Cc. The AAsQ 2 (A = alkali metals, Q = S, Se) family features one-dimensional (1D) 1/∞[AQ 2 –] chains comprising corner-sharing pyramidal AQ 3 units in which the packing of these chains is dependent on the alkali metals. The parallel 1/∞[AQ 2 –] chains interact via short As···Se contacts, which increase in length when the fraction of K atoms is increased. The increase in the As···Se interchain distance increases the band gap from 1.75 eV in γ-NaAsSe2 to 2.01 eV in Na0.35K0.65AsSe2, 2.07 eV in Na0.2K0.8AsSe2, and 2.18 eV in Na0.1K0.9AsS2. The Na1–x K x AsSe2 (x = 0.8, 0.65) compounds melt congruently at approximately 316 °C. Wavelength-dependent second harmonic generation (SHG) measurements on powder samples of Na1–x K x AsSe2 (x = 0.8, 0.65, 0.5) and Na0.1K0.9AsS2 suggest that Na0.2K0.8AsSe2 and Na0.1K0.9AsS2 have the highest SHG response and exhibit significantly higher laser-induced damage thresholds (LIDTs). Theoretical SHG calculations on Na0.5K0.5AsSe2 confirm its SHG response with the highest value of d 33 = 22.5 pm/V (χ333 (2) = 45.0 pm/V). The effective nonlinearity for a randomly oriented powder is calculated to be d eff = 18.9 pm/V (χeff (2) = 37.8 pm/V), which is consistent with the experimentally obtained value of d eff = 16.5 pm/V (χeff (2) = 33.0 pm/V). Three-photon absorption is the dominant mechanism for the optical breakdown of the compounds under intense excitation at 1580 nm, with Na0.2K0.8AsSe2 exhibiting the highest stability.

Coupling between a magnetic impurity and an external bath can give rise to many-body quantum phenomena, including Kondo and Hund's impurity states in metals, and Yu-Shiba-Rusinov states in superconductors. While advances have been made in probing the magnetic properties of d-shell impurities on surfaces, the confinement of f orbitals makes them difficult to access directly. Here we show that a 4f driven Kondo resonance can be modulated spatially by asymmetric coupling between a metallic surface and a molecule containing a 4f-like moment. Strong hybridization of dysprosium double-decker phthalocyanine with Cu(001) induces Kondo screening of the central magnetic moment. Misalignment between the symmetry axes of the molecule and the surface induces asymmetry in the molecule's electronic structure, spatially mediating electronic access to the magnetic moment through the Kondo resonance. This work demonstrates the important role that molecular ligands have in mediating electronic and magnetic coupling and in accessing many-body quantum states.

The second quantum revolution harnesses exquisite quantum control for a slate of diverse applications including sensing, communication, and computation. Of the many candidates for building quantum systems, molecules offer both...

Infrared laser systems are vital for applications in spectroscopy, communications, and biomedical devices, where infrared nonlinear optical (NLO) crystals are required for broadband frequency down‐conversion. Such crystals need to have high non‐resonant NLO coefficients, a large bandgap, low absorption coefficient, and phase‐matchability among other competing demands; for example, a larger bandgap leads to smaller NLO coefficients. Here, the successful growth of single crystals of γ ‐NaAsSe2 that exhibit a giant second harmonic generation (SHG) susceptibility of d11 = 590 pm V−1 at 2 µm wavelength is reported; this is ~18 times larger than that of commercial AgGaSe2 while retaining a similar bandgap of ~1.87 eV, making it an outstanding candidate for quasi‐phase‐matched devices utilizing d11. In addition, γ ‐NaAsSe2 is both Type I and Type II phase‐matchable, and has a transparency range up to 16 µm wavelength. Thus, γ ‐NaAsSe2 is a promising bulk NLO crystal for infrared laser applications.

In order to understand the relationship between specific growth factors and matrix synthesis by periodontal cells, we have investigated the effects of platelet-derived growth factor BB (PDGF-BB), insulin-like growth factor-I (IGF-1), and growth hormone on DNA and proteoglycan synthesis by cultured human gingival and periodontal ligament fibroblasts in vitro. PDGF-BB and IGF-1, but not growth hormone, were mitogenic for both periodontal ligament fibroblasts and gingival fibroblasts, although the periodontal ligament cells responded more strongly. The mitogenic response was accompanied by alterations in expression of matrix proteoglycan mRNA. For both the gingival and periodontal ligament cells, there was a decrease in mRNA for decorin and an increase in mRNA for versican following exposure to IGF-1 and PDGF-BB. Although no change was seen in response to PDGF, biglycan mRNA level was increased by IGF-1 in periodontal ligament fibroblasts. With the gingival fibroblasts, biglycan mRNA levels were unaffected by IGF-1, PDGF-BB, or growth hormone. These findings suggest variable responses of fibroblasts to growth factors depending upon anatomical site within the periodontium. Moreover, there appears to be a correlation between cell proliferation and the types of proteoglycan synthesised with decorin expression being suppressed, and versican being increased during fibroblast proliferation.

The isostructural heteroanionic compounds β-LiAsS2–x Se x (x = 0, 0.25, 1, 1.75, 2) show a positive correlation between selenium content and second-harmonic response and greatly outperform the industry standard AgGaSe2. These materials crystallize in the noncentrosymmetric space group Cc as one-dimensional 1/∞ [AsQ2]− (Q = S, Se, S/Se) chains consisting of corner-sharing AsQ3 trigonal pyramids with charge-balancing Li+ atoms interspersed between the chains. LiAsS2–x Se x melts congruently for 0 ≤ x ≤ 1.75, but when the Se content exceeds x = 1.75, crystallization is complicated by a phase transition. This behavior is attributed to the β- to α-phase transition present in LiAsSe2, which is observed in the Se-rich compositions. The band gap decreases with increasing Se content, starting at 1.63 eV (LiAsS2) and reaching 1.06 eV (β-LiAsSe2). Second-harmonic generation measurements as a function of wavelength on powder samples of β-LiAsS2–x Se x show that these materials exhibit significantly higher nonlinearity than AgGaSe2 (d 36 = 33 pm/V), reaching a maximum of 61.2 pm/V for LiAsS2. In comparison, single-crystal measurements for LiAsSSe yielded a d eff = 410 pm/V. LiAsSSe, LiAsS0.25Se1.75, and β-LiAsSe2 show phase-matching behavior for incident wavelengths exceeding 3 μm. The laser-induced damage thresholds from two-photon absorption processes are on the same order of magnitude as AgGaSe2, with S-rich materials slightly outperforming AgGaSe2 and Se-rich materials slightly underperforming AgGaSe2.

a b s t r a c tTo probe the influence of molecular dipole on the open circuit voltage (V OC ) of molecular heterojunction organic solar cells, we study axially fluorinated boron subphthalocyanine/ fullerene (SubPc-F/C 60 ) junctions. These exhibit an open-circuit voltage V OC = 1.00 V, a value closer to the HOMO-LUMO offset at the donor-acceptor interface = 1.69 eV than the V OC = 1.06 V measured for junctions between the archetypal chlorinated SubPc and C 60 , with corresponding HOMO-LUMO offset = 1.84 eV. Aside from the axial halogen substitution, the two compounds exhibit similar molecular structure and optical absorption. The energy levels and structure of the heteromolecular polaron pair are calculated, and the ideal organic diode model for SubPc-Cl is modified accordingly, successfully reproducing the experimental SubPc-F device characteristics. The reproducible difference in V OC is attributed to the different electric dipole strength between SubPc-F and SubPc-Cl and its influence on polaron pair dynamics at the heterojunction.