Crystallinity of the polymer poly(3,6-difuran-2-yl-2,5-di(2-octyldodecyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-altthieylenevinylene) (PDVF) adlayers
casted from low-boiling-point (L-bp), medium-bp (M-bp), and high-bp
(H-bp) solvents was investigated through scanning tunneling microscopy
(STM) and analyzed by the assistance of Hansen solubility parameter
(HSP) theory and molecular dynamics (MD) simulations. Crystallinity
of the PDVF adlayers increases evidently from the L- to H-bp solvents.
Also, the solvent with an alkyl chain such as ethylbenzene (EB) facilitates
in improving the crystallinity than the one without an alkyl chain
such as chlorobenzene (CB) if the solvent bp is present in the same
group. The HSP space discloses
that EB is a marginal solvent for PDVF in contrast to CB. Quasi-isolate
PDVF in the EB solution revealed by MD simulations facilitates the
formation of crystallized domains through surface assembling mechanism.
However, in CB, interconnected PDVF molecules through intermolecular
overlapping tend to generate amorphous structures through direct deposition
of the preformed structures in solution.
Developing
efficient organic photodetectors and revealing the crucial
factor affecting photodetection performances are of importance in
varied applications and fundamental researches. In this work, 5,15-bisdodecyl-tetrabenzoporphyrin
(C12TBP)/graphene (Gr) phototransistors were fabricated through in
situ retro-Diels–Alder reaction (as-formed),
which demonstrates ultrahigh responsivity and specific detectivity,
fast response, and broad-band detecting abilities covering UV to near-IR
radiations. The interfacial and bulk layers of C12TBP films, defined
as the adlayer on Gr sheet and the other part of the films, respectively,
were characterized in detail. The π–π stacked edge-on
C12TBP/Gr interfacial layer is suggested as the key factor enabling
the ultrasensitive photodetection through facilitating the multistep
interfacial electronic processes for photocurrent generation. Frontier
molecular orbitals overlap effectively in the neighbor π–π
stacked C12TBP, which promotes not only the diffusion of photogenerated
electron–hole pairs but also dissociation of electron–hole
pairs and charge-transfer (CT) state through weakening the electron–hole
binding by dispersing charges within C12TBP columns. The separation
of CT state is boosted by the large distance between the holes in
Gr and the electrons in the edge-on orientation of C12TBP as well.
In addition, we found that the structural evolution of the interfacial
layer has a significant difference from that of the bulk layers because
of the strong adsorption to the substrate. The results provide valuable
support for understanding the complicated relationship between the
structures and electronic properties of interfacial layers and pave
the way for fabricating high-performance organic photodetecting devices.
Phase change memory (PCM), a typical representative of new storage technologies, offers significant advantages in terms of capacity and endurance. However, among the research on phase change materials, thermal stability and switching speed performance have always been the direction where breakthroughs are needed. In this research, as a high-speed and good thermal stability material, Ta was proposed to be doped in Sb3Te1 alloy to improve the phase transition performance and electrical properties. The characterization shows that Ta-doped Sb3Te1 can crystallize at temperatures up to 232 °C and devices can operate at speeds of 6 ns and 8 × 104 operation cycles. The reduction of grain size and the density change rate (3.39%) show excellent performances, which are both smaller than that of Ge2Sb2Te5 (GST) and Sb3Te1. These properties conclusively demonstrate that Ta incorporation of Sb3Te1 alloy is a material with better thermal stability and faster crystallization rates for PCM applications.
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