108 research outputs found
Self-transformation and structural reconfiguration in coacervate-based protocells
We highlight a new approach for the design and construction of re-configurable soft colloidal scale objects (protocells) based on the pH-induced transition of dipeptide-containing coacervate micro-droplets into discrete aster-like micro-architectures.</p
Impact of Sb and Na Doping on the Surface Electronic Landscape of Cu2ZnSnS4 Thin Films
Open-circuit voltage deficiency is the key limiting factor in Cu2ZnSnS4 (CZTS) thin-film solar cells, which is commonly associated with band tails and deep gap states arising from elemental disorder. The introduction of dopants such as Na and Sb has led to improvement in device performance, yet their effects on the optoelectronic properties of CZTS are yet to be fully elucidated. In this Letter, we unraveled the effect of Sb and Na:Sb co-doping on the surface energy landscape of solution-processed CZTS films employing energy-filtered photoelectron emission microscopy. In the absence of the additives, 150 nm resolution photoemission maps reveal oscillations in the local effective work function as well as areas of low photoemission energy threshold. The introduction of dopants substantially reshapes the photoemission maps, which we rationalize in terms of Cu:Zn and Sn disorder. Finally, we establish unprecedented correlations between the photoemission landscape of thin films and the performance of over 200 devices
Direct observation of electron emission from grain boundaries in CVD diamond by PeakForce-controlled tunnelling atomic force microscopy
AbstractA detailed investigation of electron emission from a set of chemical vapour deposited (CVD) diamond films is reported using high-resolution PeakForce-controlled tunnelling atomic force microscopy (PF-TUNA). Electron field emission originates preferentially from the grain boundaries in low-conductivity polycrystalline diamond samples, and not from the top of features or sharp edges. Samples with smaller grains and more grain boundaries, such as nanocrystalline diamond, produce a higher emission current over a more uniform area than diamond samples with larger grain size. Light doping with N, B or P increases the grain conductivity, with the result that the emitting grain-boundary sites become broader as the emission begins to creep up the grain sidewalls. For heavy B doping, where the grains are now more conducting than the grain boundaries, emission comes from both the grain boundaries and the grains almost equally. Lightly P-doped diamond samples show emission from step-edges on the (111) surfaces. Emission intensity was time dependent, with the measured current dropping to âŒ10% of its initial value âŒ30h after removal from the CVD chamber. This decrease is ascribed to the build-up of adsorbates on the surface along with an increase in the surface conductivity due to surface transfer doping
âCrossâ Supermicelles via the Hierarchical Assembly of Amphiphilic Cylindrical Triblock Comicelles
Self-assembled
âcrossâ architectures are well-known
in biological systems (as illustrated by chromosomes, for example);
however, comparable synthetic structures are extremely rare. Herein
we report an in depth study of the hierarchical assembly of the amphiphilic
cylindrical PâHâP triblock comicelles with polar (P)
coronal ends and a hydrophobic (H) central periphery in a selective
solvent for the terminal segments which allows access to âcrossâ
supermicelles under certain conditions. Well-defined PâHâP
triblock comicelles MÂ(PFS-<i>b</i>-PtBA)-<i>b</i>-MÂ(PFS-<i>b</i>-PDMS)-<i>b</i>-MÂ(PFS-<i>b</i>-PtBA) (M = micelle segment, PFS = polyferrocenyldimethylsilane,
PtBA = polyÂ(<i>tert</i>-butyl acrylate), and PDMS = polydimethylsiloxane)
were created by the living crystallization-driven self-assembly (CDSA)
method. By manipulating two factors in the supermicelles, namely the
H segment-solvent interfacial energy (through the central H segment
length, <i>L</i><sub>1</sub>) and coronal steric effects
(via the PtBA corona chain length in the P segment, <i>L</i><sub>2</sub> related to the degree of polymerization DP<sub>2</sub>) the aggregation of the triblock comicelles could be finely tuned.
This allowed a phase-diagram to be constructed that can be extended
to other triblock comicelles with different coronas on the central
or end segment where âcrossâ supermicelles were exclusively
formed under predicted conditions. Laser scanning confocal microscopy
(LSCM) analysis of dye-labeled âcrossâ supermicelles,
and block âcrossâ supermicelles formed by addition of
a different unimer to the arm termini, provided complementary characterization
to transmission electron microscopy (TEM) and dynamic light scattering
(DLS) and confirmed the existence of these âcrossâ supermicelles
as kinetically stable, micron-size colloidally stable structures in
solution
High-speed AFM with a light touch
No abstract available
- âŠ