50 research outputs found
Low-frequency electronic noise in superlattice and random-packed thin films of colloidal quantum dots
We report measurements of low-frequency electronic noise in ordered
superlattice, weakly-ordered and random-packed thin films of 6.5 nm PbSe
quantum dots prepared using several different ligand chemistries. For all
samples, the normalized noise spectral density of the dark current revealed a
Lorentzian component, reminiscent of the generation-recombination noise,
superimposed on the 1/f background (f is the frequency). An activation energy
of 0.3 eV was extracted from the temperature dependence of the noise spectra.
The noise level in the ordered films was lower than that in the weakly-ordered
and random-packed films. A large variation in the magnitude of the noise
spectral density was also observed in samples with different ligand treatments.
The obtained results are important for application of colloidal quantum dot
films in photodetectors.Comment: 24 pages, 6 figures and supplemental inf
Electronic Noise Spectroscopy of Quasi-2D van der Waals Antiferromagnetic Semiconductors
We investigated low-frequency current fluctuations, i.e. electronic noise, in
FePS3 van der Waals, layered antiferromagnetic semiconductor. The noise
measurements have been used as noise spectroscopy for advanced materials
characterization of the charge carrier dynamics affected by spin ordering and
trapping states. Owing to the high resistivity of the material, we conducted
measurements on vertical device configuration. The measured noise spectra
reveal pronounced Lorentzian peaks of two different origins. One peak is
observed only near the Neel temperature and it is attributed to the
corresponding magnetic phase transition. The second Lorentzian peak, visible in
the entire measured temperature range, has the characteristics of the
trap-assisted generation-recombination processes similar to those in
conventional semiconductors but shows a clear effect of the spin order
reconfiguration near the Neel temperature. The obtained results contribute to
understanding the electron and spin dynamics in this type of antiferromagnetic
semiconductors and demonstrate the potential of electronic noise spectroscopy
for advanced materials characterization.Comment: 24 pages; 4 figure
Thermal Properties of the Binary-Filler Composites with Few-Layer Graphene and Copper Nanoparticles
The thermal properties of an epoxy-based binary composites comprised of
graphene and copper nanoparticles are reported. It is found that the
"synergistic" filler effect, revealed as a strong enhancement of the thermal
conductivity of composites with the size-dissimilar fillers, has a well-defined
filler loading threshold. The thermal conductivity of composites with a
moderate graphene concentration of ~15 wt% exhibits an abrupt increase as the
loading of copper nanoparticles approaches ~40 wt%, followed by saturation. The
effect is attributed to intercalation of spherical copper nanoparticles between
the large graphene flakes, resulting in formation of the highly thermally
conductive percolation network. In contrast, in composites with a high graphene
concentration, ~40 wt%, the thermal conductivity increases linearly with
addition of copper nanoparticles. The electrical percolation is observed at low
graphene loading, less than 7 wt.%, owing to the large aspect ratio of
graphene. At all concentrations of the fillers, below and above the electrical
percolation threshold, the thermal transport is dominated by phonons. The
obtained results shed light on the interaction between graphene fillers and
copper nanoparticles in the composites and demonstrate potential of such hybrid
epoxy composites for practical applications in thermal interface materials and
adhesives.Comment: 25 pages, 4 figure