Hard disk drives (HDDs) are used as secondary storage in digital electronic devices owing to low cost and large data storage capacity. Due to the exponentially increasing amount of data, there is a ...need to increase areal storage densities beyond ~1 Tb/in
. This requires the thickness of carbon overcoats (COCs) to be <2 nm. However, friction, wear, corrosion, and thermal stability are critical concerns below 2 nm, limiting current technology, and restricting COC integration with heat assisted magnetic recording technology (HAMR). Here we show that graphene-based overcoats can overcome all these limitations, and achieve two-fold reduction in friction and provide better corrosion and wear resistance than state-of-the-art COCs, while withstanding HAMR conditions. Thus, we expect that graphene overcoats may enable the development of 4-10 Tb/in
areal density HDDs when employing suitable recording technologies, such as HAMR and HAMR+bit patterned media.
Graphene is ideally suited for optoelectronics. It offers absorption at telecom wavelengths, high-frequency operation and CMOS-compatibility. We show how high speed optoelectronic mixing can be ...achieved with high frequency (~20 GHz bandwidth) graphene field effect transistors (GFETs). These devices mix an electrical signal injected into the GFET gate and a modulated optical signal onto a single layer graphene (SLG) channel. The photodetection mechanism and the resulting photocurrent sign depend on the SLG Fermi level (E
). At low E
(<130 meV), a positive photocurrent is generated, while at large E
(>130 meV), a negative photobolometric current appears. This allows our devices to operate up to at least 67 GHz. Our results pave the way for GFETs optoelectronic mixers for mm-wave applications, such as telecommunications and radio/light detection and ranging (RADAR/LIDARs.).
One of the pivotal questions in the physics of high-temperature superconductors is whether the low-energy dynamics of the charge carriers is mediated by bosons with a characteristic timescale. This ...issue has remained elusive as electronic correlations are expected to greatly accelerate the electron-boson scattering processes, confining them to the very femtosecond timescale that is hard to access even with state-of-the-art ultrafast techniques. Here we simultaneously push the time resolution and frequency range of transient reflectivity measurements up to an unprecedented level, enabling us to directly observe the ~16 fs build-up of the effective electron-boson interaction in hole-doped copper oxides. This extremely fast timescale is in agreement with numerical calculations based on the t-J model and the repulsive Hubbard model, in which the relaxation of the photo-excited charges is achieved via inelastic scattering with short-range antiferromagnetic excitations.
The influence of nanocrystallinity on the electronic and mechanical properties of metal nanoparticles is still poorly understood, due to the difficulty in synthesizing nanoparticles with a controlled ...internal structure. Here, we report on a new method for the selective synthesis of Au nanoparticles in either a single-domain or a polycrystalline phase maintaining the same chemical environment. We obtain quasi-spherical nanoparticles whose diameter is tunable from 6 to 13 nm with a resolution down to ≈0.5 nm and narrow size distribution (4-5%). The availability of such high-quality samples allows the study of the impact of the particle size and nanocrystallinity on a number of parameters, such as plasmon dephasing time, electron-phonon coupling, period and damping time of the radial breathing modes.
Black phosphorous (BP) is a layered semiconductor with high carrier mobility, anisotropic optical response and wide bandgap tunability. In view of its application in optoelectronic devices, ...understanding transient photo-induced effects is crucial. Here, we investigate by time- and angle-resolved photoemission spectroscopy BP in its pristine state and in the presence of Stark splitting, chemically induced by Cs ad-sorption. We show that photo-injected carriers trigger bandgap renormalization, and a concurrent valence band flattening caused by Pauli blocking. In biased samples, photo-excitation leads to a long-lived (ns) surface photovoltage of few hundreds mV that counterbalances the Cs-induced surface band bending. This allows us to disentangle bulk from surface electronic states, and to clarify the mechanism underlying the band inversion observed in bulk samples.
Abstract
Layered materials (LMs) produced by liquid phase exfoliation (LPE) can be used as building blocks for optoelectronic applications. However, when compared with mechanically exfoliated flakes, ...or films prepared by chemical vapor deposition (CVD), LPE-based printed optoelectronic devices are limited by mobility, defects and trap states. Here, we present a scalable fabrication technique combining CVD with LPE LMs to overcome such limitations. We use black phosphorus inks, inkjet-printed on graphene on Si/SiO
2
, patterned by inkjet printing based lithography, and source and drain electrodes printed with an Ag ink, to prepare photodetectors (PDs). These have an external responsivity (
R
ext
)∼337 A W
−1
at 488 nm, and operate from visible (∼488 nm) to short-wave infrared (∼2.7
µ
m,
R
ext
∼
48 mA W
−1
). We also use this approach to fabricate flexible PDs on polyester fabric, one of the most common used in textiles, achieving
R
ext
∼
6 mA W
−1
at 488 nm for an operating voltage of 1 V. Thus, our combination of scalable CVD and LPE techniques via inkjet printing is promising for wearable and flexible applications.
We show that excitons are not the unique outcome of photoexcitation in single-walled carbon nanotubes (SWNTs). Our experiments of transient photoinduced absorption suggest that charge carriers are ...formed with quantum yield of a few percent and that such species strongly affect the long-lived transient spectrum. Photogenerated charge carriers induce strong local electric fields that shift by the Stark effect the second subband exciton absorption in SWNTs, resulting in a characteristic derivative shape of the transient absorption spectra.
PDF
