Förster Resonance Energy Transfer and Enhanced Emission in CsPbBr Nanocrystals Encapsulated in Silicon Nano-Sheets for Perovskite Light Emitting Diode Applications.

Encapsulating CsPbBr quantum dots in silicon nano-sheets not only stabilizes the halide perovskite, but also takes advantage of the nano-sheet for a compatible integration with the traditional silicon semiconductor. Here, we report the preparation of un-passivated CsPbBr ellipsoidal nanocrystals and pseudo-spherical quantum dots in silicon nano-sheets and their enhanced photoluminescence (PL). For a sample with low concentrations of quantum dots in silicon nano-sheets, the emission from CsPbBr pseudo-spherical quantum dots is quenched and is dominated with Pb ion/silicene emission, which is very stable during the whole measurement period.

Optically induced quantum transitions in direct probed mesoscopic NbSe for prototypical bolometers.

Superconducting transition-edge sensors (TES) have emerged as fascinating devices to detect broadband electromagnetic radiation with low thermal noise. The advent of metallic transition metal dichalcogenides, such as NbSe, has also created an impetus to understand their low-temperature properties, including superconductivity. Interestingly, NbSe-based sensor within the TES framework remains unexplored.

Progress and Application of Halide Perovskite Materials for Solar Cells and Light Emitting Devices.

Halide perovskite materials have attracted worldwide attention in the photovoltaic area due to the rapid improvement in efficiency, from less than 4% in 2009 to 26.1% in 2023 with only a nanometer lever photo-active layer. Meanwhile, this nova star found applications in many other areas, such as light emitting, sensor, etc.

Selective CW Laser Synthesis of MoS and Mixture of MoS and MoO from (NH)MoS Film.

Very recently, the synthesis of 2D MoS and WS through pulsed laser-directed thermolysis can achieve wafer-scale and large-area structures, in ambient conditions. In this paper, we report the synthesis of MoS and MoS oxides from (NH)MoS film using a visible continuous-wave (CW) laser at 532 nm, instead of the infrared pulsed laser for the laser-directed thermolysis. The (NH)MoS film is prepared by dissolving its crystal powder in DI water, sonicating the solution, and dip-coating onto a glass slide.

Intrinsic and Strain-Dependent Properties of Suspended WSe Crystallites toward Next-Generation Nanoelectronics and Quantum-Enabled Sensors.

Two-dimensional (2D) layered materials exhibit great potential for high-performance electronics, where knowledge of their thermal and phononic properties is critical toward understanding heat dissipation mechanisms, considered to be a major bottleneck for current generation nanoelectronic, optoelectronic, and quantum-scale devices. In this work, noncontact Raman spectroscopy was used to analyze thermal properties of suspended 2D WSe membranes to access the intrinsic properties. Here, the influence of electron-phonon interactions within the parent crystalline WSe membranes was deciphered through a comparative analysis of substrate-supported WSe, where heat dissipation mechanisms are intimately tied to the underlying substrate.

Stability and degradation in triple cation and methyl ammonium lead iodide perovskite solar cells mediated via Au and Ag electrodes.

Perovskite solar cells (PSCs), particularly based on the methyl ammonium lead iodide (MAPbI) formulation, have been of intense interest for the past decade within the photovoltaics (PV) community, given the stupendous rise in power conversion efficiencies (PCEs) attributed to these perovskite formulations, where PCEs have exceeded 25%. However, their long-term stability under operational conditions and environmental storage are still prime challenges to be overcome towards their commercialization. Although studies on the intrinsic perovskite absorber stability have been conducted previously, there are no clear mechanisms for the interaction of electrode-induced absorber degradation pathways, which is the focus of this study.

Photophysical Dynamics in Semiconducting Graphene Quantum Dots Integrated with 2D MoS for Optical Enhancement in the Near UV.

The hybrid structure of zero-dimensional (0D) graphene quantum dots (GQDs) and semiconducting two-dimensional (2D) MoS has been investigated, which exhibit outstanding properties for optoelectronic devices surpassing the limitations of MoS photodetectors where the GQDs extend the optical absorption into the near-UV regime. The GQDs and MoS films are characterized by Raman and photoluminescence (PL) spectroscopies, along with atomic force microscopy. After outlining the fabrication of our 0D-2D heterostructure photodetectors comprising GQDs with bulk MoS sheets, their photoresponse to the incoming radiation was measured.

Light-matter interactions in two-dimensional layered WSe for gauging evolution of phonon dynamics.

Phonon dynamics is explored in mechanically exfoliated two-dimensional WSe using temperature-dependent and laser-power-dependent Raman and photoluminescence (PL) spectroscopy. From this analysis, phonon lifetime in the Raman active modes and phonon concentration, as correlated to the energy parameter , were calculated as a function of the laser power, , and substrate temperature, . For monolayer WSe, from the power dependence it was determined that the phonon lifetime for the in-plane vibrational mode was twice that of the out-of-plane vibrational mode for in the range from 0.

Inkjet-Printed Organohalide 2D Layered Perovskites for High-Speed Photodetectors on Flexible Polyimide Substrates.

The synthesis of solution-processed two-dimensional (2D) layered organohalide (CH(CH)NH)(CHNH)PbI ( = 2, 3, and 4) perovskites is presented, where inkjet printing was used to fabricate heterostructure flexible photodetector (PD) devices on polyimide (PI) substrates. Inks for the = 4 formulation were developed to inkjet-print PD devices that were photoresponsive to broadband incoming radiation in the visible regime, where the peak photoresponsivity was calculated to be ∼0.17 A/W, which is higher compared to prior reports, while the detectivity was measured to be ∼3.

Chemical exfoliation efficacy of semiconducting WS and its use in an additively manufactured heterostructure graphene-WS-graphene photodiode.

In the present work, various chemical exfoliation routes for semiconducting two-dimensional (2D) layered material WS are explored, which include magnetic stirring (MS), shear mixing (SM), and horn-tip (HT) sonication. Current-voltage measurements, Raman spectroscopy, and photoluminescence (PL) spectroscopy were used to characterize the drop-casted WS nanosheets produced by these three techniques and our analysis revealed that HT sonication produced the most optimal dispersions. Heterostructure photodetector devices were then fabricated using inkjet printing of the HT sonicated dispersions of WS and graphene.

Dramatic Enhancement of Optoelectronic Properties of Electrophoretically Deposited C-Graphene Hybrids.

Fullerene (C) and multilayer graphene hybrid devices were fabricated using electrophoretic deposition, where the C clusters are electrically charged upon the application of an external bias in a polar solvent, acetonitrile, mixed with toluene, which facilitates their deposition on the graphene membranes. Raman spectroscopy unveiled the unique vibrational fingerprints associated with the A mode of the C molecules at ∼1453 cm, while blue shifts of ∼6 and ∼17 cm were also attributed to the G- and 2D-bands of the hybrids relative to bare graphene, suggestive of p-doped graphene. The intensity ratio of the G- and the 2D-bands / (hybrid) dropped to ∼0.

Ultra-high Photoresponsivity in Suspended Metal-Semiconductor-Metal Mesoscopic Multilayer MoS Broadband Detector from UV-to-IR with Low Schottky Barrier Contacts.

The design, fabrication, and characterization of ultra-high responsivity photodetectors based on mesoscopic multilayer MoS is presented, which is a less explored system compared to direct band gap monolayer MoS that has received increasing attention in recent years. The device architecture is comprised of a metal-semiconductor-metal (MSM) photodetector, where Mo was used as the contact metal to suspended MoS membranes. The photoresponsivity [Formula: see text] was measured to be ~1.

Carbon nanofiber high frequency nanomechanical resonators.

Carbon nanofibers (CNFs) synthesized using a plasma-enhanced chemical vapor deposition (PECVD) process are investigated as a new class of building blocks for high-frequency vibrating nanomechanical resonators. The CNF resonators are prototyped by using vertically oriented few-μm-long cantilever-structured CNFs grown by PECVD. Undriven thermomechanical motions and photothermally driven resonances are measured in the frequency range of ∼3-10 MHz, which exhibit quality (Q) factors of ∼140-350 in moderate vacuum (milliTorr) at room temperature.

Engineering chemically exfoliated dispersions of two-dimensional graphite and molybdenum disulphide for ink-jet printing.

Stable ink dispersions of two-dimensional-layered-materials (2DLMs) MoS and graphite are successfully obtained in organic solvents exhibiting a wide range of polarities and surface energies. The role of sonication time, ink viscosity and surface tension is explored in the context of dispersion stability using these solvents, which include N-methyl-2-pyrrolidone (NMP), N,N-Dimethylacetamide (DMA), dimethylformamide (DMF), Cyclohexanone (C), as well as less-toxic and more environmentally friendly Isopropanol (IPA) and Terpineol (T). The ink viscosity is engineered through the addition of Ethyl-Cellulose (EC) which has been shown to optimize the jettability of the dispersions.

Ultra-high optical absorption efficiency from the ultraviolet to the infrared using multi-walled carbon nanotube ensembles.

The optical absorption efficiencies of vertically aligned multi-walled (MW)-carbon nanotube (CNT) ensembles are characterized in the 350-7000 nm wavelength range where CNT site densities > 1 × 10(11) /cm(2) are achieved directly on metallic substrates. The site density directly impacts the optical absorption characteristics, and while high-density arrays of CNTs on electrically insulating and non-metallic substrates have been commonly reported, achieving high site-densities on metals has been challenging and remains an area of active research. These absorber ensembles are ultra-thin (<10 μm) and yet they still exhibit a reflectance as low as ∼0.

Modeling and in-situ observation of mechanical resonances in single, vertically-oriented carbon nanofibers.

In this paper, we have analyzed mechanical resonances in carbon nanotubes (CNTs) based on single, vertically-oriented tubes for their potential application in high-frequency, high-Q, miniaturized resonators. The nano-electro-mechanical (NEM) resonators were modeled using a commercially available finite-element-simulator, where the electro-mechanical coupling of the CNT to an incoming AC signal on a probe in close proximity was examined. The modeling results confirmed that the mechanical resonance was maximized when the frequency of the input signal was equal to the first order harmonic of the CNT.

In situ characterization of vertically oriented carbon nanofibers for three-dimensional nano-electro-mechanical device applications.

We have performed mechanical and electrical characterization of individual as-grown, vertically oriented carbon nanofibers (CNFs) using in situ techniques, where such high-aspect-ratio, nanoscale structures are of interest for three-dimensional (3D) electronics, in particular 3D nano-electro-mechanical-systems (NEMS). Nanoindentation and uniaxial compression tests conducted in an in situ nanomechanical instrument, SEMentor, suggest that the CNFs undergo severe bending prior to fracture, which always occurs close to the bottom rather than at the substrate-tube interface, suggesting that the CNFs are well adhered to the substrate. This is also consistent with bending tests on individual tubes which indicated that bending angles as large as approximately 70 degrees could be accommodated elastically.

Gas sensing with long, diffusively contacted single-walled carbon nanotubes.

A carbon nanotube thermal-conductivity-based pressure or gas sensor is described, which utilizes 5-10 microm long, diffusively contacted single-walled nanotubes (SWNTs). Low temperature electrical transport measurements for these tubes were suggestive of a thermally activated hopping mechanism for electron localization, where a hopping energy of approximately 39 meV was computed. A negative differential conductance regime was also detected in suspended tubes, released using critical point drying, at high bias voltages.

Single, aligned carbon nanotubes in 3D nanoscale architectures enabled by top-down and bottom-up manufacturable processes.

We have developed manufacturable approaches for forming single, vertically aligned carbon nanotubes, where the tubes are centered precisely, and placed within a few hundred nm of 1-1.5 microm deep trenches. These wafer-scale approaches were enabled by using chemically amplified resists and high density, low pressure plasma etching techniques to form the 3D nanoscale architectures.

Electromechanical carbon nanotube switches for high-frequency applications.

We describe the fabrication and characterization of a nanoelectromechanical (NEM) switch based on carbon nanotubes. Our NEM structure consists of single-walled nanotubes (SWNTs) suspended over shallow trenches in a SiO(2) layer, with a Nb pull electrode beneath. The nanotube growth is done on-chip using a patterned Fe catalyst and a methane chemical vapor deposition (CVD) process at 850 degrees C.