Irreversible Performance of a Quantum Harmonic Heat Engine

The unavoidable irreversible losses of power in a heat engine are found to be of quantum origin. Following thermodynamic tradition a model quantum heat engine operating by the Otto cycle is analyzed. The working medium of the model is composed of an ensemble of harmonic oscillators. A link is established between the quantum observables and thermodynamical variables based on the concept of canonical invariance. These quantum variables are sufficient to determine the state of the system and with it all thermodynamical variables. Conditions for optimal work, power and entropy production show that maximum power is a compromise between the quasistatic limit of adiabatic following on the compression and expansion branches and a sudden limit of very short time allocation to these branches. At high temperatures and quasistatic operating conditions the efficiency at maximum power coincides with the endoreversible result. The optimal compression ratio varies from the square root of the temperature ratio in the quasistatic limit where their reversibility is dominated by heat conductance to the temperature ratio to the power of 1/4 in the sudden limit when the irreversibility is dominated by friction. When the engine deviates from adiabatic conditions the performance is subject to friction. The origin of this friction can be traced to the noncommutability of the kinetic and potential energy of the working medium.Comment: 25 pages, 7 figures. Revision added explicit heat-transfer expression and extended the discussion on the quantum origin of frictio

Impact of AFM-induced nano-pits in a-Si:H films on silicon crystal growth

Conductive tips in atomic force microscopy (AFM) can be used to localize field-enhanced metal-induced solid-phase crystallization (FE-MISPC) of amorphous silicon (a-Si:H) at room temperature down to nanoscale dimensions. In this article, the authors show that such local modifications can be used to selectively induce further localized growth of silicon nanocrystals. First, a-Si:H films by plasma-enhanced chemical vapor deposition on nickel/glass substrates are prepared. After the FE-MISPC process, yielding both conductive and non-conductive nano-pits in the films, the second silicon layer at the boundary condition of amorphous and microcrystalline growth is deposited. Comparing AFM morphology and current-sensing AFM data on the first and second layers, it is observed that the second deposition changes the morphology and increases the local conductivity of FE-MISPC-induced pits by up to an order of magnitude irrespective of their prior conductivity. This is attributed to the silicon nanocrystals (<100 nm) that tend to nucleate and grow inside the pits. This is also supported by micro-Raman spectroscopy

Guided assembly of nanoparticles on electrostatically charged nanocrystalline diamond thin films

We apply atomic force microscope for local electrostatic charging of oxygen-terminated nanocrystalline diamond (NCD) thin films deposited on silicon, to induce electrostatically driven self-assembly of colloidal alumina nanoparticles into micro-patterns. Considering possible capacitive, sp2 phase and spatial uniformity factors to charging, we employ films with sub-100 nm thickness and about 60% relative sp2 phase content, probe the spatial material uniformity by Raman and electron microscopy, and repeat experiments at various positions. We demonstrate that electrostatic potential contrast on the NCD films varies between 0.1 and 1.2 V and that the contrast of more than ±1 V (as detected by Kelvin force microscopy) is able to induce self-assembly of the nanoparticles via coulombic and polarization forces. This opens prospects for applications of diamond and its unique set of properties in self-assembly of nano-devices and nano-systems

Synthesis, structure, and opto-electronic properties of organic-based nanoscale heterojunctions

Enormous research effort has been put into optimizing organic-based opto-electronic systems for efficient generation of free charge carriers. This optimization is mainly due to typically high dissociation energy (0.1-1 eV) and short diffusion length (10 nm) of excitons in organic materials. Inherently, interplay of microscopic structural, chemical, and opto-electronic properties plays crucial role. We show that employing and combining advanced scanning probe techniques can provide us significant insight into the correlation of these properties. By adjusting parameters of contact- and tapping-mode atomic force microscopy (AFM), we perform morphologic and mechanical characterizations (nanoshaving) of organic layers, measure their electrical conductivity by current-sensing AFM, and deduce work functions and surface photovoltage (SPV) effects by Kelvin force microscopy using high spatial resolution. These data are further correlated with local material composition detected using micro-Raman spectroscopy and with other electronic transport data. We demonstrate benefits of this multi-dimensional characterizations on (i) bulk heterojunction of fully organic composite films, indicating differences in blend quality and component segregation leading to local shunts of photovoltaic cell, and (ii) thin-film heterojunction of polypyrrole (PPy) electropolymerized on hydrogen-terminated diamond, indicating covalent bonding and transfer of charge carriers from PPy to diamond

Length-Weight and Length-Length Relationships for Common Fish and Invertebrate Species in The North Inlet-Winyah Bay Estuarine System, South Carolina, USA

Establishing accurate weight-length relationships (WLR) and length-length relationships (LLR) is critical for effective fisheries management and ecological research. This study updates these essential metrics for commonly found fish and shrimp species in the North Inlet-Winyah Bay estuarine system, South Carolina, addressing gaps where previous data were unavailable, outdated, or sourced from other regions. Our research analyzed 7,874 specimens from 20 species across thirteen families, collected through trawl samples and bi-weekly seines from November 2022 to December 2023. The findings demonstrate robust WLRs with high coefficients of determination. Similarly, the LLRs confirmed reliable conversions between different length measurements. This study not only refines the understanding of species-specific growth patterns but also enhances regional fisheries assessments by providing updated, accurate biological models. The study provides first-time data for two species and significantly improves the sample sizes and data quality for several others

Tuning the morphology and energy levels in organic solar cells with metal–organic framework nanosheets

Metal–organic framework nanosheets (MONs) have proved themselves to be useful additives for enhancing the performance of a variety of thin film solar cell devices. However, to date only isolated examples have been reported. In this work we take advantage of the modular structure of MONs in order to resolve the effect of their different structural and optoelectronic features on the performance of organic photovoltaic (OPV) devices. Three different MONs were synthesized using different combinations of two porphyrin-based ligands meso-tetracarboxyphenyl porphyrin (TCPP) or tetrapyridyl-porphyrin (TPyP) with either zinc and/or copper ions and the effect of their addition to polythiophene-fullerene (P3HT-PC71BM) OPV devices was investigated. The power conversion efficiency (PCE) of devices was found to approximately double with the addition of MONs of Zn2(ZnTCPP) -4.7% PCE, 10.45 mA/cm2 short-circuit current density (JSC), 0.69 open-circuit voltage (VOC), 64.20% fill-factor (FF), but was unchanged with the addition of Cu2(ZnTPyP) (2.6% PCE, 3.68 mA/cm2JSC, 0.59 VOC, 46.27% FF) and halved upon the addition of Cu2(CuTCPP) (1.24% PCE, 6.72 mA/cm2JSC, 0.59 VOC, 56.24% FF) compared to devices without nanosheets (2.6% PCE, 6.61 mA/cm2JSC, 0.58 VOC, 56.64% FF). Our analysis indicates that there are three different mechanisms by which MONs can influence the photoactive layer – light absorption, energy level alignment, and morphological changes. Analysis of external quantum efficiency, UV–vis and photoelectron spectroscopy data found that MONs have similar effects on light absorption and energy level alignment. However, atomic force and Raman microscopy studies revealed that the nanosheet thickness and lateral size are crucial parameters in enabling the MONs to act as beneficial additives resulting in an improvement of the OPV device performance. We anticipate this study will aid in the design of MONs and other 2D materials for future use in other light harvesting and emitting devices

Tuning the morphology and energy levels in organic solar cells with metal organic framework nanosheets

Metal organic framework nanosheets MONs have proved themselves to be useful additives for enhancing the performance of a variety of thin film solar cell devices. However, to date only isolated examples have been reported. In this work we take advantage of the modular structure of MONs in order to resolve the effect of their different structural and optoelectronic features on the performance of organic photovoltaic OPV devices. Three different MONs were synthesized using different combinations of two porphyrin based ligands meso tetracarboxyphenyl porphyrin TCPP or tetrapyridyl porphyrin TPyP with either zinc and or copper ions and the effect of their addition to polythiophene fullerene P3HT PC71BM OPV devices was investigated. The power conversion efficiency PCE of devices was found to approximately double with the addition of MONs of Zn2 ZnTCPP 4.7 PCE, 10.45 mA cm2 short circuit current density JSC , 0.69 open circuit voltage VOC , 64.20 fill factor FF , but was unchanged with the addition of Cu2 ZnTPyP 2.6 PCE, 3.68 mA cm2 JSC, 0.59 VOC, 46.27 FF and halved upon the addition of Cu2 CuTCPP 1.24 PCE, 6.72 mA cm2 JSC, 0.59 VOC, 56.24 FF compared to devices without nanosheets 2.6 PCE, 6.61 mA cm2 JSC, 0.58 VOC, 56.64 FF . Our analysis indicates that there are three different mechanisms by which MONs can influence the photoactive layer light absorption, energy level alignment, and morphological changes. Analysis of external quantum efficiency, UV vis and photoelectron spectroscopy data found that MONs have similar effects on light absorption and energy level alignment. However, atomic force and Raman microscopy studies revealed that the nanosheet thickness and lateral size are crucial parameters in enabling the MONs to act as beneficial additives resulting in an improvement of the OPV device performance. We anticipate this study will aid in the design of MONs and other 2D materials for future use in other light harvesting and emitting device