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Modifying the geometric and electronic structure of hexagonal boron nitride on Ir(111) by Cs adsorption and intercalation
摘要： Epitaxial hexagonal boron nitride on Ir(111) is significantly modified by adsorption and intercalation of alkali-metal atoms. Regarding geometry, intercalation lifts the two-dimensional layer from its substrate and reduces the characteristic corrugation imprinted by direct contact with the metal substrate. Moreover, the presence of charged species in close proximity to the hexagonal boron nitride (hBN) layer strongly shifts the electronic structure (valence bands and core levels). We used scanning tunneling microscopy, low-energy electron diffraction, x-ray photoelectron spectroscopy (XPS), and the x-ray standing wave technique to study changes in the atomic structure induced by Cs adsorption and intercalation. Depending on the preparation, the alkali-metal atoms can be found on top and underneath the hexagonal boron nitride in ordered and disordered arrangements. Adsorbed Cs does not change the morphology of hBN/Ir(111) significantly, whereas an intercalated layer of Cs decouples the two-dimensional sheet and irons out its corrugation. XPS and angle-resolved photoelectron spectroscopy reveal a shift of the electronic states to higher binding energies, which increases with increasing density of the adsorbed and intercalated Cs. In the densest phase, Cs both intercalates and adsorbs on hBN and shifts the electronic states of hexagonal boron nitride by 3.56 eV. As this shift is not sufficient to move the conduction band below the Fermi energy, the electronic band gap must be larger than 5.85 eV.
关键词： hexagonal boron nitride,Cs adsorption,electronic structure,geometric structure,intercalation
更新于2025-09-23 15:21:01
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Probing hyperbolic polaritons using infrared attenuated total reflectance micro-spectroscopy
摘要： Hyperbolic polariton modes are highly appealing for a broad range of applications in nanophotonics, including surfaced enhanced sensing, sub-diffractional imaging, and recon?gurable metasurfaces. Here we show that attenuated total re?ectance (ATR) micro-spectroscopy using standard spectroscopic tools can launch hyperbolic polaritons in a Kretschmann–Raether con?guration. We measure multiple hyperbolic and dielectric modes within the naturally hyperbolic material hexagonal boron nitride as a function of different isotopic enrichments and ?ake thickness. This overcomes the technical challenges of measurement approaches based on nanostructuring, or scattering scanning near-?eld optical microscopy. Ultimately, our ATR approach allows us to compare the optical properties of small-scale materials prepared by different techniques systematically.
关键词： Hyperbolic polaritons,infrared attenuated total re?ectance micro-spectroscopy,hexagonal boron nitride,Kretschmann–Raether con?guration
更新于2025-09-23 15:21:01
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AIP Conference Proceedings [AIP Publishing 15th International Conference on Concentrator Photovoltaic Systems (CPV-15) - Fes, Morocco (25–27 March 2019)] 15th International Conference on Concentrator Photovoltaic Systems (CPV-15) - Towards all screen printed back-contact back-junction silicon solar cells
摘要： We report recent progress in the adoption of an optimized screen-printable boron dopant material, which enables the cost-competitive fabrication of novel n-type silicon solar cells such as “nPERT” and “IBC” cells. We manufactured first “IBC” devices with an early version of our dopant material, a co-diffusion approach and evaporated electrodes, achieving an efficiency of 20.9 % in 2016. Since then we optimized the dopant material and co-diffusion processes, as reported in this work. These optimizations now enable a long-term printing of the dopant material, suited for mass production, while maintaining crucial performance parameters. Moreover, we demonstrate a co-diffusion setup with POCl3, which does not require any additional dopant sources and can instead be adjusted with a wet chemical etch back. Combined with new commercially available electrode pastes, which have been evaluated with regard to simultaneous contacting of n- and p-type dopings, all screen printed n-type solar cells become a mass market possibility in the near future.
关键词： screen-printable boron dopant material,co-diffusion,POCl3,electrode pastes,n-type silicon solar cells,wet chemical etch back
更新于2025-09-23 15:19:57
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Microwave assisted synthesis of boron and nitrogen rich graphitic quantum dots to enhance fluorescence of photosynthetic pigments
摘要： Energy transfer between quantum dots and biomolecules is of interest due to high absorption capacity and high quantum efficiency of quantum dots. Amongst all types of quantum dots, graphene and graphitic quantum dots have great potential for energy transfer studies due to their high biocompatibility and low toxicity. In this study, a simple route to synthesize boron and nitrogen rich graphitic quantum dots (C-BN) and boron carbon nitride (BCN) quantum dots is demonstrated. Quantum dots were synthesized in a domestic microwave oven. Composition of quantum dots was controlled by tuning initial mole ratio of boron and nitrogen precursors. As molar ratio of boron precursor was increased, formation of C-BN quantum dots was favoured. C-BN quantum dots were mainly composed of boron and nitrogen (with around 10 % carbon) in their main composition, and sized around 2 nm with bright photoluminescence. To the best of our knowledge, this is the first study which proposes a bottom-up synthesis method to synthesize C-BN quantum dots based on domestic microwaves. Also, treating photosynthetic pigments with quantum dots resulted in 20 % enhancement of fluorescence of photosynthetic pigments at 670 nm, which demonstrates that C-BN and BCN quantum dots can be important constituents of artificial antenna systems for photosynthetic organisms.
关键词： Photosynthetic pigments,Boron nitride,Energy transfer,Graphitic quantum dots
更新于2025-09-23 15:19:57
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Analysis of different conductive pastes to form the contact with the boron back surface field in PERT silicon solar cells
摘要： The industrial production of solar cells of the PERC family is growing, because the potential to increase the efficiency due to the passivation of the rear face. The PERT solar cell is a cost-effective structure of the PERC configurations. The goal of this paper is to analyze the influence in the electrical parameters of different metal pastes used to form the contact with the boron back surface field of PERT solar cells passivated with silicon dioxide on both sides and developed with a cost-effective process. The boron doped BSF and phosphorus emitter were carried out with reduction of steps. Solar cells were processed with three different conductive pastes: (1) an aluminum paste (PV381), (2) a silver/aluminum paste (PV3N1) and (3) a silver paste (PV51G), with different viscosity and solids content. The pastes were produced by DuPont. The PV381 and PV3N1 pastes produced solar cells with the efficiency of 16.2% and 15.9%, respectively. The higher open circuit voltage was achieved with the aluminum paste, indicating that this paste is more effective to produce the selective back surface field. The PV51G paste is not suitable to form the rear contact.
关键词： aluminum and silver/aluminum pastes,boron back surface field,PERT silicon solar cells
更新于2025-09-23 15:19:57
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In situ reactions during direct laser deposition of Ti-B4C composites
摘要： Direct laser deposition of a mixture of titanium (Ti) and boron-carbide (B4C), using the laser engineered net shaping process, results in a complex multi-phase Ti matrix composite due to the incipient interfacial reactions between liquid titanium and solid/partially melted B4C. Detailed microstructural characterization, at multiple length scales, reveals that titanium boride (TiB) precipitates are the initial reaction product which act as heterogeneous nucleation sites for TiC precipitates. Both the TiB and TiC precipitates in turn act as heterogeneous nucleation sites for fine β-Ti grains, within the retained liquid titanium, which eventually transform into fine equiaxed α-Ti grains comprising the matrix.
关键词： Titanium matrix composites,In-situ reactions,Boron,Additive manufacturing,Carbide
更新于2025-09-23 15:19:57
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Conversionless efficient and broadband laser light diffusers for high brightness illumination applications
摘要： Laser diodes are efficient light sources. However, state-of-the-art laser diode-based lighting systems rely on light-converting inorganic phosphor materials, which strongly limit the efficiency and lifetime, as well as achievable light output due to energy losses, saturation, thermal degradation, and low irradiance levels. Here, we demonstrate a macroscopically expanded, three-dimensional diffuser composed of interconnected hollow hexagonal boron nitride microtubes with nanoscopic wall-thickness, acting as an artificial solid fog, capable of withstanding ~10 times the irradiance level of remote phosphors. In contrast to phosphors, no light conversion is required as the diffuser relies solely on strong broadband (full visible range) lossless multiple light scattering events, enabled by a highly porous (>99.99%) non-absorbing nanoarchitecture, resulting in efficiencies of ~98%. This can unleash the potential of lasers for high-brightness lighting applications, such as automotive headlights, projection technology or lighting for large spaces.
关键词： high-brightness illumination,solid-state lighting,light diffusers,laser diodes,hexagonal boron nitride
更新于2025-09-23 15:19:57
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Laser-induced nano-heater performance of B4C submicrometer spherical particles fabricated by pulsed laser melting in liquid
摘要： Gold nanoparticles as promising nano-heater particles utilizing surface plasmon resonance have been extensively studied for various chemical and medical applications, even though the suitable wavelength for nano-heater is only in the visible range and possible maximum temperature is limited due to its relatively low melting point. About a decade ago, a technique called pulsed laser melting in liquid (PLML) was developed to fabricate submicrometer spherical particles as main products. In this process, particles in the submicrometer size range are effectively heated over the melting point by laser irradiation, indicating that submicrometer spherical particles can be developed as novel heater particles that may overcome the drawback of gold nanoparticles. This study examined the potentials of PLML-fabricated B4C submicrometer spherical particles as nano-heater particles since B4C has a wider optical absorption wavelength range and higher melting point than gold. From the thermal modification induced by melting the materials in contact with the B4C particles, the highest attained temperature was estimated by laser irradiation. This experiment showed that B4C particles have sufficient response in 300–1100 nm wavelength range and can act as nano-heater even at temperatures over 2000 K. Thus, B4C submicrometer spherical particles can be used as novel space-selective heater particles.
关键词： Nano-heater,Submicrometer,Phase transition,Boron carbide,Spherical particles
更新于2025-09-23 15:19:57
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A self-powered photodetector based on two-dimensional boron nanosheets
摘要： Owing to their intriguing characteristics, the ongoing pursuit of emerging mono-elemental two-dimensional (2D) nanosheets beyond graphene is an exciting research area for next-generation applications. Herein, we demonstrate that highly crystalline 2D boron (B) nanosheets can be efficiently synthesized by employing a modified liquid phase exfoliation method. Moreover, carrier dynamics has been systematically investigated by using femtosecond time-resolved transient absorption spectroscopy, demonstrating an ultrafast recovery speed during carrier transfer. Based on these results, the optoelectronic performance of the as-synthesized 2D B nanosheets has been investigated by applying them in photoelectrochemical (PEC)-type and field effect transistor (FET)-type photodetectors. The experimental results revealed that the as-fabricated PEC device not only exhibited a favourable self-powered capability, but also a high photoresponsivity of 2.9–91.7 μA W?1 in the UV region. Besides, the FET device also exhibited a tunable photoresponsivity in the range of 174–281.3 μA W?1 under the irradiation of excited light at 405 nm. We strongly believe that the current work shall pave the path for successful utilization of 2D B nanosheets in electronic and optoelectronic devices. Moreover, the proposed method can be utilized to explore other mono-elemental 2D nanomaterials.
关键词： two-dimensional boron nanosheets,optoelectronic devices,carrier dynamics,liquid phase exfoliation,photodetector
更新于2025-09-23 15:19:57
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Excitonically Coupled Cyclic BF2 Arrays of Calix[8]a?? and Calix[16]phyrin as Neara??IRa?? Chromophores
摘要： A pair of giant calix[n]phyrin derivatives namely calix[8]- (4) and calix[16]phyrin (5), involving two and four BF2 units, respectively, were prepared via the condensation of bis-naphthobipyrrolylmethene-BF2 complex with pentafluorobenzaldehyde. Both systems and precursor 3 were fully characterized, including via single crystal X-ray diffraction analyses. Calix[n]phyrins 4 and 5 display extremely high extinction coefficients (3.67 and 4.82 105 M-1cm-1, respectively) in the near-IR region. This observation was taken as initial evidence for strong excitonic coupling within these cyclic multi-chromophoric systems. Detailed insights into the effect of excitonic coupling dynamics on the electronic structure and photophysical properties of the macrocycles came from fluorescence, time-correlated single-photon counting (TCSPC) and transient absorption (TA) measurements. Support for the experimental findings came from theoretical studies. Taken in concert this combination of theory and experiment served to confirm that the coupling between the excitons depends on the specifics of the calix[n]phyrin structure, not just its size.
关键词： Cyclic BODIPY,Boron,Exciton Coupling,Porphyrinoids,NIR Dye,Calix[n]phyrin
更新于2025-09-23 15:19:57