Zeitschriftenaufsätze

In the pursuit of high-efficiency tandem devices for solar energy conversion based on III-V-semiconductors, low-defect III-V nucleation on Si(100) substrates is essential. Here, hydrogen and arsenic are key ingredients in all growth processes with respect to industrially scalable metalorganic vapor phase epitaxy. Our study provides insight into Si(100) surface preparation for the initial stage of III-V nucleation. The samples investigated, prepared on substrates with different offcut angles, show single domain surfaces consisting of rows of preferentially buckled dimers. Low energy electron diffraction and reflection anisotropy spectroscopy confirm well-defined (1 × 2)/(2 × 1) majority domains. Fourier-transform infrared spectroscopy revealed hydrogen bonding to the surface dimers, while no impurities were found by XPS. Density functional theory calculations support the experimental results and reveal a novel surface motif of H-passivated Si-As mixed dimers.

Mankind is currently living in the era of mobile communication. Mobile communication encompasses almost all areas of our daily life and is heavily used in most sectors of economy, including agriculture, healthcare, education, and so on. With mobile devices such as smart phones, people can connect to any other people somewhere on the earth, can access huge databases via the internet, stream videos and movies, to name just a few of the many mobile services that are routinely used in the early 2020s. Artificial intelligence, virtual reality, and other emerging new applications will further boost the importance of mobile communication. It is a general trend that with progressing evolution of mobile communication, the amount of data to be transmitted wirelessly increases rapidly and continuously. To enable this, a suitable well-performing hardware infrastructure is needed. The hardware used so far in the successively introduced generations of systems for mobile communication is essentially based on fast transistors. We designate these transistors as gigahertz (GHz)-terahertz (THz) transistors, as the high data rates to be transferred require an electronic hardware operating properly at frequencies in the GHz-THz range. The present paper provides a comprehensive in-depth discussion of these transistors. After a short survey of the evolution of mobile communication systems, the different categories and classes of GHz-THz transistors are introduced, relevant transistor performance measures called figures of merit are defined, issues of transistor design are dealt with, and general design rules for GHz-THz transistors are established. This is followed by a tour through the evolution of these transistors, starting in the 1950s, when the first transistors with GHz capabilities were demonstrated, up to the latest developments since the turn of the millennium and to the state-of-the-art in mid-2024. The discussion includes evolutionary advances as well as true breakthroughs, both contributing to the significant performance improvements achieved over the years. Furthermore, some research activities on GHz-THz transistors, which, unfortunately, led to a dead end as well as ongoing efforts with still unclear outcome are presented and the approaching limits of transistor performance are critically examined. Finally, we take a short view on alternative hardware options for mobile communication systems beyond the limits of transistors.

In lithium-ion batteries, the solid electrolyte interphase (SEI) passivates the anode against reductive decomposition of the electrolyte but allows for electron transfer reactions between anode and redox shuttle molecules, which are added to the electrolyte as an internal overcharge protection. In order to elucidate the origin of these poorly understood passivation properties of the SEI with regard to different molecules, we used a four-electrode-based generator-collector setup to distinguish between electrolyte reduction current and the redox molecule (ferrocenium ion Fc+) reduction current at an SEI-covered glassy carbon electrode. The experiments were carried out in situ during potentiostatic SEI formation close to battery operation potentials. The measured generator and collector currents were used to calculate passivation factors of the SEI with regard to electrolyte reduction and with regard to Fc+ reduction. These passivation factors show huge differences in their absolute values and in their temporal evolution. By making simple assumptions about molecule transport, electron transport, and charge transfer reaction rates in the SEI, distinct passivation mechanisms are identified, strong indication is found for a transition during SEI growth from redox molecule reduction at the electrode | SEI interface to reduction at the SEI | electrolyte interface, and good estimates for the transport coefficients of both electrons and redox molecules are derived. The approach presented here is applicable to any type of electrochemical interphase and should thus also be of interest for interphase characterization in the fields of electrocatalysis and corrosion.

Semiconducting materials show high potential for solar energy harvesting due to their suitable bandgaps, which allow the efficient utilization of light energy larger than their bandgaps. However, the photon energy smaller than their bandgap is almost unused, which significantly limits their efficient applications. Herein, plasmonic Pd/SnS2 microcubes with abundant Pd nanoparticles attached to the SnS2 nanosheets are fabricated by an in situ photoreduction method. The as-prepared Pd/SnS2 microcubes extend the light-harvesting ability of SnS2 beyond its cutoff wavelength, which is attributed to the localized surface plasmon resonance (LSPR) effect of the Pd nanoparticles and the 3D structure of the SnS2 microcubes. Pd nanoparticles can also enhance the light absorption of TiO2 nanoparticles and NiPS3 nanosheets beyond their cutoff wavelengths, revealing the universality for promoting absorption above the cutoff wavelength of the semiconductors. When the plasmonic Pd/SnS2 microcubes are integrated into a hydrophilic sponge acting as the solar evaporator, a solar-to-vapor efficiency of up to 89.2% can be achieved under one sun. The high solar-to-vapor conversion efficiency and the broad applicability of extending the light absorption far beyond the cutoff wavelength of the semiconductor comprise the potential of innovative plasmonic nanoparticle/semiconductor composites for solar desalination.