The photo-Dember effect is a source of impulsive THz emission following femtosecond pulsed optical excitation. This emission results from the ultrafast spatial separation of electron-hole pairs in strong carrier gradients due to their different diffusion coefficients. The associated time dependent polarization is oriented perpendicular to the excited surface which is inaptly for efficient out coupling of THz radiation. We propose a scheme for generating strong carrier gradients parallel to the excited surface. The resulting photo-Dember currents are oriented in the same direction and emit THz radiation into the favorable direction perpendicular to the surface. This effect is demonstrated for GaAs and In(0.53)Ga(0.47)As. Surprisingly the photo-Dember THz emitters provide higher bandwidth than photoconductive emitters. Multiplexing of phase coherent photo-Dember currents by periodically tailoring the photoexcited spatial carrier distribution gives rise to a strongly enhanced THz emission, which reaches electric field amplitudes comparable to a high-efficiency externally biased photoconductive emitter.
Chirality is essential in nature and often pivotal for biological information transfer, for example, via odor messenger molecules. While the human nose can distinguish the enantiomers of many chiral odors, the technical realization by an artificial sensor or an electronic nose, e‐nose, remains a challenge. Herein, we present an array of six sensors coated with nanoporous metal–organic framework (MOF) films of different homochiral and achiral structures, working as an enantioselective e‐nose. While the achiral‐MOF‐film sensors show identical responses for both isomers of one chiral odor molecule, the responses of the homochiral MOF films differ for different enantiomers. By machine learning algorithms, the combined array data allow the stereoselective identification of all compounds, here tested for five pairs of chiral odor molecules. We foresee the chiral‐MOF‐e‐nose, able to enantioselectively detect and discriminate chiral odors, to be a powerful approach towards advanced odor sensing.
Chiralität ist von wesentlicher Bedeutung in der Natur und oft entscheidend für biologischen Informationstransfer, z. B. mittels Geruchsmolekülen. Während die menschliche Nase die Enantiomere vieler chiraler Gerüche unterscheiden kann, bleibt die technische Umsetzung durch einen künstlichen Sensor oder eine elektronische Nase, e‐nose, eine große Herausforderung. Hier präsentieren wir ein Array von sechs Sensoren, die mit nanoporösen Metall‐organischen Gerüsten (MOFs) verschiedener homochiraler und achiraler Strukturen beschichtet sind. Dieses Array funktioniert wie eine enantioselektive elektronische Nase. Während die achiralen MOF‐Sensoren identische Reaktionen für beide Isomere eines chiralen Geruchsmoleküls zeigen, unterscheiden sich die Sensorsignale der homochiralen MOF‐Filme bei verschiedenen Enantiomeren. Mittels maschineller Lern‐Algorithmen ermöglichen die kombinierten Arraydaten die stereoselektive Identifizierung, hier für fünf Paare von chiralen Geruchsmolekülen getestet. Wir sind überzeugt, dass die “chiral‐MOF‐e‐nose”, welche chirale Gerüche enantioselektiv erkennen und unterscheiden kann, zur fortgeschrittenen technischen Geruchswahrnehmung beiträgt.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.