We study the low-temperature in-plane magnetoresistance of tunnel-coupled quasi-onedimensional quantum wires. The wires are defined by two pairs of mutually aligned split gates on opposite sides of a I 1 micron thick AlGaAsIGaAs double quantum well heterostructure, allowing independent control of their widths. In the ballistic regime, when both wires are defined and the field is perpendicular to the current, a large resistance peak at -6 Tesla is observed with a strong gate voltage dependence. The data is consistent with a counting model whereby the number of subbands crossing the Fermi level chan, Des with fie!d due to the formation of an anticrossing in each pair of ID subbands.
Zur DarsteIlung l~leinerer Mengen reiner Fluorwasserstoffs~ure, respective zum Aufsehliessen von Silicaten benutzte A. H. A l l e n 1) ein einfaehes Verfahren. Dasselbe besteht darin, dass die k~ufliehe S~ure aus einem grossen Platintiegel in einen kleineren Tiegel aus demselben Metall fiberdestillirt wird. Um dies zu bewirken, ftillt man gleiche Theile Flusss~ture und starke Schwefelsiiure in den grossen Tiegel, setzt das kleinere Gefitss in diesen, bedeckt mit einem schalenfOrmigen Platindeckel und ffillt den Deckel mit Wasser. Durch Erwiirmen auf einer Eisen-oder Asbestplatte kann man leicht kleinere Mengen der S~ure iibertreibeni indem die Diimpfe an der unteren Seite des Deckels condensirt werden und in das kleinere Gef~tss hineintropfen. Will man einen Silicataufsehluss mit dieser Operation verbinden, so bringt man einige Tropfen Schwefelsiiure und das betreffende Material in den kleinen Tiegel. Naehdem etwa 10 cc Si~ure in diesen fibergegangen sind, wird derselbe herausgenommen und sein Inhalt verdampft; alsdann wird die Operation bis zum vollst~tndigen Aufschluss 2 bis 3 mal wiederholt. ~Nach B l o u n t 2) liisst sich Flusssi~ure leicht aus einer Bleiretorte durch Destillation rein gewinnen, wenn man die Retorte mit einem Platinrohr verbindet. Um nicht ganz reine (geringe Bleimengen enthaltende) Flusssiiure zu gewinnen, hat A l l e n eine ganz aus Blei gefertigte Retorte benutzt. Kalkwasser zum Titriren saurer Fllissigkeiten, z. B. yon Buttermilch, empfiehlt E. Holm 3) und zwar verwendet man am besten eine gesiittigte fiber Kalkhydrate aufbewahrte LSsung, da sich filtrirte oder abgegossene LSsungen ziemlich sehnell verandern. Man benutzt zweckm~tssig frisch gelOschten Kalk. Da die Temperatur yon grossem Einfiuss auf die LSslichkeit des Kalkhydrats in Wasser ist, so hat H olm L(islichkeitsbestimmungen bei verschiedenen Temperaturen gemacht. Aus denselben ergibt sich, dass eine KalkauflOsung in Wasser bei 20 o ziemlich genau einer 1/2 o ~Normalnatronlauge entspricht, was einer LOsliehkeit yon 1 Theil Kalkhydrat in 715 Theilen Wasser entspricht. 1) The Analyst 21, 87. 2) Daselbst 21, 87. 8) Nordisk farm. Tidskrift; durch Pharm. Centralhalle 87. 112.
This report describes the research accomplishments achieved under the LDRD Project "Double Electron Layer Tunneling Transistor." The main goal of this project was to investigate whether the recently discovered phenomenon of 2D-2D tunneling in GaAs/AlGaAs double quantum wells (DQWs), investigated in a previous LDW, could be harnessed and implemented as the operating principle for a new type of tunneling device we proposed, the double electron layer tunneling transistor (DELTT). In parallel with this main thrust of the project, we also continued a modest basic research effort on DQW physics issues, with significant theoretical support.The project was a considerable success, with our main goal of demonstrating a working prototype of the DELTT having been achieved. Additional DEL'IT advances included demonstrating good electrical characteristics at 77 K, demonstrating both NMOS and CMOS-like bi-stable memories at 77 K using the DELIT, demonstrating digital logic gates at 77 K, and demonstrating voltage-controlled oscillators at 77 K. In order to successfully fabricate the DEL'IT, we had to develop a novel flip-chip processing scheme, the epoxy-bond-and-stop-etch @BASE) technique. This technique was later improved so as to be amenable to electron-beam lithography, allowing the fabrication of DELlTs with sub-micron features, which are expected to be extremely high speed. In the basic physics area we also made several advances, including a measurement of the effective mass of electrons in the hour-glass orbit of a DQW subject to in-plane magnetic fields, and both measurements and theoretical calculations of the full Landau level spectra of DQWs in both perpendicular and in-plane magnetic fields. This last result included the unambiguous demonstration of magnetic breakdown of the Fermi surface.Finally, we also investigated the concept of a far-infrared photodector based on photon assisted tunneling in a DQW. Absorption calculations showed a narrowband absorption which persisted to temperatures much higher than the photon energy being detected. Preliminary data on prototype detectors indicated that the absorption is not only narrowband, but can be tuned in energy through the application of a gate voltage.
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