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397 research outputs found

Carbon nanotube junctions and devices

Author: Postma H.W.Ch. (author)
Postma H.W.Ch.
Publication venue
Publication date: 04/12/2001
Field of study

In this thesis Postma presents transport experiments performed on individual single-wall carbon nanotubes. Carbon nanotubes are molecules entirely made of carbon atoms. The electronic properties are determined by the exact symmetry of the nanotube lattice, resulting in either metallic or semiconducting behaviour. Due to their small diameter, electronic motion is directed in the length direction of the nanotube, making them ideal systems to study e.g. one-dimensional transport phenomena. First, we present mK-temperature current-voltage characteristics of an individual single-wall carbon nanotube showing Coulomb blockade and resonant tunnelling through individual molecular levels. We then report electrical transport measurements on carbon nanotubes with naturally occurring intramolecular junctions. We find that a metal-semiconductor junction behaves like a rectifying diode, whereas the conductance of a metal-metal junction behaves like a tunnel junction with associated power-law dependencies described by a Luttinger liquid model for tunnelling between the two nanotube segments. In order to further study carbon nanotube intramolecular junctions, we developed an atomic force microscope (AFM) manipulation technique, by means of which carbon nanotube junctions such as buckles and crossings are created. The electronic transport properties of these manipulated structures show that they form electronic nanometer-size tunnel junctions. Thereafter, room-temperature single-electron transistors are realized within metallic carbon nanotubes. The devices feature a short (down to 20 nm) nanotube section that is created by AFM manipulation. Coulomb charging is observed at room temperature. We observe unconventional power-law dependencies in the transport properties for which we develop a resonant-tunnelling Luttinger-liquid model. Finally, the low-frequency electronic noise properties of metallic carbon nanotubes are investigated. The noise power exhibits a 1/f frequency dependence that is three orders of magnitude smaller at 8 K than at 300 K. As a demonstration of how these noise properties affect nanotube devices, we present a preliminary investigation of the noise characteristics of an intramolecular carbon nanotube single-electron transistor.Applied Science

TU Delft Repository

The era of our lives: The memory of Korsakoff patients for the first Covid-19 pandemic lockdown in the Netherlands

Author: Herrmann Dianne
Oudman Erik
Postma Albert
Publication venue
Publication date: 12/12/2022
Field of study

Memories for worldwide and emotional events (such as 9/11) are more vividly relived and recalled than memories for everyday events. Previous studies have shown that flashbulb memories of a single event enhanced the memory strength in severe amnesia. It is currently unknown whether macro-events that stretch out over longer periods of time (weeks, months) strengthen memory even further. Our aim was therefore to investigate to what extent patients with severe amnesia, due to Korsakoff’s syndrome (KS), were able to relive the first Covid-19 lockdown in the Netherlands, and whether experienced emotions enhanced reliving of the participants. We included 22 KS patients and 24 age-, education-, and gender-matched healthy controls. Covid-19 related memories were assessed by measures of autobiographical memory specificity, phenomenological reliving, emotional intensity and semantic-and episodic knowledge about the first lockdown in March 2020 – May 2020 in the Netherlands. Although amnesia patients remembered significantly fewer autobiographical details regarding the Covid-19 lockdown than healthy controls, one fourth of the KS patients recalled specific events. Amnesia patients reported levels of emotional intensity equivalent to those in the control group. Stronger autobiographical reliving was associated with higher emotional intensity. Both amnesia patients and healthy controls had higher recall of episodic than semantic lockdown related information. In conclusion, results demonstrate that information for macro-events can still be memorized and relived, most specifically when emotional valence is high, even by highly amnestic patients

PubMed Central

Utrecht University Repository

18th European Conference on Information Systems (ECIS)

Author: Kroeze Jan H
Postma Dirk
Mavetera Nehemiah
Lotriet Hugo
Sewchurran Kosheek
Pfaff Mark S
Topi Heikki
Publication venue
Publication date: 01/01/2010
Field of study

PANELISTS: Jan Kroeze (chair), North-West University in Vanderbijlpark, South Africa Hugo Lotriet, University of Pretoria, South Africa Nehemiah Mavetera, Mafikeng campus of the North-West University, South Africa Mark Pfaff, School of Informatics, Indiana University, USA Dirk Postma, Department of Education Studies,University of Johannesburg, South Africa Kosheek Sewchurran, Department of Information Systems. University of Cape Town, South Africa Heikki Topi, Bentley University, Waltham, MA, USAThe audience will be stimulated to think about the relationship between the Humanities and Information Systems in a way opposite to the usual. A lot of research has been conducted on the application of computing in the Humanities, but this panel will explore the reverse process of enrichment that takes place. The purpose is to give recognition to work that has already been done in this regard by means of identifying a substantial sub-discipline, but also to stimulate more and deliberate research that explores ways to enhance Information Systems by interweaving insights and methods from the Humanities. The panel believes that such an endeavour may enhance ICT to empower the communities using these technologies

NWU Institutional Repository (North-West University)