E. Kapetanakis

Bio: E. Kapetanakis is an academic researcher from Mediterranean University. The author has contributed to research in topics: Ion implantation & Non-volatile memory. The author has an hindex of 13, co-authored 29 publications receiving 727 citations. Previous affiliations of E. Kapetanakis include American Hotel & Lodging Educational Institute & Technological Educational Institute of Crete.

Charge storage and interface states effects in Si-nanocrystal memory obtained using low-energy Si + implantation and annealing

Abstract: Thin SiO2 oxides implanted by very-low-energy (1 keV) Si ions and subsequently annealed are explored with regards to their potential as active elements of memory devices. Charge storage effects as a function of Si fluence are investigated through capacitance and channel current measurements. Capacitance–voltage and source–drain current versus gate voltage characteristics of devices implanted with a dose of 1×1016 cm−2 or lower exhibit clear hysteresis characteristics at low electric field. The observed fluence dependence of the device electrical properties is interpreted in terms of the implanted oxide structure.

Effect of annealing environment on the memory properties of thin oxides with embedded Si nanocrystals obtained by low-energy ion-beam synthesis

Abstract: The effect of annealing in diluted oxygen versus inert environment on the structural and electrical characteristics of thin silicon dioxide layers with embedded Si nanocrystals fabricated by very low-energy silicon implantation (1 keV) is reported. Annealing in diluted oxygen increases the thickness of the control oxide, improves the integrity of the oxide and narrows the size distribution of the nanocrystals without affecting significantly their mean size (∼2 nm). Strong charge storage effects at low gate voltages and enhanced charge retention times are observed through electrical measurements of metal-oxide-semiconductor capacitors. These results indicate that a combination of low-energy silicon implants and annealing in diluted oxygen allows for the fabrication of improved low-voltage nonvolatile memory devices.

Room-temperature single-electron charging phenomena in large-area nanocrystal memory obtained by low-energy ion beam synthesis

Abstract: We investigated the dependence of implantation dose on the charge storage characteristics of large-area n-channel metal–oxide–semiconductor field-effect transistors with 1-keV Si+-implanted gate oxides. Gate bias and time-dependent source–drain current measurements are reported. Devices implanted with 1×1016 cm−2 Si dose exhibit a continuous (trap-like) charge storage process under both static and dynamic conditions. In contrast, for 2×1016 cm−2 implanted devices, electrons are stored in Si nanocrystals in discrete units at low gate voltages, as revealed by a periodic staircase plateau of the source–drain current with a low gate voltage sweep rate, and the step-like decrease of the time-dependent monitoring of the channel current. These observations of room-temperature single-electron storage effects support the pursuit of large-area devices operating on the basis of Coulomb blockade phenomena.

Silicon nanocrystal memory devices obtained by ultra-low-energy ion-beam synthesis

Abstract: Si-nanocrystal memory devices aiming at low-voltage non-volatile memory applications are explored. The devices consist of a single metal-oxide-semiconductor field-effect-transistor with silicon nanocrystals fabricated through ultra-low-energy (1 keV) Si implantation of the gate oxide (7 nm in thickness) and subsequent thermal annealing. Process issues like boron contamination and parasitic currents that affect the threshold voltage and transfer characteristics of the intended devices are discussed in terms of device structure, process parameter and device simulation. It is shown that these issues can be overcome under appropriate process modifications. Threshold shift of about 2 V are obtained for a 10 ms +9 V/−9 V pulse regime where both electron and hole trapping occur. Neither degradation, nor drift in memory window is detected after 1.5 × 10 6 10 ms +9 V/−9 V cycles. Charge retention measurements reveal that the de-trapping mechanism of stored holes is faster than that of trapped electrons and independent on the temperature. Memory operation with reduced hole trapping, herein demonstrated for a 10 ms +9 V/−7 V regime leading to a 0.3 V 10-year extrapolated memory window at 150 °C, should be preferred for long non-volatile retention of years.

Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications

Abstract: Nanocrystals (NCs) discussed in this Review are tiny crystals of metals, semiconductors, and magnetic material consisting of hundreds to a few thousand atoms each. Their size ranges from 2-3 to about 20 nm. What is special about this size regime that placed NCs among the hottest research topics of the last decades? The quantum mechanical coupling * To whom correspondence should be addressed. E-mail: dvtalapin@uchicago.edu. † The University of Chicago. ‡ Argonne National Lab. Chem. Rev. 2010, 110, 389–458 389

Functionalization and post-functionalization: a step towards polyoxometalate-based materials

Abstract: Polyoxometalates (POMs) have remarkable properties and a great deal of potential to meet contemporary societal demands regarding health, environment, energy and information technologies. However, implementation of POMs in various functional architectures, devices or materials requires a processing step. Most developments have considered the exchange of POM counterions in an electrostatically driven approach: immobilization of POMs on electrodes and other surfaces including oxides, embedding in polymers, incorporation into Layer-by-Layer assemblies or Langmuir–Blodgett films and hierarchical self-assembly of surfactant-encapsulated POMs have thus been thoroughly investigated. Meanwhile, the field of organic–inorganic POM hybrids has expanded and offers the opportunity to explore the covalent approach for the organization or immobilization of POMs. In this critical review, we focus on the use of POM hybrids in selected fields of applications such as catalysis, energy conversion and molecular nanosciences and we endeavor to discuss the impact of the covalent approach compared to the electrostatic one. The synthesis of organic–inorganic POM hybrids starting from bare POMs, that is the direct functionalization of POMs, is well documented and reliable and efficient synthetic procedures are available. However, as the complexity of the targeted functional system increases a multi-step strategy relying on the post-functionalization of preformed hybrid POM platforms could prove more appealing. In the second part of this review, we thus survey the synthetic methodologies of post-functionalization of POMs and critically discuss the opportunities it offers compared to direct functionalization.

Recent advances on polyoxometalate-based molecular and composite materials

Abstract: Polyoxometalates (POMs) are a subset of metal oxides with unique physical and chemical properties, which can be reliably modified through various techniques and methods to develop sophisticated materials and devices. In parallel with the large number of new crystal structures reported in the literature, the application of these POMs towards multifunctional materials has attracted considerable attention. This critical review summarizes recent progress on POM-based molecular and composite materials, and particularly highlights the emerging areas that are closely related to surface, electronic, energy, environment, life science, etc. (171 references).

Memory effects in complex materials and nanoscale systems

Abstract: Memory effects are ubiquitous in nature and are particularly relevant at the nanoscale where the dynamical properties of electrons and ions strongly depend on the history of the system, at least within certain time scales. We review here the memory properties of various materials and systems which appear most strikingly in their non-trivial, time-dependent resistive, capacitative and inductive characteristics. We describe these characteristics within the framework of memristors, memcapacitors and meminductors, namely memory-circuit elements with properties that depend on the history and state of the system. We examine basic issues related to such systems and critically report on both theoretical and experimental progress in understanding their functionalities. We also discuss possible applications of memory effects in various areas of science and technology ranging from digital to analog electronics, biologically inspired circuits and learning. We finally discuss future research opportunities in the field.

Enhancement of Field-Effect Mobility by Surface-Mediated Molecular Ordering in Regioregular Polythiophene Thin Film Transistor

Abstract: With the aim of enhancing the field-effect mobility by promoting surface-mediated two-dimensional molecular ordering in self-aligned regioregular poly(3-hexylthiophene) (P3HT) we have controlled the intermolecular interaction at the interface between P3HT and the insulator substrate by using self-assembled monolayers (SAMs) functionalized with various groups (–NH2, –OH, and –CH3). We have found that, depending on the properties of the substrate surface, the P3HT nanocrystals adopt two different orientations—parallel and perpendicular to the insulator substrate—which have field-effect mobilities that differ by more than a factor of 4, and that are as high as 0.28 cm2 V–1 s–1. This surprising increase in field-effect mobility arises in particular for the perpendicular orientation of the nanocrystals with respect to the insulator substrate. Further, the perpendicular orientation of P3HT nanocrystals can be explained by the following factors: the unshared electron pairs of the SAM end groups, the π–H interactions between the thienyl-backbone bearing π-systems and the H (hydrogen) atoms of the SAM end groups, and interdigitation between the alkyl chains of P3HT and the alkyl chains of the SAMs.