J. Berkowitz

Bio: J. Berkowitz is an academic researcher. The author has contributed to research in topics: Molybdenum trioxide & Sublimation (phase transition). The author has an hindex of 1, co-authored 1 publications receiving 108 citations.

POLYMERIC GASEOUS SPECIES IN THE SUBLIMATION OF MOLYBDENUM TRIOXIDE. Period covered: To June 30, 1956. Technical Report No. 2 on THERMODYNAMICS OF REFRACTORY MATERIALS AS DETERMINED WITH A MASS SPECTROMETER

Abstract: Mass spectometric analysis of the vapor in thermodynamic equilibrium with powdered molybdenum trioxide, as sampled from a Knudsen effusion cell, has shown that the vapor phase consists predominantly of Mo3O9, Mo4O12 and Mo5O15 molecules. Utilizing the Clausius‐Clapeyron equation, individual heats of sublimation have been determined to be 80.5±1.5, 93.6±1.6 and 105.6±3.5 kcal/mole respectively at 850° K. The heats of formation and third law entropies have been evaluated for each of these molecules.

Transition Metal Oxides for Organic Electronics: Energetics, Device Physics and Applications

Abstract: During the last few years, transition metal oxides (TMO) such as molybdenum tri-oxide (MoO3), vanadium pent-oxide (V2O5) or tungsten tri-oxide (WO3) have been extensively studied because of their exceptional electronic properties for charge injection and extraction in organic electronic devices. These unique properties have led to the performance enhancement of several types of devices and to a variety of novel applications. TMOs have been used to realize efficient and long-term stable p-type doping of wide band gap organic materials, charge-generation junctions for stacked organic light emitting diodes (OLED), sputtering buffer layers for semi-transparent devices, and organic photovoltaic (OPV) cells with improved charge extraction, enhanced power conversion efficiency and substantially improved long term stability. Energetics in general play a key role in advancing device structure and performance in organic electronics; however, the literature provides a very inconsistent picture of the electronic structure of TMOs and the resulting interpretation of their role as functional constituents in organic electronics. With this review we intend to clarify some of the existing misconceptions. An overview of TMO-based device architectures ranging from transparent OLEDs to tandem OPV cells is also given. Various TMO film deposition methods are reviewed, addressing vacuum evaporation and recent approaches for solution-based processing. The specific properties of the resulting materials and their role as functional layers in organic devices are discussed.

Doped Organic Transistors.

Abstract: Organic field-effect transistors hold the promise of enabling low-cost and flexible electronics. Following its success in organic optoelectronics, the organic doping technology is also used increasingly in organic field-effect transistors. Doping not only increases device performance, but it also provides a way to fine-control the transistor behavior, to develop new transistor concepts, and even improve the stability of organic transistors. This Review summarizes the latest progress made in the understanding of the doping technology and its application to organic transistors. It presents the most successful doping models and an overview of the wide variety of materials used as dopants. Further, the influence of doping on charge transport in the most relevant polycrystalline organic semiconductors is reviewed, and a concise overview on the influence of doping on transistor behavior and performance is given. In particular, recent progress in the understanding of contact doping and channel doping is summarized.

Raman spectroscopy of monolayer-type oxide catalysts: Supported Mo oxides

Abstract: Oxides of the group VIb metals (Cr, Mo, W) and oxides of vanadium, rhenium, and niobium supported on a second high-surface-area metal oxide such as Al2O3, TiO2, Si02, ZrO2, and so forth are recognized as industrially important catalysts or catalyst precursors for various reactions [1–11], These materials frequently have been described as so-called monolayer catalysts based on a structural model which assumed spreading of the active oxide over the support surface. These catalysts have been investigated by a variety of techniques, conventional bulk sampling techniques as well as by surface-sensitive electron and ion spectroscopies, in an attempt to elucidate the nature of the catalyst surface species, and to study the coordination environment of the active metal center(s). Electronic spectroscopy gives rise to broad bands and the spectra are less informative than vibrational spectra. In addition, although techniques such as Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS...

Metal/Metal-Oxide Interfaces: How Metal Contacts Affect the Work Function and Band Structure of MoO3

Abstract: When transition metal oxides are used in practical applications, such as organic electronics or heterogeneous catalysis, they often must be in contact with a metal. Metal contacts can affect an oxide's chemical and electronic properties within the first few nanometers of the contact, resulting in changes to an oxide's chemical reactivity, conductivity, and energy-level alignment properties. These effects can alter an oxide's ability to perform its intended function. Thus, the choice of contacting metal becomes an important design consideration when tailoring the properties of transition-metal oxide thin films or nanoparticles. Here, metal/metal-oxide interfaces involving a widely used oxide in organic electronics, MoO3, are examined. It is demonstrated that metal contacts tend to reduce the Mo6+ cation to lower oxidation states and, consequently, alter MoO3’s valence electronic structure and work function when the oxide layer is very thin (less than 10 nm). MoO3 becomes semimetallic and has a lower work function near metal contacts. The observed behavior is attributed to two causes: 1) charge transfer from the metal Fermi level into MoO3’s low-lying conduction band and 2) an oxidation-reduction reaction between the metal and MoO3 that results in oxidation of the metal and reduction of MoO3. These results illustrate how interfaces are important to an oxide's ability to provide energy-level alignment.