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Results for “WORK FUNCTIONS”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

High-work-function molybdenum oxide hole extraction contacts in hybrid organic–inorganic perovskite solar cells

Here, we investigate the effect of high work function contacts in halide perovskite absorber-based photovoltaic devices. Photoemission spectroscopy measurements reveal that band bending is induced in the absorber by the deposition of the high work function molybdenum trioxide (MoO 3 ). We find that direct contact between MoO 3 and the perovskite leads to a chemical reaction, which diminishes device functionality. Introducing an ultrathin spiro-MeOTAD buffer layer prevents the reaction, yet the altered evolution of the energy levels in the methylammonium lead iodide (MAPbI 3 ) layer at the interface still negatively impacts device performance.

14 SOLAR ENERGY↗
DOE OSTI2011

Method of making low work function component

A method for fabricating a component is disclosed. The method includes: providing a member having an effective work function of an initial value, disposing a sacrificial layer on a surface of the member, disposing a first agent within the member to obtain a predetermined concentration of the agent at said surface of the member, annealing the member, and removing the sacrificial layer to expose said surface of the member, wherein said surface has a post-process effective work function that is different from the initial value.

42 ENGINEERING↗
DOE OSTI2015

Observation of quantum oscillation of work function in ultrathin-metal/semiconductor junctions

Quantization in energy level due to confinement is generally observed for semiconductors. This property is used for various quantum devices, and it helps to improve the characteristics of conventional devices. Here, the authors have demonstrated the quantum size effects in ultrathin metal (Ni) layers sandwiched between two large band-gap materials. The metal work function is found to oscillate as a function of its thickness. The thermionic emission current bears the signature of the oscillating work function, which has a linear relationship with barrier heights. This methodology allows direct observation of quantum oscillations in metals at room temperature using a Schottky diode and electrical measurements using source-measure-units. The observed phenomena can provide additional mechanism to tune the barrier height of metal/semiconductor junctions, which are used for various electronic devices.

42 ENGINEERING↗
NASA NTRS1972

Theoretical determination of cesiated work functions

A computer program based on the theoretical work of Gyftopoulos, Steiner, and Levine on bimetallic systems and using a modified version of Wilkins' SIMCON subroutine SURFAS was written for the Univac 1108. This program, WFGSL, accepts the operating conditions and the physical parameters pertinent to the substrate and adsorbate, and outputs the field-free work function, electron current (Richardson equation), ion current (Saha equation), and fractional substrate coverage by the adsorbate. A brief description of the theory is presented together with a program description and listing. An application of the program to a bimetallic system of cesium (adsorbate) and rhenium (substrate) is also described.

Szejn, R. M.↗
DOE OSTI2023

Asymmetric Electrode Work Function Customization via Top Electrode Replacement in Ferroelectric and Field–Induced Ferroelectric Hafnium Zirconium Oxide Thin Films

Non-volatile memory device structures such as ferroelectric random-access memory and ferroelectric tunnel junctions employ switchable spontaneous polarization to hold binary states. These devices can potentially benefit from the imposition of spontaneous internal biases and their resulting effect on the polarization properties of the ferroelectric (or field-induced ferroelectric/ antiferroelectric) layer. While HfO 2 -based thin films are ideal candidates for implementation into these devices due to their scalability and silicon compatibility, the phase purity of these oxides is sensitive to the selection of electrode material, preventing incorporation of asymmetric electrode layers into such structures. Within this work, electrode replacement following post-metallization anneal processing is introduced as a route to achieve ferroelectric and field-induced ferroelectric Hf x Zr 1–x O 2 (HZO) thin films with electrode-independent phase constitutions. The effects of this process and the corresponding internal biases imposed across the HZO layers due to asymmetric work functions are investigated. It is shown that internal biases vary in magnitude in accordance with prediction based on the work functions of the replaced electrode layers and affect remanent polarization magnitudes. Accordingly, electrode replacement presents a processing route that can readily produce HZO films with spontaneous internal biases and electrode- independent phase constitutions, facilitating implementation of these ferroelectrics into the next generation device structures.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Bare-tether cathodic contact through thermionic emission by low-work-function materials

A new material, C12A7:e{sup -} electride, which might present a work function as low as 0.6 eV and moderately high temperature stability, was recently proposed as coating for floating bare tethers. Arising from heating under space operation, current is emitted by thermionic emission along a thus coated cathodic segment. A preliminary study on the space-charge-limited (SCL) double layer in front of the cathodic segment is presented using Langmuir's SCL electron current between cylindrical electrodes and orbital-motion-limited ion-collection sheath. A detailed calculation of current and bias profiles along the entire tether length is carried out with ohmic effects and the transition from SCL to full Richardson-Dushman emission included. Analysis shows that in the simplest drag mode, under typical orbital and tether conditions, thermionic emission leads to a short cathodic section and may eliminate the need for an active cathodic device and its corresponding gas feed requirements and power subsystem, which results in a truly 'propellant-less' tether system for such basic applications as de-orbiting low earth orbit satellites.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Atomic layer deposition of Hf{sub x}Al{sub y}C{sub z} as a work function material in metal gate MOS devices

As advanced silicon semiconductor devices are transitioning from planar to 3D structures, new materials and processes are needed to control the device characteristics. Atomic layer deposition (ALD) of Hf{sub x}Al{sub y}C{sub z} films using hafnium chloride and trimethylaluminum precursors was combined with postdeposition anneals and ALD liners to control the device characteristics in high-k metal-gate devices. Combinatorial process methods and technologies were employed for rapid electrical and materials characterization of various materials stacks. The effective work function in metal–oxide–semiconductor capacitor devices with the Hf{sub x}Al{sub y}C{sub z} layer coupled with an ALD HfO{sub 2} dielectric was quantified to be mid-gap at ∼4.6 eV. Thus, Hf{sub x}Al{sub y}C{sub z} is a promising metal gate work function material that allows for the tuning of device threshold voltages (V{sub th}) for anticipated multi-V{sub th} integrated circuit devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Improving the work function of the niobium surface of SRF cavities by plasma processing

An in situ plasma processing technique using chemically reactive oxygen plasma to remove hydrocarbons from superconducting radio frequency cavity surfaces at room temperature was developed at the spallation neutron source, at Oak Ridge National Laboratory. To understand better the interaction between the plasma and niobium surface, surface studies on small samples were performed. In this article, we report the results from those surface studies. The results show that plasma processing removes hydrocarbons from top surface and improves the surface work function by 0.5₋1.0 eV. Improving the work function of RF surface of cavities can help to improve their operational performance.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

More on the Effect of Vacancies on Metal Characteristics. Work Function and Surface Energy

Within the density functional method, a simple method for determining the dependence of the work function of electrons and specific surface energy of the metal on the relative density of internal vacancies c{sub v} is proposed. Preserving the style of the stabilized jellium model, the preliminarily calculated volume shift of the conductivity zone bottom ε{sup (0)} ∝ c{sub v} in a specific homogeneous metal is introduced into a one-dimensional functional as the zero-point energy. Using the quantity c{sub v} as a small parameter, linear corrections to the abovementioned quantities are found. The expansion coefficients are expressed in terms of characteristics of a defectless metal. Calculations for Na and Al are carried out by the Kohn–Sham method. Temperature dependences of Al characteristics have been constructed in the thermodynamic limit.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗