Alexander V. Zinovev

Nucleation and Growth of Noble Metals on Oxide Surfaces Using Atomic Layer Deposition

Abstract : Noble metals supported on metal oxide surfaces have broad applications in catalysis, microelectronics and sensing. In most applications it is critical to control the dispersion and morphology of the noble metals to achieve either a smooth, continuous film or isolated particles of controlled size. Here we examine the atomic layer deposition of Pd and Pt films onto a variety of metal oxide surfaces including Al2O3, ZrO2, and TiO2. In situ quartz crystal microbalance measurements and quadrupole mass spectrometry are used to explore the nucleation and growth of the Pd and Pt on the different metal oxide surfaces. Scanning electron microscopy and X-ray photoelectron spectroscopy are used to examine the morphology and surface state of the resulting Pt and Pd coatings. By varying the support material and the deposition conditions, we can control the morphology of the ALD noble metal coatings to yield agglomerated particles or continuous films.

Metal-induced rapid transformation of diamond into single and multilayer graphene on wafer scale

The degradation of intrinsic properties of graphene during the transfer process constitutes a major challenge in graphene device fabrication, stimulating the need for direct growth of graphene on dielectric substrates. Previous attempts of metal-induced transformation of diamond and silicon carbide into graphene suffers from metal contamination and inability to scale graphene growth over large area. Here, we introduce a direct approach to transform polycrystalline diamond into high-quality graphene layers on wafer scale (4 inch in diameter) using a rapid thermal annealing process facilitated by a nickel, Ni thin film catalyst on top. We show that the process can be tuned to grow single or multilayer graphene with good electronic properties. Molecular dynamics simulations elucidate the mechanism of graphene growth on polycrystalline diamond. In addition, we demonstrate the lateral growth of free-standing graphene over micron-sized pre-fabricated holes, opening exciting opportunities for future graphene/diamond-based electronics.

The Characterization Of Secondary Electron Emitters For Use In Large Area Photo‐Detectors

The Large‐Area Picosecond Photo‐Detector Project is focused on the development of large‐area systems to measure the time‐of‐arrival of relativistic particles with, ultimately, 1 pico‐second resolution, and for signals typical of Positron‐Emission Tomography (PET), a resolution of about 30 pico‐seconds. Our contribution to this project is to help with identification and efficient fabrication of novel electron emitting materials with properties optimized for use in such detectors. We have assembled several techniques into a single ultra‐high vacuum apparatus in order to enable characterization of both photocathode and secondary electron emission (SEE) materials. This apparatus will examine how photocathode quantum efficiency and SEE material electron yield correlate to surface chemical composition, state, and band structure. The techniques employed in this undertaking are X‐ray photoelectron spectroscopy (XPS) for surface chemical composition, ultraviolet photoelectron spectroscopy (UPS) for the determinati...

Operando tribochemical formation of onion-like-carbon leads to macroscale superlubricity

Stress-induced reactions at the sliding interface during relative movement are known to cause structural or chemical modifications in contacting materials. The nature of these modifications at the atomic level and formation of byproducts in an oil-free environment, however, remain poorly understood and pose uncertainties in predicting the tribological performance of the complete tribosystem. Here, we demonstrate that tribochemical reactions occur even in dry conditions when hydrogenated diamond-like carbon (H-DLC) surface is slid against two-dimensional (2D) molybdenum disulfide along with nanodiamonds in dry nitrogen atmosphere. Detailed experimental studies coupled with reactive molecular dynamics simulations reveal that at high contact pressures, diffusion of sulfur from the dissociated molybdenum disulfide led to amorphization of nanodiamond and subsequent transformation to onion-like carbon structures (OLCs). The in situ formation of OLCs at the sliding interface provide reduced contact area as well as incommensurate contact with respect to the H-DLC surface, thus enabling successful demonstration of superlubricityStress-induced tribochemical reactions that reduce friction at sliding interfaces typically require liquid lubricants. Here, the authors discover the nanoscale tribocatalytic formation of onion-like carbon from 2D MoS2 and nanodiamond under dry and oil-free conditions, providing superlubricity at the macroscale.

Solar Absorber Cu2ZnSnS4 and its Parent Multilayers ZnS/SnS2/Cu2S Synthesized by Atomic Layer Deposition and Analyzed by X-ray Photoelectron Spectroscopy

Presented here are results of x-ray photoelectron spectroscopy (XPS) on multilayers of metal-sulfide binaries ZnS, SnS2, and Cu2S grown by atomic layer deposition (ALD) on Si substrates, and of Cu2ZnSnS4 (CZTS) formed upon 450 °C annealing of the parent multilayer ZnS/SnS2/Cu2S. Survey and detailed spectral analysis of the multilayer ZnS/SnS2/Cu2S are presented step-wise, as each layer was sequentially added by ALD. The set of data is finalized with spectra of the resulting alloy CZTS. XPS analyses indicate significant mixing between SnS2 and Cu2S, which favors CZTS formation within the ALD approach.

Laser-induced desorption of organic molecules from front- and back-irradiated metal foils

Laser‐Induced Acoustic Desorption (LIAD) from thin metal foils is a promising technique for gentle and efficient volatilization of intact organic molecules from surfaces of solid substrates. Using the Single Photon Ionization (SPI) method combined with time‐of‐flight mass‐spectrometry (TOF MS), desorbed flux in LIAD was examined and compared to that from direct laser desorption (LD). Molecules of various organic dyes were used in experiments. Translational velocities of the desorbed intact molecules did not depend on the desorbing laser intensity, which implies the presence of more sophisticated mechanism of energy transfer than the direct mechanical or thermal coupling between the laser pulse and the adsorbed molecules. The results of our experiments indicate that the LIAD phenomenon cannot be described in terms of a simple mechanical shake‐off nor the direct laser desorption. Rather, they suggest that multi‐step energy transfer processes are involved. Possible qualitative mechanism of LIAD that are base...

Characterization of surface modifications by white light interferometry: applications in ion sputtering, laser ablation, and tribology experiments.

In materials science and engineering it is often necessary to obtain quantitative measurements of surface topography with micrometer lateral resolution. From the measured surface, 3D topographic maps can be subsequently analyzed using a variety of software packages to extract the information that is needed. In this article we describe how white light interferometry, and optical profilometry (OP) in general, combined with generic surface analysis software, can be used for materials science and engineering tasks. In this article, a number of applications of white light interferometry for investigation of surface modifications in mass spectrometry, and wear phenomena in tribology and lubrication are demonstrated. We characterize the products of the interaction of semiconductors and metals with energetic ions (sputtering), and laser irradiation (ablation), as well as ex situ measurements of wear of tribological test specimens. Specifically, we will discuss: i. Aspects of traditional ion sputtering-based mass spectrometry such as sputtering rates/yields measurements on Si and Cu and subsequent time-to-depth conversion. ii. Results of quantitative characterization of the interaction of femtosecond laser irradiation with a semiconductor surface. These results are important for applications such as ablation mass spectrometry, where the quantities of evaporated material can be studied and controlled via pulse duration and energy per pulse. Thus, by determining the crater geometry one can define depth and lateral resolution versus experimental setup conditions. iii. Measurements of surface roughness parameters in two dimensions, and quantitative measurements of the surface wear that occur as a result of friction and wear tests. Some inherent drawbacks, possible artifacts, and uncertainty assessments of the white light interferometry approach will be discussed and explained.

Ion microscopy with resonant ionization mass spectrometry: time-of-flight depth profiling with improved isotopic precision.

There are four generally mutually exclusive requirements that plague many mass spectrometric measurements of trace constituents: (1) the small size (limited by the depth probed) of many interesting materials requires high useful yields to simply detect some trace elements, (2) the low concentrations of interesting elements require efficient discrimination from isobaric interferences, (3) it is often necessary to measure the depth distribution of elements with high surface and low bulk contributions, and (4) many applications require precise isotopic analysis. Resonant ionization mass spectrometry has made dramatic progress in addressing these difficulties over the past five years.

Field emission microscopy of ultra-nano-crystalline diamond films

Nitrogen-incorporated ultrananocrystalline diamond, (N)UNCD, is an unconventional field emitter that performs in planar thin film configuration and has turn-on fields on the order of 10 V/ m. To shed more light on fundamental field emission properties of (N)UNCD, we have designed and commissioned a field emission microscope (FEM). The microscope can directly image the field emission site distribution on a cathode surface by making use of anode screens in the standard parallel plate configuration with the lateral spatial resolution 1–10 m.

Vacuum effect on field emission I-V curves

In this paper, we report our first experimental findings that evidence the vacuum level in the test chamber can be responsible for variation in the field emission (Fowler-Nordheim) response of an electron source. This situation is exampled using a carbon nanotube sample measured in a parallel plate configuration.