Ivan Vlassiouk's research while affiliated with Oak Ridge National Laboratory and other places
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Publications (124)
Reduced graphene oxide (rGO) has attracted significant attention as an active electrode material for sensors and flexible energy devices due to its high electric conductivity and large surface area. rGO is usually obtained from graphene oxide(GO) through a thermal, chemical, photochemical, and electrochemical reduction process. Compared to the othe...
Selective proton permeation through atomically thin graphene while maintaining impermeability to even small gas atoms i.e. He or hydrated ions, presents potential for advancing proton exchange membranes (PEMs) across a range of energy conversion and storage applications. The incorporation of graphene into state-of-the-art proton conducting polymers...
The two main technical limitations of direct methanol fuel cells (DMFCs) are the slow kinetic reactions of the methanol oxidation reaction (MOR) in the anode and the crossing over of unreacted methanol through the proton exchange membrane (PEM). It is common practice to use Nafion membranes as PEMs, which have high ion exchange capacity. However, N...
Graphene oxide (GO) membranes, which form from the lamination of GO sheets, attract much attention due to their unique nanochannels. There is much interest in controlling the nanochannel structures and improving the aqueous stability of GO membranes so they can be effectively used in separation and filtration applications. This study employed a sim...
It is widely accepted that solid‐state membranes are indispensable media for the graphene process, particularly transfer procedures. But these membranes inevitably bring contaminations and residues to the transferred graphene and consequently compromise the material quality. This study reports a newly observed free‐standing graphene‐water membrane...
We synthesized a combinatorial library of CuxNi1−x alloy thin films via co-sputtering from Cu and Ni targets to catalyze graphene chemical vapor deposition. The alloy morphology, composition, and microstructure were characterized via scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), and X-ray diffraction (XRD), respect...
A graphene oxide (GO) membrane can be used in structural dielectric capacitors and planar micro-supercapacitors as a dielectric separator material due to its excellent through-plane and in-plane dielectric properties. The ability to tailor the dielectric properties of the GO membrane is crucial for dielectric applications. We believe this to be the...
Selective proton (H+) permeation through the atomically thin lattice of graphene and other 2D materials offers new opportunities for energy conversion/storage and novel separations. Practical applications necessitate scalable synthesis via...
Chemical vapor deposition has emerged as a promising approach for high-quality graphene synthesis. Graphene quality, including the defect density, the size of monocrystal domains, and the number of layers, depend on the growth conditions. The main experimental parameters include temperature, metal catalyst composition, growth atmosphere, and gaseou...
Being a 2D insulator with alternating sp ² hybridized B and N atoms in a honeycomb structure, Hexagonal Boron Nitride(hBN) not only have uniqure properties like high transparency, large thermal conductivity, high mechanical strength and superior chemical inertness by itself, but also be able to promote other 2D materials’ performance when serving a...
In donor acceptor dyads undergoing photoinduced electron transfer (PET), a direction or pathway for electron movement is usually dictated by the redox properties and the separation distance between the donor and acceptor subunits, while the effect of symmetry is less recognized. We have designed and synthesized two isomeric donor-acceptor assemblie...
The electrical double layer (EDL) governs the operation of multiple electrochemical devices, determines reaction potentials, and conditions ion transport through cellular membranes in living organisms. The few existing methods of EDL probing have low spatial resolution, usually only providing spatially-averaged information. On the other hand, tradi...
Proton exchange membranes are in the heart of various technologies utilizing electrochemical storage of intermittent energy sources and powering electrical devices. Current state of the art membranes are based on perfluorosulfonic acid introduced more than a half century ago. Low specificity to protons accompanied by permeance by other species is o...
Inspired by recent report on possible proton conductance through graphene we have investigated the behavior of pristine graphene and defect engineered graphene membranes for ionic conductance and selectivity with the goal of evaluating a possibility of its application as a proton selective membrane. The averaged conductance for pristine CVD (chemic...
Tip-enhanced Raman spectroscopy (TERS) has been established as one the most efficient analytical techniques for probing vibrational states with nanoscale resolution. While TERS may be a source of unique information about chemical structure and interactions, it has a limited use for materials with rough or sticky surfaces. Development of the TERS ap...
Large‐area single layers of graphene are synthesized using chemical vapor deposition techniques and are assembled onto steel substrates that are finished with a thin layer of electrodeposited zinc–nickel (ZnNi). Atomic force microscopy combined with Raman spectroscopy is used to determine the number of the assembled graphene layers and to character...
Recent developments in environmental and liquid cells equipped with electron transparent graphene windows have enabled traditional surface science spectromicroscopy tools, such as X-ray photoelectron spectroscopy (XPS), photoemission electron microscopy (PEEM), and scanning electron microscopy (SEM) to be applied to study solid-liquid and liquid-ga...
Graphene reinforced materials and related methods of manufacture are provided. The graphene reinforced materials include graphene sheet or scroll, graphene-polymer sheet or scroll, and graphene-carbon sheet or scroll, each having material properties that are attractive across a broad range of applications and industries. The graphene reinforced mat...
We explore the potential of the Helium Ion Microscope (HIM) as a tool for direct-write patterning of graphene and describe the underlying processes of graphene milling with image data processing. Controlled helium ion irradiation of suspended graphene conducted while monitoring the mill in-situ revealed the localized formation of nanopores, their g...
There is a demand for the manufacture of two-dimensional (2D) materials with high-quality single crystals of large size. Usually, epitaxial growth is considered the method of choice1in preparing single-crystalline thin films, but it requires single-crystal substrates for deposition. Here we present a different approach and report the synthesis of s...
Graphene, with unique mechanical and electrical properties, offers diverse application opportunities from beyond Moore's nano-electronics to water filtration. However, accomplishing these relies on cleaning and processing large areas of supported and suspended graphene sheets. Here, we demonstrate the use of an Ar cluster ion beam as a versatile to...
Studies of the electrified solid-liquid interfaces are crucial for the understanding of the biological and electrochemical systems. Until recently, the use of photoemission electron microscopy (PEEM) for such purposes has been hampered by the incompatibility of the liquid samples with ultra-high vacuum environment of the electron optics and detecto...
Chemical vapour deposition (CVD) has been established as the most effective way to grow large area 2D materials. Direct study of the etching process can reveal subtleties of this competing with the growth reaction and thus provide the necessary details of the overall growth mechanism. Here we investigate hydrogen induced etching of hBN and graphene...
An improved industrial manufacturability has been achieved for a hybrid water-treatment membrane that exhibits high water permeance, prolonged high salt and dye rejection under cross-flow conditions and better resistance to chlorine treatment.
Multi-Modal Processing of Graphene Towards Precisely Controlled Fabrication of a Nanoelectronic Device Using the Helium Ion Microscope and the TOF SIMS - Volume 23 Issue S1 - Songkil Kim, Anton V. Ievlev, Ivan V. Vlassiouk, Matthew J. Burch, Xiahan Sang, Chance Brown, Raymond R. Unocic, Alex Belianinov, Stephen Jesse, Olga S. Ovchinnikova
We investigated the effect of out-of-plane crumpling on the mechanical response of graphene membranes. In our experiments, stress was applied to graphene membranes using pressurized gas while the strain state was monitored through two complementary techniques: interferometric profilometry and Raman spectroscopy. By comparing the data obtained throu...
Polymer residue plays an important role in the performance of 2D heterostructured materials. Herein, we study the effect of polymer residual impurities on the electrical properties of graphene-boron nitride planar heterostructures. Large-area graphene (Gr) and hexagonal boron nitride (h-BN) monolayers were synthesized using chemical vapor depositio...
Atomic-scale thickness, molecular impermeability, low atomic number, and mechanical strength make graphene an ideal electron-transparent membrane for material characterization in liquids and gases with scanning electron microscopy and spectroscopy. Here, we present a novel sample platform made of an array of thousands of identical isolated graphene...
In this paper, a nanoscale dielectric capacitor was fabricated through wet transfer of CVD growth hexagonal boron nitride hBN as dielectric materials between monolayer graphene electrodes. The specific capacitance, power, and energy the capacitor with different hBN layer number were evaluated through cyclic voltammetry test. Different to traditiona...
Ionic transport at the nanoscale features phenomena that are not observed in larger systems. Non-linear current-voltage curves characteristics of ionic diodes as well as ion selectivity are examples of effects observed at the nanoscale. Many of men-made nanopore systems are inspired by biological channels in a cell membrane, thus measurements are o...
Biomimetic nanopores with rectifying properties are relevant components of ionic switches, ionic circuits, and biological sensors. Rectification indicates that currents for voltages of one polarity are higher than currents for voltages of the opposite polarity. Ion current rectification requires the presence of surface charges on the pore walls, ac...
Despite the frequent use of noble gas ion irradiation of graphene, the atomistic scale details, including the effects of dose, energy, and ion bombardment species on defect formation, and the associated dynamic processes involved in the irradiations and subsequent relaxation, have not yet been thoroughly studied. Here, we simulated the irradiation...
Conically shaped pores such as glass pipettes as well as asymmetric pores in polymers became an important analytics tool used for the detection of molecules, viruses, and particles. Electrokinetic or pressure driven passage of single particles through a single pore causes a transient change of the transmembrane current, called a resistive-pulse, wh...
A simple sensor for viral particles based on ionic conductivity through anodized alumina membranes was demonstrated using MS2 bacteriophage as an example. A facile two-point measuring scheme is geared toward realization using a computer’s sound card input/output capabilities suitable for a fast and inexpensive point of care testing. The lowest dete...
Passage time through single micropores is an important parameter used to quantify the surface charge and zeta potential of particles. In the resistive-pulse technique, the measured time of pressure or electric field induced translocation is assumed to be direction independent. This assumption is supported by the low velocities of the particles and...
Achieving the ultimate limits of lithographic resolution and material performance necessitates engineering of matter with atomic, molecular, and mesoscale fidelity. With the advent of scanning helium ion microscopy, maskless He(+) and Ne(+) beam lithography of 2D materials, such as graphene-based nanoelectronics, is coming to the forefront as a too...
Dipole interactions play a significant role in biological systems, influencing key functions such as protein folding and selective transport of ions through channels, among many others. Possible importance of the presence of dipoles in systems of synthetic nanopores has not yet been explored. Here, we report experiments and modeling of ionic curren...
Pores with corrugated and charged walls have recently been introduced as a new detecting platform in the resistive-pulse technique, offering high throughput and the possibility to simultaneously characterize the objects by a set of physical properties. It has also been reported that when voltage is applied across such pores, electroosmotic flow of...
Ion current rectification is one of the most exciting transport properties observed with both conically shaped nanopores as well as pores containing surface charge patterns. Ion current rectification can also be achieved by voltage-controlled electric potential of the pore walls, but these systems require building a multi-terminal set-up. The devic...
With resistive pulse technology, three types of particles with similar size but different surface charge densities have been investigated in track-etched polyethylene terephthalate (PET) single micropores. We have shown that pores with axially undulating diameter constitute a sensitive tool for spherical particles’ detection and sizing. Shape of re...
Monolayer hexagonal boron nitride (hBN) attracts significant attention due to the potential to be used as a complementary two-dimensional dielectric in fabrication of functional 2D heterostructures. Here we investigate the growth stages of the hBN single crystals and show that hBN crystals change their shape from triangular to truncated triangular...
Free-standing graphene is inherently crumpled in the out-of-plane direction
due to dynamic flexural phonons and static wrinkling. We explore the
consequences of this crumpling on the effective mechanical constants of
graphene. We develop a sensitive experimental approach to probe stretching of
graphene membranes under low applied stress at cryogeni...
Supplementary Figures 1-7 and Supplementary References
Nanopores have become a model system to understand transport properties at the nanoscale. We report experiments and modeling of ionic current in aprotic solvents with different dipole moments through conically shaped nanopores in a polycarbonate film and through glass nanopipettes. We focus on solutions of the salt LiClO4, which is of great importa...
Two-dimensional (2D) van der Waals (vdW) heterostructures are a family of artificially-structured materials that promise tunable optoelectronic properties for devices with enhanced functionalities. Compared to stamping, direct epitaxy of vdW heterostructures is ideal for clean interlayer interfaces and scalable device fabrication. Here, we explore...
Single micropores in resistive-pulse technique were used to understand a complex dependence of particle mobility on its surface charge density. We show that the mobility of highly charged carboxylated particles decreases with the increase of the solution pH due to an interplay of three effects: (i) ion condensation, (ii) formation of an asymmetric...
The remarkable mechanical and electronic properties of graphene make it an ideal candidate for next generation nanoelectronics. With the recent development of commercial-level single-crystal graphene layers, the potential for manufacturing household graphene-based devices has improved, but significant challenges still remain with regards to pattern...
Graphene presents an ideal candidate for lightweight, high strength composite materials given its superior mechanical properties (specific strength of 130GPa and stiffness of 1 TPa). To date, easily scalable graphene-like materials in a form of separated flakes (exfoliated graphene, graphene oxide and reduced graphene oxide) have been investigated...
By creating nanoscale pores in a layer of graphene, it could be used as an effective separation membrane due to its chemical and mechanical stability, its flexibility and, most importantly, its one-atom thickness. Theoretical studies have indicated that the performance of such membranes should be superior to state-of-the-art polymer-based filtratio...
Single pores in resistive-pulse technique have been successfully used for the detection of cells, viruses, particles, and even molecules such as DNA and proteins. We have investigated application of pores with undulating opening diameter for the detection of particles and characterization of their physical and mechanical properties including size,...
Proton transfer across single layer graphene is associated with large
computed energy barriers and is therefore thought to be unfavorable at room
temperature. Experiments, however, have not yet been performed to test this
prediction. Here, we subject single layer graphene on fused silica to cycles of
high and low pH and show that protons transfer r...
This paper reports images of reproducible nanopatterns on hexagonal graphene flakes, produced by modulating the input power of a Near-Field Scanning Microwave Microscope, used at the same time for the characterization of the samples. We have studied the impact of different time exposures to the microwave field, and of different power levels. A poss...
We directly measure the nanometer-scale temperature rise at wrinkles and grain boundaries (GBs) in functioning graphene devices by scanning Joule expansion microscopy with similar to 50 nm spatial and similar to 0.2K temperature resolution. We observe a small temperature increase at select wrinkles and a large (similar to 100 K) temperature increas...
Pores with undulating opening diameter emerged as an analytics tool that enhances the speed of resistive-pulse experiments, with a potential to simultaneously characterize size and mechanical properties of translocating objects. Here, we study in detail the characteristics of resistive-pulses of polystyrene particles in pores with different aspect...
Nano-immunoassay utilizing surface-enhanced Raman scattering (SERS) effect is a promising analytical technique for early detection of cancer. In its current standing the assay is capable of discriminating samples of healthy individuals from samples of pancreatic cancer patients. Further improvements in sensitivity and reproducibility will extend pr...
The adsorption of 1-hexanol from cyclohexane-d(12) at single-layer graphene/alpha-Al2O3 interfaces was probed at mole percent values as low as 0.05 in the C H stretching region using vibrational sum frequency generation (SFG). The SFG spectra are indiscernible from those obtained in the absence of graphene, and from those obtained in the presence o...
Photoelectron spectroscopy (PES) and microscopy are highly demanded for
exploring morphologically complex solid-gas and solid-liquid interfaces under
realistic conditions, but the very small electron mean free path inside the
dense media imposes serious experimental challenges. Currently, near ambient
pressure PES is conducted using sophisticated a...
Rectifying nanopores feature ion currents that are higher for voltages of one polarity compared to the currents recorded for corresponding voltages of the opposite polarity. Rectification of nanopores has been found to depend on the pore opening diameter and distribution of surface charges on the pore walls as well as pore geometry. Very little is...
Copper foil is the most commonly used substrate for chemical vapor deposition (CVD) growth of graphene, despite the impact of its surface roughness and polycrystalline structure on the resulting graphene. Here we present a method of preparing thick, ultra-flat copper substrates for growing graphene by CVD. We demonstrate the growth of graphene on t...
Kelvin probe force microscopy (KPFM) is a powerful technique for the determination of the contact potential difference (CPD) between an atomic force microscope tip and a sample under ambient and vacuum conditions. However, for many energy storage and conversion systems, including graphene-based electrochemical capacitors, understanding electrochemi...
We report a carbon-based, three-dimensional nanofluidic transport membrane that enables gated, or on/off, control of the transport of organic molecular species and metal ions using an applied electrical potential. In the absence of an applied potential, both cationic and anionic molecules freely diffuse across the membrane via a concentration gradi...
This work reports thermodynamic and electrostatic parameters for fused silica/water interfaces containing cm2-sized graphene ranging from a single layer of pristine graphene to defected graphene. Second harmonic generation (SHG) measurements carried out at pH 7 indicate that the surface charge density of the fused silica/water interface containing...
We study the effect of electrolyte concentration on the shape of ion current pulses in resistive-pulse sensing. We show that electrokinetic passage of several hundred nanometers in diameter charged polystyrene particles through a micropore leads to formation of current increase when the particles exit the pore. The particle entrance, as reported be...
Studies of DNA translocation through graphene nanopores have revealed their potential for DNA sequencing. Here we report a study of protein translocation through chemically modified graphene nanopores. A transmission electron microscope (TEM) was used to cut nanopores with diameters between 5 and 20 nm in multilayer graphene prepared by chemical va...
Conventional Kelvin probe force microscopy (KPFM) relies on closed loop (CL) bias feedback for the determination of surface potential (SP). However, SP measured by CL-KPFM has been shown to be strongly influenced by the choice of measurement parameters due to non-electrostatic contributions to the input signal of the bias feedback loop. This often...
In this paper we discuss the effect of background pressure and synthesis temperature on the graphene crystal sizes in chemical vapor deposition (CVD) on copper catalyst. For the first time, we quantitatively demonstrate a fundamental role of the background pressure and provide the activation energy for graphene nucleation in atmospheric pressure CV...
All large-scale graphene films contain extended topological defects dividing graphene into domains or grains. Here, we spatially map electronic transport near specific domain and grain boundaries in both epitaxial graphene grown on SiC and CVD graphene on Cu subsequently transferred to a SiO2 substrate, with one-to-one correspondence to boundary st...
Significant efforts are being invested in investigation of graphene, as well as its nanopatterning and shaping, owing to its promising properties. Here we present a study of hexagonal graphene flakes, deposited on a copper foil by chemical vapor deposition. In particular we have exploited a Near-Field Scanning Microwave Microscope, and investigated...
In this article, we report detection of deformable, hydrogel particles by the resistive-pulse technique using single pores in a polymer film. The hydrogels pass through the pores by electroosmosis and cause formation of a characteristic shape of resistive pulses indicating the particles underwent dehydration and deformation. These effects were expl...
The reflectivity of low energy electrons from graphene on copper substrates
is studied both experimentally and theoretically. Well-known oscillations in
the reflectivity of electrons with energies 0 - 8 eV above the vacuum level are
observed in the experiment. These oscillations are reproduced in theory, based
on a first-principles density function...
The epitaxial growth and preferred molecular orientation of copper phthalocyanine (CuPc) molecules on graphene has been systematically investigated and compared with growth on Si substrates, demonstrating the role of surface-mediated interactions in determining molecular orientation. X-ray scattering and diffraction, scanning tunneling microscopy,...
We have developed a self-consistent description of low-energy electron
reflectivity spectra, yielding results that compare well with
experimental data for graphene on SiC and on Cu substrates (obtained by
our group as well as by other groups [1]). Our approach utilizes
wavefunctions for a thin multilayer graphene slab, computed with a
first-princip...