Local density of states effects at the metal-molecule interfaces in a molecular device

Modeling Scanning Electrochemical Cell Microscopy (SECCM) in Twisted Bilayer Graphene

Twisted 2D-flat band materials host exotic quantum phenomena and novel moiré patterns, showing immense promise for advanced spintronic and quantum applications. Here, we evaluate the nanostructure-activity relationship in twisted bilayer graphene by modeling it under the scanning electrochemical cell microscopy setup to resolve its spatial moiré domains. We solve the steady state ion transport inside a 3D nanopipette to isolate the current response at AA and AB domains. Interfacial reaction rates are obtained from a modified Marcus-Hush-Chidsey theory combining input from a tight binding model that describes the electronic structure of bilayer graphene. High rates of redox exchange are observed at the AA domains, an effect that reduces with diminished flat bands or a larger cross-sectional area of the nanopipette. Using voltammograms, we identify an optimal voltage that maximizes the current difference between the domains. Our study lays down the framework to electrochemically capture prominent features of the band structure that arise from spatial domains and deformations in 2D flat-band materials.

Interfacial Stereoelectronic Effect Induced by Anchoring Orientation

Heterogeneous interfaces in most devices play a key role in the material performance. Exploring the atomic structure and electronic properties of metal-molecule interfaces is critical for various potential applications, such as surface sensing, molecular recognition, and molecular electronic devices. This study unveils a ubiquitous interfacial stereoelectronic effect in conjugated molecular junctions by combining first-principles simulation and scanning tunneling microscopy break junction technology. Single-molecule junctions with same-side interfacial anchoring (cis configuration) exhibit higher conductance than those with opposite-side interfacial anchoring (trans configuration). The cis and trans configurations can undergo reversible conversions, resulting in a conductance switching. The stability of these configurations can be adjusted by an electric field, achieving precise regulation of conductance states. Our findings provide important insights for designing high-quality materials and enhancing the device performance.

Twisto-Electrochemical Activity Volcanoes in Trilayer Graphene

In this work, we develop a twist-dependent electrochemical activity map, combining a low-energy continuum electronic structure model with modified Marcus-Hush-Chidsey kinetics in trilayer graphene. We identify a counterintuitive rate enhancement region spanning the magic angle curve and incommensurate twists in the system geometry. We find a broad activity peak with a ruthenium hexamine redox couple in regions corresponding to both magic angles and incommensurate angles, a result qualitatively distinct from the twisted bilayer case. Flat bands and incommensurability offer new avenues for reaction rate enhancements in electrochemical transformations.

Schottky barrier reduction on optoelectronic responses in heavy ion irradiated WSe2 memtransistors

Two-dimensional transition metal dichalcogenide-based memtransistors provide simulation, sensing, and storage capabilities for applications in a remotely operated aerospace environment. Swift heavy ion (SHI) irradiation technology is a common method to simulate the influences of radiation ions on electronic devices in space environments. Here, SHI irradiation technology under different conditions was utilized to produce complex defects in WSe2-based memtransistors. Low-resistance state to low-resistance state (LRS-LRS) switching behaviors under light illumination were achieved and photocurrent responses with different spike trains were observed in SHI-irradiated memtransistors, which facilitated the design of devices with enriched analog functions. Reduction of the Schottky barrier height due to the introduced defects at the metal/WSe2 interface was confirmed to be the major factor responsible for the observed behaviors. 1T phase and concentric circle-type vacancies were also created in the SHI-irradiated 2H-WSe2 channel besides the amorphous structure; these complex defects could seriously affect the transport properties of the devices. We believe that this work serves as a foundation for aerospace radiation applications of all-in-one devices. It also opens a new application field of heavy ion irradiation technology for the development of multiterminal memtransistor-based optoelectronic artificial synapses for neuromorphic computing.

Increased Surface Density of States at the Fermi Level for Electron Transport Across Single-Molecule Junctions

Fermi's golden rule, a remarkable concept for the transition probability involving continuous states, is applicable to the interfacial electron-transporting efficiency via correlation with the surface density of states (SDOS). Yet, this concept has not been reported to tailor single-molecule junctions where gold is an overwhelmingly popular electrode material due to its superior amenability in regenerating molecular junctions. At the Fermi level, however, the SDOS of gold is small due to its fully filled d-shell. To increase the electron-transport efficiency, herein, gold electrodes are modified by a monolayer of platinum or palladium that bears partially filled d-shells and exhibits significant SDOS at the Fermi energy. An increase by 2-30 fold is found for single-molecule conductance of α,ω-hexanes bridged via common headgroups. The improved junction conductance is attributed to the electrode self-energy which involves a stronger coupling with the molecule and a larger SDOS participated by d-electrons at the electrode-molecule interfaces.

Hydrogen Peroxide Oxidation Reaction on a 4-Mercaptopyridine Self-Assembled Monolayer on Au(111) Metallized by Platinum Nanoislands

A systematic investigation of the hydrogen peroxide oxidation reaction (HPOR) in phosphate buffer (pH = 7.3) on an Au(111) single crystal modified with a 4-mercaptopyridine self-assembled monolayer (SAM) has been conducted before and after metallization with Pt. While bare Au(111) shows considerable electrocatalytic activity towards the HPOR, the inhibition of the oxidation reaction after modification with the SAM implies that adsorbed 4-mercaptopyridine molecules do not catalyze the HPOR. However, SAM-modified Au(111) recovers catalytic activity for the HPOR already after a single metallization step fabricating Pt islands on-top. Hydrogen peroxide (HP) may then either react at the (non-metallic) Pt nanoislands or on reactivated Au sites, made accessible by structural changes of the SAM induced by the metallization. The shape of the voltammetric profiles for the HPOR on repeatedly metallized SAMs suggests that the contribution of Au to the total current density gradually diminishes with increasing Pt coverage while the contribution of the Pt islands increases. The electrochemical behavior is dominated by the Pt islands at a coverage of 0.5 ML obtained by three subsequent metallization steps.

Graphical abstract

Density Functional Theory Study of Pd Aggregation on a Pyridine-Terminated Self-Assembled Monolayer

By using density functional theory calculations, the initial steps towards Pd metal cluster formation on a pyridine-terminated self-assembled monolayer (SAM) consisting of 3-(4-(pyridine-4-yl)phenyl)propane-1-thiol on an Au(1 1 1) surface are investigated. Theoretical modelling allows the investigation of structural details of the SAM surface and the metal/SAM interface at the atomic level, which is essential for elucidating the nature of Pd-SAM and Pd-Pd interactions at the liquid/solid interface and gaining insight into the mechanism of metal nucleation in the initial stage of electrodeposition. The structural flexibility of SAM molecules was studied first and the most stable conformation was identified, planar molecules in a herringbone packing, as the model for Pd adsorption. Two binding sites are found for Pd atoms on the pyridine end group of the SAM. The strong interaction between Pd atoms and pyridines illustrates the importance of SAM functionalisation in the metal nucleation process. Consistent with an energetic driving force of approximately -0.3 eV per Pd atom towards Pd aggregation suggested by static calculations, a spontaneous Pd dimerisation is observed in ab initio molecular dynamic studies of the system. Nudged elastic band calculations suggest a potential route with a low energy barrier of 0.10 eV for the Pd atom diffusion and then dimerisation on top of the SAM layer.

Coordination controlled electrodeposition and patterning of layers of palladium/copper nanoparticles on top of a self-assembled monolayer

A scheme for the generation of bimetallic nanoparticles is presented which combines electrodeposition of one type of metal, coordinated to a self-assembled monolayer (SAM), with another metal deposited from the bulk electrolyte. In this way PdCu nanoparticles are generated by initial complexation of Pd²⁺ to a SAM of 3-(4-(pyridine-4-yl)phenyl)propane-1-thiol (PyP3) on Au/mica and subsequent reduction in an acidic aqueous CuSO₄ electrolyte. Cyclic voltammetry reveals that the onset of Cu deposition is triggered by Pd reduction. Scanning tunneling microscopy (STM) shows that layers of connected particles are formed with an average thickness of less than 3 nm and lateral dimensions of particles in the range of 2 to 5 nm. In X-ray photoelectron spectra a range of binding energies for the Pd 3d signal is observed whereas the Cu 2p signal appears at a single binding energy, even though chemically different Cu species are present: normal and more noble Cu. Up to three components are seen in the N 1s signal, one originating from protonated pyridine moieties, the others reflecting the SAM-metal interaction. It is suggested that the coordination controlled electrodeposition yields layers of particles composed of a Pd core and a Cu shell with a transition region of a PdCu alloy. Deposited on top of the PyP3 SAM, the PdCu particles exhibit weak adhesion which is exploited for patterning by selective removal of particles employing scanning probe techniques. The potential for patterning down to the sub-10 nm scale is demonstrated. Harnessing the deposition contrast between native and PdCu loaded PyP3 SAMs, structures thus created can be developed into patterned continuous layers.

Experimental and first-principles investigation of the adsorption and entrapping of guanine with SiO2 clusters of sol–gel silicate material for understanding DNA photodamage

A sol–gel silicate matrix containing entrapped guanine was prepared. The SiO₂ matrix provides UVA protection by reducing the light penetration to the entrapped guanine molecules.

Interface engineering to control magnetic field effects of organic-based devices by using a molecular self-assembled monolayer

Organic semiconductors hold immense promise for the development of a wide range of innovative devices with their excellent electronic and manufacturing characteristics. Of particular interest are nonmagnetic organic semiconductors that show unusual magnetic field effects (MFEs) at small subtesla field strength that can result in substantial changes in their optoelectronic and electronic properties. These unique phenomena provide a tremendous opportunity to significantly impact the functionality of organic-based devices and may enable disruptive electronic and spintronic technologies. Here, we present an approach to vary the MFEs on the electrical resistance of organic-based systems in a simple yet reliable fashion. We experimentally modify the interfacial characteristics by adding a self-assembled monolayer between the metal electrode and the organic semiconductor, thus enabling the tuning of competing MFE mechanisms coexisting in organic semiconductors. This approach offers a robust method for tuning the magnitude and sign of magnetoresistance in organic semiconductors without compromising the ease of processing.

X-ray photoemission spectroscopy investigation of the interaction between 4-mercaptopyridine and the anatase TiO2 surface

In polymer-metal oxide hybrid solar cells, an extremely careful engineering of the interface is required to ensure good device performances. Recently, very promising results have been obtained by functionalizing titanium dioxide (TiO2) by means of 4-mercaptopyridine (4-MPy) molecules, showing the beneficial effect of these molecules on the interface morphology. This study investigates the nature of the interaction of 4-MPy molecules with the TiO2 surface by means of X-ray photoemission spectroscopy. In order to mimic the device processing conditions, our analysis is carried out on molecules adsorbed from solution on a nanocrystalline surface. According to our analysis, 4-MPy molecules (C5H5NS) are likely bound with the oxide through the nitrogen atom. The bonding precedes either via a covalent interaction with Lewis surface sites, or via hydrogen mediation, possibly in the form of hydrogen bonds. Interestingly, in the latter case, we also observe strong changes in the spectroscopic features attributed to the thiol group.

Solution-processed soldering of carbon nanotubes for flexible electronics

We report a simple lithography-free, solution-based method of soldering of carbon nanotubes with Ohmic contacts, by taking specific examples of multi-walled carbon nanotubes (MWNTs). This is achieved by self-assembling a monolayer of soldering precursor, Pd(2+) anchored to 1,10 decanedithiol, onto which MWNTs could be aligned across the gap electrodes via solvent evaporation. The nanosoldering was realized by thermal/electrical activation or by both in sequence. Electrical activation and the following step of washing ensure selective retention of MWNTs spanning across the gap electrodes. The soldered joints were robust enough to sustain strain caused during the bending of flexible substrates as well as during ultrasonication. The estimated temperature generated at the MWNT-Au interface using an electro-thermal model is ∼150 °C, suggesting Joule heating as the primary mechanism of electrical activation. Further, the specific contact resistance is estimated from the transmission line model.

A periodic charge-dipole electrostatic model: parametrization for silver slabs

We present an extension of the charge-dipole model for the description of periodic systems. This periodic charge-dipole electrostatic model (PCDEM) allows one to describe the linear response of periodic structures in terms of charge- and dipole-type gaussian basis functions. The long-range electrostatic interaction is efficiently described by means of the continuous fast multipole method. As a first application, the PCDEM method is applied to describe the polarizability of silver slabs. We find that for a correct description of the polarizability of the slabs both charges and dipoles are required. However a continuum set of parametrizations, i.e., different values of the width of charge- and dipole-type gaussians, leads to an equivalent and accurate description of the slabs polarizability but a completely unphysical description of induced charge-density inside the slab. We introduced the integral squared density measure which allows one to obtain a unique parametrization which accurately describes both the polarizability and the induced density profile inside the slab. Finally the limits of the electrostatic approximations are also pointed out.

Surface Modification of a n-Si(111) Electrode through Aldehyde Grafting and Subsequent Metallization: Theory and Experiment

Motivated by our previous studies on metallic substrates, in the present work we addressed the functionalization and the subsequent metallization of a hydrogen-terminated n-Si(111) electrode. DFT provides atomistic insights on the grafting mechanism of 4-pyridinecarboxaldehyde (C6H5NO) what encouraged electrochemical investigations, i. e. cyclic voltammetry and in-situ STM, combined with XPS measurements which together provide evidence for a successful transfer of the so far obtained knowledge from metal single crystal to semiconductor surfaces.

Contrast in electron-transfer mediation between graphene oxide and reduced graphene oxide

The properties of graphene oxide (GO) and DNA-stabilised reduced graphene-oxide (rGO) sheets as electron-transfer mediators in partially blocked electrodes are evaluated employing electrochemical impedance spectroscopy. Evidences obtained from UV/Vis, Raman and FTIR spectroscopies, as well as atomic force microscopy, confirm that the reduction of exfoliated GO single sheets by hydrazine yields partially reduced graphene oxide featuring a high defect density. Two-dimensional assemblies of GO and rGO were formed through electrostatic adsorption at Au electrodes, sequentially modified with 11-mercaptoundecanoic acid (MUA) and poly-diallyldimethylammonium chloride (PDADMAC). The MUA:PDADMAC generates a strong blocking layer to the electron-transfer reaction involving the ferri/ferrocyanide redox couple. This blocking behaviour is not significantly affected upon adsorption of GO. However, adsorption of a sub-monolayer of rGO decreases the charge-transfer resistance by more than two orders of magnitude. Analysis of cyclic voltammograms and impedance spectra suggests that electron transfer in rGO assemblies is mediated by occupied states located just below the redox Fermi energy of the probe. These findings are discussed in the context of on-going controversies regarding the electrochemical reactivity of sp(2)-carbon basal planes.

Multilayer graphene-coated atomic force microscopy tips for molecular junctions

Multilayer graphene tips are developed for conducting probe atomic force microscopy for the formation of molecular junctions. Molecular junctions using graphene tips show very small tip-to-tip variance, excellent operational stability, good endurance, and long shelf-life. These properties, together with high yield and the simple processing involved, suggest that commercial mass-production of graphene tips is viable for molecular electronic applications.

Complex surface chemistry of 4-mercaptopyridine self-assembled monolayers on Au(111)

The adsorption of 4-mercaptopyridine on Au(111) from aqueous or ethanolic solutions is studied by different surface characterization techniques and density functional theory calculations (DFT) including van der Waals interactions. X-ray photoelectron spectroscopy and electrochemical data indicate that self-assembly from 4-mercaptopyridine-containing aqueous 0.1 M NaOH solutions for short immersion times (few minutes) results in a 4-mercaptopyridine (PyS) self-assembled monolayer (SAM) with surface coverage 0.2. Scanning tunneling microscopy images show an island-covered Au surface. The increase in the immersion time from minutes to hours results in a complete SAM degradation yielding adsorbed sulfur and a heavily pitted Au surface. Adsorbed sulfur is also the main product when the self-assembly process is made in ethanolic solutions irrespective of the immersion time. We demonstrate for the first time that a surface reaction is involved in PyS SAM decomposition in ethanol, a surface process not favored in water. DFT calculations suggest that the surface reaction takes place via disulfide formation driven by the higher stability of the S-Au(111) system. Other reactions that contribute to sulfidization are also detected and discussed.

Influence of water on the properties of an Au/Mpy/Pd metal/molecule/metal junction

The geometric and electronic structure of the metal-molecule interface in metal/molecule/metal junctions is of great interest since it affects the functionality of such units in possible nanoelectronic devices. We have investigated the interaction between water and a palladium monolayer of a Au(111)/4-mercaptopyridine/Pd junction by means of DFT calculations. A relatively strong bond between water and the palladium monolayer of the Au/Mpy/Pd complex is observed via a one-fold bond between the oxygen atom of the water molecule and a Pd atom. An isolated H(2)O molecule adsorbs preferentially in a flat-lying geometry on top of a palladium atom that is at the same time also bound to the nitrogen atom of a Mpy molecule of the underlying self-assembled monolayer. The electronic structure of these Pd atoms is considerably modified which is reflected in a reduced local density of states at the Fermi energy. At higher coverages, water can be arranged in a hexagonal ice-like bilayer structure in analogy to water on bulk metal surfaces, but with a much stronger binding which is dominated by O-Pd bonds.

Interaction of alkanethiols with nanoporous cluster-assembled Au films

This article presents a study of the interaction of octadecanethiol molecules (C(18)) with nanoporous cluster-assembled gold films under a liquid environment based on a combined spectroscopic ellipsometry and X-ray photoelectron spectroscopy investigation. By comparing the optical response, following the deposition of C(18), of cluster-assembled films with varying degrees of porosity with that of flat surfaces and by resolving the corresponding features of the molecule-Au bond, we have been able to define the conditions that either favor molecular in-depth diffusion into the pores or promote the formation of a molecular self-assembled monolayer (SAM) restricted to the film surface. In the presence of abundant open pores, C(18) molecules strongly diffuse within the film interior and bind to the pore walls, whereas in the presence of porous films with less abundant open pores we have observed that the molecules tend to remain confined to the surface region, adopting a SAM-like configuration.

Electrodeposition of palladium onto a pyridine-terminated self-assembled monolayer

The electrodeposition of Pd onto self-assembled monolayers (SAMs) of 3-(4-pyridine-4-ylphenyl)propane-1-thiol on Au(111) has been investigated by scanning tunneling microscopy. Two schemes are compared: One involves an established two-step procedure where Pd(2+) ions are first coordinated to the pyridine moieties and subsequently reduced in Pd(2+)-free electrolyte. The second deposition routine involves electroreduction in an electrolyte containing low concentration of Pd(2+) which merges both steps and, thus, significantly simplifies metal deposition onto pyridine-terminated SAMs. Both strategies produce identical Pd nanoparticles (NPs) which exhibit a narrow size distribution and an apparent STM height of ∼2.4 nm. The observation of a Coulomb blockade and easy displacement of the nanoparticles in STM experiments evidence deposition on top of the SAM. The NPs are concluded to be essentially spherical. Growth of the NPs is found to be self-limiting since repeating the complexation-deposition cycle increases the density of the nanoparticles rather than their size but only close to full coverage. At high concentration of the Pd(2+) electrolyte, deposition on top of the SAM is impeded by a competitive mushroom-type growth.

Metallization of organic surfaces: Pd on thiazole

Results from electrochemical studies, in situ STM, and ex situ angle-resolved XPS on self-assembled monolayers (SAMs) of thiazole on Au(111) are reported for the first time. Although STM seems to indicate a low density of molecules organized in small ordered domains, a quantitative chemical analysis of the sample surface by XPS clearly points toward the formation of a densely packed molecular layer. The stability of the thiazole SAM against reductive desorption is found to be very comparable with that for thiol-SAMs on gold. This results from the formation of Au-S bonds between the molecules and their support as evidenced by XPS, thereby rebuting speculations that the ring nitrogen is responsible for the attachment of such molecules to gold surfaces. Consequently, the N-atoms terminating the molecular layer are available as active sites for the complexation with Pd ions thereby allowing the deposition of Pd islands with monatomic height on top of the thiazole SAM. The importance of such studies for metal-molecule interconnections is briefly addressed.

Towards an accurate description of the electronic properties of the biphenylthiol/gold interface: the role of exact exchange

We investigate the role of the exact exchange in describing the biphenylthiol/gold interface. The study is performed by simulating the electronic properties of mercaptobiphenylthiol and aminobiphenylthiol molecules adsorbed on a Au(23) cluster, using local, semilocal and hybrid functionals and an effective exact exchange method, namely, the localized Hartree-Fock (LHF). We find that the local/semilocal functionals strongly underestimate the charge transfer and the bond dipole at the interface due to the self-interaction-error (SIE), which alters the correct level alignment. On the other hand the LHF method is SIE free and predicts a larger charge transfer and bond dipole. We also found that LHF results can be reproduced using hybrid functionals and that conventional local/semilocal correlation functionals are unable to improve over the exchange-only description.

Progress with molecular electronic junctions: meeting experimental challenges in design and fabrication

Molecular electronics seeks to incorporate molecular components as functional elements in electronic devices. There are numerous strategies reported to date for the fabrication, design, and characterization of such devices, but a broadly accepted example showing structure-dependent conductance behavior has not yet emerged. This progress report focuses on experimental methods for making both single-molecule and ensemble molecular junctions, and highlights key results from these efforts. Based on some general objectives of the field, particular experiments are presented to show progress in several important areas, and also to define those areas that still need attention. Some of the variable behavior of ostensibly similar junctions reported in the literature is attributable to differences in the way the junctions are fabricated. These differences are due, in part, to the multitude of methods for supporting the molecular layer on the substrate, including methods that utilize physical adsorption and covalent bonds, and to the numerous strategies for making top contacts. After discussing recent experimental progress in molecular electronics, an assessment of the current state of the field is presented, along with a proposed road map that can be used to assess progress in the future.

Metallization of Organic Monolayers: Electroless Deposition of Cu onto Cross-Linked Aromatic Self-Assembled Monolayers

We demonstrate the metallization of amino-terminated, cross-linked biphenylthiol self-assembled monolayers (SAMs) via Pd catalysed electroless deposition (ELD) of Cu. Angle resolved X-ray photoelectron spectroscopy and atomic force microscopy were used for characterization. Lateral cross-linking and generation of terminal amino groups are induced by irradiation with low energy electrons. The cross-linked SAM suppresses the ELD of Cu onto the Au substrate. By the immobilization of Pd atoms to the terminal amino groups, catalytic sites are created in cross-linked areas. These sites then facilitate the electroless deposition of Cu on top of the SAM.

Bis(terpyridine)-based surface template structures on graphite: a force field and DFT study

Host-guest networks formed by ordered organic layers are promising candidates for applications in molecular storage and quantum computing. We have studied 2-dimensionally ordered surface template structures of bis(terpyridine)-derived molecules (BTPs) on graphite using force field and DFT methods and compared the results to recent experimental observations. In order to determine the force field best suited for surface calculations, bond lengths and angles, torsional potentials, adsorption and stacking energies of smaller aromatic molecules were calculated with different force fields (Compass, UFF, Dreiding and CVFF). Density functional perturbation theory calculations were used to study the intermolecular interactions between 3,3'-BTP molecules. Structural properties, adsorption energies and rotational barriers of the 3,3'-BTP surface structure and its host-guest systems with phthalocyanine (PcH(2)) or excess 3,3'-BTP as guest molecules have been addressed. In addition, STM images of oligopyridine and phthalocyanine molecules were simulated based on periodic and local density functional theory calculations.

Self-assembly of a pyridine-terminated thiol monolayer on Au(111)

Self-assembled monolayers (SAMs) of 3-(4-pyridine-4-yl-phenyl)-propane-1-thiol (PyP3) on Au(111)/mica have been studied by scanning tunneling microscopy (STM), polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS), high-resolution X-ray photoemission spectroscopy (HRXPS), and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The quality of the SAM is found to be strongly dependent on the solvent. Substantial gold corrosion is observed if pure ethanol is used. In contrast, highly ordered and densely packed SAMs are formed from acetonitrile or a KOH/ethanol mixture. The structure is described by a 2 radical3 x radical3 unit cell with the aromatic moiety oriented nearly perpendicular to the surface. The PyP3 films form with the pyridine moiety deprotonated. Variation of pH allows reversible protonation without measurable damage of the SAM.

Selective electroless metallization of patterned polymeric films for lithography applications

The fabrication of electrical interconnects to provide power for and communication with computers as their component complementary metal oxide semiconductor (CMOS) devices continue to shrink in size presents significant materials and processing compatibility challenges. We describe here our efforts to address these challenges using top-surface imaging and hybrid photoresist/self-assembled monolayer patterning approaches, in conjunction with selective electroless metal deposition, to develop processes capable of fabricating appropriate submicron and nanoscale metal features useful as electrical interconnects, as well as plasma-etch-resistant masks and metal diffusion barriers. Our efforts focus on the development of cost-effective methods compatible with a manufacturing environment that satisfy materials and process constraints associated with CMOS device production. We demonstrate the fabrication of approximately 50-nm-width features in metal with high fidelity and sufficient control of edge acuity to satisfy current industry design rules using our processes and discuss the challenges and opportunities for fabrication of analogous sub-10-nm metal features.