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Effects of atomic defects on electronic properties, mechanical stability, and elemental diffusivity in CuS (or covellite) were investigated by first-principles calculations. The metallic CuS shows higher structural and mechanical stabilities compared to CuxS phases. Strong covalent bonds in pristine CuS restrict the self-diffusion of Cu and S atoms; however, different band orientations in presence of atomic vacancies result in a high degree of self-diffusion. Specially, sulfur vacancies play a prominent role in increasing the diffusion of both Cu and S. Calculated self-diffusion coefficients between 100 °C and 150 °C are of the order of 10−6 cm2/s, comparable to experiments.

Advances in self-terminating etching processes have brought dissolvable supports to selective laser-melted stainless-steel alloys. Preliminary data showed that the amount of support material removed could be larger than the amount of material removed from the bulk material. This article details a small study aimed at understanding this phenomenon. First, the material removed and roughness as a function of applied bias is studied. From this, two different potentials were selected, 400 mVSHE, which removes 120 µm through intergranular corrosion, and 550 mVSHE, which removes material 39 µm through uniform corrosion. Next, a simulated set of support structures with wall thicknesses varying from 82 µm to 544 µm was etched under these two different potentials to report the range of thicknesses that can be reasonably removed.

This manuscript expands the existing framework for single-material laser powder bed fusion printed dissolvable supports to Inconel 718 (IN718). Prior work with stainless steel leveraged a sensitization heat treatment using sodium hexacyanoferrate to precipitate chromium carbides over the top 100 μm to 200 μm of material, decreasing the corrosion resistance within this top layer relative to the bulk material. The component is then etched at an anodic potential with a high selectivity toward the “sensitized” surface over the base component material. This creates an etching process that self-terminates once the sensitized layer is removed. Since supports are typically less than 200 μm thick, they are completely sensitized and dissolved. Additionally, the surface roughness of the component is often improved once the sensitized region is removed. In this work, two different sensitization heat schedules were investigated: 750 °C for 24 h to understand the impact of preferential chromium carbide precipitation and 1050 °C for 8 h to understand the impact of primary carbide precipitations. At 1050 °C, the formation of a protective oxide scale inhibits material removal in an electrolyte of 0.48 M HNO3. At 750 °C, 70 μm of material is removed after quenching to avoid the precipitation of corrosion resistant oxides. This manuscript investigates the effect of targeting different carbide precipitation regimes and oxides to produce an ideal microstructure for dissolvable supports post-sensitization. To demonstrate the utility of the process, the supports from a mock IN718 turbine blade were removed using this process.

Ultra near-field electrohydrodynamic (UNF-EHD) jetting of highly conductive self-reducing silver inks is investigated and compared to a theoretical cone-jet breakup model. While models connecting spray angle to fluid properties exist for large substrate-nozzle gap and inks with high ionic conductivity, little is known about the validity of these models when operating under UNF conditions. Using a pulsed cone-jet approach, data on the effects of nozzle height, applied voltage, and waveform (pulse length, pulse frequency, number of pulses/bursts, and delay between bursts) on spot size were collected showing high conductivity inks have a feature resolution very dependent on substrate-nozzle gap.

Many emerging photovoltaic technologies, such as silicon heterojunction (SHJ) cells and perovskites, are temperature sensitive and are not compatible with the high sintering temperatures required for commercial screen-printed metallization pastes. Newer, low-temperature reactive silver inks exhibit good electrical conductivity and are compatible with temperature-sensitive substrates. However, preliminary investigations showed that the adhesion and reliability of these metallizations could vary dramatically with ink composition. This work evaluates the adhesion performance of printed reactive inks on indium tin oxide-coated SHJ cells to show that puckering phenomena originating from the porous nature of the printed reactive inks are responsible for lowering the as-printed adhesion strength. Adhesion performance was qualitatively determined using 180° peel test followed by optical imaging to quantify the amount of adhesive failure. Post-print scanning electron microscopy was used to observe the surface morphology. Diluting the reactive ink to reduce silver ion concentration decreased the observed puckering phenomenon and improved adhesion performance. This new understanding enables a more systematic design of reactive inks for novel photovoltaic applications.

Functionally gradient materials (FGM) have many important applications due to their ability to possess vastly different material properties across the gradient. Recent work on dissolvable supports in stainless steel components fabricated using directed energy deposition (DED) show the utility of exploiting differences in the corrosion suseptibility in FGM metals. In order to better control the feature resolution of DED dissolvable supports, it is first necessary to understand how dilution and mixing within the gradient impact the local corrosion susceptibility and etch rates. In this work, FGMs with varying numbers of tracks and layers were fabricated onto a 304 stainless steel build plate; first one to three layers of 91 carbon steel followed by one to ten layers of 431 stainless steel. Metallography, potentiodynamic polarization plots, energy dispersive x-ray spectroscopy, and 3D contact profilometry data were collected to show that mixing within the gradient is very inhomogeneous. Incomplete mixing is observed throughout individual tracks along with widely varying composition and material properties from track-to-track, even within a single track. This paper demonstrates that the impact of incomplete mixing and composition gradients within a layer must be considered for DED-fabricated FGM dissolvable supports.

This work demonstrates, for the first time, two approaches for dissolvable supports in powder bed fusion-printed metal parts. Expanding on our recent innovations with dissolvable supports in multimaterial direct energy deposition printing, this work brings dissolvable support capabilities to additive manufacturing systems that are limited to single-material builds. First, a direct dissolution approach is demonstrated with the supports electrochemically dissolved. While this process works, it is not self-terminating and maintaining dimensional accuracy for complex geometries is thus difficult. The second approach incorporates a sensitizing agent during the normal stress, relieving thermal annealing step to decrease the chemical stability of the top 100–200 μm of the component surface. The component is then etched under etching conditions with a high selectivity toward the “sensitized” surface over the base component material. This creates an etching process that self-terminates once the sensitized...

Formation of high-conductivity metal contacts at low temperatures expands optoelectronic device opportunities to include thermally sensitive layers, while reducing expended thermal budget for fabrication. This includes high-efficiency silicon heterojunction solar cells with intrinsic amorphous silicon layers. Efficiencies of these cells are limited by series resistance; the primary cause of this is the relatively high resistivity of the low-temperature silver paste used to form front-grid metallization. In this paper, we report the formation of highly conductive features by drop-on-demand printing of reactive silver ink (RSI) at a low temperature of 78 °C, resulting in media resistivities of 3–5 μΩ·cm. When used as a front grid on a silicon heterojunction solar cell, RSI fingers give cell series resistance of 1.8 Ω·cm2 (without optimization of the process), which is impressively close to 1.1 Ω·cm2 for our commercially available screen-printed low-temperature silver paste metallization. We present here the promising first results of RSI as metallic finger for photovoltaics, which upon optimization of design parameters has the potential to outperform the screen-printed low-temperature silver paste counterpart.

Nano-inkjet printing using an Electrohydrodynamic’s (EHD) pulsed cone-jet approach has the potential to bring affordable additive manufacturing to the micro and nanoscale. Ink technology is a major limitation of current EHD techniques. Specifically, most EHD printing processes print either nanoparticles or polymers. The materials are structurally weak and often have poor electrical or mechanical properties. For example, printing nanoparticles effectively creates a cluster of nanoparticles that must be sintered to create a continuous material. To address these issues, we have been adapting reactive inks to work with an EHD pulsed cone-jet. Specifically, we demonstrate that silver micron-scale structures can be printed using an EHD pulsed cone-jet regime. These inks produce solid structures without sintering steps and with good electrical properties.1,2 This work shows that reactive ink chemistries can be combined with EHD printing to produce fine-resolution features consisting of solid metal without an annealing step.

Fabrication methods and performance characteristics of spiral stretchable interconnects fabricated using drop-on-demand printing of silver reactive inks are discussed. This work details ink optimization, device fabrication, and device characterization while demonstrating the potential applications for reactive inks and new design strategies in stretchable electronics. Devices were printed with an ethanol stabilized silver diamine reactive ink and cycled to 160 % over 100 cycles with less than 10% increase in electrical resistance. Maximum deformation before failure was measured at 180% elongation. A novel method for fabrication of a stretchable electronics device has been studied and verified.

Reactive metal inks have the potential to replace particle-based inks for printed metals and electrodes. Recent advances in self-reducing silver inks have dropped the reduction temperature from >180 °C down to room temperature. However, most reactive inks are printed at room temperature and sintered at an elevated temperature to achieve good electrical resistivity. In this work, we demonstrate that low electrical resistivity (1.8 μΩcm) can be achieved by adjusting solvent selection and printing at slightly elevated temperatures. This work examines the impact of solvent type and substrate temperature on the resulting morphology and electrical properties of silver films printed with a self-reducing silver-diamine ink. We show that morphology, porosity, and media resistivity can be controlled to produce a dense film without sintering. The porosity was adjusted from 93% down to 50% and the media resistivity two orders of magnitude from 180 μΩcm down to 1.8 μΩcm. The lowest media resistivity was found for a 10:1-EtOH:Ag ink printed at 66 °C. Overall, this process demonstrates that highly conductive silver films can be printed at low temperatures with broad control over morphology and without post-print annealing. Reactive inks print silver with controllable porosity.

Additive manufacturing (AM) offers the ability to fabricate complex metallic structures and shapes in a layer-by-layer process. However, overhanging surfaces often require support structures to be fabricated and minimize thermally induced distortion. Unlike polymer AM processes, soluble sacrificial support materials have not been identified and characterized for metallic materials, and, as a result, support structures in 3D printed metals must be removed using additional machining operations. In this work, we demonstrate that sacrificial metal supports can be fabricated by taking advantage of differences in the chemical and electrochemical stability between different metals. As a demonstration, a stainless steel bridged structure with a 90° overhang was fabricated using a carbon steel sacrificial support that was later removed through electrochemical etching in 41 wt.% nitric acid with bubbling O2. Open circuit potentials and potentiodynamic polarization curves were gathered to verify etch select...

The advent of Additive Manufacturing (AM) has widened the design space for Ti-6Al-4 V (Ti64) components. However, the complex geometries fabricated using AM can result in high post-processing costs due to challenges associated with support removal, powder removal, and improving surface finish. To address these issues, this work introduces a novel, self-terminating etching process for Ti64 alloys that can remove support structures and trapped powder while also improving surface finish for both exterior and interior features. The component is first treated in a furnace to sulfidize the outer 50–150 µm of its surface and the supports. Next, this sulfide layer is selectively dissolved in a solution of 5 M H2SO4 and 0.25 M Na2MoO4. This solution readily dissolves sulfides without dissolving the Ti64 base metal and enables this etching process to be uniquely self-terminating at the sulfide/Ti64 interface. For this work, the amount of Ti64 converted to sulfides as a function of sulfidation temperature, the surface roughness before and after each sulfidation-dissolution cycle, and the microstructural evolution was quantified. The inherently self-terminating nature of this novel process means that, for the first time, post-processing of Ti64 components can be done in a geometry agnostic manner with the knowledge that a specified and known amount of material will be removed from all surfaces. As a result, support structures and trapped powder can be removed with ease at the same time that the surface finish is improved. This process is expected to reduce post-processing costs while expanding the design space for additively manufactured Ti64 parts.

Recently, metal-assisted chemical etching (MaCE) has been demonstrated as a promising technology in fabrication of uniform high-aspect-ratio (HAR) micro- and nanostructures on silicon substrates. In this work, MaCE experiments on 2 μm-wide line patterns were conducted using Au or Ag as catalysts. The performance of the two catalysts show sharp contrast. In MaCE with Au, a HAR trench was formed with uniform geometry and vertical sidewall. In MaCE with Ag, shallow and tapered etching profiles were observed, which resembled the results from isotropic etching. The sidewall tapering phenomena can be explained by the dissolution and re-deposition of the Ag catalyst in the etchant solution. The existence of Ag that was redeposited on the sidewall was further confirmed by energy dispersive spectrum. Also, etchant composition is found to play a profound role in influencing the etching profile by the Ag catalysts.

For this work, a cure-in-place polydimethylsiloxane (PDMS) reactive ink was developed and its utility demonstrated by printing a complete microfluidic mixer with integrated electrodes to measure fluid conductivity, concentration, and mixing completeness. First, a parameter-space investigation was conducted to generate a set of PDMS inks and printing parameters compatible with drop-on-demand (DOD) printing constraints. Next, a microfluidic mixer was fabricated using DOD-printed silver reactive inks, PDMS reactive inks, and a low-temperature polyethylene glycol fugitive ink. Lastly, the device was calibrated and tested using NaCl solutions with concentrations ranging from 0.01 to 1.0 M to show that electrolyte concentration and mixing completeness can be accurately measured. Overall, this work demonstrates a set of reactive inks and processes to fabricate sophisticated microfluidic devices using low-cost inks and DOD printing techniques.

This work introduces and explores vapor phase metal-assisted chemical etching (VP-MaCE) of silicon as a method to bypass some of the challenges found in traditional liquid phase metal-assisted chemical etching (LP-MaCE). Average etch rates for Ag, Au, and Pd/Au catalysts are established at 31, 70, and 96 nm/min respectively, and the relationship between etch rate and substrate temperature is examined experimentally. Just as with LP-MaCE, 3D catalyst motion is maintained and three-dimensional structures are fabricated with nanoparticle- and lithography-patterned catalysts. VP-MaCE produces less microporous silicon compared with LP-MaCE and the diffusion/reduction distance of Ag+ ions is significantly reduced. This process sacrifices etch rate for increased etch uniformity and lower stiction for applications in micro-electromechanical systems (MEMS) processing.

Metal-assisted Chemical Etching of silicon has recently emerged as a powerful technique to fabricate 1D, 2D, and 3D nanostructures in silicon with high feature fidelity. This work demonstrates that out-of-plane rotational catalysts utilizing polymer pinning structures can be designed with excellent control over rotation angle. A plastic deformation model was developed establishing that the catalyst is driven into the silicon substrate with a minimum pressure differential across the catalyst thickness of 0.4-0.6 MPa. Force-displacement curves were gathered between an Au tip and Si or SiO(2) substrates under acidic conditions to show that Derjaguin and Landau, Verwey and Overbeek (DLVO) based forces are capable of providing restorative forces on the order of 0.2-0.3 nN with a calculated 11-18 MPa pressure differential across the catalyst. This work illustrates that out-of-plane rotational structures can be designed with controllable rotation and also suggests a new model for the driving force for catalyst motion based on DLVO theory. This process enables the facile fabrication of vertically aligned thin-film metallic structures and scalloped nanostructures in silicon for applications in 3D micro/nano-electromechanical systems, photonic devices, nanofluidics, etc.

This chapter summarizes the current state-of-the-art for semiconductor and optoelectronic device fabrication using Metal-assisted chemical Etching (MacEtch). It details MacEtch’s history, the physics and chemistry, processing considerations, and applications in device fabrication.

Stretchable electronics have important applications in health monitoring and integrated lab-on-a-chip devices. This paper discusses the performance of serpentine stretchable interconnects printed using self-reducing, silver reactive inks. It details process optimization, device fabrication, and device characterization, while demonstrating the potential applications for reactive inks and new design strategies in stretchable electronics. Devices were printed with an ethanol stabilized silver diamine reactive ink and cycled to stretch ratios of 140 and 160% over 1000 cycles with less than 2.5% variation in electrical resistance. Maximum deformation before failure was measured at 180% elongation. Additionally, interconnect deformation was compared to finite element analysis (FEA) simulations to show that FEA can be used to accurately model the deformation of low-strain printed interconnects. Overall, this paper demonstrates a simple and affordable route toward stretchable electrical interconnects.

Pinned structures in conjunction with shaped catalysts are used in metal-assisted chemical etching (MACE) of silicon to induce out-of-plane rotational etching. Sub-micro- and nanostructures are fabricated in silicon, which include scooped-out channels and curved subsurface horns, along with vertically oriented thin metal structures. Five different etching modes induced by catalyst and pinning geometry are identified: 1) fully pinned–no etching, 2) rotation via twist, 3) rotation via delamination, 4) in-plane bending, and 5) swinging. The rotation angle is roughly controlled through catalyst geometry. The force and pressure experienced by the catalyst are calculated from the deformation of the catalyst and range between 0.5–3.5 μN and 0.5–3.9 MPa, respectively. This is a new, simple method to fabricate 3D, heterogeneous sub-micro- and nanostructures in silicon with high feature fidelity on the order of tens of nanometers while providing a method to measure the forces responsible for catalyst motion during MACE.

We report the superior capacitance of functionalized graphene prepared by controlled reduction of graphene oxide (GO). In a solvothermal method, GO dispersed in dimethylformamide (DMF) was thermally treated at a moderate temperature (150 °C), which allows a fine control of the density of functionalities. Surface functionalities on graphene would enable a high pseudocapacitance, good wetting property, and acceptable electric conductivity. A specific capacitance up to 276 F/g was achieved based on functionalized graphene at a discharge current of 0.1 A/g in a 1 M H2SO4 electrolyte, which is much higher than the benchmark material. The excellent performance of the functionalized graphene signifies the importance of controlling the surface chemistry of graphene-based materials.

Metal-assisted chemical etching (MaCE) of silicon in conjunction with shaped catalysts was used to fabricate 3D nanostructures such as sloping channels, cycloids, and spirals along with traditional vertical channels. The investigation used silver nanorods, nanodonuts along with electron beam lithography (EBL)-patterned gold nanodiscs, nanolines, squares, grids, and star-shaped catalysts to show how catalyst shape and line width directly influence etching direction. Feature sizes ranging from micrometers down to 25 nm were achieved with aspect ratios of at least 10:1 and wall roughness of 10 nm or less. This research demonstrates the potential of MaCE as a new, maskless nanofabrication technology.

Interest in silicon heterojunction with intrinsic thin layer and newly proposed wider bandgap carrier selective contact solar cells in recent years motivates the investigation of low temperature contact formation in order to preserve the order of electronic quality of these layers as well as the chemical surface passivation provided by hydrogenated passivation layers. The realization of low temperature contacts may also broaden solar cell and other optoelectronic devices opportunities, e.g. to use thermally sensitive materials, such as flexible polymer substrates, while at the same time reducing the thermal budget expended on device fabrication. In this work, two methods for low-temperature ohmic contact formation are investigated. The first is a rapid localized annealing technique using electromagnetic induction and the second a deposition method using inkjet printing of reactive silver inks. These techniques are evaluated for use in solar cell devices (not only silicon-based) by comparing demonstrated properties to those targeted for front contacts to solar cells, i.e. finger width, aspect ratio, resistivity, specific contact resistance, and apparent adhesion.

Thisworkintroducesasimpleprocesstofabricate3Dmetallicstructureswithmicrotonano-sizedfeatures.Star-shapedgoldcatalysts were fabricated using electron beam lithography and used as catalysts in MaCE to form spiraling 3D structures. High fidelity was verified by adding 30 nm wide holes in some catalysts for form 30 nm wide spiraling silicon pillars. The gold catalyst remaining at the bottom of the 3D MaCE template was used as a seed for electroless deposition of Pd and the resulting structure extracted using

Room temperature liquid-metal microfluidic devices are attractive systems for hyperelastic strain sensing. These liquid-phase electronics are intrinsically soft and retain their functionality even when stretched to several times their original length. Currently two types of liquid metal-based strain sensors exist for in-plane measurements: single-microchannel resistive and two-microchannel capacitive devices. With a winding serpentine channel geometry, these sensors typically have a footprint of about a square centimeter. This large footprint of an individual device limits the number of sensors that can be embedded into, for example, electronic fabric or skin. In this work we introduce an alternative capacitor design consisting of two liquid metal electrodes separated by a liquid dielectric material within a single straight channel. Using a liquid insulator instead of a solid elastomer enables us to tailor the system's capacitance by selecting high or low dielectric constant liquids. We quantify the effects of the electrode geometry including the diameter, spacing, and meniscus shape as well as the dielectric constant of the insulating liquid on the overall system's capacitance. We also develop a procedure for fabricating the two-liquid capacitor within a single straight polydiemethylsiloxane channel and demonstrate that this device can have about 25 times higher capacitance per sensor's base area when compared to two-channel liquid metal capacitors. Lastly, we characterize the response of this compact device to strain and identify operational issues arising from complex hydrodynamics near liquid-liquid and liquid-elastomer interfaces.

Metal assisted chemical etching (MaCE) is a promising technology for next generation micro- and nano- semiconductor fabrication, where noble metals are used as catalyst to anisotropically etch into bulk materials in solution. In this study, we report the first silicon vias (SV) with sub-100 nm diameter etched by MaCE. The distinct structure of thus fabricated SVs enables the successful copper filling from the bottom of the vias, which is manifested by scanning electron microscope (SEM) and energy dispersive X-ray spectroscope (EDS). The report demonstrates the applicability of nano-scale interconnection in 3D package from the view of fabrication. Also, this novel approach marks the significance in functional filling of semiconductor for nano-photonic devices as well as template-based synthesis of functional nanomaterials.

The ease of fabrication and wide application of printed microelectronics are driving advances in reactive inks. The long-term performance of structures printed using reactive ink is important for their application in microelectronics. In this study, silver lines are printed with low-temperature, self-reducing, silver-diamine based ink. The electromigration failure of the printed silver is first studied using Black's equation. However, due to the porous nature of the printed Ag line, Black's equation is not the best fit for predicting the lifetime, this is because Black's equation does not take into account morphology-induced current crowding. We find that the resistivity of the printed Ag lines can be described (as a function of void fraction) by percolation theory. In addition, we also demonstrate that the failure lifetimes of the printed Ag can be predicted quite well by a percolative model of failure.

The ability to fabricate 3D spiraling structures using metal-assisted chemical etching (MaCE) is one of the unique advantages of MaCE over traditional etching methods. However, control over the chirality of the spiraling structures has not been established. In this work, a systematic parametric study was undertaken for MaCE of star-shaped catalysts, examining the influence of arm shape, arm length, number of arms, center core diameter, and catalyst thickness on the rotation direction. This data was used to identify a set of geometric parameters that reliably induce rotation in a predefined direction such that large arrays of 3D spiraling structures can be fabricated with the same chirality. Electroless deposition into the MaCE template was used to examine the full etch path of the catalyst and an experimental fit was established to control rotation angle by adjusting the catalyst's center core diameter. The ability to fabricate large arrays of 3D spiraling structures with predefined chirality could have important applications in photonics and optoelectronics.

A solvothermal method was used to synthesize functionalized graphene, which exhibits an ultrahigh capacitance. This solvothermal method allows a fine control of the density of functionalities on graphene surface. The structure of resulting functionalized graphene is characterized by X-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis (TGA), FTIR and Raman. Pseudocapacitance is provided by functionalities on graphene surface, such as carboxyl, carbonyl and hydroxyl. The significance of these functional also includes improving the wetting properties of electrode material, especially for supercapacitors using aqueous electrolyte. However, there is a penalty for functionalities since these oxygen-containing functional groups will disrupt the π-conjugated system and lower the electrical conductivity. Therefore for functionalized graphene as supercapacitor, a tradeoff exists between the high psudeocapacitance and low conductivity, both are arising from the surface functionalities. Our systematic study shows a successful control of the density of functionalities, which is essential to achieve high performance of graphene-based supercapacitors. The capacitance of graphene is measured in a three electrode system using cyclic voltammetry (CV) and galvanostatic charging/discharging techniques. At a proper reduction condition, a high capacity of 276 F/g was achieved at a discharging current of 0.1 A/g in H 2 SO 4 solutions. The superior capacitive performance of functionalized graphene demonstrates the importance of surface property engineering, which will greatly promote the study and application of graphene-based supercapacitors.

In recent years metal-assisted chemical etching (MaCE) of silicon, in which etching is confined to a small region surrounding metal catalyst templates, has emerged as a promising low cost alternative to commonly used three-dimensional (3D) fabrication techniques. We report a new methodology for controllable folding of 2D metal catalyst films into 3D structures using MaCE. This method takes advantage of selective patterning of the catalyst layer into regions with mismatched characteristic dimensions, resulting in uneven etching rates along the notched boundary lines that produce hinged 2D templates for 3D folding. We explore the dynamics of the folding process of the hinged templates, demonstrating that the folding action combines rotational and translational motion of the catalyst template, which yields topologically complex 3D nanostructures with intimately integrated metal and silicon features.

A process that allows control over the 3D motion of catalyst nanostructures during metal-assisted chemical etching by their local pinning prior to etching is demonstrated. The pinning material acts as a fulcrum for rotation of the catalyst structures resulting in etching of silicon features with rotational geometry.

In this work, we introduce a maskless, resist-free rapid prototyping method to fabricate three-dimensional structures using electron beam induced deposition (EBID) of amorphous carbon (aC) from a residual hydrocarbon precursor in combination with metal-assisted chemical etching (MaCE) of silicon. We demonstrate that EBID-made patterned aC coating, with thickness of even a few nanometers, acts as a negative "mask" for the etching process and is sufficient for localized termination of the MaCE of silicon. Optimal aC deposition settings and gold film thickness for fabrication of high-aspect-ratio nanoscale 3D silicon structures are determined. The speed necessary for optimal aC feature deposition is found to be comparable to the writing speed of standard Electron Beam Lithography and the MaCE etching rate is found to be comparable to standard deep reactive ion etching (DRIE) rate.

This paper demonstrates the use of tungsten as a viable, low cost catalyst for Metal-assisted Chemical Etching (MaCE) of silicon to create high aspect ratio nanostructures in silicon. The effect of etchant composition and etching time is reported along with Scanning Electron Microscope (SEM) and Atomic Force Microscopy (AFM) images confirming that tungsten acted as a catalyst for MaCE.

There are a number of emerging technologies such as metamaterials, photonic wave-guides, nano-imprint lithography (NIL), field emission devices and through silicon via (TSV), that require high resolution and high aspect ratio nanofabrication techniques for good performance. Unfortunately, current nanofabrication techniques, including photolithography and e-beam lithography, are limited to low aspect ratios on the order of 7:1 and cannot fabricate the high aspect ratio nanostructures needed for these emerging nanotechnologies. Deep reactive ion etching has traditionally been used to increase the aspect ratio nanostructures produced from traditional lithography techniques; however, the process is expensive, time consuming and cannot produce smooth sidewalls, lowering device performance. To overcome these obstacles our group has developed a new wet chemical nanofabrication technique that uses shaped catalysts to etch high aspect ratio nanostructures into silicon. The process is fast, does not require expensive equipment and has been used to produce features less than 25 nm wide, 25 µms long and microns deep in silicon using nanorod catalysts. 10 nm wide features were also fabricated using nano-donuts. This new, patented technique is compatible with existing silicon fabrication technologies and could be used for a wide variety of applications that require nanometer sized features and high aspect ratios.

Conformal coatings are widely used by the electronics industry to protect sensitive equipment from moisture and corrosion [i]. Of these, parylene thin-film coatings have many material properties such as low dielectric and dissipation factors, high operating temperatures, excellent conformability and low moisture permeability, which make them an attractive conformal material for numerous applications. However, adhesion of parylene coatings is critical to the overall reliability of the coating and is especially problematic on inorganic surfaces. A number of techniques can potentially improve adhesion including adhesion promoters and plasma treatment, but a robust method for evaluating adhesion has been lacking. In response, we developed a method based upon a standard die-shear test that can calculate the adhesion strength of different interfaces when multiple failure modes are active. This process uses pre-shear and post-shear images to calculate the area of each failure mode. Those areas are then used in combination with the measured breaking load to calculate the adhesion strength of the different interfaces using an iterative solver. This method provides an accurate, quantitative measure of thin-film adhesion even when mixed failure modes are active.

Carbon nanotubes (CNTs) are an attractive electrical interconnect material due to their excellent mechanical, electrical and thermal properties. Despite these advantages CNTs have not been widely adopted by industry primarily because of the difficulties associated with integrating CNTs into device electronics. In this paper we demonstrate that bundles of aligned CNTs can be extracted directly from a CNT film using solder ball grid arrays (BGA). The resulting CNT bundles adhere directly to the solder balls and show good vertical alignment. The affect of flux, CNT application displacement and solder ball phase (liquid or solid) on CNT bundle alignment and coverage area were examined. This simple process could be used to mechanically decouple the BGA from the substrate, reducing solder ball fatigue due to thermal cycling and increasing device reliability.

This paper addresses the state of art nano science and technology regarding next generation high density microelectronics and photonics packaging applications, including carbon nanotubes (CNTs) for electrical/thermal devices, nano lead-free alloy, molecular wires for electrical interconnects, etc.

A low-temperature flexible process, named "chemical transfer", was developed to assemble well-aligned carbon nanotube (ACNT) structures onto various substrates. The technology was featured by (1) in situ functionalization of ACNTs with reactive functional groups during the CVD process and (2) covalently bonded interface with a self-assembled monolayer (SAM) of conjugated thiol molecules as the bridging ligand and conduction path at the ACNT/gold interface. The effectiveness of the in situ functionalization was characterized by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). I-V response and the interfacial strength of the chemically transferred structure were studied. Results showed an Ohmic contact, low electrical resistivity, and improved CNT-substrate adhesion. This novel technique shows promising applications for positioning ACNTs as electrical interconnects or thermal interface materials on temperature-sensitive substrates.

Metal-assisted chemical etching (MaCE) of silicon has proven to be a fast and effective method to fabricate 1D, 2D, and 3D micro- to nano-scale features in silicon. It has been shown that platinum catalysts deposited using focused ion beam (FIB) are a viable catalyst for MaCE; however, the feature fidelity of channels etched with FIB patterned catalysts are found to be significantly lower than catalysts formed using e-beam lithography. In this work we show that gallium (Ga+) ions implanted into the silicon during sample exposure result in significant etching in the irradiated regions as well as long-distance etching peripheral regions. The accelerating voltage, dose, and etching time were varied to show that the etch depth depends primarily on accelerating voltage and is largely independent of dose while the width of the peripheral region was found to scale with dose. The slope of the peripheral etching region was found to vary with both accelerating voltage and dose with three different etching times evaluated to examine how the etch profile evolves over time. These results show that Ga+ ions do participate in MaCE and care must be taken when a Ga+ ion based FIB is used.Metal-assisted chemical etching (MaCE) of silicon has proven to be a fast and effective method to fabricate 1D, 2D, and 3D micro- to nano-scale features in silicon. It has been shown that platinum catalysts deposited using focused ion beam (FIB) are a viable catalyst for MaCE; however, the feature fidelity of channels etched with FIB patterned catalysts are found to be significantly lower than catalysts formed using e-beam lithography. In this work we show that gallium (Ga+) ions implanted into the silicon during sample exposure result in significant etching in the irradiated regions as well as long-distance etching peripheral regions. The accelerating voltage, dose, and etching time were varied to show that the etch depth depends primarily on accelerating voltage and is largely independent of dose while the width of the peripheral region was found to scale with dose. The slope of the peripheral etching region was found to vary with both accelerating voltage and dose with three different etching times eva...

Conformally coating vertically aligned carbon nanotubes (v-CNT) with metals or oxides can be difficult because standard line-of-sight deposition methods, such as dc sputter coating and electron-beam evaporation, are hindered by the low mean-free-path within the vertically aligned array. In this work, we present a facile method to conformally coat dense arrays of v-CNTs using thermal decomposition of iron pentacarbonyl at 205 °C and 30 mTorr. The resulting coatings were found to be uniform from top-to-bottom across an entire 1 × 1 cm2 array of v-CNTs. The thickness of the deposited coating was found to be 2–3 nm/cycle and the resulting film thickness were found to be 13 ± 3 nm after five cycles and 55 ± 5 nm after 20 cycles. This process demonstrates that metal organic chemical vapor deposition can be used to fabricate conformal coatings on v-CNTs.