Nicholas A. Charipar

United States Naval Research Laboratory, Washington, Washington, D.C., United States

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Publications (35)65.63 Total impact

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    Nicholas A. Charipar · Heungsoo Kim · Scott A. Mathews · Alberto Piqué
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    ABSTRACT: We report the design, fabrication, and characterization of broadband terahertz emitters based on the semiconductor-metal transition in thin film VO2 (vanadium dioxide). With the appropriate geometry, picosecond electrical pulses are generated by illuminating 120 nm thick VO2 with 280 fs pulses from a femtosecond laser. These ultrafast electrical pulses are used to drive a simple dipole antenna,generating broadband terahertz radiation.
    Preview · Article · Jan 2016 · AIP Advances
  • H. Kim · N. Charipar · E. Breckenfeld · A. Rosenberg · A. Piqué
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    ABSTRACT: Vanadium dioxide (VO2) thin films were prepared on single crystal sapphire substrates by pulsed laser deposition. VO2 films exhibited a significant resistivity drop (>104 Ω-cm) and large optical transmittance change (>60%) in the near-infrared region across their semiconductor-to-metal transition. Hybrid metamaterial devices designed for the THz frequency regime were fabricated by combining double split-ring resonators (SRRs) with phase changing VO2 films. By changing the conductivity of VO2 via temperature, the behavior of the SRR gap was adjusted from capacitive to resistive in order to modulate the THz beam transmission at their resonance frequencies. A modulation efficiency greater than 50% was achieved at the magnetic resonance frequencies (0.3THz and 0.7THz) in these hybrid SRR-VO2 metamaterial devices.
    No preview · Article · Jul 2015 · Thin Solid Films
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    ABSTRACT: We explore the effect of variations in laser fluence and donor-receiver substrate distance on the laser-induced forward transfer technique for high viscosity Ag nanopaste. By transferring 50 μm × 50 μm voxels with thicknesses between 0.8 and 8.7 μm at different laser fluences, we are able to systematically determine a thickness-fluence regime for successful transfer that widens with increasing voxel thickness. We use these results to study congruent transfer of square voxels with lateral dimensions spanning 2 orders of magnitude: 5 μm × 5 μm, 50 μm × 50 μm, and 500 μm × 500 μm. We conclude by linking a multitude of voxels together in 1 mm and 3 mm lines to fabricate the center conductor in coplanar waveguides (CPWs) with relatively low loss up to 10 GHz.
    No preview · Article · Mar 2015 · Applied Surface Science
  • Scott A. Mathews · Nicholas A. Charipar · R.C.Y. Auyeung · Heungsoo Kim · Alberto Piqué
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    ABSTRACT: The progressive miniaturization of electronic devices requires an ever-increasing density of interconnects attached via solder joints. As a consequence, the overall size and spacing (or pitch) of these solder joint interconnects keeps shrinking. When the pitch between interconnects decreases below 200 μm, current technologies, such as stencil printing, find themselves reaching their resolution limit. Laser direct-write (LDW) techniques based on laser-induced forward transfer (LIFT) of functional materials ofter unique advantages and capabilities for the printing of solder pastes. At NRL, we have demonstrated the successful transfer, patterning, and subsequent reow of commercial Pb-free solder pastes using LIFT. Transfers were achieved both with the donor substrate in contact with the receiving substrate and across a 25 μm gap, such that the donor substrate does not make contact with the receiving substrate. We demonstrate the transfer of solder paste features down to 25 μm in diameter and as large as a few hundred microns, although neither represents the ultimate limit of the LIFT process in terms of spatial dimensions. Solder paste was transferred onto circular copper pads as small as 30 μm and subsequently reowed, in order to demonstrate that the solder and ux were not adversely affected by the LIFT process.
    No preview · Article · Mar 2015 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: Electronic paper, or e-Paper, for use in displays has seen rapid growth in the past decade because of its potential as an alternative to traditional transmissive displays. Offering several critical advantages over current display technologies, including high contrast in direct sunlight, wide viewing angles, and compatibility with flexible substrate processing, electrowetting displays (EWDs) have made it to the forefront of e-Paper research and development efforts. Here, we describe a new design for the fabrication of multi-color, bistable electrowetting displays. Using a laser-based process to pattern an in-plane electrode design, liquid can be manipulated out-of-plane. This process relies on electromechanical pressure forcing water in and out of channels, causing colored oil to be displaced. When voltage is removed, the oil remains in its current position, resulting in bistability. We have demonstrated multi-color, bistable pixels that maintain their state at ${\rm V}= 0$ for several days, which drastically reduces the power required to drive the display.
    No preview · Article · Feb 2015 · Journal of Display Technology
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    ABSTRACT: Additive manufacturing techniques such as 3D printing are able to generate reproductions of a part in free space without the use of molds; however, the objects produced lack electrical functionality from an applications perspective. At the same time, techniques such as inkjet and laser direct-write (LDW) can be used to print electronic components and connections onto already existing objects, but are not capable of generating a full object on their own. The approach missing to date is the combination of 3D printing processes with direct-write of electronic circuits. Among the numerous direct write techniques available, LDW offers unique advantages and capabilities given its compatibility with a wide range of materials, surface chemistries and surface morphologies. The Naval Research Laboratory (NRL) has developed various LDW processes ranging from the non-phase transformative direct printing of complex suspensions or inks to lase-and-place for embedding entire semiconductor devices. These processes have been demonstrated in digital manufacturing of a wide variety of microelectronic elements ranging from circuit components such as electrical interconnects and passives to antennas, sensors, actuators and power sources. At NRL we are investigating the combination of LDW with 3D printing to demonstrate the digital fabrication of functional parts, such as 3D circuits. Merging these techniques will make possible the development of a new generation of structures capable of detecting, processing, communicating and interacting with their surroundings in ways never imagined before. This paper shows the latest results achieved at NRL in this area, describing the various approaches developed for generating 3D printed electronics with LDW.
    No preview · Article · Feb 2014 · Proceedings of SPIE - The International Society for Optical Engineering
  • Alberto Piqué · Heungsoo Kim · Nicholas A. Charipar · Michael Osofsky
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    ABSTRACT: Conventional metals with high carrier concentrations have served to date as the materials of choice for plasmonic and metamaterial devices. However, typical metals are not well suited for near IR (NIR) plasmonic applications because their associated plasma frequencies correspond to the visible and ultraviolet regions of the spectrum. On the other hand, materials with lower plasma frequencies such as conducting oxides like ZnO and VO2 are capable of more efficiently coupling the electromagnetic radiation for optical metamaterial and plasmonic applications in the NIR. Furthermore, unlike metals, the electrical transport properties of conductive oxides can be modulated intrinsically by doping or extrinsically by applying heat, light or an electrical bias, thus allowing tuning of their electro-optical behavior. At the Naval Research Laboratory (NRL), we have investigated the use of laser processing techniques for the deposition and processing of various types of conducting oxides, such as Al-doped ZnO and W-doped VO2, which can be optimized over a wide range of optical/electrical properties. This paper will describe the laser deposition of these oxide films and their electrical and optical characterization in the NIR.
    No preview · Article · Feb 2014 · Proceedings of SPIE - The International Society for Optical Engineering
  • H. Kim · N. Charipar · M. Osofsky · S.B. Qadri · A. Pique
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    ABSTRACT: High quality VO2 epitaxial thin films were deposited on sapphire single crystal substrates by pulsed laser deposition and their semiconductor-to-metal transitions (SMTs) were characterized as a function of film growth conditions. Varying the oxygen pressure during deposition affected the number of oxygen vacancies, which allowed tuning of the crystal structure and phase transition properties of the VO2 films. Films grown at optimized conditions exhibited a significant resistivity drop (>104 Ω-cm) across the SMT that is correlated with the strain due to oxygen vacancies. This resistivity drop is mainly accounted for by a large change in carrier density at the SMT.
    No preview · Article · Feb 2014 · Applied Physics Letters
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    ABSTRACT: Advanced fabrication technologies are poised to revolutionize the manufacturing environment. While the development of additive manufacturing technologies for mechanical components has been rapidly evolving, the application of these methods to the fabrication of RF and microwave components has been limited. Hybrid manufacturing processes, which combine distinct techniques such as fused deposition modeling (FDM), and laser micromachining, enable the creation of complex three-dimensional (3D) electromagnetic components. At NRL, we have investigated the combination of 3D printing techniques with direct-write processes that allow for the metallization, laser patterning and room temperature processing of electromagnetic patterns on 3D printed surfaces. The resolution and print volume achieved with these methods are well suited for the rapid prototyping of electromagnetic structures. Several example structures fabricated using these techniques will be presented.
    No preview · Article · Jan 2014
  • S. A. Mathews · R. C. Y. Auyeung · H. Kim · N. A. Charipar · A. Piqué
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    ABSTRACT: High-speed video (100 000 fps) is used to examine the behavior of silver nanoparticle suspensions ejected from a donor substrate during laser-induced forward transfer (LIFT) as a function of viscosity, donor film thickness, and voxel area. Both high-speed video and inspection of the post-transferred material indicate dramatic changes in the behavior of the fluid as the viscosity of the nano-suspensions increases from that of inks (∼0.01 Pa·s) to pastes (>100 Pa·s). Over a specific range of viscosities (90–150 Pa·s) and laser fluences (35–65 mJ/cm2), the ejected voxels precisely reproduce the size and shape of the laser spot. This LIFT regime is known as laser decal transfer or LDT. Analysis of the high-speed video indicates that the speeds of the voxels released by the LDT process do not exceed 1 m/s. Such transfer speeds are at least an order of magnitude lower than those associated with other LIFT processes, thus minimizing voxel deformation during flight and upon impact with the receiving substrate. Variation in the threshold fluence for initiating the LDT process is measured as a function of donor film thickness and transfer spot size. Overall, the congruent nature of the silver nanopaste voxels deposited by LDT is unique among non-contact digital printing techniques given its control of the voxel's size and shape, thus allowing partial parallelization of the direct-write process.
    No preview · Article · Aug 2013 · Journal of Applied Physics
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    ABSTRACT: Pulse shape discrimination (PSD) is a common method to distinguish between pulses produced by gamma rays and neutrons in scintillator detectors. This technique takes advantage of the property of many scintillators that excitations by recoil protons and electrons produce pulses with different characteristic shapes. Unfortunately, many scintillating materials with good PSD properties have other, undesirable properties such as flammability, toxicity, low availability, high cost, and/or limited size. In contrast, plastic scintillator detectors are relatively low-cost, and easily handled and mass-produced. Recent studies have demonstrated efficient PSD in plastic scintillators using a high concentration of fluorescent dyes. To further investigate the PSD properties of such systems, mixed plastic scintillator samples were produced and tested. The addition of up to 30 wt. % diphenyloxazole (DPO) and other chromophores in polyvinyltoluene (PVT) results in efficient detection with commercial detectors. These plastic scintillators are produced in large diameters up to 4 inches by melt blending directly in a container suitable for in-line detector use. This allows recycling and reuse of materials while varying the compositions. This strategy also avoids additional sample handling and polishing steps required when using removable molds. In this presentation, results will be presented for different mixed-plastic compositions and compared with known scintillating materials
    No preview · Conference Paper · May 2013
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    ABSTRACT: The field of metamaterials has expanded to include more than four orders of magnitude of the electromagnetic spectrum, ranging from the microwave to the optical. While early metamaterials operated in the microwave region of the spectrum, where standard printed circuit board techniques could be applied, modern designs operating at shorter wavelengths require alternative manufacturing methods, including advanced semiconductor processes. Semiconductor manufacturing methods have proven successful for planar 2D geometries of limited scale. However, these methods are limited by material choice and the range of possible feature sizes, thus hindering the development of metamaterials due to manufacturing challenges. Furthermore, it is difficult to achieve the wide range of scales encountered in modern metamaterial designs with these methods alone. Laser direct-write processes can overcome these challenges while enabling new and exciting fabrication techniques. Laser processes such as micromachining and laser transfer are ideally suited for the development and optimization of 2D and 3D metamaterial structures. These laser processes are advantageous in that they have the ability to both transfer and remove material as well as the capacity to pattern non-traditional surfaces. This paper will present recent advances in laser processing of various types of metamaterial designs.
    No preview · Conference Paper · Mar 2013
  • Alberto Pique · Nicholas Charipar · Heungsoo Kim · Matthew Kirleis · Andrew Smith
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    ABSTRACT: The use of metamaterials structures has been the subject of extensive discussions given their wide range of applications. However, a large fraction of the work available to date has been limited to simulations and proof-of-principle demonstrations. One reason for the limited success inserting these structures into functioning systems and real-world applications is the high level of complexity involved in their fabrication. Direct-write processes are ideally suited for the fabrication of arbitrary periodic and aperiodic structures found in most metamaterial and plasmonic designs. For these applications, laser-based processes offer numerous advantages since they can be applied to virtually any surface over a wide range of scales. Furthermore, laser direct-write or LDW allows the precise deposition and/or removal of material thus enabling the fabrication of novel metamaterial designs. This presentation will show examples of metamaterial and plasmonic structures developed at the Naval Research Lab using LDW, and discuss the benefits of laser processing for these applications.
    No preview · Article · Mar 2013
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    ABSTRACT: Laser forward transfer of arbitrary and complex configurable structures has recently been demonstrated using a spatial light modulator (SLM). The SLM allows the spatial distribution of the laser pulse, required by the laser transfer process, to be modified for each pulse. The programmable image on the SLM spatially modulates the intensity profile of the laser beam, which is then used to transfer a thin layer of material reproducing the same spatial pattern onto a substrate. The combination of laser direct write (LDW) with a SLM is unique since it enables LDW to operate not only in serial fashion like other direct write techniques but instead reach a level in parallel processing not possible with traditional digital fabrication methods. This paper describes the use of Digital Micromirror Devices or DMDs as SLMs in combination with visible (λ = 532 nm) nanosecond lasers. The parallel laser printing of arrayed structures with a single laser shot is demonstrated together with the full capabilities of SLMs for laser printing reconfigurable patterns of silver nano-inks Finally, an overview of the unique advantages and capabilities of laser forward transfer with SLMs is presented.
    No preview · Article · Mar 2013 · Proceedings of SPIE - The International Society for Optical Engineering
  • Alberto Piqué · Scott A. Mathews · Nicholas A. Charipar · Andrew J. Birnbaum
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    ABSTRACT: The ability to manufacture and assemble complex three-dimensional (3D) systems via traditional photolithographic techniques has attracted increasing attention. However, most of the work to date still utilizes the traditional patterning and etching processes designed for the semiconductor industry where 2D structures are first fabricated, followed by some alternative technique for releasing these structures out-of-plane. Here we present a novel technique called Laser Origami, which has demonstrated the ability to generate 3D microstructures through the controlled out-of-plane folding of 2D patterns. This non-lithographic, and non silicon-based process is capable of microfabricating 3D structures of arbitrary shape and geometric complexity on a variety of substrates. The Laser Origami technique allows for the design and fabrication of arrays of 3D microstructures, where each microstructure can be made to fold independently of the others. Application of these folded micro-assemblies might make possible the development of highly complex and interconnected electrical, optical and mechanical 3D systems. This article will describe the unique advantages and capabilities of Laser Origami, discuss its applications and explore its role for the assembly and generation of 3D microstructures.
    No preview · Article · Feb 2012 · Proceedings of SPIE - The International Society for Optical Engineering
  • N.A. Charipar · H. Kim · S.A. Mathews · R.C.Y. Auyeung · A. Piqué
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    ABSTRACT: As interest in metamaterials continues to grow it has become apparent that traditional manufacturing technologies do not provide a suitable toolset for the realization of these novel structures. Traditional lithographic approaches are limited to planar substrates that are compatible with a specific lithographic process. Non-lithographic techniques, also known as direct-write processes, offer the advantages of mask free fabrication and open the realm of threedimensional patterning. Examples of various non-lithographic techniques will be discussed; however, the focus of this work will be on laser-based processes. Laser processes have advantages over traditional fabrication techniques, such as the ability to both transfer and remove material. The combination of these abilities paves the way for spatially varying conformal metamaterial structures. Terahertz resonators fabricated by laser direct write will be presented as an example of metamaterials fabricated by these processes.
    No preview · Article · Jan 2012
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    ABSTRACT: The opportunities presented by the use of metamaterials have been the subject of extensive discussions. However, a large fraction of the work available to date has been limited to simulations and proof-of-principle demonstrations. One reason for the limited success inserting these structures into functioning systems and real-world applications is the high level of complexity involved in their fabrication. Most approaches to the realization of metamaterial structures utilize traditional lithographic processing techniques to pattern the required geometries and then rely on separate steps to assemble the final design. Obviously, composite structures with arbitrary and/or 3-D geometries present a challenge for their implementation with these approaches. Non-lithographic processes are ideally suited for the fabrication of arbitrary periodic and aperiodic structures needed to implement many of the metamaterial designs being proposed. Furthermore, non-lithographic techniques are true enablers for the development of conformal or 3-D metamaterial designs. This article will show examples of metamaterial structures developed at the Naval Research Laboratory using non-lithographic processes. These processes have been applied successfully to the fabrication of complex 2-D and 3-D structures comprising different types of materials.
    No preview · Article · Jan 2012 · Proceedings of SPIE - The International Society for Optical Engineering
  • Alberto Piqué · Scott Mathews · Andrew Birnbaum · Nicholas Charipar

    No preview · Article · Nov 2011 · SPIENewsroom
  • Article: SPIE LASE
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    ABSTRACT: Digital microfabrication processes are non-lithographic techniques ideally capable of directly generating patterns and structures of functional materials for the rapid prototyping of electronic, optical and sensor devices. Laser Direct-Write is an example of digital microfabrication that offers unique advantages and capabilities. A key advantage of laser directwrite techniques is their compatibility with a wide range of materials, surface chemistries and surface morphologies. These processes have been demonstrated in the fabrication of a wide variety of microelectronic elements such as interconnects, passives, antennas, sensors, power sources and embedded circuits. Recently, a novel laser direct-write technique able to digitally microfabricate thin film-like structures has been developed at the Naval Research Laboratory. This technique, known as Laser Decal Transfer, is capable of generating patterns with excellent lateral resolution and thickness uniformity using high viscosity metallic nano-inks. The high degree of control in size and shape achievable has been applied to the digital microfabrication of 3-dimensional stacked assemblies, MEMS-like structures and freestanding interconnects. Overall, laser forward transfer is perhaps the most flexible digital microfabrication process available in terms of materials versatility, substrate compatibility and range of speed, scale and resolution. This paper will describe the unique advantages and capabilities of laser decal transfer, discuss its applications and explore its role in the future of digital microfabrication.© (2011) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
    No preview · Article · Feb 2011
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    ABSTRACT: Digital microfabrication processes are non-lithographic techniques ideally capable of directly generating patterns and structures of functional materials for the rapid prototyping of electronic, optical and sensor devices. Laser Direct-Write is an example of digital microfabrication that offers unique advantages and capabilities. A key advantage of laser directwrite techniques is their compatibility with a wide range of materials, surface chemistries and surface morphologies. These processes have been demonstrated in the fabrication of a wide variety of microelectronic elements such as interconnects, passives, antennas, sensors, power sources and embedded circuits. Recently, a novel laser direct-write technique able to digitally microfabricate thin film-like structures has been developed at the Naval Research Laboratory. This technique, known as Laser Decal Transfer, is capable of generating patterns with excellent lateral resolution and thickness uniformity using high viscosity metallic nano-inks. The high degree of control in size and shape achievable has been applied to the digital microfabrication of 3-dimensional stacked assemblies, MEMS-like structures and freestanding interconnects. Overall, laser forward transfer is perhaps the most flexible digital microfabrication process available in terms of materials versatility, substrate compatibility and range of speed, scale and resolution. This paper will describe the unique advantages and capabilities of laser decal transfer, discuss its applications and explore its role in the future of digital microfabrication.
    No preview · Article · Feb 2011 · Proceedings of SPIE - The International Society for Optical Engineering