Advancements in biological and chemical warfare has allowed for the creation of novel toxins necessitating a universal,
real-time sensor. We have used a function-based biosensor employing impedance spectroscopy using a low current
density AC signal over a range of frequencies (62.5 Hz-64 kHz) to measure the electrical impedance of a confluent
epithelial cell monolayer at 120 sec intervals. Madin Darby canine kidney (MDCK) epithelial cells were grown to
confluence on thin film interdigitated gold electrodes. A stable impedance measurement of 2200 Ω was found after 24
hrs of growth. After exposure to cytotoxins anthrax lethal toxin and etoposide, the impedance decreased in a linear
fashion resulting in a 50% drop in impedance over 50hrs showing significant difference from the control sample (~20%
decrease). Immunofluorescent imaging showed that apoptosis was induced through the addition of toxins. Similarities of
the impedance signal shows that the mechanism of cellular death was the same between ALT and etoposide. A revised
equivalent circuit model was employed in order to quantify morphological changes in the cell monolayer such as tight
junction integrity and cell surface area coverage. This model showed a faster response to cytotoxin (2 hrs) compared to
raw measurements (20 hrs). We demonstrate that herein that impedance spectroscopy of epithelial monolayers serves as
a real-time non-destructive sensor for unknown pathogens.
Direct-Write techniques have the potential to revolutionize the way miniature sensor devices and microbattery systems are designed and fabricated. The Naval Research Laboratory has developed an advanced laser-based forward transfer process for direct writing novel structures and devices comprising of metals, ceramics, polymers and composites under ambient conditions on both ceramic and plastic substrates. Using this forward transfer technique, we have demonstrated the ability to rapidly prototype various types of physical and chemical sensor devices, and microbatteries. The laser forward transfer process is computer controlled which allows the design of the devices to be easily modified and adapted to any specific application. Furthermore, the same process enables the fabrication of complete sensor or power-source systems by incorporating the passive electronic components required for sensor readout or power management. Examples are provided of various types of miniature sensors, and prototype alkaline and Li-ion microbatteries fabricated using this technique.
This paper outlines investigations into a potentially revolutionary approach to tissue engineering. Tissue is a complex 3D structure that contains many different biomaterials such as cells, proteins, and extracellular matrix molecules that are ordered in a very precise way to serve specific functions. In order to replicate such complex structure, it is necessary to have a tool that could deposit all these materials in an accurate and controlled fashion. Most methods to fabricate living 3D structures involve techniques to engineer biocompatible scaffolding, which is then seeded with living cells to form tissue. This scaffolding gives the tissue needed support, but the resulting tissue inherently has no microscopic cellular structure because cells are injected into the scaffolding where they adhere ta random. Wee have developed a novel technique that actually engineers tissue, not scaffolding, that includes the mesoscopic cellular structure inherent in natural tissues. This approach uses a laser-based rapid prototyping system known as matrix assisted pulsed laser evaporation direct write to construct living tissue cell-by- cell. This manuscript details our efforts to rapidly and reproducibly fabricate comlpex 2D and 3D tissue structures with MAPLE-DW by placing different cells and biomaterials accurately and adherently on the mesoscopic scale.
KEYWORDS: Sensors, Chemical fiber sensors, Polymers, Silver, Temperature sensors, Fabrication, Biosensors, Chemical elements, Manufacturing, Electrodes
The use of direct-write techniques in the design and manufacture of sensor devices provides a flexible approach for next generation commercial and defense sensor applications. Using a laser forward transfer technique, we have demonstrated the ability to rapidly prototype temperature, biological and chemical sensor devices. This process, known as matrix assissted pulsed laser evaporation direct-write or MAPLE-DW is compatible with a broad class of materials ranging form metals and electronic ceramics to chemoselective polymers and biomaterials. Various types of miniature sensor designs have been fabricated incorporating different materials such as metals, polymers, biomaterials or composites as multilayers or discrete structures on a single substrate. The MAPLE-DW process is computer controlled which allows the sensor design to be easily modified and adapted to any specific application. To illustrate the potential of this technique, a functional chemical sensor system is demonstrated by fabricating all the passive and sensor components by MAPLE-DW on a polyimide substrate. Additional devices fabricated by MAPLE DW including biosensors and temperature sensors and their performance are shown to illustrate the breadth of MAPLE DW and how this technique may influence current and future sensor applications.
Transparent conducting indium tin oxide (ITO) tin films were grown by pulsed-laser deposition (PLD) on glass and single crystal yttria-stabilized zirconia (YSZ) substrates. The structural, electrical and optical properties of these films were investigated as a function of substrate deposition temperature and background gas pressure. Films were deposited using a KrF excimer laser (248nm, 30 ns FWHM) at a fluence of 1.2 J/cm2. Films were deposited at substrate temperature of 300 degree(s)C in mixed gases (12 mTorr of argon and 1-50 mTorr of oxygen). X-ray diffraction, scanning electron microscopy and atomic force microscopy were used to characterize the structure and morphology of the deposited films. UV/VIS/NIR spectroscopy and Hall effect measurements were used to characterize the optical and electrical properties of the films. ITO films (300 nm thick), deposited by PLD on YSZ at 300 degree(s)C in a gas mixture of 12 mTorr of argon and 5 mTorr of oxygen, exhibit a low electrical resistivity (1.6 x 10-4(Omega) -cm) with a high transparency (~74%) at 550 nm. ITO films deposited by PLD on both glass and YSZ substrates have been used as an anode contact in organic light-emitting diodes. A comparison of the device performance for the two substrates shows that the device fabricated on the ITO/YSZ has a higher external quantum efficiency than that of the device fabricated on the ITO/glass.
Transparent conducting indium tin oxide (ITO) thin films were grown by pulsed laser deposition (PLD) on glass and on flexible polyethylene teraphthalate (PET) substrates. The structural, electrical and optical properties of these films were investigated as a function of substrate deposition temperature and background gas pressure. Films were deposited using a KrF excimer laser (248 nm, 30 ns FWHM) at a fluence of 1.2 J/cm2. Films were deposited at substrate temperatures ranging from 25 degree(s)C to 150 degree(s)C in oxygen pressures ranging from 10 to 60 mTorr. ITO films (280 nm thick), deposited by PLD on PET at 25 degree(s)C and 45 mTorr of oxygen, exhibit a low electrical sheet resistance (20 - 25 (Omega) /sq.) and high transparency (approximately 85%) in the visible range (400-700 nm). We have also used the ITO thin films deposited on both glass and PET substrates by PLD as the anode contact in organic light emitting devices (OLEDs) and measured the device performance. The external quantum efficiency measured at a current density of 250 A/m2 for the device on PET was approximately 0.9%, which is higher than that (approximately 0.5%) for the device on glass. The reduction in the driving voltage and high external quantum efficiency made an ITO coated PET substrate very promising for future large scale OLED application.
Transparent and highly conducting zirconium-doped indium oxide (ZIO) thin films have been grown by pulsed laser deposition (PLD) on glass substrates without a post- deposition anneal. The structural, electrical and optical properties of these films were investigated as a function of film composition and substrate deposition temperature. Films were deposited using a KrF excimer laser (248 nm, 30 ns FWHM) at a fluence of 1 J/cm2 at growth temperatures ranging from 20 degrees Celsius to 400 degrees Celsius in oxygen pressure ranging from 1 mTorr to 25 mTorr. The films (approximately 2000 angstrom thick) deposited at 200 degrees Celsius in 25 mTorr of oxygen show electrical resistivities as low as 2.7 X 10-4 (Omega) -cm, the average visible transmittance of 89%, the refractive index of 1.99 and optical band gap of 4.1 eV. These ZIO films were used as a transparent anode contact in organic light emitting diodes (OLEDs) and the device performance was studied. The external quantum efficiency measured at 100 A/m2 for the [ZIO/TPD/Alq3/MgAg] diodes was about 0.9%. Low driving voltage and high light emission were observed for the OLEDs with the ZIO anode.
A novel laser-based direct-write technique, called Matrix Assisted Pulsed Laser Evaporation Direct Write (MAPLE-DW), has been developed for the rapid prototyping of electronic devices. MAPLE-DW is a maskless deposition process operating under ambient conditions which allows for the rapid fabrication of complex patterns of electronic materials. The technique utilizes a laser transparent substrate with one side coated with a matrix of the materials of interest mixed with an organic vehicle. The laser is focused through the transparent substrate onto the matrix coating which aids in transferring the materials of interest to an acceptor substrate placed parallel to the matrix surface. With MAPLE-DW, diverse materials including metals, dielectrics, ferroelectrics, ferrites and polymers have been transferred onto various acceptor substrates. The capability for laser-modifying the surface of the acceptor substance and laser-post-processing the transferred material has been demonstrated as well. This simple yet powerful technique has been used to fabricate passive thin film electronic components such as resistors, capacitors and metal lines with good functional properties. An overview of these key results along with a discussion of their materials and properties characterization will be presented.
Transparent conducting indium tin oxide (ITO) thin films were grown by pulsed laser deposition (PLD) on glass substrates. The structural, electrical and optical properties of these films were investigated as a function of film thickness. Films were deposited using a KrF excimer laser at a fluence of 2 J/cm2, at substrate temperature of 300 degrees C and 10 mTorr of oxygen pressure. For ITO films deposited at 300 degrees C in 10 mTorr of oxygen pressure, the resistivity of 2-4 X 10-4 (Omega) - cm was observed and the average transmission in the visible range was about 85-90 percent. The Hall mobility and carrier density for ITO films were observed to be in the range of 24-27 cm2/V-s and 5-9 X 1020 cm-3, respectively. We have used the ITO thin films, deposited by PLD on silica substrates, as the anode contact in organic light emitting devices and studied the effect of ITO film thickness on the device performance. The optimum thickness of the ITO anode for the maximum device efficiency was observed to be about 500-1000 angstrom. The device shoed an external quantum efficiency of about 0.8 percent at 100 A/m2.
MAPLE direct write is anew laser-based direct write technique which combines the basic approach employed in laser induced forward transfer with the unique advantages of matrix assisted pulsed laser evaporation. The technique utilizes a laser transparent donor substrate with one side coated with a matrix consisting of the electronic material to be transferred mixed with an organic binder or vehicle. As with LIFT, the laser is focused through the transparent substrate onto the matrix coating. When a laser pulse strikes the coating, the matrix is transferred to an acceptor substrate placed parallel to the donor surface. Ex situ thermal or laser treatments can be used to decompose the matrix and anneal the transferred material, thus forming structures with the desired electronic properties. MAPLE DW is a maskless deposition process designed to operate in air and at room temperature that allows for the generation of complex patterns with micron scale linewidths. The various structures produced by MAPLE DW were characterized using 3D surface profilometry, scanning electron microscopy and optical microscopy. The electrical resistivity of the silver metal lines made by MAPLE DW was measured using an impedance analyzer. Patterns with Zn2SiO4:Mn powders were fabricated over the surface of a dragon fly wing without damaging it. An overview of the key elements of the MAPLE DW process including our current understanding of the material transfer mechanisms and its potential as a rapid prototyping technique will be discussed.
Two transparent conducting oxides (TCO) thin films including tin-doped indium oxide (ITO) and aluminum-doped zinc oxide (AZO) were grown on glass substrates by pulsed laser deposition (PLD). The structural, electrical and optical properties of these films were investigated as a function of target composition and film growth temperature. Films were deposited using a KrF excimer laser (248 nm, 30 ns FWHM) at a fluence of 2 J/cm2 at growth temperatures ranging from 25 degrees Celsius to 400 degrees Celsius in oxygen pressures ranging from 1 to 100 mTorr. For a 300 nm thick ITO film deposited at 300 degrees Celsius in oxygen pressure of 10 mTorr, the resistivity was 2 X 10-4 (Omega) -cm and the average transmission in visible range (400 - 700 nm) was 85%. The Hall mobility and carrier density for a 150 nm thick ITO film deposited at 300 degrees Celsius were 27 cm2/V-s and 1.4 X 1021 cm-3, respectively. For a 100 nm thick AZO film deposited at 200 degrees Celsius in an oxygen pressure of 5 mTorr, the resistivity was 3.8 X 10-4 (Omega) -cm and the average transmission in visible range (400 - 700 nm) was 90%. The Hall mobility and carrier density for the same AZO film were 18 cm2/V-s and 9.1 X 1020 cm-3, respectively. AFM measurements indicated that the RMS surface roughness of the ITO films (approximately 5 angstrom) was slightly lower than that of the AZO films (approximately 7 angstrom). XPS measurements showed that the work function of ITO films grown at 250 degrees Celsius was 4.51 plus or minus 0.05 eV, which is higher than that (4.05 plus or minus 0.05 eV) of the AZO films grown at 200 degrees Celsius. The PLD ITO films were used to fabricate organic light-emitting diodes (OLEDs). The electroluminescent (EL) performance was measured and the luminous power efficiency was calculated to be 0.6 lm/W, which is comparable to that measured with commercially available sputter-deposited ITO anodes.
A novel approach for maskless deposition of numerous materials has been developed at the Naval Research Laboratory. This technique evolved from the combination of laser induced forward transfer and Matrix Assisted Pulsed Laser Evaporation (MAPLE), and utilizes a computer controlled laser micromachining system. The resulting process is called MAPLE-DW for MAPLE Direct Write. MAPLE-DW can be used for the rapid fabrication of circuits and their components without the use of masks. Using MAPLE-DW, a wide variety of materials have been transferred over different types of substrates such as glass, alumina, plastics, and various types of circuit boards. Materials such as metals, dielectrics, ferrites, polymers and composites have been successfully deposited without any loss in functionality. Using a computer controlled stage, the above mentioned materials were deposited at room temperature over various substrates independent of their stage, the above mentioned materials were deposited at room temperature over various substrates independent of their surface morphology, with sub-10micrometers resolution. In addition, multilayer structures comprising of different types of materials were demonstrated by this technique. These multilayer structures from the basis of prototype thin film electronics devices such as resistors, capacitors, cross-over lines, inductors, etc. An overview of the result obtained using MAPLE-DW as well as examples of several devices made using this technique is presented.
The effect of spin-polarized injection on the superconductivity order parameter is investigated in a device consisting of YBa2Cu3O7-(delta )/Au/Ni0.8Fe0.2 layers. A non-equilibrium theory which qualitatively agrees with the results of measurements made on superconductor/insulator/ferromagnet structures is presented. A quantitative analysis shows that this theory predicts injection currents that are several orders of magnitude too large. Recent results suggest that superconductivity in thin films can be strongly influenced by the injection of a spin- polarized current from a ferromagnetic material. The effect has been found to occur in both low Tc (Sn) and high Tc (YBa2Cu3O7-(delta )) superconductors when either a conventional ferromagnetic metal, permalloy (Ni0.8Fe0.2), or a colossal magnetoresistive material were used as the source of spin polarization. Control experiments showed that unpolarized current from a nonmagnetic metal had comparatively little effect on the same superconductors. A phenomenological model, in which the energy gap of the superconductor is perturbed by the presence of excess spin polarized electrons, has been shown to qualitatively mimic the experimental results. However, an estimate of the current needed to significantly suppress the gap is shown to be several orders of magnitude larger than is observed.
A novel polymer processing technique, matrix assisted pulsed laser evaporation (MAPLE), for the deposition of organic and inorganic polymers and other materials, as ultrathin and uniform coatings has been developed. The technique involves directing a pulsed excimer laser beam onto a frozen matrix target composed of the polymeric material in a solvent. The process gently lifts polymeric material into the gas phase with no apparent decomposition. A plume of material is developed normal to the target, and a substrate positioned incident to this plume is coated with the polymer. The MAPLE technique offers a number of features that are difficult to achieve with other polymer coating techniques, including: nano-meter to micron thickness range, sub monolayer thickness precision, high uniformity, applicability to photosensitive materials, and patterning of surfaces. Highly functionalized polysiloxanes have been synthesized and deposited on a range of substrates by the MAPLE technique and characterized by: infrared spectroscopy, and optical microscopy. High quality, uniform and adherent polysiloxane coatings are produced by the optimized MAPLE technique. The physicochemical properties of the coating are unaffected by the process, and precise thickness control of the coating is straightforward.
Low loss ferroelectric thin films deposited by pulsed laser deposition (PLD) are currently being used to develop a new class of tunable microwave circuits based on the electric field dependence of the dielectric constant. Single phase, (100) oriented Ba0.5Sr0.5TiO3 (BST) films have been deposited onto (100) LaAlO3, SrTiO3, and MgO substrates. Interdigitated capacitors have been used to measure the dielectric constant and dissipation factor of these films as a function of DC bias and temperature at 1 MHz and as a function of DC bias at 1 to 20 GHz at room temperature. A low phase noise voltage controlled oscillator is currently being developed for use at frequencies from 1 - 20 GHz. To achieve low phase noise in the oscillator will require the loss tangent in the ferroelectric to be <EQ 5 X 10-3. Origins of the dielectric loss are being investigated using optical techniques. Optical imaging of the ferroelectric films using confocal scanning optical microscopy shows reproducible polarization fluctuations over sub-micrometer length scales for BST films deposited onto SrTiO3 which are not observed for films deposited onto MgO. Dielectric loss in the ferroelectric film is reduced through a combination of post deposition processing and donor/acceptor doping of the films. The lowest dielectric loss measured at microwave frequencies (tan(delta) equals 0.01 at 1 - 10 GHz) has been in a post-deposition annealed Ba0.5Sr0.5TiO3 film doped with approximately 1 - 2 atomic % Mn.
Pulsed laser deposition has been used for the growth of high quality YBa2Cu3O7 and La0.67Sr0.33MnO3 thin films and multilayers for electronic device applications. In particular, YBa2Cu3O7 - (SrTiO3, CeO2) - La0.67Sr0.33MnO3 trilayer devices were fabricated to study the supercurrent suppression by the injection of a spin-polarized quasiparticle current. Our results show that the critical current for a YBa2Cu3O7 - 50 angstroms SrTiO3 - La0.67Sr0.33MnO3 device was found to decrease from 120 mA to 15 mA, for an injection current of 60 mA of spin polarized current yielding a negative current gain of approximately 1.8. The effect of film microstructure on the critical current suppression was investigated. Defects in the SrTiO3 and CeO2 layers were found to control the device properties. Once optimized, spin injection represents a new approach to fabricating superconducting transistors which could impact electronic systems for many important next generation.
High quality thin films of SrxBa(1-x)TiO3 are currently being grown using pulsed laser deposition (PLD). These films are being used for the construction of frequency tunable microwave electronic devices. In particular, a low phase noise, voltage controlled oscillator (1.5 - 2.5 GHz) is currently being developed. Single phase and oriented SrxBa(1-x)TiO3 films have been deposited by PLD onto (100) LaAlO3 and MgO and single crystal Ag films. The dielectric properties of these films has been measured at 1 MHz and between 1 and 20 GHz. A 75% change in the capacitance can be achieved using a 40 V bias across a 5 micrometer interdigital capacitor gap (80 kV/cm). The dissipation factor (measured at 1 MHz) depends on film composition and temperature. Dielectric loss measurement at 1 - 20 GHz have shown a dielectric loss tangent as small as 1.25 multiplied by 10-2.
Pulsed laser deposition (PLD) has been used to deposit high quality thin films of Ni81Fe19/Au/YBa2Cu3O7- (delta ) onto (100) oriented substrates of MgO and SrTiO3 for the purpose of fabricating a novel high temperature superconducting three terminal device. The ferromagnet-normal metal-superconductor (F-N-S) structure is currently being investigated to determine the effect of the injection of a spin-polarized current on the order parameter of a high temperature superconducting thin film. High quality films with sharp interfaces, free of defects, are required in order to maximize the spin-injection effect. The surface morphology and transport properties of the YBa2Cu3O7-(delta ) films have been investigated using scanning electron microscopy and ac susceptibility measurements, respectively, as a function of increasing laser fluence. Deposition at 2.0 - 2.4 J/cm2, 790 degrees Celsius and 320 m Torr O2 produces films with a sharp superconducting transition and a smooth surface. The growth of Au on YBCO under different PLD conditions has been observed by atomic force microscopy. Surface clustering of Au occurs at elevated temperatures and is attributed to increased surface mobility. The presence or absence of a background gas influences the cluster size. These results are discussed within the framework of the role of excess energy of PLD adatoms with changing laser fluence and background gas.
James Horwitz, Paul Dorsey, N. Koon, M. Rubinstein, J. Byers, D. Gillespie, Michael Osofsky, V. Harris, K. Grabowski, D. Knies, Edward Donovan, Randolph Treece, Douglas Chrisey
The effect of substrate temperature and oxygen deposition pressure on the structure and properties of thin films of LaxCa1-xMnO(delta ) has been investigated. Thin films (approximately 1000 angstroms) of La0.67Ca0.33MnO(delta ) were deposited onto LaAlO3 (100) substrates by pulsed laser deposition at a substrate temperature of 600 and 700 degree(s)C. A series of films were grown on different oxygen pressures, between 15 and 400 mTorr, which systematically changed the oxygen concentrations in the films. As-deposited films exhibited an oriented orthorhombic structure. At low oxygen deposition pressures films were preferentially (202) oriented. At high pressures deposited films had a (040) preferred orientation. A 900 degree(s)C anneal in flowing oxygen of a film deposited at low oxygen pressure resulted in a decrease in the a lattice parameter and a change in the preferred orientation from (202) to (040). Vacuum annealing at 550 degree(s)C resulted in an increase in the a lattice parameter. The resistivity as a function of temperature showed a significant variation as a function of growth conditions. The peak in the resistivity curve (Tm) varied between 73 and 150 K depending upon the growth conditions. The activation energy associated with the semiconducting phase was approximately the same for all films (approximately 100 meV).
Pulsed laser deposition is a superior technique for the growth of high quality thin films (<EQ 1 micrometers ) of electronic ceramics and has satisfied many applications. To meet developing applications, there is a need for thick films (>= 1 micrometers ) of electronic ceramics. Two film qualities principally control the growth of thick films: the film surface morphology and film stress. The deposition parameters which affect these qualities include: film deposition rate, film-substrate lattice mismatch, film-substrate thermal coefficient of expansion mismatch, and film growth kinetics. Our results suggest that it will be difficult to fabricate thick ceramic films of suitable electronic quality by conventional physical vapor deposition techniques.
We describe the deposition of SrxBa1-xTiO3 (0.5 <EQ x <EQ 0.8) thin films by pulsed laser deposition and the issues related the their application as active microwave device components. The SrxBa1-xTiO3 thin films (approximately equals 5000 angstrom) deposited at 775-850 degree(s)C in 350 mTorr of oxygen onto (100) MgO and LaAlO3 were smooth, single phase, and epitaxial with the underlying substrate. Highly oriented Sr0.5Ba0.5TiO3 films on LaAlO3 with x- ray rocking curves of 72 arc seconds were observed. The dielectric constant of Sr0.5Ba0.5TiO3 thin films, determined from the signal in patterned transmission lines between 100 kHz and 0.1 GHz, was approximately equals 20% of that observed for the bulk and the zero field temperature dependence was broad in comparison to the sharply peaked behavior seen in bulk. The dielectric loss tangent was measured as a function of stoichiometry for SrxBa1-xTiO3 (0.2 <EQ x <EQ 0.8) thin films (3-5 micrometers ) at room temperature and at 9.2 GHz. Loss tangent values were found to be highly sensitive to the Curie temperature of the film. Loss tangent values as low as 0.1% were obtained for Sr0.8Ba0.2TiO3. The results for SrxBa1-xTiO3 thin films presented in this paper are encouraging for future applications in active microwave devices.
The ejection of sub-micron size particulates from a metal target as a result of the interaction of an excimer laser with a Pt target was investigated. To study the effect of laser fluence, particulates were collected on Pt films prepared on MgO(100) substrates over a fluence range of 0.83 - 3.3 J/cm2. Films were prepared at several substrate temperatures: 25 degree(s)C, 350 degree(s)C, 450 degree(s)C, and 550 degree(s)C, and under 0.05 Torr of an inert gas (Ar). It was found that, for a substrate temperature of 450 degree(s)C, the Pt particulates would stick easily to the growing Pt film with little evidence for deformation. The size distributions and areal densities of the metal particulates were measured from low magnification scanning electron micrographs of the thin film surfaces prepared at 450 degree(s)C and compared. In general, spherical particulates were produced with diameters ranging from about 0.05 to 1.0 micrometers . The shape of the size distribution of particulates on the film surface was roughly constant radially outward from the plume center, although the magnitude of the particulates decreased from the plume center. As the fluence increased, the mean diameter of the particulates increased slightly (from 0.25 to 0.35 micrometers ) while the number density of particulates decreased by over two orders of magnitude (from 1.04 X 105 to about 1.0 X 103 particulates/cm2 per angstrom of film deposited) near the plume center.
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