Temperature-sensitive Substrates Research Articles

Structural control of carbon nickel nano-composite thin films without substrate heating

A variety of characterization techniques have been employed to study the growth and structure of carbon nickel thin films fabricated by ionised magnetron sputter deposition. A two target magnetron system is used along with an RF powered coil to create a secondary plasma, with a DC bias applied at the substrate. By varying the substrate bias it is possible to control the flux and energy of the depositing species and therefore the resulting film microstructure. Films typically consist of nickel-based nano-particles within a carbon matrix. It has been observed that a change between the metastable hexagonal structure of nickel and the stable face centred cubic phase can be induced. This change in metal crystallinity is accompanied by a change in carbon ordering. The ability to control the film structure and morphology without the need for post-deposition heat treatments opens up the possibility of depositing a range of structures onto temperature sensitive substrates such as polymers.

Solution-processed ZnO nanoparticle-based transistors via a room-temperature photochemical conversion process

We report on zinc oxide (ZnO) nanoparticle-based transistors in which the solution-processed semiconducting layers are post-treated using UV light irradiation instead of high temperature annealing. Field-effect transistors based on these ZnO nanoparticle films exhibit n-channel characteristics with electron mobilities on the order of ∼10−3 cm2 V−1s−1—a value comparable to that obtained from devices thermally annealed at 250 °C. Because of the photochemical nature of the process, the sample temperature during UV irradiation remains low and close to room temperature. This enables facile fabrication of ZnO transistors onto inexpensive, temperature-sensitive substrate materials such as plastic.

Efficient Coupling of Optical Energy for Rapid Catalyzed Nanomaterial Growth: High-Quality Carbon Nanotube Synthesis at Low Substrate Temperatures

The synthesis of high-quality nanomaterials depends on the efficiency of the catalyst and the growth temperature. To produce high-quality material, high-growth temperatures (often up to 1000 °C) are regularly required and this can limit possible applications, especially where temperature sensitive substrates or tight thermal budgets are present. In this study, we show that high-quality catalyzed nanomaterial growth at low substrate temperatures is possible by efficient coupling of energy directly into the catalyst particles by an optical method. We demonstrate that using this photothermal-based chemical vapor deposition method that rapid growth (under 4 min, which includes catalyst pretreatment time) of high-density carbon nanotubes can be grown at substrate temperatures as low as 415 °C with proper catalyst heat treatment. The growth process results in nanotubes that are high quality, as judged by a range of structural, Raman, and electrical characterization techniques, and are compatible with the requirements for interconnect technology.

Room-Temperature ALD of Metal Oxide Thin Films by Energy-Enhanced ALD

Room temperature ALD (RT-ALD) processes are of interest for applications using temperature-sensitive substrates, yet they are not so commonly reported. The challenges associated with RT-ALD arise when surface groups are not sufficiently reactive toward incoming precursors and vice versa, the precursors are not sufficiently volatile, and purge times become impractically long. These challenges can be overcome using energy-enhanced ALD. We demonstrate here viable energy-enhanced RT-ALD (25 °C) processes for Al2O3 and SiO2 from trimethylaluminium (TMA) and bis(diethylamino)silane (SAM.24) precursors, enabled using an O2 plasma or ozone as co-reactants. Saturated ALD growth was obtained at room temperature for the TMA/O2 plasma, TMA/ozone, and SAM.24/O2 plasma processes, whereas the SAM.24/ozone RT-ALD process gave no growth. Using these results, the essential and desirable criteria that are necessary to obtain a viable RT-ALD process are discussed.

Post-fabrication, in situ laser reduction of graphene oxide devices

We report on post-fabrication, in situ, laser induced reduction of graphene oxide (GO) field effect transistors. Our one-step method is efficient, fast, and elevates the conductivity of GO transistor channels by two orders of magnitude. Compared to other reduction techniques, it is facile and simple since it does not require any stringent experimental conditions. Most importantly, we show here that it can be applied for, in situ, post-fabrication reduction of GO devices without compromising any of its components. The physical properties of the laser-reduced graphene oxide were assessed by micro-Raman and X-ray photoelectron spectroscopy analysis and the electrical properties by electric field effect measurements. The application of this technique in other graphene-based optoelectronic devices, especially those fabricated on inexpensive and temperature sensitive flexible substrates such as plastic, is envisaged.

Atomic layer deposition: medical and biological applications

Atomic layer deposition (ALD) is being used for deposition of conformal thin films on a variety of materials, including medical device materials and biologically derived materials. This review describes thin film deposition on materials using ALD for bioelectronic device, implantable device, biosensor, drug delivery device, tissue engineering scaffold and bioassay device applications. Recent advances in ALD technology, including low temperature ALD of thin films on temperature sensitive substrates, are considered. Finally, translation of ALD to commercial use, including use of ALD by the medical device industry, is described.

Low temperature processing of redispersed tin doped indium oxide nanoparticle coatings

The deposition of transparent conducting oxide (TCO) coatings using for example chemical vapor deposition, spray pyrolysis or a conventional sol–gel routine usually needs high temperatures and is therefore only applicable to temperature-stable substrates like glass. The deposition of TCO coatings on temperature-sensitive substrates requires low-temperature deposition processes like redispersed nanoparticle suspensions combined with e.g. the dip-coating technique. To obtain a tin doped indium oxide (ITO) nanoparticle suspension for the coating process, ITO nanopowder is redispersed in a mixture of solvents, cross-linking agents and stabilizers. In this work it is shown that four different stabilizers and mixtures of these stabilizers can be used and how the choice of the stabilizers influences the properties of the coatings concerning the reflectance of the surface, the layer composition, that means the porosity and the surface roughness of the layers, and the electrical conductivity.

UHF Electromagnetic Structures Inkjet Printed on Temperature Sensitive Substrates: a Comparative Study of Conductive Inks and Sintering Methods to Enable Low Cost Manufacture

UHF Electromagnetic Structures Inkjet Printed on Temperature Sensitive Substrates: a Comparative Study of Conductive Inks and Sintering Methods to Enable Low Cost Manufacture

Transfer of highly porous nanoparticle layers to various substrates through mechanical compression

A new two-step layer transfer process is introduced that is capable of fabricating mechanically stabilized highly porous nanoparticle layers on various substrates. In a first step titanium dioxide nanoparticles were synthesized with Flame-Spray-Pyrolysis and accumulated on a filter paper in the gas phase. In a second step this highly porous filter cake is subsequently transferred to a final substrate via low pressure lamination at room temperature. This leads to mechanical restructuring and stabilization of the porous layer. Pore size analysis indicates homogenization of the layers through rearrangement of the aggregates inside the layers that increases with applied pressure. Additionally, the Young's moduli of the layers were quantified through Colloidal-Probe-Technique indentation measurements with an Atomic-Force-Microscope. The highest lamination pressure of 2.5 MPa resulted in triplication of the Young's modulus. The results show that our novel two-step layer transfer process leads to mechanically stabilized layers that preserve their high porosity. Through the decoupling of the high temperature nanoparticle synthesis and the final substrate the process also enables the possibility to apply temperature sensitive substrates such as polypropylene foil.

Photonic flash sintering of silver nanoparticle inks: a fast and convenient method for the preparation of highly conductive structures on foil

Abstract

Enhanced Electrical Conductivity of Silver Nanoparticles for High Frequency Electronic Applications

An enhancement in the electrical performance of low temperature screen-printed silver nanoparticles (nAg) has been measured at frequencies up to 220 GHz. We show that for frequencies above 80 GHz the electrical losses in coplanar waveguide structures fabricated using nAg at 350 °C are lower than those found in conventional thick film Ag conductors consisting of micrometer-sized grains and fabricated at 850 °C. The improved electrical performance is attributed to the better packing of the silver nanoparticles resulting in lower surface roughness by a factor of 3. We discuss how the use of silver nanoparticles offers new routes to high frequency applications on temperature sensitive conformal substrates and in sub-THz metamaterials.

Low temperature diamond growth by linear antenna plasma CVD over large area

AbstractRecently, there is a great effort to increase the deposition area and decrease the process temperature for diamond growth which will enlarge its applications including use of temperature sensitive substrates. In this work, we report on the large area (20 × 30 cm2) and low temperature (250 °C) polycrystalline diamond growth by pulsed linear antenna microwave plasma system. The influence of substrate temperature varied from 250 to 680 °C, as controlled by the table heater and/or by microwave power, is studied. It was found that the growth rate, film morphology and diamond to non‐diamond phases (sp3/sp2 carbon bonds) are influenced by the growth temperature, as confirmed by SEM and Raman measurements. The surface chemistry and growth processes were studied in terms of activation energies (Ea) calculated from Arrhenius plots. The activation energies of growth processes were very low (1.7 and 7.8 kcal mol−1) indicating an energetically favourable growth process from the CO2CH4H2 gas mixture. In addition, from activation energies two different growth regimes were observed at low and high temperatures, indicating different growth mechanism.

Growth Pathways in Ultralow Temperature Ge Nucleation from Au

Device integration on flexible or low-cost substrates has driven interest in the low-temperature growth of semiconductor nanostructures. Using in situ electron microscopy, we examine the Au-catalyzed growth of crystalline Ge at temperatures as low as 150 °C. For this materials system, the model for low temperature growth of nanowires, we find three distinct reaction pathways. The lowest temperature reactions are distinguished by the absence of any purely liquid state. From measurements of reaction rates and parameters such as supersaturation, we explain the sequence of pathways as arising from a kinetic competition between the imposed time scale for Ge addition and the inherent time scale for Ge nucleation. This enables an understanding of the conditions under which catalytic Ge growth can occur at very low temperatures, with implications for nanostructure formation on temperature-sensitive substrates.

Solution-processible electrode materials for a heat-sensitive piezoelectric thin-film sensor

Piezoelectric sensors are needed in a wide range of applications from physiological measurement applications to industrial monitoring systems. Custom-designed, highly integratable and cost-effective sensor elements can be manufactured by using flexible materials in combination with high-throughput printing for fabrication. This would also enable the embedding of ubiquitous sensors in our living environment to improve the common welfare. Here, we have fabricated flexible piezoelectric sensor elements using printing methods. We demonstrated that alternative, printable electrode materials are compatible with temperature-sensitive functional substrates. Low-temperature curable electrodes were printed on both sides of unmetallized, polyvinylidene fluoride film. Various solution-processible materials – for example, carbon nanotube–cellulose composite, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate), carbon ink and silver flake ink – were used. DC sheet resistances of the electrodes and sensitivities of the sensor elements were measured. Sheet resistance varied from 10−1 to 106Ω/□ and sensitivities varied from 23 to 29pC/N. Evaporated metal electrodes as well as commercially available sensor elements were used as reference sensors. The sensing capability of printed sensors was quite insensitive to the sheet resistance of the electrodes. Further, the electrode conformation was studied by microscopy; reliability of the sensors was studied by vibration tests. In addition, sensors were tested for measuring physiological signals.

Use of single-wall carbon nanohorns as counter electrodes in dye-sensitized solar cells

The catalytic activity of single-wall carbon nanohorns (SWNH) as counter electrodes (CE) of dye-sensitized solar cells (DSC) was studied for the iodide/triiodide redox reaction. The catalytic activities of SWNH and high surface SWNH (HS-SWNH) obtained by partial oxidation of SWNH were assessed based on charge-transfer resistances (Rct) and current–voltage curves. A half-cell configuration was used, and CE performances were compared to CEs made of carbon black (CB) and Pt. A CE assembled with HS-SWNH and mixed with 10 wt.% of hydroxyethyl cellulose (HEC) - HS-SWNH/HEC was found to have the highest electrocatalytic activity (lowest Rct) among all the carbon-based CEs tested when annealed at 180 °C (Rct = 141 Ω cm2); however, a very thick film (several tens of µm) would be required in order to perform comparably to a Pt CE. The annealing of such CE at higher temperatures (above 400 °C) did not improve its catalytic activity, contrary to the other studied carbonaceous CEs. The redox catalytic activity of SWNH and HS-SWNH decorated with Pt was also studied on a half-cell configuration and compared to that of Pt/CB and pristine Pt. The Pt/SWNH/HEC CE showed the highest electrocatalytic activity per mass of Pt, needing just 50% of Pt load to yield the same electrocatalytic activity of a DSC equipped with a Pt CE, but having half of its transparency. Additionally, applications in temperature-sensitive substrates are envisioned for the Pt/SWNH/HEC CE due to the use of lower annealing temperatures. Copyright © 2012 John Wiley & Sons, Ltd.

Closed-loop control of laser assisted chemical vapor deposition growth of carbon nanotubes

Laser-assisted chemical vapor deposition growth is an attractive mask-less process for growing locally aligned nanotubes in selected places on temperature sensitive substrates. An essential parameter for a successful and reproducible synthesis of nanotubes is the temperature during growth. Here, we demonstrate a temperature feedback control mechanism based on the dynamic, in situ monitoring of the infrared radiation coupled with reflectivity information. With the information provided by these sensors, an infrared laser, focused on a silicon substrate covered with aluminum-oxide and iron catalyst layers, can be controlled. The growth takes place in a gaseous mixture of argon (carrier gas), hydrogen (process gas), and ethylene (carbon-containing gas). Scanning electron microscopy and Raman spectroscopy analysis demonstrate the excellent reproducibility of the closed-loop control process over multiple experiments. Furthermore, we developed a unique method to identify the onset for catalyst formation and activation by monitoring the fluctuation of the reflected laser beam.

Efficient laser induced consolidation of nanoparticulate ZnO thin films with reduced thermal budget

Layers of ZnO nanoparticles with thicknesses of about 40 nm were prepared on Si substrates. It was shown that UV laser irradiation is suitable for consolidation and significant densification of the ZnO particle layers under ambient conditions. Both experiments and simulations show that an underlying SiO2 particle layer has a beneficial effect in inhibiting heat transfer towards the substrate and thus enables the application of temperature-sensitive carrier substrates like polymer foils despite the extremely high melting temperature of ZnO.

Identification of Mammalian Protein Quality Control Factors by High-Throughput Cellular Imaging

Protein Quality Control (PQC) pathways are essential to maintain the equilibrium between protein folding and the clearance of misfolded proteins. In order to discover novel human PQC factors, we developed a high-content, high-throughput cell-based assay to assess PQC activity. The assay is based on a fluorescently tagged, temperature sensitive PQC substrate and measures its degradation relative to a temperature insensitive internal control. In a targeted screen of 1591 siRNA genes involved in the Ubiquitin-Proteasome System (UPS) we identified 25 of the 33 genes encoding for 26S proteasome subunits and discovered several novel PQC factors. An unbiased genome-wide siRNA screen revealed the protein translation machinery, and in particular the EIF3 translation initiation complex, as a novel key modulator of misfolded protein stability. These results represent a comprehensive unbiased survey of human PQC components and establish an experimental tool for the discovery of genes that are required for the degradation of misfolded proteins under conditions of proteotoxic stress.

Three dimensional ZnO nanostructures realized through a polymer mediated aqueous chemical route: candidate for transparent flexible electronics

A brand new three dimensional zinc oxide nanosheet array was developed through manipulating its crystal growth habits with the anionic polymer, polysodium 4-styrene sulfonate (PSS). Along with being low cost, the process separates itself from other nanosheet array production protocols not only in its unique hierarchical assembly but as it is also devoid of any post-growth high temperature pyrolysis thus offering the opportunity to integrate devices over temperature sensitive substrates. Efficient electron emissions with low operating fields (turn-on field 3.5 V μm−1) are registered from the transparent field emitter based on three dimensional nanosheet assemblies on polymeric substrates and it can preserve its high performance even in a bended state. UV photodetectors based on the same material exhibit photocurrent gains as high as 1.95 × 105 which is 42 times higher when compared to nanowires and this is attributable to the much higher surface area; even after 100 consecutive bending cycles the detector performance degradation is negligible. This study will motivate the development of new morphologies in chemical synthesis routes employing polymers as growth modifiers.

Piezoresistivity of polycrystalline silicon applying the AIC process-route

Piezoresistors of polycrystalline silicon were obtained by the aluminum induced crystallization (AIC) process-route. Tri-layer samples with the layer sequence Si/Al/Si were deposited by means of e-beam evaporation. The Si layer thickness was held constant at 300 nm, whereas the Al thickness was varied between 25 and 125 nm. The annealing was performed in vacuum at temperatures between 330 and 660 °C for up to 6 h. The piezoresistors exhibit gauge factors ( GFs) of 4.5 up to 17, with temperature coefficients of resistance ( TCR) between −0.4 and −0.1%/K and temperature coefficients of GF ( TCGF) between −0.1 and 0.4%/K. These values depend on the annealing conditions applied and the Al layer thickness of the sample. Complementary measurements on a bi-layer system of Al/Si = 300 nm/300 nm were performed after annealing under vacuum conditions and a subsequent wet-etch removal of the Al top-layer. GFs up to 24, TCRs of −0.4 to −0.2%/K, and TCGFs of −0.2 to 0.2%/K were determined for these samples. As piezoresistive AIC-silicon is obtained using much lower process temperatures, compared to common high temperature processes, the process route presented becomes interesting for sensor applications on temperature sensitive substrates.