Selective-Area Atomic Layer Deposition

Atomic layer deposition (ALD) is a method to deposit thin films from gaseous precursors to the substrate layer-by-layer so that the film thickness can be tailored with atomic layer accuracy. Film tailoring is even further emphasized with selective-area ALD which enables the film growth to be controlled also on the substrate surface. Selective-area ALD allows the decrease of a process steps in preparing thin film devices. This can be of a great technological importance when the ALD films become into wider use in different applications. Selective-area ALD can be achieved by passivation or activation of a surface. In this work ALD growth was prevented by octadecyltrimethoxysilane, octadecyltrichlorosilane and 1-dodecanethiol SAMs, and by PMMA (polymethyl methacrylate) and PVP (poly(vinyl pyrrolidone) polymer films. SAMs were prepared from vapor phase and by microcontact printing, and polymer films were spin coated. Microcontact printing created patterned SAMs at once. The SAMs prepared from vapor phase and the polymer mask layers were patterned by UV lithography or lift-off process so that after preparation of a continuous mask layer selected areas of them were removed. On these areas the ALD film was deposited selectively. SAMs and polymer films prevented the growth in several ALD processes such as iridium, ruthenium, platinum, TiO2 and polyimide so that the ALD films did grow only on areas without SAM or polymer mask layer. PMMA and PVP films also protected the surface against Al2O3 and ZrO2 growth. Activation of the surface for ALD of ruthenium was achieved by preparing a RuOX layer by microcontact printing. At low temperatures the RuCp2-O2 process nucleated only on this oxidative activation layer but not on bare silicon.

Substrate-mediated purification and characterization of a 3-hydroxybenzoic acid-6-hydroxylase from Micrococcus

3-Hydroxybenzoic acid-6-hydroxylase from Micrococcus sp. was purified to homogeneity in a single step using the substrate-mediated interaction of the enzyme with blue-Sepharose. The enzyme was bound to the affinity matrix in the presence of 3-hydroxybenzoic acid and was eluted in its absence. The molecular weight of the purified enzyme is 70,000 with no subunit structure. The flavoenzyme required the exogenous addition of FAD for its complete activity and had a strict preference for NADH over NADPH. The activity of the enzyme was drastically inhibited by Cu2+ and Hg2+ and the inhibition was reversed by thiol reagents.

Performance study of a pressure transducer with meandering-path thin film strain gauges

The performance of a pressure transducer with meandering-path thin film strain gauges has been studied. Details of the procedure followed to prepare the thin film strain gauge system on the pressure transducer diaphragm are given. The effect of post-deposition heat treatment on the resistance of the sensing films of the strain gauges and the insulating base layers are discussed. The output of the pressure transducer was studied with various input pressures and excitation voltages. It was found that up to a maximum of 10 V bridge excitation the output was stable and repetitive. The maximum non-linearity and hysteresis observed are ±0.15%, ±0.16% and ±0.14% FSO (full-scale output) for 5, 7.5 and 10 V excitation respectively. Information on the output behaviour of the pressure transducer with temperature is also included.

Detection of a CpA methylase in an insect system: characterization and substrate specificity

A cytosine-specific DNA methyltransferase (EC 2.1.1.37) has been purified to near homogeneity from a mealybug (Planococcus lilacinus). The enzyme can methylate cytosine residues in CpG sequences as well as CpA sequences. The apparent molecular weight of the enzyme was estimated as 135,000 daltons by FPLC. The enzyme exhibits a processive mode of action and a salt dependance similar to mammalian methylases. Mealybug methylase exhibits a preference for denatured DNA substrates.

Effect of substrate temperature on the properties of ZrO2 films prepared by d.c. reactive magnetron sputtering

Studies of ZrO2 films prepared by d.c. reactive magnetron sputtering are described. The effects of substrate temperature on the packing density, refractive index, extinction coefficient and crystallinity phase have been investigated in the temperature range 25–450 °C. The refractive index varied from 1.84 to 1.95 and extinction coefficient from 2 × 10−3 to 9.6 × 10−3. This was explained on the basis of an increase in packing density from 0.686 to 0.813. The change in packing density has been attributed to a decrease in the oxygen condensation at higher temperatures. Annealing results in a decrease in refractive index and increase in extinction coefficient. The films deposited at 150 °C showed a monoclinic phase which transforms to a tetragonal phase at higher substrate temperatures.

A novel laser direct write technique for fabrication of thin film MICs

A technique for fabrication of thin-film circuits for microwave integrated circuit (MIC) application is presented. This low-cost fabrication technique utilizes laser direct write of copper patterns on alumina substrates. The method obviates the need for photomasks and photolithography. The film deposition mechanism, deposit film analysis, and MIC fabrication sequence are presented. Performance evaluation of MICs fabricated using this technique is also included

The roles of nitrification and nitrate reduction pathways in nitrogen cycling of Baltic Sea

The Baltic Sea is one of the largest brackish water bodies in the world. Primary production in the Baltic Sea is limited by nitrogen (N) availability with the exception of river outlets and the northernmost phosphorus limited basin. The excess human induced N load from the drainage basin has caused severe eutrophication of the sea. The excess N loads can be mitigated by microbe mediated natural N removal processes that are found in the oxic-anoxic interfaces in sediments and water column redoxclines. Such interfaces allow the close coupling between the oxic nitrification process, and anoxic denitrification and anaerobic ammonium oxidation (anammox) processes that lead to the formation of molecular nitrogen gas. These processes are governed by various environmental parameters. The effects of these parameters on N processes were investigated in the northern Baltic Sea sediments. During summer months when the sediment organic content is at its highest, nitrification and denitrification reach their maximum rates. However, nitrification had no excess potential, which was probably because of high competition for molecular oxygen (O2) between heterotrophic and nitrification microbes. Subsequently, the limited nitrate (NO3-) availability inhibited denitrification. In fall, winter and spring, nitrification was limited by ammonium availability and denitrification limited by the availability of organic carbon and occasionally by NO3-. Anaerobic ammonium oxidation (anammox) was not an important N removal process in the northern Baltic Sea. Modeling studies suggest that when hypoxia expands in the Baltic Sea, N removal intensifies. However, the results of this study suggest the opposite because bottom water hypoxia (O2< 2 ml l-1) decreased the denitrification rates in sediments. Moreover, N was recycled by the dissimilatory nitrate reduction to ammonium (DNRA) process instead of being removed from the water ecosystem. High N removal potentials were found in the anoxic water column in the deep basins of the Baltic Proper. However, the N removal in the water column appeared to be limited by low substrate availability, because the water at the depths at which the substrate producing nitrification process occurred, rarely mix with the water at the depths at which N removal processes were found. Overall, the natural N removal capacity of the northern Baltic Sea decreased compared to values measured in mid 1990s and early 2000. The reason for this appears to be increasing hypoxia.

Computer modeling studies on the binding of 2',5'-linked dinucleoside phosphates to ribonuclease T1-influence of subsite interactions on the substrate specificity

The modes of binding of Gp(2',5')A, Gp(2',5')C, Gp(2',5')G and Gp(2',5')U to RNase T1 have been determined by computer modelling studies. All these dinucleoside phosphates assume extended conformations in the active site leading to better interactions with the enzyme. The 5'-terminal guanine of all these ligands is placed in the primary base binding site of the enzyme in an orientation similar to that of 2'-GMP in the RNase T1-2'-GMP complex. The 2'-terminal purines are placed close to the hydrophobic pocket formed by the residues Gly71, Ser72, Pro73 and Gly74 which occur in a loop region. However, the orientation of the 2'-terminal pyrimidines is different from that of 2'-terminal purines. This perhaps explains the higher binding affinity of the 2',5'-linked guanine dinucleoside phosphates with 2'-terminal purines than those with 2'-terminal pyrimidines. A comparison of the binding of the guanine dinucleoside phosphates with 2',5'- and 3',5'-linkages suggests significant differences in the ribose pucker and hydrogen bonding interactions between the catalytic residues and the bound nucleoside phosphate implying that 2',5'-linked dinucleoside phosphates may not be the ideal ligands to probe the role of the catalytic amino acid residues. A change in the amino acid sequence in the surface loop region formed by the residues Gly71 to Gly74 drastically affects the conformation of the base binding subsite, and this may account for the inactivity of the enzyme with altered sequence i.e., with Pro, Gly and Ser at positions 71 to 73 respectively. These results thus suggest that in addition to recognition and catalytic sites, interactions at the loop regions which constitute the subsite for base binding are also crucial in determining the substrate specificity.

Diaphragm-type sputtered platinum thin film strain gauge pressure transducer

A diaphragm-type pressure transducer with a sputtered platinum film strain gauge (sensing film) has been designed and fabricated. The various steps followed to prepare thin film strain gauges on the diaphragm are described. M-bond 450 adhesive (Measurements Group, USA) has been employed as the insulating layer. A detailed procedure to cure this layer is given. A d.c. sputtering method is employed to prepare the platinum films. This paper also includes details of the strain gauge pattern and its location on the diaphragm. A description of the output characteristics and overall behaviour of the platinum thin film pressure transducer is reported.

Random sequential multilayer deposition of different‐sized k mers on a one dimensional infinite substrate

Kinetics of random sequential, irreversible multilayer deposition of macromolecules of two different sizes on a one dimensional infinite lattice is analyzed at the mean field level. A formal solution for the corresponding rate equation is obtained. The Jamming limits and the distribution of gaps of exact sizes are discussed. In the absence of screening, the jamming limits are shown to be the same for all the layers. A detailed analysis for the components differing by one monomer unit is presented. The small and large time behaviors and the dependence of the individual jamming limits of the k mers and (k−1) mers on k and the rate parameters are analyzed.

Multilayer Bi1.5Zn1.0Nb1.5O7/Ba0.6Sr0.4TiO3/Bi1.5Zn1.0Nb1.5O7 thin films for tunable microwave applications

Bi1.5Zn1.0Nb1.5O7/Ba0.6Sr0.4TiO3/Bi1.5Zn1.0Nb1.5O7 tunable multilayer thin film has been fabricated by pulsed laser ablation and characterized. Phase composition and microstructure of multilayer films were characterized by X-ray diffraction, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The film has very smooth surface with RMS roughness of 1.5-2nm and grain size of 100-150 nm. Total film thickness has been measure to be 375 nm. The BZN thin films at 300 K, on Pt(1 1 1)/SiO2/Si substrate showed zero-field dielectric constant of 105 and dielectric loss tangent of 0.002 at frequency of 0.1 MHz. Thin films annealed at 700 degrees C shows the dielectric tunability of 18% with biasing field 500 kV/cm at 0.1 MHz. The multilayer thin film shows nonferroelectric behavior at room temperature. The good physical and electrical properties of multilayer thin films make them promising candidate for tunable microwave device applications. (C) 2010 Elsevier B.V. All rights reserved.

Interfaces and traps in pentacene field-effect transistor

The equivalent circuit parameters for a pentacene organic field-effect transistor are determined from low frequency impedance measurements in the dark as well as under light illumination. The source-drain channel impedance parameters are obtained from Bode plot analysis and the deviations at low frequency are mainly due to the contact impedance. The charge accumulation at organic semiconductor-metal interface and dielectric-semiconductor interface is monitored from the response to light as an additional parameter to find out the contributions arising from photovoltaic and photoconductive effects. The shift in threshold voltage is due to the accumulation of photogenerated carriers under source-drain electrodes and at dielectric-semiconductor interface, and also this dominates the carrier transport. The charge carrier trapping at various interfaces and in the semiconductor is estimated from the dc and ac impedance measurements under illumination. (c) 2010 American Institute of Physics. doi: 10.1063/1.3517085]

Pulsed laser deposition film of a donor-acceptor-donor polymer as possible active layer in devices

A molecule having a ketone group between two thiophene groups was synthesized. Presence of alternating electron donating and accepting moieties gives this material a donor-acceptor-donor (DAD) architecture. PolyDAD was synthesized from DAD monomer by oxidative polymerization. Device quality films of polyDAD were fabricated using pulsed laser deposition technique. X-ray photoelectron spectroscopy (XPS) and fourier transform infrared spectra (FTIR) data of both as synthesized and film indicate the material does not degrade during ablation. Optical band gap was determined to be about 1.45 eV. Four orders of magnitude increase in conductivity was observed from as synthesized to pulsed laser deposition (PLD) fabricated film of polyDAD. Annealing of polyDAD films increase conductivity, indicating better ordering of the molecules upon heating. Rectifying devices were fabricated from polyDAD, and preliminary results are discussed.

Instability and dewetting of ultrathin solid viscoelastic films on homogeneous and heterogeneous substrates

Instability and dewetting engendered by the van der Waals force in soft thin (<100 nm) linear viscoelastic solid (e. g., elastomeric gel) films on uniform and patterned surfaces are explored. Linear stability analysis shows that, although the elasticity of the film controls the onset of instability and the corresponding critical wavelength, the dominant length-scale remains invariant with the elastic modulus of the film. The unstable modes are found to be long-wave, for which a nonlinear long-wave analysis and simulations are performed to uncover the dynamics and morphology of dewetting. The stored elastic energy slows down the temporal growth of instability significantly. The simulations also show that a thermodynamically stable film with zero-frequency elasticity can be made unstable in the presence of physico-chemical defects on the substrate and can follow an entirely different pathway with far fewer holes as compared to the viscous films. Further, the elastic restoring force can retard the growth of a depression adjacent to the hole-rim and thus suppress the formation of satellite holes bordering the primary holes. These findings are in contrast to the dewetting of viscoelastic liquid films where nonzero frequency elasticity accelerates the film rupture and promotes the secondary instabilities. Thus, the zero-frequency elasticity can play a major role in imposing a better-defined long-range order to the dewetted structures by arresting the secondary instabilities. (C) 2011 American Institute of Physics. doi: 10.1063/1.3554748]