Metal nanocrystal memory with sol-gel derived HfO2 high-κ tunnel oxide

An all-solution processed metal-oxide-semiconductor (MOS) capacitor structure containing gold (Au) nanoparticles (NPs) within HfO₂ high-κ oxide was fabricated. The ultra-thin (~ 10 nm) HfO₂ high-κ tunnel oxide layer was prepared by sol-gel process and showed good electrical properties, which were critical to superior memory property of the MOS structure. Au NPs with particle size of about 3.3 nm were synthesized by chemical reduction method and then self-assembled onto HfO₂ tunnel oxide. Finally, a Si/HfO₂/Au NPs/HfO₂ memory structure was constructed after the substrate had been covered with a sol-gel-derived HfO₂ control oxide layer (~ 13 nm). By utilizing high-quality HfO₂ as tunnel oxide, the MOS structure containing Au NPs showed memory effect even at a low voltage of ± 3 V. Although its memory window was only 0.8 V by a swapping voltage between ± 5 V, the MOS showed desirable retention characteristics. Therefore, we have fabricated nanocrystal memory device with sol-gel derived HfO₂ high-k tunnel oxide which are attractive for low operation voltage non-volatile memory applications.     

Flexible electrochromic devices based on crystalline WO3 nanostructures produced with hot-wire chemical vapor deposition

Crystalline WO₃ nanoparticles are employed in the development of flexible electrochromic (EC) devices. The nanoparticles are synthesized at high-density with a hot-wire chemical vapor deposition process where the hot filament provides the source of the tungsten metal. Polyethylene terephthalate coated with indium tin oxide is employed as a transparent flexible substrate. A simple electrophoresis technique is employed to deposit the WO₃ nanoparticles on the polymer, resulting in a uniform thin film. The EC performance is optimized for WO₃ particles that were baked at ~ 300 °C for 2 h prior to electrode fabrication. The transmittance is modulated between ~ 94% and ~ 28% without degradation for 100 cycles.     

Synthesis of nano-TiC powder using titanium gel precursor and carbon particles

The paper presents a novel process for synthesis of nano-size titanium carbide by reaction between titanium bearing precursor gel and nano carbon particles derived from soot at different temperatures in the range of 1300-1580 °C for 2 h under argon cover. The HRTEM studies of TiC powder synthesized by heating at 1580 °C show the presence of cube shaped particles (~ 60-140 nm) and hollow rods (diameter ~ 30-185 nm). The average particle size of crystallites, calculated by Scherer equation is observed to be ~ 35 nm while the surface area-density measurements indicate it to be ~ 113 nm. The surface area decreases with increase in reaction temperature.     

Synthesis of cube-shaped gold nanostructures by electron irradiation

The needle-like gold nanostructures were synthesized by using chloroauric acid (HAuCl₄) as a metal precursor and sodium borohydride (NaBH₄) as the reducing agent. These needle-like nanostructures of gold were irradiated with high energy electrons (E ~ 6 MeV, ? ~ 10¹² e cm⁻² s⁻¹). The pre- and post-irradiated gold nanostructures were characterized by Scanning Electron Microscopy (SEM), UV-vis spectroscopy, X-ray Diffraction (XRD) and contact angle measurement (GBX-Model Digidrop) techniques. The results of the SEM revealed that after electron irradiation, the needle-like gold structures got fragmented into identical cube-shaped gold nanostructures, though of different sizes. The XRD analysis indicated that the average crystallite size of the gold nanostructures remained unchanged even after irradiation with high energy electrons. A glass surface showed hydrophilic behavior when coated with needle-like nanostructures and became ultra hydrophilic when coated with cube-shaped gold nanostructures.     

Doping optimization and surface modification of aluminum doped zinc oxide films as transparent conductive coating

Aluminum doped zinc oxide (ZnO:Al) films were grown using spray pyrolysis technique. Effect of doping on structural, electrical, optical and morphological properties was studied. Aluminum doping improved the prominence of [002] growth while maintaining the grain size ~ 48 nm. Using an intermediate Al/Zn atomic ratio in precursor (1.5:100), we could achieve a low resistivity ρ ~ 7 × 10^− 4 Ωcm. These films possessed an average visible transmittance ~ 88%, an optical gap ~ 3.7 eV and plasma wavelength at 1.87 μm. A simultaneous use of methanol and iso-propanol in the precursor lead to a moderate surface roughness ~ 12 nm. The films were surface modified using wet chemical etching in diluted hydrochloric acid, for varied time intervals (5 s-15 s) and etchant concentrations (0.125%-1%). The etching experiments could be used to know the building of the film as also to modify the surface for desired optical and morphological properties.     

Ellipsometric detection of gases with the surface plasmon resonance effect on gold top-coated with sensitive layers

An ellipsometric gas sensor based on the surface Plasmon resonance (SPR) effect of ~ 43 nm thick gold layers was investigated. To protect the gold layer from contamination and to improve the detection limits, the gold layers were top-coated with 5-6 nm thick layers of organic a-C:H or with inorganic metal oxides TiO₂ or ZrO₂. The additional layers increased the long-term stability, whereas the metal oxide layers protect better than a-C:H. Furthermore, the additional layers decreased the detection limits by one order of magnitude in case of a-C:H and two orders of magnitude in case of the oxides. It could be shown that the detection limits also depend on the kind of preparation (sol-gel process or physical vapour deposition) of the additional layers.     

Tensile strain and water vapor transport testing of flexible, conductive and transparent indium-zinc-oxide/silver/indium-zinc-oxide thin films

Thin film laminates composed of sputtered indium zinc oxide and silver, optimized for conductance and transparency, were tested for water vapor permeation as well as mechanical durability in tension. The ~ 82 nm thick optimized indium-zinc-oxide/silver/indium-zinc-oxide (IZO/Ag/IZO) films were > 80% transparent in the visible range (400 nm-700 nm) with measured sheet resistances less than 5 Ω/sq. The water vapor permeation measurements using Ca test methods at several temperature/ humidity conditions indicated that the addition of the thin Ag layer provided little improvement relative to a single indium-zinc-oxide (IZO) layer of similar thickness. However, the critical strain in bending tests for IZO/Ag/IZO films was improved compared to IZO films. The modulus (E ~ 113 GPa), hardness (H ~ 7 GPa), fracture toughness (K_IC ~ 1.1 MPa⋅m^0.5), and interfacial shear (“adhesion”) (τ_c ~ 16 MPa) of/related to IZO, and measured by nanoindention are consistent with other brittle ceramic thin film materials.     

Ultrathin TaOx film based photovoltaic device

Application of the economical metal oxide thin-film photovoltaic devices is hindered by the poor energy efficiency. This paper investigates the photovoltaic effect with an ultrathin tantalum oxide (TaOx) tunnel barrier, formed by the plasma oxidation of a pre-deposited tantalum (Ta) film. These ~ 3 nm TaOx tunnel barriers showed approximately 160 mV open circuit voltage and 3-5% energy efficiency, for varying light intensity. The ultrathin TaOx (~ 3 nm) could absorb approximately 12% of the incident light radiation in 400-1000 nm wavelength range; this strong light absorbing capability was found to be associated with the dramatically large extinction coefficient. Spectroscopic ellipsometry revealed that the extinction coefficient of 3 nm TaOx was ~ 0.2, two orders higher than that of tantalum penta oxide (Ta₂O₅). Interestingly, refractive index of this 3 nm thick TaOx was comparable with that of stochiometeric Ta₂O₅. However, heating and prolonged high-intensity light exposure deteriorated the photovoltaic effect in TaOx junctions. This study provides the basis to explore the photovoltaic effect in a highly economical and easily processable ultrathin metal oxide tunnel barrier or analogous systems.     

Thin film transistors by solution-based indium gallium zinc oxide/carbon nanotubes blend

Solution-based indium gallium zinc oxide (IGZO)/single-walled carbon nanotubes (SWNTs) blend have been used to fabricate the channel of thin film transistors (TFTs). The electrical characteristics of the fabricated devices were examined. We found a low leakage current and a higher on/off currents ratio for TFT with SWNTs compared to solution-based TFTs made without SWNTs. The saturation field effect mobility (μ_sat) of about 0.22 cm²/Vs, the current on/off ratio is ~ 10⁵, the subthreshod swing is ~ 2.58 V/decade and the threshold voltage (V_th) is less than − 2.3 V. We demonstrated that the solution-based blend active layer provides the possibility of producing higher performance TFTs for low-cost large area electronic and flexible devices.     

Effect of grain size on the tensile deformation of wrought Mg-MM-Al-Zn-Sn alloy

The effect of grain size on the tensile deformation of Mg-MM-Al-Zn-Sn (EAZT211) alloy sheet has been investigated. Specimens with grain size varying from ~ 10 to ~ 20 μm have been obtained by altering the annealing conditions after rolling. The yield strength of EAZT211 sheet exhibits grain size dependence according to Hall-Petch relationship from room temperature to 200 °C. Occurrence of yield phenomenon and decrease of Hall-Petch slope (k) with increasing strain suggest that non-basal slip system operates during deformation. In addition, deformation mechanism changes from slip mechanism to grain boundary sliding mechanism at ~ 150 °C.     

Nanoparticle formation by the debris produced by femtosecond laser ablation of silicon in ambient air

The debris produced by femtosecond laser ablation (180 fs, 775 nm, 1 kHz) of Si in ambient air is deposited around the ablated craters in a circular zone with diameters between ~ 40 and 300 μm for laser fluences (F) in the region F = 0.2-8 J/cm². The debris consists of nanoparticles. The mean height of the nanoparticles increases with laser fluence (from ~ 70 to 500 nm for fluences in the range F = 0.25-4.38 J/cm²) but at high fluences (F = 8 J/cm²) becomes equal to ~ 170 nm. The average horizontal dimension of the nanoparticles increases with laser fluence. Their average vertical dimension increases in proportion to their average horizontal dimension, but at high fluences becomes much smaller than their corresponding average horizontal dimension. The nanoparticles were found to be single crystals with d spacing of 1.71 ± 0.08 Å (corresponding to {311}).     

Synthesis of monodisperse gold nanoparticles in ionic liquid by applying room temperature plasma

Sub-atmospheric dielectric barrier discharge (SADBD) plasma was used for the reduction of gold trichloride to synthesize gold nanoparticles. By introducing poly vinyl pyrrolidone (PVP) as a capping agent, the nanoparticle size has been controlled to be ~ 1.7 nm in average with a narrow size distribution. These nanoparticles show enhanced activity and stability for electro-oxidation of methanol.     

Amorphous carbon-silicon heterojunctions by pulsed Nd:YAG laser deposition

Amorphous carbon (a-C) films were deposited at 10^− 4 Pa on n-Si (Si-111) and p-Si (Si-100) substrates using a pulsed Nd:YAG laser with fundamental, second- and third-harmonic outputs. These unhydrogenated and undoped a-C films were characterized by visible and UV Raman spectroscopy which indicated the presence of substantial amount of sp³ hybridized carbon network depending on the laser wavelength. The bulk resistivity in the Au/a-C/indium tin oxide structure varied between (10⁹-10¹³) Ω cm — the lowest resistivity was obtained for films deposited by the fundamental laser output at 1064 nm while the highest value was by the third-harmonic laser output at 355 nm. All the a-C/Si heterostructures exhibited a nonlinear current density-voltage characteristic. Under light illumination, by taking into consideration the fill factor of ~ 0.2 for a-C/n-Si, the conversion efficiency at the highest photovoltage and photocurrent, at an illumination density of 0.175 mW/cm² was estimated to be ~ 0.28%.     

Study on the antimony tin oxide as a hole injection layer for polymer light emitting diodes

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) is commonly used as a hole transfer layer in polymer light emitting diodes (PLEDs). However, Indium tin oxide transparent electrodes are corroded by poly(styrenesulfonate) and the erupted indium diffuses into the active layer, which in turn decreases the brightness, efficiency and lifetime of the device. In this study, therefore, antimony tin oxide (ATO) was introduced as a hole injection layer (HIL) in PLEDs. The work function and pH of ATO were − 5.1 eV and ~ 7.5, respectively. When annealed at 200 °C, high conductivity (~ 0.18 S/cm) was observed, which represents good HIL characteristics. Here, the maximum luminance (26,114 cd/m²) and maximum efficiency (1.55 cd/A) of the PLEDs were increased by 33% and 20% respectively. Their stability improved as well.     

Study of defects and thermal stability of ultrathin Cu films on Ta(110) and Ta(100) by thermal helium desorption spectrometry

Thermal helium desorption spectrometry has been used to study the interaction of helium with defects in Cu films (5-300 Å) deposited on Ta(110) and Ta(100) single crystals by ultrahigh vacuum electron beam evaporation. The thermal stability of the Cu films was also investigated. Cu films on Ta(110) and Ta(100) at room temperature are metastable and on heating, the films transform into islands. The temperature at which this takes place is strongly dependent on the Cu film thickness and for a given thickness (> 40 Å) occurs at a lower temperature on Ta(100) than on Ta(110). The activation energy for island formation is 1.6 ± 0.4 eV for 50 Å Cu/Ta(110) and 0.8 ± 0.1 eV for 100 Å Cu/Ta(100) obtained by Kissinger analysis. The geometry of the Cu islands resulting from annealing 50 Å Cu films at 1000 K for 10 s depends strongly on the Ta substrate orientation. There is evidence for the stressed states of both the Cu films and the Ta substrates. Helium release from monovacancies and vacancy clusters in Cu films (> 75 Å) on Ta(110) and Ta(100) was detected at ~ 750 K and ~ 800-1000 K respectively. The sublimation of the Cu films from the Ta substrates could be observed by the release of retained helium at ~ 1300 K.     

Dielectric properties of (1 − x)(Mg0.95Zn0.05)TiO3-x(Na0.5Nd0.5)TiO3 ceramic system at microwave frequencies

Ceramics in the system (1 − x)(Mg_0.95Zn_0.05)TiO₃-x(Na_0.5Nd_0.5)TiO₃ were prepared by the conventional mixed oxide route. It shows a two-phase system of an ilmenite structured (Mg_0.95Zn_0.05)TiO₃ and a perovskite structured (Na_0.5Nd_0.5)TiO₃, which were confirmed by XRD and EDX. In addition, (Mg_0.95Zn_0.05)Ti₂O₅ was identified as a second phase. It was also responsible for a rapid drop in the Q × f value. The temperature coefficient of resonant frequency was a function of compositional ratio. Specimen with x = 0.16 possessed an excellent combination of microwave dielectric properties: ε_r ~ 24.27, Q × f ~ 82,000 GHz (at 9 GHz) and τ_f ~ 0 ppm/°C.     

Nano-arrays of SAM by dip-pen nanowriting (DPN) technique for futuristic bio-electronic and bio-sensor applications

Nano-arrays of bio-molecules have potential applications in many areas namely, bio-sensors, bio/molecular electronics and virus detection. Spot array, micro-contact printing and photolithography are used for micron size array fabrications while Dip-Pen Nanowriting (DPN) is employed for submicron/nano size arrays. We have fabricated nano-dots of 16-MHA (16-mercaptohexadecanoic acid) self-assembled monolayer (SAM) on gold substrate by DPN technique with different dwell time under varying relative humidity. These patterns were imaged in the same system in LFM (Lateral Force Microscopy) mode with fast scanning speed (5 Hz). The effect of humidity on size variation of nano-dots has been studied. During experiments, relative humidity (RH) was varied from 20% to 60%, while the temperature was kept constant ~ 25 °C. The minimum measured diameter of the dot is ~ 294 nm at RH = 20% for a dwell time of 2 s. The thickness of the 16-MHA dots, estimated in NanoRule image analysis software is ~ 2 nm, which agrees well with the length of single MHA molecule (2.2 nm). The line profile has been used to estimate the size and thickness of dots. The obtained results will be useful in further development of nano-array based bio-sensors and bio-electronic devices.     

Influence of Zr on structure, mechanical and thermal properties of Ti-Al-N

Multinary Ti-Al-N thin films are used for various applications where hard, wear and oxidation resistant materials are needed. Here, we study the effect of Zr addition on structure, mechanical and thermal properties of Ti_1-xAl_xN based coatings under the guidance of ab initio calculations. The preparation of Ti_1-x-zAl_xZr_zN by magnetron sputtering verifies the suggested cubic (NaCl-type) structure for x below 0.6-0.7 and z ≤ 0.4. Increasing the Zr content from z = 0 to 0.17, while keeping x at ~ 0.5, results in a hardness increase from ~ 33 to 37 GPa, and a lattice parameter increase from 4.18 to 4.29 Å. The latter are in excellent agreement with ab initio data. Alloying with Zr also promotes the formation of cubic domains but retards the formation of stable wurtzite AlN during thermal annealing. This leads to high hardness values of ~ 40 GPa over a broad temperature range of 700-1100 °C for Ti_0.40Al_0.55Zr_0.05N. Furthermore, Zr assists the formation of a dense oxide scale. After 20 h exposure in air at 950 °C, where Ti_0.48Al_0.52N is already completely oxidized, only a ~ 1 μm thin oxide scale is formed on top of the otherwise still intact ~ 2.5 μm thin film Ti_0.40Al_0.55Zr_0.05N.     

High sensitivity and wide bandwidth image sensor using CuIn1 − xGaxSe2 thin films

We have fabricated a novel image sensor using Cu(In,Ga)Se₂ (CIGS). A combined process of dry etching using HBr and Ar gasses and wet etching using dilute HCl solution was developed as isolation process of CIGS photodiode deposited at 400 °C. Etchant residues of the dry etching, which consist of Cu complex, were almost completely cleaned using the wet etching process and favorable vertical side wall of CIGS films was obtained without mechanical damages. As a result, high performance image sensors with low leakage current of ~ 10^− 8 A/cm² and wide wavelength range up to ~ 1240 nm were achieved. The developed image sensor consisted of 352 × 288 pixels with 10 µm × 10 µm pixel sizes, was able to capture clear images of night scenes.     

Improved electrical properties of tin-oxide films by using ultralow-pressure sputtering process

The improved structural and electrical properties of tin-oxide films produced by using ultralow-pressure sputtering (ULPS) method are reported. The Hall mobility of the film (~ 13 cm²/V s) deposited using ULPS was about 1.5 times higher than that of the film (~ 8 cm²/V s) sputtered using a pressure of 4.0 × 10^− 1 Pa. As the sputtering pressure was decreased, the film was transformed from an amorphous structure to a nano-crystalline one and gained a stoichiometric SnO₂ composition. These changes in the film structure sufficiently decreased the carrier concentration to facilitate application to thin film transistors.