Nanopatterning of diamond films with composite oxide mask of metal octylates in electron beam lithography

The fabrication of diamond nanopatterns by electron cyclotron resonance (ECR) oxygen plasma with a composite metal octylate mask was investigated using electron beam lithography technology. A high etching selectivity of 14 was obtained with Bi₄Ti₃O₁₂ octylate film as a mask under the plasma-etching conditions of microwave power of 300 W and oxygen gas flow rate of 3 sccm. The metal naphthenates and metal octylates exhibited negative exposure characteristics. The sensitivity of metal naphthenates (1.2×10^–3 C cm^–2) was ten times lower than that of polymethyl methacrylate (PMMA) resist, while that of octylates (8.0×10^–5 C cm^–2) was in good agreement with that of PMMA resist (6.0×10^–5 C cm^–2). The resulting minimum chemical vapor deposited (CVD) diamond line-width of 100 nm with a height of approximately 1 m was fabricated with a Bi₄Ti₃O₁₂ octylate mask.     

Nanoimprint glass-like carbon molds fabricated with ECR oxygen ion beams using polysiloxane oxide mask

We have investigated the nanofabrication for glass-like carbon molds with electron cyclotron resonance oxygen ion beam etching technologies using polysiloxane [-R₂SiO-]_n as an electron beam mask and a room-temperature imprint resist material. The maximum etching selectivity of polysiloxane film against glass-like carbon was 27, which was obtained with ion energy of 400 eV. It was found that the optimum etching time to fabricate dots of 500 nm in height was 5 min, which was explored according to the computer simulation. The glass-like carbon molds with square pole and cylinder dots were fabricated with 500 nm in width and diameter, respectively. The optimum imprinting pressure and its depth obtained after the press for 5 min were 0.5 MPa and 0.5 μm, respectively. We carried out the room-temperature nanoimprint lithography process using glass-like carbon molds. The resulting width of imprinted polysiloxane patterns was obtained in good agreement with that of the mold.     

LEDs (λ<Subscript>max</Subscript> = 3.6 μm) with cone-shaped light-emitting surfaces

A series of light-emitting diodes (LEDs) operating at λ_max = 3.6 μm are created using cone-shaped mesas with heights of 10–130 μm and concave side surfaces. The dependence of the efficiency of room-temperature (T = 298 K) emission on the mesa height at various injection currents has been studied. The character of the observed dependence agrees with the results of theoretical calculations. The output radiation power of LEDs with the maximum mesa height (130 μm) at a pumping current of 220 mA amounts to 53 μW, which is 1.5 times higher than the power of LEDs with a mesa height of 10 μm.     

Patterning of fine particles by means of supercritical CO2

A new method for positioning fine particles on surfaces has been developed. Supercritical CO₂-assisted printing (SCAP) was utilized to spray and deposit the prepared particles on solid substrates. By means of masks, regular arrays of the particles were successfully created in designed patterns. Typical size of the particles employed was in the range of submicrometers to micrometers. Supercritical CO₂ (sc-CO₂) acted as an effective dispersion and transportation medium in this process. Good dispersion state of the particles was achieved by stirring in sc-CO₂. Fabrications of fine patterns of solder particles and other ceramic powders on smooth plates were demonstrated. Under optimum operation conditions, fine structures of 30 μm in width can be formed in a minimal pitch of 60 μm. Ultra high yield of the patterning was obtained since the deposition rate could be as high as 100 μm per second. Main factors affecting the process were discussed. The research results indicate that the SCAP is a potential approach to the organization of fine particles into microstructures. Hopefully, it may find wide industrial applications where lithography is needed, such as solder printing in surface mounting technology for higher density electronics and thick film fabrication for miniature systems.     

Refraction properties of PECVD of silicon nitride film

Using a neural network, the refractive index of a film deposited in a plasma enhanced chemical vapor deposition is characterized. The deposition process was characterized by a 2^6-1 fractional factorial experiment. Experimental variables and ranges include 20-40 W radio frequency (RF) power, 80-160 Pa pressure, 180-260 sccm SiH₄ flow rate, 1-1.4 sccm NH₃ flow rate, 0-1000 sccm N₂ flow rate, and 200-300°C substrate temperature. To examine the effect of the interaction between variables on the refractive index, a predictive neural network model was constructed. Prediction accuracy was optimized as a function of training factors. Model predictions were certified experimentally. Many complex interactions between the variables not reported previously were revealed. The power effect was transparent only in such plasma conditions as high SiH₄ or NH₃ flow rate. The temperature effect was conspicuous under high pressure. Deposition mechanisms were qualitatively estimated in conjunction with the reported linear dependency of refractive index on SiH/NH ratio.     

Microstructure evolution of gold thin films under spherical indentation for micro switch contact applications

RF MEMS (Radio Frequency Micro Electro Mechanical System) switches are promising devices but their gold-on-gold contacts, assimilated for this study to a sphere/plane contact, represent a major reliability issue. A first step toward understanding failure mechanisms is to investigate the contact metal microstructure evolution under static and cyclic loading. After static and cyclic loading of sputtered gold thin films under spherical indentation, high-resolution Electron Back Scatter Diffraction (EBSD) is used to investigate the contact area. Grain rotation against {111} fiber texture of 1-μm-thick sputtered gold thin film is a signature of plastic deformation. Grain rotation is observed above 1.6 mN under static loading using a spherical diamond indenter with 50-μm tip radius. The heterogeneity in grain rotation observed corresponds to a greater plastic deformation in the middle of the indent than at the edge. A 30° grain rotation due to cyclic work hardening is observed for a half-million mechanical cycles under 300 μN load using a spherical gold tip (20 μm radius). The same test in hot switching mode induces a grain growth in the contact area. Therefore, thermal effects occurring during hot switching are underlined.     

Vapor-phase formation of single-helix carbon microcoils by using WS2 catalyst and the morphologies

Very regular single-helix carbon microcoils of outer coil diameter 1–;3 m, inner coil diameter 0.5–;2 m, and coil pitch 1–;2 m were prepared by the WS₂-catalyzed pyrolysis of acetylene in the presence of thiophene impurity. The effects of reaction temperature and thiophene gas flow rate on the growth of single-helix carbon microcoils and the morphology were examined in detail. The optimum reaction temperature was 780°C, and optimum gas flow rate of thiophene, acetylene, hydrogen and argon for obtaining regular single-helix carbon coils with a constant coil diameter were 0.2, 40, 90, and 30 sccm, respectively. The formation mechanism of the single-helix carbon microcoils is discussed.     

Sintering behaviour of the diamond-super invar alloy system at high temperature and pressure

In the diamond-super invar alloy system, effect of the grain size of the starting diamond powder on the sintering behaviour was investigated at 5.8 G Pa and 1300 to 1500 ° C for 30 to 60 min. Abnormal grain growth was often observed in the sintered diamond using fine diamond powder, but a homogeneous sintered diamond was easily synthesized using 5 to 10m diamond. By the rigorous control of sintering conditions, a 3m grain size homogeneous sintered diamond was synthesized under conditions of 5.8 G Pa and 1350 ° C for 30 min. The Vickers hardness and thermal resistance of the fine grained sintered diamond was examined.     

Polystyrene as a zwitter resist in electron beam lithography based electroless patterning of gold

The resist action of polystyrene (M _w, 2,600,000) towards electroless deposition of gold on Si(100) surface following cross-linking by exposing to a 10 kV electron beam, has been investigated employing a scanning electron microscope equipped with electron beam lithography tool. With a low dose of electrons (21 μC/cm²), the exposed regions inhibited the metal deposition from the plating solution due to cross-linking—typical of the negative resist behaviour of polystyrene, with metal depositing only on the developed Si surface. Upon increased electron dosage (160 μC/cm²), however, Au deposition took place even in the exposed regions of the resist, thus turning it into a positive resist. Raman measurement revealed amorphous carbon present in the exposed region that promotes metal deposition. Further increase in dosage led successively to negative (220 μC/cm²) and positive (13,500 μC/cm²) resist states. The zwitter action of polystyrene resist has been exploited to create line gratings with pitch as low as 200 nm and gap electrodes down to 80 nm.     

Low-loss,high-purity (TeO<Subscript>2</Subscript>)<Subscript>0.75</Subscript>(WO<Subscript>3</Subscript>)<Subscript>0.25</Subscript> glass

By melting a mixture of high-purity oxides in a platinum crucible under flowing purified oxygen, we have prepared (TeO₂)_0.75(WO₃)_0.25 glass with a total content of 3d transition metals (Fe, Ni, Co, Cu, Mn, Cr, and V) within 0.4 ppm by weight, a concentration of scattering centers larger than 300 nm in size below 10² cm⁻³, and an absorption coefficient for OH groups (λ ∼ 3 μm) of 0.008 cm⁻¹. The absorption loss in the glass has been determined to be 115 dB/km at λ = 1.06 μm, 86 dB/km at λ = 1.56 μm, and 100 dB/km at λ = 1.97 μm. From reported specific absorptions of impurities in fluorozirconate glasses and the impurity composition of the glass studied here, the absorption loss at λ ∼ 2 μm has been estimated at ≤100 dB/km. The glass has been drawn into a glass-polymer fiber, and the optical loss spectrum of the fiber has been measured.     

The effects of oxygen on diamond synthesis by hot-filament chemical vapor deposition

The effects of oxygen addition on the synthesis of diamond are extensively studied by using the hot-filament chemical vapor deposition (HFCVD) method, in which it is simple and easy to control the deposition parameters independently. Diamond films are deposited on silicon wafers under the conditions of substrate temperature 530–950 C; total reaction pressure 700–8000 Pa; and methane concentration 0.4–2.4% in both CH₄–H₂ and CH₄–H₂–O₂ systems.At deposition conditions of low substrate temperature, high CH₄ concentration or high total pressure, soot-like carbon and/or graphite are deposited without oxygen addition. When even a small amount of oxygen (about 0.6%) is added, well-faceted diamond films are observed in scanning electron microscopy micrographs and a sharp diamond peak in the Raman spectra appears. The range of deposition parameters for high-quality diamond syntheses are extended by oxygen addition (low substrate temperature, high methane concentration and high reaction pressure).     

Electrical and structural parameters of YBCO films obtained by repeated growth cycles

We have studied changes in the electrical and structural characteristics of YBa₂Cu₃O_{7 − δ} (YBCO) films in the course of step-by-step increase in their thicknesses up to about 1 μm in a series of repeated magnetron sputtering growth cycles. It is established that high quality of the films is not deteriorated by interrupts in the growth process, which involve the formation of patterns on the sample and measurement of its electrical properties in liquid nitrogen. These results show the possibility of introducing intermediate stages of lithography into the process of YBCO deposition for the formation of structures with nonuniform thicknesses.     

Highly parallel fabrication of nanopatterned surfaces with nanoscale orthogonal biofunctionalization imprint lithography

Large areas of nanopatterns of specific chemical functionality are needed for biological experiments and biotechnological applications. We present nanoscale orthogonal biofunctionalization imprint lithography (NOBIL), a parallel top-down imprinting and lift-off technique based on step-and-flash imprint lithography (SFIL) that is able to create centimetre-scale areas of nanopatterns of two biochemical functionalities. A photoresist precursor is polymerized with a template in place, and the thin resist layer is etched to create an undercut for lift-off. Gold nano-areas on a silicon dioxide background are then independently functionalized using self-assembly that translates the nanopattern into a cell-adhesive/cell-rejective functionality pattern. We demonstrate the technique by creating fibronectin areas down to a pattern size of 60?nm against a polyethylene glycol (PEG) background, and show initial results of cells stably seeded over an array of 1?mm(2) areas of controlled size and pitch.     

Electron field emission properties of carbon nanoflakes prepared by RF sputtering

Carbon nanoflakes (CNFs) with corrugated geometry were synthesized using RF sputtering process with Ar/CH₄ gas mixture. Transmission electron microscopic examination reveals that the introduction of H₂ in sputtering chamber leads to the preferential etching of amorphous carbons, while maintaining integrity for the nano-crystalline phases. The proportion of nano-sized crystalline clusters is thus increased, which improved the electron field emission (EFE) properties of the materials, viz. with turn-on field of E ₀ = 6.22 V/μm and FEE current density of J _e = 90.1 μA/cm² at 11.0 V/μm. The cathodes made of screen printing of CNFs-Ag paste exhibit even better EFE properties than the as-deposited CNFs. The EFE of the CNFs cathodes can be turned on at E ₀ = 5.71 V/μm, achieving J ₀ = 340.1 μA/cm² at 11.0 V/μm applied field. These results showed that the CNFs are inheritantly more robust in device fabrication process than the other carbon materials and thus possess better potential for electron field emitter applications.     

Immersion holography based on amorphous chalcogenide films

A solid immersion holographic method for the recording of refractive index and surface-relief modulated gratings with a period of 0.1–1 μm in amorphous films of chalcogenide semiconductors As₂S₃ and As–S–Se has been developed and studied. The laser immersion interference lithography can be used as a low-cost method for the exposure of large surfaces with regular patterns like subwavelength-gratings and microsieves. The polarization sensitive properties of the subwavelength refractive-index modulated transmission gratings were studied. The possibility to use the amorphous chalcogenide films as a media for holographic recording and storage of information with high density is discussed.     

Stress tuning in AIN thin films

Aluminium nitride films were deposited on fused silica by reactive dc magnetron sputtering from an Al-target in an Ar/N₂ atmosphere. In-situ measurements during deposition provided data concerning mechanical stresses inherent to the growing thin films. By variation of both the gas composition (Ar, N₂) and the total gas flow in the vacuum chamber, the occuring intrinsic stresses could be shifted in magnitude and direction. Stress values of the AIN films ranged from ?0.9 GPa (compressive) to +1.2 GPa (tensile) when the Ar/N₂ ratio was varied between 3:1 and 1:3 for the different total gas flows of 50 sccm, 100 sccm, and 200 sccm (corresponding to total gas pressures of approximately 2 × 10^?1 Pa, 4 × 10^?1 Pa, and 8 × 10^?1 Pa respectively). Investigations of optical and structural film properties were carried out and the results were related to the observed film stress.     

Adhesion of PE modified by capacitively coupled radio frequency plasma-induced graft polymerization of glycidyl methacrylate

A graft polymerization of glycidyl methacrylate (GMA) on the pretreated polyethylene (PE) sheet samples by oxygen capacitively coupled radio frequency (RF) plasma was carried out to improve the adhesive properties of PE. The PE samples were treated with a RF power of 200W for a treatment time of 40s and then exposed to an oxygen atmosphere for a saturation time of 10min. The grafting of the plasma pretreated PE performed in an aqueous GMA solution with the monomer concentration from 20vol.% to 100vol.% at a temperature from 20°C to 90°C for a reaction period up to 50h. The optimum wettability of the graft polymerized PE surface with the concentration of 40vol.% at the temperature of 70°C and for the time of 24h was obtained as the static contact angle decreased from 104.2° for the original PE to 67.6° for the graft polymerized. After the graft polymerization, a strong absorption peak of C―O bonding was shown at 1050cm⁻¹ in Fourier transform infrared spectrum, indicating an introduction of epoxy groups on the graft polymerized surface. Correspondingly, the surface roughness (Ra) increased from 0.137μm for the original PE to 1.660μm for the graft polymerized. The maximal lap adhesive strength of the graft polymerized PE samples lapped using a mixture of epoxy resin and curing agent was achieved to about 160N·cm⁻². The fractured surfaces by tearing of the PE sheet matrix were observed on the tensioned PE samples due to the higher adhesive strength than that of the PE matrix.     

Growth, structure and properties of sputtered niobium oxide thin films

Niobium oxide (NbO_x) films were deposited by pulsed dc magnetron sputtering at different total gas pressures and oxygen flow rates. Various film properties were characterized by X-ray photoelectron spectroscopy, atomic force microscopy, variable angle spectroscopic ellipsometry and four point probe. It was found that oxygen flow rates required for preparing NbO, NbO₂ and Nb₂O₅ at a constant total pressure of 0.93 Pa were approximately 2, 4 and > 6 sccm, respectively. The results showed that the film properties, specifically composition can be significantly changed by the total gas pressure and the oxygen flow rate.     

Effects of oxygen partial pressures on microstructures and compositions of BaO-SrO-ZnO-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> thin films by RF-sputtering method

Ceramic thin films have been deposited by radio frequency magnetron sputtering method, using a mixture of 1 mol (Ba_0.3Sr_0.7)(Zn_1/3Nb_2/3)O₃ and 1 mol ZnO as target. The effects of oxygen partial pressures on crystallization and morphologies of thin films have been investigated in detail by X-ray diffraction, scanning electron microscope (SEM), and atomic force microscope. X-ray photoelectron spectroscopy (XPS) analysis was carried out to identify the composition and chemical state near the films’ surface. It is observed that the diffraction intensity of (001) peak increases dramatically when a small amount of oxygen is added to Ar atmosphere. The cross-sectional SEM images verify that the growth rate decreases sharply due to existence of oxygen, because the thickness decreases from 3.10 μm (pure Ar) to 1.38 μm (O₂/Ar ratio of 0.2:1). The morphologies indicate that the thin films are crackfree with perfect crystallization and all the particles are uniform in size when the O₂/Ar flow ratios are 0.2:1 and 0.4:1. The ceramics thin films grown at O₂/Ar flow ratio of 0.2:1 does not contain adsorbed oxygen, which is confirmed by XPS.     

Nanosecond pulsed excimer laser machining of chemical vapour deposited diamond and highly oriented pyrolytic graphite: Part I An experimental investigation

A laser beam offers the benefits of high precision, contamination-free, high speed, and low bulk temperature for machining of chemically vapour deposited (CVD) diamond thin films that in turn enable ultrafine finishing of diamond coated cutting tool inserts and drills, and for finishing and drilling of diamond coated multichip module applications. In this work, laser hole drilling and polishing of CVD diamond (free-standing diamond and coated tool inserts) and HOPG (highly oriented pyrolytic graphite) using a 248 nm wavelength, 23 ns pulsed excimer laser were conducted. The threshold energy fluence required for ablation of diamond and graphite was nearly the same but the material removal rate rapidly increases with the energy fluence for the graphite compared to diamond. At an energy fluence of 10 J cm^-2, the depth removed per pulse was 0.05 μm and 0.30 μm for diamond and graphite respectively. Raman microprobe analysis indicates that the laser machining induced the transformation of diamond to disordered forms of carbon in CVD diamond and some transformation of graphite to diamond in HOPG. The experimental data indicates that the transformation of diamond to graphite requires an energy input of 1.44 × 10⁷ J per mole. For a given set of laser parameters, the depth per pulse was substantially higher for diamond coated tool inserts compared to the free-standing diamond. The surface roughness of CVD diamond was reduced by 0.25 μm per pulse at an energy fluence of 16 J cm^-2 This revised version was published online in November 2006 with corrections to the Cover Date.