Slight Etching Research Articles

Highly reflective Bragg gratings in slightly etched step-index polymer optical fiber.

During the past few years, a strong progress has been made in the photo-writing of fiber Bragg gratings (FBGs) in polymer optical fibers (POFs), animated by the constant wish to enhance the grating reflectivity and improve the sensing performances. In this paper, we report the photo-inscription of highly reflective gratings in step-index POFs, obtained thanks to a slight etching of the cladding. We demonstrate that a cladding diameter decrease of ~12% is an ideal trade-off to produce highly reflective gratings with enhanced axial strain sensitivity, while keeping almost intact their mechanical resistance. For this, we make use of Trans-4-stilbenemethanol-doped photosensitive step-index poly(methyl methacrylate) (PMMA) POFs. FBGs are inscribed at ~1550 nm by the scanning phase mask technique in POFs of different external diameters. Reflectivity reaching 97% is achieved for 6 mm long FBGs, compared to 25% for non-etched POFs. We also report that a cladding decrease enhances the FBG axial tension while keeping unchanged temperature and surrounding refractive index sensitivities. Finally and for the first time, a measurement is conducted in transmission with polarized light, showing that a photo-induced birefringence of 7 × 10(-6) is generated (one order of magnitude higher than the intrinsic fiber birefringence), which is similar to the one generated in silica fiber using ultra-violet laser.

Dependence of Atomic-Scale Si(110) Surface Roughness on Hydrogen Introduction Temperature after High-Temperature Ar Annealing

The atomic-scale surface roughness of Si(110) reconstructed via high-temperature Ar annealing is immediately increased by non uniform accidental oxidation during the unloading process (called reflow oxidation) during high-temperature Ar annealing. In particular, for a reconstructed Si(110) surface, characteristic line-shaped oxidation occurs at preferential oxidation sites appearing in pentagonal pairs in the directions of Si[-112] and/or [-11-2]. We previously reported that the roughness increase of reconstructed Si(110) due to reflow oxidation can be restrained by replacing Ar gas with H2 gas at 1000&#176C during the cooling to 100&#176C after high-temperature Ar annealing. It was speculated that preferential oxidation sites on reconstructed Si(110) were eliminated by H2 gas etching and hydrogen termination of dangling bonds. Thus, it is necessary to investigate the effect of H2 gas etching and hydrogen termination behavior on the reconstructed Si(110) surface structure. In this study, we evaluated in detail the relationship between the temperature at which the H2 gas replaces the Ar in high-temperature Ar annealing and the reconstructed Si(110) surface structure. The maximum height of the roughness on the reconstructed surface was the same as if Ar gas was used when the H2 gas introduction temperature was 200&#176C, although the amount of reflow oxidation was decreased to 70% by hydrogen termination. Furthermore, line-shaped oxidation still occurs when H2 gas replaces Ar at this low temperature. Therefore, we conclude that oxidation is caused by slight Si etching at low temperatures, and thus the preferential oxidation sites on the reconstructed structure must be eliminated by hydrogen etching in order to form an atomically smooth Si(110) surface.

Study of InP Surfaces after Wet Chemical Treatments

The influence of different wet chemical treatments (HCl, H2SO4, NH4OH) on the composition of InP surfaces is studied by using synchrotron radiation photoemission spectroscopy (SRPES). It is shown that a significant amount of oxide remains present after immersion in a NH4OH solution which is ascribed to the insolubility of In3+ at higher pH values. Acidic treatments efficiently remove the native oxide, although components like P0, In0 and P(2±Δ)+ suboxides are observed. Alternatively, the influence of a passivation step in (NH4)2S solution on the surface composition was investigated. The InP surface after immersion into (NH4)2S results in fewer surface components, without detection of P0 and P(2±Δ)+ suboxides. Finally, slight etching of InP surfaces in HCl/H2O2 solution followed by a native oxide removal step, showed no significant effect on the surface composition.

Colloidal Polarization of Yolk/Shell Particles by Reconfiguration of Inner Cores Responsive to an External Magnetic Field

Yolk/shell particles, which were hollow silica particles containing a movable magnetic silica core (MSC), were prepared by removing a middle polystyrene layer from multilayered particles of MSC/polystyrene/silica shell with heat treatment followed by a slight etching with a basic solution. An ac electric field was applied to the suspension of the yolk/shell particles to form pearl chains (1D structure) of yolk/shell particles. Observation with an optical microscope showed that the MSCs in the silica compartment of the pearl chains had a zigzag structure under the electric field. An external magnetic field applied to the suspension could form a novel structure of doublet MSC in the shell compartment of the quasi-pearl chain structure. Application of a magnetic field was also performed for 2D hexagonally close-packed assemblies of the yolk/shell particles, which could two-dimensionally form a doublet structure of MSCs as if they were polarized in the compartment. Switching on/off the magnetic field successfully controlled the positional ordering of cores in the consolidated silica shell.

Selective lateral etching of InAs/GaSb tunnel junctions for mid-infrared photonics

We have studied selective etching of the InAs/GaSb tunnel junction (TJ). We show that efficient lateral etching can be achieved with a citric acid:hydrogen peroxide solution. A slight etching anisotropy of around 10% is observed between [1 1 0] and [1 0 0] crystal orientations. The electrical properties of etched TJs do not depend on the diameter of the device which reveals efficient passivation and the absence of current leakage. Specific resistivities in the 2–5 × 10−5 Ω cm−2 range are measured even for diameters compatible with vertical-cavity surface emitting lasers. This work demonstrates that selective lateral etching of an InAs/GaSb tunnel junction is an efficient means to confine the current in GaSb-based heterostructures.

Direct observation of micron-sized silica rattles to demonstrate movability of inner spheres in the silica compartment suspended in aqueous media

Micron-sized silica rattle particles were directly observed in aqueous media with an optical microscope to demonstrate the movability of inner silica spheres within the compartment of the silica shell. The rattle particles were prepared by a combined method of fabricating multilayered particles (silica sphere/polystyrene (PSt) inner shell/silica outer shell) and removing the polymer component in the multilayered particles. The polymer component of PSt was removed by heating the multilayered particles at 500 °C for 4 h, which resulted in a successful preparation of silica rattle particles without any residual polymer component. The silica rattle particles in the presence of polyvinylpyrrolidone used as a viscosity enhancer were observed with the optical microscope under an alternating electric field, revealing that less than 10% of inner spheres in the pearl chain of rattle particles could be randomly moved in the compartment of the silica shell. For increasing the percentage of inner spheres randomly moving, the silica rattle particles were slightly etched with a diluted NaOH solution to detach the inner spheres from the inside wall of the silica shell. The slight etching of the silica component led to the observation of approximately 75% inner spheres randomly moving under the applied electric field. This is the first direct observation to show that the single spheres incorporated in the shell compartment are capable to freely move without sticking to the inside wall of the shell.

Effect of HF etching on the surface quality and laser-induced damage of fused silica

The surface hardness of polished and HF etched fused silica has been investigated by nanoindentation technique. The results of polished fused silica indicate that the hardness of surface layer is greater than that of the bulk material. The difference should be attributed to the polishing induced deformation of the thin surface layer. The various removal depths of surface layer by HF etching has been confirmed by the surface hardness results. The initial laser damage threshold and damage possibility of unetched and etched samples were also measured. The results show a great improvement of damage resistance by slight etching and a reduction by excess etching. The correlation between surface hardness and damage threshold indicates that the mechanical strength plays an important role in the initiation of laser-induced damage.

Metal-Free Disordered Vertical Sub-Micron Silicon Wires Produced from Electrochemical p-Type Porous Silicon Layers

In this paper, we propose a simple, original and costless method to produce monocrystalline silicon sub-micron wires by electrochemical etching of silicon wafers. For this purpose, 30–50 Ω cm p-type silicon samples were etched in a HF (50 wt %):H2O:acetic acid (4.63:1.45:2.14) electrolyte applying various current densities. As the resulting material is made of macroporous silicon filled with mesoporous silicon, when a slight KOH or TMAH etching is performed, we are able to produce vertical wires with an aspect ratio up to 500. The thinnest measured wire diameters are about 200 nm for an average wire density above 107cm−2.

Toward sub-20 nm hybrid nanofabrication by combining the molecular ruler method andelectron beam lithography

It is of great interest and importance to develop new nanofabrication processes to fabricatesub-20 nm structures with sub-2 nm resolution for next-generation nanoelectronic devices. Acombination of electron beam lithography (EBL) and a molecular ruler is one of thepromising methods to make these fine structures. Here we successfully develop a hybridmethod to fabricate sub-20 nm nanogap devices at the desired positions with a complexstructure by developing a post-EBL process, which enabled us to avoid damaging themolecular ruler with the high-energy electron beam, and to fully utilize the EBLresolution. It was found that slight etching of the Ti adhesion layer of the parent metal(Pt) by ACT935J solution assisted the removal of molecular rulers, resultingin improved enhancement in the product yield (over 70%) of nanogap devices.

XPS study of the O 2/SF 6 microwave plasma oxidation of (0 0 1) GaAs surfaces

O 2SF 6 plasma effects on processed GaAs surfaces have been investigated. The influence of plasma parameters such as composition, power and exposure time has been studied. The microwave plasma treatment efficiency has been studied by surface depth profiling (cycles consisting of XPS measurements followed by a slight etching) coupled with an original modelling calculation. We have pointed out that SF 6 addition in plasma increases the oxidative rule of oxygen by increasing the total oxide thickness and that the quantity of the different oxidative and passivating species does not limit the oxidative mechanism, in the O 2:SF 6 ratio range 80:20 to 40:60. The increase in the plasma power leads to a change in the composition of the outer region of the oxide layer with an increase in the gallium content on the surface, and to an increase in the total oxide layer. The exposure time to the plasma increases also these two phenomena.

Evidence and analysis of thermal static strain aging in the deformed surface zone of finish-machined hardened steel

After heat treating, finish machining of the hardened steel represents the last manufacturing step of machine elements. The practically most important operation of grinding is applied to achieve edge zone compressive residual stresses, best surface quality, and dimensional accuracy. Metal removal involves high plastic deformation work. Glide and intersection processes raise the density and produce lower energy substructures of dislocations. The temperature and time behavior of postmachining thermal treatment is analyzed on ground and honed martensitic SAE 52100 rolling bearing steel. Microstructure stabilization is reflected in a large XRD peak width decrease in the surface. The kinetics are modeled by rate-controlling carbide dissolution as the carbon source for Cottrell-type segregation at dislocations. This thermal static strain aging is verified by the formation of a slight white etching surface layer. The model is also extended to consider superimposed thermal dislocation recovery. Both effects are separable. In rolling contact fatigue tests under mixed friction conditions, air reheating below the tempering temperature, which avoids hardness loss, leads to a significant lifetime increase. The effect also occurs after cold working.

Formation of Porous Aluminum Films with Isolated Columnar Structure Using Physical Vapor Deposition for Medium-Voltage and High-voltage Capacitors

An attempt was made to tailor porous aluminum films with an isolated columnar structure by magnetron sputtering for potential application to medium-voltage and high-voltage electrolytic capacitors. The aluminum film was deposited at a relatively high Ar pressure of 3.3 Pa on rough aluminum substrate with a cellular texture. Shadowing effects, which were enhanced by the random incident angle of aluminum atoms at the high Ar pressure and the use of a rough substrate, produced the isolated columnar structure of the deposited film. However, gaps separating neighboring columns were not high enough to maintain high surface roughness after anodic oxide formation, due to the large Pilling-Bedworth ratio for the Al/Al2O3 system. The gaps became filled with anodic oxide during anodic film formation. Slight alkaline etching of the deposited film the increased the gaps such that high surface area was maintained to high formation voltages.

High pressure in situ HCl etching of Si1−xGex versus Si for advanced devices

We have studied the gaseous hydrochloric acid selective etching of SiGe versus silicon in a reduced pressure-chemical vapor deposition reactor. Non-classical metal oxide semiconductor field effect transistors (MOSFETs) architectures, such as silicon on nothing (SON) and multi-bridge channels (MBC) devices require high SiGe:Si etch selectivities in order to get rid of the sacrificial SiGe layers. We have probed the in situ HCl etching of Si and SiGe blanket layers of SiGe/Si stacks grown selectively in the Si windows of patterned wafers (‘SON-like’ substrates) and of SiGe/Si superlattices (‘MBC-like’ substrates) as a function of the reverse absolute temperature. A switch from high temperature, diffusion-limited/low temperature, Cl-desorption-limited etch regimes to a unique LT regime, together with a significant etch rate increase, has been evidenced when drastically increasing the HCl partial pressure. Very good selectivities (versus Si) have been obtained when laterally etching high Ge content Si1−xGex layers (typically ⩾30%). A preferential etch by HCl of the {1 0 0} crystallographic planes compared to the {1 1 0} ones has been noticed both for the lateral etch of the ‘SON-like’ patterns (preferential etch of the pattern corners) and for the ‘MBC-like’ patterns (fullsheet (0 0 1) etch rates ≈10 times the {1 1 0} lateral etch rates). A slight etch rate difference between ‘bottom-located’ and ‘top-located’ Si1−xGex layers in Si/SiGe superlattices has also been highlighted. This etching technique is thus usable for the processing of SON or MBC devices provided that the selective {1 0 0}:{1 1 0} HCl etch reported here is taken into account.

Secondary Nucleation and Growth of ZnO

Recently we discovered that under certain conditions new crystal growth (branch) can be induced on specific crystalline planes of the same material. This is a new phenomenon and is in sharp contrast to typical nucleation and growth in which a crystal will simply grow larger in preferred directions depending on the surface energy of the specific crystalline planes. Based on our observation, we developed a sequential nucleation and growth technique offering the power to assemble complex hierarchical crystals step-by-step. However, the key questions of when and how the secondary nucleation takes place have not been answered. Here we systematically study secondary ZnO crystal growth using organic diamine additives with a range of chain lengths and concentration. We found that ZnO branches form for a narrow diamine concentration range with a critical lower and upper critical nucleation concentration limit, which increases by about a factor of 5 for each additional carbon in the diaminoalkane chain. Our results suggest that the narrow window for secondary growth is dictated by the solubility of the ZnO crystals, where the low critical nucleation concentration is determined by slight etching of the surface to produce new nucleation sites, and the upper critical concentration is determined by the supersaturation concentration. Kinetic measurements show that the induction time and growth rate increase with increasing diamine concentration and follow classical nucleation and growth theory. Observations of branch morphological evolution reveal the mechanisms guiding the tunable crystal size and morphology.

Effect of absorbed moisture on the atmospheric plasma etching of polyamide fibers

A potential problem for the atmospheric pressure plasma treatment is that the moisture absorbed by the substrate may influence plasma surface modification processes. This study evaluated the effect of moisture regain on the surface morphology change of polyamide fibers by plasma etching. Polyamide 6, poly( p-phenylene terephthalamide) (PPTA, aromatic polyamide), wool (polyamide 2), and ultrahigh modulus polyethylene (UHMPE, polyamide infinity) fibers, were selected to represent various polyamide molecular structures. The fibers were plasma treated at three moisture regains corresponding to three different relative humidity levels (10, 65, and 100%). Scanning electron microscope (SEM) showed that no apparent morphology change was observed on the surface of UHMPE and PPTA fibers. Under the nano-scale surface analysis of atomic force microscopy (AFM), however, rougher surface of UHMPE and PPTA fibers appeared with elevated relative humidity or higher moisture regain. In terms of polyamide 6 and wool, SEM images revealed that compared to the slight plasma etching effect of fibers with the lowest moisture regain, a thin surface layer of the treated fibers with higher moisture regain was partially or completely peeled off. It may be concluded that fiber moisture regain plays an important role in atmospheric pressure plasma etching of polyamide fibers, which may be mainly due to the interaction between the absorbed water and the polymer molecules. It can be concluded that the etching rate of atmospheric pressure plasma for a polymer depends on its moisture regain, intermolecular forces, crystallinity, and molecular structure.

Fabrication of Sub-Micron Period Surface Structures in LiNbO3

Sub-micron period reversed domain patterns are fabricated in congruent LiNbO 3 by using electric field overpoling. Slight wet etching of the domain engineered samples in HF solution generates surface relief structures faithfully reproducing the resist pattern geometries generated by holographic lithography. Moiré holographic lithography is also used to fabricate more complicated resist templates to be transferred onto the LiNbO 3 substrates as surface structures. A wide variety of structures is presented and discussed. The preliminary results show the possibility to use the fabricated structures for the realization of photonic crystal devices such as Bragg gratings, micro-ring resonators, etc. for telecom applications.

Performance Improvement of Organic Thin-Film Transistors by Electrode/Pentacene Interface Treatment Using a Hydrogen Plasma

Pentacene-based organic thin-film transistors (TFTs) have been fabricated with and without treatment by hydrogen (H2) plasma at the interface between the electrode and the pentacene surface. Processing with a H2 plasma was carried out in a plasma-enhanced chemical vapor deposition with varying treatment times. The interface treatment by H2 plasma resulted in improved device electrical properties. Removal of oxygen from the pentacene surface occurs due to slight etching by the plasma. Sufficient flux density of the H2 plasma leads to full pentacene-surface coverage by rearranging the hydrogen with carbon instead of oxygen. Atomic force microscopy profiles reveal the morphology changes of the pentacene surface after treatment, and secondary ion mass spectrometry shows the change via compositional depth profiles indicating H2 , O2, and C-H binding. Hydrogen treatment, therefore, appears to modify the interface by removing the surface oxygen layer, resulting in better performance of the organic TFT

Oxygenation cracks in top seeded melt growth Y–Ba–Cu–O bulk superconductors

The distribution of the cracks parallel to the {100} type planes (a/c-cracks) are formed during oxygenation in the single-grain YBa2Cu3O7/Y2BaCuO5 (YBCO) bulk superconductor prepared by the top seeded melt-growth process (TSMG) was characterised by measuring the crack spacing and length on the different distances from the seed in the a- and c-growth sectors. The a/c-cracks were visualized by slight etching after careful grinding and polishing. Generally, more cracks were found in the parts of the sample with lower concentration of 211 particles. Moreover, the density of the a/c-cracks was influenced by macroscopic dilatation stresses developed during cooling from the processing temperature due to macroscopic inhomogeneity of 211 particle concentration in the samples.

Research on Effects of Slurry Additives in Cu CMP for ULSI Manufacturing

In this paper, in order to analyze the oxidation, dissolution and corrosive inhibition effects of additives in the slurry for copper Chemical-mechanical polishing(CMP), the slurry(pH5) with the peroxide as an oxidant, the citric acid as a complexing agent and the benzotriazole(BTA) as an inhibitor is studied. The static etching rate and polishing rate of the Cu-H2O2-Citric acid-BTA slurry are measured. The electrochemical behavior involved in the dissolution and corrosive inhibition of copper in the solutions containing additives is investigated by the electrochemical impedance spectroscopy (EIS) studies. The surface roughness is measured using ZYGO 3-D surface profiler. It is observed that when the slurry is with only 5wt% peroxide existing, copper is stable and slight etching rate on the copper is produced, and the etching rate is only 8.7nm/min. When 0.6wt% citric acid presents after adding 5wt% hydrogen peroxide, the etching rate will increase by 5.3 times, with a blue complexing product emerging. When the inhibitor BTA is added, the corrosion will be effectively restrained. From the EIS results, the impedance of copper in 5wt% peroxide solution which is in passivation can be greatly decreased by adding the citric acid as a complexing reagent. And the impedance of copper in the solution containing peroxide and citric acid can be increased by the addition of BTA. The surface roughness of the wafer polished with the slurry of 5wt% peroxide+0.6wt% citric acid+0.12wt% BTA slurry is Ra 4.7 Å.

Mass-analyzed CFx+ (x=1,2,3) ion beam study on selectivity of SiO2-to-SiN etching and a-C:F film deposition

To clarify the origins of high selectivity in SiO2-to-SiN etching in fluorocarbon gas plasma, mass-analyzed CFx+ (x=1,2,3) ions with a definite kinetic energy of 250–2000eV were irradiated on SiN and SiO2 surfaces. Selectivity in SiO2-to-SiN etching varies greatly for different CFx+ ions. For CF3+ ions, the etch yield of SiN is almost the same as that of SiO2, causing poor selectivity. For CF+ ions, on the other hand, the etch yield of SiN is much smaller than that of SiO2. An amorphous fluorinated carbon (a-C:F) film grows without any neutral radicals on the SiN surface at energies below 1250eV and on the SiO2 surface at energies below 500eV due to CF+ ion irradiation. The difference in threshold energy of a-C:F film deposition causes high selectivity in SiO2-to-SiN etching. Slight etching of substrate films first takes place at the initial stage of deposition, then etching stops, and a homogeneous a-C:F film is grown. Accumulated carbons during the initial etching reaction modify the surface reaction layer, which causes drastic changes in reactions such as etching to “etch stop” and a-C:F film growth.