Tetramethylammonium Hydroxide Treatment Research Articles

Highly efficient industrial large-area black silicon solar cells achieved by surface nanostructured modification

Traditional black silicon solar cells show relatively low efficiencies due to the high surface recombination occurring at the front surfaces. In this paper, we present a surface modification process to suppress surface recombination and fabricate highly efficient industrial black silicon solar cells. The Ag-nanoparticle-assisted etching is applied to realize front surface nanostructures on silicon wafers in order to reduce the surface reflectance. Through a further tetramethylammonium hydroxide (TMAH) treatment, the carrier recombination at and near the surface is greatly suppressed, due to a lower surface dopant concentration after the surface modification. This modified surface presents a low reflectivity in a range of 350–1100nm. Large-area solar cells with an average conversion efficiency of 19.03% are achieved by using the TMAH treatment of 30s. This efficiency is 0.18% higher than that of standard silicon solar cells with pyramidal surfaces, and also a remarkable improvement compared with black silicon solar cells without TMAH modifications.

1/f Noise Characteristics of AlGaN/GaN FinFETs with and without TMAH surface treatment

In this paper, we have fabricated and investigated the AlGaN/GaN fin-shaped field-effect transistors (FinFETs) with and without TMAH surface treatment. DC and noise characteristics of the FinFETs were compared to evaluate the interface quality between Al2O3 layer and the side-wall GaN surface. The tetramethyl ammonium hydroxide (TMAH)-treated device with a fin width of 70nm and gate length, Lg=5μm exhibited excellent device performances, such as drain current of 0.16mA and transconductance (gm) of 0.11ms, both 30% improved, and extremely small gate leakage current of about 10−9A at Vgs=−5V which is approximately two orders lower in magnitude compared to that of the device without TMAH treatment. Improved low-frequency noise performances were obtained for TMAH treated device due to the enhanced side-wall quality after the TMAH surface treatment. The trap density was found to be reduced approximately one order after TMAH treatment. Thus, simple surface treatment not only smoothens the sidewall surface but also eliminates the plasma damage caused during the fin etching, which leads to the reduction of trap density in AlGaN/GaN FinFETs.

1/<inline-formula> <tex-math notation="LaTeX">$f$ </tex-math></inline-formula> Noise Characteristics of Surface-Treated Normally-Off Al<sub>2</sub>O<sub>3</sub>/GaN MOSFETs

Normally off Al 2 O 3 /GaN MOSFETs are fabricated with a tetramethylammonium hydroxide (TMAH) treatment as a postgate recess etch. The effects of the surface treatment on the etched GaN surface are investigated using low-frequency (1/f ) noise and capacitance-voltage (C-V) measurements. For a quantitative comparison with conventional devices, the oxide trap density (N ot ) is extracted using the unified 1/f noise model, whereas the interface trap density (D it ) is extracted using the high-low-frequency C-V method. After the TMAH treatment, N ot is found to have decreased from 5.40 × 10 19 to 2.50 × 10 19 eV -1 cm -3 , whereas D it is decreased from 2.8 × 10 12 to 1.1 × 10 11 eV -1 cm -2 , as compared with conventional devices. The surface treatment is thus shown to lower trap density in the Al 2 O 3 /GaN MOSFETs by smoothing the surface and suppressing plasma damage in the recessed GaN surfaces.

Influence of tetramethylammonium hydroxide treatment on the electrical characteristics of Ni/Au/GaN Schottky barrier diode

The effect of tetramethylammonium hydroxide (TMAH) treatment on the electrical properties of Ni/Au/GaN Schottky diodes have been investigated by current–voltage (I–V) and capacitance–voltage (C–V) techniques. The barrier heights and ideality factors measured from I–V characteristics are found to be 0.70 eV and 1.32 for without TMAH treatment, and 0.78 eV and 1.14 for with TMAH treatment, respectively. Cheung method is used to measure the series resistance and barrier height of the Schottky diodes, and the barrier height consistency is checked using the Norde method. The magnitude of interface state density for the diodes without and with TMAH treatment are varied from 7.45 × 1013 eV−1 cm−2 to 6.09 × 1012 eV−1 cm−2 and 4.03 × 1013 eV−1 cm−2 to 1.79 × 1012 eV−1 cm−2 in the below the conduction band from EC-0.19 eV to EC-0.63 eV and EC-0.22 eV to EC-0.73 eV. Based on the results, the TMAH treatment effectively removes of surface oxide (GaxOy) layer, formed due to the incorporation of the residual oxygen with Ga atom at the GaN surface during the plasma etching. The decrease in interface state density at the Ni/Au/GaN interface could be the reason for the improvement in the electrical properties.

Biological treatment of TMAH (tetra-methyl ammonium hydroxide) in a full-scale TFT-LCD wastewater treatment plant

This study evaluated biological treatment of TMAH in a full-scale methanogenic up-flow anaerobic sludge blanket (UASB) followed by an aerobic bioreactor. In general, the UASB was able to perform a satisfactory TMAH degradation efficiency, but the effluent COD of the aerobic bioreactor seemed to increase with an increased TMAH in the influent wastewater. The batch test results confirmed that the UASB sludge under methanogenic conditions would be favored over the aerobic ones for TMAH treatment due to its superb ability of handling high strength of TMAH-containing wastewaters. Based on batch experiments, inhibitory chemicals present in TFT-LCD wastewater like surfactants and sulfate should be avoided to secure a stable methanogenic TMAH degradation. Finally, molecular monitoring of Methanomethylovorans hollandica and Methanosarcina mazei in the full-scale plant, the dominant methanogens in the UASB responsible for TMAH degradation, may be beneficial for a stable TMAH treatment performance.

Effects of TMAH Treatment on Device Performance of Normally Off $\hbox{Al}_{2}\hbox{O}_{3}/\hbox{GaN}$ MOSFET

Normally off Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /GaN MOSFETs are fabricated by utilizing a simple tetramethylammonium hydroxide (TMAH) treatment as a postgate-recess process. The TMAH-treated device with a gate length of 2.5 μm exhibited excellent device performances, such as a threshold voltage of 3.5 V, a maximum drain current of 336 mA/mm, and a breakdown voltage of 725 V, along with extremely small gate leakage current of about 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> A/mm at <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">gs</sub> = 15 V, which is approximately six orders lower in magnitude compared to that of the device without TMAH treatment.

Large-scale Facile Synthesis of Monodisperse Iron Oxide Nanoparticles in Alcohol

A large-scale synthetic method of hydrophobic soluble Fe2O3 and Fe3O4 nanoparticles was developed with the thermal decomposition technique. From the characteristic analysis with a transmission electron microscopy and Xray diffraction, the obtained iron oxide nanomaterials showed a cubic structure with a size of ca. 2 nm. The oxidation states of the nanoparticles were investigated via X-ray photoelectron spectroscopy analysis. The tetramethylammonium hydroxide treatment might be induced a phase transfer of the iron oxide nanocrystals from a hydrophobic state to a hydrophilic one. The carbon-coated hydrophilic soluble Fe2O3 nanoparticles could be prepared by a solvothermal reaction of the particles, glucose, and H2O.

Tandem size-exclusion chromatography-polyacrylamide gel electrophoresis fractionation of aquatic humic substances: characterization of size-separates with TMAH treatment and pyrolysis-GC/MS

Aquatic humic (HA) and fulvic acids (FA) from two different origins were fractionated by the tandem size-exclusion chromatography and polyacrylamide gel electrophoresis (tandem SECPAGE). Three HA and two FA fractions exhibited different molecular sizes, electrophoretic mobilities and structural compositions based on elemental analyses and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) after tetramethyl-ammonium hydroxide (TMAH) treatment. Based on comparison of the size-separates and unfractionated bulk samples, the highest molecular size fractions of aquatic humic substances (HS) appear to be enriched in fatty acids (mainly C16 and C18), which are strictly linked to the humic core. This and the presence of low chain fatty acids and unsaturated and di-tri acids may suggest a microbial rather than a vascular plant origin. Even if the majority of lignin derived components in aquatic HS represent relatively high state of biodegradation (oxidation), a certain variation between different sizefractions also exists, supporting a high heterogeneity and composite nature of aquatic HS. Although SEC-PAGE fractionation appears to produce fairly homogeneous HS fractions, the absorption of some urea into of the separates cannot be completely avoided in this method, which limits its suitability for evaluating, especially the presence of N-containing constituents.

Characterisation of lake-aquatic humic matter isolated with two different sorbing solid techniques: tetramethylammonium hydroxide treatment and pyrolysis-gas chromatography/mass spectrometry

Tetramethylammonium hydroxide (TMAH) treatment followed up with pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) was applied to characterise the structural composition of lake aquatic humic matter (HM). The HM samples were isolated with two different chromatographic methods: (1) non-ionic sorbing solid (standard XAD technique) with preacidification of a water sample to pH 2; and (2) weakly basic anion exchanger (DEAE, diethylaminoethyl cellulose) without any preacidification. A detailed structural analysis of degradation products was performed and compositional differences between different HM samples were evaluated. The main degradation products, in addition to varying proportions of different nitrogen and sulphur compounds, were methyl derivatives of different phenols, alkylphenols, phenolic acids and aliphatic mono- and dicarboxylic acids, which speak for the importance of ester linkages between the different structural subunits of aquatic HM. Despite all HM samples yielded qualitatively quite similar organic compounds, some fundamental quantitative differences existed. As a general rule, the DEAE isolate and two main XAD fractions: conventional fulvic (FA) and humic (HA) acids, seem to consist of almost similar organic matter dominating by different phenols and aliphatic acids. The other two special XAD fractions appear to belong to different structural categories yielding more alkylbenzenes/styrenes, alkanes and aliphatic monocarboxylic acids. The structural analyses and statistical calculations on the different HM samples support the postulation that the structural composition of the DEAE isolate corresponds to a certain average of the four different acidic XAD fractions.

Degradation of TMAH treated aquatic humic matter at different temperatures

Lake aquatic fulvic acid was investigated with tetramethylammonium hydroxide (TMAH) treatment and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). TMAH treatment was performed as an off-line procedure at 100°C without significant thermochemolytic degradation (ensured with a solvent extraction) and the product distributions at three different pyrolysis temperatures (300, 450 and 600°C) were studied. The degradation of TMAH treated fulvic acid was strongly thermally controlled. The number of degradation products and their total ion currents (TIC) increased significantly when the pyrolysis temperature was raised from 300 to 600°C. Furthermore, the highest temperature yielded significant amounts of aromatic structural constituents (especially alkylmethoxybenzenes) which were not found at lower sub-pyrolysis temperatures. According the results, the utilisation of high temperature pyrolysis of TMAH treated humic matter seems to be needful, because TMAH thermochemolysis is not necessarily enough to split off the most strictly bound aromatic subunits of the heterogeneous humic matter.

Analytical in source pyrolytic methylation electron impact mass spectrometry of phenolic acids in biological matrices

AbstractPhenolic acids in complex biological matrices are easily decarboxylated under pyrolysis electron impact (EI) conditions depending on their binding to other plant cell wall compounds. Pyrolysis gas chromatography/mass spectrometry (Py‐GC/MS) of phenolic acids reveals only the decarboxylated compound but this product may also be derived from the alcoholic lignin monomers. Discrimination between the acidic and alcoholic phenol can be obtained by stabilization of the molecular ion of the two compounds. Samples of p‐coumaric acid, of sporopollenin from Pinus pollen wings, of bamboo milled wood lignin (MWL) and of tobacco leaf nerve MWL were analysed by analytical Py‐EIMS. Mass peaks for the molecular ion of p‐coumaric acid and of the decarboxylated product may be observed. Results are compared with Py‐MS data of samples treated with tetramethylammonium hydroxide (TMAH), a compound used to methylate the phenolic hydroxyl group and the carboxyl group of the phenolic acid in the ion source of the mass spectrometer. Mass spectra of samples treated with this agent show a high content of double methylated p‐coumaric acid (m/z 192). TMAH treatment allows discrimination between phenolic acids and alcohols under Py‐MS and Py‐GC/MS conditions by producing more stable molecular ions.