Modified Stranski-Krastanov Growth of Amino Acid Arrays toward Piezoelectric Energy Harvesting

Biomolecule-based piezoelectric nanostructures emerged as a new class of energy-converse materials, and designing tailored piezoelectric amino acid arrays is essential to achieve efficient electrical-mechanical coupling and fulfill their application potential. However, the controlled growth of amino acid nanostructures is still challenging due to the limited understanding of their growth mechanism. Herein, we base on the Stranski-Krastanov (S-K) growth mode and propose a mechanism for the growth of ordered amino acid array structures via physical vapor deposition. The growth of vertical valine sheet arrays is examined by changing the substrate temperature, chamber pressure, and source-substrate distance, and a "layer-plus-sheet" growth process is revealed. The modified S-K growth mode is applied to fabricate other amino acid nanostructures like leucine and isoleucine. The growth mode not only explains the formation of uniform and controllable morphology of amino acid structures but also leads to the significant enhancement of their piezoelectric properties. The maximal effective piezoelectric constant of valine sheets is 11.4 pm V^-1, which approaches its highest predicted value. The output voltage of the valine array-based nanogenerator is ∼4.6 times the output voltage of the valine powder-based nanogenerator. This work provides new insights into the growth mechanism of ordered piezoelectric amino acid arrays, making them promising candidates for applications in wearable or implantable electronic devices.

Influence of Supersaturation on Growth Behavior and Mechanical Properties of Polycrystalline 3C-SiC on W Wire Substrate

As an important reinforcement for metal matrix composites, the microstructure and mechanical properties of W-core SiC filament have drawn increasing attentions among researchers. In this work, the growth behavior of polycrystalline 3C-SiC on W-wire substrate in the chemical vapor deposition (CVD) process and the evolution of mechanical properties in preparation of W-core SiC filament, were investigated as a function of gas-phase supersaturation. Kinetic studies revealed that the growth of 3C-SiC grains was limited by surface reactions at both 850 °C and 1050 °C, and the deposit experienced similar morphological changes from a porous structure to large clusters, with the increase in supersaturation. Structural analyses and mechanical tests show that the production of pores and the amorphous phase with a low supersaturation, of 9.6 × 107 at 850 °C, resulted in a reduction in the modulus and hardness of the polycrystalline deposits, to 270.3 GPa and 33.9 GPa, while the reduced structural defects (e.g., stacking faults and twins) in highly (111) orientated 3C-SiC grains, as well as the improved surface quality obtained with the medium supersaturation of 1.6 × 107 at 1050 °C, enhanced the tensile strength and the Weibull modulus of W-core SiC filament to 2.88 GPa and 11.2, respectively. During the growth of 3C-SiC grains, the variation in structural defects density is controlled by the critical nucleation energy of the two-dimensional (2D) nucleus.

Morphological Control of Silicon Carbide Deposited on Hi-Nicalon Type S Fiber Using Atmospheric Pressure Chemical Vapor Infiltration

Silicon carbide coated onto Hi-Nicalon Type S fiber is of great interest to the aerospace industry. This work focuses on tuning the reaction parameters of atmospheric pressure SiC CVI using CH₃SiCl₃ to control the morphology of the coatings produced. Depth of CH₃SiCl₃ from 1 to 14 cm, temperature from 1000 to 1100 °C, and flow rate of H₂ carrier gas from 5 to 30 SCCM were examined. Coating morphologies ranged from smooth to very nodular, where spherical growths were present along the entire deposition zone. The parameters that yielded a smooth deposition throughout the 20 cm deposition zone were 4-6 cm of CH₃SiCl_3(l) depth, 1100 °C, and 10 SCCM of H₂ as a carrier gas. Tensile testing using acoustic emission sensors was performed on SiC_f/BN/CVI-SiC minicomposites with different coating morphologies. The tensile tests revealed that smooth coatings have better mechanical performance than the nodular coatings; nodular coatings promote premature ultimate brittle failure, while smooth coatings exhibit toughening mechanisms. Smooth coatings had higher average matrix cracking strength (248 MPa) and ultimate tensile strength (541 MPa) than average nodular coating matrix cracking strength (147 MPa) and ultimate strength (226 MPa).

Structural Controlling of Highly-Oriented Polycrystal 3C-SiC Bulks via Halide CVD

Highly-oriented polycrystal 3C-SiC bulks were ultra-fast fabricated via halide chemical vapor deposition (CVD) using tetrachlorosilane (SiCl₄) and methane (CH₄) as precursors. The effects of deposition temperature (T_dep) and total pressure (P_tot) on the orientation and surficial morphology were investigated. The results showed that the growth orientation of 3C-SiC columnar grains was strongly influenced by T_dep. With increasing T_dep, the columnar grains transformed from <111>- to <110>-oriented. The arrangement of <111>-oriented columnar grains was controlled by P_tot. Lotus-, turtle-, thorn-, and strawberry-like surface morphologies were naturally contributed by different arrangements of <111>-oriented grains, and the deposition mechanism was discussed. The wetting behaviors of CVD-SiC samples by molten aluminum were also examined at 1173 K in a high vacuum atmosphere.

Substrate-free growth, characterization and growth mechanism of ZnO nanorod close-packed arrays

ZnO nanorod close-packed arrays are successfully fabricated in a substrate-free manner by a citric acid assisted annealing process at a low growth temperature of 400 °C. Each nanorod of ZnO nanorod close-packed arrays grows along the [0001] direction and is single crystalline with an average diameter of 50 nm, and an average length of 0.5 µm. The aspect ratio is 10. The ZnO nanorod close-packed arrays show a strong exciton absorption peak at 372 nm in UV-visible absorption spectra, exhibiting a blue-shift relative to the bulk exciton absorption (387 nm). Finally, a new growth mechanism is proposed for the substrate-free preparation of ZnO nanorod close-packed arrays by a citric acid assisted annealing process.