arXiv subjects

Stanislaus S. Wong

Publications and source records attributed to Stanislaus S. Wong.

6 recordsLinked to original sources

arXiv2026

Robotic Nanoparticle Synthesis via Solution-based Processes

We present a screw geometry-based manipulation planning framework for the robotic automation of solution-based synthesis, exemplified through the preparation of gold and magnetite nanoparticles. The synthesis protocols are inherently long-horizon, multi-step tasks, requiring skills such as pick-and-place, pouring, turning a knob, and periodic visual inspection to detect reaction completion. A central challenge is that some skills, notably pouring, transferring containers with solutions, and turning a knob, impose geometric and kinematic constraints on the end-effector motion. To address this, we use a programming by demonstration paradigm where the constraints can be extracted from a single demonstration. This combination of screw-based motion representation and demonstration-driven specification enables domain experts, such as chemists, to readily adapt and reprogram the system for new experimental protocols and laboratory setups without requiring expertise in robotics or motion planning. We extract sequences of constant screws from demonstrations, which compactly encode the motion constraints while remaining coordinate-invariant. This representation enables robust generalization across variations in grasp placement and allows parameterized reuse of a skill learned from a single example. By composing these screw-parameterized primitives according to the synthesis protocol, the robot autonomously generates motion plans that execute the complete experiment over repeated runs. Our results highlight that screw-theoretic planning, combined with programming by demonstration, provides a rigorous and generalizable foundation for long-horizon laboratory automation, thereby enabling fundamental kinematics to have a translational impact on the use of robots in developing scalable solution-based synthesis protocols.

cs.RO↗

arXiv2016

Size-Dependent Structural Phase Transitions in SrTiO3 Nanoparticles

Understanding the structural phase diagram of nano scale SrTiO3 has important implications on the basic physics and applications of the general class of transition metal oxide perovskites. Pressure dependent structural measurements on monodispersed nanoscale SrTiO3 samples with average diameters of 10 to ~80 nm were conducted. A robust pressure independent polar structure was detected in the 10 nm sample for pressures of up to 13 GPa while a size dependent cubic to tetragonal transition occurs (at P = Pc) for larger particle sizes. The results suggest that the growth of ~10 nm STO particles on substrates with large lattice mismatch will not alter the polar state of the system for a large range of strain values, possibly enabling device use.

cond-mat.mtrl-sci↗

arXiv2014

Polar State in Freestanding Strontium Titanate Nanoparticles

Monodispersed strontium titanate nanoparticles were prepared and studied in detail. It is found that ~10 nm as-prepared stoichiometric nanoparticles are in a polar structural state (with possibly ferroelectric properties) over a broad temperature range. A tetragonal structure, with possible reduction of the electronic hybridization is found as the particle size is reduced. In the 10 nm particles, no change in the local Ti-off centering is seen between 20 and 300 K. The results indicate that nanoscale motifs of SrTiO3 may be utilized in data storage as assembled nano-particle arrays in applications where chemical stability, temperature stability and low toxicity are critical issues.

cond-mat.mtrl-sci↗

arXiv2013

A First-Principles Study of Thiol Ligated CdSe Nanoclusters

A first-principles study of small CdnSen Quantum Dots (QD) ('n' =6, 12, 13, and 33) has been performed for application to QD solar cell development. We separately assess the effects of the particle size and the passivating ligands upon the optimized structure and the energy gap (from a density functional theory (DFT) calculation) and the corresponding absorption spectrum (from a time-dependent density functional theory (TDDFT) calculation). The structures of four thiol ligands, namely - cysteine (Cys), mercaptopropionic acid (MPA), and their reduced-chain analogues, are investigated. We have documented significant passivation effects of the surfactants upon the structure and the optical absorption properties of the CdSe quantum dots: The surface Cd-Se bonds are weakened, whereas the core bonds are strengthened. A blue shift of the absorption spectrum by ~0.2 eV is observed. Also, the optical absorption intensity is enhanced by the passivation. By contrast, we have observed that varying the length of ligands yields only a minor effect upon the absorption properties: a shorter alkane chain might induce a slightly stronger interaction between the -NH2 group and the nearest surface Se atom, which is observed as a stronger ligand binding energy. For Cd12Se12, which is regarded as the 'non-magic' size QD, neither the self-relaxation nor the ligand passivation could fully stabilize the structure or improve the poor electronic properties. We also observe that the category of thiol ligands possesses a better ability to open the band gap of CdSe QD than either phosphine oxide or amine ligands. Our estimation of the absorption peak of the Cys-capped QDs ranges from 413 nm to 460 nm, which is consistent to the experimental peak as 422 nm.

cond-mat.mes-hall↗

arXiv2013

A First-Principles Study of CdSe Nanoclusters Capped by Thiol Ligands

A first-principles study of small CdnSen quantum dots (QDs) (n = 6, 13, and 33) has been performed for the study of QD-sensitized solar cells. We assessed the effects of the passivating thiol-radical ligands on the optimized structure, the energy gap, and on the absorption spectrum. The simplest thiol, methanethiol, and four other thiol type ligands, namely - cysteine (Cys), mercaptopropionic acid (MPA), and their reduced-chain analogues, were investigated. We have come to the following conclusions. (a) Thiol-radical ligands possessed greater effects on the structure and electronic properties of the CdSe QDs than thiol ligands alone. (b) The sulfur 3p orbitals were localized as the midgap states for the thiol-radical-ligated complex, which altered the absorption spectrum of bare Cd6Se6 by inducing a new lower energy absorption peak at 2.37 eV. (c) The thiol-radical-ligated complex was also found to be sensitive to the position and number of ligands. (d) Both the amine group on Cys and the carboxyl group on Cys and MPA showed a strong tendency to bond with the neighboring Cd atom, especially when the length of the ligand was reduced. This formation of Cd-N and Cd-O bonds resulted in smaller HOMO-LUMO gaps and a stronger binding between the ligands and the surface atoms of CdSe nanoclusters.

cond-mat.mtrl-sci↗

arXiv2012

Surface phase transitions in BiFeO3 below room temperature

We combine a wide variety of experimental techniques to analyze two heretofore mysterious phase transitions in multiferroic bismuth ferrite at low temperature. Raman spectroscopy, resonant ultrasound spectroscopy, EPR, X-ray lattice constant measurements, conductivity and dielectric response, specific heat and pyroelectric data have been collected for two different types of samples: single crystals and, in order to maximize surface/volume ratio to enhance surface phase transition effects, BiFeO3 nanotubes were also studied. The transition at T=140.3K is shown to be a surface phase transition, with an associated sharp change in lattice parameter and charge density at the surface. Meanwhile, the 201K anomaly appears to signal the onset of glassy behaviour.

cond-mat.mtrl-sci↗