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Time-of-flight secondary ion mass spectrometry fragment regularity in gallium-doped zinc oxide thin films.

ABSTRACT: Time-of-flight secondary ion mass spectrometry fragment analysis remains a challenging task. The fragment appearance regularity (FAR) rule is particularly useful for two-element compounds such as ZnO. Ion fragments appearing in the form of Zn_xO_y obey the rule [Formula: see text] in the positive secondary ion spectrum and [Formula: see text] in the negative spectrum where the valence of Zn is + 2 and that of O is - 2. Fragment analysis in gallium-doped ZnO (GZO) films can give insights into the bonding of the elements in this important semiconductor. Fragment analysis of 1 and 7 wt% GZO films shows that only the negative ion fragments obey the FAR rule where ZnO^‒, ⁶⁶ZnO^‒, ⁶⁸ZnO^‒ and ZnO₂^‒ ion fragments appear. In the positive polarity, subdued peaks from out-of-the-rule ZnO⁺, ⁶⁶ZnO⁺ and ⁶⁸ZnO⁺ ion fragments are observed. The Ga ion peaks are present in both the positive and negative spectra. The secondary ion spectra of undoped ZnO also shows consistency with the FAR rule. This implies that Ga doping even in amounts that exceed the ZnO lattice limit of solubility does not affect the compliance with the FAR rule.

SUBMITTER: Saw KG

PROVIDER: S-EPMC8027856 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:N-Hydroxysuccinimide (NHS) esters are widely used as leaving groups to activate covalent coupling of amine-containing biomolecules onto surfaces in academic and commercial surface immobilizations. Their intrinsic hydrolytic instability is well-known and remains a concern for maintaining stable, reactive surface chemistry, especially for reliable longer term storage. In this work, we use X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry (TOF-SIMS) to investigate surface hydrolysis in NHS-bearing organic thin films. Principal component analysis (PCA) of both positive and negative ion TOF-SIMS data was used to correlate changes in the well-defined NHS ester oligo(ethylene glycol) (NHS-OEG) self-assembled monolayers to their surface treatment. From PCA results, multivariate peak intensity ratios were developed for monitoring NHS reactivity, thin-film thickness, and oxidation of the monolayers during surface hydrolysis. Aging in ambient air for up to 7 days resulted in hydrolysis of some fraction of bound NHS groups, oxidation of some resident thiol groups, and deposition of adventitious hydrocarbon contaminants onto the monolayers. Overnight film immersion under water produced complete hydrolysis and removal of the NHS chemistry, as well as removal of some of the thiolated OEG chains. NHS regeneration of the hydrolyzed surfaces was assessed using the same multivariable peak intensity ratio as well as surface coupling with amine-terminated molecules. Both aqueous and organic NHS regeneration methods produced surfaces with bound NHS concentrations approximately 50% of the bound NHS concentration on freshly prepared NHS-OEG monolayers. Precise methods for quantifying NHS chemistry on surfaces are useful for quality control processes required in surface technologies that rely on reliable and reproducible reactive ester coupling. These applications include microarray, microfluidic, immunoassay, bioreactor, tissue engineer-ing, and biomedical device fabrication.

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Time-of-flight secondary ion mass spectrometry fragment regularity in gallium-doped zinc oxide thin films.

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