A Novel Sample Preparation Method for Frontside Inspection of GaN Devices after Backside Analysis

Frontside die inspection by Scanning Electron Microscopy (SEM) is critical to investigate failures that appear dispersed over the GaN die surface and that will be very difficult to localize by the typical Focus Ion Beam (FIB) or Transmission Electron Microscopy (TEM) analysis. Frontside sample preparation is; however, extremely challenging if the device was already subjected to sample preparation for backside Photo Emission Microscopy (PEM). In this paper, a novel sample preparation method is presented where all front side layers are removed and only the 5μm GaN die is left for inspection.

Towards Cellular Ultrastructural Characterization in Organ-on-a-Chip by Transmission Electron Microscopy

Organ-on-a-chip technology is a 3D cell culture breakthrough of the last decade. This rapidly developing field of bioengineering intertwined with microfluidics provides new insights into disease development and preclinical drug screening. So far, optical and fluorescence microscopy are the most widely used methods to monitor and extract information from these models. Meanwhile transmission electron microscopy (TEM), despite its wide use for the characterization of nanomaterials and biological samples, remains unexplored in this area. In our work we propose a TEM sample preparation method, that allows to process a microfluidic chip without its prior deconstruction, into TEM-compatible specimens. We demonstrated preparation of tumor blood vessel-on-a-chip model and consecutive steps to preserve the endothelial cells lining microfluidic channel, for the chip’s further transformation into ultrathin sections. This approach allowed us to obtain cross-sections of the microchannel with cells cultured inside, and to observe cell adaptation to the channel geometry, as well as the characteristic for endothelial cells tight junctions. The proposed sample preparation method facilitates the electron microscopy ultrastructural characterization of biological samples cultured in organ-on-a-chip device.

Simultaneous Analysis of Fenpropimorph and Fenpropimorph Acid in Six Different Livestock Products Using a Single-Sample Preparation Method Followed by Liquid Chromatography–Tandem Mass Spectrometry

Pesticides in livestock products must be measured to ensure food safety. We developed a single-sample preparation method followed by liquid chromatography–tandem mass spectrometry (LC-MS/MS) for simultaneous determination of fenpropimorph and fenpropimorph acid in six different livestock products. The extraction method was a modification of the quick, easy, cheap, effective, rugged, and safe (QuEChERS) method and was validated according to the CODEX guidelines. The matrix-matched calibration curves for fenpropimorph and fenpropimorph acid exhibited good linearity, with coefficients of determination (R2 values) higher than 0.998. The limit of detection (LOD) and the limit of quantitation (LOQ) were 1.25 and 5.0 µg kg−1, respectively. The average recovery values ranged from 61.5% to 97.1% for samples fortified to the LOQ, 2 × LOQ, and 10 × LOQ. The method fully complied with the CODEX guidelines and was successfully applied to real samples obtained from domestic markets.

Small-Strain Shear Modulus of Calcareous Sand under Anisotropic Consolidation

In this study, the small strain shear modulus of a calcareous sand was investigated by conducting bender element tests on both horizontal and vertical planes. The effects of sample preparation method, stress path and stress history on the developing of void ratio, the parameters in the modified Hardin equation and the stiffness anisotropy were examined. The test results show that the moist tamping samples have the least void ratio variation among the five samples. The void ratio recovery in σ'h = 100 kPa tests is higher than that in the σ'v = 100 kPa tests. The samples prepared in dry state have lower stiffness than those prepared in moisture state, which is not influenced by the anisotropic stress state. The stiffness anisotropy induced by the sample preparation method is significant under anisotropic consolidation. In σ'h = 100 kPa tests, the stiffness ratios at the end of the unloading stage are lower than the initial values at the loading stage, which is not found in the σ'v = 100 kPa tests, meaning that the stress history and stress path could affect the stiffness anisotropy and cover the impact of fabric anisotropy.