A THz spectroscopy nondestructive identification method for transgenic cotton seed based on GA-SVM

Terahertz (THz) spectroscopy and imaging were used for probing defects in potential imaging phantoms. Imaging phantoms are materials that can be used to mimic biological systems or general industrial materials. Polyvinyl acetate, silicone and plaster of Paris were used to simulate thin, gel-like, and solid systems, respectively. Defects and impurities were introduced for each material. The THz properties and images of the samples were determined using THz time-domain spectroscopy (THz-TDS). The THz absorption spectra and images were able to reveal variations between the control samples and samples with defects. This clearly shows that these variations are correlated with the defects introduced into the material. These results demonstrate the effectiveness of THz-TDS and imaging in detecting defects even across a wide variety of materials. Furthermore, using principal component analysis (PCA) of the THz images, it was observed that the THz properties varied depending on the type of defect introduced into the samples. PCA results showed distinct clusters for different defects and impurities in the samples. These results highlight a promising non-destructive method for identifying material defects, which can complement other non-destructive evaluation methods, ensuring the quality and safety of materials and products across various industries.

Summary form only given. The terahertz (THz) band of the electromagnetic spectrum has long held interest in the science and engineering community for its unique applications in imaging and spectroscopy. However, due to the difficulty in generating and receiving THz radiation, only very recently practical and efficient THz systems become available. Due to recent advances in the development and manufacturing of commercially available THz spectroscopy and imaging system many of these applications are coming to fruition. As such, the practical implementation of THz in applications needs to be investigated in order to determine the advantages of THz technology. In this work, THz spectroscopy of photovoltaic semiconductor devices will be performed throughout various critical stages in the fabrication process. Due to the few millimeter penetrating and none-destructive properties of THz radiation it will be possible to monitor semiconductor wafers using THz spectroscopy. This technology has a potential to provide insight into the development of wafer defects earlier in the fabrication process. Using a pulsed Terahertz imaging and spectroscopy system at the University of Arkansas, our group will investigate the electrical properties of semiconductor photovoltaics and will conduct THz imaging of defected ones. Testing the wafers throughout various key steps in fabrication is a process known to produce a functional device. This will then be repeated for the same process, only now with a critical fatal defect such as a buried crack, surface crack or a defect in the doping level. These defects will be intentionally inserted at an early stage to determine if THz spectroscopy can be used to detect them early on. THz characterization of the semiconductors for the impurity doping levels and crystal orientation to be studied will be performed to determine the electrical properties in this frequency range. This will allow for accurate numerical simulation to compare with the experimental results.

Investigations were initiated for developing a rapid and nondestructive detection method to measure the illegal additive of melamine into milk powder by using terahertz (THz) spectroscopy and the correlation analysis algorithm. The absorption coefficients exhibited a maximum absorption peak at 2.04 THz, which would normally increase along with the concentration of melamine additive. In the current study, correlation analysis was carried out to select a pair-variable at 2.04 and 2.34 THz for improving the predictive ability of the multiple linear regression (MLR) model. Compared with the partial least square (PLS) model in full spectrum, the MLR model for powder samples could be considered successful in terms of quality control of milk powder with correlation coefficient R2 of 0.97 and root mean square error of prediction (RMSEP) of 1.38%. At the same time, the MLR model was simple and easier to interpret than the PLS one. The results of the research suggested that THz spectroscopy in combination with the correlation analysis algorithm has a significant potential in the quantitative analysis of the illegal additive of melamine in milk powder.

Terahertz (THz) spectroscopy has high sensitivity for the interaction between molecules and vibration of large molecules. Besides, it is well known that infrared (IR) spectroscopy can be used to detect the vibration of functional groups. Hence, the comparison of the conventional diagnosis method using IR spectroscopy and THz spectroscopy is expected for more potential diagnosis. In this study, the comparison between THz spectroscopy and IR spectroscopy for deteriorated hydrocarbon liquids has been conducted for the degraded insulating oils. The surveyed samples are pure dodecane and mineral oil. The degraded samples are made by heating in the oxygen atmosphere. In addition, we also measured the breakdown voltage and the volume resistivity to know the states of degraded insulating oil. The experimental results show that oxidation causes spectral changes in the both of THz and IR regions. The spectral change in the IR region is due to carbonyl group and hydroxyl group vibrations. Whereas, in the THz region, the spectral change originates from the modification of intermolecular interaction. The degradation phenomena of the insulating oil contribute to higher carbonyl/hydroxyl content and associated by stronger intermolecular interaction that leads to its lower breakdown voltage.

Metal-organic frameworks (MOFs) are porous crystalline materials. Their large pores make them particularly interesting for membranes, gas separation, and gas storage. Furthermore, MOFs are ultralight, making them suitable for a large realm of exciting applications ranging from wearable devices to space technology. Optimizing MOFs for these applications demands a detailed understanding of their low energy dynamics and photophysics, which can be provided by terahertz (THz) spectroscopy. MOFs exhibit structural modes, or phonons, with energies in the meV range, which corresponds to the THz spectral range (0.1–10 THz, 0.4–40 meV). Understanding these modes is crucial in determining how a MOF interacts with guest molecules in the process of gas capture and storage. In this perspective, we discuss how gas-MOF interactions alter the MOFs’ spectral fingerprints. We demonstrate that THz spectroscopy can be used for gas adsorption monitoring and explain how density functional theory, together with THz spectra, can illuminate the dynamic structure of MOFs, providing unique insight into their functionality. THz is also a contact free probe for conductivity and allows us to measure short range conductivity within an individual MOF crystal. We will discuss the advantages of THz as a conductivity probe for MOFs as compared to more established direct current techniques. We will then expand our view to incorporate ultrafast photoconductivity in MOFs measured via optical pump-THz probe spectroscopy, in comparison to more established ultrafast spectroscopic tools such as optical transient absorption and photoluminescence. We will supplement this section with a discussion of THz studies on perovskites, which unveiled electron–phonon interactions not yet explored in MOFs.

Effects of Hydration Levels on the Bandwidth of Microwave Resonant Absorption Induced by Confined Acoustic Vibrations

A new high-temperature polymorph of 5-(4-pyridyl)tetrazole has been discovered and characterized using X-ray crystallography and terahertz (THz) spectroscopy. The THz spectrum of the new polymorph was compared to the previously published form and was replicated by means of solid-state density functional theory. Terahertz spectroscopy was used to determine the influence of the different packing motifs on the molecular and low energy lattice vibrations displayed in the region from 10 to 100 cm(-1). It was found that there is only a ∼2 cm(-1) difference in the primary peak location, caused by a whole molecule rotation along the principal a axis, between the two polymorphic forms. In addition, the energy of formation was determined, and it was found that the previously known polymorphic form is more stable by ∼0.25 kJ/mol, compared to the newly discovered form.

Over the past few decades, terahertz (THz) spectroscopy has become an established technique for studying the dielectric and transient photoconductive properties of materials. THz spectroscopy is a contact-free probe of electrical conductivity with subpicosecond time resolution, and it has proven especially useful for studying emerging materials. We highlight recent work used to study metal halide perovskites, metal oxides, metal–organic frameworks, and 2D materials in addition to providing an overview of methods in pump–probe THz spectroscopy. We focus on the ways in which THz spectroscopy can be used to study charge transport mechanisms and factors that might limit carrier mobility in emerging materials. This Perspective will provide a general understanding of pump–probe THz spectroscopy and how it can be applied to next-generation materials and will identify challenges and advantages in data processing to extract broadband complex conductivity spectra.

As one of the main functional substances, carbohydrates account for a large proportion of the human diet. Conventional analysis and detection methods of dietary carbohydrates and related products are destructive, time-consuming, and labor-intensive. In order to improve the efficiency of measurement and ensure food nutrition and consumer health, rapid and nondestructive quality evaluation techniques are needed. In recent years, terahertz (THz) spectroscopy, as a novel detection technology with dual characteristics of microwave and infrared, has shown great potential in dietary carbohydrate analysis. The current review aims to provide an up-to-date overview of research advances in using the THz spectroscopy technique in analysis and detection applications related to dietary carbohydrates. In the review, the principles of the THz spectroscopy technique are introduced. Advances in THz spectroscopy for quantitative and qualitative analysis and detection in dietary carbohydrate-related research studies from 2013 to 2022 are discussed, which include analysis of carbohydrate concentrations in liquid and powdery foods, detection of foreign body and chemical residues in carbohydrate food products, authentication of natural carbohydrate produce, monitoring of the fermentation process in carbohydrate food production and examination of crystallinity in carbohydrate polymers. In addition, applications in dietary carbohydrate-related detection research using other spectroscopic techniques are also briefed for comparison, and future development trends of THz spectroscopy in this field are finally highlighted.

Characterization of Pesticide Residue, cis-Permethrin by Terahertz Spectroscopy

In this work, the terahertz (THz) spectroscopy system was used for the detecting and evaluation of hidden damages in a glass fiber reinforced plastic (GFRP). The interaction between THz and the GFRP was analyzed including the effects of reflecting, scattering and absorption of THz radiations with respect to the type of hidden damage. Both the transmission and reflective configurations were used to investigate the hidden damages including the delamination, fiber fracture and moisture absorption. Finally, the hidden damages inside of the composite laminates were successfully imaged simultaneously based on the time-domain spectroscopy of THz radiation. Additionally, the moisture absorption damage in the GFRP could be detected by analyzing of the frequency domain spectrum. It is expected that the developed THz nondestructive evaluation (NDE) technique can be widely used to evaluate the health of the composite structures.

The role of water in biomolecule dynamics has attracted much interest over the past decade, due in part to new probes of biomolecule–water interactions and developments in molecular simulations. Terahertz (THz) spectroscopy, among the most recent experimental methods brought to bear on this problem, is able to detect even small solute‐induced changes of the collective water network dynamics at the biomolecule–water interface. When studying the properties of water in aqueous solutions via THz absorption, proteins show a long‐ranged influence on water network dynamics, and even small saccharides influence the dynamics of several hydration layers. The THz spectrum of water solvating a protein is sensitive to mutations and depends on the surface charge and flexibility of the protein. Influence on the solvation shell appears most pronounced for native wild‐type proteins and decreases upon partial unfolding or mutation. THz spectra of solvated saccharides reveal that the number of water molecules coupled dynamically to a saccharide forming a dynamic hydration shell around it is related to the number of exposed oxygen atoms on the solute surface. The thickness of this layer appears correlated with the bioprotection efficiency of the saccharide. All findings support the thesis of a long‐range dynamic coupling between biomolecules and solvent. Kinetic terahertz absorption (KITA) studies of protein folding recently revealed that solvent dynamics are coupled to secondary structure formation of the protein. The solvent water network is dynamically rearranged in milliseconds before the protein folds to its native state in the following seconds. THz spectroscopy gives experimental evidence that collective long‐range dynamics are a key factor of biomolecular hydration.

Gold-hyperdoped germanium extends photodetection into the infrared wavelengths. Pulsed-laser processing makes single crystal material with ultrahigh dopant concentrations. The laser parameters influence the dopant’s atomic position which leads to different light absorption and carrier transport properties. OCIS codes: 160.6990 Transition-metal-doped materials, 300.6495 Spectroscopy, terahertz, 140.3390 Laser materials processing Short wavelength infrared radiation detection is important in many applications and conventional detector materials are expensive, toxic or require low operation temperatures [1-3]. Developing novel semiconductor materials that overcome these limitations are important. Germanium (Ge) is a good material candidate due to its high absorption coefficients across a broad band in short wavelength infrared region (SWIR) and high carrier mobilities [4]. Bandgap energy of Ge is 0.67 eV (1.8 µm) and hence further engineering methods are of great interest to obtain photodetection beyond this cut-off wavelength of elemental Ge. Laser hyperdoping is a viable method to incorporate dopants in ultra-high non-equilibrium concentrations above the solid solubility limit, which enables the formation of an intermediate band between the conduction and valance bands [5]. Hyperdoped Ge has shown to be a promising candidate for efficient SWIR photodetection [6] . Laser hyperdoping can be achieved with ultrashort laser pulses or with nanosecond laser pulses but the resulting material is polycrystalline and has roughened surfaces. A better method to fabricate a hyperdoped material is the ion implantation followed by nanosecond pulsed laser melting which produces high quality materials that is single crystalline (Figure 1). High flux of dopant atoms implanted in the host semiconductor damages the lattice structure and amorphizes the material. Therefore, the pulsed laser process is carried out to melt the material deeper than the damaged layer. This process is followed by rapid solidification, where the material grows epitaxially from the crystalline substrate underneath, as the material cools down. During this rapid re-solidification, the dopants are trapped at concentrations above the thermodynamic solubility limit and hence ultra-high concentrations are achieved while preserving the material quality. The rapid solidification process must be slow enough to ensure the recrystallization and at the same time it must be fast enough to allow the incorporation of non-equilibrium dopant concentrations into the sample. Thus, the energy density (fluence) of the pulsed laser have significant effect on the material quality. This is a well-established method for chalcogen dopants (S, Se, Te) in silicon, but incorporating transition metals at supersaturating concentrations with better properties has more room for study [7]. Figure 01 – Hyperdoping by ion implantation followed by pulse laser melting. Figure adapted from ref. [5] In this work, we use ion implantation followed by pulsed laser melting to incorporate high concentrations of gold (Au) in Ge. Au hyperdoped Ge (Ge:Au) with different dopant doses and various pulsed laser melting fluences are studied. We evaluate the material quality using time resolved terahertz (THz) spectroscopy to investigate the charge carrier lifetime of the material. THz spectroscopy is a photoconductivity measurement with sub-picosecond time resolution. We use a 400-nm fs-laser pump pulse to excite the charge carriers in the material and probe with a broadband sub-picosecond THz pulse to map the photoconductivity decay dynamics [8]. Apart from the charge carrier lifetime analysis (Figure 2), the dopant concentration profile is analyzed by Rutherford Backscattering Spectrometry (RBS). Moreover, the sub band gap absorptance and DFT modelling of dopant distribution and their effect on band structure are being investigated. Figure 02 – Left: The change in photoconductivity of Ge:Au as a function of time. Charge carrier decay dynamics of different dopant concentrations and PLM fluences are investigated. The samples are LD_HF (low dose-high fluence), LD_LF (low dose-low fluence) HD_HF (high dose-high fluence) and HD_LF (high dose-low fluence) respectively. HD_LF has a significantly shorter lifetime than the rest. Right : Upper panel - The inverse of experimentally obtained half-lives. Triangles and circles represent LF and HF respectively. Sub-band gap absorptances are represented by unfilled triangles and circles. Lower panel - Total and substitutional dose of Au in hyperdoped Ge samples from RBS analysis. The unfilled bars and filled bars represent the total and substitutional doses, respectively. HD_LF has the most substitutional Au incorporation, while substitutional Au incorporation in HD_HF sample is much more similar to the two LD samples. In this study, we found that laser fluence determines the fraction of substitutional dopant (Figure 2). Material characterization shows that lifetime and absorption correlate with substitutional dose. Moreover, DFT modeling indicates that substitutional dopants are deep level defects which lead to high absorption and short lifetime. We found that the charge carrier lifetime is very long even after high concentration of Au is incorporated. We also found laser parameters that lead to highly substitutional dopant incorporation which enhances infrared light absorption. THz lifetime characterization allows optimizing processing parameters and shows hyperdoped germanium is a promising material for SWIR photodetectors.

Water content of the skin is an important parameter for controlling the penetration rate of chemicals through the skin barrier; therefore, for transdermal patches designed for drug delivery to be successful, the effects of the patches on the water content of the skin must be understood. Terahertz (THz) spectroscopy is a technique which is being increasingly investigated for biomedical applications due to its high sensitivity to water content and non-ionizing nature. In this study, we used THz measurements of the skin (in vivo) to observe the effect of partially and fully occlusive skin patches on the THz response of the skin after the patches had been applied for 24 h. We were able to observe an increase in the water content of the skin following the application of the patches and to identify that the skin remained hyper-hydrated for four hours after the removal of the fully occlusive patches. Herein, we show that THz spectroscopy has potential for increasing the understanding of how transdermal patches affect the skin, how long the skin takes to recover following patch removal, and what implications these factors might have for how transdermal drug patches are designed and used.

Combinatorial method to investigate cystine enantiomers using vibrational spectroscopies