Germanium Crystals Research Articles

Characterization of fluoroelastomers compounds by ATR-FTIR

Fluoroelastomers (FKM) are used to manufacture seals and other rubber devices that can withstand harsh operating conditions, including aggressive media and extreme low and high temperatures. Even though nuclear magnetic resonance, Fourier-transform infrared spectroscopy (FTIR), and chromatographic techniques have been extensively used in the characterization of raw FKM molecules, the identification of cured compounds entails a characterization method that is able to overcome the complexity related to this kind of structure. In this sense, attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy can outperform other characterization techniques because it does not require solubilization or any special preparation of the sample. In this study, 10 FKM compounds were produced in this study utilizing four commercial types of FKM and the fillers carbon black, barium sulfate, and iron oxide. All unfilled-FKM (as received) and their compounds were analyzed by ATR-FTIR with germanium crystal. Between 15 and 25 analyses were performed for all each FKM type sample and their respective compounds. All spectra were analyzed, and the bands were assigned. Findings regarding the interference of the fillers in the spectra were also reported. From relationships between the height of the spectral zones and the bands at 1397 and 1428 cm−1, it was possible to distinguish all sample compositions of FKM types 1, 2, 3, and 5. This study demonstrates that ATR-FTIR has the potential to be utilized as a technique to detect the type of FKM compounds, an important rubber used in harsh industrial applications. Replacing carbon with BaSO4 reduces the tensile at 50% strain of FKM types 1 and 2 composites. FKM types 3 and 5 composites filled with 30 phr of carbon black have a higher tensile at 50% strain than those of FKM type 1.

Reversible modulations of insulator–metal transition in an epitaxial VO2 film through thermal crystallization and femtosecond laser-induced-amorphization of capping Ge2Sb2Te5 layer

We demonstrate reversible modulation of an insulator–metal transition (IMT) of a VO2 film grown on an Al2O3 (001) substrate through crystallization and re-amorphization of a chalcogenide germanium–antimony–telluride (Ge2Sb2Te5: GST) capping layer. After succeeding in the negative shift of IMT temperature (Tr) of the VO2 film through the crystallization of the GST layer accompanied by volume reduction, we performed re-amorphization of the crystalline GST by femtosecond laser irradiation. Under the optimized conditions of laser irradiation considering the penetration depth, re-amorphization of the GST layer was fully achieved, resulting in the shift-back of Tr toward a high-temperature side. Such a reversal of IMT through the crystallization and re-amorphization of the capping GST layer was demonstrated over two cycles. It was suggested that capping GST effectively induces interfacial strain modifications in the VO2 film underneath. Although the shifts in the IMT are still small, reversible modulation of IMT shown here will be beneficial for applications of VO2 films with controllable IMT.

Energy and time characterization of the newly acquired clover detector in Jordan

A comprehensive overview of the Balqarad clover detector acquired by Al-Balqa Applied University in Jordan is given in detail. The detector consists of four high-purity germanium crystals, accompanied by a composite scintillation active shield. Through meticulous testing involving a range of radioactive sources such as 137Cs, 60Co, and 241Am, we evaluate the performance of the clover detector. The associated digital data acquisition system incorporates specialized and unconventional time registers, operating in event-by-event mode. Our objective is to elucidate the energy and time characteristics exhibited by the new system under different operational modes, employing specifically designed offline software. Our findings encompass vital aspects. These aspects include the determination of the optimal time window value for processing data obtained from gamma detection measurements. Another issue that has been considered is the analysis of hit pattern distribution within each individual crystal. Additionally, we calculate the addback factor for the 60Co source, accounting for gamma energies of 1173 keV and 1332 keV while also considering the influence of time window increment.

Self-power, multiwavelength photodetector based on a Sn-doped Ge quantum dots/hexagonal silicon nanowire heterostructure.

Tin-doped germanium quantum dots (Sn-doped Ge QDs)-decorated hexagonal silicon nanowires (h-Si NWs) were adopted to overcome the low infrared response of silicon and the excess dark current of germanium. High-quality Sn-doped Ge QDs with a narrow bandgap can be achieved through Ge-Sn co-sputtering on silicon nanowires by reducing the contact area between heterojunction materials and Sn-induced germanium crystallization. The absorption limit of the heterostructure is extended to 2.2 µm, and it is sensitive to 375-1550 nm light at 0 V, which has optimality at 1342 nm, with a photo-to-dark current ratio of over 815, a responsivity of 0.154 A/W, and a response time of 0.93 ms. The superior performance of the Sn-doped Ge QDs/h-Si NW photodetector in multiwavelength is attractive for multi-scenario applications.

Low-temperature crystallization of BeO-assisted polycrystalline germanium layer for monolithic 3D integration

We demonstrated a new method for the low-temperature solid-phase crystallization (SPC) of germanium on beryllium oxide (BeO) films for monolithic 3D (M3D) integration. Using a wurtzite crystal BeO film, known for its high thermal conductivity of 370 W/m-k at 300 K and covalent bonding characteristics, as the underlying layer, we crystallized Ge at a reduced temperature of 410 °C. For the Ge-on-BeO, the formation of larger grains was consistently promoted at annealing temperatures of 410–500 °C, with a notable 125 % increase in the grain size at 500 °C compared to that at the SiO2 underlayer. The polycrystalline Ge layers crystallized on the BeO retained their tensile strain, as confirmed by the Raman spectra. Furthermore, its optical bandgap of ∼ 1.36 eV and average roughness of 0.847 nm at an annealing temperature of 450 °C make it more suitable for an M3D upper channel layer than Ge-on-SiO2. A comprehensive experimental analysis confirmed the enhanced crystallinity, stability, and channel properties of poly-Ge layers crystallized on BeO. Hence, this study developed a new method for the low-temperature SPC process and highlighted the potential of BeO as a crystallization-assistance thermal-management material for next-generation 3D integrated technology.

Exploring surface properties and premelting in crystals.

Crystal surfaces play a pivotal role in governing various significant processes, such as adsorption, nucleation, wetting, friction, and wear. A fundamental property that influences these processes is the surface free energy, γ. We have directly calculated γ(T) for low-index faces of Lennard-Jones (LJ), germanium, and silicon crystals along their sublimation lines using the computational cleavage technique. Our calculations agree well with experimental values for Si(111) and Ge(111), highlighting the accuracy of the method and models used. For LJ crystals, we identified a premelting onset at Tpm = 0.75Tm, marked by a sharp increase in atom mobility within the second outermost surface layer. Notably, Tpm closely aligned with the endpoint of the LJ melting line at negative pressures, Tend = 0.76Tm. We hypothesize that the emergence and coexistence of a liquid film atop the LJ crystal at Tpm < T < Tm correspond to the metastable melting line under negative pressures experienced by stretched crystal surfaces. Furthermore, our study of thin LJ crystal slabs reveals that premelting-induced failure leads to recrystallization below the homogeneous freezing limit, offering a promising avenue to explore crystal nucleation and growth at extremely deep supercoolings. Finally, no evidence of premelting was detected in the model crystals of Ge and Si, which is consistent with the experimental observations. Overall, our findings offer valuable insights into crystal surface phenomena at the atomic scale.

Improving the detection limit in lung counting with a segmented HPGe detector

A segmented High-Purity Germanium (HPGe) detector with a thin front segment together with various active and passive shield configurations was simulated with the aim of reducing the level of background events in lung counting applications. Eight different detector models were tested in a Geant4 simulation environment in a scenario where inhaled 241Am activity was deposited in the lungs of an ICRP adult reference computational phantom. In lung counting measurements, the Compton continuum in the spectrum is generated by the natural and man-made radionuclides inside the human body and the natural background radiation from the environment. The reduction in Minimum Detectable Activity (MDA) using the segmented HPGe detector combined with an active shield compared to a model with a single germanium crystal was investigated. A reduction in MDA up to 30% and 66% was obtained for internal and external sources, respectively. The results show that the detection limit and/or the measurement time in lung counting can be reduced using such a detector configuration. Furthermore, combining the segmented HPGe detector with an active shield would be particularly useful in field measurements.

Post-growth tuning of detachable Ge membranes adhesion strength via porous Ge transformation

Single crystal germanium (Ge) membranes have recently gained increasing interest for lightweight and low-cost solar cells and flexible optoelectronic devices. These membranes achieved similar material quality as bulk Ge substrate. However, the control of the membrane detachment is still challenging. In this work, we explore post-growth engineering of the adhesion strength of a Ge membrane on a porous germanium (PGe) substrate by inducing morphological transformations in the separation layer through Thermal Budget (TB) control. Indeed, the pillars formed through PGe sintering during epitaxy are found to evolve with post-growth thermal annealing. Scanning electron microscopy (SEM) based analysis of the residue of the post-detachment broken pillars has been performed showing that the pillar's diameter and density can be tuned by thermal annealing. Depending on the post-growth annealing temperature, the membrane adhesion strength can be successively tailored from 0.5 to up to 3.5 MPa while ensuring 100 % detachment yield. The experimental results have been correlated with Finite Element Modeling (FEM) considering realistic pillar distribution revealing that pillar size and density are the dominant factors influencing the membrane adhesion strength.

Modeling of N and P-Type of Coaxial Ge Detectors Using MCNPX and the Effect of Dead Layer Variation on Its Response Function

Abstract This study assessed the response function of a p-type and n-type coaxial high-purity germanium (HPGe) detector via Monte Carlo N-Particle eXtended (MCNPX). MCNPX was employed to model the Coaxial Ge detectors, and for a precise simulation, the dimensions of the dead layer of germanium crystals were added. The dead layer was separated into front and lateral surfaces, and the thickness of each dead layer was modeled. In this work, the simulated detectors have been performed at different energy lines using a radioactive source Eu-152 to study the response function of each with dead layer variations for the front dead layer and study the range of relative deviation of the Monte Carlo simulation outputs from the manufactured declared data. The results proved that the n-type coaxial HPGe detector is more sensitive to the dead layer change than the p-type with a thick change of 0.01 mm. This research has significant effects on the efficiencies of the radiation detection systems in the energy range ∼ (120–1410) keV.

Design of GRETA Cooling Systems

The Gamma-Ray Energy Tracking Array (GRETA) is a full 4π gamma-ray tracking detector capable of reconstructing the energy and three-dimensional position of gamma-ray interactions within a compact sphere of high-purity germanium crystals. The GRETA Detector Array Sphere will have the capacity to accommodate a total of 30 Germanium Quad Detector Modules (QDM). The 30 QDMs are to be cooled and maintained below 100 K using liquid nitrogen (LN) at all times while the array is in normal operation, and will require regular filling of a LN Dewar on each module. The Dewar is designed to allow the Quad Module to be operated in any orientation with a LN holding time of no less than 12 hours when the detector module is fully powered. An automated LN cooling and refilling system is required to supply LN to the 30 QDMs and ensure them maintained below 100 K. Each of the GRETA QDMs houses a total of 148 pre-amplifier units within the module, and with the high power consumption of each pre-amplifier, active cooling of the pre-amplifier compartment is required. Additionally, each Quad Module will have 4 digitizer modules attached to it, which generate heat and require cooling as well. A closed-loop liquid (Glycol) cooling system will provide the required temperature stability and dissipate power generated heat for electronics. This paper presents design of the GRETA LN cooling system for detectors and the closed-loop liquid cooling system for electronics including technical requirements, design schemes, key components, operation modes, and so on.

Low temperature metal induced crystallization of orientation-preferred polycrystalline germanium with n- and p-type doping for device applications

A metal-induced crystallization (MIC) doping method is proposed for the fabrication of n- and p-type doping polycrystalline germanium (poly-Ge). This method involves the use of amorphous- (α-) Ge/metal/α-Ge/crystal-Ge stacked structure to achieve orientation-preferred poly-Ge on Ge (100) substrate at a very low temperature of 240℃. Aluminum (Al) and bismuth (Bi) metal layers are selected for p- and n- type doping sources, respectively. The thickness ratio of metal to α-Ge is optimized to obtain dense poly-Ge. Raman spectrum, scanning electron microscopy and electron backscattered diffraction characterizations confirm that the crystallized α-Ge exhibits a preferred orientation along (100) with a smooth surface. The p- and n- type doping concentrations are evaluated to be 2.2×1021 cm−3 and 2.7×1019 cm−3, respectively, by Hall effect measurement. Furthermore, p-type poly-Ge/n-Ge and n-type poly-Ge/p-Ge junctions are formed with significant rectification ratios of 103 and 102@±2 V, respectively. These findings indicate that the low-temperature MIC approach holds great potential for the fabrication of n- and p-type poly-Ge, enabling the development of Ge-based active devices at low temperature.

Study of cosmogenic activation in 76Ge enriched germanium detectors during fabrication and transportation above ground

Rare event search experiments using germanium detectors are operated in underground laboratories to minimize the background induced by cosmic rays. However, the cosmogenic activation in germanium crystals on the ground during fabrication and transportation generates long half-life radionuclides and contributes a considerable background. We simulated the production rates of cosmogenic radionuclides in germanium and calculated the specific activities of cosmogenic radionuclides according to the scheduled fabrication and transportation processes of 76Ge enriched germanium detectors. The impact of cosmogenic background in germanium crystals for the next generation CDEX experiment was assessed with the scheduled exposure history above ground.

Self‐Powered Photodetector Based on Perovskite/Ge Heterojunction with High Responsivity

AbstractSelf‐powered photodetectors (SPDs) are regarded as a new type of photodetectors without external energy sources, exhibiting great potential in the next generation of image sensing, biological detection, and robotics. Here, single crystal CH(NH2)2PbBr3 (FAPbBr3) perovskite with a low trap density of 1.64 × 109 cm−3 is directly integrated onto single crystal germanium (Ge). The band structure of the heterojunction belongs to type‐II alignment type, which is beneficial to the achievement of high responsivity. Therefore, the fabricated Au/FAPbBr3/Ge/Au detector exhibits a high responsivity of 0.33 A W−1, detectivity up to 3.83 × 1011 Jones and relatively fast decay time of 4.94 ms without external bias under 520 nm laser illumination. In addition, a prototype of an imaging system is set up utilizing the photodetector as a sensing pixel, from which the imaging function is verified. This work demonstrates a facile strategy for designing high‐performance SPDs.

NIR to LWIR Dichroic Beamsplitter Designed and Manufactured for Space Optical Remote Sensor

The infrared dichroic beamsplitter plays an important role in infrared multi-band imaging systems, especially for infrared remote sensing. This paper presents the design and preparation of a dichroic beamsplitter that is capable of reflecting near infrared (NIR) and shortwave infrared (SWIR), and transmitting medium wave infrared (MWIR) as well as longwave infrared (LWIR). A single crystal germanium (Ge) sheet is used as the substrate of the dichroic beamsplitter, while Ge, zinc sulfide (ZnS) and ytterbium trifluoride (YbF3) are selected as coating materials. The average reflectance of the dichroic beamsplitter is more than 95% in bands 1.28 to 1.38 μm, 1.58 to 1.83 μm, and 1.95 to 2.32 μm, and the average transmittance is more than 92% in bands 3.7 to 6.2 μm and 7.5 to 12.5 μm at an incident angle of 45°. The dichroic beamsplitter has been successfully applied in the optical system of infrared remote sensing. It provides a technical approach for other optical systems to separate the optical spectrum from NIR to LWIR.

Passively mode-locked Er-doped fiber laser with single and double wavelength pulses based on germanene saturable absorber

In this paper, we focus on the single crystal material germanium (Ge), which is fabricated into saturable absorbers (SAs) employing liquid phase exfoliation, and validate it with an erbium-doped fiber laser (EDFL). The Ge SA was obtained with a modulation depth of 9.8% and a saturation intensity of 11.02 MW cm−2. The single-wavelength mode-locked pulse with a minimum pulse width of 847 fs was obtained at a cavity length of 10.5 m. In addition, at a cavity length of 106 m, a dual-wavelength mode-locked phenomenon was obtained in which the central wavelengths were located at 1559.20 nm and 1561.31 nm. The experimental results show that Ge nanosheets in an EDFL provide a strong basis for the development of nonlinear optics and have a wide range of applications in the field of pulsed fiber lasers.

Investigating Influential Parameters for High-Purity Germanium Crystal Growth

This paper focuses on the research and development of high-purity germanium (HPGe) crystals for detector fabrication, specifically targeting applications in rare-event physics searches. The primary objective was to produce large-scale germanium crystals weighing &gt;1 kg with a controlled diameter of ∼10 cm and an impurity range of approximately 1010/cm 3. Ensuring structural integrity and excellent crystalline quality requires a thorough assessment of dislocation density, a critical aspect of the crystal development process. Dislocation density measurements play a crucial role in maximizing the sensitivity of HPGe detectors, and our findings confirmed that the dislocation density fell within acceptable ranges for detector fabrication. Additionally, this paper examines the segregation coefficient of various contaminants during the crystal development process. Comprehensive analysis of impurity segregation is essential for reducing contaminant quantities in the crystal lattice and customizing purification processes. This, in turn, minimizes undesired background noise, enhancing signal-to-noise ratios for rare-event physics searches and overall detector performance. The investigation included the segregation coefficients of three major acceptors and one donor in crystals grown at the University of South Dakota, providing valuable insights for optimizing crystal purity and detector efficiency.

Enhancement of Mg-induced lateral crystallization of amorphous germanium on an insulating substrate by two-step annealing

Magnesium (Mg)-induced lateral crystallization (Mg-ILC) of amorphous germanium (Ge) on a SiO2 stacked structure was investigated. From Raman mapping images, the critical annealing temperature necessary to induce Mg-ILC of amorphous Ge was estimated to be about 350 °C. Furthermore, the Mg-ILC length was truly narrow (∼2 μm) compared with other metal catalysts after annealing at 350 °C for 1 h. To enhance the Mg-ILC, we have examined a two-step annealing method for Mg-ILC of amorphous Ge on SiO2. The Mg-ILC length is significantly enhanced (∼4.5 times) by using a two-step annealing process, which is due to the enhancement of Mg diffusion into amorphous Ge during first-stage low-temperature annealing.

The history of the first germanium crystals along with a descendant of the novel “Bulgarians of old time”

This article represents a review of studies on the determination of germanium and the intriguing history behind it. The purpose of this paper is to familiarize readers with one outstanding figure in Bulgaria on the second half of the 19th century and his scientific activities - in particular, the Bulgarian trace in the discovery of the element Ge. The advantages of this research item are many and diverse, of course, but the main issue is to get closer for the umpteenth time to the chemistry that was created for us. Since then, the name of Stoycho Karavelov, the first Bulgarian metallurgical engineer, is quite forgotten and is not mentioned or spoken of today. Another positive issue is that inorganic chemistry during the germanium isolation is considered in depth herein including the foundations of chemical science in Bulgaria. In addition, the fascinating story of an incredible tradition and continuity among inorganic chemists in Bulgaria that lasted a hundred years, whose passing an ampoule of crystals from hand to hand is well worth telling. Keywords: discovery of germanium, metallurgy, Clemens Winkler, Stoycho Karavelov, inorganic chemistry.

Investigating mixed-precision for AGATA pulse-shape analysis

Investigating mixed-precision for AGATA pulse-shape analysis

N3G project: front-end electronics and mechanical advances

The higher counting-rate and radiation hardness required by modern gamma spectroscopy experiments highlight the need for a new generation of High-Purity Germanium detectors based on electrons-collecting electrodes. To achieve this goal, new doping technologies are required. The one studied by the N3G (Next Generation Germanium Gamma detectors) project is the Pulsed Laser Melting. Besides the development of innovative segmented High-Purity Germanium crystals, the project is also aimed at developing a detector case complete of contact structures and front-end electronics. A specific integrated circuit pre-amplifier is being designed: a first version was tested at room temperature, using a pulser as pre-amplifier input. A resolution of 1.08 keV with 15 pF input capacitance, reproducing the one of a detector single segment, was obtained with 6 µs shaping time.