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In this study, the degradation effects of inverted metamorphic four-junction (IMM4J) solar cells were investigated after 1 MeV electron irradiation using spectral response and electrical property measurements. The results show that, similar to traditional tri-junction (TJ) GaInP/GaAs/Ge solar cells, the electrical properties (such as I sc , V oc , and P max ) degrade as a function of logφ, where φ represents the electron fluence. In particular, the degradation of V oc is more serious than that of I sc because of the sum rule for V oc and the limit rule for I sc in IMM4J cells. Analysis of the spectral response curves indicates that, unlike traditional TJ cells, the In 0.3 Ga 0.7 As (1.0 eV) sub-cell exhibits the most severe damage in the irradiated IMM4J cells and the In 0.58 Ga 0.42 As sub-cell becomes a limits part for the electrical properties of the IMM4J solar cells.

Polyethylene/carbon nanotube (PE/CNT) composites with high hydrogen content as a kind of structural material for space radiation shielding have extensive potential applications in future aerospace field due to their unusual radiation shielding, lightweight, and easy processing. In the space irradiation environment, the composites are sensitive to radiation damage, which changes their microstructures, directly affecting their mechanical performances and shielding effectiveness. Low energy electrons (200 keV) are important radiation environmental factors. Effects and mechanisms for mechanical damage of PE/CNTs composites induced by low energy electrons are studied, which has important academic value and practical significance. Previous research mainly involves the qualitative evaluations of the changes in the mechanical performance index of polymer nanocomposites. The inner relationship between microstructural change induced by radiation and mechanical behavior of the nanocomposites, especially in the PE/CNTs composites has not been studied in depth so far. In this paper, low-density polyethylene (LDPE)/ multi-walled carbon nanotube (MWCNT) composites are chosen as a research object. Based on 110 keV electron irradiation, tensile deformation mechanism of the LDPE/MWCNT composite is studied. The synchrotron radiation X-ray small angle scattering (SAXS) and wide angle diffraction (WAXD) are used to reveal the real-time microstructure evolutions of the nanocomposites after and before irradiation in the process of stretching. Tensile deformation mechanisms of LDPE/MWCNT composite after and before the 110 keV electron irradiation are revealed. Experimental results show that the tensile deformation behavior for the irradiated LDPE by 110 keV electrons is different from that for unirradiated sample. The electron irradiation increases the tensile strength of the LDPE/MWCNT composite and reduces the elongation at break. Moreover, with increasing the irradiation fluence, the tensile strength and the elongation at break of the LDPE/MWCNT composite significantly increases and decreases, respectively. The electron irradiation could hinder the deformations of the LDPE matrix including crystalline case and amorphous case, constrain the fragmentation of original lamellae, the directional arrangement of the MWCNTs, the formation of new crystal and the rotation of lamellae, especially in higher irradiation fluence. During tensile deformation, the main strengthening mechanism for the irradiated LDPE/MWCNT composites by the 110 keV electrons is crosslinking strengthening effect in LDPE matrix. On the other hand, enhanced interaction (mainly interface strengthening) between MWCNTs and LDPE matrix induced by irradiation is attributed to the main strengthening mechanism for the irradiated LDPE/MWCNT composites. These results could provide a theoretical basis and technical support for the reasonable design and successful application of CNT-based polymer composites as structural material for space radiation shielding.

Electrons are an important constituent part of radiation space of charged particles and could damage microelectronic devices. Therefore, effective radiation protection is very important for the electronic device. So, a radiation protecting material with lightweight, high performance and low cost is urgently needed. Polyethylene (PE) with high hydrogen content/carbon nanotube (CNT) composite as a space shielding material is very promising for spacecraft application in the future. In order to meet the requirement of space applications for PE/CNT composite, it is of important academic value and practical significance to explore melting and crystallization behaviors of LDPE/MWCNT composites. In this paper, melting and crystallization behaviours of the irradiated LDPE/MWCNT composites irradiated by 110 keV electrons are studied by differential scanning calorimetry (DSC), synchrotron radiation X-ray small angle scattering (SAXS) and wide angle diffraction (WAXD). Experimental results show that the irradiation by 110 keV electrons does not affect the thermal characteristics of the LDPE, but can enhance the initial melting temperature and the melting-terminating temperature of LDPE/2% MWCNT composites during melting. Also, the radiation by 110 keV electrons could reduce the initial crystallization temperature and the crystallization-terminating temperature during crystallization. MWCNTs could enhance the initial melting temperature and reduce the melting-terminating temperature of LDPE/2% MWCNT composites during melting. Moreover, MWCNTs could enhance the initial crystallization temperature and crystallinity, and reduce the crystallization-terminating temperature during crystallization. SAXS and WAXD analyses show that with increasing the temperature, long periods of the irradiated/unirradiated LDPE increase during melting. Compared with that of the unirradiated LDPE, at a given temperature, long period of the irradiated LDPE is small. During crystallization, with reducing the temperature, long period of the irradiated/unirradiated LDPE begins to appear and gradually decreases. At the same temperature, long period of the irradiated LDPE is larger than that of the unirradiated one. For LDPE/2% MWCNT composites, long periods of the irradiated/unirradiated samples during melting and crystallization do not exist. The 110 keV electron irradiation mainly influences LDPE matrix of LDPE/2% MWCNT composites during melting and crystallization. The 110 keV electron irradiation can slow down the amorphous region expansion and the initial melting of lamellae of the LDPE matrix during melting. The 110 keV electron irradiation can slow down the amorphous region shrinkage and inhibit crystal from growing up during crystallization. During melting, MWCNTs can hinder the amorphous and crystalline molecular chains of LDPE from moving, which hinders the LDPE matrix from initially melting, but promotes the melting process after the initial melting has begun. During crystallization, MWCNTs could promote the formation of crystal of the LDPE matrix and inhibit the crystal from growing up.

Due to their unusual electrical conductivity, carbon nanotubes as the ideal candidates for making future electronic components have extensive application potentiality. In order to meet the requirements in space electronic components for carbon nanotubes, effect of 170 keV proton irradiation on structure and electrical conductivity of multi-walled carbon nanotubes (MWCNTs) film is investigated in this paper. Surface morphologies and microstructure of the carbon nanotube films are examined by scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR) spectroscopy, respectively. Electrical conductivities of the carbon nanotube films before and after 170 keV proton irradiation are measured using four-point probe technique. SEM analysis reveals that when proton irradiation fluence is greater than 51015 p/cm2, the surface of the carbon nanotube film becomes rough and loose, and obvious bending, shrinkage, and entanglement of nanotubes are observed. Moreover, the shrinkage phenomenon of MWCNTs caused by proton irradiation is found the first time so far as we know. Based on Raman and XPS analyses, it is confirmed that 170 keV protons can improve the ordered structure of the MWCNTs, and irradiation fluence plays a key role in reducing the disorder in the MWCNTs. Improvement of the irradiated MWCNTs by 170 keV protons can be attributed to restructuring of defect sites induced by knock-on atom displacements. On the other hand, carbon impurities on surface of the MWCNT film are reduced due to the effect of sputtering by the 170 keV proton irradiation, which is also helpful to the improvement of the structure of carbon nanotubes. EPR spectra show that the electrons delocalized over carbon nanotubes decrease with increasing irradiation fluence, implying that the carbon nanotube film is not sensitive to ionizing radiation induced by the 170 keV protons, and the electrical conductivities of the MWCNTs films may be decreased. Four-point probe technical analysis shows that with increasing irradiation fluence, electrical properties of the carbon nanotubes film deteriorate, which can be attributed to the changes in electronic properties and morphology of the MWCNT films induced by 170 keV protons. Acquired results could be beneficial to tailoring of structure and properties for the carbon nanotubes film irradiated by protons to develop nanoelectronics of radiation-resistant systems.

The characteristic degradations in a silicon NPN bipolar junction transistor (BJT) of 3DG142 type are examined under irradiation with 40-MeV chlorine (Cl) ions under forward, grounded, and reverse bias conditions, respectively. Different electrical parameters are in-situ measured during the exposure under each bias condition. From the experimental data, a larger variation of base current (IB) is observed after irradiation at a given value of base-emitter voltage (VBE), while the collector current is slightly affected by irradiation at a given VBE. The gain degradation is affected mostly by the behaviour of the base current. From the experimental data, the variation of current gain in the case of forward bias is much smaller than that in the other conditions. Moreover, for 3DG142 BJT, the current gain degradation in the case of reverse bias is more severe than that in the grounded case at low fluence, while at high fluence, the gain degradation in the reverse bias case becomes smaller than that in the grounded case.

An investigation of ionization and displacement damage in silicon NPN bipolar junction transistors (BJTs) is presented. The transistors were irradiated separately with 90-keV electrons, 3-MeV protons and 40-MeV Br ions. Key parameters were measured in-situ and the change in current gain of the NPN BJTS was obtained at a fixed collector current (Ic = 1 mA). To characterise the radiation damage of NPN BJTs, the ionizing dose Di and displacement dose Dd as functions of chip depth in the NPN BJTs were calculated using the SRIM and Geant4 code for protons, electrons and Br ions, respectively. Based on the discussion of the radiation damage equation for current gain, it is clear that the current gain degradation of the NPN BJTs is sensitive to both ionization and displacement damage. The degradation mechanism of the current gain is related to the ratio of Dd/(Dd + Di) in the sensitive region given by charged particles. The irradiation particles leading to lower Dd/(Dd + Di) within the same chip depth at a given total dose would mainly produce ionization damage to the NPN BJTs. On the other hand, the charged particles causing larger Dd/(Dd + Di) at a given total dose would tend to generate displacement damage to the NPN BJTs. The Messenger–Spratt equation could be used to describe the experimental data for the latter case.