The interface of SiO_2/ZnS films studied by high resolution X-ray photoluminescence

Sharp interfaces in optoelectronic devices are key for proper band alignment. Despite its benefits as buffer layer, ZnS deposited via atomic layer deposition(ALD) renders intermixed interfaces to its substrate, which can be detrimental for device performance. Here, we are attempting to elucidate the chemical species deriving from this metal-oxide to metal-sulfide transition studying ultrathin film ZnS on SiO_2 using high resolution X-ray photoluminescence spectroscopy(XPS).Regarding the S 2p spectra after a deposition of only three cycles of ZnS, we discover the many different chemical species in which S is present. These include intermediate oxides such as SO_4^(2-).These species become more obvious as we tilt the sample in the XPS chamber to shallower angles.Comparing the Si 2p and S 2p high resolution peaks in the depth profile, one can clearly uncover the confinement of SO_4^(2-) to the interface of the underlying substrate. This may indicate that SiO_2/ZnS interfaces contain interfacial sulphates that likely alter the electronic configuration of this interface.

Test of a High Throughput Detector on the X-ray Crystal Spectrometer of the EAST

An attempt was made to improve the spatio-temporal resolution of the tangen- tial X-ray crystal spectrometer （XCS） on the Experimental Advanced Superconducting Tokamak （EAST） by evaluating experimentally the applicability of a novel X-ray photon detection tech- nology for measuring the satellite spectra of Ar XVII with a high counting rate. High-resolution experimental data on the profiles of ion temperature and plasma rotation velocity facilitate the studies of the mechanisms underlining important physical phenomena, such as plasma heating, L-H transition and momentum transport. Based on silicon diode array and single-photon counting technology, a relatively small area （83.8 x 33.5 mm~） two-dimensional detector was successfully in- stalled and tested in the recent EAST campaign. X-ray photon counting rate higher than 20 MHz was observed for the first time, and high quality satellite spectra were recorded for ion temperature and plasma rotation measurement, indicating that the new technology is suitable for the next-step high-resolution XCS on EAST, and the deployment of a detector array with a much larger X-ray sensing area is planned for better plasma coverage.

Tb^(3+)-doped borosilicate glass scintillators for highresolution X-ray imaging

Scintillators are the vital component in X-ray perspective image technology that is applied in medical imaging,industrial nondestructive testing,and safety testing.But the high cost and small size of single-crystal commercialized scintillators limit their practical application.Here,a series of Tb^(3+)-doped borosilicate glass(BSG)scintillators with big production size,low cost,and high spatial resolution are designed and fabricated.The structural,photoluminescent,and scintillant properties are systematically investigated.Benefiting from excellent transmittance(87%at 600 nm),high interquantum efficiency(60.7%),and high X-ray excited luminescence(217%of Bi4Ge3O12),the optimal sample shows superhigh spatial resolution(exceeding 20 lp/mm).This research suggests that Tb^(3+)-doped BSG scintillators have potential applications in the static X-ray imaging field.

透射电子显微术和高分辨X射线衍射技术研究AlN单晶生长习性

采用透射电子显微术和高分辨X射线衍射技术对氮化硼坩埚中自发成核的AlN单晶生长习性进行了研究。结果表明,在低温下,AlN单晶显露面为(0001)面,随着温度的升高,AlN单晶显露面转化为(112-0)面。沟槽结构是高温下得到的AlN单晶共有的显著特征,其取向沿[0001]方向。

高分辨X射线衍射法研究碳化硅单晶片中的多型结构

我们采用高分辨X射线衍射法对SiC单晶片中的多型结构进行了研究 ,研究发现在以 4H SiC为籽晶的晶体生长过程中 ,4H SiC、6H SiC、1 5R SiC出现两相共存或三相共存现象。在单相、两相或三相共存区 ,X射线摇摆曲线具有明显不同的特征。根据多型结构 。

不同籽晶对KDP晶体质量的影响

采用Z片籽晶和锥头籽晶分别进行传统降温法生长KDP晶体,并对其高分辨摇摆曲线、锥光干涉图以及消光比进行测试研究。实验发现,KDP晶体在不同籽晶下均能实现较好的生长稳定性,采用锥头籽晶生长的KDP晶体具有相对更好的晶体质量。

高分辨X射线衍射术对NdP_5O_(14)晶体的自发应变及铁弹畴结构的研究

利用助溶剂法 ,已经生长出 15mm× 2 5mm× 6 0mm的大尺寸NdP5O14 (NPP)晶体。用高分辨X射线衍射术对自发应变及铁弹畴结构进行了研究。对几个不同的反射 ,可在其摇摆曲线上观测到由基体畴和铁弹畴之间的取向差导致的反射峰的分离。通过反射峰分离的特点 ,可以确定铁弹畴结构。NPP晶体中大多数铁弹畴为a型畴 ,b型畴只出现在严重形变的区域。基于NdP5O14 晶体畴结构 ,我们分别计算了 80 2 ,40 2和 2 0 4反射的峰分离量。实验测量结果符合计算结果。另外 ,通过测量基体畴和铁弹畴的 80 0反射的峰分离量我们确定了NdP5O14 的自发应变是 0 .0 0 82。通过结构和对称性分析 ,我们对这种晶体的畴结构进行了详细讨论。

PEALD-deposited crystalline GaN films on Si(100) substrates with sharp interfaces

Polycrystalline gallium nitride(GaN) thin films were deposited on Si(100) substrates via plasma-enhanced atomic layer deposition(PEALD) under optimal deposition parameters. In this work, we focus on the research of the GaN/Si(100)interfacial properties. The x-ray reflectivity measurements show the clearly-resolved fringes for all the as-grown GaN films, which reveals a perfectly smooth interface between the GaN film and Si(100), and this feature of sharp interface is further confirmed by high resolution transmission electron microscopy(HRTEM). However, an amorphous interfacial layer(~ 2 nm) can be observed from the HRTEM images, and is determined to be mixture of Ga_xO_y and GaN by xray photoelectron spectroscopy. To investigate the effect of this interlayer on the GaN growth, an AlN buffer layer was employed for GaN deposition. No interlayer is observed between GaN and AlN, and GaN shows better crystallization and lower oxygen impurity during the initial growth stage than the GaN with an interlayer.

Epitaxial growth of Ge_(1-x)Sn_x films with x up to 0.14 grown on Ge(00l) at low temperature

We characterize the structures of Ge1-xSnx films with x up to 0.14 grown on Ge （001） by molecular-beam epitaxy at low temperature. The results show that Ge1-xSnx films are fully strained even at high Sn composition. The in-plane lattice parameters remain exactly the same as that of the substrate. Depth sensitivity analysis of the lattice parameters indicates that the strains of the epitaxial films are all in homogeneity. The films are fully strained. Poisson ratios, the force constants for the bonds between Ge and Sn are estimated and discussed in the present paper. Raman results show Ge-Ge, Ge-Sn, Sn-Sn vibrational modes. The Sn-Sn bond aggregation may respond to the high quality of our films. The fully strained epitaxy films with high content of Sn may be useful in designing the high quality GeSn films.

Analysis of electro-optical intensity modulator for bunch arrival-time monitor at SXFEL

A bunch arrival-time monitor(BAM) based on an electro-optical intensity modulation scheme is currently under development at Shanghai Soft X-ray Free-Electron Laser to meet the high-resolution requirements for bunch stability. The BAM uses a radio frequency signal generated by a pickup cavity to modulate the reference laser pulses in an electro-optical intensity modulator(EOM), and the bunch arrival-time information is derived from the amplitude change of the laser pulse after laser pulse modulation.EOM is a key optical component in the BAM system.Through the basic principle analysis of BAM, many parameters of the EOM are observed to affect the measurement resolution of the BAM system. Therefore, a systematic analysis of the EOM is crucial. In this paper, we present two schemes to compare and analyze an EOM and provide a reference for selecting a new version of the EOM.

The role of defects association in structural and transport properties of the Ce_(1-x)(Nd_(0.74)Tm_(0.26))_xO_(2-x/2) system

An experimental investigation of the crystallographic,Raman and transport properties of the Ce_(1-x)(Nd_(0.74)Tm_(0.26))_xO_(2-x/2)(0.1≤x≤0.6) doped ceria system was performed with the aim of setting out correlations between structural features and ionic conductivity of the material.The chosen composition ensures that the average size of the Nd^(3+) and Tm^(3+) doping ions coincides with the one of Sm^(3+);even so,the studied system presents larger cell parameters and a wider compositional extent of the CeO_(2)-based solid solution than Sm-doped ceria.Moreover,the occurrence of two different activation energies to ionic conduction below and above ~750 K determines the existence of two distinct conduction regimes.The described experimental results agree with the formation below the threshold temperature of1 V_O2 Tm'_(Ce) trimers,which promote the incorporation of Nd'_(Ce) isolated defects into the CeO_(2)-based solid solution.In the high temperature range the dissociation of trimers induces the appearance of a lower activation energy;the extrapolation of its value at infinite dilution provides a result in good accordance with the expected binding energy of 1 V_ORE'_(Ce) dimers,pointing at their stability even in the high temperature conduction regime.

Role of Radiological Investigations of COVID-19 Patients with Pneumonia, Karachi Pakistan

The study was conducted to determine the role of radiological investigation in assessing the severity of COVID-19 pneumonia with the help of chest X-ray (CXR), high resolution computed tomography (HRCT), and ultrasound. This was a retrospective study conducted on 105 COVID-19 patients with symptoms of fever, cough, dyspnea, loss of sense of smell and taste, body ache. Diagnostic tests PCR were positive for COVID-19 included from Medicare Cardiac and General Hospital and Jinnah Medical College Hospital Korangi (JMCH) from April to November 2020. Written informed consent was taken from all participants. This study was approved by ethical review committee, Jinnah Medical & Dental College. Real time-PCR (RT-PCR) was done for the confirmation. Radiological imaging including Chest X-ray, HRCT chest, and ultrasound was done to study the severity of symptoms. Sixty-five patients had mild to moderate symptoms with oxygen saturation between 96% - 98% and 30 patients with severe pneumonia had between saturation 50% - 55%. Patients with mild symptoms were followed up by chest X-ray showing mostly normal chest X-rays but single or patches of ground glass opacities (HRCT). HRCT of 10 patients with low oxygen saturation 50% were already done showing bilateral peripheral patchy consolidation predominantly involving mid and lower lobes. 3 patients presented with patchy lung opacities and ultrasound showing similar findings with pleural effusion and ascites. Radiological imaging, specially CT-Scan was highly significant for diagnosing COVID-19 and severity of infection even in patients with negative PCR. Chest X-ray and ultrasound were also found to be a very useful tool.

X-ray reflectivity and atomic force microscopy studies of MOCVD grown AI_xGa_(1-x)N/GaN superlattice structures

The grazing incidence X-ray reflectivity(GIXR) technique and atomic force microscopy(AFM) were exploited to obtain an accurate evaluation of the surfaces and interfaces for metalorganic chemical vapor deposition grown AlGaN/GaN superlattice structures.The X-ray diffraction results have been combined with reflectivity data to evaluate the layer thickness and Al mole fraction in the AlGaN layer.The presence of a smooth interface is responsible for the observation of intensity oscillation in GIXR,which is well correlated to step flow observation in AFM images of the surface.The structure with a low Al mole fraction(x = 0.25) and thin well width has a rather smooth surface for the R,of AFM data value is 0.45 nm.

Influence of initial growth conditions and Mg-surfactant on the quality of GaN film grown by MOVPE

The initial growth conditions of a 100 nm thick GaN layer and Mg-surfactant on the quality of the GaN epilayer grown on a 6H-SiC substrate by metal-organic vapor phase epitaxy have been investigated in this research. Experimental results have shown that a high V/III ratio and the initially low growth rate of the GaN layer are favorable for two-dimension growth and surface morphology of GaN and the formation of a smoother growth surface. Mg-surfactant occurring during GaN growth can reduce the dislocations density of the GaN epilayer but increase the surface RMS, which are attributed to the change of growth mode.