基于抛光基材的热蒸镀铜箔生长高平整单层石墨烯薄膜

在石墨烯的化学气相沉积工艺中,铜箔是决定石墨烯薄膜质量的重要因素。传统铜箔由于制备工艺的限制,存在大量的缺陷,导致石墨烯薄膜的成核密度较高。本工作选用抛光铝板、抛光不锈钢板、微晶玻璃和SiO₂/Si作为基材,用热蒸镀法制备了不同粗糙度的铜箔,并详细讨论了以该系列铜箔生长高平整度石墨烯薄膜的条件及铜箔对石墨烯薄膜品质的影响。实验结果表明,铜箔以(111)取向为主,与基材分离后,表面具有纳米级平整度。在生长石墨烯后,从SiO₂/Si剥离的铜箔成核密度是4种基材中最小的。同时,从SiO₂/Si剥离的铜箔晶体结构变化最不明显,具有良好的结晶性,表面几乎不存在铜晶界缺陷。当压强为3 000 Pa,氢气和甲烷流速分别为300 mL/min和0.5 mL/min时,可以获得约1 mm横向尺寸的石墨烯单晶晶畴。     

Comprehensive performance of a ball-milled La0.5Pr0.5Fe11.4Si1.6B0.2Hy/Al magnetocaloric composite

Due to the hydrogen embrittlement effect, La(Fe,Si)₁₃-based hydrides can only exist in powder form, which limits their practical application. In this work, ductile and thermally conductive Al metal was homogeneously mixed with La_0.5Pr_0.5Fe_11.4Si_1.6B_0.2 using the ball milling method. Then hydrogenation and compactness shaping of the magnetocaloric composites were performed in one step via a sintering process under high hydrogen pressure. As the Al content reached 9 wt.%, the La_0.5Pr_0.5Fe_11.4Si_1.6B_0.2H_y/Al composite showed the mechanical behavior of a ductile material with a yield strength of ~44 MPa and an ultimate strength of 269 MPa accompanied by a pronounced improvement in thermal conductivity. Due to the ease of formation of Fe-Al-Si phases and the several micron and submicron sizes of the composite particles caused by ball milling process, the magnetic entropy change of the composites was substantially reduced to ~1.2 J/kg· K-1.5 J/kg· K at 0 T-1.5 T.     

Multifunctional Sulfur-Hyperdoped Silicon Nanoparticles with Engineered Mid-Infrared Sulfur-Impurity and Free-Carrier Absorption

Si nanoparticles (NPs), which are innovative promising light-harvesting components of thin-film solar cells and key-enabling biocompatible theranostic elements of infrared-laser and radiofrequency hyperthermia-based therapies of cancer cells in tumors and metastases, are significantly advanced in their near/mid-infrared band-to-band and free-carrier absorption via donor sulfur-hyperdoping during high-throughput facile femtosecond-laser ablative production in liquid carbon disulfide. High-resolution transmission electron microscopy and Raman microscopy reveal their mixed nanocrystalline/amorphous structure, enabling the extraordinary sulfur content of a few atomic percents and very minor surface oxidation/carbonization characterized by energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. A 200-nm thick layer of the nanoparticles exhibits near−mid-infrared absorbance, comparable to that of the initial 380-micron thick n-doped Si wafer (phosphor-dopant concentration ≈10¹⁵ cm⁻³), with the corresponding extinction coefficient for the hyperdoped NPs being 4–7 orders higher over the broadband spectral range of 1–25 micrometers. Such ultimate, but potentially tunable mid-IR structured, multi-band absorption of various sulfur-impurity clusters and smooth free-carrier absorption are break through advances in mid-infrared (mid-IR) laser and radiofrequency (RF) hyperthermia-based therapies, as envisioned in the RF-heating tests, and in fabrication of higher-efficiency thin-film and bulk photovoltaic devices with ultra-broad (UV−mid-IR) spectral response.     

Engineering Carbon Distribution in Silicon-Based Anodes at Multiple Scales

The successful commercialization of promising silicon-based anode materials has been hampered by their poor cycling stability caused by the huge volume change. Integration of the carbon matrix with silicon-based (C/Si-based) anode materials has been demonstrated to be a powerful solution to achieve satisfactory electrochemical performance. This minireview aims to outline recent developments on C/Si-based composites, with the emphasis on the importance of carbon distribution at multiple scales. In addition, the forms of the carbon framework (carbon sources and doping of heteroatoms) have been summarized. Particularly, a novel C/Si-based hybrid with carbon distributed at the atomic scale has been highlighted.     

Structure transition and photoluminescence of CdS/Si nanoheterostructure array on thermal annealing

CdS/Si heterojunctions have been prepared through growing CdS nanocrystallites (nc-CdS) on the silicon nanoporous pillar array (Si-NPA) by the chemical bath deposition method. Cadmium nanocrystallites (nc-Cd) have been observed and ascribed to the reducibility of Si-NPA. The reason for the appearance of CdO is indistinct and the related work will be done in the future. The blue, green and red emissions are ascribed to the silicon oxide layer, band gap of nc-CdS and the sulphur vacancies, respectively. Redshift and blueshift with the annealing temperature about green emissions are contributed to quantum size effect and the structure transition from nc-Cd to CdO. It is beneficial for investigating the structures and defects to the application of CdS/Si in the optoelectronic field.     

SiNWs:Tb3+的光学稳定性及Si纳米线对其发光特性的影响

荧光纳米材料不但具备纳米材料的优势，同时还具有优异的光学性质，被广泛应用于荧光标记、离子识别、荧光免疫分析、光学成像和医学诊断等方面。因此，荧光纳米材料的制备、结构分析和荧光特性等方面的研究备受人们的关注。为了获得发光强度大、荧光量子效率高和制备过程可控的Si基荧光纳米材料，实验进一步研究了Si纳米线对样品发光特性的影响和样品的光学稳定性。首先，基于固-液-固生长机制，在反应温度为1 100 ℃、N₂气流量为1 500 sccm、生长时间为15～60 min等工艺条件下，分别以“抛光”和“金字塔”织构表面的单晶Si(100)为衬底，生长出不同长度和分布的Si纳米线；以Au或Au-Al合金膜层作为金属催化剂，生长出密度分别约为108和1010 cm-2的Si纳米线；然后，利用L4514自动控温管式加热炉，基于高温固相法，在温度为1 100 ℃、掺杂时间为60 min和N₂气流量为1 000 sccm等工艺条件下，以高纯Tb₄O₇(99.99%)粉末为稀土掺杂剂对不同Si纳米线衬底进行稀土掺杂，制备一系列的荧光纳米材料SiNWs:Tb3+样品；室温下利用Hitachi F-4600型荧光分光光度计，固定激发光波长为243 nm、激发光狭缝为2.5 nm、发射光狭缝为2.5 nm、扫描波长范围为450～650 nm、光电倍增管(photomultiplier lube, PMT)电压为600 V等参数下，测量了不同样品的光致发光特性；最后，实验测试了该荧光纳米材料的光学稳定性，如时间(0～30 d)、温度(300～500 K)、酸碱(pH 1和11)、抗光漂白(0～120 min)等稳定性以及水溶性和分散性。结果显示，在衬底为“金字塔”织构表面上、生长时间为30 min、以Au为金属催化剂等条件下制备的Si纳米线为Tb3+掺杂衬底时，SiNWs:Tb3+的绿光发射强度较大，其发光强峰值位于554 nm，属于能级5D₄→7F₅的跃迁，另外在波长为494，593和628 nm出现了三条发光谱带，它们分别属于能级5D₄→7F₆，5D₄→7F₄和5D₄→7F₃的跃迁。另外，样品展示出了优异的时间、温度、酸碱和抗光漂白等光学稳定性，同时还具有良好的水溶性和分散性。如温度升高到500 K时，光发射强度仅降低了约8.9%左右；抗光漂白能力较强，用波长为365 nm、功率为450 W的紫外光源照射120 min，样品的绿光发射强度无衰减；酸、碱稳定性好，在pH 1的强酸(HCl)溶液中120 min未见衰减，在pH 11的强碱(NaOH)溶液中15 min内衰减较小, 随后发光强度出现了缓慢下降的趋势；当60 min后，样品的发光强度变得极其微弱。分析认为，在SiNWs:Tb3+表面有一层SiO₂包覆层，而NaOH溶液容易和SiO₂发生化学反应，随着时间延长SiO₂层被破坏，故样品发光强度降低；样品溶于水中放置30 d未见沉淀物，发光亮度均匀且分散性较好。在研究了制备温度、气体流量和掺杂时间等工艺条件之后，深入研究了Si纳米线自身变化对Tb3+绿光发射的影响。该材料展示出了良好的光学稳定性、水溶性和分散性，使其作为荧光标记物具有一定的应用价值。     

煤直接液化油中混合酚的分离研究

利用分子筛择形特点，对煤直接液化油中的混合酚实施高效分离。本研究选取间甲酚和对甲酚作为分离煤直接液化油馏分段混合酚的模型化合物，采用化学液相沉积法对HZSM-5吸附剂的孔口结构进行改变，分析分子筛硅铝比及颗粒粒径对模型化合物间甲酚和对甲酚吸附分离性能的影响，以获得高性能固相吸附剂，并将其应用于180-190℃馏分段混合酚分离。结果表明，当分子筛硅铝比为25、粒径为3-5 μm时，分子筛的孔口结构调节效果最优；当正硅酸乙酯的最小用量为0.2 mL/g时，固相吸附剂的吸附量为0.03 g/g，对甲酚选择性高于95%。由于外表面沉积物对吸附剂的孔口结构变化，导致对甲酚选择性的提高。进一步采用HZSM-5（1）吸附剂对真实煤直接液化油混合酚的分离中发现，苯酚和对甲酚的选择性均达到100%。     

Influence of the Si–O–C interplayer on the flexural behaviors of C/Si–C–N composites

Carbon fiber reinforced Si–C–N matrix composite(C/Si–C–N) with a Si–O–C interlayer (C/Si–O–C/Si–C–N) was fabricated via CVI and PIP process. The flexural behaviors of C/Si–O–C/Si–C–N were investigated using the three-point-bending method and the SEM technique. The results indicated that the flexural strengh of the C/Si–O–C/Si–C–N increases with increasing temperature and the modulus of the composite is essentially unchanged. The strength of C/Si–O–C/Si–C–N is comparable to that of C/PyC/Si–C–N, and the role of Si–O–C interlayer in C/Si–C–N can rival that of the PyC interlayer. The weaker interfacial bonding and the larger thickness of Si–O–C interlayer make a contribution to this at RT while the thinner interlayer and unstable structure of Si–O–C interphase do it above 1300 °C.     

MoO_3/Si界面区钼掺杂非晶氧化硅层形成的第一性原理研究

采用基于密度泛函理论的第一性原理计算方法,通过模拟MoO_3/Si界面反应,研究了MoO_x薄膜沉积中原子、分子的吸附、扩散和成核过程,从原子尺度阐明了缓冲层钼掺杂非晶氧化硅(a-SiO_x(Mo))物质的形成和机理.结果表明,在1500 K温度下, MoO_3/Si界面区由Mo, O, Si三种原子混合,可形成新的稳定的物相.热蒸发沉积初始时, MoO_3中的两个O原子和Si成键更加稳定,同时伴随着电子从Si到O的转移,钝化了硅表面的悬挂键. MoO_3中氧空位的形成能小于SiO_2中氧空位的形成能,使得O原子容易从MoO_3中迁移至Si衬底一侧,从而形成氧化硅层;替位缺陷中, Si替位MoO_3中的Mo的形成能远远大于Mo替位SiO_2中的Si的形成能,使得Mo容易掺杂进入氧化硅中.因此,在晶硅(100)面上沉积MoO_3薄膜时, MoO_3中的O原子先与Si成键,形成氧化硅层,随后部分Mo原子替位氧化硅中的Si原子,最终形成含有钼掺杂的非晶氧化硅层.