不同降温方式对单晶石墨烯氢气刻蚀的改善

以化学气相沉积(CVD)的方法在铜衬底上制备了大尺寸的单晶石墨烯。研究了在3种不同降温方式下,石墨烯受氢气刻蚀程度的变化,以及在降温过程中通入甲烷后,对刻蚀的影响与改善,并对刻蚀机理进行了探讨。结果表明:经开盖降温的石墨烯受刻蚀最轻,随炉降温的样品受刻蚀次之,缓慢降温的样品受刻蚀最为严重。在降温过程中通入甲烷之后,3种样品的刻蚀都得到了进一步的改善,且开盖降温样品的结晶质量有大幅提升;随炉降温样品的结晶质量有小幅提升;缓慢降温样品的结晶质量有所下降。     

光电化学刻蚀方法去除SiC衬底外延石墨烯缓冲层及其表征

高温条件下裂解碳化硅(SiC)单晶,在直径5cm的4H-SiC(0001)面制备出单层石墨烯。利用光电化学刻蚀方法,使KOH刻蚀液与SiC发生反应,降低石墨烯与衬底之间的相互作用力,去掉原位生长过程中SiC衬底与石墨烯之间存在的缓冲层,获得准自由的双层石墨烯。首先通过对比不同的电流密度和光照强度,总结出电流密度为6mA·cm-2、紫外灯与样品间距为3cm时,石墨烯缓冲层的去除效率以及石墨烯质量皆为最佳。采用此优化后工艺处理的样品,拉曼光谱表明原位生长的缓冲层与衬底脱离,表现出准自由石墨烯的特性。X射线光电子能谱(XPS)C1s谱图中代表上层石墨烯与衬底Si悬键结合的S1、S2特征峰消失,即石墨烯缓冲层消失。通过分析刻蚀过程中的电化学曲线,提出了刻蚀过程的化学反应过程中的动态特性。     

光电化学刻蚀方法去除SiC衬底外延石墨烯缓冲层及其表征

高温条件下裂解碳化硅（SiC）单晶,在直径5 cm的4H-SiC（0001）面制备出单层石墨烯。利用光电化学刻蚀方法,使KOH刻蚀液与SiC发生反应,降低石墨烯与衬底之间的相互作用力,去掉原位生长过程中SiC衬底与石墨烯之间存在的缓冲层,获得准自由的双层石墨烯。首先通过对比不同的电流密度和光照强度,总结出电流密度为6 mA·cm^-2、紫外灯与样品间距为3 cm时,石墨烯缓冲层的去除效率以及石墨烯质量皆为最佳。采用此优化后工艺处理的样品,拉曼光谱表明原位生长的缓冲层与衬底脱离,表现出准自由石墨烯的特性。X射线光电子能谱（XPS）C1s谱图中代表上层石墨烯与衬底Si悬键结合的S1、S2特征峰消失,即石墨烯缓冲层消失。通过分析刻蚀过程中的电化学曲线,提出了刻蚀过程的化学反应过程中的动态特性。     

透明成核剂作用下的聚丙烯共聚物的等温结晶形态

利用偏光显微镜观察了聚丙烯共聚物（CPP）在透明成核剂TM-3作用下的等温结晶形态。结果表明：随结晶时间延长，CPP的球晶尺寸变大，形态也趋于完善；结晶温度并非越高越有利，CPP样品在140℃的结晶形态最好；球晶尺寸随TM-3含量提高而有所减小，但含有TM-3的CPP样品能够形成比CPP本体更大、更完善的球晶。TM-3在CPP结晶过程中提供了少量而有效的晶核，使丙烯链段能够附着在上面进行生长。     

废旧聚酯纺织品制备的rp-PBAT非等温结晶动力学

废旧聚酯纺织品经乙二醇(EG)醇解，再与1,4-丁二醇(BDO)酯交换制备得到对苯二甲酸双羟基丁酯(BHBT),其与己二酸双羟基丁酯(BHAT)熔融缩聚得到再生聚酯基的生物可降解共聚酯聚对苯二甲酸-己二酸丁二醇酯(rp-PBAT)。采用¹H-NMR对共聚产物进行结构表征，利用差示扫描量热法(DSC)对其进行非等温结晶及动力学研究。结果表明，由废旧聚酯纺织品制备的共聚样品是rp-PBAT,样品中BA和BT摩尔含量与投料摩尔比基本相同；rp-PBAT共聚酯的结晶温度(T_c)随着BA含量和降温速率的增加而降低；所有样品相对结晶度-时间(C_t-t)曲线斜率均随降温速率增加而增大，半结晶时间t_1/2减小；在相同降温速率下，随着BA含量的增加，样品的t_1/2呈逐渐增大的趋势，样品结晶速率下降；莫志深方程(Mo方程)能够很好地描述实验体系中的PBAT共聚酯的非等温结晶过程。     

降温模式对甲烷水合物形成的影响

在定容条件下,以两种不同的降温模式(缓慢降温和快速降温)进行甲烷水合物在沉积物中的形成实验. 结果表明,甲烷水合物在沉积物中的形成过程包括气液溶解、核化、生长、稳定4个阶段. 在相同的初始条件下,降温模式对水合物生成的热力平衡影响较小,但对水合物生成动力学有显著改变. 快速降温下水合物生长速度明显快于缓慢降温,随着水合物初始条件不同,缓慢降温比快速降温水合物形成时间约增加21.4%~28.8%.     

成型温度对β晶型聚丙烯冲击强度的影响

测定了两种含β晶聚丙烯（β-PP）在23、-20℃下的冲击强度，研究了β-PP的冲击强度随成型温度的变化规律。结果表明，随着成型温度的上升，pPP在23℃下的冲击强度降低。成型温度为80℃时，-20℃下两种β-PP的冲击强度均呈峰值，分别为3．8kJ／m^2和3．2kJ／m^2。差示扫描量热分析表明，随着成型温度的升高，β晶的含量先上升后下降，在100℃附近出现峰值，β晶含量为73％；β-PP的冲击强度随成型温度变化的趋势与-20℃下的一致，此条件下为5．0kJ／m^2。不同降温速率的非等温结晶实验结果表明，在降温速率为20℃／min即样品结晶温度为117℃左右时，样品中β晶含量最大（58．7％）。     

UHMWPE非等温结晶动力学研究

用DSC法研究了3种不同相对分子质量UHMWPE的非等温结晶过程。结果表明．在2．5，5．0，10．0℃／min的降温速率范围内能很好地符合Gupta法和莫志深法的动力学方程；相对分子质量较小的UHMWPE易结晶；冷却速率增加，UHMWPE需更高的过冷度才能结晶。     

聚丙烯/共聚酯/蒙脱土复合材料结晶行为的研究

采用热台偏光显微镜研究了聚丙烯(PP)/共聚酯(COPET)以及PP/COPET/蒙脱土(MMT)复合材料等温结晶时的结晶形态,结果表明:两样品均呈现清晰的球晶所特有的黑十字消光图像,PP/COPET/MMT复合材料的球晶尺寸比PP/COPET样品的球晶尺寸大大减小。采用差示扫描量热法对PP/COPET以及PP/COPET/MMT复合材料的非等温结晶行为进行了研究,结果表明:随着MMT含量的增加,复合材料样品的结晶初始温度和结晶峰温基本呈现逐渐降低趋势,结晶放热焓随MMT含量增加先增加后减小;在不同的降温速率下结晶,两种样品结晶峰温均随降温速率的增大而降低,结晶放热焓也随着结晶速率的增大而降低。采用Jeniorny法处理了PP/COPET和PP/COPET/MMT样品的非等温结晶过程,得出了两体系的结晶速率总体上随着冷却速率的增加而加快,为多维结晶生长体系。     

PET/分子筛复合材料的非等温结晶性能

采用原位聚合法制备了PET／分子筛复合材料并研究了其非等温结晶性能。结果表明：分子筛的加入有明显的异相成核效应，加快了结晶速度，增加了结晶度，减小了晶粒粒径分布；PET及PET／分子筛体系的热结晶峰温随着降温速率的增加而移向低温，半结晶时间、结晶度随降温速率的增加而减小，晶粒粒径分布则增大；分子筛的加入降低了降温速率对PET半结晶时间的影响；随着分子筛用量的增加，半结晶时间t1／2、结晶热焓ΔH、结晶峰半峰宽ΔW都能达到一个较佳值。     

Wrinkle-dependent hydrogen etching of chemical vapor deposition-grown graphene domains

Hexagonal single-crystal graphene domains were grown on copper (Cu) foil via chemical vapor deposition and were etched with hydrogen at 950 °C from 7 to 60 min at atmospheric pressure. Numerous trenches were observed on the initial graphene domains after etching, and the trench patterns were closely associated with the Cu crystal orientation. No trenches were found if the etching process was conducted before cooling down. Thus, the etching trenches were bound up with the wrinkles formed during the cooling down process. Then, the process of etching on the wrinkles was examined. This simple hydrogen etching technology proved that wrinkles and point defects existed even in hexagonal single-crystal graphene domains. This method could be a convenient way to detect the distribution and morphology of wrinkles in graphene.     

The influence of residual oxidizing impurities on the synthesis of graphene by atmospheric pressure chemical vapor deposition

The growth of graphene on copper by atmospheric pressure chemical vapor deposition in a system free of pumping equipment is investigated. The emphasis is put on the necessity of hydrogen presence during graphene synthesis and cooling. In the absence of hydrogen during the growth step or during cooling at slow rate, weak carbon coverage, consisting mostly of oxidized and amorphous carbon, is obtained on the copper catalyst. The oxidation originates from the inevitable occurrence of residual oxidizing impurities in the reactor’s atmosphere. Graphene with appreciable coverage can be grown within the vacuum-free furnace only upon admitting hydrogen during the growth step. After formation, graphene is preserved from the destructive effect of residual oxidizing contaminants if exposure at high temperature is minimized by fast cooling or if cooling down is performed under the protection of hydrogen. Under these conditions, micrometer-sized hexagon-shaped graphene domains of high structural quality are achieved.     

Effect of hydrogen flow during cooling phase to achieve uniform and repeatable growth of bilayer graphene on copper foils over large area

The growth of single-layer graphene on copper foil by chemical vapor deposition (CVD) method has been investigated extensively by several groups, however, achieving the same for the bilayer graphene, using a fast and reproducible process, is proven to be difficult and most of the efforts in this direction so far have been on controlling the nucleation phase during active growth regime. In this article we show that by regulating the gases introduced during the cooling phase, uniform and continuous growth of both the single and bilayer graphene can be obtained on copper foils with growth phase duration reduced to 3 min (i.e., 5–60 times faster than previous methods). We demonstrated growth of bilayer graphene on 30 × 30 cm copper foils. We show that the use of vacuum cooling enhanced the growth of single-layer graphene while the introduction of hydrogen gas during the cooling phase promoted the growth of bilayer graphene. We explain observed results elucidating a crucial role of hydrogen leading to a growth of bilayer graphene. The characterization of single and bilayer graphene have been supported by extensive statistical analysis of Raman spectroscopy, selected area electron diffraction measurements as well as fabrication of graphene field effect transistors.     

冷却速率影响NaCl结晶粒度的研究

通过对冷却速率影响NaC l在NaOH高浓溶液中的结晶规律进行研究,分析了冷却速率影响NaC l结晶的规律,认为先缓后急的冷却速率有利于提高NaC l结晶大小。导出了冷却结晶过程中冷却速率的表达式,并对最佳冷却速率进行了证明。通过对氯碱工艺现状进行分析,提出了改进的冷却方案来优化NaC l的结晶粒度分布,以提高烧碱产品质量。     

绝缘衬底上化学气相沉积法生长石墨烯材料

利用化学气相沉积法,在Si衬底、蓝宝石衬底和SiC衬底上生长石墨烯材料,研究石墨烯的表面形貌、缺陷、晶体质量和电学特性。原子力显微镜、光学显微镜和拉曼光谱测试表明,Si₃N₄覆盖层可以有效抑制3C-SiC缓冲层的形成;低温生长有利于保持材料表面的平整度,高温生长有利于提高材料的晶体质量。5.08 cm蓝宝石衬底上石墨烯材料,室温下非接触Hall测试迁移超过1000 cm²·V^-1·s^-1,方块电阻不均匀性为2.6%。相对于Si衬底和蓝宝石衬底,SiC衬底上生长石墨烯材料的表面形态学更好,缺陷更低,晶体质量和电学特性更好,迁移率最高为4900 cm²·V^-1·s^-1。     

Suitable cooling program for chicken fat dry fractionation

The impacts of the cooling program on crystal morphology, crystal suspension filtration properties and the characteristics of fractions resulting from chicken fat dry fractionation were assessed. The quality of the fractions was found to depend on the nature of the crystallized material and was also closely related to the filtration properties of the crystal suspension, which in turn were controlled by the cooling conditions. A slow cooling rate during the nucleation step was necessary to enhance process selectivity, and this rate could be accelerated once the first crystals had formed. These findings enhanced our understanding of the mechanisms involved during dry fractionation and highlighted the efficacy of a three‐phase cooling program, including (1) cooling from 70 to 26 °C, (2) slowdown in the cooling rate, and (3) a second rapid cooling down to the final temperature at which the fat is held for a specified time.     

冷却方式对熟料矿物及C3S晶型的影响

C₃S矿物是熟料的主要成分,是水泥熟料强度的主要提供者,熟料的强度不仅受C₃S含量影响,与C₃S晶型也直接相关。为研究冷却方式式对熟料矿物成分和晶型结构的影响,将不同水泥厂工业生料经制样烘干后在1 450 ℃下煅烧保温30 min,采用液氮淬冷、空气快冷和随炉慢冷的方式制备熟料。通过TG-DSC、XRD、Rietveld全谱拟合、岩相分析等对熟料矿物组成、含量、晶型、形貌以及固溶情况进行分析。结果表明:冷却速度加快,熟料中C₃S含量提高,β-C₂S、C₃A及C₄AF含量降低,铝率较大生料的冷却速度对C₃S、C₃A含量影响更显著;冷却方式不同,C₃S晶型不同,液氮冷却和空气冷却时C₃S多为M1或M3型,随炉冷却时C₃S多为T型,冷却速度减慢使C₃S晶型从M型向T型转变。     

Induction heating-assisted repeated growth and electrochemical transfer of graphene on millimeter-thick metal substrates

Chemical vapor deposition in a hot wall reactor is the most common technique for the production of large area single layer graphene. However, growth in this type of reactors is time consuming and the results are limited by the surface quality of the widely used catalytic metal foils as growth substrates. In this work we demonstrate the use of millimeter-thick Cu and Pt substrates for graphene growth via inductive magnetic heating, which allows for fast temperature ramps during heat up and cooling. Based on a detailed growth study, a two-step growth process resulting in continuous monolayer graphene films of high crystal quality with grain size of larger than 90 μm is established. An electrochemical transfer process is used to separate the graphene film from the metallic substrate, yielding excellent results in terms of defect density, doping and residual contamination. Back-gated graphene field-effect transistors fabricated on Si/SiO₂ structures exhibit a high reproducibility with a peak mobility higher than 4000 cm²/Vs. The combination of the highly time efficient graphene growth and electrochemical transfer together with the reusability of the growth substrates and the possibility of applying novel surface pretreatments pave the way for the use of high quality substrates in industrial applications.     

Identification of structural defects in graphitic materials by gas-phase anisotropic etching

We developed a method of identifying the structural defects in graphitic materials by an anisotropic etching technique. Intrinsic and oxygen- or argon- plasma induced artificial defects' density and domain size can be obtained easily and precisely. It was inferred, through our investigations, that the grade ZYA highly oriented pyrolytic graphite (HOPG) sample has a better crystal quality, with a lower defect density, while the Kish graphite has a larger grain size and higher defect density. Defect types and lattice orientations can also be extracted by this technique. Furthermore, this method could apply to various graphitic materials including graphene.