这项工作得到了德国福雄斯格梅因沙夫特的卓越集群"汉堡超高速成像中心——原子尺度上的物质结构、动力学和控制"和赫尔姆霍尔茨虚拟研究所的"多维景观中的动态路径"的支持。

1. 实验设置的描述
气相分子束设置和偏转器的示意图显示在 图221中。它包括
<ol><li>含有分子样本的脉冲偶拉维阀29。 只要形成冷分子束（O（1 K），其他脉冲分子束阀就可以同样使用。以下参数是特定于使用偶拉维阀门的。在此处介绍的实验中，阀门以 20 Hz 重复率运行，背压高（氦在 50 酒吧），并扩展到真空室，疏散到< 10-6 mbar。</li>
	<li>分子束掠过器（直径2毫米）位于阀门下游22厘米处，将分子束合在一起，导致脉冲阀阀与真空系统其他部分之间的差别泵送条件。</li>
	<li>掠过后，分子立即进入静电偏转装置。这包括一根杆（半径3.0毫米）和一个槽（曲率3.2毫米的半径），每个24厘米长。设备中心电极之间的垂直间隙为 2.3 mm。0-26 kV 之间的潜在差异应用在杆和槽之间，产生一个强大的异构电场，几乎恒定的场梯度30，如 图 2的开始所示。</li>
	<li>直接在偏转分子通过第二次掠过进入相互作用区域后，提供进一步的差分泵送阶段。</li>
	<li>交互区域（疏散到压力<10-9 毫巴）包含标准的威利-麦克拉伦飞行时间（TOF）设置。分子通过在提取区域中心、转速器和提取器电极之间的聚焦激光脉冲电电化。产生的离子加速向多通道板 （MCP） 探测器移动，该探测器记录到质量谱。</li>
	<li>激光脉冲来自 Nd：YAG 泵染料激光器，提供大约 283 nm（鞋底实验）或 272 nm（3 氟酚实验）的典型输出波长以及几 mJ 的脉冲能量。脉冲持续时间在 10 nsec 的顺序上，脉冲以 f = 750 mm 镜头聚焦，在交互区域的点大小为 +100 μm。</li>
	<li>正时序列由提供主时钟的数字延迟生成器控制。这触发了 Nd：YAG 激光（闪光灯和 Q 开关）、脉冲阀和用于记录质谱的数字化卡。</li>
	<li>质谱记录在数字化卡上，与激光 Q 开关同时触发。分子束密度从记录的飞行时间光谱中适当的质量门中提取。</li>
</ol>2. 符合者选定分子束的生产和特征
<ol><li>目标分子的冷分子束 是通过 超音速膨胀产生的，其特征是使用空间（x，y方向）和时间（z方向）分析。</li>
	<li>用化学样品装载脉冲阀的样品储液。将固体样品溶解在适当的溶剂中，并在插入样品盒的一小块滤纸上放置几滴。将液体样品直接放在滤纸上。</li>
	<li>使用高纯度高压背气生产超音速膨胀。调整阀内样品储层的温度，使样品的部分压力约为10毫巴。 注意：对于液体样品，通常无需加热。阀门打开时间取决于所使用的脉冲阀的确切模型，因为这里介绍的实验中，Even-Lavie 阀的电动脉冲持续时间为 10 μsec。</li>
	<li>将产生的分子束与静电偏转器关闭进行特征。将电流激光器设置为已知波长，以便样品特定构象器的共振增强多光子电电增电 （REMPI）。通过监测 MCP 探测器上的总母离子产量，作为阀-激光延迟的函数，记录分子束脉冲的时间轮廓。</li>
	<li>修复阀门激光延迟在最大强度的位置，为所有后续测量。</li>
	<li>通过监测总母离子产量作为激光对焦 y 位置的函数，记录分子束的横向空间剖面。通过将对焦镜头垂直于激光传播方向来达到此目标，使对焦相对于分子束朝 y 方向移动。</li>
	<li>重复对光束中所有感兴趣的构象体的时间和空间分析。 注意：这些通常具有明显的 REMPI 共振，因此每个符合者都可以单独进行探测。但是，在没有偏转场的情况下，所有构象器的时间和空间轮廓是相同的。</li>
	<li>偏转光束的特征。打开偏转器的高压电源，并记录所有等位器的空间配置文件。现在，这些应根据质量与二极位的瞬间比率进行偏转。 注意：对于出现大偏转的物种，可能需要立即在偏转器之后移动掠过物，以确保偏转光束向检测区域的良好传输。</li>
	<li>通过确保相互作用（例如交叉激光束）在分子束中只包含感兴趣的物种的一部分内进行对分子束的构合体或大小选择部分的实验。</li>
</ol>

作者没有什么可透露的。

在整个手稿中，假设熟悉超高真空组件、脉冲分子束阀门和激光源，并始终遵守相关的安全程序。在为偏转器处理高压电极时，需要特别小心。它们的表面需要抛光到高标准，并且必须绝对清洁，以避免在真空室内弧形。在首次使用之前，电极应在真空下调节。施加的电压缓慢增加，电流通过电极测量。电极不应绘制电流（最多按几个 nA 的顺序），与施加的电压无关。逐步增加应用电压的典型调理时间表如下：...

现代气相分子物理和物理化学实验通常使用目标分子的超音速膨胀在分子束内产生旋转冷分子样本。然而，即使在1K的低旋转温度下，大分子仍然可以在光束1内保持多个构象。同样，在光束源中产生分子簇不会导致单一物种，而是形成"聚类汤"，其中含有许多不同的聚类聚变，以及剩余的纯父分子。这使得对这些系统的研究变得困难，因为这些系统需要新的技术，如分子轨道2成像，分子帧光电子角分布3-5 或电子6-10 和X射线衍射11-13， 因为这些需要纯，一致，同质的样品在气体相。
虽然现在可用于在气相（如 离子移动漂移管14，15）中分离带电物种的不同构象体和带电聚类的带电聚类，但这些技术不适用于中性物种。我们最近证明，使用静电偏转装置16，17可以克服这些问题，从而能够分离分子构象器和星团，并产生旋转冷分子束。
静电偏转是一种经典的分子束技术，其起源可以追溯到18，19年。斯特恩于1926年20年提出了利用静电偏转分离量子态的第一个想法。虽然在高温下对小分子进行了早期实验，但我们证明了这项技术在16，21年低温下应用于大极分子和星团。
由于潜在能量的空间差异，极地分子在异质电场（E）内产生力。这种力 <img fo:content-width="0.25in" src="/files/ftp_upload/51137/force.jpg" width="30px"> 取决于分子的有效偶极极时刻，μ eff，可以评估为
<img src="/files/ftp_upload/51137/51137eq1.jpg"> (1) 
由于不同的分子构象器通常具有不同的偶极态时刻和不同数量的溶剂分子在集群中导致不同的团团质量和偶极位，这些物种将经历不同的加速度在强大的同位素电场的存在。因此，来自同质电场的斯塔克效应力可用于构合体和量子态22的分离。这表示在图1中，显示计算的斯塔克曲线为J = 0，1，2旋转状态的cis和转符合 3 氟酚， 分别.这导致μ eff的巨大差异，如图1c和1d所示，因此两个符合者在异构电场中经历了不同的加速度。因此，静电偏转装置可用作质量与二极位的瞬间比（m/μ eff）分离器，与质谱仪类比，充当质量电荷比（m/z）滤波器23。
此外，这些技术允许旋转量子状态24，25的分离。由于地面旋转状态（ 图1a 和 1b中的蓝色曲线）显示最大的斯塔克移位，这些将偏转最多，可以在空间上从高 J 状态17的分子分离。因此，分子束中最冷的部分可以选择，显著有助于许多应用，如目标分子17、26-28的对齐和方向。
在这项贡献中，我们展示了静电偏转装置如何用于空间上分离不同种类的大型极地分子和星团。示例数据用于生成单个构象器的纯光束和定义明确的大小和比率的溶解剂集群。具体来说，我们提供3氟酚的数据，其中只含有转顺从器的纯光束，在鞋底水簇上，鞋底（H2O）1簇可以在空间上与水分离，鞋底，鞋底（H2O）2等。

<table border="0" cellpadding="0" cellspacing="0" width="687">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Vacuum system</td>
			<td style="width:175px;">various, e.g. Pfeiffer Vacuum, Varian, Edwards, Leybold</td>
			<td style="width:119px;"></td>
			<td style="width:177px;"></td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Dye laser system</td>
			<td style="width:175px;">various, e.g. Coherent, Spectra Physics, Syrah, LIOP-TEC, Radiant Dyes&#8230;</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Pulsed valve</td>
			<td style="width:175px;">Even-Lavie</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">High voltage power supply</td>
			<td style="width:175px;">eg. FUG</td>
			<td style="width:119px;">HCP 14-20000</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Deflector</td>
			<td style="width:175px;"></td>
			<td style="width:119px;"></td>
			<td>Custom made</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Time-of-flight spectrometer</td>
			<td style="width:175px;">Jordan TOF</td>
			<td style="width:119px;">C-677</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">TOF power supply</td>
			<td style="width:175px;">Jordan TOF</td>
			<td style="width:119px;">D-603</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Focusing lens</td>
			<td style="width:175px;">e.g. Thorlabs</td>
			<td>LA4745</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Translation stage</td>
			<td style="width:175px;">e.g. Vision Lasertechnik</td>
			<td style="width:119px;">8MT167-25</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Digitizer</td>
			<td style="width:175px;">e.g. Agilent</td>
			<td style="width:119px;">Acquiris DC440</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Digital delay generator</td>
			<td style="width:175px;">e.g. Stanford Systems</td>
			<td style="width:119px;">SRS DG645</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Molecular beam skimmer</td>
			<td style="width:175px;">Beam Dynamics Inc.</td>
			<td style="width:119px;"></td>
			<td>http://www.beamdynamicsinc.com/</td>
		</tr>
	</tbody>
</table>

spatial separation of molecular conformers and clusters

气相分子物理和物理化学实验通常使用超音速膨胀通过脉冲阀门生产冷分子束。然而，这些光束通常包含多个构象和星团，即使在低旋转温度下也是如此。我们提出了一种实验方法，允许分子束膨胀的这些成分的空间分离。使用电动偏转器，光束按质量与偶极态的瞬时比分离，类似于弯管或电扇形质谱仪，根据质量与电荷比在空间上分散带电分子。这种偏转器利用了同质电场中的斯塔克效应，并允许分离单个物种的极性中性分子和星团。此外，它允许选择分子束中最冷的部分，因为低能旋转量子态通常经历最大的偏转。由于功能组的不同排列，物种的不同结构同构体（构造体）可以分离，从而导致不同的偶极时刻。这些被静电偏转器利用，用于从分子束中生成符合纯样品。同样，也可以选择特定的聚类测定，因为特定星团的质量和偶极时刻取决于母分子周围的沉降程度。这允许对特定的星团大小和结构进行实验，从而能够系统地研究中性分子的索尔夫。

静电偏转技术已成功地应用于结构同构体16和中性星团21的分离，以及生产旋转量子态选定的分子样本31。我们用具有代表性的结果来证明这一点，即分离3氟酚的顺从和反式符合物，以及选定的尺寸（H2O）n集群。 
3-氟酚符合者在分子束中与50根氦气的超音速膨胀分离。个别物种通过其独特的REMPI共振约272纳米32</s...

Watch this Scientific Journal Video about Spatial Separation of Molecular Conformers and Clusters at JoVE.com

Spatial Separation of Molecular Conformers and Clusters

我们提出了一种技术，允许分子束中存在的不同构象体或星团的空间分离。静电偏转器用于按质量与偶极时比将物种分开，从而产生单一构象器或聚类气相的气相合奏。

分子构象器和星团的空间分离

Gas-phase molecular physics and physical chemistry experiments commonly use supersonic expansions through pulsed valves for the production of cold ...

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8.8K 次观看.  CFEL, DESY. 我们提出了一种技术，允许分子束中存在的不同构象体或星团的空间分离。静电偏转器用于按质量与偶极时比将物种分开，从而产生单一构象器或聚类气相的气相合奏。

视频: Spatial Separation of Molecular Conformers and Clusters

Molecular Beam Mass Spectrometry With Tunable Vacuum Ultraviolet (VUV) Synchrotron Radiation

Tunable soft ionization coupled to mass spectroscopy is a powerful method to investigate isolated molecules, complexes and clusters and their spectroscopy and dynamics1-4. Fundamental studies of photoionization processes of biomolecules provide information about the electronic structure of these systems. Furthermore determinations of ionization energies and other properties of biomolecules in the gas phase are not trivial, and these experiments provide a platform to generate these data. We have developed a thermal vaporization technique coupled with supersonic molecular beams that provides a gentle way to transport these species into the gas phase. Judicious combination of source gas and temperature allows for formation of dimers and higher clusters of the DNA bases. The focus of this particular work is on the effects of non-covalent interactions, i.e., hydrogen bonding, stacking, and electrostatic interactions, on the ionization energies and proton transfer of individual biomolecules, their complexes and upon micro-hydration by water1, 5-9.
We have performed experimental and theoretical characterization of the photoionization dynamics of gas-phase uracil and 1,3-dimethyluracil dimers using molecular beams coupled with synchrotron radiation at the Chemical Dynamics Beamline10 located at the Advanced Light Source and the experimental details are visualized here. This allowed us to observe the proton transfer in 1,3-dimethyluracil dimers, a system with pi stacking geometry and with no hydrogen bonds1. Molecular beams provide a very convenient and efficient way to isolate the sample of interest from environmental perturbations which in return allows accurate comparison with electronic structure calculations11, 12. By tuning the photon energy from the synchrotron, a photoionization efficiency (PIE) curve can be plotted which informs us about the cationic electronic states. These values can then be compared to theoretical models and calculations and in turn, explain in detail the electronic structure and dynamics of the investigated species 1, 3.

Molecular Beam Mass Spectrometry With Tunable Vacuum Ultraviolet VUV Synchrotron Radiation

A molecular beam coupled to tunable vacuum ultraviolet photoionization mass spectrometer at a synchrotron provides a convenient tool to explore the electronic structure of isolated gas phase molecules and clusters. Proton transfer mechanisms in DNA base dimers were elucidated with this technique.

可调式真空紫外（VUV）同步辐射分子束质谱分析

Tunable soft ionization coupled to mass spectroscopy is a powerful method to investigate isolated molecules, complexes and clusters and their spectroscopy ...

科研

工程学

Concurrent Quantitative Conductivity and Mechanical Properties Measurements of Organic Photovoltaic Materials using AFM

Organic photovoltaic (OPV) materials are inherently inhomogeneous at the nanometer scale. Nanoscale inhomogeneity of OPV materials affects performance of photovoltaic devices. Thus, understanding of spatial variations in composition as well as electrical properties of OPV materials is of paramount importance for moving PV technology forward.1,2 In this paper, we describe a protocol for quantitative measurements of electrical and mechanical properties of OPV materials with sub-100 nm resolution. Currently, materials properties measurements performed using commercially available AFM-based techniques (PeakForce, conductive AFM) generally provide only qualitative information. The values for resistance as well as Young's modulus measured using our method on the prototypical ITO/PEDOT:PSS/P3HT:PC61BM system correspond well with literature data. The P3HT:PC61BM blend separates onto PC61BM-rich and P3HT-rich domains. Mechanical properties of PC61BM-rich and P3HT-rich domains are different, which allows for domain attribution on the surface of the film. Importantly, combining mechanical and electrical data allows for correlation of the domain structure on the surface of the film with electrical properties variation measured through the thickness of the film.

Organic photovoltaic (OPV) materials are inherently inhomogeneous at the nanometer scale. Nanoscale inhomogeneity of OPV materials affects performance of photovoltaic devices. In this paper, we describe a protocol for quantitative measurements of electrical and mechanical properties of OPV materials with sub-100 nm resolution.

并行定量的导电性和力学性能测试的有机光伏材料利用原子力显微镜

Organic photovoltaic  (OPV) materials are inherently inhomogeneous at the nanometer scale. Nanoscale  inhomogeneity of OPV materials affects performance ...

Ultrahigh Density Array of Vertically Aligned Small-molecular Organic Nanowires on Arbitrary Substrates

In recent years &pi;-conjugated organic semiconductors have emerged as the active material in a number of diverse applications including large-area, low-cost displays, photovoltaics, printable and flexible electronics and organic spin valves. Organics allow (a) low-cost, low-temperature processing and (b) molecular-level design of electronic, optical and spin transport characteristics. Such features are not readily available for mainstream inorganic semiconductors, which have enabled organics to carve a niche in the silicon-dominated electronics market. The first generation of organic-based devices has focused on thin film geometries, grown by physical vapor deposition or solution processing. However, it has been realized that organic nanostructures can be used to enhance performance of above-mentioned applications and significant effort has been invested in exploring methods for organic nanostructure fabrication.	
A particularly interesting class of organic nanostructures is the one in which vertically oriented organic nanowires, nanorods or nanotubes are organized in a well-regimented, high-density array. Such structures are highly versatile and are ideal morphological architectures for various applications such as chemical sensors, split-dipole nanoantennas, photovoltaic devices with radially heterostructured "core-shell" nanowires, and memory devices with a cross-point geometry. Such architecture is generally realized by a template-directed approach. In the past this method has been used to grow metal and inorganic semiconductor nanowire arrays. More recently &pi;-conjugated polymer nanowires have been grown within nanoporous templates. However, these approaches have had limited success in growing nanowires of technologically important &pi;-conjugated small molecular weight organics, such as tris-8-hydroxyquinoline aluminum (Alq3), rubrene and methanofullerenes, which are commonly used in diverse areas including organic displays, photovoltaics, thin film transistors and spintronics.	
Recently we have been able to address the above-mentioned issue by employing a novel "centrifugation-assisted" approach. This method therefore broadens the spectrum of organic materials that can be patterned in a vertically ordered nanowire array. Due to the technological importance of Alq3, rubrene and methanofullerenes, our method can be used to explore how the nanostructuring of these materials affects the performance of aforementioned organic devices. The purpose of this article is to describe the technical details of the above-mentioned protocol, demonstrate how this process can be extended to grow small-molecular organic nanowires on arbitrary substrates and finally, to discuss the critical steps, limitations, possible modifications, trouble-shooting and future applications.

We report a simple method for fabricating an ultrahigh density array of vertically ordered small-molecular organic nanowires. This method allows for synthesis of complex heterostructured hybrid nanowire geometries, which can be inexpensively grown on arbitrary substrates. These structures have potential applications in organic electronics, optoelectronics, chemical sensing, photovoltaics and spintronics.

超高密度垂直对齐的任意基质的小分子有机纳米线阵列

In  recent years &pi;-conjugated  organic semiconductors have emerged as the active material in a number of  diverse applications including large-area, ...

Measurement and Analysis of Atomic Hydrogen and Diatomic Molecular AlO, C2, CN, and TiO Spectra Following Laser-induced Optical Breakdown

In this work, we present time-resolved measurements of atomic and diatomic spectra following laser-induced optical breakdown. A typical LIBS arrangement is used. Here we operate a Nd:YAG laser at a frequency of 10 Hz at the fundamental wavelength of 1,064 nm. The 14 nsec pulses with anenergy of 190 mJ/pulse are focused to a 50 &#181;m spot size to generate a plasma from optical breakdown or laser ablation in air. The microplasma is imaged onto the entrance slit of a 0.6 m spectrometer, and spectra are recorded using an 1,800 grooves/mm grating an intensified linear diode array and optical multichannel analyzer (OMA) or an ICCD. Of interest are Stark-broadened atomic lines of the hydrogen Balmer series to infer electron density. We also elaborate on temperature measurements from diatomic emission spectra of aluminum monoxide (AlO), carbon (C2), cyanogen (CN), and titanium monoxide (TiO).
The experimental procedures include wavelength and sensitivity calibrations. Analysis of the recorded molecular spectra is accomplished by the fitting of data with tabulated line strengths. Furthermore, Monte-Carlo type simulations are performed to estimate the error margins. Time-resolved measurements are essential for the transient plasma commonly encountered in LIBS.

Measurement and Analysis of Atomic Hydrogen and Diatomic Molecular AlO, C2, CN, and TiO Spectra Following Laser-induced Optical Breakdown

Time-resolved atomic and diatomic molecular species are measured using LIBS. The spectra are collected at various time delays following the generation of optical breakdown plasma with Nd:YAG laser radiation&#160;and are analyzed to infer electron density and temperature.

测量和原子氢和双原子分子ALO，C分析<sub&gt; 2</sub&gt;，CN和二氧化钛光谱承接激光诱导光学击穿

In this work, we present time-resolved measurements of atomic and diatomic spectra following laser-induced optical breakdown. A typical LIBS arrangement ...

Probing C84-embedded Si Substrate Using Scanning Probe Microscopy and Molecular Dynamics

This paper reports an array-designed C84-embedded Si substrate fabricated using a controlled self-assembly method in an ultra-high vacuum chamber. The characteristics of the C84-embedded Si surface, such as atomic resolution topography, local electronic density of states, band gap energy, field emission properties, nanomechanical stiffness, and surface magnetism, were examined using a variety of surface analysis techniques under ultra, high vacuum (UHV) conditions as well as in an atmospheric system. Experimental results demonstrate the high uniformity of the C84-embedded Si surface fabricated using a controlled self-assembly nanotechnology mechanism, represents an important development in the application of field emission display (FED), optoelectronic device fabrication, MEMS cutting tools, and in efforts to find a suitable replacement for carbide semiconductors. Molecular dynamics (MD) method with semi-empirical potential can be used to study the nanoindentation of C84-embedded Si substrate. A detailed description for performing MD simulation is presented here. Details for a comprehensive study on mechanical analysis of MD simulation such as indentation force, Young&#39;s modulus, surface stiffness, atomic stress, and atomic strain are included. The atomic stress and von-Mises strain distributions of the indentation model can be calculated to monitor deformation mechanism with time evaluation in atomistic level.

Probing C84-embedded Si Substrate Using Scanning Probe Microscopy and Molecular Dynamics

This paper reports the nanomaterial fabrication of a fullerene Si substrate inspected and verified by nanomeasurements and molecular dynamic simulation.

探测ç<sub&gt; 84</sub&gt; - 嵌入式硅衬底利用扫描探针显微镜和分子动力学

This paper reports an array-designed C84-embedded Si substrate fabricated using a controlled self-assembly method in an ultra-high vacuum chamber. The ...

Nanostructured Ag-zeolite Composites as Luminescence-based Humidity Sensors

Small silver clusters confined inside zeolite matrices have recently emerged as a novel type of highly luminescent materials. Their emission has high external quantum efficiencies (EQE) and spans the whole visible spectrum. It has been recently reported that the UV excited luminescence of partially Li-exchanged sodium Linde type A zeolites [LTA(Na)] containing luminescent silver clusters can be controlled by adjusting the water content of the zeolite. These samples showed a dynamic change in their emission color from blue to green and yellow upon an increase of the hydration level of the zeolite, showing the great potential that these materials can have as luminescence-based humidity sensors at the macro and micro scale. Here, we describe the detailed procedure to fabricate a humidity sensor prototype using silver-exchanged zeolite composites. The sensor is produced by suspending the luminescent Ag-zeolites in an aqueous solution of polyethylenimine (PEI) to subsequently deposit a film of the material onto a quartz plate. The coated plate is subjected to several hydration/dehydration cycles to show the functionality of the sensing film.

A protocol for the synthesis of moisture-responsive luminescent Ag-zeolite composites is described in this report.

纳米银沸石复合材料作为基于发光的湿度传感器

Small silver clusters confined inside zeolite matrices have recently emerged as a novel type of highly luminescent materials. Their emission has high ...

Plasma-assisted Molecular Beam Epitaxy of N-polar InAlN-barrier High-electron-mobility Transistors

Plasma-assisted molecular beam epitaxy is well suited for the epitaxial growth of III-nitride thin films and heterostructures with smooth, abrupt interfaces required for high-quality high-electron-mobility transistors (HEMTs). A procedure is presented for the growth of N-polar InAlN HEMTs, including wafer preparation and growth of buffer layers, the InAlN barrier layer, AlN and GaN interlayers and the GaN channel. Critical issues at each step of the process are identified, such as avoiding Ga accumulation in the GaN buffer, the role of temperature on InAlN compositional homogeneity, and the use of Ga flux during the AlN interlayer and the interrupt prior to GaN channel growth. Compositionally homogeneous N-polar InAlN thin films are demonstrated with surface root-mean-squared roughness as low as 0.19 nm and InAlN-based HEMT structures are reported having mobility as high as 1,750 cm2/V&#8729;sec for devices with a sheet charge density of 1.7 x 1013 cm-2.

Molecular beam epitaxy is used to grow N-polar InAlN-barrier high-electron-mobility transistors (HEMTs). Control of the wafer preparation, layer growth conditions and epitaxial structure results in smooth, compositionally homogeneous InAlN layers and HEMTs with mobility as high as 1,750 cm2/V&#8729;sec.

N极性InAlN阻高电子迁移率晶体管的等离子体辅助分子束外延

Plasma-assisted molecular beam epitaxy is well suited for the epitaxial growth of III-nitride thin films and heterostructures with smooth, abrupt ...

An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids

An analog, macroscopic method for studying molecular-scale hydrodynamic processes in dense gases and liquids is described. The technique applies a standard fluid dynamic diagnostic, particle image velocimetry (PIV), to measure: i) velocities of individual particles (grains), extant on short, grain-collision time-scales, ii) velocities of systems of particles, on both short collision-time- and long, continuum-flow-time-scales, iii) collective hydrodynamic modes known to exist in dense molecular fluids, and iv) short- and long-time-scale velocity autocorrelation functions, central to understanding particle-scale dynamics in strongly interacting, dense fluid systems. The basic system is composed of an imaging system, light source, vibrational sensors, vibrational system with a known media, and PIV and analysis software. Required experimental measurements and an outline of the theoretical tools needed when using the analog technique to study molecular-scale hydrodynamic processes are highlighted. The proposed technique provides a relatively straightforward alternative to photonic and neutron beam scattering methods traditionally used in molecular hydrodynamic studies.

An experimentally accessible analog method for studying molecular hydrodynamic processes in dense fluids is presented. The technique uses particle image velocimetry of vibrated, high-restitution grain piles and allows direct, macroscopic observation of dynamical processes known and predicted to exist in strongly interacting, high density gases and liquids.

一种研究稠密气体和液体分子流体力学过程的模拟宏观技术

An analog, macroscopic method for studying molecular-scale hydrodynamic processes in dense gases and liquids is described. The technique applies a ...

Fabrication of Schottky Diodes on Zn-polar BeMgZnO/ZnO Heterostructure Grown by Plasma-assisted Molecular Beam Epitaxy

Heterostructure field effect transistors (HFETs) utilizing a two dimensional electron gas (2DEG) channel have a great potential for high speed device applications. Zinc oxide (ZnO), a semiconductor with a wide bandgap (3.4 eV) and high electron saturation velocity has gained a great deal of attention as an attractive material for high speed devices. Efficient gate modulation, however, requires high-quality Schottky contacts on the barrier layer. In this article, we present our Schottky diode fabrication procedure on Zn-polar BeMgZnO/ZnO heterostructure with high density 2DEG which is achieved through strain modulation and incorporation of a few percent Be into the MgZnO-based barrier during growth by molecular beam epitaxy (MBE). To achieve high crystalline quality, nearly lattice-matched high-resistivity GaN templates grown by metal-organic chemical vapor deposition (MOCVD) are used as the substrate for the subsequent MBE growth of the oxide layers. To obtain the requisite Zn-polarity, careful surface treatment of GaN templates and control over the VI/II ratio during the growth of low temperature ZnO nucleation layer are utilized. Ti/Au electrodes serve as Ohmic contacts, and Ag electrodes deposited on the O2 plasma pretreated BeMgZnO surface are used for Schottky contacts.

Attainment of high-quality Schottky contacts is imperative for achieving efficient gate modulation in heterostructure field effect transistors (HFETs). We present the fabrication methodology and characteristics of Schottky diodes on Zn-polar BeMgZnO/ZnO heterostructures with high-density two dimensional electron gas (2DEG), grown by plasma-assisted molecular beam epitaxy on GaN templates.

等离子体辅助分子束外延法制备的锌极性 BeMgZnO/氧化锌异质结构肖特基二极管的制备

Heterostructure field effect transistors (HFETs) utilizing a two dimensional electron gas (2DEG) channel have a great potential for high speed device ...

Assembling Molecular Shuttles Powered by Reversibly Attached Kinesins

This protocol describes how to create kinesin-powered molecular shuttles with a weak and reversible attachment of the kinesins to the surface. In contrast to previous protocols, in this system, microtubules recruit kinesin motor proteins from solution and place them on a surface. The kinesins will, in turn, facilitate the gliding of the microtubules along the surface before desorbing back into the bulk solution, thus being available to be recruited again. This continuous assembly and disassembly leads to striking dynamic behavior in the system, such as the formation of temporary kinesin trails by gliding microtubules.
Several experimental methods will be described throughout this experiment: UV-Vis spectrophotometry will be used to determine the concentration of stock solutions of reagents, coverslips will first be ozone and ultraviolet (UV) treated and then silanized before being mounted into flow cells, and total internal reflection fluorescence (TIRF) microscopy will be used to simultaneously image kinesin motors and microtubule filaments.

We present a protocol to build molecular shuttles, where surface-adhered kinesin motor proteins propel dye-labelled microtubules. Weak interactions of the kinesins with the surface enables their reversible attachment to it. This creates a nanoscale system which exhibits dynamic assembly and disassembly of its components while retaining its functionality.

由可逆连接的运动素提供动力的分子穿梭机的组装

This protocol describes how to create kinesin-powered molecular shuttles with a weak and reversible attachment of the kinesins to the surface. In contrast ...