This work is supported by the U.S. Army Research Office under the grant W911NF-15-1-0414.

1. Preparation of the Homemade Knudsen Cell
<ol>
	<li>Prepare components for Knudsen cell
	<ol>
		<li>Purchase a CF flanged based power feedthrough (2.75&#34; CF, 4 pins stainless steel). Drill two threaded holes through the feedthrough, at the cross points between one diameter 1.30&#34; line and its circumference.</li>
		<li>Prepare a glass tube (0.315&#34; outside diameter (OD), 2.50&#34; length).</li>
		<li>Purchase thin copper sheets (99.9%) with 0.005&#34; thickness. Cut one sheet to the dimensions of 7.5&#34; L x 5.0&#34; W using a pair of scissors, then curl it to a hollow columniform shield with a 1.45&#34; diameter by hand (Figure 1a).</li>
		<li>Prepare the type K thermocouple (chromel/alumel) with a 0.005&#34; diameter by cutting a 3&#34; length for both the chromel and alumel wires. Peel the insulator layers about 0.5&#34; in length from both ends of both wires.</li>
		<li>Cut a 0.01&#34; diameter tungsten wire (99.95%) to a length of approximately 60&#34;. Coil it into a spring shape with a diameter 0.315&#34; by wrapping tightly it around a rod of a comparable diameter of the glass tube.</li>
		<li>Purchase a ceramic piece. Prepare one suitable cuboid piece with a hole in the middle that fits the dimension of the glass (5 in Figure 1b).</li>
		<li>Cut 2 standard steel threaded 0.10&#34; diameter rods to a 7&#34; length by banding and sawing with a lathe machine.</li>
		<li>Cut a soft, 0.01&#34; diameter copper wire to an approximate 30&#34; length using a scissor.</li>
		<li>Prepare 4 hollow copper rods with a 0.094&#34; OD diameter by cutting three rods to a 2&#34; length, and one rod to a 4&#34; length using a side cutter.</li>
	</ol>
	</li>
	<li>Assemble these pieces in the Knudsen cell
	<ol>
		<li>Clean all the components mentioned in step 1.1 using ultrasonic cleaning at 42 kHz in acetone for 30 min.</li>
		<li>Mount 2 standard steel threaded rods in the drilled holes in the CF flange of the power feedthrough. 
		NOTE: The holes are threaded (7 in Figure 1b).</li>
		<li>Mount the bottom half of the 4 hollow copper rods in the top part of the 4 pins of the CF flanged power feedthrough by inserting the pin into the hollow copper rods and fixing them by a side cutter (6 in Figure 1b).</li>
		<li>Mount the ceramic piece at the position of 2.5&#34; high from the bottom of the threaded rods with soft copper wire. 
		NOTE: This piece will support the glass tube in the following step (5 in Figure 1b).</li>
		<li>Slide the glass tube into the curled tungsten spring. Squeeze the bottom of the glass tube into the hole of the ceramic piece. Use soft copper wire to hold the top end of the glass tube to the top end of the threaded rods (3 and 4 in Figure 1b).</li>
		<li>Grip the top end of the spring into the longer copper rod, defined as A. Grip the bottom end of the spring into one of the shorter copper rods, defined as B (A and B in Figure 1b).</li>
		<li>Twist one peeled end of both the chromel and alumel wires together (2 in Figure 1b).</li>
		<li>Position the twisted joint end so that it closely touches the outside bottom of the glass tube. Immobilize it with the help of the ceramic piece.</li>
		<li>Grip the other peeled end of the chromel wire into one of the left 2 shorter copper rods, defined as C. Grip the other peeled end of the alumel wire into the left shorter copper rod, defined as D (C and D in Figure 1b).</li>
		<li>Put the curled copper hollow columniform shield on the CF flanged power feedthrough (Figure 1a).</li>
	</ol>
	</li>
</ol>
2. Prepare the C60 Source in the Homemade Knudsen Cell
<ol>
	<li>Load the C60 source in the homemade Knudsen cell.
	<ol>
		<li>Load approximately 50 mg of C60 powder (99.5% purity) into the glass tube of the homemade Knudsen cell. 
		NOTE: Precision beyond 1 mg of the mass of the powder is unnecessary.</li>
		<li>Mount the Knudsen cell back onto one branch of the load lock.</li>
	</ol>
	</li>
	<li>Pump the load lock.
	<ol>
		<li>Turn on the pump for the load lock. First turn on the water valve for cooling the turbo pump, then turn on the fan to cool the mechanical pump. Then turn on the mechanical pump and finally turn on the turbo pump.</li>
		<li>Check the pressure in the load lock and wait about 10 h. 
		NOTE: The pressure at the outlet of the turbo pump should be 6.0 x 10-2 mbar.</li>
		<li>Turn on the ion gauge mounted in the load lock to a lower pressure (typically below 10-6 mbar).</li>
		<li>Check the pressure in the load lock: the pressure should be in the range of 10-8 mbar after 10 h pumping.</li>
	</ol>
	</li>
	<li>Anneal the C60 source in the homemade Knudsen cell.
	<ol>
		<li>Anneal the C60 source in the homemade Knudsen cell gradually (1.5 &#176;C/min) at 250 &#176;C for 2 h for degassing by connecting a power supply on two pins of the CF flanged power feedthrough, which are connected to the curled tungsten spring.</li>
		<li>Increase the annealing temperature to 300 &#176;C, which is above the deposition temperature (270 &#176;C).</li>
		<li>Anneal at 300 &#176;C for 0.5 h for further degassing.</li>
		<li>Decrease the temperature to 270 &#176;C for deposition.</li>
	</ol>
	</li>
</ol>
3. Prepare Atomically Clean Graphene in the UHV Chamber
<ol>
	<li>Transfer the graphene (on copper foil) from the sample storage carousel to the annealing plate in the ultra-high vacuum preparation chamber of the STM system (a special place for preparing and annealing a sample under ultra-high vacuum).</li>
	<li>Anneal the graphene substrate at a base pressure of low 10-10 mbar within the preparation chamber by gradually increasing the temperature to 400 &#176;C.</li>
	<li>Wait for 12 h to remove residual impurities on the graphene surface.</li>
	<li>Decrease the annealing temperature for graphene substrate gradually to room temperature.</li>
</ol>
4. Deposit the C 60 onto Graphene Substrate Using the Homemade Knudsen Cell in Load Lock
<ol>
	<li>Transfer the graphene substrate to the load lock.
	<ol>
		<li>Arrange the plate in the preparation chamber in the transferring position. Transfer the atomically clean graphene to the load lock for deposition C60, after having the atomically clean graphene and C60 source ready.</li>
		<li>Open the valve between the load lock and the preparation chamber.</li>
		<li>Transfer the graphene substrate from the plate in the preparation chamber to the load lock with the loadout tool.</li>
		<li>Put the graphene substrate face down (the C60 comes from the source below).</li>
	</ol>
	</li>
	<li>Deposit the C60 onto the graphene substrate. 
	NOTE: C60 molecules transfer from the homemade Knudsen cell to the graphene substrate at 270 &#176;C.
	<ol>
		<li>Wait for 1 min with a deposition rate of 0.9 monolayer/min.</li>
		<li>Transfer the C60/graphene sample back to the preparation chamber.</li>
	</ol>
	</li>
</ol>
5. Prepare the C 60 /Graphene Sample to be Measured in STM Main Chamber
<ol>
	<li>Anneal the C60/graphene sample to 150 &#176;C with a rate of 3.1 &#176;C/min for 2 h in the ultra-high vacuum preparation chamber.</li>
	<li>Scan the C60/graphene sample with STM in the STM main chamber.</li>
	<li>Anneal the C60/graphene sample to 210 &#176;C with a rate of 3.1 &#176;C/min for 2 h.</li>
	<li>Scan the C60/graphene sample with STM.</li>
</ol>

<ol>
	<li>Gutzler, R., Heckl, W. M., Lackinger, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Combination+of+a+Knudsen+effusion+cell+with+a+quartz+crystal+microbalance:+In+situ+measurement+of+molecular+evaporation+rates+with+a+fully+functional+deposition+source.">Combination of a Knudsen effusion cell with a quartz crystal microbalance: In situ measurement of molecular evaporation rates with a fully functional deposition source.</a> Review of Scientific Instruments. 81, 015108 (2010).</li><li>de Barros, A. L. F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+simple+experimental+arrangement+for+measuring+the+vapour+pressures+and+sublimation+enthalpies+by+the+Knudsen+effusion+method:+Application+to+DNA+and+RNA+bases.">A simple experimental arrangement for measuring the vapour pressures and sublimation enthalpies by the Knudsen effusion method: Application to DNA and RNA bases.</a> Nuclear Instruments &amp; Methods in Physics Research Section a-Accelerators Spectrometers Detectors and Associated Equipment. 560, (2006).</li><li>Shukla, A. K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Versatile+UHV+compatible+Knudsen+type+effusion+cell.">Versatile UHV compatible Knudsen type effusion cell.</a> Review of Scientific Instruments. 75, 4467 (2004).</li><li>Cho, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structural+and+Electronic+Decoupling+of+C60+from+Epitaxial+Graphene+on+SiC.">Structural and Electronic Decoupling of C60 from Epitaxial Graphene on SiC.</a> Nano Letters. 12, 3018 (2012).</li><li>Jung, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Atomically+resolved+orientational+ordering+of+C60+molecules+on+epitaxial+graphene+on+Cu(111).">Atomically resolved orientational ordering of C60 molecules on epitaxial graphene on Cu(111).</a> Nanoscale. 6 (111), 11835 (2014).</li><li>Li, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Self-assembly+of+C60+monolayer+on+epitaxially+grown,+nanostructured+graphene+on+Ru(0001)+surface.">Self-assembly of C60 monolayer on epitaxially grown, nanostructured graphene on Ru(0001) surface.</a> Applied Physics Letters. 100 (0001), 013304 (2012).</li><li>Lu, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Using+the+Graphene+Moire+Pattern+for+the+Trapping+of+C60+and+Homoepitaxy+of+Graphene.">Using the Graphene Moire Pattern for the Trapping of C60 and Homoepitaxy of Graphene.</a> Acs Nano. 6, 944 (2012).</li><li>Zhou, H. T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+imaging+of+intrinsic+molecular+orbitals+using+two-dimensional,+epitaxially-grown,+nanostructured+graphene+for+study+of+single+molecule+and+interactions.">Direct imaging of intrinsic molecular orbitals using two-dimensional, epitaxially-grown, nanostructured graphene for study of single molecule and interactions.</a> Applied Physics Letters. 99, 153101 (2011).</li><li>Belaish, I., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spin+Cast+Thin-Films+of+Fullerenes+and+Fluorinated+Fullerenes+-+Preparation+and+Characterization+by+X-Ray+Reflectivity+and+Surface+Diffuse-X-Ray+Scattering.">Spin Cast Thin-Films of Fullerenes and Fluorinated Fullerenes - Preparation and Characterization by X-Ray Reflectivity and Surface Diffuse-X-Ray Scattering.</a> Journal of Applied Physics. 71, 5248 (1992).</li><li>Bezmel'nitsyn, V. N., Eletskii, A. V., Okun', M. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fullerenes+in+solutions.">Fullerenes in solutions.</a> Uspekhi Fizicheskikh Nauk. 168, 1195 (1998).</li><li>Ma, D. N., Sandoval, S., Muralidharan, K., Raghavan, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+surface+preparation+of+copper+on+spin-coating+driven+self-assembly+of+fullerene+molecules.">Effect of surface preparation of copper on spin-coating driven self-assembly of fullerene molecules.</a> Microelectronic Engineering. 170, 8 (2017).</li><li>Chen, C. H., Zheng, H. S., Mills, A., Heflin, J. R., Tao, C. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Temperature+Evolution+of+Quasi-one-dimensional+C60+Nanostructures+on+Rippled+Graphene.">Temperature Evolution of Quasi-one-dimensional C60 Nanostructures on Rippled Graphene.</a> Scientific Reports. 5, 14336 (2015).</li></ol>

We have nothing to disclose.

The techniques described in this protocol are designed for thermal deposition of organic materials and other high vapor pressure materials. These techniques can be integrated with ultra-high vacuum systems that have sample preparation areas capable of supporting molecular evaporation as well as thermal annealing. The aim for this specific experiment is to deposit C60 molecules on graphene substrate and study the self-assembly of C60 and the thermal effect.
The benefit of the method is that it provides a super clean sample when compared with other thin film preparation methods, like spin coating. Compared with more complex technologies like chemical vapor deposition (CVD), this physical thermal evaporation is much easier to realize and fit for stable atoms and molecules deposition. Atomic and molecular resolution imaging are required to observe the C60/graphene hybrid nanostructures. STM is used in this exposition. It is critical to maintain the purity of the substrate and C60 source throughout deposition by degassing and annealing ahead of time and maintaining a high vacuum throughout the process. Proper post-deposition annealing is crucial to obtain the 1D and quasi-1D nanostructures, as this technique exploits the variable nature of C60 surface mobility under various thermal conditions.
STM measurement demonstrates that the C60/graphene sample synthesized by the physical thermal deposition method is atomically clean. The space in the load lock is designed to be very limited to achieve an ultra-high vacuum in a rather short time. The molecule deposition needs to be completed in such a small space that a homemade Knudsen cell becomes necessary. The homemade Knudsen cell evaporator is mounted in the load lock chamber and can be baked separately, which is also helpful for changing the molecules or refilling the evaporator12. The highest deposition temperature for this homemade Knudsen cell is 450 &#176;C, as determined by the CF Flanged Power Feedthrough. It is critical to degas the C60 source in the homemade Knudsen cell at 300 &#176;C to guarantee the purity of C60 when deposited at 270 &#176;C. It is also very important to anneal the graphene substrate just before the molecule deposition so that it is at its cleanest state at the beginning of the deposition. A binary system can also be achieved by adding one more homemade Knudsen cell evaporator on the opposite side of the first one.

This protocol explains how to deposit and manipulate C60 molecules on graphene such that 1D and quasi-1D C60 chain structures can be realized. The techniques in this experiment were developed to address the need to guide adsorbates into desirable configurations without having to rely on manual manipulation, which is slow and can require great effort. The procedures described here rely on the use of a high vacuum system with a sample preparation area capable of supporting molecular deposition and thermal annealing of the samples. STM is used to characterize the samples, but other molecular resolution techniques may be applied.
The thermal evaporation of molecules within a Knudsen cell is an efficient and clean way to prepare thin films. In this protocol, a Knudsen cell is used to evaporate C60 molecules onto a graphene substrate. This Knudsen cell evaporator mainly consists of a quartz tube, a heating filament, thermocouple wires, and feedthroughs1,2,3. The quartz tube is used to accommodate the molecules, the tungsten filament heats the molecules in the quartz tube through applied current, and the thermocouple wires are used to measure the temperature. In the experiments, the deposition rate is controlled by tuning the temperature source in the Knudsen cell. The thermocouple wires are attached to the outside wall of the quartz tube and therefore typically measure a temperature of the outside wall that is slightly different from the temperature inside of the cell where the molecular source is located. To obtain the exact temperature in the quartz tube, we performed calibration using two thermocouple setups to measure temperatures inside and outside the tube and recorded the temperature difference. In this way, we can more precisely control the temperature of the source during the molecular evaporation experiments using thermocouple wires attached to the outside of the quartz tube. Because a small amount of the sublimated molecules will be in a gaseous phase at a lower pressure, when the molecules are evaporated, there is usually an associated pressure change. Therefore, we monitor the change of the pressure in the load lock carefully.
This evaporator can be used to deposit various molecule sources such as C60, C70, boron subphthalocyanine chloride, Ga, Al, and Hg4,5,6,7,8. Compared with other thin film preparation techniques, for instance, spin casting9,10,11, the thermal evaporation in high vacuum is much cleaner and versatile since there is no solvent required for the deposition. Furthermore, the degassing process before deposition improves the purity of the source, eliminating possible impurities.

<table>
	<tbody>
		<tr>
			<td>CF Flanged power feedthrough</td>
			<td>Kurt J. Lesker</td>
			<td>EFT0042033</td>
			<td></td>
		</tr>
		<tr>
			<td>Copper sheets</td>
			<td>Alfa Aesar</td>
			<td>7440-50-8</td>
			<td></td>
		</tr>
		<tr>
			<td>Thermocouple chromel/alumel wires</td>
			<td>Omega Engineering</td>
			<td>ST032034/ST080042</td>
			<td></td>
		</tr>
		<tr>
			<td>Tungsten wires</td>
			<td>Alfa Aesar</td>
			<td>7440-33-7</td>
			<td></td>
		</tr>
		<tr>
			<td>Stainless steel rods</td>
			<td>McMaster-Carr</td>
			<td>95412A868</td>
			<td></td>
		</tr>
		<tr>
			<td>Copper wires</td>
			<td>McMaster-Carr</td>
			<td>8873K28</td>
			<td></td>
		</tr>
		<tr>
			<td>Hollow copper rods</td>
			<td>McMaster-Carr</td>
			<td>7190K52</td>
			<td></td>
		</tr>
		<tr>
			<td>C60</td>
			<td>MER Corporation</td>
			<td>MR6LP</td>
			<td></td>
		</tr>
	</tbody>
</table>

preparation and characterization of c60/graphene hybrid nanostructures

Physical thermal deposition in a high vacuum environment is a clean and controllable method for fabricating novel molecular nanostructures on graphene. We present methods for depositing and passively manipulating C60 molecules on rippled graphene that advance the pursuit of realizing applications involving 1D C60/graphene hybrid structures. The techniques applied in this exposition are geared towards high vacuum systems with preparation areas capable of supporting molecular deposition as well as thermal annealing of the samples. We focus on C60 deposition at low pressure using a homemade Knudsen cell connected to a scanning tunneling microscopy (STM) system. The number of molecules deposited is regulated by controlling the temperature of the Knudsen cell and the deposition time. One-dimensional (1D) C60 chain structures with widths of two to three molecules can be prepared via tuning of the experimental conditions. The surface mobility of the C60 molecules increases with annealing temperature allowing them to move within the periodic potential of the rippled graphene. Using this mechanism, it is possible to control the transition of 1D C60 chain structures to a hexagonal close packed quasi-1D stripe structure.

Following evaporation, the graphene with the newly deposited C60 is annealed at 150 &#176;C for 2 h. The large-scale STM image in Figure 2a shows a characteristic quasi-1D C60 chain structure found after this initial annealing process. A closer inspection in Figure 2b reveals detailed information of this 1D structure, in which each bright spherical protrusion represents one single C60 molecule. Typically, the 1D chains occur as bimolecular and trimolecular C60 chains with an average C60-C60 distance of 1.00 &#177; 0.01 nm, indicating that the C60 molecules arrange in a hexagonal close packed manner. The line profile in Figure 2c corresponding to the dashed green line in Figure 2b shows clear separation between the C60 chains where the second and the third peaks in the profile are nearest neighbor molecules on adjacent chains. According to observations, the chains exist exclusively as bimolecular or trimolecular rows with the bimolecular chains occurring twice as frequently as the trimolecular chains. As observed in the high-resolution STM images, the chains are well arranged in either a 3-2-2 or 2-3-2 manner. There may occur some junctions within one chain where a trimolecular segment can jump to a bimolecular arrangement, or vice versa.
The growth of the quasi-1D C60 chains is induced by the underneath graphene substrate. The high-resolution STM image of the atomically clean graphene substrate (Figure 1c) shows a rippled structure. This well-defined linear periodic modulation causes C60 molecules to form the quasi-1D chains. The sample is subsequently annealed at 210 &#176;C for 2 h in order to investigate thermal influences on the C60/graphene 1D nanostructures. Annealing at a higher temperature increases the surface mobility of the C60 molecules, allowing them to self-assemble into a more compact, hexagonal close packed quasi-1D stripe structure, as shown in Figure 3a. These structures orient along the same direction as the C60 chains and are observed with widths varying between 3 and 8 molecules per stripe, as shown in Figure 3b. The most common stripes have a width of six C60 rows, occurring 45% of the time, while 5-row stripes are the second most likely stripe structure. In this structure, there is no space separating neighboring stripes. An obvious difference from the gently annealed C60 chain structure is that the stripes are not formed on a single flat terrace, but on staggered narrow terraces, shown as nearly straight and parallel step edges (Figure 3b, c). The two rows at the boundary of each step edge, one on the upper terrace and one on the lower terrace, assume a denser arrangement relative to one another, having only a lateral inter-row spacing of 0.75 &#177; 0.01 nm. This arrangement presumably accommodates the underlying terraces that formed after the higher temperature annealing. On the terrace planes, the C60 molecules still maintain a close-packed pattern with the same intermolecular spacing characteristic of C60-C60. The C60 row near the step edge on the upper terrace appears to be around 0.5 &#197; higher than the other C60 rows on the same terrace; this is likely due to different local electronic environments as shown in Figure 3b, c. Similar to the previous chain structure, there are junctions for neighboring stripes. To compare these two different structures more systematically, we use 3D models to illustrate them. Figure 4a, c is the top and side view of the schematic model for the C60 chains, respectively, with C60 molecules (dark green spheres) and honeycomb structure of graphene substrate (small blue spheres). Here, the unit of the chain structure is defined to be a bimolecular cell (chain plus one interchain spacing) plus an adjacent trimolecular cell. The 3D model clearly shows the size of one unit as 5.08 &#177; 0.02 nm. The larger gap spacing (1.23 nm) between adjacent chains is labeled in Figure 4a, c. Figure 4b,d shows the 3D schematic model of the 6-row stripe structure. The narrower inter-row spacing between two adjacent C60 stripes is 0.75 nm as labeled in Figure 4b, which is smaller than the typical hexagonal close packed structure. These typical 6-row stripes have a lateral periodicity of 5.08 &#177; 0.02 nm, almost exactly equal to the lateral spacing of the unit size of the chain structure12.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/57257/57257fig1.jpg" /> 
Figure 1. Homemade Knudsen cell and atomically resolved STM image of graphene substrate. (a) The homemade Knudsen cell with the copper shell. (b) The detailed structure of the homemade Knudsen cell showing the main components inside the copper shell. 1 is CF flange, 2 is thermocouple wire, 3 is W heating filament, 4 is glass tube, 5 is ceramic piece, 6 is hollow copper rods (A, B, C, D), 7 is supporting rods, 8 is feedthrough. (c) Atomically resolved STM topographic image of a clean graphene surface12. Figure 1c has been modified from12. <a href="/files/ftp_upload/57257/57257fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/57257/57257fig2.jpg" /> 
Figure 2. STM images of C60 chains after annealing at 150 &#176;C. (a) C60 forms well-ordered 1D chains on graphene over scales much larger than an individual chain (Vs = 2.255 V, I = 0.300 nA). (b) Molecular resolution STM image of C60 nanostructures showing the occurrence of only bimolecular or trimolecular chains. Intermolecular spacing within a chain is 1.0 nm while the distance between the centers of adjacent C60 rows belonging to neighboring chains is 1.23 nm, which is much larger than the inter-row distance of 0.87 nm in the close packed C60 structure (I = 0.500 nA, Vs = 1.950 V). (c) A line profile showing the intermolecular distance and gap between adjacent chains along the dashed green line in (b)12. This figure has been modified from12. <a href="/files/ftp_upload/57257/57257fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/57257/57257fig3.jpg" /> 
Figure 3. Self-assembled quasi-hexagonal close packed 1D C60 stripe structure on graphene after raising the annealing temperature to 210 &#176;C. (a) STM image showing quasi-hexagonal close packed C60 1D stripes oriented along the same axis (I = 0.200 nA, Vs = 2.200 V). (b) High-resolution STM image of C60 1D stripes (I = 0.200 nA, Vs = 2.400 V). (c) A line profile showing the hexagonal close packed C60 1D stripes on two terraces along the dashed green line in (b)12. This figure has been modified from12. <a href="/files/ftp_upload/57257/57257fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/57257/57257fig4.jpg" /> 
Figure 4. Schematic models. Schematic models for both C60 chains and stripes depicting the graphene as the smaller, underlying blue spheres and the C60 molecules as the dark green, space-filling spheres. (a, c) Top and side views of bimolecular and trimolecular C60 chains on graphene. (b, d) Top and side views of the typical C60 stripe with 6-row width12. This figure has been modified from12. <a href="/files/ftp_upload/57257/57257fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Preparation and Characterization of C60/Graphene Hybrid Nanostructures at JoVE.com

Preparation and Characterization of C60/Graphene Hybrid Nanostructures

Here we present a protocol for the fabrication of C60/graphene hybrid nanostructures by physical thermal evaporation. Particularly, the proper manipulation of deposition and annealing conditions allow the control over the creation of 1D and quasi 1D C60 structures on rippled graphene.

Preparation and Characterization of C60/Graphene Hybrid Nanostructures

Physical thermal deposition in a high vacuum environment is a clean and controllable method for fabricating novel molecular nanostructures on graphene. We ...

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9.4K Views.  Virginia Tech. Here we present a protocol for the fabrication of C60/graphene hybrid nanostructures by physical thermal evaporation. Particularly, the proper manipulation of deposition and annealing conditions allow the control over the creation of 1D and quasi 1D C60 structures on rippled graphene.

Video: Preparation and Characterization of C60/Graphene Hybrid Nanostructures

Gyroid Nickel Nanostructures from Diblock Copolymer Supramolecules

Nanoporous metal foams possess a unique combination of properties - they are catalytically active, thermally and electrically conductive, and furthermore, have high porosity, high surface-to-volume and strength-to-weight ratio. Unfortunately, common approaches for preparation of metallic nanostructures render materials with highly disordered architecture, which might have an adverse effect on their mechanical properties. Block copolymers have the ability to self-assemble into ordered nanostructures and can be applied as templates for the preparation of well-ordered metal nanofoams. Here we describe the application of a block copolymer-based supramolecular complex - polystyrene-block-poly(4-vinylpyridine)(pentadecylphenol) PS-b-P4VP(PDP) - as a precursor for well-ordered nickel nanofoam. The supramolecular complexes exhibit a phase behavior similar to conventional block copolymers and can self-assemble into the bicontinuous gyroid morphology with two PS networks placed in a P4VP(PDP) matrix. PDP can be dissolved in ethanol leading to the formation of a porous structure that can be backfilled with metal. Using electroless plating technique, nickel can be inserted into the template&#39;s channels. Finally, the remaining polymer can be removed via pyrolysis from the polymer/inorganic nanohybrid resulting in nanoporous nickel foam with inverse gyroid morphology.

This article describes the preparation of well-ordered nickel nanofoams via electroless metal deposition onto nanoporous templates obtained from self-assembled diblock copolymer based supramolecules.

Nanoporous metal foams possess a unique combination of properties - they are catalytically active, thermally and electrically conductive, and furthermore, ...

Split-and-pool Synthesis and Characterization of Peptide Tertiary Amide Library

Peptidomimetics are great sources of protein ligands. The oligomeric nature of these compounds enables us to access large synthetic libraries on solid phase by using combinatorial chemistry. One of the most well studied classes of peptidomimetics is peptoids. Peptoids are easy to synthesize and have been shown to be proteolysis-resistant and cell-permeable. Over the past decade, many useful protein ligands have been identified through screening of peptoid libraries. However, most of the ligands identified from peptoid libraries do not display high affinity, with rare exceptions. This may be due, in part, to the lack of chiral centers and conformational constraints in peptoid molecules. Recently, we described a new synthetic route to access peptide tertiary amides (PTAs). PTAs are a superfamily of peptidomimetics that include but are not limited to peptides, peptoids and N-methylated peptides. With side chains on both &#945;-carbon and main chain nitrogen atoms, the conformation of these molecules are greatly constrained by sterical hindrance and allylic 1,3 strain. (Figure 1) Our study suggests that these PTA molecules are highly structured in solution and can be used to identify protein ligands. We believe that these molecules can be a future source of high-affinity protein ligands. Here we describe the synthetic method combining the power of both split-and-pool and sub-monomer strategies to synthesize a sample one-bead one-compound (OBOC) library of PTAs.

Peptide tertiary amides (PTAs) are a superfamily of peptidomimetics that include but are not limited to peptides, peptoids and N-methylated peptides. Here we describe a synthetic method which combines&#160;both split-and-pool and sub-monomer strategies to synthesize a one-bead one-compound library of PTAs.

Peptidomimetics are great sources of protein ligands. The oligomeric nature of these compounds enables us to access large synthetic libraries on solid ...

Synthesis and Characterization of Functionalized Metal-organic Frameworks

Metal-organic frameworks have attracted extraordinary amounts of research attention, as they are attractive candidates for numerous industrial and technological applications. Their signature property is their ultrahigh porosity, which however imparts a series of challenges when it comes to both constructing them and working with them. Securing desired MOF chemical and physical functionality by linker/node assembly into a highly porous framework of choice can pose difficulties, as less porous and more thermodynamically stable congeners (e.g., other crystalline polymorphs, catenated analogues) are often preferentially obtained by conventional synthesis methods. Once the desired product is obtained, its characterization often requires specialized techniques that address complications potentially arising from, for example, guest-molecule loss or preferential orientation of microcrystallites. Finally, accessing the large voids inside the MOFs for use in applications that involve gases can be problematic, as frameworks may be subject to collapse during removal of solvent molecules (remnants of solvothermal synthesis). In this paper, we describe synthesis and characterization methods routinely utilized in our lab either to solve or circumvent these issues. The methods include solvent-assisted linker exchange, powder X-ray diffraction in capillaries, and materials activation (cavity evacuation) by supercritical CO2 drying. Finally, we provide a protocol for determining a suitable pressure region for applying the Brunauer-Emmett-Teller analysis to nitrogen isotherms, so as to estimate surface area of MOFs with good accuracy.

Synthesis, activation, and characterization of intentionally designed metal-organic framework materials is challenging, especially when building blocks are incompatible or unwanted polymorphs are thermodynamically favored over desired forms. We describe how applications of solvent-assisted linker exchange, powder X-ray diffraction in capillaries and activation via supercritical CO2 drying, can address some of these challenges.

Metal-organic frameworks have attracted extraordinary amounts of research attention, as they are attractive candidates for numerous industrial and ...

Preparation and Characterization of SDF-1&#945;-Chitosan-Dextran Sulfate Nanoparticles

Chitosan (CS) and dextran sulfate (DS) are charged polysaccharides (glycans), which form polyelectrolyte complex-based nanoparticles when mixed under appropriate conditions. The glycan nanoparticles are useful carriers for protein factors, which facilitate the in vivo delivery of the proteins and sustain their retention in the targeted tissue. The glycan polyelectrolyte complexes are also ideal for protein delivery, as the incorporation is carried out in aqueous solution, which reduces the likelihood of inactivation of the proteins. Proteins with a heparin-binding site adhere to dextran sulfate readily, and are, in turn, stabilized by the binding. These particles are also less inflammatory and toxic when delivered in vivo. In the protocol described below, SDF-1&#945; (Stromal cell-derived factor-1&#945;), a stem cell homing factor, is first mixed and incubated with dextran sulfate. Chitosan is added to the mixture to form polyelectrolyte complexes, followed by zinc sulfate to stabilize the complexes with zinc bridges. The resultant SDF-1&#945;-DS-CS particles are measured for size (diameter) and surface charge (zeta potential). The amount of the incorporated SDF-1&#945; is determined, followed by measurements of its in vitro release rate and its chemotactic activity in a particle-bound form.

The objective of this protocol is to incorporate SDF-1&#945;, a stem cell homing factor, into dextran sulfate-chitosan nanoparticles. The resultant particles are measured for their size and zeta potential, as well as the content, activity, and in vitro release rate of SDF-1&#945; from the nanoparticles.

Chitosan (CS) and dextran sulfate (DS) are charged polysaccharides (glycans), which form polyelectrolyte complex-based nanoparticles when mixed under ...

Preparation and Characterization of Individual and Multi-drug Loaded Physically Entrapped Polymeric Micelles

Amphiphilic block copolymers like polyethyleneglycol-block-polylactic acid (PEG-b-PLA) can self-assemble into micelles above their critical micellar concentration forming hydrophobic cores surrounded by hydrophilic shells in aqueous environments. The core of these micelles can be utilized to load hydrophobic, poorly water soluble drugs like docetaxel (DTX) and everolimus (EVR). Systematic characterization of the micelle structure and drug loading capabilities are important before in vitro and in vivo studies can be conducted. The goal of the protocol described herein is to provide the necessary characterization steps to achieve standardized micellar products. DTX and EVR have intrinsic solubilities of 1.9 and 9.6 &#181;g/ml respectively Preparation of these micelles can be achieved through solvent casting which increases the aqueous solubility of DTX and EVR to 1.86 and 1.85 mg/ml, respectively. Drug stability in micelles evaluated at room temperature over 48 hr indicates that 97% or more of the drugs are retained in solution. Micelle size was assessed using dynamic light scattering and indicated that the size of these micelles was below 50 nm and depended on the molecular weight of the polymer. Drug release from the micelles was assessed using dialysis under sink conditions at pH 7.4 at 37 oC over 48 hr. Curve fitting results indicate that drug release is driven by a first order process indicating that it is diffusion driven.

The goal of this protocol is to describe the preparation and characterization of physically entrapped, poorly water soluble drugs in micellar drug delivery systems composed of amphiphilic block copolymers.

Amphiphilic block copolymers like polyethyleneglycol-block-polylactic acid (PEG-b-PLA) can self-assemble into micelles above their critical micellar ...

Synthesis, Characterization, and Functionalization of Hybrid Au/CdS and Au/ZnS Core/Shell Nanoparticles

Plasmonic nanoparticles are an attractive material for light harvesting applications due to their easily modified surface, high surface area and large extinction coefficients which can be tuned across the visible spectrum. Research into the plasmonic enhancement of optical transitions has become popular, due to the possibility of altering and in some cases improving photo-absorption or emission properties of nearby chromophores such as molecular dyes or quantum dots. The electric field of the plasmon can couple with the excitation dipole of a chromophore, perturbing the electronic states involved in the transition and leading to increased absorption and emission rates. These enhancements can also be negated at close distances by energy transfer mechanism, making the spatial arrangement of the two species critical. Ultimately, enhancement of light harvesting efficiency in plasmonic solar cells could lead to thinner and, therefore, lower cost devices. The development of hybrid core/shell particles could offer a solution to this issue. The addition of a dielectric spacer between a gold nanoparticles and a chromophore is the proposed method to control the exciton plasmon coupling strength and thereby balance losses with the plasmonic gains. A detailed procedure for the coating of gold nanoparticles with CdS and ZnS semiconductor shells is presented. The nanoparticles show high uniformity with size control in both the core gold particles and shell species allowing for a more accurate investigation into the plasmonic enhancement of external chromophores.

The synthesis of uniform gold nanoparticles coated with semiconductor shells of CdS or ZnS is performed. The semiconductor coating is conducted by first depositing a silver sulfide shell and exchanging the silver cations for zinc or cadmium cations.

Plasmonic nanoparticles are an attractive material for light harvesting applications due to their easily modified surface, high surface area and large ...

Synthesis and Characterization of Supramolecular Colloids

Control over colloidal assembly is of utmost importance for the development of functional colloidal materials with tailored structural and mechanical properties for applications in photonics, drug delivery and coating technology. Here we present a new family of colloidal building blocks, coined supramolecular colloids, whose self-assembly is controlled through surface-functionalization with a benzene-1,3,5-tricarboxamide (BTA) derived supramolecular moiety. Such BTAs interact via directional, strong, yet reversible hydrogen-bonds with other identical BTAs. Herein, a protocol is presented that describes how to couple these BTAs to colloids and how to quantify the number of coupling sites, which determines the multivalency of the supramolecular colloids. Light scattering measurements show that the refractive index of the colloids is almost matched with that of the solvent, which strongly reduces the van der Waals forces between the colloids. Before photo-activation, the colloids remain well dispersed, as the BTAs are equipped with a photo-labile group that blocks the formation of hydrogen-bonds. Controlled deprotection with UV-light activates the short-range hydrogen-bonds between the BTAs, which triggers the colloidal self-assembly. The evolution from the dispersed state to the clustered state is monitored by confocal microscopy. These results are further quantified by image analysis with simple routines using ImageJ and Matlab. This merger of supramolecular chemistry and colloidal science offers a direct route towards light- and thermo-responsive colloidal assembly encoded in the surface-grafted monolayer.

A protocol for the synthesis and characterization of colloids coated with supramolecular moieties is described. These supramolecular colloids undergo self-assembly upon the activation of the hydrogen-bonds between the surface-anchored molecules by UV-light.

Control over colloidal assembly is of utmost importance for the development of functional colloidal materials with tailored structural and mechanical ...

Low-energy Cathodoluminescence for (Oxy)Nitride Phosphors

Nitride and oxynitride (Sialon) phosphors are good candidates for the ultraviolet and visible emission applications. High performance, good stability and flexibility of their emission properties can be achieved by controlling their composition and dopants. However, a lot of work is still required to improve their properties and to reduce the production cost. A possible approach is to correlate the luminescence properties of the Sialon particles with their local structural and chemical environment in order to optimize their growth parameters and find novel phosphors. For such a purpose, the low-voltage cathodoluminescence (CL) microscopy is a powerful technique. The use of electron as an excitation source allows detecting most of the luminescence centers, revealing their luminescence distribution spatially and in depth, directly comparing CL results with the other electron-based techniques, and investigating the stability of their luminescence properties under stress. Such advantages for phosphors characterization will be highlighted through examples of investigation on several Sialon phosphors by low-energy CL.

Low-energy Cathodoluminescence for OxyNitride Phosphors

An excellent chemical and luminescence stabilities of (oxy)nitride phosphors present it as an promising alternative to currently used sulfide and oxide phosphors. In this paper, we present the way to investigate its local luminescence properties using low-energy cathodoluminescence (CL).

Nitride and oxynitride (Sialon) phosphors are good candidates for the ultraviolet and visible emission applications. High performance, good stability and ...

Preparation and In Vitro Characterization of Dendrimer-based Contrast Agents for Magnetic Resonance Imaging

Paramagnetic complexes of gadolinium(III) with acyclic or macrocyclic chelates are the most commonly used contrast agents (CAs) for magnetic resonance imaging (MRI). Their purpose is to enhance the relaxation rate of water protons in tissue, thus increasing the MR image contrast and the specificity of the MRI measurements. Current clinically approved contrast agents are low molecular weight molecules that are rapidly cleared from the body. The use of dendrimers as carriers of paramagnetic chelators can play an important role in the future development of more efficient MRI contrast agents. Specifically, the increase in local concentration of the paramagnetic species results in a higher signal contrast. Furthermore, this CA provides a longer tissue retention time due to its high molecular weight and size. Here, we demonstrate a convenient procedure for the preparation of macromolecular MRI contrast agents based on poly(amidoamine) (PAMAM) dendrimers with monomacrocyclic DOTA-type chelators (DOTA &#8211; 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate). The chelating unit was appended by exploiting the reactivity of the isothiocyanate (NCS) group towards the amine surface groups of the PAMAM dendrimer to form thiourea bridges. Dendrimeric products were purified and analyzed by means of nuclear magnetic resonance spectroscopy, mass spectrometry, and elemental analysis. Finally, high resolution MR images were recorded and the signal contrasts obtained from the prepared dendrimeric and the commercially available monomeric agents were compared.

Preparation and In Vitro Characterization of Dendrimer-based Contrast Agents for Magnetic Resonance Imaging

This protocol describes the preparation and characterization of a dendrimeric magnetic resonance imaging (MRI) contrast agent that carries cyclen-based macrocyclic chelates coordinating paramagnetic gadolinium ions. In a series of MRI experiments in vitro, this agent produced an amplified MRI signal when compared to the commercially available monomeric analogue.

Paramagnetic complexes of gadolinium(III) with acyclic or macrocyclic chelates are the most commonly used contrast agents (CAs) for magnetic resonance ...

Influence of Hybrid Perovskite Fabrication Methods on Film Formation, Electronic Structure, and Solar Cell Performance

Hybrid organic/inorganic halide perovskites have lately been a topic of great interest in the field of solar cell applications, with the potential to achieve device efficiencies exceeding other thin film device technologies. Yet, large variations in device efficiency and basic physical properties are reported. This is due to unintentional variations during film processing, which have not been sufficiently investigated so far. We therefore conducted an extensive study of the morphology and electronic structure of a large number of CH3NH3PbI3 perovskite where we show how the preparation method as well as the mixing ratio of educts methylammonium iodide and lead(II) iodide impact properties like film formation, crystal structure, density of states, energy levels, and ultimately the solar cell performance.

We present an extensive study on the effects of different fabrication methods for organic/inorganic perovskite thin films by comparing crystal structures, density of states, energy levels, and ultimately the solar cell performance.

Hybrid organic/inorganic halide perovskites have lately been a topic of great interest in the field of solar cell applications, with the potential to ...