Ever wondered how that amazing track you found in a “Bangers to Kill For” playlist on Spotify got there? Or why some musicians released their albums digitally in one bunch lately, instead of doing the old and tried “touring/increase of name recognition/record sales” shtick? Do you want to know why Diane Warren’s name is as significant to the music industry as that of Sir Paul McCartney or Elvis? And, most importantly, how do you convert that sudden boost of popularity that your new song just experienced on SoundCloud into solid cash? Or, at the very least, solid numbers on the screen of your banking app (so “non-hipster,” I know).
One of the keys to seeing those numbers is understanding that “being talented” alone is often not enough to translate songs into dollar signs. All the books written by lawyers on the topic of the “music business” exist for a good reason. If you want to make music your livelihood, you need to treat it like any other business. What do I mean by that and how do you go about it? Let me show you.
Imagine: You are extremely talented, the voice of an angel, your mom and all her friends tell you how amazing you are. Seems probable so far, right? So, you go to your friend’s apartment (let’s call her Amy) and chill out. You listen to some music with a couple of friends, partake in a round or two of drinking adult beverages, and do some freestyle. You already had some ideas in your head, so you start a verse. You sing. It’s beautiful. Everyone is ecstatic. Now Amy has some recording equipment, and she thinks you guys can make a hit out of that verse. Amy’s friends throw a couple of lines into the mix. One of them sits around and thinks of the concepts. You sing and Amy records the music. At the end of the day, you’re sure that you have a hit. You can actually feel that, with the right dose of mastering and a little bit of auto-tuning this could be the next “Insert Popular Track Here.” You go home, put the track up on SoundCloud or YouTube and – who knew?! – It really IS a hit. There are hundreds of thousands of views and downloads. People are calling you the next Justin Bieber. You get a Direct Message from an A&R representative (“Artist and Repertoire” representatives source new artists to sign) of a major record label. They would like for you to come in for an interview.
Of course, this is a pipe dream. A best-case scenario. But do you know what you missed? Let me show you that same situation again, but from a lawyer’s perspective. Instant replay in “(s)law-mo,” so to say.
That recording equipment that was used by Amy to produce your hit – you didn’t happen to have Amy sign a “Work-For-Hire” agreement before allowing her to record you, did you? It looks like Amy now owns the Copyright to the sound recording of your new hit and will be the one reaping the majority of the benefits if the track is downloaded from iTunes/Amazon/Google Play. As the composer, you would get 9.1 cents per download out of her 99 cents. But doesn’t getting the whole 99 cents (less the platform’s percentage) sound better?
What about her friends that chimed in with their lines or general concept ideas? I would guess there was no Songwriter “Split Agreement” involved, and now you need to negotiate with some of them retrospectively. Some of them are even going to go after you with their own lawyers. Yes, believe me, once you’ve reached any kind of success, you will get sued. It might be some producer who helped you with a track, a (former) buddy who was in the room when you came up with the idea, a person who helped you with mastering in exchange for helping them with their taxes, or all of the above. Yes, all of them will sue you. And once they do, since you didn’t protect yourself by setting up a company that would take the brunt of the blame, they can sue you not only for your music-related income, but for any other personal assets, property, and even real estate that you own.
So, what do we have as a result here? You came up with the track. Your voice is amazing. Your mom was right this one time, it seems. You recorded a hit, a real wonder, once in a lifetime song. And now Amy gets all the profits and her friends are trying to freeze your bank accounts. You will have to sell your apartment in the city to pay them off because it’s money that you don’t really have.
The lesson? Amy is a horrible friend. Aside from that? Get yourself a good music attorney. I might not be much help with the former, but I will try to give you a tip or two about the intricacies of dealing with the latter and with what agreements a music lawyer should provide you. In this article, I will go over (1) the basics of the rights that musicians obtain from the moment that they create their music and (2) what additional steps they need to take to protect themselves under current legislation.
Buckle up, folks. Let’s see how the sausage is made.
The most important thing that any music attorney must relay to a prospective client (if you already have somebody as your client and still didn’t tell them about this little tidbit, you might well be breaking one of the professional ethics rules on keeping the client informed, in my opinion) is the difference between the two existing types of music copyright under the Copyright Act of 1976. The act provides that for a work to be protectable, it must be an “original work of authorship fixed in any tangible medium of expression” and, furthermore, lists several categories of works in question.1 The two types that we are interested in are 1) the copyright in the musical composition (Composition Copyright) and; 2) the copyright in the sound recording (Sound Recording Copyright. I know, lawyers are very inventive with jargon). What is the difference between the two?
In the above-mentioned scenario, if, while enjoying your time at Amy’s apartment, you decided to put some of those concepts that were brewing in your head on paper (or any other tangible medium of expression), be it the lyrics of the future hit or its musical notes, then that expression would be covered by the Composition Copyright and you would be considered its author. However, the recording of your song, the actual version of your composition that Amy recorded using her equipment, creates a separate type of copyright, the Sound Recording Copyright. And, since it was Amy who recorded and produced your track, and since there was no agreement between the parties to determine the percentage of ownership in the newly created recording… well, you get the idea.
It is very important to distinguish between the two music-related copyrights in any publishing, demo, recording or other agreement where the transfer of ownership or licensing of the rights mentioned above is present, especially if you’re just starting out and those percentage points might be your only viable source of income for quite some time. Make sure any contracts you sign have a clear distinction between the two copyrights. Don’t forget to ask your music attorney or the counter-party to a contract the correct questions and make them clarify anything that you don’t understand. After all, you want to make sure that the judge, who’s going to be looking at your contract with the shady label that you signed when you were 18 and who knows nothing about the music industry, recognizes what rights to the song you gave away. Also, if you see the word “song” used in a contract without a proper definition as to what type of copyright the parties intend to cover by this term, run (in the direction of an experienced music attorney, preferably).
Now, how do you protect yourself in all of these scenarios and do you need to register your work with the government bodies and pay them some ridiculous fees? I’m glad you asked!
Why do you need to register your work? There is this myth going around that sending yourself a sealed envelope with a flash drive (throughout the years the tape became the CD, the CD became the DVD, and the DVD became a flash drive. O tempora, o mores!) would be good enough. Unfortunately, that might only serve as proof in some rare cases, where someone else is claiming the ownership of your song without having registered the song themselves. But in the real world, you are missing out on significant potential benefits of the registration.
Before I tell you the pros, let me cover some of the cons. The fact that there are not a lot of those cons only makes my duty of candor easier. It’s simple. For every work that you want to register you need to pay a fee: from $35 for a single electronic application to potential increases to up to $55 per application if there are multiple authors or the work in question was made for hire. Additionally, if the musical composition and sound recording are owned by different people, you won’t be able to register them with a single application and might have to pay double. Lastly, if you decide that the internet is the devil’s invention and end up filing your application on paper, you have to pay at least $85 per application. There are also loopholes that allow a musician to register an album (usually consisting of 10+ songs) in one title, for the price of one application. What else is there, aside from the fees? You have to register an account with the Copyright Office’s website or have your music or IP attorney do so (if they’re any good, they already have one). Upload a final, mastered track in the prescribed format onto the Copyright Office website (www.copyright.gov), and you’re good to go.
So, what does this process give you? Let’s look at those pros. Any infringement of your copyright (that is created by your “fixing” (meaning: recording in one way or another) an original work of authorship onto a tangible medium of expression, and not by registration, remember) leads to certain potential consequences for the infringers. Such an infringer could be an Internet pirate, a copycat, or a shady record company not performing its obligations on royalty payments to you as a songwriter. Take that “pirate” for ease of explanation. A person who decides to upload your track onto Apple Music and sells a hundred downloads would potentially steal the price of those downloads (minus all the fees to the administrators of your music and actual distribution platforms, payments to various funds and royalties to the songwriters) from you, correct?
The problem is that if you don’t have your copyright registered, the most you can sue them for is the amount of those damages (including interest and costs). This wouldn’t constitute that much, given the number of downloads. Is it worth it to hire a good IP litigation attorney to collect $40? That’s what the actual damages would amount to. However, if you were a smart and diligent professional, who treats music as livelihood and business, and who went through the hassle of hiring a music attorney (or even doing it yourself) to register a copyright to her music, then it might be worth it after all. The Copyright Act states that if your work was registered2, you could claim statutory damages in the amount of not more than $150,0003 per willful infringement, $750 to $30,000 per non-willful infringement and not less than $200 per innocent infringement, as well as attorney costs. Don’t think that you will get $150,000 for each download, since the copyright owner is usually restricted to one award of statutory damages regardless of the number of acts of infringement, whether they are separate, isolated or occurring over many years.4 However, regardless of whether it is $200, $750, $30,000 or $150,000 plus attorney fees – it all sounds a lot better than approximately $40, doesn’t it? Now, should you register your music with the Copyright Office? I think you know the answer.
This part is always tricky. Nobody wants to be the person who brings paperwork to a jam session. Nobody likes to ask that friend who is helping you out with radio promotions or DJ-ing gigs to sign a management agreement. We all hate it. It feels like it puts a strain on a relationship; somehow making it dirty and non-creative. But think, what would be more strenuous on your relationship with a friend and collaborator: a transparent agreement outlining responsibilities and percentages, or a lawsuit where both parties are going to try to prove that they were the reason for the song’s success? The latter seems more strenuous to me. These arguments often lead to an impasse. No matter how hard you argue that it was your chorus and not your friend’s verse that made the song a hit, the case law is clear that absent a written agreement between the parties, the courts will split the ownership 50/50. No judge wants to be responsible for the calculation of the worth of a particular note in a song.
So be that annoying person. Bring paperwork to a jam session. Better yet, have your lawyer prepare the paperwork, and send it out to all the parties involved days before the jam session, so that everyone has a chance to voice his objections and take part in negotiations for a song that has not yet been sold. It might sound like too much trouble, but you never know which song is going to be a success and where the lawsuit will come from. Be smart. Treat music as a business, not a hobby. And protect yourself.
Whom else do you need to have a contract with? Basically, everyone that helps you in the creation of the final version of your work along the way. Your producer, the one whose studio you used to record the track, the sound engineer who mixes everything, all of them can potentially claim that their input is entitled to federal copyright protection as well. In ABS Entm’t, Inc. v. CBS Corp5, the court found that a sound engineer’s remastering of a pre-1972 sound recording, through subjectively and artistically altering the work’s timbre, spatial imagery, sound balance, and loudness range, but otherwise leaving the work unedited, was entitled to federal copyright protection as a derivative sound recording, since it “has undergone sufficient changes.” This means that absent a proper agreement in place, all the above-mentioned participants in your success can claim ownership of your work in one way or another. How do you avoid this problem?
One of the possible solutions is making sure that all the people involved in your creative process assign any rights that they might have in the sound recording back to you, either in the form of a “Work For Hire” (WFH) agreement or as a straight-up assignment of rights. What is a WFH? It is an agreement that automatically transfers all the work performed by a producer, mixer, or sound engineer to you. You are the owner of the intellectual property – rights in the music –that comes out as a result. It’s the same document used by large companies to make sure that the work their independent contractors do becomes the property of the company and not that of an individual contractor. It allows such companies to be as secure as if the workers in question were the company’s employees (which would make their work performed in the “normal course of the employment” the company’s property). The second most common scenario outside the employment context is stipulated in paragraph (b) of Section 101 of the Copyright Act, which provides a list of the types of works that could be “specially ordered or commissioned for use”6 and be considered a work made for hire.
It is also important to include the “assignment clause” as an alternative in the WFH agreement in case a judge in a particular jurisdiction will have a problem with your sound recording being subject to the WFH agreement, since the statutory definition of a work made for hire ((Section 101(b) mentioned above) doesn’t mention “sound recordings” per se. However, the legal community has long ago found a loophole that allows the parties to presume either that the album is a “collective work” within the statutory meaning or consider an individual work to be one made for hire if there’s an employment relationship present (under sections 101(b) and 101(a) respectively). Once again, the safe option would be to have the sound engineer or producer in question sign the Work For Hire Agreement prepared by a competent music attorney. You will come out on top, having full ownership of your music.
Let’s look at that completely hypothetical, yet completely possible, scenario that I made up at the beginning of this article, taking into account everything that we have covered. Would you be so naive as to think that Amy’s your friend and there is no need for any written agreements? I don’t think so. I’m pretty confident that you would have her sign one of those “Work for Hire” agreements to make sure you are the owner of anything that comes out of that recording process. Would you enter into agreements with her buddies who pitched in with some lines or melody proposals? Of course, you would, since you want to make sure they do not get more than they contributed to the work in question, as opposed to the blanket 50% (or other equal share distribution if there were more than two collaborators). And would you register your copyright to both the musical composition and the sound recording once you have all of these agreements in place and you have a clear understanding, in black and white, about who owns what portion of which of the two copyrights? I think we both know the answer to that question, and I’m sure you want to know more.
• 17 U.S.C.A. § 412.
• 17 U.S.C.A. § 504(c)(2).
• ABS Entm’t, Inc. v. CBS Corp., 2016 WL 4259846, at *1 (C.D. Cal. May 30, 2016), judgment entered, 2016 WL 3436443 (C.D. Cal. May 30, 2016).
• 17 U.S.C.A. § 101(b).
ABS Entm’t, Inc. v. CBS Corp., 2016 WL 4259846, at *1 (C.D. Cal. May 30, 2016), judgment entered, 2016 WL 3436443 (C.D. Cal. May 30, 2016).


text:
DECIDED DECEMBER 2, 1975. REHEARING DENIED DECEMBER 15, 1975.
Contempt. Cobb Superior Court. Before Judge Ravan.
Flournoy Still, Charles A. Evans, for appellant.
Greene, Smith, Davis Dodson, H. Darrell Greene, Morgan McNeel Robertson, for appellee.
This appeal is from a judgment finding the appellant father in contempt for failure to make certain child support payments awarded to the appellee mother in a divorce and alimony action between the parties.
The agreement of the parties, which was made the judgment of the court, provided that the $30 per week per child payment for the support of their two minor children would continue "until such time each child shall reach the age of 20 years, and is able to support his or herself, marries, dies; and it is further understood if either one of said children, upon reaching age 20, is still dependent upon the wife for over half of his support, i.e., if earning less than $50 per week said support payment shall continue for that child until he or she becomes self supporting, that is, to be able to pay for over half of his or her own support. When each child shall reach age 20 years, marry, die or become self-supporting, said maintenance and support of each child shall cease and the total amount paid as stated shall be reduced in the amount paid as supporting maintenance for that child, that is, the sum of $30 per week."
1. The father asserts error in the ruling of the trial judge that his obligation continued to make support payments for his son, who was not self-supporting as that term is defined in the divorce and alimony decree, after his son became 21 years of age on July 12, 1974.
The divorce decree was entered in 1966, when the age of majority was 21, and the father does not dispute the obligation to make support payments prior to his son's 21st birthday. See Jenkins v. Jenkins, 233 Ga. 902 (1) ( 214 S.E.2d 368) (1975).
The statutory duty to support a child ceases when the child reaches majority. Tilly v. Canedy, 217 Ga. 63 ( 121 S.E.2d 144) (1961); Newton v. Newton, 222 Ga. 175 (2) ( 149 S.E.2d 128) (1966); Bateman v. Bateman, 224 Ga. 20 (2a) ( 159 S.E.2d 387) (1968); Futch v. Futch, 224 Ga. 350 ( 161 S.E.2d 868) (1968); Golden v. Golden, 230 Ga. 867 (3) ( 199 S.E.2d 796) (1973); Jenkins v. Jenkins, supra.
In McClain v. McClain, 235 Ga. 659 (1975), this court held that where the contract of the parties settling alimony is incorporated in a divorce decree, and such contract obligates the father to provide maintenance and education for the child beyond minority, the decree approving the contract is enforceable by contempt.
The present case is not controlled by the McClain case. In the McClain case the contract, in clear and precise language, provided that the father should provide a college education for each of his minor children. In the present case there is no clear language stating that the father is obligated to support his minor children after they reached majority. The support specified was until the age of 20 years, unless the child was then not self-supporting, in which event the support was to continue. In the absence of specific language stating that the support would continue beyond the age of 21, we must conclude that the parties intended that the obligation would cease at the age of 21, when the statutory duty to support the child terminated.
The trial judge therefore erred in holding the father in contempt for refusing to make the support payments which accrued after his son became 21 years of age.
It is directed that the contempt judgment be modified to conform to this ruling.
2. The father contends that the trial judge erred in failing to give him credit for sums received by his son for support under the Social Security Administration Supplemental Security Income Act, and from the Cobb Department of Family and Children Services.
The notice of appeal states that there is no transcript for inclusion in the record. From the judgment of the trial judge, which we must assume to be supported by the evidence, these sums were public assistance from the county and federal governments. The cases of Brooks v. Brooks, 204 Ga. 412 ( 49 S.E.2d 881) (1948); and Horton v. Horton, 219 Ga. 177 ( 132 S.E.2d 200) (1963), dealt with sums attributable to the service and labor of the father and are distinguishable from the present case.
The trial judge did not err in holding that the father was not entitled to credit on the support payments due by him for the amounts supplied by the local and federal governments as public assistance to his son.
Judgment affirmed in part and reversed in part, with direction. All the Justices concur, except Ingram, Hall and Hill, JJ., who dissent.
ARGUED OCTOBER 14, 1975 — DECIDED DECEMBER 2, 1975 — REHEARING DENIED DECEMBER 15, 1975.
I respectfully dissent from Division 1 of the majority opinion. McClain v. McClain, 235 Ga. 659, holds that "The agreement of the parties which was incorporated in and made a part of the divorce decree is enforceable after the majority of each child." In the present case the agreement of the parties provided for the contingency that "if either one of said children, upon reaching age 20, is still dependent upon the wife for over half of his support, i.e., if earning less than $50 per week said support payment shall continue for that child until he or she becomes self supporting, that is, to be able to pay for over half of his or her own support." The child is now over 21 but, due to a disability, is not self-supporting. The trial court found, and I agree, that the intent of the parties was to provide support for the child until he is self-supporting, even beyond the age of 21. In my view McClain v. McClain, supra, requires affirmance of the trial court.
I am authorized to state that Justice Ingram and Justice Hall join in this dissent.

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NEW ENGLAND ELECTRIC SYSTEM et al.
Philip A. Loomis, Jr., Washington, D.C., for petitioner.
John R. Quarles, Boston, Mass., for respondents.
By § 11(b)(1)6 a holding company system is to be limited in operations by the Commission 'to a single integrated public-utility system,'7 provided, however, that it may be permitted to control one or more additional 'integrated public-utility systems' if the Commission finds, inter alia, that '(e)ach of such additional system cannot be operated as an independent system without the loss of substantial economies which can be secured by the retention of control by such holding company of such system.' § 11(b)(1)(A). (Italics supplied.) It is on the meaning of this proviso that the present controversy depends. The Commission found that divestment of NEES' gas utilities would not result in a 'loss of substantial economies' to these companies within the meaning of § 11(b)(1)(A). It construed Clause (A) to require a showing that the 'additional system cannot be operated under separate ownership without the loss of economies so important as to cause a serious impairment of that system.' The Commission ruled that it was unable 'to find that the gas companies could not be soundly and economically operated independently of NEES.' It found that any losses of economies would be offset by the benefits that would flow from the healthy competition between the independently controlled gas and electric companies, promotion of competition between gas utilities and electric utilities being an important purpose of the Act. Accordingly, it ordered that the gas utilities be divested.
On petition for review the Court of Appeals reversed on the ground that the Commission had misinterpreted the statutory phrase 'loss of substantial economies.' 346 F.2d 399. The court held that Clause (A) 'called for a business judgment of what would be a significant loss, not for a finding of total loss of economy or efficiency' (346 F.2d, at 406), and, believing that on this record and with the statute so interpreted there could have been a finding in favor of NEES, remanded the case to the Commission. We granted certiorari, 382 U.S. 953, 86 S.Ct. 436, 15 L.Ed.2d 358.
We agree with the Commission's reading of Clause (A) and remand the cause to the Court of Appeals so that there may be a review of the challenged order in light of the proper meaning of the statutory term.
'Section 11 of both bills (i.e. the House and Senate versions), therefore, authorizes the Securities and Exchange Commission to require a holding company to limit its control over operating utility companies to one integrated public-utility system.
'The legislative history of Section 11(b)(1) indicates that it was the intent of Congress to create only a limited exception to the general rule confining holding companies to a single system, and that this exception was created to deal with the situation in which the proven inability of the additional system to stand by itself would result in substantial hardship to investors and consumers were its relationship with the holding company terminated.' Philadelphia Co., 28 S.E.C. 35, 46.
Competitive advantages to be gained by a separation are difficult to forecast. The gains to competition might well be in the public interest and might well offset the estimated loss in economies of operation16 resulting from a separation of the gas properties from the utility system. This is a matter for Commission expertise on the total competitive situation, not merely on a prediction whether, for example, a gas company in a holding company system may make more for investors than a gas company converted into an independent regime.
The phrase 'without the loss of substantial economies' is admittedly not crystal clear. But the Commission's construction seems to us to be well within the permissible range given to those who are charged with the task of giving an intricate statutory scheme practical sense and application. Power Reactor Development Co. v. International Union of Electricians, etc., 367 U.S. 396, 408, 81 S.Ct. 1529, 1535, 6 L.Ed.2d 924. And see Philadelphia Co. v. SEC, 85 U.S.App.DC. 327, 177 F.2d 720, 725.
Mr. Justice HARLEN, whom Mr. Justice STEWART joins, dissenting.
The question before the Court is the meaning of the phrase 'loss of substantial economies' as it appears in § 11(b)(1) of the Public Utility Holding Company Act of 1935.1 The Court of Appeals ruled that the phrase 'called for a business judgment of what would be a significant loss,' 346 F.2d, at 406, and I agree with this rendering which is both sensible and, in my view, obvious. This Court's opinion on the other hand seems to hold that the phrase demands a loss great enough to imperil 'sound' corporate operations.2 That holding, as I shall indicate, is at odds with the Act's wording, has little basis in legitimate statutory history or the aims of the Act, and cannot be sustained by agency or judicial precedent.
Inquiry naturally begins with the language of the Act, and with our reiterated principle that 'the words of statutes * * * should be interpreted where possible in their ordinary, everyday senses.' Crane v. Commissioner, 331 U.S. 1, 6, 67 S.Ct. 1047, 1051, 91 L.Ed. 1301; Malat v. Riddell, 383 U.S. 569, 571, 86 S.Ct. 1030, 1032, 16 L.Ed.2d 102. In this instance plainly the normal meaning of 'substantial economies' is a significant amount of money and not that amount, whatever its size, which guarantees corporate survival. The first reading would be given by lawyers and laymen alike automatically while the second could hardly be imagined without the prompting of persuasive legislative evidence. If Congress had intended the Court's test to govern, it could easily have said so in shorter space and with far greater precision.3 In addition, the Court's decision will apparently result in 'substantial economies' being read its way in § 11(b)(1) but in a quite different, more normal fashion where the same phrase appears in § 2(a)(29)(B), defining an integrated gas utility system (see ante, n. 4, of the Court's opinion). None of this is to say that the many subtle choices to be made in deciding what is a substantial sum in the present context are dictated by the terse language of the Act. See infra, n. 11. The choice here, however, is between two broad approaches, and the Act's language invites the first and repels the second.
Legislative history and purpose, heavily relied on by the Court, furnish no reason for departing from the natural reading of the Act. There was very little direct explanation of the 'substantial economies' provision in Congress; the majority opinion sets out in full the two important statements, one by the House Conference Committee (ante, p. 180-181) and the other by Senator Wheeler (ante, p. 181).5 The Committee Report, highly authoritative but unilluminating, says merely that there must be 'a real economic need' to justify retention of an additional system. Indisputably, substantial savings can be labeled a real economic need, the more so since Congress was sharply concerned with the lack of economic justification for many utility combinations. That the Committee's language is also compatible with the SEC's reading of 'substantial economies' does no more than make that language a useless guidepost.
Far more weight is given by the Court's opinion to the Act's supposed hostility toward common control of gas and electric utility systems with its danger of stifled competition. First of all, this hostility appears to be an illusion. The House and Senate Committees in identical language expressly stated that common ownership of competing forms of energy was 'a field which is essentially a question of State policy'; the present § 8, 15 U.S.C. § 79h (1964 ed.), was enacted to support this approach by using federal power to limit common ownership only where it is contrary to state law. See S.Rep.No. 621, 74th Cong., 1st Sess., 29—30; H.R.Rep.No. 1318, 74th Cong., 1st Sess., 14—15.8 In its decision in this very case the SEC stated: 'We do not take the view that the Act expresses a federal policy against combined gas and electric operations as such.' Holding Company Act Release No. 15035, p. 15. This was apparently so clear at the time the Act passed that in an early and now-repudiated decision the SEC went so far as to hold that gas and electric companies could be combined in the same single integrated public utility system. American Water Works & Elec. Co., 2 S.E.C. 972 (1937).
There remains to be answered only the Court's claim that its reading of the statute is 'supported by consistent administrative practice' (ante, p. 182, n. 12). Analysis of the SEC decisions shows that the Court is mistaken. The first important construction of 'substantial economies' came in North American Co., 11 S.E.C. 194, decided in 1942 only seven years after the Act took effect. Rejecting the assertion that any saving beyond a wholly nominal one would do, the SEC stated: 'The normal and usual meaning of the word 'substantial' is a meaning connoting 'important.' And we think that this normal and usual meaning is compelled here.' Id., at 209. At least four subsequent decisions cite North American and adopts its 'importance' test, a natural reading of the Act rather the unusual and specialized one adopted today. Cities Serv. Power & Light Co., 14 S.E.C. 28, 37 (1943); Middle West Corp., 15 S.E.C. 309, 319 (1944); Cities Serv. Co., 15 S.E.C. 962, 984 (1944); American Gas & Elec. Co., 21 S.E.C. 575, 597 (1945). Also during this first decade of the Act's enforcement two decisions, including one just cited, said that inability to operate independently was 'one of the guides which (among others) Congress intended to be used * * *.' Cities Serv. Power & Light Co., 14 S.E.C. 28, 62 (1943); Commonwealth & Southern Corp., 26 S.E.C. 464, 489 (1947). In one other case the SEC stated the loss must be one which would 'seriously impair * * * effective operations.' Engineers Pub. Serv. Co., 12 S.E.C. 41, 61 (1942).
To conclude, I think it should be noted that the Court's departure from the statute is not just an abstract legal error but does immediate, tangible harm in a most practical sense. The annual losses which respondent has forecast for its gas system because of separation exceed $1,000,000, a figure the SEC has questioned in part but not yet properly considered. The respondent's analysis also shows annual losses of $800,000 for the electrical system, although the SEC deems irrelevant losses to the primary system and the Court of Appeals did not reach this issue. The heavy losses in this case will presumably be borne by investors and consumers if the figures are accurate and separation occurs; it is noteworthy that the Massachusetts Department of Public Utilities appeared at the hearings in this case to oppose divestiture. The SEC has wide latitude in deciding how to gauge and compute 'substantial economies' and it has used that freedom in the past.11 What the Commission has no right to do, however, is to substitute to the detriment of business interests and the public alike a quite different standard for the one enacted by Congress. Neither does this Court have that right. I would affirm the Court of Appeals' well considered decision.
49 Stat. 812, 15 U.S.C. § 79e (1964 ed.).
NEES, the electric companies, and the gas companies are all parties respondent and are hereafter referred to as respondent.
49 Stat. 820, 15 U.S.C. § 79k (1964 ed.).
49 Stat. 820, 15 U.S.C. § 79k(b)(1) (1964 ed.).
The Commission has long held that a single 'integrated public-utility system' cannot include both gas and electric properties. See Columbia Gas & Electric Corp., 8 S.E.C. 443, 462 463; The United Gas Improvement Co., 9 S.E.C. 52, 77—83; Philadelphia Co., 28 S.E.C. 35, 44. Respondent does not contest this aspect of the Commission's reading of the Act.
North American Co. v. SEC, 327 U.S. 686, 704, n. 14, 66 S.Ct. 785, 795, 90 L.Ed. 945; S.Rep. No. 621, 74th Cong., 1st Sess., 11.
North American Co. v. SEC, supra, at 696—697, 66 S.Ct. at 792.
S. 2796, § 11(b), 74th Cong., 1st Sess. And see S.Rep. No. 621, 74th Cong., 1st Sess., 32.
S. 2796, § 11(b), as passed by the House of Representatives, and sent to the Senate on July 9, 1935. And see H.R.Rep. No. 1318, 74th Cong., 1st Sess., 17.
Respondent concedes that the Commission has, since 1948, 'articulated' a test 'like the present test'. See Philadelphia Co., 28 S.E.C. 35, 46—47, 53—74; General Public Utilities Corp., 32 S.E.C. 807, 814—815, 826—827, 831; Middle South Utilities, Inc., 35 S.E.C. 1, 11—13. Respondent contends, however, that previous decisions of the Commission applied a less restrictive standard of 'substantial economies.' The Commission disagrees, urging that while there was 'some variation in choice of words,' it has maintained a basically consistent position and that any semantic differences are due largely to 'the varying contentions with which the Commission was dealing.' The cases referred to are North American Co., 11 S.E.C. 194, 208—213; Engineers Public Service Co., 12 S.E.C. 41; Cities Service Power & Light Co., 14 S.E.C. 28, 37; Middle West Corp., 15 S.E.C. 309, 319; Cities Service Co., 15 S.E.C. 962, 984; American Gas & Electric Co., 21 S.E.C. 575, 596—597. We do not read those cases as being inconsistent with the Commission's position since 1948. In each of these cases the Commission found no showing of 'substantial economies' under whatever test might be applied; thus it was not there compelled to go further. There are, to be sure, a few cases in which the Commission permitted retention of small additional systems on the ground that the requirements of § 11(b)(1) were met; in these, however, the Commission did not articulate any standard. See, e.g., Federal Light & Traction Co., 15 S.E.C. 675, 683; Republic Service Corp., 23 S.E.C. 436, 451. But cf. North American Co., 11 S.E.C. 194, 243—244.
We cannot say that these early decisions show any clear inconsistency with the standard which the Commission today applies, and has applied since 1948. Under these circumstances, we feel justified in regarding the Commission's reading of the statute as supported by consistent administrative practice.
See S.Rep. No. 621, 74th Cong., 1st Sess., 29; Report of National Power Policy Committee, H.R.Doc. No. 137, 74th Cong., 1st Sess., 10 (Appendix to S.Rep. No. 621, 74th Cong., 1st Sess.).
Congress was well aware of the anti-competitive potential of corporate structures through which control of gas and electric utility companies rests under the umbrella of a single holding company. That a holding company so situated might retard expansion of the gas utility company in favor of the electric utility company was expressly discussed in the Senate Hearings on an earlier version of the Act. See Hearings before the Senate Committee on Interstate Commerce on S. 1725, 74th Cong., 1st Sess., 783.
By fostering competition between gas and electric utility companies, the Act promotes what has been described as 'variegated competition.' Hearings before the Subcommittee on Antitrust and Monopoly of the Senate Committee on the Judiciary, 89th Cong., 1st Sess., pt. 2, 840 (1965) (statement of Dr. Samuel M. Loescher). 'But since the distribution of electricity, following geographical divorcements, was to remain a natural monopoly in every region, the only kind of competition to be enhanced was that of 'variegated competition." Ibid.
See, e.g., Hearings before House Committee on Interstate and Foreign Commerce on H.R. 5423, 74th Cong., 1st Sess., 1249, 1402—1403, 1530—1531, 2257—2277; Hearings before Senate Committee on Interstate Commerce on S. 1725, 74th Cong., 1st Sess., 65. It was only the loss of 'substantial economies' that Congress thought would justify an exception from the separation rule of § 11.
I say 'seems' to hold both because two statements in the opinion (ante, pp. 179, 184-185) emphasize a supposed offsetting economic saving to be found in divestiture and because the SEC has stated the test in this case in varying terms.
'It * * * (is) wrong to deny the natural meaning of language its proper primacy; like Cardozo's 'Method of Philosophy,' it 'is the heir presumptive. A pretender to the title will have to fight his way." Friendly, Mr. Justice Frankfurter and the Reading of Statutes, in Felix Frankfurter: The Judge 40 (1964).
One other legislative comment on the provision favors the Commission, 79 Cong.Rec. 14165—16166 (remarks of Mr. Cooper), but the Court of Appeals properly disregarded it as an opponent's attempt to blacken the Act, cf. National Labor Relations Board v. Fruit and Vegetable Packers and Warehousemen, Local 760, 377 U.S. 58, 66, 84 S.Ct. 1063, 1068, 12 L.Ed.2d 129, and the SEC no longer relies upon it in its brief.
The statement was quoted as cumulative, minor evidence on another matter in 1941, the SEC admitting that it 'may not strictly be considered part of the legislative history' but saying it deserved 'some consideration.' Engineers Pub. Serv. Co., 9 S.E.C. 764, 782—783. In 1942, it was quoted as bearing on the present question but its test was not adopted. North American Co., 11 S.E.C. 194, 209. The following year the statement was thought to reveal 'one' of the various criteria to be used along with others. Cities Serv. Power & Light Co., 14 S.E.C. 28, 62.
For its 'decidedly the exception' characterization, the Court cites (ante, p. 180, n. 9) North American Co. v. SEC, 327 U.S. 686, 66 S.Ct. 785. That decision imparted no such gloss to the ABC clauses but gave a most cursory summary in passing on the constitutionality of § 11(b)(1).
The Court's opinion (ante, p. 184, n. 14) quotes from p. 7 of the above-cited Senate report, borrowing from its language that suggests § 11 was forwarding the same policy as § 8. What the Court overlooks is that this discussion was directed to an earlier and very different version of § 8, in which it also embodied other restrictions on holding company ownership having nothing to do with common control of gas and electricity, but closely related to § 11's policy of federally imposed simplification. A reading of the Court's quotation in context along with the relevant version of S. 2796, 74th Cong., 1st Sess., §§ 8, 11 (as reported on May 13, 1935), will quickly show that its reliance is misplaced. The majority's other citations in the same footnote are also infirm. The first two citations are statements on behalf of the rule that is now § 8, which allows the States to decide the issue. The remaining citation to the Senate Hearings does indeed reveal one Senator's general concern with common ownership's impact on competition; the respondent states it is 'the only such reference in the entire Senate hearing.' Brief, p. 37, n. 45.
It should again be remembered also that the present provision is not the only legislative safeguard. Even to obtain ownership over two systems, a holding company must, along with proving 'substantial economies,' show that there is geographical unity and that the combination is not so large as to impair 'the advantages of localized management, efficient operation, or the effectiveness of regulation' (supra, n. 1). Section 8 (supra, p. 190) acts as a further restraint in some cases. Other sections of the Act regulate transactions between utility companies and require disclosure of reports and maintenance of accounting data and other records. §§ 12(f) 13(a), 14, 15, 15 U.S.C. §§ 79l(f), 79m(a), 79n, 79o (1964 ed.).
The Fifth Circuit case is Louisiana Pub. Serv. Comm'n v. SEC, 235 F.2d 167. It was reversed here on jurisdictional grounds, 353 U.S. 368, 77 S.Ct. 855, 1 L.Ed.2d 897, which does not of course impair statement on the merits. The Second Circuit decision is North American Co. v. SEC, 133 F.2d 148, aff'd on constitutional questions, 327 U.S. 686, 66 S.Ct. 785, 90 L.Ed. 945. The District of Columbia decision is Philadelphia Co. v. SEC, 85 U.S.App.D.C. 327, 177 F.2d 720; that court thought it was following its earlier two-to-one decision in Engineers Pub. Serv. Co. v. SEC, 78 U.S.App.D.C. 199, 138 F.2d 936, cert. granted, 322 U.S. 723, 64 S.Ct. 1273, 88 L.Ed. 1561, vacated as moot, 332 U.S. 788, 68 S.Ct. 96, 92 L.Ed. 370, but Engineers is ambiguous.
Among examples—and I do not mean to approve or disapprove the ones I cite—are SEC rulings that as noted it will not consider losses to the principal system, General Pub. Utils. Corp., 32 S.E.C. 807, 838—839 (1951); that it will not consider tax losses as a very significant factor, Cities Serv. Co., 15 S.E.C. 962, 985 (1944); that it will give only limited weight to capital costs of divestiture, Eastern Utils. Associates, 31 S.E.C. 329, 349 (1950); and that it will offset predicted gains resulting from separation against the losses, North American Co., 18 S.E.C. 611 (1945).


Debtors filed suit against a debt collection agency, its employee and its outside counsel alleging various violations of the federal Fair Debt Collection Practices Act (FDCPA) and Oregon’s Unfair Debt Collection Practices Act. The defense and debtors filed cross-motions for summary judgment; the district court granted the motion brought by the attorney, partially granted the motion brought by the debt collector, and denied the motion brought by the debtors. The Ninth Circuit affirmed in part and reversed in part. Clark v. Capital Credit & Collection Services, Inc., ___ F.3d ___, 2006 WL 2441705 (9th Cir. August 24, 2006). We provide a brief summary of the case, which the Ninth Circuit characterized as “present[ing] a complicated web of problems that has required us to address a litany of issues for which there is a dearth of applicable precedent” and for which it “endeavored to adopt a construction of the FDCPA that recognizes ‘there is room within the [FDCPA] for ethical debt collectors to make occasional unavoidable errors,” Slip Opn., at 10165 (citation omitted).
In an effort to collect a debt, a debt collector sent the debtor a collection notice letter. The debtor disputed the debt and detailed billing problems with the creditor. The debt collector sent a second notice, enclosing an itemized statement from the creditor and claiming that the statement adequately verified the debt. The debtor requested “proper verification” and instructed the debt collector to cease making telephone calls. Slip Opn., at 10143. The debt collector then retained counsel who, in response to a demand for verification of the debt and an end to telephone communications, responded with the same itemized statement previously provided to the debtor. The debtor subsequently called the attorney to discuss the debt, but received a return call from the debt collection agency that “so upset [her] that she was required to obtain therapy.” Id., at 10144. The debtors filed suit.
The Circuit Court noted that it reviews de novo the district court’s interpretation of the FDCPA, Slip Opn., at 10145, and addressed first the debtors’ § 1692c(c) violations based on their claim that their “cease communication” letter prohibited the collection agency from telephoning, even in response to their inquiry, id.. The district court held that the telephone call constituted a waiver with respect to any return call; the Ninth Circuit noted, “Whether a consumer may waive a so-called ‘cease communication directive’ appears to be an issue of first impression in this and other circuits,” id., at 10146. In holding that a debtor may waive this directive, the Court explained, “to hold that a debt collector may not respond to a debtor’s telephone call regarding his or her debt would, in many cases, ‘force honest debt collectors seeking a peaceful resolution of the debt to file suit in order to resolve the debt-something that is clearly at odds with the language and purpose of the FDCPA.’” Id., at 10149 (citation omitted).
The Ninth Circuit held “a debtor may waive the rights created by a cease communication directive,” but that “a heightened standard of voluntariness is appropriate” because the statute FDCPA “measures the behavior of debt collectors under the rubric of the ‘least sophisticated debtor.’” Slip Opn., at 10150. Thus measured, the Court concluded that a waiver clearly existed as to a return call from the attorney, id., at 10152, but not as to the debt collection agency, as to which there remained a triable issue of fact, id., at 10153. The Court explained, “we decline to create a rule that by waiving the protection of § 1692c(c) as to one debt collector, a debtor waives that protection with regard to any other debt collector with which that debt collector may be collaborating to collect the same debt.” Id., at 10152 (footnote omitted).
With respect to the debtors’ § 1692g violation claims, alleging the failure to properly verify the alleged debt, the Ninth Circuit clarified that its opinion in Mahon v. Credit Bureau of Placer County, Inc., 171 F.3d 1197 (9th Cir. 1999), did not “set a standard below which a debt collector’s verification efforts must not fall.” Slip Opn., at 10155. Rather, the Court adopted the standard applicable in the Fourth Circuit: “At the minimum, ‘verification of a debt involves nothing more than the debt collector confirming in writing that the amount being demanded is what the creditor is claiming is owed.’” Id. (quoting Chaudhry v. Gallerizzo, 174 F.3d 394, 406 (4th Cir. 1999). In this regard, both the debt collection agency and its outside counsel relied on the information provided by the creditor, and forwarded that statement to the debtors. Id. The Court held, “Within reasonable limits, [they] were entitled to rely on their client’s statements to verify the debt.” Id., at 10156. Specifically, “the FDCPA did not impose upon them any duty to investigate independently the claims presented by [the creditor].” Id. Summary judgment was therefore proper as to these claims.
The Circuit Court turned next to a claim that defendants knew the debt was invalid, and thus violated § 1692e(2)(a). Slip Opn., at 10156. Here, too, the Court was confronted with an issue of first impression – viz., “[w]hether a violation of § 1692e may be predicated upon conduct that is neither knowing nor intentional,” id. The Court noted that the statute used words “that connote volition,” id., at 10157, but that sister circuits have held that “the FDCPA is a strict liability statute,” id., at 10159 (citations omitted). The Ninth Circuit adopted the “strict liability” interpretations given by the Second and Seventh Circuits because “[r]equiring a violation of § 1692e to be knowing or intentional needlessly renders superfluous § 1692k(c).” Id. Accordingly, the Court held that “intent is only relevant to the determination of damages.” Id., at 10160.
In examining the judgment in light of its holdings, the Ninth Circuit observed that a debt collector’s § 1692k(c) bona fide error defense to FDCPA violations is an affirmative defense, but that neither the debt collection agency nor its outside counsel had introduced any evidence concerning the reasonableness of their reliance on the creditor’s representations. Accordingly, summary judgment was inappropriate as to these claims. Slip Opn., at 10161-62.
Finally, we jump to the Ninth Circuit’s consideration of another issue of first impression – or least an issue “never squarely addressed” in the circuit: “the issue of overlapping liability under the FDCPA,” Slip Opn., at 10162. The Circuit Court held that “one action can give rise to multiple violations of the Act,” id.
NOTE: In a concurring and dissenting opinion, Judge O’Scannlain argued that the debt collector “did not violate 1692c(c) by returning [the debtor’s] call,” Slip Opn., at 10166.


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WATKINS v. CITY OF OAKLAND CALIFORNIA May 29, 1998 No. 96-17239.
UNITED STATES v. KLIMAVICIUS VILORIA UNITED STATES May 29, 1998 Nos. 96-50546, 96-50547, 96-50548, 96-50549, 96-50550, 96-50551, 96-50552, 96-50553, 96-50554, 96-50556.
UNITED STATES v. MARTINEZ SALAZAR May 28, 1998 No. 94-10158.
JENSEN v. CITY OF OXNARD May 28, 1998 No. 97-55936.
KENNEDY v. UNITED STATES POSTAL SERVICE May 28, 1998 No. 97-35375.
DOE v. MADISON SCHOOL DISTRICT NO 321 321 May 27, 1998 No. 97-35642.
LESLIE v. COMMISSIONER OF INTERNAL REVENUE May 27, 1998 No. 96-70880.
DODDS v. AMERICAN BROADCASTING COMPANY INC May 27, 1998 No. 96-56300.
VIRGINIA SURETY COMPANY v. NORTHROP GRUMMAN CORPORATION May 27, 1998 No. 96-56804.
UNITED STATES HOCHMAN v. NACKMAN May 27, 1998 No. 96-56790.
UNITED STATES v. MARSH UNITED STATES May 27, 1998 Nos. 96-10287, 96-10288, 96-10289, 96-10291, 96-10292, 96-10293.
UNITED STATES BIDDLE v. BOARD OF TRUSTEES OF THE LELAND STANFORD JR UNIVERSITY May 26, 1998 No. 96-16911.
BALINT v. CARSON CITY NEVADA May 26, 1998 No. 96-17342.
UNITED STATES BIDDLE v. BOARD OF TRUSTEES OF LELAND STANFORD JR UNIVERSITY May 26, 1998 No. 96-16911.
LEWIS v. UNITED STATES May 22, 1998 No. 97-15987.
ACE BEVERAGE COMPANY v. LOCKHEED INFORMATION MANAGEMENT SERVICES May 20, 1998 No. 96-56316.
CRANDELL v. BUNNELL May 19, 1998 No. 96-56644.
WOLSEY LTD v. FOODMAKER INC May 19, 1998 No. 96-56345.
MAIER v. COMMISSIONER OF THE SOCIAL SECURITY ADMINISTRATION May 18, 1998 No. 97-35423.
LEGAL AID SOCIETY of HAWAII, Legal Services of Northern California, Inc., San Fernando Valley Neighborhood Legal Services, Legal Aid Society of Orange County, Alaska Legal Services Corporation, California State Client Council, The Hawaii Justice Foundat.. May 18, 1998 No. 97-16567.
Maria WALTERS; William Walters; Cesar Corona-Alvarez; Antonio Alvarez; Ninfa de Adames, Guadalupe Adames, husband and wife; Camila Garcia-Cruz; Omar Kayyam Meziab, Leslie Meziab, husband and wife, on behalf of themselves and all others s May 18, 1998 No. 96-36304.
STECKMAN v. HART BREWING INC May 14, 1998 No. 97-55199.
BUTLER v. APFEL May 14, 1998 No. 97-15497.
UNITED STATES v. MONTGOMERY UNITED STATES May 13, 1998 Nos. 97-30142, 97-30163.
UNITED STATES v. RILEY III May 13, 1998 No. 97-30114.
CALDERON v. UNITED STATES DISTRICT COURT FOR NORTHERN DISTRICT OF CALIFORNIA May 13, 1998 No. 97-70631.
BAKER v. LIBERTY MUTUAL INSURANCE COMPANY May 12, 1998 No. 97-15781.
QUEVEDO v. TRANS PACIFIC SHIPPING INC BHP May 12, 1998 No. 97-15817.
UNITED STATES v. MARTINEZ May 12, 1998 No. 96-30214.
UNITED STATES v. G.L., Defendant-Appellant. May 12, 1998 No. 97-30228.
THOMAS v. GOMEZ May 12, 1998 No. 97-55702.
SOUSA v. CALLAHAN May 11, 1998 No. 96-17256.
KIRKINGBURG v. ALBERTSON INC May 11, 1998 No. 96-35002.
UNITED STATES v. HOTAL May 11, 1998 No. 97-10302.
DELEW v. WAGNER May 11, 1998 No. 97-15778.
CANELL v. LIGHTNER May 8, 1998 No. 95-35161.
VICKERS v. STEWART May 8, 1998 No. 96-99022.
UNITED STATES v. BURT May 8, 1998 No. 94-10309.
UNITED STATES v. OMENE May 8, 1998 No. 96-10359.
ELBERT v. HOWMEDICA INC DIVISION OF PFIZER HOSPITAL PRODUCTS GROUP INC May 8, 1998 No. 96-16249.
DUFFIELD v. ROBERTSON STEPHENS COMPANY May 8, 1998 No. 97-15698.
METRO DISPLAY ADVERTISING INC v. CITY OF VICTORVILLE May 6, 1998 No. 96-55317.
IN RE: Ceresa Annette ROTHERY May 6, 1998 No. 97-56151.
NELSON v. CITY OF IRVINE May 6, 1998 No. 96-56813.
FLANAGAN v. ARNAIZ III May 6, 1998 No. 96-16694.
UNITED STATES v. GRAVES May 5, 1998 No. 97-10202.
SIEGEL v. FEDERAL HOME LOAN MORTGAGE CORPORATION May 5, 1998 No. 97-55174.
UNITED STATES v. GARIBAY May 5, 1998 No. 96-50606.
TAYLOR v. UNITED STATES May 4, 1998 Nos. 97-16069, 97-16071.
SOUTHWEST CENTER FOR BIOLOGICAL DIVERSITY, a non-profit corporation, Plaintiff-Appellant, Arizona Power Authority; Metropolitan Water District of Southern California; Southern Nevada Water Authority; Salt River Valley Water Users Association; May 4, 1998 Nos. 97-16768, 97-17110.
GARNEAU v. CITY OF SEATTLE May 4, 1998 No. 95-35920.
PARRETTI v. UNITED STATES May 1, 1998 No. 95-56586.
ABBASSI v. IMMIGRATION AND NATURALIZATION SERVICE May 1, 1998 No. 98-70375.
FOTI v. CITY OF MENLO PARK May 1, 1998 No. 97-16061.

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This article is part of the Thematic Series "Advances in nanocarbon composite materials".
This contribution reviews plasma polymer nanoparticles produced by gas aggregation cluster sources either via plasma polymerization of volatile monomers or via radio frequency (RF) magnetron sputtering of conventional polymers. The formation of hydrocarbon, fluorocarbon, silicon- and nitrogen-containing plasma polymer nanoparticles as well as core@shell nanoparticles based on plasma polymers is discussed with a focus on the development of novel nanostructured surfaces.
“A macromolecule is a molecule of high relative molecular mass, the structure of which essentially comprises the multiple repetition of units derived, actually or conceptually, from molecules of low relative molecular mass.” “A polymer is a substance composed of macromolecules.” These are the definitions the IUPAC gives to macromolecules and polymers, respectively . The ubiquity of polymers in everyday life is due to the huge diversity of chemical composition and architecture they may possess, both factors leading to an extremely broad spectrum of polymer properties. Nevertheless, the word “plasma” was added to the title of this article to reflect the fact that this manuscript will not deal with conventional polymers per se, regardless of the attractiveness and utility of these may be, but will rather focus on materials that are created as a result of a low-temperature non-equilibrium plasma operating in organic vapours. The term “plasma polymer” was introduced in the 1960s to convey the interrelation between the use of a gas discharge and the formation of solid deposits from low molar mass organic precursors [2-4], although the history of plasma polymers is much longer. Organic deposits created as by-products of electrical discharges have been known presumably since the end of the18th century (see  and references therein). The significant scientific interest in plasma polymers was motivated by the attractive possibility to introduce various organic monomers into the plasma, including those which do not polymerize by conventional chemical routes. A new kind of polymer with advanced properties was anticipated. It was however soon realized that these materials have little in common with conventional polymers due mainly to the fact that they typically have random, highly cross-linked and highly branched structures in which regularly repeating monomeric units can hardly be expected. The lack of predictable structure hampered the extensive use of plasma polymers in real world applications, although a multitude of potential utilizations have been suggested.
In the mid-twentieth century, such deposits were studied as possible candidates for the production of thin dielectric films for microelectronics . The choice of hydrocarbon, halocarbon and organosilicon precursors in these studies logically stemmed from the requirement of the compatibility with technological processes used in the semiconductor industry. The formation of disperse polymeric particulates in the gas volume was also observed at about that time [7-10]. The phenomenon was earlier considered as unwanted and as something to be avoided; later, it laid a foundation for the field of dusty plasmas in which the research was focused on particle–plasma interactions . A legacy from the semiconductor processing phase explains the fact that close attention was paid to silane-based plasmas [9,11-22] followed by hydrocarbon [16,17,23-27] and fluorocarbon plasmas [27-36].
In recent years, scientific interest spread to the investigation of the properties of plasma polymer particles themselves, regardless of the effects their presence produces on the plasma. It was recognized that polymeric nanoparticles (NPs) can be highly desired in various fields including photonics  and biomedical applications where they can be used as biomolecule and drug carriers [38-40]. Gas aggregation cluster sources (GAS) were considered feasible for the synthesis of plasma polymer NPs with a tuneable size distribution, retention of functional groups and cross-link density. The concept of GAS was originally developed for the production of metal NPs by vacuum thermal evaporation with subsequent condensation of atomic metal vapours on a cool buffer gas and later thermal evaporation was replaced by magnetron sputtering . At least one work investigated the formation of polymeric NPs by thermal evaporation of poly(N-vinyl-2-pyrrolidone) in a GAS .
At present, a typical GAS consists of a tubular vacuum chamber equipped with a DC or RF electrode (or magnetron) which is used to ignite a plasma and which serves as a source of material to be “vaporized” (Figure 1). In the case of the production of plasma polymer NPs, carbonaceous precursors are introduced into the GAS in the form of volatile vapours of organic monomers or as a result of evaporation or sputtering of a solid polymer target attached to the electrode. The latter process was shown to lead to a release of volatile fragments of macromolecules which can be further used as precursors for plasma polymerization [43-52]. Depending on the experimental conditions, plasma polymerization can be forced to proceed in a gas phase which results in the formation of NPs of different chemical and physical properties and with different size distribution. The GAS configuration offers an advantage of creating a co-axial gas flow to transport the NPs away from the discharge zone through an orifice into another vacuum chamber where they can be collected on solid supports.
Figure 1: Scheme of a gas aggregation cluster source.
Figure 2a–d shows scanning electron microscopy (SEM) examples of NPs created as a result of plasma polymerization of n-hexane and hexamethyldisiloxane (HMDSO)  or as a result of RF magnetron sputtering of nylon  and poly(tetrafluoroethylene) (PTFE) . One can readily judge the diversity of shape and morphology of the NPs with diameters ranging from tens to hundreds of nanometers. Here and further in this Review, for simplicity, we shall use the designation “NPs” to describe all particles in this size range having in mind that objects of hundreds of nanometers are more accurately described as submicrometer-sized particles.
Figure 2: SEM images of different types of plasma polymer nanoparticles produced: a) by plasma polymerization of n-hexane in its mixture with N2; b) by plasma polymerization of HMDSO in its mixture with Ar (obtained in a similar manner as ); c) by RF magnetron sputtering of nylon in the Ar/N2 mixture (republished from  with permission IOP Publishing Ltd.); d) by RF magnetron sputtering of PTFE in Ar (obtained in a similar manner as ). The references shown here and in the following figures cite the authors’ previous works where similar (but not necessarily identical) data were presented; the unreferenced data represent the authors’ new material which has not been published yet, but which is necessary for a comparative analysis in this review.
It has been recognized that NPs grow via a three-step process involving nucleation, coagulation and growth by accretion. The nucleation stage is often considered to be governed by negative ions [19,56-59], leading to the formation of nanometer-sized nuclei. These embryonic clusters may be neutral or bear either negative or positive charge [60,61] which results in their effective coagulation into larger NPs with a typical diameter of 10–20 nm. Negative charge begins to dominate for NPs of this and larger size because of the high mobility of electrons with respect to positive ions. The coagulation is therefore suppressed by Coulomb repulsion, and further NP growth proceeds by accretion via the accumulation of polymer-forming neutral species (radicals) and positive ions from the gas phase.
The resultant plasma polymer NPs have a spherical symmetry but can exhibit different morphology. Although it is very difficult to generalize about the shape of the NPs prepared in different experiments, it seems that larger plasma polymer particles typically reveal a more complex structure (Figure 2), the exact understanding of which is still lacking. The phenomenon can be associated with the changes in the heat balance of NPs during their growth in plasma. It has been shown both theoretically and experimentally that smaller NPs may reach the temperature that significantly exceeds that of a neutral gas, whereas larger NPs are heated much less [58,62,63]. Thus, the continuous growth of NPs in plasma may be accompanied by radially directed changes in the material properties (cross-link density and branching) induced by temperature changes and resulting in the accumulation of mechanical stress. If the critical value of stress is achieved, the surface of a NP relaxes with the formation of the surface instabilities, similar to a popcorn effect observed in conventional polymer particles . As it was mentioned, the involvement of low-temperature plasma represents a unique feature that distinguishes this approach from other non-plasma-based methods: NPs acquire an electrical charge when nucleating, growing and passing through the zone of the glow discharge. Clouds of charged NPs may exhibit collective behaviour coupled with plasma instabilities, a phenomenon of high scientific interest in the field of dusty plasmas . In the framework of GAS, the gas flow conditions are deliberately chosen to overcome trapping of NPs by electromagnetic fields and to extrude beams of NPs into the separate deposition chamber. Haberland  was one of the first to realize that NPs (metallic in his case) ionized in the magnetron plasma can be advantageous in terms of size separation in accord with their mass-to-charge ratio. It can be shown that plasma polymer NPs also leave GAS partially charged and can be manipulated by an electrostatic field. Electrostatic plates can be installed at a close distance from the exit orifice of the GAS to deflect the charged NPs. Figure 3a shows the scheme of such arrangement used for the production of NPs by RF magnetron sputtering of nylon . Here, photos of glass substrates taken after the depositions with or without the electrostatic field applied are shown. The nylon-sputtered NPs produce a circular deposit opposing the exit orifice when no voltage is applied to the deflection plates. In contrast, the deposit becomes spread towards the edges when 200 V voltage of different polarity is applied to the deflection plates. Remarkably, the presence of both negatively and positively charged NPs can be observed as the deposit is smeared in both directions from the central point. From the opacity of the deposit, it can be qualitatively estimated that neutral NPs are in minority and that negatively charged NPs constitute the majority of all the charged NPs.
Figure 3: Experimental arrangements allowing estimation of plasma polymer NP charging: a) electrostatic plates used for deflection of charged nylon-sputtered NPs  by applying 200 V voltage of different polarity across the NP beam; b) electrostatic grids used for retardation of charged PTFE-sputtered NPs by applying 1000 V voltage of different polarity along the NP beam (obtained in a similar manner as ).
For a quantitative evaluation, a system of electrostatic retarding grids can be utilized as shown in Figure 3b. Quartz crystal microbalance (QCM) can measure the total mass flux of the NPs (neutral, positively and negatively charged) without any voltage applied to the grids. A highly positive or negative potential applied to the central grid repels the NPs of the opposite charge and allows the rest to pass through. One can obtain the ratio between the neutral, the positively and the negatively charged NPs by measuring their mass fluxes with opposing voltages on the central grid. The calculations performed for the PTFE-sputtered NPs  support the qualitative data obtained for nylon sputtering and prove that the majority of the NPs bear the electric charge and that negatively charged NPs are the most abundant.
Chemical composition can also vary drastically depending on the precursor/target used as can be seen in Figure 4 where high-resolution C 1s XPS peaks are shown for a number of chosen NPs. Starting from C/H plasma polymers (Figure 2a), the chemistry of the resulting NPs may range from nitrogen-containing (Figure 2b) to fluorocarbon (Figure 2c) plasma polymers, to cite just a few, in which multitudes of chemical bonding environments can be present.
Figure 4: C 1s XPS of the NPs prepared a) by plasma polymerization of n-hexane in its mixture with Ar (total pressure 88 Pa, discharge power 40 W, C6H14 flow 1.2 sccm, Ar flow 12.2 sccm); b) by RF magnetron sputtering of nylon in the Ar/N2 3:1 mixture (obtained in a similar manner as ); c) by RF magnetron sputtering of PTFE in Ar (reprinted from , with permission from Elsevier).
The choice of the working gas strongly influences the plasma chemistry and may be used as a tool for tuning the chemical composition of resultant NPs. For example, adding nitrogen to a hydrocarbon plasma may trigger the formation of nitrogen-containing NPs [68,69]. Figure 5a,b shows the NPs produced by plasma polymerization from the mixtures of n-hexane with Ar and with nitrogen, and for comparison Figure 5c shows the NPs produced by RF magnetron sputtering of nylon in the Ar/N2 mixture .
Figure 5: SEM images of nitrogen-containing NPs prepared a) by plasma polymerization of n-hexane in its mixture with Ar (total pressure 88 Pa, discharge power 40 W, C6H14 flow 1.2 sccm, Ar flow 12.2 sccm); b) by plasma polymerization of n-hexane in its mixture with N2 (total pressure 88 Pa, discharge power 40 W, C6H14 flow 1.2 sccm, N2 flow 12.2 sccm); c) by RF magnetron sputtering of nylon in the Ar/N2 3:1 mixture (obtained in a similar manner as ).
The chemical composition of these NPs is shown in Figure 6a in terms of FTIR spectra and in Figure 6b in terms of the XPS elemental nitrogen content as a function of the concentration of N2 in the working gas. Apart from narrowing the size distribution, adding nitrogen results in an increase of the nitrogen content in the NPs. Incorporation of nitrogen-bearing species into thin films of plasma polymers has been considered to be of paramount importance, especially in terms of retention of primary amines which are attractive in biomedical applications as linkers for binding biomolecules. Yet, it has been recently argued that primary amines find it difficult to survive the influence of the plasma and that amino groups overwhelmingly reported for plasma polymers are actually other nitrogen-containing functionalities . The data obtained for the NPs confirm that plasma polymerization of n-hexane in N2 does not lead to the substantial retention of amines as can be seen from the absence of the characteristic IR band at >3000 cm−1. Carbonyl-, amide- and, to a lesser extent, imine-based functionalities constitute an ensemble of nitrogen-bearing species. In contrast, RF magnetron sputtering of nylon in the Ar/N2 mixture results in a much better retention of nitrogen which is, at least to some extent, bound in amine functionalities. Nevertheless, a reliable and quantitative control over the amount of amines in both NPs and thin films of plasma polymers still represents a formidable challenge.
Figure 6: Chemical composition of nitrogen-containing NPs shown in Figure 5: a) FTIR spectra; b) the nitrogen content calculated from the XPS spectra as a function of the N2 concentration in the working gas.
Another example of a strong dependence of the chemical composition of NPs on the composition of the gas mixture can be found for plasma polymerization of HMDSO. It has been known for a long time in the thin film deposition community that adding oxygen to HMDSO switches plasma chemistry to preferential oxidation of carbonaceous species. A pumping system effectively evacuates gaseous carbon oxides whereas siloxane moieties tend to adsorb on surfaces and form silicon oxide coatings. The amount of added oxygen determines the chemical composition of the coatings. The same paradigm can be adapted for the synthesis of NPs in the configuration of GAS . Plasma polymerization can be performed at elevated pressure in a mixture of HMDSO and Ar with the constant ratio of both components. The process results in the formation of 210 ± 40 nm diameter spherical particles with a more structured surface (Figure 7a). Adding O2 to the working mixture results in morphological changes and produces NPs with fewer irregularities on the surface (Figure 7b,c). Remarkably, the NP diameter does not change significantly and reaches 180 ± 40 nm for the most oxygen-rich gas mixture.
Figure 7: SEM images of NPs prepared by plasma polymerization of HMDSO mixed with Ar: a) without adding oxygen; b) with addition of oxygen at O2/HMDSO 1:1 ; c) with addition of oxygen at O2/HMDSO 5:1 (obtained in a similar manner as ). Total pressure is 55 Pa, discharge power is 30 W, HMDSO flow is 0.2 sccm, Ar flow is 2 sccm.
The stability of the size distribution becomes even more remarkable when compared to the chemical changes induced by the addition of oxygen. FTIR and XPS (Figure 8a,b) analyses demonstrate the organosilicon character of the NPs produced without O2 and its gradual transfer to the inorganic state with the addition of O2. The gas phase composition can be optimized to produce nearly stoichiometric SiO2 NPs (Figure 7c), which are rare examples of organic plasma-derived material with well-established chemical composition. As it was discussed above, plasma polymers are typically cross-linked macromolecular networks having the chemical composition of more diverse character than that of the precursors. Mono-functional plasma polymers are still beyond reach and even preferential retention of a specific functional group with a good control over the surface chemistry represents a significant challenge for the scientific community today.
Figure 8: Chemical composition of the NPs shown in Figure 7: a) FTIR spectra b) the elemental content calculated from the XPS spectra as a function of the O2 concentration in the working gas (republished from  with permission of IOP Publishing Ltd.).
The discharge power and the gas flow in the GAS are additional parameters to control the NP properties. In close analogy with the Yasuda parameter (see  and the following debate), both determine the specific energy supplied to a precursor molecule and, as a result, the intensity of precursor fragmentation. A typical pressure of tens of Pa ensures a viscous and laminar gas flow regime, and hence the gas flow rate determines also the time that NPs spend in the GAS (the residence time). Figure 9a,b summarizes the data available in the literature. Here, the mean NP diameter is given as a function of the residence time and discharge power for nylon-  and PTFE-sputtered  NPs as well as for plasma polymerization of HMDSO in Ar .
Figure 9: Mean diameter of nylon-sputtered, PTFE-sputtered and HMDSO plasma polymer NPs as a function of a) the residence time and b) the power of the discharge. The data are calculated from the results presented in [53,54,67].
For nylon and HMDSO, an increase is observed of the NP diameter with the residence time (under constant power) which simply reflects the kinetics of the NP growth when they travel along the GAS. The opposite trend of decreasing NP diameter with the discharge power is readily explained by stronger fragmentation of precursor molecules. The fragmentation results in a larger amount of free radicals that serve as nucleation centres and, under constant supply of the precursor (constant gas flow rate), these produce larger amounts of smaller NPs. Nevertheless, the data for the NPs produced by magnetron sputtering of PTFE  by no means obey the above trend. These NPs are also in contradiction with other fluorocarbon NPs produced by plasma polymerization of heptadecafluorodecyl acrylate  showing the same trend as the nylon-sputtered and the HMDSO NPs. For PTFE-sputtered NPs, neither the residence time nor the discharge power has influence on the NP diameter which stays constant over the entire range of both parameters. The formation of the NPs in close proximity to the PTFE target and their subsequent transport through the GAS volume saturated with low sticking probability CF2 bi-radicals were suggested as possible explanations of the phenomenon. It can be concluded that, although the opposing influence of the residence time and the discharge power on the NP diameter is fulfilled in many cases, a global generalization should be made with caution and each particular combination of precursor and GAS parameters should be thoroughly investigated. For example, other experiments with PTFE-sputtered NPs revealed that their diameter can be controlled over a wide range by changing the intensity of the magnetic field above the magnetron target . Figure 10a,b shows SEM images of the NPs prepared under identical conditions in the GAS but with different permanent magnet circuits installed in the magnetron, giving either a 100 G or 250 G field above the position of the erosion track on the PTFE target. An increase of the intensity of the magnetic field leads to a decrease of the magnetron self-bias from 620 V to 350 V due to more effective trapping of electrons within the magnetic channel. This in turn results in the formation of particles which are an order of magnitude larger (250 nm) as compared to the ones fabricated with the weaker magnetic field (30 nm). Apparently, the differences in intensity of ion bombardment should be manifested in the change of the plasma chemistry, although the exact reason for this interesting phenomenon is still not clear and requires further investigation.
Figure 10: SEM images of the PTFE-sputtered NPs deposited with different intensity of the magnetic field: a) 100 G, b) 250 G; Ar pressure is 100 Pa, flow rate is 9.2 sccm, residence time is 9 s, discharge power is 140 W, deposition time is 20 min; obtained in a similar manner as in .
Apart from being of scientific interest, tuning the NP size by replacement of magnetic circuits can hardly be viewed as practical and technological reasons. More feasible is to control the power/flow parameters or to modify the construction of the GAS itself. A GAS can be constructed to allow the length of the aggregation chamber to be changed, and Figure 11a,b shows the results of plasma polymerization of HMDSO in Ar with two values of the aggregation length . Logically, a shorter aggregation zone reduces the NP residence time and prevents them from growing larger. Figure 11c shows the dual-scale surface obtained as a result of the combined deposition when a layer of 220 nm NPs was prepared with the longer aggregation zone and it was subsequently over coated by another layer of 40 nm NPs prepared with the shorter aggregation zone. Manipulation of the discharge power can also be effective for the creation of dual- and even multi-scale structures. For example, NPs of three different sizes can be prepared in a single run by a stepwise increase of power, in this case resulting in the deposition of 200, 110 and 70 nm NPs. Figure 11d shows the outcome of such a triple deposition method and the histogram in Figure 11e confirms the formation of the triple-scale surface. Thus, plasma polymer NPs produced by GAS prove to be very versatile for the design of hierarchical structures, which can be very efficient for fine tuning of optical properties, surface wettability, interaction with cells, and in other applications.
Figure 11: SEM images of NPs prepared by plasma polymerization of HMDSO in Ar: a) 220 nm NPs produced with 10 cm aggregation length; b) 40 nm NPs produced with 4 cm aggregation length; c) dual-scale structure produced by sequential deposition of a) and b); d) triple-scale structure produced by power-dependent sequential deposition of 200, 110 band 70 nm diameter NPs; e) size distribution histogram corresponding to d) (republished from  with permission of IOP Publishing Ltd.).
The versatility of GAS may be further extended if two different processes are combined in one experimental run. One can take advantage of magnetron sputtering of metals and plasma polymerization of organic precursors to create heterogeneous NPs in which metallic inclusions are enveloped by layers of plasma polymer (core@shell NPs). For example, the process can be performed in the GAS by RF magnetron sputtering of metal in argon with the addition of an organic precursor (Figure 12a) or metal NPs can be pre-formed in the GAS by DC magnetron sputtering and the beam of the NPs can be allowed to pass through an auxiliary glow discharge in organic vapours (Figure 12b).
Figure 12: Scheme of synthesis of core@shell NPs by GAS: a) core@shell NPs are produced in the GAS by RF magnetron sputtering of Ag target in the gas mixture of Ar and HMDSO; b) metal NPs are produced by DC magnetron sputtering of Ti target in the GAS and then covered by shells of C/H plasma polymer in the auxiliary plasma reactor with external RF excitation.
In the first case, the conditions should be optimized to provide the supply of atomic metal supersaturated vapours into the gas phase where they start to condense by homogeneous nucleation. Simultaneously, fragmentation of organic molecules in the plasma proceeds with the formation of free radicals that subsequently recombine to create the plasma polymer phase. Remarkably, the two processes do not interfere, probably due to strong cohesive forces between metal atoms and weak metal–polymer interaction. As a result, phase-separated core@shell NPs are created, an example of which is shown in Figure 13a. Here, silver NPs enveloped by shells of HMDSO plasma polymer are shown. The structure of the NPs, in which multiple metal inclusions of about 5 nm diameter are concentrated within a single plasma polymer shell producing 36 nm diameter multicore@shell NPs, is appealing. The multicore-in-one-shell structure can be explained by the initial formation of single core@shell NPs which subsequently coalesce into one bigger NP joining multiple metal inclusions in a single shell.
Figure 13: TEM images of core@shell NPs: a) Ag@HMDSO NPs prepared in configuration of Figure 12a (total pressure 190 Pa, discharge power 50 W, HMDSO flow 0.45 sccm, Ar flow 105 sccm); b) Ti@C/H NPs prepared in configuration of Figure 12b (Ar pressure/flow in the GAS is 40 Pa/4.0 sccm, DC 0.4 A, total pressure in the auxiliary plasma zone is 1 Pa (0.65 Pa of Ar and 0.35 Pa of C6H14), RF power is 10 W).
The second strategy relies on spatial separation of the formation of metal NPs and their embedding into polymer or plasma polymer shells, similar to what has been realized in [72,73]. This strategy allows the decoupling of the processes of magnetron sputtering and plasma polymerization and may prove advantageous, especially if more reactive metals are considered. For example, titanium is known to form strong TiC bonds when sputtered in organic plasma . Carbidization of titanium atoms may hinder metal–polymer phase separation and it may even change the properties of titanium inclusions themselves. Instead, Ti NPs can be created in the GAS by magnetron sputtering in Ar and then their beams can be transported by the gas flow through an auxiliary glass tube attached to the GAS and equipped with an external ring electrode for RF excitation of plasma. Vapours of n-hexane are introduced into the glass tube via a separate inlet port and the conditions of plasma polymerization should be optimized to produce in-flight coating of Ti NPs with hydrocarbon plasma polymer. Figure 13b shows that both single core@shell NPs as well as their agglomerations can be obtained by this procedure. The thickness of the overcoat can be controlled by the flight velocity of the NPs and by the deposition rate of the plasma polymer. Overall, gas-phase fabrication of metal–polymer core@shell NPs may offer new possibilities in preventing metal particles from oxidation, in fine tuning the optical properties and biological interactions, and, in general, in designing novel materials with advanced properties.
The configuration of GAS allows the deposition of NPs onto any high-vacuum-compatible supports. Typical operational conditions used in GAS produce NP beams that deposit on substrates with subsonic velocity . If the range of masses of NPs is taken into account, one may conclude that NPs hit the substrate in a soft-landing regime in which the kinetic energy borne by a NP as a single entity is too small to break bonds between the highly numerous species constituting this NP. Hence, NP interaction with the substrate does not induce noticeable changes either in the NPs or in the substrates. Preservation of the NP shape and structure may or may not be of benefit, depending on the target application. A major drawback of the situation is related to the weak van der Waals forces acting between NPs and substrate so that a NP layer can be easily destroyed by a tiny mechanical impact. This drawback can be overcome by depositing a capping layer that should be sufficiently robust to fix the NPs on the surface yet sufficiently thin so as not to introduce morphological changes to the surface, unless otherwise required. The layer can be of the same or similar material as the underlying NPs to preserve the surface chemistry. For example, hydrocarbon NPs produced by plasma polymerization of n-hexane in GAS can be fixed on the surface by coating them with a thin film of hydrocarbon plasma polymer (Figure 14a). The capping layer can also be made of a different material as can be seen in Figure 14b where the same NPs are shown over-coated with a magnetron-sputtered Ti film.
Figure 14: C/H NPs prepared in GAS by plasma polymerization of n-hexane and overcoated a) with a thin film of C/H plasma polymer (reprinted from , with permission from Elsevier) and b) with a Ti thin film (obtained in a similar manner as in ).
In both of the above cases, the overlayer was deposited to preserve the initial surface morphology. Certain applications however may require control over the structure in a broader range covering both nanometer and micrometer scales. Plasma polymer NPs may be useful for this purpose as well, especially if glancing angle deposition (GLAD) is considered. Evaporative GLAD was developed in the late 20th century for creating metallic films with a highly porous structure . It has been known that time and spatial fluctuations exist in atomic fluxes arriving onto the substrate from the gas phase during evaporation or sputtering. The noise in the atomic flux results in the situation that some spots on the surface may receive a larger amount of particles deposits than the others, and generally, noise is responsible for roughening the growing front. In contrast, surface diffusion tends to redistribute the arriving material over the larger area and leads to smoothening of the surface. The competition between the two phenomena determines the resultant roughness/smoothness of the film. If deposition is performed onto a sufficiently cold substrate, surface diffusion can be suppressed and roughening will dominate. It has been also recognized that roughening can be significantly enhanced if shadowing instabilities are present on the surface, especially if the depositing flux is collimated and tilted at an oblique (glancing) angle to the surface normal. Nuclei of the adsorbed material create shadow zones in areas opposite to the direction of the incoming flux. Arrays of well isolated zig-zag, spiral or pillar nanostructures made of metals and other inorganics have been successfully fabricated by GLAD. GLAD of polymeric materials has also been demonstrated [74,79,80]. However, the separation between the individual polymer nano-columns is typically worse than in the case of metals, probably due to a relatively large characteristic surface diffusion length of macromolecular species which compromises the shadowing effect. To enhance the shadowing mechanism, blank substrates can be preseeded with NPs produced by GAS (Figure 15a) that will serve as artificially created obstacles to the incoming flux in the second step (Figure 15b).
Figure 15: Scheme of GLAD: a) preseeding of substrates with nylon-sputtered NPs produced by GAS; b) GLAD of nylon-sputtered plasma polymer over the preseeded NPs.
Figure 16a,b shows the top view and cross-sectional images of a plasma polymer film created as a result of RF magnetron sputtering of nylon at normal (0°) and glancing angle (80°) deposition on blank silicon substrates whereas Figure 16c,d shows their counterparts deposited over the preseeded nylon-sputtered NPs. As expected, normal depositions produce compact coatings with the surface replicating the underlying structure (correspondingly, smooth blank Si or roughened NP seeds). Using GLAD, a columnar structure develops with columns inclined towards the direction of the deposition. Obviously, the porosity of the coatings is greatly increased when it is deposited over the preseeded NPs. This approach also offers the possibility to combine different materials, and hence, to independently tune the surface morphology and the chemical composition. Thus, it represents an attractive route for designing nanocomposite coatings with advanced properties.
Figure 16: SEM images with combined top view and cross-sections of the deposits produced as a result of RF magnetron sputtering of nylon: a) normal deposition on blank Si substrate; b) GLAD at 80° on blank Si substrate; c) normal deposition over preseeded nylon-sputtered NPs; d) GLAD at 80° over preseeded nylon-sputtered NPs (reprinted from , with permission from Elsevier).
Plasma polymer NPs have great potential and may provide a valuable addition to the field of nanoscale-dispersed polymers. The involvement of gas aggregation cluster sources in the production of plasma polymer NPs opens new horizons in precise tuning of their size, shape, chemical composition, surface charge and wettability. There are great potential benefits for the use of plasma polymer NPs in photonics, nanomedicine and other applications, but also significant challenges remain unresolved. Fundamental knowledge on the mechanisms of plasma polymer nanoparticle formation is still far from being complete. Although rich information regarding the nucleation and growth of nanoparticles in organosilicon and hydrocarbon plasmas is available, a deep understanding of these processes for other precursors is missing. The lack of knowledge is especially striking in the field of the plasma-based fabrication of functionalized polymeric NPs and core@shell NPs, which remains in its budding stage. The retention of specific functional groups, control over their concentration, control over the cross-link density and the concentration of radicals captured within plasma polymer NPs, control over the morphology and shape of NPs, and nanophase separation within core@shell NPs are only a few issues that scientists in this research field face. The solution of these issues requires finding correlations between the properties of the plasma (energy distribution functions, plasma density, floating and plasma potential), the gas phase composition and the gas flow dynamics. Therefore, future research work should join efforts of scientists with different expertise to cope effectively with these complex issues.
This work was supported by the grant GACR 17-12994S from the Grant Agency of the Czech Republic. The authors would like to acknowledge the contribution of the COST Action CA15107 (MultiComp) and support by the grant LTC17062 from the Ministry of Education, Youth and Sports of the Czech Republic. The authors thank Prof. Miroslav Cieslar and Dr. Ivan Khalakhan for their assistance with the preparation of this manuscript.
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© 2017 Choukourov et al.; licensee Beilstein-Institut.

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